Module 4

Question 1

What is the best-known feature of skeletal muscle?

Answer 1

Its ability to contract and cause movement

Question 2

How do muscles maintain skeletal stability and prevent skeletal structure damage or deformation?

Answer 2

By preventing excess movements of the bones and joints

Question 3

What functions do skeletal muscles allow to be controlled voluntarily?

Answer 3

Swallowing, urination and defecation

Question 4

How do skeletal muscles protect internal organs?

Answer 4

By acting as an external barrier or shield to external trauma and by supporting the weight of the organs.

Question 5

How do skeletal muscles contribute to the maintenance of homeostasis?

Answer 5

By generating heat

Question 6

What does muscle contraction require so that heat can be produced?

Answer 6

Energy

Question 7

What are the three layers of connective tissue that a skeletal muscle has? What is its purpose?

Answer 7

Mysia; it encloses the skeletal muscle and provides structure to the muscle as a whole, and also compartmentalizes the muscle fibres within the muscle.

Question 8

What is the purpose of epimysium?

Answer 8

It allows a muscle to contract and move powerfully while maintaining its structural integrity.
It also separates muscle from other tissues and organs in the area, allowing the muscle to move independently.

Question 9

What is a fascicle?

Answer 9

Individual bundle of organized muscle fibers inside each skeletal muscle.

Question 10

What is the middle layer of connective tissue inside a skeletal muscle?

Answer 10

Perimysium

Question 11

What is the importance of the fascicular organization in the muscles of the limbs?

Answer 11

It allows the nervous system to trigger a specific movement of a muscle by activating a subset of muscle fibers within a bundle, or fascicle of the muscle

Question 12

What is endomysium?

Answer 12

A thin connective tissue layer of collagen and reticular fibers in which each muscle fiber inside each fascicle is encased in.

Question 13

What are skeletal muscle cells commonly referred to as? Why?

Answer 13

Muscle fibres because the skeletal muscle cells are long and cylindrical.

Question 14

What is the plasma membrane of the muscle fibers?

Answer 14

Sarcolemma

Question 15

What is the cytoplasm of muscle fibers called?

Answer 15

Sarcoplasm

Question 16

What is the sarcoplasmic reticulum (SR)?

Answer 16

A specialized smooth endoplasmic reticulum which stores, releases, and retrieves calcium ions

Question 17

What is the functional unit of skeletal muscle fiber?

Answer 17

Sarcomere

Question 18

The sarcomere is a highly organized arrangement of the contractile of what two myofilaments?

Answer 18

Actin (thin filament) and myosin (thick filament)

Question 19

What causes the striated appearance of skeletal muscle fibers?

Answer 19

The arrangement of the myofilaments of actin and myosin in sequential order from one end of the muscle fiber to the other.

Question 20

What is each packet of microfilaments and their regulatory proteins, troponin and tropomyosin along with other proteins called?

Answer 20

Sarcomere

Question 21

What happens to the entire muscle as myofibrils contract?

Answer 21

It ccontracts

Question 22

What is another specialization of the skeletal muscle which is the site where a motor neuron’s terminal meets the muscle fiber called?

Answer 22

The neuromuscular junction (NMJ)

Question 23

What is the neuromuscular junction (NMJ)?

Answer 23

This is where the muscle fiber first responds to signaling by the motor neruon.

Question 24

What is the only way to functionally activate the fiber to contract?

Answer 24

Excitation signals from the neuron.

Question 25

Both neurons and skeletal muscle cells are electrically excitable, what does this mean?

Answer 25

They are able to generate action potentials.

Question 26

What is an action potential?

Answer 26

It is a special type of electrical signal that can travel along a cell membrane as a wave?

Question 27

What must happen first for a skeletal muscle fiber to contract?

Answer 27

Its membrane must first be excited, i.e., it must be stimulated to fire an action potential

Question 28

Explain the excitation-contraction coupling.

Answer 28

For a skeletal muscle fiber to contract, it must be first “excited” (stimulated to fire an action potential). The muscle fiber action potential, which sweeps along the sarcolemma as a wave, is “coupled” to the actual contraction through the release of calcium ions from the SR. Once released, the calcium ions interact with the shielding proteins, forcing them to move aside so that the actin-binding sites are available for attachment by the myosin head. The myosin then pulls the actin filaments toward the center, shortening te muscle fiber.

Question 29

How does the excitation-contration coupling begin in skeletal muscle?

Answer 29

It begins with signals from the somatic motor division of the nervous system

Question 30

Where do the motor neurons, that tell the skeletal muscle to contract, originate?

Answer 30

In the spinal cord with a smaller number located in the brainstem

Question 31

What are the long processes that the motor neurons have? What is the function?

Answer 31

Axons are specialized to transmit action potentials long distances

Question 32

What is a triad?

Answer 32

The arrangement of a T-tubule with the membranes of SR on either side.

Question 33

What is the function of T-tubules?

Answer 33

They carry the action potential into the interior of the cell.

Question 34

When does muscle contraction usually stop?

Answer 34

When signalling from motor neuron ends

Question 35

When can a muscle also stop contracting (aside from signalling from motor neuron ends)?

Answer 35

When it runs out of ATP and becomes fatigued.

Question 36

Why is the zone where thin and thick filaments overlap very important to muscle contraction?

Answer 36

As it is the site filament movement starts.

Question 37

Myofibrils and muscle cells contract as the sarcomeres contract, why is that?

Answer 37

Because a myofibril is composed of many sarcomeres running along its length.

Question 38

Describe the process known as the sliding filament model of muscle contraction.

Answer 38

When signalled by a motor neuron, a skeletal muscle fiber contracts as the thin filaments are pulled and then slide past the thick filaments within the fiber’s sarcomeres.

Question 39

When can the sliding only occur?

Answer 39

When myosin-binding sites on the actin filaments are exposed by a series of steps that begins with calcium ions entry into the sarcoplasm.

Question 40

What is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin?

Answer 40

Tropomyosin

Question 41

Tropomyosin binds to troponin to form what?

Answer 41

The troponin-tropomyosin complex

Question 42

What is the importance of the troponin-tropomyosin complex?

Answer 42

It prevents the myosin “heads” from binding to the active sites on the actin microfilaments.

Question 43

What does the tropomyosin have to do to initiate muscle contraction?

Answer 43

Tropomyosin has to expose the myosin-binding site on the actin filament to allow cross-bridge formation between the actin and myosin microfilaments.

Question 44

What is the cross-bridge cycle?

Answer 44

The repeated movements of myosin head pulling the actin at the binding stes, detaching, re-cocking, and attaching to more binding sites during muscle contraction for thin filaments to continue to slide past thick filaments.

Question 45

When does cross-bridge formation occur?

Answer 45

When the myosin head attaches to the actin while adenosine diphosphate (ADP) and inorganic phosphate are still bound to myosin.