Muscle Anatomy and Physiology Quiz

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Questions and Answers

Which of the following is NOT a key feature of muscle cells?

Excitability

Contractility

Invisibility (correct)

Extensibility

Which connective tissue layer directly surrounds a muscle fascicle?

Endomysium

Perimysium (correct)

Epimysium

Sarcolemma

What is the smallest contractile element within a muscle unit?

Myofibril

Sarcomere

Myofilament (correct)

Muscle Fiber

Which of these is the correct order of muscle structure from smallest to largest?

Myofilament - myofibril - muscle fiber Signup and view all the answers

What is the primary function of tendons in relation to skeletal muscles?

To attach muscles to bones Signup and view all the answers

Which structure is described as the functional unit of a muscle?

Sarcomere Signup and view all the answers

Which of the following is the layer that insulates individual muscle fibers?

Endomysium Signup and view all the answers

Which of the following myofilaments directly binds to myosin?

Actin Signup and view all the answers

What is the primary role of tropomyosin in muscle contraction?

To cover the active sites on actin Signup and view all the answers

What is the significance of the presence of numerous mitochondria in muscle cells?

To provide the ATP needed for muscle contraction Signup and view all the answers

Which of the following best describes the composition of the A band in a sarcomere?

Both thick and thin filaments Signup and view all the answers

What is the primary function of titin in muscle fibers?

To prevent excessive stretching of the sarcomere Signup and view all the answers

Which protein connects the Z line to the cell membrane?

Desmin Signup and view all the answers

What function do T tubules perform within a muscle fiber?

They transmit the action potential Signup and view all the answers

What is a 'triad' in skeletal muscle composed of?

One T tubule and two terminal cisternae Signup and view all the answers

What is the role of the sarcoplasmic reticulum (SR) in muscle contraction?

To release calcium ions into the sarcoplasm Signup and view all the answers

Which event directly facilitates the exposure of actin's active sites during skeletal muscle contraction?

Calcium ion binding to troponin Signup and view all the answers

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

To degrade acetylcholine in the synaptic cleft Signup and view all the answers

According to the sliding filament theory, which event directly causes the power stroke?

Release of ADP and phosphate from the myosin head Signup and view all the answers

What is the function of the SERCA (Sarcoplasmic Reticulum Calcium-ATPase) pump during muscle relaxation?

To actively transport calcium ions into the sarcoplasmic reticulum Signup and view all the answers

Which of the following steps in the muscle contraction cycle requires ATP hydrolysis?

The separation of the myosin head from actin Signup and view all the answers

What is the primary role of creatine phosphate in muscle contraction?

To convert to creatine and provide phosphate, which is then used to replenish ATP. Signup and view all the answers

What is the role of tropomyosin in a resting muscle?

To cover the active sites on actin Signup and view all the answers

Which of the following best defines a motor unit?

A single motor neuron and all the muscle fibers it innervates. Signup and view all the answers

In the sequence of events during muscle contraction, what process immediately follows the formation of acto-myosin cross-bridges?

The release of phosphate, initiating the power stroke Signup and view all the answers

Which of the following describes how ATP is directly used to make muscle cells ready for a new contraction cycle?

ATP is used to reset the sodium-potassium gradient. Signup and view all the answers

If a muscle contraction requires high precision, which type of motor units are likely to be activated?

Small motor units with a few muscle fibers. Signup and view all the answers

What is the term for the progressive decrease in muscle tension despite consistent nervous stimulation?

Muscle fatigue. Signup and view all the answers

What does the term 'recruitment' refer to in the context of muscle contraction?

The activation of additional motor units to increase contraction strength. Signup and view all the answers

Which energy system is used first during a muscle contraction?

Stored ATP Signup and view all the answers

What is the immediate product of glucose breakdown in the process of anaerobic glycolysis, before entering the Krebs cycle?

Pyruvate Signup and view all the answers

Which of the following is NOT a determinant of the strength of a muscle contraction?

The amount of oxygen available to the muscle Signup and view all the answers

Study Notes

Skeletal Muscle Contraction

Skeletal muscles are responsible for movement, posture maintenance, heat production, and protecting internal organs.
Key features of muscle cells include excitability (responding to stimuli), contractility (shortening and thickening to generate force), extensibility (extending without damage), and elasticity (returning to original shape).

Muscle Types

Skeletal muscle: Striated, voluntary, multi-nucleated fibers, usually attached to the skeleton.
Smooth muscle: Non-striated, involuntary, spindle-shaped, uninucleated fibers, found in internal organs.
Cardiac muscle: Striated, involuntary, branched, uninucleated fibers, found only in the heart.

Skeletal Muscle Structure

Organized into:
- Myofilaments (actin and myosin).
- Myofibrils.
- Muscle fibers.
- Muscle fascicles.
- Skeletal muscle.
Connective tissue layers surround muscle units: Endomysium (surrounds individual muscle fibers). Perimysium (surrounds muscle fascicles). Epimysium (surrounds the entire skeletal muscle).

Sarcomere Structure

I band: Thin (actin) filaments.
H zone: Only thick (myosin) filaments.
A band: Both thick and thin filaments.
Z line: Region between two I bands.
M line: Middle of the H zone, where myosin filaments connect.

Muscle Proteins

Dystrophin, titin, actinin, desmin, nebulin are important intracellular skeletal proteins that maintain sarcomere structure and function.
Dystrophin connects actin to the extracellular matrix.
Titin stabilizes the sarcomere.

Sarcotubular System

T tubules: Inward folds of the muscle fiber membrane, allowing the action potential to travel through the cell.
Sarcoplasmic reticulum (SR): Stores Ca²⁺ ions.
The triad: A combination of one T-tubule and two terminal cisternae of SR.

Neuromuscular Junction

Junction between a motor neuron and a muscle fiber.
Acetylcholine (ACh) released from the motor neuron triggers an action potential in the muscle fiber, leading to muscle contraction.

Muscle Fatigue

Repeated stimulation of muscle fibers can lead to decreased tension.
Characteristics include reduced shortening rate and slower relaxation rate.

Skeletal Muscle Fiber Types

Slow-twitch fibers (Type 1): Longer twitch duration, involved in sustained contractions, high endurance, and use oxidative phosphorylation more than glycolysis for ATP production.
Fast-twitch fibers (Type 2): Rapid contractions, used for powerful movements, and use glycolysis more than oxidative phosphorylation for ATP production.
Fast-oxidative-glycolytic (Type 2A) fibers: Intermediate characteristics between slow and fast-twitch fibers.
Fast-glycolytic (Type 2X/2B) fiber: Fastest twitch duration, primarily anaerobic and fastest fatigue.

ATP Energy in Muscle Contraction

ATP is essential for several phases of muscle contraction and relaxation.
ATP binding to myosin allows the detachment of myosin from actin.
ATP hydrolysis powers the power stroke, which brings about shortening of the muscle fiber.
The SERCA pump uses ATP to re-establish the appropriate Na-K gradient in the muscle cell.

Skeletal Muscle Metabolism

Stored ATP is utilized first for brief contractions.
Creatine phosphate stores are used next.
Oxidative phosphorylation is the primary long-term energy source.
Anaerobic glycolysis is used for brief, powerful contractions or when oxygen availability is low, which can lead to muscle soreness or pain as byproducts are produced.

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Description

Test your knowledge on the structure and function of muscle cells with this comprehensive quiz. It covers key features, connective tissues, contractile elements, and the roles of various proteins in muscle contraction. Perfect for students of anatomy and physiology.