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Questions and Answers
What are the main minerals stored in bones?
What are the main minerals stored in bones?
Which component of the bone imparts flexible strength to the bone matrix?
Which component of the bone imparts flexible strength to the bone matrix?
Intramembranous ossification is the mode of development in these bones, except:
Intramembranous ossification is the mode of development in these bones, except:
Active bone resorption is a function of which of the following bone cells?
Active bone resorption is a function of which of the following bone cells?
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Blood calcium levels depend on the movement of this mineral in and out of the bone. Levels of calcium in the blood are controlled by?
Blood calcium levels depend on the movement of this mineral in and out of the bone. Levels of calcium in the blood are controlled by?
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Which of the following is NOT a function of the skeletal system?
Which of the following is NOT a function of the skeletal system?
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Which structure helps to hold bones together in the skeletal system?
Which structure helps to hold bones together in the skeletal system?
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What role does cartilage play in the skeletal system?
What role does cartilage play in the skeletal system?
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Which bone disorder is characterized by poorly mineralized bones with adequate osteoid production?
Which bone disorder is characterized by poorly mineralized bones with adequate osteoid production?
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Which condition describes an abnormal lateral curvature of the spine?
Which condition describes an abnormal lateral curvature of the spine?
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What blood test marker is indicative of enhanced osteoblastic activity?
What blood test marker is indicative of enhanced osteoblastic activity?
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Which mineral is primarily stored in bones alongside calcium?
Which mineral is primarily stored in bones alongside calcium?
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Which of the following bones does not undergo intramembranous ossification?
Which of the following bones does not undergo intramembranous ossification?
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What is the primary function of osteoclasts?
What is the primary function of osteoclasts?
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Which type of bone is characterized by collagen fibers that are randomly oriented?
Which type of bone is characterized by collagen fibers that are randomly oriented?
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What structure is known as the functional unit of compact bone?
What structure is known as the functional unit of compact bone?
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How are osteocytes arranged in lamellar bone?
How are osteocytes arranged in lamellar bone?
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Which feature distinguishes compact bone from spongy bone?
Which feature distinguishes compact bone from spongy bone?
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What is the role of canaliculi in spongy bone?
What is the role of canaliculi in spongy bone?
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Which bone type is organized into thin concentric sheets?
Which bone type is organized into thin concentric sheets?
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What do perforating canals primarily connect?
What do perforating canals primarily connect?
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What is the primary characteristic of trabeculae found in spongy bone?
What is the primary characteristic of trabeculae found in spongy bone?
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What is the primary role of osteoblasts in bone histology?
What is the primary role of osteoblasts in bone histology?
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Which lamellae are found at the outer surfaces of compact bone?
Which lamellae are found at the outer surfaces of compact bone?
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Which cells are responsible for the process of ossification?
Which cells are responsible for the process of ossification?
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Which component of bone matrix is responsible for its organic characteristics?
Which component of bone matrix is responsible for its organic characteristics?
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What is the function of canaliculi in bone histology?
What is the function of canaliculi in bone histology?
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What unique feature distinguishes osteoclasts from other bone cells?
What unique feature distinguishes osteoclasts from other bone cells?
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What initiates the recruitment of osteoclasts to a bone remodeling site?
What initiates the recruitment of osteoclasts to a bone remodeling site?
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What mainly comprises the inorganic component of bone matrix?
What mainly comprises the inorganic component of bone matrix?
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Which statement accurately describes osteocytes?
Which statement accurately describes osteocytes?
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What are osteochondral progenitor cells primarily derived from?
What are osteochondral progenitor cells primarily derived from?
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Which of the following statements about osteoclasts is true?
Which of the following statements about osteoclasts is true?
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What is the primary initiation site for intramembranous ossification?
What is the primary initiation site for intramembranous ossification?
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At what point in development does endochondral ossification begin?
At what point in development does endochondral ossification begin?
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Which part of the skeletal system is formed primarily through intramembranous ossification?
Which part of the skeletal system is formed primarily through intramembranous ossification?
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What is the main function of the epiphyseal plate in bone growth?
What is the main function of the epiphyseal plate in bone growth?
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How do hormones influence bone growth?
How do hormones influence bone growth?
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What is the role of calcitonin in calcium homeostasis?
What is the role of calcitonin in calcium homeostasis?
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Which vitamin is essential for collagen synthesis in bones?
Which vitamin is essential for collagen synthesis in bones?
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What primarily regulates calcium levels in the blood?
What primarily regulates calcium levels in the blood?
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What is the function of the basic multicellular unit (BMU) in bone remodeling?
