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 (C)</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 (D)</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. (C)</p> Signup and view all the answers

What is the primary inorganic component of bone?

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

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

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

What percentage of bone is made up of mineral salts?

<p>70% (A)</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. (D)</p> Signup and view all the answers

Which component do mineral salts crystallize around in bone?

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

Which statement accurately describes the inorganic components of bone?

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

What role do osteoclasts play in bone health?

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

How do proteoglycans and glycoproteins influence bone functionality?

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

Which process facilitates the healing of bone after an injury?

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

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

<p>70% (A)</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 (D)</p> Signup and view all the answers

Which statement is true about osteocytes?

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

What is the primary function of osteoclasts in bone tissue?

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

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

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

Bone lining cells are primarily involved in:

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

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

<p>Providing tensile strength and flexibility (A)</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 (B)</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 (B)</p> Signup and view all the answers

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

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

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

<p>Osteoblast (C)</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. (A)</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. (B)</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. (B)</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. (D)</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 (C)</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. (A)</p> Signup and view all the answers

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

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

What is primarily stored in the bone marrow of bones?

<p>Adipose tissue and blood cells (D)</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. (B)</p> Signup and view all the answers

What characteristic feature differentiates osteoclasts from other bone cells?

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

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

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

Osteogenic cells can differentiate into which type of bone cells?

<p>Osteoblasts and osteoclasts (D)</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. (A)</p> Signup and view all the answers

Bone lining cells primarily function to:

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

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

<p>Osteogenesis (C)</p> Signup and view all the answers

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

<p>Hardness and strength (B)</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. (A)</p> Signup and view all the answers

What role does calcium phosphate play in bone structure?

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

What term is commonly used to refer to the osteon?

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

Which structural element primarily characterizes the osteon?

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

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

<p>Different directions (D)</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. (A)</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. (C)</p> Signup and view all the answers

What is the primary structural feature of an osteon?

<p>A hollow tube of bone matrix (B)</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 (D)</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 (C)</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 (D)</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 (B)</p> Signup and view all the answers

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

<p>Canaliculi (D)</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 (C)</p> Signup and view all the answers

Where do osteocytes reside within the osteon?

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

How do osteocytes in lacunae communicate with each other?

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

What is a key characteristic of bones regarding their vascularization?

<p>Bones have a rich blood supply. (A)</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 (B)</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 (C)</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. (B)</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. (B)</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. (A)</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. (C)</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 (D)</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. (D)</p> Signup and view all the answers

What structures make up the framework of spongy bone?

<p>Trabeculae and bars of bone (C)</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 (B)</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. (C)</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. (A)</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. (C)</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 (B)</p> Signup and view all the answers

The design of spongy bone allows it to:

<p>Absorb shock and reduce weight while maintaining strength. (C)</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 (A)</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. (D)</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. (B)</p> Signup and view all the answers

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

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

How do mechanical forces influence bone remodeling?

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

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

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

How much calcium is typically found in the human body?

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

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

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

Which hormone decreases blood calcium levels when they are elevated?

<p>Calcitonin (D)</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. (A)</p> Signup and view all the answers

What do osteoclasts release to digest the bone matrix?

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

What happens to osteoid after it is secreted by osteoblasts?

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

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

<p>Bone remodeling (B)</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. (C)</p> Signup and view all the answers

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

<p>Osteoclasts (B)</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 (D)</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% (D)</p> Signup and view all the answers

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

<p>Estrogen/Testosterone (B)</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 (B)</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 (D)</p> Signup and view all the answers

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

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

What initiates primary ossification?

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

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

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

During endochondral ossification, what happens to the cartilage?

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

What persists after the ossification of the epiphyses?

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

What defines a nondisplaced fracture?

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

Which statement accurately describes a displaced fracture?

<p>The ends of the bone are out of alignment (D)</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 (C)</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) (A)</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 (A)</p> Signup and view all the answers

Where is yellow marrow primarily located in adults?

<p>In the epiphyses of long bones (D)</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 (C)</p> Signup and view all the answers

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

<p>Insulin production and uptake (B)</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. (C)</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. (B)</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. (A)</p> Signup and view all the answers

Which hormone associated with fat metabolism is stimulated by osteocalcin?

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

How does insulin interact with osteocalcin in bone tissues?

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

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

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

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

<p>Adiponectin (D)</p> Signup and view all the answers

Which statement best describes the relationship between osteocalcin and insulin?

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

What is the primary function of osteocalcin secretion by osteoblasts?

<p>Insulin production and uptake (B)</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. (A)</p> Signup and view all the answers

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

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

How does insulin interact with osteocalcin in bone tissue?

