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Questions and Answers
What percentage of total body weight do skeletal muscles comprise?
What percentage of total body weight do skeletal muscles comprise?
What is the primary role of tendons in muscle anatomy?
What is the primary role of tendons in muscle anatomy?
Which component covers the binding sites on actin for myosin?
Which component covers the binding sites on actin for myosin?
How many myosin molecules are approximately present per thick filament?
How many myosin molecules are approximately present per thick filament?
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What are sarcomeres primarily considered in muscle structure?
What are sarcomeres primarily considered in muscle structure?
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What occurs when Sodium (Na+) enters the axon?
What occurs when Sodium (Na+) enters the axon?
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What is the membrane potential when the sodium gates close?
What is the membrane potential when the sodium gates close?
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Which ion's movement primarily causes repolarization of the axon?
Which ion's movement primarily causes repolarization of the axon?
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What happens at a membrane potential of +30 mV?
What happens at a membrane potential of +30 mV?
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What best describes the depolarization phase of the axon?
What best describes the depolarization phase of the axon?
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What is the primary function of afferent neurons?
What is the primary function of afferent neurons?
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What role do Golgi tendon organs play in muscle contraction?
What role do Golgi tendon organs play in muscle contraction?
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What are muscle spindles sensitive to?
What are muscle spindles sensitive to?
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How do eafferenct neurons facilitate muscle activity?
How do eafferenct neurons facilitate muscle activity?
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What happens when a muscle is stretched rapidly?
What happens when a muscle is stretched rapidly?
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What happens to the length of the filaments during muscle contraction?
What happens to the length of the filaments during muscle contraction?
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What role does the sarcoplasmic reticulum play in muscle contraction?
What role does the sarcoplasmic reticulum play in muscle contraction?
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Which event occurs last in the cross-bridge cycle when a muscle contracts?
Which event occurs last in the cross-bridge cycle when a muscle contracts?
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What effect does a decrease in calcium or ATP levels have on muscle contraction?
What effect does a decrease in calcium or ATP levels have on muscle contraction?
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In the length-tension relationship, what is the consequence of excessive lengthening of the muscle fiber?
In the length-tension relationship, what is the consequence of excessive lengthening of the muscle fiber?
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How does the force-velocity relationship affect muscle performance during rapid movements?
How does the force-velocity relationship affect muscle performance during rapid movements?
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Which characteristic is typically associated with Type I muscle fibers?
Which characteristic is typically associated with Type I muscle fibers?
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What is the primary structural protein that helps form the sarcomere?
What is the primary structural protein that helps form the sarcomere?
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What happens when the potassium gates open during repolarization?
What happens when the potassium gates open during repolarization?
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What is the role of the sodium-potassium pump after action potential?
What is the role of the sodium-potassium pump after action potential?
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Which sequence correctly describes the events at the neuromuscular junction?
Which sequence correctly describes the events at the neuromuscular junction?
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What occurs during the propagation of action potential?
What occurs during the propagation of action potential?
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What is the effect of acetylcholine at the motor end plate?
What is the effect of acetylcholine at the motor end plate?
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What happens to acetylcholine after the action potential ceases?
What happens to acetylcholine after the action potential ceases?
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Which statement correctly describes efferent neurons?
Which statement correctly describes efferent neurons?
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During which phase does the membrane potential reset back to resting levels?
During which phase does the membrane potential reset back to resting levels?
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What components make up a motor unit?
What components make up a motor unit?
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How does the myelin sheath affect nerve impulses?
How does the myelin sheath affect nerve impulses?
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What occurs at the Nodes of Ranvier during nerve impulse transmission?
What occurs at the Nodes of Ranvier during nerve impulse transmission?
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Which part of the motor neuron receives messages from other cells?
Which part of the motor neuron receives messages from other cells?
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What happens to sodium ions (Na+) during the arrival of an action potential?
What happens to sodium ions (Na+) during the arrival of an action potential?
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What is the primary function of the motor neuron?
What is the primary function of the motor neuron?
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How many fibers are typically found in a motor unit for fine movements?
How many fibers are typically found in a motor unit for fine movements?
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What type of muscle contraction is regulated by feedback from sensory receptors?
What type of muscle contraction is regulated by feedback from sensory receptors?
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What is the resting membrane potential of a neuron?
What is the resting membrane potential of a neuron?
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What is the role of the terminal branches of the axon?
What is the role of the terminal branches of the axon?
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Study Notes
Skeletal Muscle: Structure and Function
- Skeletal muscle is an organ, comprising 40-60% of total body weight. There are approximately 600 muscles in the human body.
- Skeletal muscle's main functions include producing force, transmitting force to the skeleton via tendons, facilitating movement, stabilizing joints, and maintaining posture.
Learning Objectives
- Describe muscle structure
- Identify differences in muscle characteristics of fast-twitch and slow-twitch fibers
- Define the sliding filament mechanism
- Explain the process of the cross-bridge cycle
Muscle Anatomy (Gross)
- Force produced by the muscle is transmitted to the skeleton via tendons.
- Muscles cause movement or stabilize joints or maintain posture.