What is the function of the basic multicellular unit (BMU) in bone remodeling?
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What happens to the epiphyseal plates as a bone reaches full growth during puberty?
What happens to the epiphyseal plates as a bone reaches full growth during puberty?
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What is the role of tropomyosin during muscle contraction?
What is the role of tropomyosin during muscle contraction?
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Which component invaginates into the interior of skeletal muscle fibers?
Which component invaginates into the interior of skeletal muscle fibers?
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During an isometric contraction, which of the following occurs?
During an isometric contraction, which of the following occurs?
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Which sequence of events correctly describes the muscle contraction process?
Which sequence of events correctly describes the muscle contraction process?
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What is the primary function of ATPase associated with myosin?
What is the primary function of ATPase associated with myosin?
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What is a primary cause of muscle cramps?
What is a primary cause of muscle cramps?
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Which condition is characterized by the chronic widespread pain in skeletal muscles?
Which condition is characterized by the chronic widespread pain in skeletal muscles?
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What happens to muscle fibers as people age?
What happens to muscle fibers as people age?
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How is Duchenne muscular dystrophy primarily identified diagnostically?
How is Duchenne muscular dystrophy primarily identified diagnostically?
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What physiological mechanism is primarily associated with muscle fatigue?
What physiological mechanism is primarily associated with muscle fatigue?
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What is myasthenia gravis primarily classified as?
What is myasthenia gravis primarily classified as?
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What common feature characterizes tendinitis?
What common feature characterizes tendinitis?
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Which of the following is associated with the aging process of the muscular system?
Which of the following is associated with the aging process of the muscular system?
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What is the primary function of the neuromuscular junction in the muscular system?
What is the primary function of the neuromuscular junction in the muscular system?
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What is a common cause of muscle soreness after exercise?
What is a common cause of muscle soreness after exercise?
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What does the presynaptic terminal do when an action potential arrives?
What does the presynaptic terminal do when an action potential arrives?
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Which of the following is an important diagnostic tool for identifying autoantibodies in myasthenia gravis?
Which of the following is an important diagnostic tool for identifying autoantibodies in myasthenia gravis?
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What role do acetylcholine receptors play at the neuromuscular junction?
What role do acetylcholine receptors play at the neuromuscular junction?
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What is the space called that separates axon terminals and muscle fibers?
What is the space called that separates axon terminals and muscle fibers?
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Which component of the neuromuscular junction contains synaptic vesicles?
Which component of the neuromuscular junction contains synaptic vesicles?
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Which statement accurately describes the motor end plate?
Which statement accurately describes the motor end plate?
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What is the primary trigger for muscle contraction at the neuromuscular junction?
What is the primary trigger for muscle contraction at the neuromuscular junction?
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What is the first step in the process of muscle contraction at the neuromuscular junction?
What is the first step in the process of muscle contraction at the neuromuscular junction?
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What is the role of troponin in muscle contraction?
What is the role of troponin in muscle contraction?
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During muscle relaxation, which process occurs first?
During muscle relaxation, which process occurs first?
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What characterizes isotonic contractions?
What characterizes isotonic contractions?
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What triggers the rise in intracellular calcium levels necessary for muscle contraction?
What triggers the rise in intracellular calcium levels necessary for muscle contraction?
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Which of the following components directly binds to active sites on actin molecules during contraction?
Which of the following components directly binds to active sites on actin molecules during contraction?
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What is the primary function of myosin heads in muscle contraction?
What is the primary function of myosin heads in muscle contraction?
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Which statement correctly describes the process of excitation-contraction coupling?
Which statement correctly describes the process of excitation-contraction coupling?
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In which type of muscle contraction does the muscle shorten while maintaining constant tension?
In which type of muscle contraction does the muscle shorten while maintaining constant tension?
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What happens to tropomyosin during muscle contraction?
What happens to tropomyosin during muscle contraction?
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What primarily occurs during isometric contractions?
What primarily occurs during isometric contractions?
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What process involves the release of acetylcholine from synaptic vesicles?
What process involves the release of acetylcholine from synaptic vesicles?
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What happens after acetylcholine binds to ligand-gated sodium channels on the motor end plate?
What happens after acetylcholine binds to ligand-gated sodium channels on the motor end plate?
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What happens to acetylcholine after it unbinds from the ligand-gated channels?
What happens to acetylcholine after it unbinds from the ligand-gated channels?
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Which component of actin myofilament prevents active sites on G actin from being uncovered in relaxed muscle?
