MSK 2
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Questions and Answers

What is the primary cell type found in bone tissue?

  • Osteocytes (correct)
  • Osteoblasts
  • Osteoclasts
  • Chondrocytes

    • What does osteoid refer to in bone?

  • The outer layer of bone
  • The fatty tissue in bone marrow
  • The mineralized part of bone
  • The matrix of the bone that contains proteoglycans and glycoproteins (correct)

    • Which component is primarily responsible for the tensile strength of bone?

  • Hydroxyapatite
  • Bone marrow
  • Osteocytes
  • Collagen fibers (correct)

    • What is the role of collagen fibers in bone tissue?

    <p>To contribute to flexibility and tensile strength</p> Signup and view all the answers

    Which property of bone is attributed to the bonds between collagen fibers?

    <p>Toughness and ability to dissipate energy</p> Signup and view all the answers

    When collagen fibers break due to impact, what is the primary benefit?

    <p>It dissipates energy that could cause a fracture.</p> Signup and view all the answers

    What is the primary inorganic component of bone?

    <p>Calcium phosphates</p> Signup and view all the answers

    Approximately what percentage of bone's volume is made up of mineral salts?

    <p>50%</p> Signup and view all the answers

    What percentage of bone is made up of mineral salts?

    <p>70%</p> Signup and view all the answers

    What is the primary contribution of mineral salts to the properties of bone?

    <p>They contribute to bone hardness.</p> Signup and view all the answers

    Which component do mineral salts crystallize around in bone?

    <p>Collagen fibers</p> Signup and view all the answers

    Which statement accurately describes the inorganic components of bone?

    <p>They provide compressive strength to the bone.</p> Signup and view all the answers

    What role does calcium phosphate have in maintaining bone health?

    <p>It contributes to the hardness and strength of bone.</p> Signup and view all the answers

    Which statement best describes osteoporosis in relation to bone's organic components?

    <p>It leads to a reduction in organic material, making bones more brittle.</p> Signup and view all the answers

    What role do osteoclasts play in bone health?

    <p>They break down old bone tissue.</p> Signup and view all the answers

    What is the effect of collagen's arrangement on bone tissue?

    <p>It contributes to bone's toughness and energy dissipation.</p> Signup and view all the answers

    Which statement best describes the role of the mineral component in bone?

    <p>It gives the bone its hardness and strength.</p> Signup and view all the answers

    How do proteoglycans and glycoproteins influence bone functionality?

    <p>They provide structural resilience and flexibility.</p> Signup and view all the answers

    Which process facilitates the healing of bone after an injury?

    <p>Organics providing a scaffold for repair.</p> Signup and view all the answers

    What role does energy dissipation play in bone's response to impact?

    <p>It reduces the chances of fractures.</p> Signup and view all the answers

    What percentage of bone's weight is primarily attributed to inorganic components?

    <p>70%</p> Signup and view all the answers

    Which cell type plays a key role in the formation of new bone by secreting bone matrix?

    <p>Osteoblast</p> Signup and view all the answers

    Which statement is true about osteocytes?

    <p>They are embedded in the bone matrix</p> Signup and view all the answers

    What is the primary function of osteoclasts in bone tissue?

    <p>Absorb bone tissue</p> Signup and view all the answers

    Which property of mineral salts is most critical to bone structure?

    <p>They contribute to bone hardness</p> Signup and view all the answers

    Bone lining cells are primarily involved in:

    <p>Maintaining the bone matrix on surfaces not undergoing remodeling</p> Signup and view all the answers

    What is the main role of collagen fibers in bone tissue?

    <p>Providing tensile strength and flexibility</p> Signup and view all the answers

    Which statement about the inorganic components of bone is correct?

    <p>They provide compressive strength to the bone</p> Signup and view all the answers

    What term is used to describe the process by which bone matrix is formed by osteoblasts?

    <p>Osteogenesis</p> Signup and view all the answers

    Which of the following components is primarily responsible for increasing the hardness of bone?

    <p>Calcium phosphate</p> Signup and view all the answers

    Which cell type arises from osteogenic cells and is crucial for bone formation?

    <p>Osteoblast</p> Signup and view all the answers

    What role do proteoglycans and glycoproteins primarily serve in bone tissue?

    <p>They provide strength and flexibility to bone.</p> Signup and view all the answers

    What is the main benefit of collagen fibers breaking upon impact?

    <p>It dissipates energy that could cause a fracture.</p> Signup and view all the answers

    Which of the following is true about the organic components of bone?

    <p>They provide a buffer against mechanical forces, reducing fracture risks.</p> Signup and view all the answers

    What is the primary function of collagen fibers in bone tissue?

    <p>To contribute to flexibility and tensile strength.</p> Signup and view all the answers

    What property of bone is significantly influenced by the arrangement of collagen fibers?

    <p>Toughness and ability to dissipate energy</p> Signup and view all the answers

    What is the primary significance of mineral salts in bone tissue?

    <p>They confer hardness and strength to bone.</p> Signup and view all the answers

    Approximately what percentage of bone's overall structure is made up of organic components?

    <p>30%</p> Signup and view all the answers

    What is primarily stored in the bone marrow of bones?

    <p>Adipose tissue and blood cells</p> Signup and view all the answers

    What is the primary function of osteocytes in bone tissue?

    <p>They communicate mechanical stress signals to remodeling cells.</p> Signup and view all the answers

    What characteristic feature differentiates osteoclasts from other bone cells?

    <p>They absorb bone tissue.</p> Signup and view all the answers

    Which component of bone is primarily associated with providing compressive strength?

    <p>Mineral salts</p> Signup and view all the answers

    Osteogenic cells can differentiate into which type of bone cells?

    <p>Osteoblasts and osteoclasts</p> Signup and view all the answers

    What is the main function of osteoblasts in the context of bone health?

    <p>They form new bone by secreting bone matrix.</p> Signup and view all the answers

    Bone lining cells primarily function to:

    <p>Maintain the bone matrix on surfaces not undergoing remodeling.</p> Signup and view all the answers

    Which process describes the creation of new bone matrix by osteoblasts?

    <p>Osteogenesis</p> Signup and view all the answers

    The presence of mineral salts in bone primarily contributes to which property?

    <p>Hardness and strength</p> Signup and view all the answers

    What occurs when collagen fibers in bone matrix are subjected to significant impact?

    <p>They break, allowing for energy dissipation.</p> Signup and view all the answers

    What role does calcium phosphate play in bone structure?

    <p>It contributes to hardness and strength.</p> Signup and view all the answers

    What term is commonly used to refer to the osteon?

    <p>Haversian system</p> Signup and view all the answers

    Which structural element primarily characterizes the osteon?

    <p>A hollow tube of bone matrix</p> Signup and view all the answers

    What arrangement do collagen fibers have in adjacent lamellae of an osteon?

    <p>Different directions</p> Signup and view all the answers

    What is the primary function of the tiny weight-bearing pillars found within osteons?

    <p>They provide resistance to strain and torsion.</p> Signup and view all the answers

    How do the crystals of bone salts interact with collagen fibers in osteons?

    <p>They align with and alternate the direction of collagen fibers.</p> Signup and view all the answers

    What is the primary structural feature of an osteon?

    <p>A hollow tube of bone matrix</p> Signup and view all the answers

    How do the collagen fibers in adjacent lamellae of an osteon orient?

    <p>They run in different directions</p> Signup and view all the answers

    What is the role of tiny weight-bearing pillars within osteons?

    <p>They provide resistance to strain and torsion</p> Signup and view all the answers

    What is significant about the structure of an osteon in relation to its function?

    <p>It demonstrates the connection between structure and function</p> Signup and view all the answers

    What role do lamellae play in an osteon's structure?

    <p>They form the concentric rings of bone matrix</p> Signup and view all the answers

    What are the tiny channels that connect lacunae to the central canal called?

    <p>Canaliculi</p> Signup and view all the answers

    What is the primary function of the canaliculi in the bone structure?

    <p>To facilitate communication between osteocytes and the Haversian canal</p> Signup and view all the answers

    Where do osteocytes reside within the osteon?

    <p>In the lacunae</p> Signup and view all the answers

    Which structure serves as the main pathway for nutrients and waste products to travel in the bone?

    <p>Haversian canal</p> Signup and view all the answers

    How do osteocytes in lacunae communicate with each other?

    <p>Through tiny canaliculi connecting lacunae</p> Signup and view all the answers

    What is a key characteristic of bones regarding their vascularization?

    <p>Bones have a rich blood supply.</p> Signup and view all the answers

    Which canals contain the blood vessels that supply nutrients to the bone?

    <p>Haversian canals and Volkmann’s canals</p> Signup and view all the answers

    What is the primary function of the blood vessels running between and around osteons?

    <p>To supply nutrients and remove waste</p> Signup and view all the answers

    Which of the following statements is true regarding bone growth and healing?

    <p>A rich blood supply is crucial for bone growth and healing.</p> Signup and view all the answers

    What role do Volkmann's canals play in bone structure?

    <p>They connect Haversian canals to each other and to the periosteum.</p> Signup and view all the answers

    How does the blood supply in bones affect their overall health?

    <p>It aids in nutrient delivery and waste removal, promoting bone health.</p> Signup and view all the answers

    What happens to the bone if its blood supply is compromised?

    <p>It may weaken, leading to impaired healing and growth.</p> Signup and view all the answers

    Which of the following structures is responsible for the direct supply of nutrients to osteons?

