Muscle Physiology Quiz

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Questions and Answers

Which of the following accurately describes the role of ATP in muscle contraction?

ATP is solely responsible for maintaining the Na-K gradient in the muscle cell.

ATP is only used for the re-uptake of calcium into the sarcoplasmic reticulum.

ATP is only used to power the power stroke of the myosin head.

ATP is required for both the binding and detachment of the myosin head to actin. (correct)

What is the primary function of tropomyosin in muscle contraction?

Tropomyosin binds to calcium ions, triggering muscle contraction.

Tropomyosin directly pulls on the actin filament, causing it to slide past the myosin filaments.

Tropomyosin covers the active sites on actin, preventing myosin binding in the resting muscle. (correct)

Tropomyosin acts as an ATPase, hydrolyzing ATP to provide energy for contraction.

Which of the following events occurs directly AFTER the myosin head releases ADP and phosphate during the power stroke?

A new ATP molecule binds to the myosin head, causing detachment from actin. (correct)

Calcium ions bind to troponin, triggering the movement of tropomyosin.

The sarcoplasmic reticulum releases calcium ions into the cytosol.

The myosin head binds to the active site on actin, forming a cross-bridge.

What is the role of acetylcholinesterase (AChE) in muscle relaxation?

AChE breaks down acetylcholine, removing it from the synaptic cleft. Signup and view all the answers

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

Tropomyosin shifts, exposing the active sites on the actin filament. Signup and view all the answers

What is the primary source of energy for muscle contraction once the stored ATP is depleted?

Creatine phosphate stores. Signup and view all the answers

What is the physiological significance of the Na-K gradient in muscle cells?

It allows for the propagation of action potentials along the muscle fiber. Signup and view all the answers

Which of the following is NOT a direct consequence of acetylcholine (ACh) binding to its receptor on the muscle fiber?

Inhibition of the enzymatic activity of acetylcholinesterase (AChE). Signup and view all the answers

Which of the following is NOT a primary function of muscles?

Regulation of blood pH Signup and view all the answers

Which characteristic of muscle tissue allows it to respond to stimuli by producing action potentials?

Excitability Signup and view all the answers

Which of the following muscle types is characterized by having a central nucleus and being under involuntary control?

Smooth muscle Signup and view all the answers

What is the correct order of structural organization in skeletal muscle, from smallest to largest?

Myofilament, myofibril, muscle fiber, muscle fascicle, skeletal muscle Signup and view all the answers

Which connective tissue layer directly surrounds individual muscle fibers?

Endomysium Signup and view all the answers

What is the name of the structure that surrounds the muscle fiber?

Sarcolemma Signup and view all the answers

What is the functional unit of muscle contraction?

Sarcomere Signup and view all the answers

What are muscle tendons primarily composed of?

Collagen fibers Signup and view all the answers

What type of filaments are actin and tropomyosin classified as?

Thin myofilaments Signup and view all the answers

Which component connects myosin to the Z line in the sarcomere?

Titin Signup and view all the answers

What is the function of the sarcoplasmic reticulum in muscle fibers?

To store calcium ions Signup and view all the answers

What structure is formed by one T tubule and two terminal cisternae?

Triad Signup and view all the answers

What is the primary role of dystrophin in muscle fibers?

To provide intracellular stability Signup and view all the answers

Which protein is responsible for covering the active sites of actin?

Tropomyosin Signup and view all the answers

What is the primary function of the neuromuscular junction?

To transmit action potentials from motor neurons to muscle fibers Signup and view all the answers

In which zone of the sarcomere do only thick filaments reside?

H zone Signup and view all the answers

What is the initial energy source used by muscle fibers for contraction?

ATP stored in the muscle fiber Signup and view all the answers

During aerobic glycolysis, what substance is generated from glucose?

Pyruvate Signup and view all the answers

What is the role of motor neurons in muscle contraction?

To stimulate muscle fibers for contraction Signup and view all the answers

Which term describes the stimulus that increases contraction power by activating more motor units?

Recruition Signup and view all the answers

What primarily influences the strength of a muscle contraction?

Intensity of the nervous system stimulus and number of activated motor units Signup and view all the answers

Which muscle fiber characteristics are associated with small motor units?

Precise movements with fewer muscle cells Signup and view all the answers

What defines muscle fatigue in skeletal muscle fibers?

Decreased tension despite ongoing stimulation Signup and view all the answers

How does the number of cells per motor unit relate to motor unit size?