Which component of actin myofilament prevents active sites on G actin from being uncovered in relaxed muscle?
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What is the first step in the muscle contraction process at the neuromuscular junction?
What is the first step in the muscle contraction process at the neuromuscular junction?
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How is choline transported back into the presynaptic terminal?
How is choline transported back into the presynaptic terminal?
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What structure does globular (G) actin form when it polymerizes?
What structure does globular (G) actin form when it polymerizes?
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What is the role of acetylcholinesterase in muscle contraction?
What is the role of acetylcholinesterase in muscle contraction?
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What initiates the generation of an action potential in a muscle fiber?
What initiates the generation of an action potential in a muscle fiber?
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Which statement about tropomyosin is true?
Which statement about tropomyosin is true?
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Study Notes
Skeletal System Functions
- Support: Serves as the body's primary weight-bearing framework, providing rigid structure.
- Protection: Safeguards vital organs.
- Movement: Facilitates movement by providing attachment points for muscles.
- Storage: Acts as a repository for essential minerals, primarily calcium and phosphorus.
- Blood Cell Production: Red bone marrow within bones is responsible for hematopoiesis, the production of blood cells.
Bone Histology
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Bone Matrix: Composed of organic and inorganic components.
- Organic (35%): Collagen and proteoglycans
- Inorganic (65%): Hydroxyapatite (calcium phosphate crystals)
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Bone Cells:
- Osteochondral Progenitor Cells: Bone stem cells derived from mesenchymal cells.
- Osteoblasts: Responsible for bone formation, producing collagen and proteoglycans.
- Osteocytes: Mature bone cells responsible for maintaining bone matrix.
- Osteoclasts: Large, multinucleated cells responsible for bone resorption.
Bone Development
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Intramembranous Ossification:
- Begins during the 8th week of embryonic development.
- Responsible for the development of skull bones, part of the mandible, and the diaphysis of clavicles.
- Characterized by the formation of bone directly within connective tissue membranes.
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Endochondral Ossification:
- Also begins during the 8th week of embryonic development, but some processes may not begin until 18-20 years of age.
- Responsible for the development of the base of the skull, part of the mandible, the epiphyses of the clavicle, and most of the remaining skeletal system.
- Involves formation of bone within a cartilage model.
Bone Growth
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Growth in Length:
- Occurs at the epiphyseal plate, a specialized cartilaginous region.
- Involves endochondral ossification.
- Epiphyseal plate closure marks the end of long bone growth.
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Growth in Bone Width:
- Occurs at the periosteum, the outer covering of bones.
- Increases bone diameter.
Bone Remodeling
- Continuous process of bone resorption and formation, replacing old bone with new bone.
- Involves the basic multicellular unit (BMU), a group of osteoclasts and osteoblasts working together.
- Essential for bone growth, shaping, adaptation to stress, repair, and calcium ion regulation.
Bone Repair
- Involves a complex series of events:
- Hematoma Formation: A blood clot forms at the site of fracture.
- Soft Callus Formation: Fibrocartilaginous tissue forms a temporary bridge between the broken bone ends.
- Hard Callus Formation: The soft callus is gradually replaced by a hard callus of woven bone.
- Remodeling: Woven bone is remodeled into lamellar bone, restoring bone strength.
Abnormalities of Bone
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Rickets:
- A disease of children characterized by inadequate mineralization of the epiphyseal plate, leading to soft and deformed bones.
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Osteomalacia:
- A disease of adults characterized by poorly mineralized bone, leading to bone weakness and pain.
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Osteomyelitis:
- Infection of bone tissue.
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Osteoporosis:
- Characterized by decreased bone density, increasing the risk of fractures.
Diagnostic Tests
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Blood Tests:
- Serum Calcium: Measures calcium levels in the blood.
- Alkaline Phosphatase: An enzyme that indicates increased osteoblastic activity.
- C-telopeptide: A marker for bone resorption.
- Procollagen Type 1 N-terminal Propeptide (P1NP): A marker for bone formation.
- Serum 25 Hydroxyvitamin D Level: Measures vitamin D3 levels, important for calcium absorption.
- Serum Vitamin C Level: Measures vitamin C levels, essential for collagen synthesis by osteoblasts.
Calcium Homeostasis
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Parathyroid Hormone (PTH):
- Released in response to low blood calcium levels.
- Increases blood calcium by stimulating osteoclast activity, promoting calcium reabsorption in the kidneys, and indirectly enhancing calcium absorption in the intestines.
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Calcitriol (Active Vitamin D):
- Increases blood calcium by promoting intestinal absorption of calcium.