    <p>Haversian canals</p> Signup and view all the answers

    What is a key characteristic of spongy bone compared to compact bone?

    <p>Spongy bone is lighter and less dense than compact bone.</p> Signup and view all the answers

    What structures make up the framework of spongy bone?

    <p>Trabeculae and bars of bone</p> Signup and view all the answers

    What is found within the small, irregular cavities adjacent to trabeculae in spongy bone?

    <p>Red bone marrow</p> Signup and view all the answers

    How do canaliculi function in spongy bone compared to compact bone?

    <p>They connect to adjacent cavities instead of a central Haversian canal.</p> Signup and view all the answers

    What is the primary advantage of the organization of trabeculae in spongy bone?

    <p>It provides maximum strength.</p> Signup and view all the answers

    In spongy bone, how do trabeculae respond to changes in stress?

    <p>They can realign to follow the lines of stress.</p> Signup and view all the answers

    Which type of bone is primarily involved in the production of blood cells due to the presence of red bone marrow?

    <p>Spongy bone</p> Signup and view all the answers

    The design of spongy bone allows it to:

    <p>Absorb shock and reduce weight while maintaining strength.</p> Signup and view all the answers

    What is the primary function of a negative feedback loop in the body?

    <p>To maintain homeostasis by reversing deviations from a set point</p> Signup and view all the answers

    What role do calcium ions (Ca²⁺) play in the body?

    <p>They are involved in muscle contraction and nerve impulse transmission.</p> Signup and view all the answers

    When blood calcium levels rise above the normal range, what happens in a negative feedback loop?

    <p>Calcitonin secretion increases to lower calcium levels.</p> Signup and view all the answers

    What is the primary hormone responsible for increasing blood calcium levels?

    <p>Parathyroid hormone (PTH)</p> Signup and view all the answers

    How do mechanical forces influence bone remodeling?

    <p>They stimulate bone formation in areas subjected to stress.</p> Signup and view all the answers

    What effect do gravitational forces have on bone structure?

    <p>They influence the alignment and strength of bone trabeculae.</p> Signup and view all the answers

    What is the result of prolonged inactivity on bone density?

    <p>Bone density decreases due to lack of mechanical stress.</p> Signup and view all the answers

    In calcium homeostasis, what triggers the secretion of parathyroid hormone (PTH)?

    <p>Low levels of calcium in the blood</p> Signup and view all the answers

    What is the normal range of calcium ions (Ca²⁺) in the blood?

    <p>9 – 11 mg/dl</p> Signup and view all the answers

    How much calcium is typically found in the human body?

    <p>1200 – 1400 g</p> Signup and view all the answers

    What percentage of total body calcium is stored in bone mineral?

    <p>99%</p> Signup and view all the answers

    Which hormone decreases blood calcium levels when they are elevated?

    <p>Calcitonin</p> Signup and view all the answers

    Why is maintaining blood calcium levels important for the body?

    <p>It is crucial for muscle contraction, nerve function, and blood clotting.</p> Signup and view all the answers

    What do osteoclasts release to digest the bone matrix?

    <p>Proteolytic enzymes and H⁺ ions</p> Signup and view all the answers

    What happens to osteoid after it is secreted by osteoblasts?

    <p>It undergoes mineralization.</p> Signup and view all the answers

    What process allows for the continuous renewal and maintenance of bone tissue?

    <p>Bone remodeling</p> Signup and view all the answers

    How well-defined is the process of mineralization of osteoid in adult bone?

    <p>It is not well defined.</p> Signup and view all the answers

    Which cells are responsible for the breakdown of bone tissue during remodeling?

    <p>Osteoclasts</p> Signup and view all the answers

    At what age does the rate of bone remodeling and deposition begin to decline significantly?

    <p>Up to age 25</p> Signup and view all the answers

    What is the typical percentage of bone mass lost each decade after the age of 40?

    <p>~10%</p> Signup and view all the answers

    Which hormone's decline primarily influences bone remodeling as individuals age?

    <p>Estrogen/Testosterone</p> Signup and view all the answers

    What condition is associated with a significant decline in bone formation after age 35?

    <p>Higher risk of fractures and osteoporosis</p> Signup and view all the answers

    What factors influence the rate of bone remodeling and deposition as one ages?

    <p>Diet and physical activity levels</p> Signup and view all the answers

    Which type of cartilage is predominant in the skeleton before 8 weeks of gestation?

    <p>Hyaline cartilage</p> Signup and view all the answers

    What initiates primary ossification?

    <p>Secretion of osteoid by periosteal osteoblasts</p> Signup and view all the answers

    What structure encircles the diaphysis during the early stages of bone development?

    <p>Bone collar</p> Signup and view all the answers

    During endochondral ossification, what happens to the cartilage?

    <p>It gradually becomes calcified.</p> Signup and view all the answers

    What persists after the ossification of the epiphyses?

    <p>Only at the epiphyseal plates and articular cartilages</p> Signup and view all the answers

    What defines a nondisplaced fracture?

    <p>A fracture where the bone retains its normal position</p> Signup and view all the answers

    Which type of fracture is characterized by a break that goes all the way through the bone?

    <p>Complete fracture</p> Signup and view all the answers

    What is an incomplete fracture?

    <p>A fracture that doesn't break all the way through the bone</p> Signup and view all the answers

    How does an open (compound) fracture differ from a closed (simple) fracture?

    <p>The bone penetrates the skin in an open fracture</p> Signup and view all the answers

    Which statement accurately describes a displaced fracture?

    <p>The ends of the bone are out of alignment</p> Signup and view all the answers

    In infants, red marrow is primarily located in which part of the bone?

    <p>In the medullary cavity of the diaphysis and all areas of spongy bone</p> Signup and view all the answers

    What is the main role of red marrow in the human body?

    <p>Haematopoiesis (production of blood cells)</p> Signup and view all the answers

    In adults, red marrow is predominantly found in which areas?

    <p>In the diploe of flat bones like the pelvis, sternum, and skull</p> Signup and view all the answers

    Where is yellow marrow primarily located in adults?

    <p>In the epiphyses of long bones</p> Signup and view all the answers

    For clinical procedures, the best source of red marrow in adults is typically found in which part of the body?

    <p>The flat bones, such as the pelvis</p> Signup and view all the answers

    What physiological process is primarily influenced by osteocalcin secretion from osteoblasts?

    <p>Insulin production and uptake</p> Signup and view all the answers

    What is the effect of osteocalcin on pancreatic beta cells?

    <p>It promotes the proliferation and insulin production of beta cells.</p> Signup and view all the answers

    In individuals with type 2 diabetes, how are osteocalcin levels typically affected?

    <p>They are reduced, indicating impaired metabolic function.</p> Signup and view all the answers

    What role does insulin have on osteocalcin levels in bone?

    <p>It promotes the activation of inactive osteocalcin.</p> Signup and view all the answers

    Which hormone associated with fat metabolism is stimulated by osteocalcin?

    <p>Adiponectin, which restricts fat storage.</p> Signup and view all the answers

    What effect does osteocalcin secretion by osteoblasts primarily have on the body?

    <p>It influences insulin production and uptake.</p> Signup and view all the answers

    How does insulin interact with osteocalcin in bone tissues?

    <p>It activates the inactive form of osteocalcin.</p> Signup and view all the answers

    In individuals with type 2 diabetes, how do osteocalcin levels typically change?

    <p>They decrease.</p> Signup and view all the answers

    Which substance is stimulated by osteocalcin and is known to influence fat metabolism?

    <p>Adiponectin</p> Signup and view all the answers

    Which statement best describes the relationship between osteocalcin and insulin?

    <p>There exists a reciprocal synergistic relationship.</p> Signup and view all the answers

    What is the primary function of osteocalcin secretion by osteoblasts?

    <p>Insulin production and uptake</p> Signup and view all the answers

    What role does osteocalcin play in relation to pancreatic beta cells?

    <p>It targets beta cells to divide and produce insulin.</p> Signup and view all the answers

    What happens to osteocalcin levels in individuals with type 2 diabetes?

    <p>They are reduced.</p> Signup and view all the answers

    How does insulin interact with osteocalcin in bone tissue?

    <p>It activates inactive osteocalcin.</p> Signup and view all the answers

    Which hormone is stimulated by osteocalcin and plays a role in fat metabolism?

    <p>Adiponectin</p> Signup and view all the answers

    What is the functional contractile unit of a skeletal muscle?

    <p>Sarcomere</p> Signup and view all the answers

    Which characteristic of skeletal muscle allows it to respond to stimuli?

    <p>Excitability</p> Signup and view all the answers

    What is the primary function of skeletal muscle contraction?

    <p>To move bones</p> Signup and view all the answers

    Which process occurs when skeletal muscle receives a neural stimulus?

    <p>It becomes excitable and contracts</p> Signup and view all the answers

    Which statement accurately describes skeletal muscles?

    <p>They contract to produce movement.</p> Signup and view all the answers

    What is the structure called that enables each myofiber to receive signals from a nerve?

    <p>Neuromuscular junction</p> Signup and view all the answers

    What mechanism initiates muscle contraction?

    <p>An action potential traveling down the motor neuron</p> Signup and view all the answers

    Which neurotransmitter is released at the neuromuscular junction to facilitate muscle contraction?

    <p>Acetylcholine</p> Signup and view all the answers

    What is the immediate effect of acetylcholine binding to the muscle fiber membrane?

    <p>It triggers the muscle fiber to generate its own action potential.</p> Signup and view all the answers

    What occurs at the neuromuscular junction when an action potential from the motor neuron arrives?

