Physiology Lab 7 Homework Quiz

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Questions and Answers

Which of the following is proportional to the amount of tension produced by a skeletal muscle?

The length of the latent period

The number of motor units activated (correct)

The threshold voltage

The length of the relaxation phase

NO force is generated during which of the following?

The latent period (correct)

A muscle twitch

The contraction phase

The relaxation phase

What is the minimum voltage needed to generate active force in the skeletal muscle?

Recruitment voltage

Stimulus voltage

Threshold voltage (correct)

Contraction voltage

A motor unit is defined as _______.

a single motor neuron and all of the muscle fibers that it stimulates Signup and view all the answers

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?

Arrival of an action potential Signup and view all the answers

The binding of calcium to which molecule causes the myosin binding sites to be exposed?

Troponin Signup and view all the answers

A myosin head binds to which molecule to form a cross bridge?

Actin Signup and view all the answers

What causes the myosin head to disconnect from actin?

Binding of ATP Signup and view all the answers

What causes the power stroke?

Release of ADP and Pi Signup and view all the answers

What causes muscle contractions to be graded?

Both increasing stimulus strength and increasing stimulus frequency Signup and view all the answers

Excitation-contraction coupling refers to a series of events occurring after what?

Events of the neuromuscular junction Signup and view all the answers

What specific event initiates the contraction of skeletal muscles?

Calcium release from the sarcoplasmic reticulum Signup and view all the answers

What is a triad composed of?

A T-tubule and two adjacent terminal cisternae Signup and view all the answers

What is the name given to the regularly spaced infoldings of the sarcolemma?

Transverse or T tubules Signup and view all the answers

Which of the following is directly responsible for coupling excitation to contraction of skeletal muscle fibers?

Calcium ions Signup and view all the answers

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron Signup and view all the answers

What is the role of calcium in the cross bridge cycle?

Calcium binds to troponin, altering its shape Signup and view all the answers

What role does tropomyosin play in the cross bridge cycle?

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form Signup and view all the answers

How does troponin facilitate cross bridge formation?

Troponin controls the position of tropomyosin on the thin filament Signup and view all the answers

What, specifically, is a cross bridge?

Myosin binding to actin Signup and view all the answers

Which event causes cross bridge detachment?

ATP binding to the myosin head Signup and view all the answers

Where in the cross bridge cycle does ATP hydrolysis occur?

During the cocking of the myosin head Signup and view all the answers

How does the myosin head cock back to store energy for the next cycle?

After detachment, energy from ATP hydrolysis is used to re-cock the myosin head Signup and view all the answers

BMD inhibits myosin, preventing hydrolysis of ATP. What effect would BMD have on the cross bridge cycle?

Myosin heads would remain attached to actin, unable to detach Signup and view all the answers

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?

There are always some myosin heads attached during detachment Signup and view all the answers

Study Notes

Muscle Contraction and Mechanisms

Tension produced by skeletal muscle is proportional to the number of motor units activated.
During the latent period, no force is generated; this is the time before contraction begins.
The threshold voltage is the minimum voltage required to initiate active force in skeletal muscle.
A motor unit consists of a single motor neuron and all the muscle fibers it stimulates.
An action potential's arrival at the T tubule leads to the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.

Calcium and Muscle Contraction

Calcium binds to troponin, leading to a shape change that exposes myosin binding sites on actin.
Myosin heads form cross bridges by binding to actin.
The release of ATP from myosin causes the myosin head to disconnect from actin.
The power stroke is caused by the release of ADP and inorganic phosphate after the binding of calcium.

Graded Muscle Contraction

Muscle contractions are graded by increasing stimulus strength and frequency.
Excitation-contraction coupling involves action potentials propagating along the sarcolemma, which prompts calcium release and subsequent muscle contraction.

Structural Components

A triad consists of a T-tubule and two adjacent terminal cisternae.
T-tubules are the infoldings of the sarcolemma that allow excitation to penetrate the muscle fiber.
Calcium ions are crucial for the coupling of excitation to contraction in muscle fibers.

Cross Bridge Cycle

The cross bridge is defined as myosin binding to actin.
The binding of ATP to the myosin head causes cross bridge detachment.
ATP hydrolysis occurs during the cocking of the myosin head, storing energy for the next cycle.
Myosin heads will remain attached to actin if they cannot detach due to factors like the inhibition of ATP hydrolysis.

Regulation of Muscle Fiber Activity

Tropomyosin covers active sites on actin; its displacement allows cross bridge formation.
The role of troponin is to regulate tropomyosin positioning, enabling myosin heads to bind to active sites.
During contraction, always having some myosin heads attached prevents actin from sliding backward.

Effects of Inhibitors

BMD (2,3-butanedione 2-monoxime) inhibits myosin's ability to hydrolyze bound ATP, preventing myosin heads from cocking and affecting the cross bridge cycle's progression.

These notes summarize the essential aspects of skeletal muscle contraction, detailing the roles of ions, proteins, and mechanical processes involved in the cross bridge cycle and overall muscle functionality.

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Description

Test your understanding of skeletal muscle tension and muscle twitch dynamics with this Lab 7 homework quiz. Assess your knowledge of terms like latency and motor unit activation. Ideal for students revising for physiology exams.