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

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

<p>Adiponectin (A)</p> Signup and view all the answers

What is the functional contractile unit of a skeletal muscle?

<p>Sarcomere (B)</p> Signup and view all the answers

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

<p>Excitability (D)</p> Signup and view all the answers

What is the primary function of skeletal muscle contraction?

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

Which process occurs when skeletal muscle receives a neural stimulus?

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

Which statement accurately describes skeletal muscles?

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

What mechanism initiates muscle contraction?

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

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

<p>Acetylcholine (B)</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. (B)</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. (D)</p> Signup and view all the answers

What structure does each myofiber receive from a nerve?

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

What initiates muscle contraction?

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

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

<p>Acetylcholine (B)</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. (D)</p> Signup and view all the answers

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

<p>Calcium (A)</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. (D)</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+ (A)</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). (A)</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 (C)</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. (B)</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. (C)</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 (D)</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 (D)</p> Signup and view all the answers

What are T-tubules in skeletal muscle cells?

<p>Continuous extensions of the sarcolemma (A)</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 (A)</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 (D)</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 (B)</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 (D)</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 (C)</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 (A)</p> Signup and view all the answers

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

<p>Sarcoplasmic reticulum (A)</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 (B)</p> Signup and view all the answers

How is the sarcoplasmic reticulum best described?

<p>An elaborate smooth endoplasmic reticulum surrounding each myofibril (D)</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. (C)</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 (B)</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 (C)</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 (D)</p> Signup and view all the answers

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

<p>The muscle fiber relaxes. (D)</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. (D)</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. (A)</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. (C)</p> Signup and view all the answers

What is the composition of the troponin complex?

<p>Three subunits: Troponin C, I, and T. (D)</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. (B)</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. (B)</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. (C)</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. (A)</p> Signup and view all the answers

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

<p>Calcium ions (Ca2+) (A)</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. (C)</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. (A)</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. (A)</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. (B)</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. (A)</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. (A)</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 (A)</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 (B)</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. (A)</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 (A)</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. (B)</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. (D)</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. (B)</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. (B)</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. (B)</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. (D)</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. (D)</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. (B)</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. (A)</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. (D)</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. (B)</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. (D)</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. (C)</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. (D)</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. (D)</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. (B)</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. (A)</p> Signup and view all the answers

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

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

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

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

What prevents cross-bridge formation during muscle relaxation?

<p>The absence of calcium in the cytoplasm (B)</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 (B)</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 (D)</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 (A)</p> Signup and view all the answers

What physiological change triggers muscle contraction after death?

<p>Leakage of calcium ions into the cytoplasm (A)</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 (C)</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. (D)</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. (D)</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. (A)</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. (A)</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. (D)</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. (D)</p> Signup and view all the answers

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

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

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

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

What prevents cross-bridge formation during muscle relaxation?

<p>The absence of calcium in the cytoplasm (A)</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 (D)</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 (B)</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 (A)</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 (A)</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 (D)</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 (A)</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. (C)</p> Signup and view all the answers

What is the primary function of muscle tone?

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

What mechanism is primarily responsible for maintaining muscle tone?

<p>Spinal reflexes that activate motor units. (D)</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. (C)</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. (A)</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. (B)</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. (C)</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. (A)</p> Signup and view all the answers

What defines a motor unit?

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

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

<p>Contraction phase (B)</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. (C)</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. (D)</p> Signup and view all the answers

Which muscle fiber type is expected to contract the fastest?

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

Why do some muscle contractions last longer than others?

<p>All of the above. (D)</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 (C)</p> Signup and view all the answers

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

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

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

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

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

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

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

<p>Anaerobic glycolysis (D)</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 (D)</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 (B)</p> Signup and view all the answers

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

<p>Type IIb fibers (D)</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 (B)</p> Signup and view all the answers

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

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

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

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

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

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

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

<p>Anaerobic glycolysis (C)</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 (D)</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 (A)</p> Signup and view all the answers

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

<p>Type IIb fibers (A)</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 (D)</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 (A)</p> Signup and view all the answers

Which energy pathway do endurance muscles predominantly rely on?

<p>Aerobic oxidative phosphorylation (A)</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. (D)</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. (B)</p> Signup and view all the answers

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

<p>Type IIb fibers (C)</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. (C)</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 (B)</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. (D)</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 (A)</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 (B)</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. (A)</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. (C)</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 (C)</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. (C)</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 (D)</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. (D)</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 (A)</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 (B)</p> Signup and view all the answers

What is the main goal of endurance training?

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

Which adaptation is specifically linked to strength training?

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

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

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

What is the main goal of endurance training?

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

Which adaptation is specifically linked to strength training?

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

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

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

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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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