Muscle Advanced

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Questions and Answers

What function of skeletal muscle is least dependent on its connections to other tissues?

Movement

Stability

Heat generation (correct)

Protection of organs

Which muscle type does not contract spontaneously?

Skeletal muscle (correct)

Cardiac muscle

Smooth muscle in digestive tract

Smooth muscle in blood vessels

What is the role of Ca2+ in the muscle action potential?

Depolarisation

Repolarisation

None - Ca2+ only regulates contraction (correct)

Hyperpolarisation

What is the role of T-tubules in skeletal muscle function?

Ensure the muscle is excited as quickly and evenly as possible Signup and view all the answers

A motor unit containing few muscle fibres produces:

Fine movements Signup and view all the answers

Curare completely blocks cholinergic transmission at the neuromuscular junction. It will therefore cause:

Complete paralysis & relaxation Signup and view all the answers

When a whole motor nerve is stimulated electrically, increasing strength of stimulus causes the muscle to contract more strongly. Why is the all-or-none law apparently not obeyed?

A motor nerve contains many motor units. Greater stimulation causes additional motor units to become active. Signup and view all the answers

Which organs are capable of generating heat?

Skeletal muscle and the liver Signup and view all the answers

What component of a sarcomere does the I-band represent?

The portion of thin filaments (on both sides of the Z line) not overlapping with thick filaments Signup and view all the answers

What component of a sarcomere does the A-band represent?

The area where thick and thin filaments overlap Signup and view all the answers

Which of the following correctly describes the sarcomere during contraction?

A-band is constant, I band gets smaller, Z-lines move closer together. Signup and view all the answers

If a muscle is stretched until the zone of overlap disappears, it:

It can no longer contract Signup and view all the answers

At the molecular level, the energy source for contraction is:

ATP Signup and view all the answers

The energy-dependent rotation of the myosin head during muscle contraction is responsible for:

Pushing the actin filament Signup and view all the answers

What is the first step in the contraction of a skeletal muscle fibre?

An action potential is triggered at the neuromuscular junction Signup and view all the answers

What is the role of the sarcoplasmic reticulum in skeletal muscle?

Store Ca2+ and release it when triggered by an action potential Signup and view all the answers

During excitation-contraction coupling, troponin binds Ca2+. How does this enable contraction to occur?

Troponin shifts to expose the myosin binding site on the actin filament Signup and view all the answers

While Ca2+ is present in the sarcoplasmic reticulum:

The muscle will continue to contract Signup and view all the answers

During peak activity muscles cannot generate enough energy (ATP) from oxygen-dependent metabolism. What happens in this situation?

Energy is derived from oxygen-independent mechanisms Signup and view all the answers

Accumulation of lactic acid in contracting skeletal muscle is also called the 'oxygen debt'. What does this mean?

Lactic acid is a waste product of oxygen-independent glucose metabolism. It is converted back into glucose during recovery, consuming oxygen. Signup and view all the answers

Study Notes

Skeletal Muscle Function

Heat generation is the least dependent function on connections to other tissues.
Movement, stability, and protection of organs rely on connections to other tissues, such as bones, tendons, and ligaments.

Muscle Types

Skeletal muscle doesn't contract spontaneously, while cardiac muscle, smooth muscle in the digestive tract, and smooth muscle in blood vessels do.

Ca2+ Role in Muscle Action Potential

Ca2+ is not involved in the muscle action potential itself.
It plays a crucial role in regulating muscle contraction.

T-Tubules Function in Skeletal Muscle

T-tubules are responsible for ensuring quick and even excitation of the muscle.
This is achieved by rapidly distributing the muscle action potential throughout the muscle fiber.

Motor Unit and Muscle Movement

A motor unit with few muscle fibers produces fine movements, while a motor unit with many muscle fibers produces powerful movements.

Curare and Neuromuscular Junction

Curare completely blocks cholinergic transmission at the neuromuscular junction.
This results in complete paralysis and relaxation of the muscle.

All-or-None Law and Motor Units

The apparent violation of the all-or-none law is explained by the presence of multiple motor units within a motor nerve.
Increasing stimulus strength activates additional motor units, leading to stronger contractions.

Organs Capable of Generating Heat

Skeletal muscle and the liver are the primary organs responsible for generating heat.
The gastrointestinal tract, nervous system, and lungs also contribute to a lesser extent.

Sarcomere Components

The I-band represents the portion of thin filaments on both sides of the Z-line that don't overlap with thick filaments.
The A-band encompasses the entire length of the thick filaments, including the region where thick and thin filaments overlap.

Sarcomere During Contraction

During contraction, the A-band remains constant.
The I-band gets smaller, and the Z-lines move closer together.
The zone of overlap increases.

Muscle Stretch and Contraction

If a muscle is stretched until the zone of overlap disappears, it can no longer contract effectively.
This is because the actin and myosin filaments are no longer able to interact.

Energy Source for Muscle Contraction

ATP is the direct energy source for muscle contraction.
Glucose and other molecules provide the fuel for ATP production.

Myosin Head Rotation and Muscle Contraction

The energy-dependent rotation of the myosin head is responsible for pushing the actin filament during muscle contraction.

First Step in Skeletal Muscle Fiber Contraction

The first step in muscle fiber contraction is the arrival of an action potential at the neuromuscular junction.
This triggers the release of acetylcholine, which initiates the cascade of events leading to muscle contraction.

Sarcoplasmic Reticulum Role

The sarcoplasmic reticulum stores Ca2+ and releases it when triggered by an action potential.
This release of Ca2+ is essential for muscle contraction.

Troponin and Muscle Contraction

Troponin binds Ca2+, causing a conformational change in tropomyosin.
This change exposes the myosin binding site on the actin filament, allowing myosin to bind and initiate contraction.

Ca2+ and Muscle Contraction

While Ca2+ is present in the sarcoplasm, tropomyosin prevents the binding of myosin to actin.
This keeps the muscle in a relaxed state.

Muscle Fatigue and ATP Production

During peak activity, muscles may not generate enough ATP from oxygen-dependent metabolism.
In this situation, energy is derived from oxygen-independent mechanisms, leading to the accumulation of lactic acid.

Oxygen Debt and Lactic Acid Accumulation

The accumulation of lactic acid is referred to as the oxygen debt.
During recovery, lactic acid is converted back into glucose, consuming oxygen.
This process replenishes the oxygen stores used during heavy activity.

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Description

Explore the functions and types of skeletal muscle, including their role in movement, heat generation, and connections to other tissues. This quiz covers the importance of Ca2+ in muscle contraction and the function of T-tubules in muscle excitation. Test your understanding of motor units and their contribution to muscle movement.