    <p>Neurotransmitters are released from the motor neuron.</p> Signup and view all the answers

    What structure does each myofiber receive from a nerve?

    <p>Neuromuscular junction</p> Signup and view all the answers

    What initiates muscle contraction?

    <p>An action potential traveling down the motor neuron</p> Signup and view all the answers

    Which neurotransmitter is released at the neuromuscular junction to facilitate muscle contraction?

    <p>Acetylcholine</p> Signup and view all the answers

    What occurs when acetylcholine binds to receptors on the muscle fiber membrane?

    <p>It triggers the muscle fiber to generate its own action potential.</p> Signup and view all the answers

    Which ion is primarily responsible for triggering muscle contraction after the action potential is generated?

    <p>Calcium</p> Signup and view all the answers

    What happens when acetylcholine (ACh) binds to its receptors on the muscle fiber membrane?

    <p>Ligand-gated ion channels open.</p> Signup and view all the answers

    Which ions pass through the ligand-gated ion channels after ACh binds to its receptors?

    <p>Na+ and K+</p> Signup and view all the answers

    What is the result of more Na+ diffusing into the muscle fiber than K+ diffusing out?

    <p>A transient change in membrane potential occurs (local depolarization).</p> Signup and view all the answers

    What is the net effect on the membrane potential when acetylcholine opens ligand-gated ion channels?

    <p>Local depolarization</p> Signup and view all the answers

    Why does more sodium (Na+) diffuse into the muscle fiber than potassium (K+) diffuses out during local depolarization?

    <p>The electrochemical gradient favors sodium influx.</p> Signup and view all the answers

    What is the immediate consequence of local depolarization in the muscle fiber membrane?

    <p>The action potential spreads across the sarcolemma.</p> Signup and view all the answers

    What triggers the opening of ligand-gated ion channels in the neuromuscular junction?

    <p>Binding of acetylcholine to the receptor</p> Signup and view all the answers

    What type of ion channel is opened by the binding of acetylcholine at the neuromuscular junction?

    <p>Ligand-gated ion channel</p> Signup and view all the answers

    What are T-tubules in skeletal muscle cells?

    <p>Continuous extensions of the sarcolemma</p> Signup and view all the answers

    What is the primary function of T-tubules in muscle fibers?

    <p>To transmit electrical impulses deep within the muscle cell</p> Signup and view all the answers

    How do T-tubules contribute to muscle contraction?

    <p>By allowing the action potential to penetrate deep into the muscle fiber</p> Signup and view all the answers

    What is the result of the electrical impulse traveling through the T-tubules?

    <p>The whole muscle cell contracts almost simultaneously</p> Signup and view all the answers

    Where are T-tubules located in relation to the sarcomere?

    <p>At the A-band/I-band junction</p> Signup and view all the answers

    What happens when an electrical impulse travels down the T-tubules?

    <p>Calcium ions are released from the sarcoplasmic reticulum</p> Signup and view all the answers

    Why is it important for T-tubules to transmit electrical impulses deep into the muscle fiber?

    <p>To ensure the entire muscle fiber contracts simultaneously</p> Signup and view all the answers

    Which structure does the T-tubule system work closely with to trigger muscle contraction?

    <p>Sarcoplasmic reticulum</p> Signup and view all the answers

    What is the primary role of the sarcoplasmic reticulum in muscle fibers?

    <p>Regulating muscle contraction by storing and releasing calcium</p> Signup and view all the answers

    How is the sarcoplasmic reticulum best described?

    <p>An elaborate smooth endoplasmic reticulum surrounding each myofibril</p> Signup and view all the answers

    What occurs when the sarcoplasmic reticulum releases calcium ions?

    <p>The myosin heads bind to actin filaments, triggering contraction.</p> Signup and view all the answers

    In which location is calcium stored in a muscle fiber prior to contraction?

    <p>In the sarcoplasmic reticulum</p> Signup and view all the answers

    How does the sarcoplasmic reticulum contribute to muscle contraction regulation?

    <p>By storing calcium and releasing it on demand</p> Signup and view all the answers

    What triggers the sarcoplasmic reticulum to release calcium ions?

    <p>An action potential traveling down the T-tubules</p> Signup and view all the answers

    What happens when calcium is pumped back into the sarcoplasmic reticulum?

    <p>The muscle fiber relaxes.</p> Signup and view all the answers

    What is the relationship between the sarcoplasmic reticulum and the myofibrils in a muscle fiber?

    <p>The SR surrounds the myofibrils and regulates calcium release for contraction.</p> Signup and view all the answers

    What is the role of tropomyosin in muscle contraction?

    <p>Blocks myosin binding sites on actin in the absence of calcium.</p> Signup and view all the answers

    Which of the following accurately describes troponin's functions?

    <p>Binds to calcium ions to initiate muscle contraction.</p> Signup and view all the answers

    What is the composition of the troponin complex?

    <p>Three subunits: Troponin C, I, and T.</p> Signup and view all the answers

    How do troponin and tropomyosin interact during muscle contraction?

    <p>Calcium binding to troponin causes tropomyosin to shift and expose actin sites.</p> Signup and view all the answers

    What clinical significance do troponin levels in the blood indicate?

    <p>Damage to cardiac muscle signaling a potential heart attack.</p> Signup and view all the answers

    What is the outcome when calcium ions bind to troponin during muscle contraction?

    <p>Troponin changes shape, causing tropomyosin to move.</p> Signup and view all the answers

    How does the movement of tropomyosin affect muscle contraction?

    <p>It exposes the myosin-binding sites on actin.</p> Signup and view all the answers

    Which ion is crucial for triggering the movement of tropomyosin during muscle contraction?

    <p>Calcium ions (Ca2+)</p> Signup and view all the answers

    What is the primary function of tropomyosin in resting muscle fibers?

    <p>It blocks myosin-binding sites on actin, preventing contraction.</p> Signup and view all the answers

    What effect does the removal of calcium from troponin have on muscle fibers?

    <p>Tropomyosin blocks the myosin-binding sites again.</p> Signup and view all the answers

    What initiates the exposure of myosin-binding sites on actin during contraction?

    <p>Calcium ions binding to troponin.</p> Signup and view all the answers

    In the absence of calcium ions, what happens to the position of tropomyosin on actin filaments?

    <p>Tropomyosin blocks the myosin-binding sites.</p> Signup and view all the answers

    What is a direct consequence of calcium ions binding to troponin?

    <p>Troponin undergoes a conformational change affecting tropomyosin.</p> Signup and view all the answers

    What is excitation-contraction coupling?

    <p>The link between the action potential and the mechanical contraction of the muscle.</p> Signup and view all the answers

    What triggers the wave of depolarization in the muscle fiber?

    <p>The influx of sodium ions through ligand-gated channels</p> Signup and view all the answers

    Which structure transmits the action potential deep into the muscle fiber during excitation-contraction coupling?

    <p>The T-tubules</p> Signup and view all the answers

    What is the immediate effect of the action potential traveling down the T-tubules?

    <p>Calcium ions are released from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What is released from the sarcoplasmic reticulum in response to the action potential traveling through the T-tubules?

    <p>Calcium ions</p> Signup and view all the answers

    How does calcium contribute to the excitation-contraction coupling process?

    <p>It binds to troponin, which causes tropomyosin to move away from the myosin-binding sites on actin.</p> Signup and view all the answers

    What happens after calcium is released from the sarcoplasmic reticulum during excitation-contraction coupling?

    <p>Calcium binds to troponin, allowing contraction to begin.</p> Signup and view all the answers

    Which of the following events directly follows the spread of depolarization across the sarcolemma?

    <p>Calcium ions are released from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What happens to calcium (Ca2+) when the action potential (AP) stops?

    <p>It is pumped back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    What occurs to cross-bridge formation when calcium is removed from the cytoplasm?

    <p>Cross-bridge formation is inhibited, and actin and myosin can slide past each other.</p> Signup and view all the answers

    What causes the muscle fibers to relax after the action potential ends?

    <p>Calcium is actively transported back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    Why do actin and myosin filaments slide past each other when no cross-bridges are formed?

    <p>Due to contraction of another muscle or the muscle’s own weight.</p> Signup and view all the answers

    What ensures that the muscle is ready for the next action potential?

    <p>Calcium is stored in the cisternae of the sarcoplasmic reticulum.</p> Signup and view all the answers

    Why is calcium concentration in the cisternae of the sarcoplasmic reticulum high after muscle relaxation?

    <p>To ensure calcium can quickly diffuse into the cytoplasm when the next action potential arrives.</p> Signup and view all the answers

    Which mechanism is responsible for returning calcium to the sarcoplasmic reticulum?

    <p>Active transport mediated by calcium pumps.</p> Signup and view all the answers

    What is the primary role of ATP during muscle contraction and relaxation?

    <p>To provide energy for cross-bridge cycling.</p> Signup and view all the answers

    What occurs to calcium (Ca2+) after the action potential (AP) ceases?

    <p>It is pumped back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    What happens to cross-bridge formation when calcium is removed from the cytoplasm?

    <p>Cross-bridge formation is inhibited, and actin and myosin can slide past each other.</p> Signup and view all the answers

    What is the primary reason that muscle fibers relax after the action potential ends?

    <p>Calcium is actively transported back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    Why do actin and myosin filaments slide past each other when no cross-bridges are formed?

    <p>Due to contraction of another muscle or the muscle’s own weight.</p> Signup and view all the answers

    What ensures that the muscle is prepared for the next action potential?