Muscle Structure (Detailed)
- Muscle: The whole muscle
- Epimysium (Deep fascia): Outer layer of the muscle
- Fasciculus: Bundles of muscle fibers
- Perimysium: Surrounds individual fasciculi
- Endomysium: Connective tissue layer surrounding individual muscle fibers
- Single muscle fiber: Individual muscle cell
- Sarcoplasm: Cytoplasm of muscle fiber
- Myofibril: Contractile fibers within the muscle fiber
- Sarcolemma: Cell membrane of the muscle fiber
- Nuclei: Multiple nuclei per muscle fiber
- Tendon: Attaches muscle to bone
- Muscle belly: The main body of the muscle
Muscle Fiber
- Nucleus: Located in the muscle fiber
- Light I band: Light band within the myofibril
- Dark A band: Dark band within the myofibril
- Myofibril: Contractile filament
- Mitochondrion: Powerhouse of the cell, generates energy
- Sarcolemma: Membrane surrounding the muscle fiber
- Myofibrils: Contractile proteins
- Each myofibril is comprised of thousands of sarcomeres.
Sarcomere Structure
- Sarcomeres are the functional units of a muscle.
- Sarcomeres are joined in series and parallel to one another.
- Myofilaments make up sarcomeres; these include actin and myosin proteins.
- Myosin (thick filament)
- Composed of around 300 myosin molecules per thick filament.
- Contains two subunits: S1 (globular head) and S2 (flexible region and tail).
- Actin (thin filament)
- Subunits in double helical strands.
- Tropomyosin interacts with actin and covers binding sites allowing thick filaments to bind.
- Other structural proteins include Titin, Nebulin, and Desmin.
Sliding Filament Mechanism
- Huxley 1954
- During muscle contraction, filaments slide past each other.
- The filaments themselves remain relatively unchanged in length despite changes in muscle length.
Sarcoplasmic Reticulum
- Interconnecting tubules surrounding myofibrils
- Regulates intracellular calcium levels
- Stores calcium and releases calcium on stimulation to allow muscle contraction.
The Cross-Bridge Cycle
- Myosin heads attach to actin, forming cross-bridges.
- Myosin heads undergo a conformational change, pulling the actin filaments inward.
- ATP is necessary for the detachment of myosin heads from actin.
- The process repeats to shorten the sarcomere.
Length-Tension Relationship
- Filaments that don't overlap don't generate tension.
- Optimal tension is generated when filaments can butt against the Z-lines.
- As the muscle stretches further, the overlap between myosin and actin decreases resulting in less tension.
Force-Velocity Relationship
- During shortening, force is less than isometric force (the faster the movement the less time myosin heads have to attach).
- During lengthening, force is greater than isometric force (the myosin is stretched further and then a forceful detachment).
Fibre Type Characteristics
- Different fiber types (Type I, Type IIA, and Type IIX) have varying characteristics.
- Speed of contraction
- Force production
- Metabolic profile
- Appearance
- Oxidative capacity
- Glycolytic capacity
Study Questions
- Explain how nerve impulses are propagated down the axon towards the neuromuscular junction.
- How does excitation of a neuron result in excitation of a muscle cell? Describe the process with reference to the appropriate neurotransmitter.
- Describe how feedback from sensory receptors can regulate muscle contraction.
Skeletal Muscle II: Innervation and Control
-
Objectives:
- Name the basic structures of a motor neuron
- Explain how nerve impulses are transmitted from the spine to the muscle to cause contraction
- Describe how feedback from sensory receptors can regulate muscle contraction
The Nervous System
- Central nervous system (CNS)
- Peripheral nervous system (PNS)
- Afferent (sensory) division
- Efferent (motor) division
- Somatic nervous system
- Autonomic nervous system
- Sympathetic division
- Parasympathetic division
The Motor Neuron
- Motor neuron: a single motor neuron and all the fibers it innervates
- Gross movements involve 2,000-3,000 fibers per motor unit.
- Fine movements involve 1-2(or 3) fibers per motor unit.
- Motor neuron components:
- Cell body
- Dendrites
- Axon
- Myelin sheath
- Nodes of Ranvier
- Terminal branches
- Synaptic vesicles
Transmission of Nerve Impulses (Action Potential)
- The electrical signal that propagates down a neuron's axon
- Depolarization and repolarization occur as Na+ and K+ ions flow in and out of the axon
- Action potentials propagate down the axon through saltatory conduction along the myelinated segments.
Neuromuscular Junction
- The synapse between a motor neuron and a muscle fiber
- Acetylcholine (neurotransmitter) is released into the synaptic cleft
- Acetylcholine binds to receptors on the muscle fiber, initiating muscle contraction.
Golgi Tendon Organs (GTO)
- Sensory receptors located in the tendons
- Detects muscle tension and send inhibitory signals to reduce muscle contraction when tension is excessive.
Muscle Spindles
- Sensory receptors located within muscles
- Detects changes in muscle length
- Sends signals to the central nervous system to regulate muscle contraction to prevent overstretching.
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Description
Test your knowledge on skeletal muscle anatomy and functionality. This quiz covers muscle structure, characteristics of muscle fibers, and key mechanisms such as the sliding filament theory and the cross-bridge cycle. Perfect for students of anatomy and physiology.