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Calcitonin:
- Lowers blood calcium by inhibiting osteoclast activity.
Neuromuscular Junction
- The area where a muscle cell is stimulated by nerve
- Consists of axonal endings, motor end plate, and the synaptic cleft
- Axonal endings contain synaptic vesicles that store acetylcholine
- Motor end plate is a specialized area of muscle plasma membrane containing acetylcholine receptors
Muscle Contraction Steps
- Action potential arrives at presynaptic terminal
- Voltage-gated calcium channels open in presynaptic membrane
- Calcium triggers the release of acetylcholine from synaptic vesicles
- Acetylcholine diffuses across the synaptic cleft
- Acetylcholine binds to ligand-gated sodium channels on the motor end plate
- Sodium enters the muscle fiber and depolarization occurs
- If depolarization reaches threshold, an action potential is generated in muscle fiber
- Acetylcholine unbinds from the ligand-gated channels, and sodium channels close
- Acetylcholinesterase breaks down acetylcholine in the synaptic cleft
- Choline is transported back into the presynaptic terminal with sodium
- Acetylcholine is resynthesized within the presynaptic terminal
Actin and Myosin Myofilament Structure
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Actin Myofilament: Consists of globular (G) actin, tropomyosin, and troponin.
- G actin subunits form fibrous (F) actin.
- Tropomyosin covers active sites on G actin in relaxed muscle.
- Troponin binds to actin and prevents tropomyosin from uncovering active sites.
- Troponin also binds calcium during muscle contraction.
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Myosin Myofilament: Consists of two myosin heavy chains and two myosin heads.
- Myosin heads bind to active sites on actin during cross-bridge formation.
- Myosin heads have hinge regions that allow for movement.
- Myosin heads are ATPase enzymes that break down ATP to fuel muscle contraction.
Excitation-Contraction Coupling
- Process that links electrical stimulation of muscle (action potential) to mechanical contraction
- Occurs at the triad, which is a junction formed by a T tubule and two terminal cisternae of sarcoplasmic reticulum
- Action potential travels along the sarcolemma and into the T tubule
- This triggers the release of calcium from the sarcoplasmic reticulum
- Calcium binds to troponin, causing a conformational change
- This change in troponin pulls tropomyosin away from the active sites on actin
- Myosin heads can now bind to actin and initiate the power stroke
Cross-Bridge Movement
- Myosin head binds to active site on actin, forming a cross-bridge
- Myosin head pivots, pulling the thin filament towards M line - This is the power stroke
- ATP binds to the myosin head, causing it to detach from actin
- ATP is hydrolyzed to ADP and phosphate, providing energy for the myosin head to return to its cocked position
- Cycle repeats as long as calcium levels remain elevated and ATP is available
Muscle Relaxation
- Acetylcholine release stops at the neuromuscular junction.
- Action potentials cease, halting calcium release from the sarcoplasmic reticulum.
- Calcium diffuses away from troponin molecules.
- Tropomyosin moves back to cover the active sites on actin.
- Cross-bridge formation is blocked, and muscle fibers relax.
Types of Muscle Contractions
- Isometric contractions: Muscle does not shorten, but tension increases.
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Isotonic contractions: Muscle shortens, and tone remains constant during contraction.
- Concentric contraction: Muscle shortens while tension increases.
- Eccentric contraction: Muscle lengthens while tension is maintained.
Disorders of the Muscular System
- Aging: Muscle atrophy, loss of muscle fibers, reduced NMJ surface area, and fewer motor neurons.
- Muscle fatigue: Temporary state of reduced work capacity due to factors like acidosis, ATP depletion, oxidative stress, and localized inflammation.
- Muscle soreness: Painful condition after vigorous exercise, caused by inflammation.
- Cramps: Painful, spastic contractions of muscles, often due to dehydration or electrolyte imbalance.
- Tendonitis: Inflammation of a tendon or its attachment point, caused by overuse.
- Fibromyalgia: Chronic, widespread muscle pain with no known cure.
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Myasthenia gravis: Autoimmune disease where antibodies block acetylcholine receptors, causing muscle weakness.
- Diagnostics: Electromyography and antibody testing.
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Duchenne muscular dystrophy: X-linked genetic disorder with progressive muscle weakness and degeneration.
- Diagnostics: Serum creatinine, muscle biopsy, and immunohistochemical studies.
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Description
Explore the essential functions of the skeletal system, including support, protection, movement, storage, and blood cell production. Additionally, delve into bone histology, examining the composition of the bone matrix and the various types of bone cells involved in its maintenance and formation.