    <p>Calcium is stored in the cisternae of the sarcoplasmic reticulum.</p> Signup and view all the answers

    Why is there a high concentration of calcium in the cisternae of the sarcoplasmic reticulum after muscle relaxation?

    <p>To ensure calcium can quickly diffuse into the cytoplasm when the next action potential arrives.</p> Signup and view all the answers

    Which mechanism is responsible for returning calcium to the sarcoplasmic reticulum?

    <p>Active transport via calcium pumps.</p> Signup and view all the answers

    What happens to muscle contraction when cross-bridges are broken down by ATP?

    <p>Muscle relaxation occurs as actin and myosin detach.</p> Signup and view all the answers

    What process is primarily responsible for maintaining muscle contraction during active transport?

    <p>Active transport using ATP</p> Signup and view all the answers

    What is the primary reason for the rigidity of muscles after death?

    <p>ATP depletion preventing myosin detachment</p> Signup and view all the answers

    What prevents cross-bridge formation during muscle relaxation?

    <p>The absence of calcium in the cytoplasm</p> Signup and view all the answers

    What happens to calcium ions in muscle fibers after death?

    <p>Calcium leaks into the cytoplasm, promoting contraction</p> Signup and view all the answers

    Which of the following effects of rigor mortis is observed as time progresses after death?

    <p>Rigidity peaks and then diminishes</p> Signup and view all the answers

    What role does ATP play in muscle contraction and relaxation mechanisms?

    <p>ATP is required for myosin heads to detach from actin</p> Signup and view all the answers

    What physiological change triggers muscle contraction after death?

    <p>Leakage of calcium ions into the cytoplasm</p> Signup and view all the answers

    Which statement best describes the role of calcium in muscle contraction?

    <p>Calcium binds to troponin, facilitating cross-bridge formation</p> Signup and view all the answers

    What occurs to calcium (Ca2+) when the action potential stops?

    <p>It is pumped back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    What is the effect of removing calcium from the cytoplasm on cross-bridge formation?

    <p>Cross-bridge formation is inhibited, allowing actin and myosin to slide past each other.</p> Signup and view all the answers

    What causes muscle fibers to relax after the action potential ends?

    <p>Calcium is actively transported back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    Why do actin and myosin slide past each other when no cross-bridges are formed?

    <p>Due to contraction of another muscle or the muscle’s own weight.</p> Signup and view all the answers

    What ensures that the muscle is ready for the next action potential?

    <p>Calcium is stored in the cisternae of the sarcoplasmic reticulum.</p> Signup and view all the answers

    Why is calcium concentration in the cisternae of the sarcoplasmic reticulum high after muscle relaxation?

    <p>To ensure calcium can quickly diffuse into the cytoplasm with the next action potential.</p> Signup and view all the answers

    Which mechanism is responsible for returning calcium to the sarcoplasmic reticulum?

    <p>ATP-dependent calcium pumps.</p> Signup and view all the answers

    What role does ATP play in muscle relaxation?

    <p>It fuels the active transport of calcium back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    What is the primary mechanism of muscle contraction that involves energy usage?

    <p>Active transport using ATP</p> Signup and view all the answers

    What prevents cross-bridge formation during muscle relaxation?

    <p>The absence of calcium in the cytoplasm</p> Signup and view all the answers

    What physiological process contributes to the rigidity observed during rigor mortis?

    <p>ATP depletion leading to myosin attachment to actin</p> Signup and view all the answers

    Which event occurs after death that contributes to the phenomenon of rigor mortis?

    <p>Calcium leakage into the cytoplasm triggering contractions</p> Signup and view all the answers

    Why do muscles remain contracted in rigor mortis despite the lack of ATP?

    <p>Due to the binding of calcium to troponin allowing continuous contraction</p> Signup and view all the answers

    What role does ATP play in muscle contraction and relaxation?

    <p>It facilitates the removal of calcium from the cytoplasm after contraction</p> Signup and view all the answers

    What causes the sustained contraction in muscle fibers post-mortem?

    <p>Retention of calcium ions due to impaired regulation</p> Signup and view all the answers

    What physiological change primarily leads to the rigidity of muscles after death?

    <p>Inability of myosin to detach from actin due to ATP depletion</p> Signup and view all the answers

    What describes muscle tone?

    <p>A state of partial contraction that keeps muscles firm without producing active movement.</p> Signup and view all the answers

    What is the primary function of muscle tone?

    <p>To maintain posture and stabilize joints.</p> Signup and view all the answers

    What mechanism is primarily responsible for maintaining muscle tone?

    <p>Spinal reflexes that activate motor units.</p> Signup and view all the answers

    How are small motor units characterized compared to large motor units?

    <p>Small motor units control fine movements, while large motor units control large muscles.</p> Signup and view all the answers

    Which statement best describes the function of large motor units?

    <p>They produce powerful, large-scale movements such as those in the thighs or back.</p> Signup and view all the answers

    What role do spinal reflexes have concerning muscle tone?

    <p>By intermittently activating motor units, keeping muscles ready for action.</p> Signup and view all the answers

    Which option correctly defines a small motor unit?

    <p>A single neuron controlling only a few muscle fibers, allowing for precise movement.</p> Signup and view all the answers

    What factor allows large motor units to produce powerful movements?

    <p>They are connected to a larger number of muscle fibers.</p> Signup and view all the answers

    What defines a motor unit?

    <p>A single motor neuron and all the muscle fibers it innervates.</p> Signup and view all the answers

    What characterizes the latent phase of a muscle contraction?

    <p>There is a delay between the action potential and the onset of contraction.</p> Signup and view all the answers

    During which phase do muscle fibers actively generate tension and shorten?

    <p>Contraction phase</p> Signup and view all the answers

    What is the primary event during the relaxation phase of muscle contraction?

    <p>Calcium is pumped back into the sarcoplasmic reticulum, and tension decreases.</p> Signup and view all the answers

    Which factor primarily influences the speed and duration of muscle contractions?

    <p>The enzyme and metabolic properties of myofibrils.</p> Signup and view all the answers

    Which muscle fiber type is expected to contract the fastest?

    <p>Type IIb fibers (fast-twitch, glycolytic)</p> Signup and view all the answers

    Why do some muscle contractions last longer than others?

    <p>All of the above.</p> Signup and view all the answers

    What type of muscle contraction is characterized by a rapid and brief response to a single action potential?

    <p>Twitch contraction</p> Signup and view all the answers

    Which type of muscle fiber is primarily associated with endurance activities?

    <p>Type I fibers</p> Signup and view all the answers

    What is a key characteristic of slow-twitch (Type I) muscle fibers?

    <p>High myoglobin content</p> Signup and view all the answers

    Fast-twitch muscle fibers are best suited for which type of activity?

    <p>Sprinting or weightlifting</p> Signup and view all the answers

    What is the primary energy source for fast-twitch (Type II) muscle fibers?

    <p>Anaerobic glycolysis</p> Signup and view all the answers

    Which of the following best describes the contraction velocity of fast-twitch muscle fibers?

    <p>Rapid and powerful</p> Signup and view all the answers

    Why do slow-twitch (Type I) fibers have more blood capillaries than fast-twitch (Type II) fibers?

    <p>To supply oxygen for aerobic metabolism</p> Signup and view all the answers

    Which muscle fiber type would you expect to have a larger diameter?

    <p>Type IIb fibers</p> Signup and view all the answers

    Fast-twitch fibers (Type II) can be further divided into which categories?

    <p>Type IIa and Type IIb</p> Signup and view all the answers

    Which type of muscle fiber is primarily associated with endurance activities?

    <p>Type I fibers</p> Signup and view all the answers

    What is a key characteristic of slow-twitch (Type I) muscle fibers?

    <p>High myoglobin content</p> Signup and view all the answers

    Fast-twitch muscle fibers are best suited for which type of activity?

    <p>Sprinting or weightlifting</p> Signup and view all the answers

    What is the primary energy source for fast-twitch (Type II) muscle fibers?

    <p>Anaerobic glycolysis</p> Signup and view all the answers

    Which of the following best describes the contraction velocity of fast-twitch muscle fibers?

    <p>Rapid and powerful</p> Signup and view all the answers

    Why do slow-twitch (Type I) fibers have more blood capillaries than fast-twitch (Type II) fibers?

    <p>To supply oxygen for aerobic metabolism</p> Signup and view all the answers

    Which muscle fiber type would you expect to have a larger diameter?

    <p>Type IIb fibers</p> Signup and view all the answers

    Fast-twitch fibers (Type II) can be further divided into which categories?

    <p>Type IIa and Type IIb</p> Signup and view all the answers

    What primarily causes glycolytic muscles to fatigue quickly?

    <p>Due to lactic acid build-up from anaerobic metabolism</p> Signup and view all the answers

    Which energy pathway do endurance muscles predominantly rely on?

    <p>Aerobic oxidative phosphorylation</p> Signup and view all the answers

    What advantage do slow-twitch fibers have during endurance activities?

    <p>They can sustain prolonged activity due to a constant supply of ATP.</p> Signup and view all the answers

    How can muscle function affect fiber type distribution?

    <p>Different activities and training can lead to adaptations in fiber type distribution.</p> Signup and view all the answers

    Which muscle fibers are primarily engaged in short bursts of high-intensity activity?

    <p>Type IIb fibers</p> Signup and view all the answers

    What is the effect of prolonged exercise on ATP production in muscle fibers?

