Skeletal Muscle Contraction Review

These flashcards cover key concepts related to skeletal muscle contraction, including anatomy, the contraction cycle, the role of calcium, the neuromuscular junction, and muscle fiber types.

What is the sliding filament theory?

Muscle contraction occurs due to the shortening of sarcomeres, where thick and thin filaments slide past each other.

What structure attaches muscle to bone?

Tendon.

What are the contractile proteins in skeletal muscle?

Actin and Myosin.

What role does calcium play in muscle contraction?

Calcium ions (Ca2+) are released and bind to troponin, causing a conformational change that allows myosin to bind to actin.

What are the three layers of connective tissue in muscle anatomy?

Epimysium, Perimysium, and Endomysium.

What is the function of the neuromuscular junction?

It is the synapse between a somatic motor neuron and a skeletal muscle fiber, facilitating communication for muscle contraction.

During muscle contraction, what happens to the I bands and H band?

I bands shorten, and the H band shortens or disappears.

What type of muscle fiber has high resistance to fatigue?

Slow Oxidative/Type I fibers.

Describe the resting state of a muscle fiber in the contraction cycle.

In the resting state, the cross bridge is not attached to actin.

What occurs during the power stroke in the contraction cycle?

The myosin head pulls the actin filament inward, leading to the sliding of filaments.

How does acetylcholine contribute to muscle contraction?

Acetylcholine is released from the motor neuron, causing end plate potentials and action potentials that lead to muscle contraction.

What is the effect of stretching on muscle tension?

Maximal tension occurs at normal resting length; increasing or decreasing length reduces muscle tension.

What is a sarcomere?

The structural unit of a muscle fiber, extending from one Z disc to the next.

What is a fascicle in muscle anatomy?

A bundle of muscle fibers surrounded by perimysium.

What are the membranes associated with skeletal muscle?

Epimysium, Perimysium, and Endomysium.

What are the characteristics of a muscle cell?

Multinucleated, contains striations, and has a sarcolemma.

What connects skeletal muscle to bone?

Tendon.

What is the function of the epimysium?

It surrounds the entire muscle, providing support and protection.

What is the role of the sarcolemma in muscle cells?

The sarcolemma is the cell membrane that encloses a muscle fiber.

What are the contractile proteins in skeletal muscle?

Actin and Myosin.

What are the regulatory proteins in skeletal muscle?

Troponin and Tropomyosin.

What is a Z disc in muscle anatomy?

The Z disc marks the boundary between adjacent sarcomeres, acting as an anchor for thin filaments.

What is the I band in a sarcomere?

The I band is the region of the sarcomere that contains only thin filaments (actin) and is lighter in appearance.

What is the A band in a sarcomere?

The A band is the length of the thick filaments (myosin) and includes overlapping thin filaments.

What is the H zone in a sarcomere?

The H zone is the central part of the A band where there are only thick filaments (myosin) and no thin filaments.

What is the M line in a sarcomere?

The M line is the middle line in the sarcomere, where thick filaments (myosin) are attached.

What is the neuromuscular junction?

The synapse between a somatic motor neuron and a skeletal muscle fiber.

What are the components of the neuromuscular junction?

Somatic Motor Neuron, Synaptic cleft, and Motor end plate.

What is the role of the somatic motor neuron in the neuromuscular junction?

It transmits signals from the nervous system to the muscle fibers to initiate contraction.

What is the function of the synaptic cleft?

It serves as the gap between the somatic motor neuron and the muscle fiber, allowing neurotransmitters to diffuse across.

What is the motor end plate?

The region of the muscle fiber membrane that is folded to increase surface area for receiving signals from the motor neuron.

What causes muscle contraction according to the sliding filament theory?

Muscle contraction occurs due to the shortening of sarcomeres.

What happens to the distance from Z disc to Z disc during contraction?

The distance shortens as the sarcomeres contract.

Do A bands change in length during muscle contraction?

No, A bands do not change in length; they move closer together.

What happens to the I bands during muscle contraction?

I bands shorten.

What happens to the H band during muscle contraction?

The H band shortens or may disappear.

What occurs regarding the overlap of thick and thin filaments during contraction?

There is increased overlap of thick and thin filaments.

What is the resting state of a muscle fiber in the contraction cycle?

In the resting state, the cross bridge is not attached to actin.

What occurs during the second step of the contraction cycle?

The cross bridge binds to actin.

What happens during the third step of the contraction cycle?

Pi is released, causing a conformational change in myosin.

What occurs during the power stroke in the contraction cycle?