Fewer cells indicate a smaller motor unit Signup and view all the answers

Study Notes

Skeletal Muscle Contraction

Skeletal muscles are responsible for movement, posture maintenance, and heat production.
They protect bones and internal organs.
Muscle cells are excitable, meaning they respond to stimuli by producing action potentials.
Muscles shorten and thicken to generate force.
Muscles are extensible, meaning they can extend without damage.
Muscles are elastic, meaning they return to their original shape.

Muscle Types

Skeletal muscle:
- Peripheral nuclei
- Voluntary
- Striated, tubular, multi-nucleated fibers
- Attached to the skeleton
Smooth muscle:
- Central nuclei
- Involuntary
- Non-striated, spindle-shaped, single nuclei
- Lines internal organs
Cardiac muscle:
- Central nuclei
- Involuntary
- Striated, branched, single nuclei
- Found only in the heart

Skeletal Muscle Structure

Organized into:
- Myofilaments (actin and myosin)
- Myofibrils
- Muscle fibers
- Fascicles
- Muscle
Surrounded by connective tissue layers: endomysium, perimysium, epimysium
Muscle fibers are electrically isolated by endomysium.
Fascicles are surrounded by perimysium.
Epimysium surrounds the skeletal muscle.

Sarcomere Structure

I band: thin filament (actin) region.
H zone: thick filament (myosin) region.
A band: thick and thin filaments.
M line: middle of H band, connects myosins.
Z line: region between two I bands.

Muscle Proteins

Dystrophin, titin, actinin, desmin, nebulin are sarcomere intracellular proteins.
Titin connects myosin to the Z line.
Nebulin produces F-actin from G-actins.
α-actinin connects actin to the Z-line.
Desmin connects the Z line to the cell membrane.
Dystrophin-glycoprotein complex maintains muscle fiber and myofibril integrity.
Duchenne and Becker muscular dystrophies are associated with dystrophin mutations.

Sarcotubular System

Sarcolemma: surrounds the muscle fiber.
Sarcoplasm: muscle cell cytoplasm.
Sarcoplasmic reticulum (SR): stores calcium.
T-tubules: extensions of sarcolemma into the cell, transmit action potentials.
Terminal cisternae: enlargements of SR, release calcium to initiate contraction.
Triad: T-tubule and two terminal cisternae.

Neuromuscular Junction

Junction of axon terminal and motor end plate.
Action potential travels down axon, releasing acetylcholine.
Acetylcholine binds to receptors, initiating muscle fiber action potential.

Muscle Contraction

Requires ATP energy.
Sliding filament theory: actin and myosin filaments slide past each other.
Ca2+ release initiates contraction.
Myosin heads bind to actin, forming cross-bridges.
Power stroke: myosin pulls actin filaments.
ATP binds to myosin to detach it from actin.
ATP hydrolysis cocks myosin head for next cycle.
Cycle repeats until Ca2+ levels fall and muscle relaxes.

End of Skeletal Muscle Contraction

Acetylcholine is degraded by acetylcholinesterase.
Sarcoplasmic reticulum (SR) reuptakes Ca2+.
Myosin heads detach from actin, relaxing muscle fibers.

Muscle Metabolism

Stored ATP is used first.
Creatine phosphate stores are used next.
Anaerobic (lactic acid) system for short-duration, high-intensity exercise.
Oxidative phosphorylation (aerobic) for longer durations.

Motor Neuron

Motor neuron extends from CNS to muscle, stimulating contraction.
Motor unit is a motor neuron and its innervated muscle fibers.
Motor unit size dictates precision or strength of contraction.
Recruitment: increasing the number of active motor units increases contraction force.

Muscle Fatigue

Repeated stimulation of a muscle fiber leads to decreased tension and eventually muscle fatigue.
Characteristics of muscle fatigue include slower relaxation, reduced shortening velocity.
Factors contributing to fatigue can include reduced ATP production and ionic imbalances within muscle cells.

Skeletal Muscle Fiber Types

Slow-twitch (Type I): adapted for endurance activities.
Fast-twitch (Type IIa): intermediate properties
Fast-twitch (Type IIb or IIx): suited for rapid, powerful movements..
Different fiber types (Slow or Fast twitch) are categorized further into subdivisions, using the oxygen-using capacity and glycolysis efficiency criteria.

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Description

Test your knowledge on the physiology of muscle contraction, including the roles of ATP, tropomyosin, and calcium ions. This quiz covers essential concepts related to muscle function, energy sources, and cellular responses. Perfect for students specializing in biology or sports science!