    <p>Type I fibers maintain a constant ATP production through aerobic processes.</p> Signup and view all the answers

    What adaptation is commonly observed in athletes training for endurance events?

    <p>Increased number of slow-twitch fibers and mitochondrial density</p> Signup and view all the answers

    What role does lactic acid play in muscle fatigue during high-intensity exercise?

    <p>It contributes to the feeling of fatigue and discomfort.</p> Signup and view all the answers

    Why do glycolytic (fast-twitch) muscles fatigue quickly?

    <p>Due to lactic acid build-up from anaerobic metabolism</p> Signup and view all the answers

    Which energy production pathway is primarily used by endurance muscles with high content of slow-twitch (Type I) fibers?

    <p>Aerobic oxidative phosphorylation</p> Signup and view all the answers

    What is the main advantage of slow-twitch (Type I) fibers in endurance activities?

    <p>They can sustain prolonged activity due to a constant supply of ATP.</p> Signup and view all the answers

    How does muscle function influence fiber type composition?

    <p>Different activities and training can lead to adaptations in fiber type distribution.</p> Signup and view all the answers

    Which type of muscle fibers is primarily used during short bursts of high-intensity activity?

    <p>Type IIb fibers</p> Signup and view all the answers

    What happens to ATP production in muscle fibers during prolonged exercise?

    <p>Type I fibers maintain a constant ATP production through aerobic processes.</p> Signup and view all the answers

    Which of the following adaptations would you expect to see in athletes training for endurance events?

    <p>Increased number of slow-twitch fibers and mitochondrial density</p> Signup and view all the answers

    What role does lactic acid play in muscle fatigue during high-intensity exercise?

    <p>It contributes to muscle fatigue and discomfort.</p> Signup and view all the answers

    What is a primary adaptation to endurance training?

    <p>Increase in the number of mitochondria and capillaries in fibers</p> Signup and view all the answers

    Which adaptation occurs as a result of strength training?

    <p>Fusion of satellite cells to increase nuclear content</p> Signup and view all the answers

    What is the main goal of endurance training?

    <p>To improve aerobic capacity and stamina</p> Signup and view all the answers

    Which adaptation is specifically linked to strength training?

    <p>Increased cross-sectional area of muscle fibers</p> Signup and view all the answers

    What happens to the number of myofibers as a result of resistance training?

    <p>Myofiber numbers do not increase</p> Signup and view all the answers

    What is the primary reason for the increase in fiber diameter during strength training?

    <p>Increase in the amount of actin and myosin</p> Signup and view all the answers

    What type of muscle fibers are primarily recruited during endurance training?

    <p>Slow-twitch (Type I)</p> Signup and view all the answers

    Which of the following statements is true regarding muscle adaptations to training?

    <p>Strength training increases the nuclear content of muscle fibers without increasing myofiber numbers.</p> Signup and view all the answers

    What is a primary adaptation to endurance training?

    <p>Increase in the number of mitochondria and capillaries in fibers</p> Signup and view all the answers

    Which adaptation occurs as a result of strength training?

    <p>Fusion of satellite cells to increase nuclear content</p> Signup and view all the answers

    What is the main goal of endurance training?

    <p>To improve aerobic capacity and stamina</p> Signup and view all the answers

    Which adaptation is specifically linked to strength training?

    <p>Increased cross-sectional area of muscle fibers</p> Signup and view all the answers

    What happens to the number of myofibers as a result of resistance training?

    <p>Myofiber numbers do not increase</p> Signup and view all the answers

    What is the primary reason for the increase in fiber diameter during strength training?

    <p>Increase in the amount of actin and myosin</p> Signup and view all the answers

    What type of muscle fibers are primarily recruited during endurance training?

    <p>Slow-twitch (Type I)</p> Signup and view all the answers

    Which of the following statements is true regarding muscle adaptations to training?

    <p>Strength training increases the nuclear content of muscle fibers without increasing myofiber numbers.</p> Signup and view all the answers

    Study Notes

    Bone Tissue

    • Osteocytes are the primary cell type found in bone tissue.
    • Osteoid refers to the matrix of the bone that contains proteoglycans and glycoproteins, providing flexibility and strength.
    • Collagen fibers are primarily responsible for the tensile strength of bone, contributing to its flexibility and ability to dissipate energy.
    • The organic components of bone, like collagen fibers, proteoglycans, and glycoproteins, provide a buffer against mechanical forces, reducing the risk of fractures.
    • Calcium phosphates are the primary inorganic component of bone, contributing to its hardness.
    • Approximately 50% of bone's volume and 70% of its weight is made up of inorganic components.
    • Mineral salts crystalize around collagen fibers, increasing the hardness of the bone.
    • Calcium phosphate plays a crucial role in contributing to the hardness and strength of bone.
    • Hydroxyapatite is the main mineral component of bone, contributing to its hardness.
    • Bone marrow is the soft, spongy tissue found inside bones, responsible for blood cell production and fat storage.
    • Osteoblasts are responsible for building new bone tissue.
    • Osteoclasts are responsible for breaking down bone tissue.

    Bone Tissue: Cells and Composition

    • Osteocytes are the primary cell type found in bone tissue
    • Osteoid refers to the organic matrix of bone, which contains proteoglycans and glycoproteins
    • Collagen fibers provide tensile strength and flexibility to bone, contributing to its toughness and ability to dissipate energy
    • Proteoglycans and glycoproteins contribute to the strength and flexibility of bone, acting as a buffer against mechanical forces and reducing the risk of fractures
    • Calcium phosphates are the primary inorganic component of bone, contributing to its hardness
    • Mineral salts make up approximately 50% of bone's volume and 70% of its weight, crystalizing around collagen fibers to increase hardness
    • Osteogenic cells are the precursor cells that give rise to osteoblasts and most other bone cells
    • Osteoblasts form new bone by secreting bone matrix, a process known as osteogenesis
    • Osteocytes are formed when osteoblasts become embedded in the bone matrix and communicate mechanical stress signals to remodeling cells
    • Osteoclasts are responsible for absorbing bone tissue during growth and healing
    • Bone lining cells maintain the bone matrix on surfaces not undergoing remodeling
    • Osteocytes are not directly involved in the formation or absorption of bone tissue.

    Bone Structure

    • Osteocytes are the primary cell type in bone tissue. They are responsible for maintaining the bone matrix and communicating mechanical stress signals to remodeling cells.
    • Osteoid is the unmineralized portion of bone, containing proteoglycans and glycoproteins.
    • Collagen fibers provide the tensile strength of bone.
    • Hydroxyapatite (calcium phosphate) provides compressive strength to bone.
    • Bone's organic components (collagen and osteoid) buffer against mechanical forces and reduce the risk of fractures.
    • Around 50% of bone's volume is made up of mineral salts, accounting for 70% of bone's weight.

    Bone Cells

    • Osteoblasts form new bone by secreting bone matrix during the process called osteogenesis.
    • Osteoclasts absorb bone tissue during growth and healing.
    • Osteogenic cells are the precursors to both osteoblasts and other bone cells.
    • Bone lining cells maintain the matrix on surfaces not undergoing remodeling.

    Bone Remodeling

    • Bone remodeling involves coordinated activity of osteoblasts and osteoclasts.
    • Osteoblasts lay down new bone matrix to form new bone.
    • Osteoclasts resorb bone tissue and break down bone.
    • The continuous process of bone remodeling is essential for maintaining bone strength and responding to changes in mechanical stress.

    Osteon

    • The osteon is also known as the Haversian system.
    • It is a structural unit of compact bone.
    • The primary feature is a hollow tube of bone matrix.
    • Collagen fibers in adjacent lamellae (concentric rings of bone matrix) run in different directions.
    • This arrangement of collagen fibers provides resistance to strain and torsion.
    • Bone salts align with and alternate the direction of collagen fibers, further strengthening the osteon.
    • The osteon's structure is an example of how structure relates to function.
    • Elongated cylinders of an osteon are oriented parallel to the long axis of the bone.

    Osteon Structure and Function

    • The osteon, also known as the Haversian system, is a primary structural unit of compact bone.
    • The osteon is characterized by a hollow tube of bone matrix, which provides strength and resistance to strain and torsion.
    • Collagen fibers within adjacent lamellae of an osteon run in different directions, contributing to the bone’s strength and flexibility.
    • Tiny weight-bearing pillars within osteons provide resistance to strain and torsion, enhancing the bone’s structural integrity.
    • Crystals of bone salts, such as hydroxyapatite, align with and alternate the direction of collagen fibers within the lamellae, contributing to the bone’s hardness and rigidity.
    • The structure of the osteon is a clear example of how structure relates to function, as its intricate design maximizes strength and resilience.
    • The elongated cylinders of an osteon are oriented parallel to the long axis of the bone, providing support and stability.
    • Lamellae, concentric rings of bone matrix, form the structural framework of the osteon, encasing the central canal which contains blood vessels and nerves.

    Osteon Structure

    • The central canal or Haversian canal, is the main channel within the osteon, containing blood vessels and nerves that supply the bone tissue.
    • Osteocytes, mature bone cells, reside in small spaces called lacunae, which are embedded within the lamellae, concentric rings of bone matrix.
    • Canaliculi are tiny channels that connect the lacunae to the central canal, allowing for communication and transport of nutrients and waste products between osteocytes.

    Osteocyte Communication and Function

    • Osteocytes rely on the canaliculi network to communicate with each other and with the central canal.
    • This communication system enables the passage of nutrients, oxygen, and waste products, ensuring the survival and function of osteocytes.
    • The canaliculi are essential for maintaining the health and integrity of the bone tissue.