The power stroke causes filaments to slide; ADP is released.

What does ATP do in the contraction cycle?

A new ATP binds to myosin head, allowing it to release from actin.

What happens when ATP is hydrolyzed in the contraction cycle?

ATP is hydrolyzed, causing the cross bridge to return to its original orientation.

What happens when muscle cells are stimulated?

Ca²⁺ is released inside the muscle fiber.

What does Ca²⁺ bind to in muscle contraction?

Calcium binds to troponin C.

What effect does Ca²⁺ have on troponin and tropomyosin?

It causes a conformational change in troponin and tropomyosin.

What happens after myosin binds to actin?

Myosin forms cross bridges.

What initiates muscle contraction during excitation-contraction coupling?

Muscle contraction occurs when enough Ca²⁺ binds to troponin.

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

SR is a modified endoplasmic reticulum that stores Ca²⁺ when the muscle is at rest.

Where is most Ca²⁺ stored in the sarcoplasmic reticulum?

Most is stored in the terminal cisterne.

What happens when a muscle fiber is stimulated?

Ca²⁺ diffuses out of calcium release channels.

What happens to Ca²⁺ at the end of a contraction?

Ca²⁺ is actively pumped back into the sarcoplasmic reticulum (SR).

What is released from the motor neuron during the stimulation of a muscle fiber?

Acetylcholine is released from the motor neuron.

What are end plate potentials similar to?

End plate potentials are the same as EPSP in neurons.

What type of events are action potentials?

Action potentials are generated as all-or-none events.

What happens to voltage-gated calcium channels in transverse tubules?

Voltage-gated calcium channels change shape and cause calcium channels in the sarcoplasmic reticulum (SR) to open.

What happens to calcium during excitation-contraction coupling?

Calcium is released and can bind to troponin C.

What is the length-tension relationship in muscle contraction?

Tension is maximal when sarcomeres are at normal resting length.

What happens to muscle tension when sarcomere length is increased?

Increasing sarcomere length decreases muscle tension, as there are fewer interactions between myosin and actin.

What occurs at a certain point when sarcomere length is increased?

At a certain point, no tension can be generated.

What effect does decreasing sarcomere length have on muscle tension?

Decreasing sarcomere length decreases muscle tension because the fiber gets shorter and thicker.

What contributes to decreased muscle tension when sarcomere length decreases?

Increased fluid pressure and increased distance between the actin and myosin.

What is the diameter of Slow Oxidative/Type I muscle fibers?

Small.

What is the diameter of Fast Glycolytic/Type IIX muscle fibers?

Large.

How does the Z-line thickness compare between Slow Oxidative/Type I and Fast Oxidative-Glycolytic/Type IIA muscle fibers?

Slow Oxidative/Type I has a wide Z-line, while Fast Oxidative-Glycolytic/Type IIA has an intermediate Z-line.

What is the glycogen content in Slow Oxidative/Type I muscle fibers?

Low.

What is the resistance to fatigue in Fast Glycolytic/Type IIX muscle fibers?

Low.

What is the capillary count in Fast Oxidative-Glycolytic/Type IIA muscle fibers?

Many.

What is the myoglobin content in Fast Glycolytic/Type IIX muscle fibers?

Low.

What type of respiration do Slow Oxidative/Type I muscle fibers use?

Aerobic.

What is the oxidative capacity of Fast Oxidative-Glycolytic/Type IIA muscle fibers?

High.

How does the twitch rate of Slow Oxidative/Type I muscle fibers compare to Fast Glycolytic/Type IIX?

Slow Oxidative/Type I has a slow twitch rate, while Fast Glycolytic/Type IIX has the fastest twitch rate.

What muscle fiber type is predominant in a world-class sprinter?

Fast type IIX fibers are predominant in a world-class sprinter.

Which muscle fiber type is more prevalent in an extreme endurance athlete?

Slow type I fibers are more prevalent in an extreme endurance athlete.

What is the muscle fiber composition of an average couch potato?

An average couch potato has a balanced composition of muscle fiber types, with moderate amounts of slow type I and fast type II fibers.

How does the muscle fiber composition of a middle-distance runner differ from that of a person with a spinal injury?

A middle-distance runner has a higher proportion of fast type IIA fibers, while a person with a spinal injury has reduced muscle fiber overall.

What general trend can be observed between muscle fiber types and athletic performance?

Higher performance athletes (like marathon runners) tend to have a greater proportion of slow type I fibers, while sprinters have more fast type IIX fibers.