    Cells of the Osteon

    • Osteocytes are the mature bone cells responsible for maintaining the bone tissue, and they reside in the lacunae within the osteon.
    • Osteoblasts are responsible for forming new bone matrix, while osteoclasts break down bone tissue, contributing to bone remodeling.
    • The Haversian canal serves as the main route for the delivery of nutrients and the removal of waste products from osteocytes.

    Bone Vascularization

    • Bones have a rich blood supply which is essential for their growth, healing, and overall health.
    • Haversian canals and Volkmann's canals contain blood vessels that supply nutrients to the bone.
    • Haversian canals run longitudinally through the bone, while Volkmann's canals connect them to each other and the periosteum.
    • Blood vessels within the canals deliver nutrients and oxygen to osteocytes, removing waste products as well.

    Blood Supply and Bone Health

    • A compromised blood supply can lead to weakened bones, impaired healing, and stunted growth.
    • Nutrient delivery and waste removal via blood vessels are crucial for maintaining bone health.
    • Medullary cavity is a large central space within the bone also supplies nutrients and blood cells.

    Further Key Points

    • Osteocytes, the mature bone cells, reside in lacunae within the bone matrix.
    • Canaliculi are small channels that connect lacunae to each other and to the Haversian canals, facilitating communication between osteocytes.

    Spongy Bone vs. Compact Bone

    • Spongy bone is lighter and less dense than compact bone.

    Spongy Bone Structure

    • Trabeculae and bars of bone make up the framework of spongy bone.
    • Red bone marrow is found within the small, irregular cavities adjacent to trabeculae.

    Canaliculi Function

    • Canaliculi in spongy bone connect to adjacent cavities instead of a central Haversian canal.

    Trabeculae Advantages

    • Trabeculae provide maximum strength.
    • Trabeculae can realign to follow lines of stress, which allows for bone adaptation.

    Blood Cell Production

    • Spongy bone is primarily involved in blood cell production due to the presence of red bone marrow.

    Spongy Bone Design

    • Spongy bone design allows it to absorb shock and reduce weight while maintaining strength.

    Negative Feedback Loops

    • Maintain homeostasis by reversing deviations from a set point.
    • Act to counter changes in the body's internal environment.

    Calcium in the Body

    • Essential for:
      • Muscle contraction
      • Nerve impulse transmission
      • Bone structure

    Calcium Homeostasis

    • High blood calcium levels: Trigger the release of calcitonin, which lowers calcium levels.
    • Low blood calcium levels: Trigger the release of parathyroid hormone (PTH), which increases calcium levels.
    • PTH:
      • Stimulates calcium reabsorption in the kidneys.
      • Increases calcium absorption from the gut.
      • Promotes bone resorption (breakdown of bone tissue).

    Bone Remodeling

    • Mechanical forces:
      • Stimulate bone formation in areas subjected to stress.
      • Influence the alignment and strength of bone trabeculae.
    • Prolonged inactivity:
      • Decreases bone density due to lack of mechanical stress.

    Calcium in the Blood

    • The normal blood calcium ion (Ca²⁺) concentration ranges between 9 and 11 mg/dl.

    Calcium in the Body

    • The human body typically contains between 1200 and 1400 grams of calcium.
    • 99% of the body's calcium is stored in bones.
    • 1.5 grams of calcium are typically present in the blood.

    Calcium Homeostasis

    • The hormonal control loop is the primary mechanism responsible for maintaining stable blood calcium levels.
    • Calcitonin is a hormone that decreases blood calcium levels when they are elevated.
    • Parathyroid hormone (PTH) increases blood calcium levels. PTH stimulates bone resorption, calcium reabsorption in the kidneys, and calcium absorption in the intestines.

    Importance of Calcium

    • Calcium is crucial for various bodily functions, including:
      • Muscle contraction
      • Nerve function
      • Blood clotting

    Osteoclasts and Bone Resorption

    • Osteoclasts release proteolytic enzymes and H⁺ ions to digest the bone matrix.
    • The primary function of osteoclasts is to release calcium and phosphorus into the blood circulation.
    • Osteoclasts are responsible for the breakdown of bone tissue during bone remodeling.

    Osteoblasts and Bone Formation

    • Osteoblasts secrete osteoid, an unmineralized matrix that contributes to bone formation.
    • After secretion, osteoid undergoes mineralization, a process that is not fully understood.
    • Approximately 5% of adult bone is remodeled each week.

    Bone Remodeling

    • Bone remodeling is a continuous process that allows for the renewal and maintenance of bone tissue. This involves both bone formation by osteoblasts and bone resorption by osteoclasts.

    Bone Remodeling and Deposition

    • Bone remodeling and deposition are most vigorous up to age 25.
    • Between ages 25 and 35, the rate of bone remodeling slowly declines.
    • After age 40, bone reabsorption exceeds bone formation.
    • About 10% of bone mass is lost each decade after age 40.
    • This decline in bone formation after age 35 leads to a higher risk of fractures and osteoporosis.

    Factors Influencing Bone Health

    • Physical activity levels and diet significantly influence the rate of bone remodeling and deposition as one ages.
    • Estrogen and testosterone, which decrease with age, are key hormones that influence bone remodeling.

    Maintaining Bone Health After Age 40

    • It is crucial to maintain bone health after age 40 to reduce the risk of osteoporosis and fractures.

    Cartilage Types and Development

    • Hyaline cartilage is the primary cartilage in the skeleton before 8 weeks of gestation.

    Primary Ossification

    • Primary ossification is the process of bone formation from hyaline cartilage.
    • The first step is the secretion of osteoid by periosteal osteoblasts.
    • A bone collar forms around the diaphysis during primary ossification.

    Endochondral Ossification

    • Endochondral ossification is the process by which cartilage is replaced by bone.
    • Calcification of cartilage occurs during this process.

    Periosteal Bud and Ossification

    • The periosteal bud, containing blood vessels, nerves, and red marrow, infiltrates the diaphysis during ossification.

    Bone Formation and Elongation

    • As the diaphysis elongates and the medullary cavity appears, spongy bone is formed.

    Epiphyseal Ossification

    • The epiphyses ossify, but hyaline cartilage persists at the epiphyseal plates and articular surfaces.
    • Hyaline cartilage remains only at the epiphyseal plates and articular cartilages after the epiphyses ossify.

    Fracture Types

    • Nondisplaced fracture: Bone remains in its normal position, no misalignment.
    • Displaced fracture: Bone ends are out of alignment, requiring medical intervention.
    • Complete fracture: Break extends completely through the bone.
    • Incomplete fracture: Break does not go all the way through the bone, it's partial.
    • Open (compound) fracture: Bone protrudes through the skin, increasing risk of infection.
    • Closed (simple) fracture: Skin remains intact, no bone protrusion.

    Red Marrow Location and Function

    • Red marrow is found in the medullary cavity of the diaphysis and all areas of spongy bone in infants.
    • The primary function of red marrow is haematopoiesis (production of blood cells).
    • In adults, red marrow is mostly found in the diploe of flat bones like the pelvis, sternum, and skull.
    • In adults, red marrow is specifically found in the head of long bones.

    Yellow Marrow

    • Yellow marrow primarily consists of fat.
    • In adults, yellow marrow extends into the epiphyses of long bones.

    Bone Marrow Biopsy

    • Bone marrow is most commonly taken from the hip bone (pelvis) for clinical bone marrow biopsies.
    • The flat bones, such as the pelvis, are typically the best source of red marrow for clinical procedures in adults.

    Osteocalcin and Insulin

    • Osteocalcin is a hormone secreted by osteoblasts, primarily influencing insulin production and uptake.
    • Osteocalcin targets pancreatic beta cells to divide and produce insulin.
    • Osteocalcin levels are reduced in patients with type 2 diabetes.
    • Insulin activates inactive osteocalcin in bone.

    Osteocalcin and Adiponectin

    • Osteocalcin stimulates the release of adiponectin from adipocytes.
    • Adiponectin restricts fat storage.

    FGF23

    • Fibroblast growth factor 23 (FGF23) regulates phosphate reabsorption in the kidneys.

    Osteocalcin and Insulin: Synergistic Relationship

    • Osteocalcin and insulin have a two-way synergistic mechanism.
    • Osteocalcin promotes insulin production, and insulin activates osteocalcin.

    Osteocalcin and Insulin Production

    • Osteocalcin, secreted by osteoblasts, primarily influences insulin production and uptake.
    • Osteocalcin directly targets pancreatic beta cells to promote their division and insulin production.
    • In patients with type 2 diabetes, osteocalcin levels are reduced.
    • Insulin activates inactive osteocalcin in bone.

    Adiponectin and Fat Storage

    • Adiponectin, a hormone released by adipocytes, is stimulated by osteocalcin.
    • Adiponectin restricts fat storage and promotes energy expenditure.

    FGF23 and Phosphate Regulation

    • Fibroblast growth factor 23 (FGF23) regulates phosphate reabsorption in the kidneys.

    The Relationship between Osteocalcin and Insulin

    • There is a two-way synergistic mechanism between osteocalcin and insulin.
    • This means that they both influence each other's function and activity.

    Osteocalcin & Insulin

    • Osteocalcin is secreted by osteoblasts and primarily influences insulin production and uptake.
    • Osteocalcin targets pancreatic beta cells to divide and produce insulin.
    • Osteocalcin levels are reduced in patients with type 2 diabetes.
    • Insulin activates inactive osteocalcin in bone.

    Osteocalcin & Adiponectin

    • Osteocalcin stimulates the release of adiponectin from adipocytes.
    • Adiponectin restricts fat storage.

    Osteocalcin & FGF23

    • FGF23 regulates phosphate reabsorption in the kidneys.

    Relationship between Osteocalcin & Insulin

    • There is a two-way synergistic mechanism between osteocalcin and insulin.

    The Functional Contractile Unit of Skeletal Muscle

    • The sarcomere is the functional contractile unit of a skeletal muscle.

    Characteristics of Skeletal Muscle

    • Excitability: The ability of skeletal muscle to respond to stimuli, such as nerve impulses.

    Primary Function of Skeletal Muscle Contraction

    • The primary function of skeletal muscle contraction is to move bones.

    Muscle Contractility

    • Contractility refers to the muscle's ability to shorten and produce movement.

    The Sarcomere in a Skeletal Muscle

    • The sarcomere is the area between two Z discs.

    Neural Stimulation and Skeletal Muscle

    • When skeletal muscle receives a neural stimulus, it becomes excitable and contracts.

    The Role of Skeletal Muscle Contraction in Maintaining Posture

    • Skeletal muscle contraction keeps the body upright and stable, maintaining posture.

    Skeletal Muscle Contraction and Movement

    • Skeletal muscles contract to produce movement.

    Neuromuscular Junction

    • The neuromuscular junction is a specialized synapse where a motor neuron communicates with a muscle fiber.
    • A single motor neuron can innervate multiple muscle fibers.
    • Acetylcholine is the neurotransmitter released at the neuromuscular junction.
    • Acetylcholine binding to receptors on the muscle fiber membrane triggers an action potential in the muscle fiber.
    • This action potential travels along the muscle fiber, leading to muscle contraction.

    Muscle Contraction Initiation

    • An action potential traveling down a motor neuron initiates muscle contraction.
    • This action potential triggers the release of acetylcholine from the motor neuron's axon terminal.
    • Acetylcholine diffuses across the synaptic space and binds to receptors on the muscle fiber membrane.
    • This binding triggers an action potential in the muscle fiber, leading to the release of calcium ions from the sarcoplasmic reticulum.
    • Calcium ions bind to troponin, initiating the sliding filament mechanism of muscle contraction.

    The Neuromuscular Junction

    • The neuromuscular junction is the specialized synapse between a motor neuron and a muscle fiber.

    • It is responsible for transmitting signals from the nervous system to the muscles, initiating muscle contraction.

    Muscle Contraction Initiation

    • Muscle contraction is initiated by an action potential traveling down the motor neuron.

    • This action potential triggers the release of acetylcholine from the motor neuron's axon terminal.

    • Acetylcholine diffuses across the synapse and binds to receptors on the muscle fiber membrane.

    • This binding triggers the muscle fiber to generate its own action potential.

    Role of Calcium

    • The action potential in the muscle fiber travels along the sarcolemma and into the T-tubules.

    • This triggers the release of calcium ions from the sarcoplasmic reticulum.

    • Calcium ions bind to troponin, a protein that regulates the interaction between actin and myosin filaments.

    • This binding allows the actin and myosin filaments to slide past each other, shortening the muscle fiber and causing contraction.

    Acetylcholine and Muscle Contraction

    • Acetylcholine (ACh) binding to its receptors on the muscle fiber membrane opens ligand-gated ion channels
    • These channels allow sodium (Na+) and potassium (K+) ions to pass through
    • More Na+ diffuses into the muscle fiber than K+ diffuses out due to the electrochemical gradient favoring sodium influx
    • This causes a transient change in membrane potential, known as local depolarization
    • Local depolarization triggers the action potential to spread across the sarcolemma

    Neuromuscular Junction: The Key to Muscle Activation

    • The binding of acetylcholine (ACh) to its receptors at the neuromuscular junction opens ligand-gated ion channels
    • These are not voltage-gated, mechanically-gated, or leak channels
    • The opening of these channels allows for the influx of sodium and potassium ions, triggering the sequence of events that lead to muscle contraction

    T-tubules in Muscle Cells

    • T-tubules are continuous extensions of the sarcolemma (muscle cell membrane) that penetrate deep into the muscle fiber.
    • They are essential for transmitting electrical impulses from the surface of the muscle fiber to the interior, ensuring a coordinated contraction of the entire cell.
    • This transmission is crucial because it triggers the release of calcium ions from the sarcoplasmic reticulum (SR), which are necessary for muscle contraction.
    • T-tubules are located at the A-band/I-band junction of the sarcomere, the functional unit of muscle contraction.
    • They work closely with the SR to initiate muscle contraction by allowing the electrical impulse to reach the SR, stimulating calcium release.
    • Without T-tubules, the electrical impulse would only affect the surface of the muscle fiber, resulting in a weak and uncoordinated contraction.
    • The T-tubule system ensures the synchronized release of calcium ions along the entire length of the muscle fiber, resulting in a strong and coordinated contraction.

    Sarcoplasmic Reticulum (SR) and Muscle Contraction

    • Primary Role of SR: The SR's primary role is to regulate muscle contraction by storing and releasing calcium ions (Ca2+).

    • Structure: The SR is an elaborate smooth endoplasmic reticulum that surrounds each myofibril within a muscle fiber.

    • Calcium Release: When an action potential travels down a T-tubule, it triggers the release of Ca2+ from the SR.

    • Contraction Initiation: The release of Ca2+ into the sarcoplasm allows myosin heads to bind to actin filaments, initiating muscle contraction.

    • Calcium Reuptake: After contraction, Ca2+ is actively pumped back into the SR by the SR Ca2+ ATPase pump, leading to muscle relaxation.

    • Relationship with Myofibrils: The SR is positioned around the myofibrils, ensuring that Ca2+ release is precisely targeted to the contractile proteins for efficient contraction.

    Troponin

    • A protein complex found in skeletal and cardiac muscle fibers
    • Controls muscle contraction by regulating the interaction of actin and myosin
    • Binds calcium ions (Ca²⁺) to trigger contraction
    • Composed of three subunits:
      • Troponin C: Binds calcium.
      • Troponin I: Inhibits actin-myosin interactions.
      • Troponin T: Binds to tropomyosin.
    • Elevated blood troponin levels indicate damage to cardiac muscle, often used as a biomarker for myocardial infarction (heart attack)

    Tropomyosin

    • A long, coiled protein found along the length of actin filaments
    • Regulates muscle contraction by blocking myosin binding sites on actin in the absence of calcium.
    • Composed of two identical polypeptide chains forming a coiled-coil structure
    • Positions itself along actin filaments, stabilizing them.
    • Allows contraction when calcium binds to troponin, triggering a shift in tropomyosin, exposing active sites on actin for myosin.

    Interaction Between Troponin and Tropomyosin

    • Both proteins work together to regulate muscle contraction.
    • Calcium binding to troponin leads to a shift in tropomyosin, exposing active sites on actin.
    • Essential for the contraction mechanism in both skeletal and cardiac muscle.

    Muscle Contraction and Troponin

    • Calcium ions (Ca2+) bind to troponin during muscle contraction.
    • This binding causes troponin to change shape, pulling tropomyosin away from the myosin-binding sites on actin.
    • The exposure of myosin-binding sites allows myosin heads to bind to actin, forming cross-bridges.
    • Tropomyosin blocks myosin-binding sites on actin filaments when the muscle is at rest, preventing contraction.
    • This blocking action is reversed when calcium binds to troponin.
    • When calcium is removed from troponin, tropomyosin returns to its blocking position, preventing further cross-bridge formation and muscle contraction.

    Excitation-Contraction Coupling

    • The link between the action potential and muscle contraction.

    Muscle Fiber Depolarization

    • Triggered by the influx of sodium ions through ligand-gated channels.

    T-tubules

    • Transmit the action potential deep into the muscle fiber.

    Calcium Release

    • The action potential traveling down T-tubules triggers the release of calcium ions from the sarcoplasmic reticulum.

    Calcium and Contraction

    • Calcium binds to troponin, causing tropomyosin to move away from the myosin-binding sites on actin.
    • This allows myosin heads to bind to actin filaments, initiating contraction.

    Relaxation

    • After the action potential is over, calcium is actively transported back into the sarcoplasmic reticulum.
    • This allows tropomyosin to cover the myosin binding sites on actin again, ending the contraction.

    Muscle Relaxation and Calcium

    • When the action potential stops, calcium (Ca2+) is pumped back into the sarcoplasmic reticulum.
    • This is achieved through active transport, which requires ATP.

    Cross-Bridge Formation and Muscle Relaxation

    • When calcium is removed from the cytoplasm, cross-bridge formation is inhibited.
    • This is because calcium binds to troponin, which moves tropomyosin away from the myosin-binding sites on actin.
    • Without calcium, tropomyosin blocks the myosin-binding sites, preventing cross-bridge formation.
    • This allows actin and myosin filaments to slide past each other, leading to muscle relaxation.

    Actin and Myosin Sliding

    • During relaxation, actin and myosin filaments slide past each other due to contraction of another muscle or the muscle's own weight.
    • This is not due to any active process within the muscle fiber itself.

    The Sarcoplasmic Reticulum and Muscle Relaxation

    • After muscle relaxation, calcium is stored in the cisternae of the sarcoplasmic reticulum, ensuring it's readily available for the next muscle contraction.
    • This high concentration of calcium in the sarcoplasmic reticulum facilitates rapid diffusion into the cytoplasm when the next action potential arrives.

    Preventing Cross-Bridge Formation

    • The absence of calcium in the cytoplasm prevents cross-bridge formation during muscle relaxation.
    • This is because calcium is essential for moving tropomyosin away from the myosin-binding sites on actin.

    Rigor Mortis

    • Rigor mortis refers to the stiffening of muscles after death.
    • It starts about 4 hours after death, peaks at approximately 13 hours, and lasts about 50 hours.
    • The lack of ATP after death causes the myosin heads to remain attached to the actin filaments, resulting in a sustained muscle contraction.
    • As ATP is required to detach the myosin heads from the actin filaments and pump calcium back into the sarcoplasmic reticulum, the muscles stay contracted in rigor mortis.
    • Calcium leakage from the sarcoplasmic reticulum into the cytoplasm further contributes to the formation of cross-bridges between actin and myosin.
    • Without ATP, the muscle fibers cannot relax, leading to the stiffening associated with rigor mortis.

    Rigor Mortis

    • ATP Depletion

      • ATP is vital for muscle contraction & relaxation.
      • Muscle cells require ATP to detach myosin heads from the actin filaments after contraction.
      • ATP production ends after death due to lack of oxygen, preventing ATP regeneration.

    • Cross-Bridge Formation

      • Without ATP, myosin heads remain attached to actin filaments, causing continuous & sustained contraction.
      • This inability of myosin to detach from actin results in muscle rigidity.

    • Calcium Leakage

      • After death, calcium ions leak from the sarcoplasmic reticulum (SR) into the cytoplasm. - This leakage triggers calcium binding to troponin, moving tropomyosin away from actin's myosin-binding sites.
      • This promotes cross-bridge formation, but the lack of ATP prevents the cycle from completing, sustaining contraction.

    • Lack of Relaxation

      • ATP is also needed to pump calcium back into the SR.
      • The persistent excess calcium in the cytoplasm maintains the contraction and rigidity.

    •  Rigor Mortis onset: >4 hours after death

      • Rises to a peak at ~13 hours
      • Persists for ~50 hours

    Muscle Tone

    • Muscle Tone is a state of partial contraction that maintains muscle firmness without active movement.
    • Spinal reflexes activate motor units, which are responsible for maintaining muscle tone.

    Function of Muscle Tone

    • The function of muscle tone is to maintain posture and stabilize joints.

    Motor Units

    • Small motor units control fine movements, while large motor units control large muscles.
    • A small motor unit is a single neuron controlling a few muscle fibers, enabling precise movement.
    • Large motor units are found in muscles that produce powerful, large-scale movements like those in the thighs or back.

    Spinal Reflexes and Muscle Tone

    • Spinal reflexes contribute to muscle tone by intermittently activating motor units, ensuring muscles are ready for action.

    Importance of Muscle Tone

    • Muscle tone, even in relaxed muscles, ensures muscles are primed for immediate response to stimuli.

    Motor Units

    • A motor unit is a single motor neuron and all the muscle fibers it innervates
    • Each motor neuron can innervate multiple muscle fibers, but each muscle fiber is only innervated by one motor neuron

    Muscle Contraction Phases

    • Latent Phase: A brief delay between the action potential and the onset of contraction
    • Contraction Phase: Muscle fibers generate tension and shorten
    • Relaxation Phase: Calcium is pumped back into the sarcoplasmic reticulum, and tension decreases

    Muscle Fiber Types and Contraction Speed and Duration

    • There are three main types of muscle fibers:
      • Type I fibers (slow-twitch): Slow contraction speed, high resistance to fatigue, used for endurance activities
      • Type IIa fibers (fast-twitch, oxidative): Faster contraction speed than type-I, high resistance to fatigue, used for activities requiring both power and endurance
      • Type IIb fibers (fast-twitch, glycolytic): Fastest contraction speed, low resistance to fatigue, used for short bursts of power

    Factors Influencing Contraction Speed and Duration

    • Muscle fiber type: Type I fibers are slowest while Type IIb are fastest.
    • Metabolic properties: Type I fibers are highly aerobic and use oxygen efficiently, while Type IIb fibers are glycolytic and utilize anaerobic metabolism.
    • Number of motor units activated: Recruiting more motor units increases contraction strength and speed.
    • Frequency of action potentials: More frequent action potentials lead to a stronger contraction.

    Types of Muscle Contractions

    • Twitch contraction: A rapid and brief response to a single action potential.
    • Tetanic contraction: A sustained, powerful contraction resulting from a high frequency of action potentials.

    Muscle Fiber Types

    • Type I fibers are primarily associated with endurance activities.
    • Type I fibers are slow-twitch and have a high myoglobin content, which allows for aerobic respiration.
    • Type II fibers are fast-twitch and are best suited for activities like sprinting or weightlifting.
    • Type II fibers primarily use anaerobic glycolysis for energy production.
    • Type II fibers have a rapid and powerful contraction velocity.
    • Type I fibers have a higher capillary density than Type II fibers to supply oxygen for aerobic metabolism.
    • Type IIb fibers have a larger diameter than Type I fibers.
    • Type I fibers can sustain prolonged activity due to increased myoglobin and capillary density.
    • Type II fibers can be further divided into Type IIa and Type IIb.

    ### Muscle Fiber Types

    • Type I fibers are primarily associated with endurance activities.
    • Type I fibers have a high myoglobin content which allows for greater oxygen storage and aerobic metabolism.
    • Type I fibers have a slower contraction velocity but can sustain prolonged activity.
    • Type I fibers have a higher density of blood capillaries to deliver oxygen for sustained aerobic metabolism.
    • Type I fibers have a smaller diameter compared to Type II fibers.

    Fast-twitch Muscle Fibers

    • Fast-twitch fibers (Type II) are best suited for high-intensity, short-duration activities such as sprinting or weightlifting.
    • Type II fibers primarily rely on anaerobic glycolysis for energy production.
    • Type II fibers have a rapid and powerful contraction velocity.
    • Type II fibers have a larger diameter than Type I fibers.
    • Type II fibers can be further divided into Type IIa and Type IIb.

    ### Type IIa and Type IIb Fibers

    • Type IIa fibers are intermediate in their characteristics, possessing some qualities of both Type I and Type IIb fibers.
    • Type IIb fibers are fastest-twitching and have the largest diameter. They are the most powerful but fatigue quickly

    Muscle Fatigue and Fiber Types

    • Fast-twitch (Type IIb) muscle fibers fatigue quickly due to lactic acid build-up from anaerobic metabolism.
    • Slow-twitch (Type I) muscle fibers primarily use aerobic oxidative phosphorylation for energy production, allowing them to sustain prolonged activity.
    • Slow-twitch fibers are advantageous for endurance activities due to their ability to constantly supply ATP.

    Muscle Function and Fiber Type Adaptation

    • Different activities and training can lead to adaptations in muscle fiber type distribution.
    • Short bursts of high-intensity activity primarily utilize Type IIb fibers.

    ATP Production and Prolonged Exercise

    • Type I fibers maintain a constant ATP production through aerobic processes during prolonged exercise.

    Endurance Training Adaptations

    • Endurance training leads to an increased number of slow-twitch fibers and mitochondrial density.

    Lactic Acid and Muscle Fatigue

    • Lactic acid build-up during high-intensity exercise decreases muscle pH, contributing to fatigue.

    Muscle Fatigue and Fiber Types

    • Fast-twitch (Type IIb) muscle fibers fatigue quickly due to lactic acid build-up from anaerobic metabolism.
    • Endurance muscles rely primarily on aerobic oxidative phosphorylation for energy production, fueled by slow-twitch (Type I) fibers.
    • Slow-twitch fibers are suited for endurance activities because they can sustain prolonged activity with a constant supply of ATP.
    • Muscle fiber type composition is adaptable based on activity and training.
    • High-intensity, short-burst activities primarily utilize fast-twitch (Type IIb) fibers.
    • Type I fibers maintain consistent ATP production through aerobic processes during prolonged exercise.
    • Endurance training leads to increased slow-twitch fibers and mitochondrial density.
    • Lactic acid contributes to muscle fatigue during high-intensity exercise by lowering pH in the muscle environment.

    Muscle Adaptations to Training

    • Endurance training leads to an increase in the number of mitochondria and capillaries in muscle fibers. This enhances the muscle's aerobic capacity.
    • Strength training primarily leads to the fusion of satellite cells to increase nuclear content in muscle fibers. This increases the cross-sectional area of muscle fibers and thus muscle strength.
    • Slow-twitch (Type I) muscle fibers are primarily recruited during endurance training, while strength training primarily impacts the cross-sectional area of muscle fibers.
    • The number of myofibers in a muscle does not increase as a result of either endurance or strength training.
    • Strength training increases the nuclear content of muscle fibers without increasing myofiber numbers, primarily due to an increase in the amount of actin and myosin.

    Muscle Adaptations to Training

    • Endurance training primarily leads to an increase in the number of mitochondria and capillaries within muscle fibers.
    • Strength training results in an increase in the nuclear content of muscle fibers through the fusion of satellite cells. This does not increase the number of myofibers.
    • The main goal of endurance training is to improve aerobic capacity and stamina.
    • Strength training mainly leads to an increase in the cross-sectional area of muscle fibers.
    • The increase in fiber diameter during strength training occurs because of an increase in the amount of actin and myosin.
    • Endurance training mainly recruits slow-twitch (Type I) muscle fibers.

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