Question 1

In skeletal muscle, the sarcoplasmic reticulum (SR):

Accepted Answer

The sarcoplasmic reticulum (SR) in skeletal muscle is responsible for storing and releasing calcium ions (Ca^2+) upon stimulation, which is essential for triggering muscle contraction. The formula "Ca²⁺" is a stylized way of representing calcium ions, emphasizing their pivotal role in this process.

Question 2

The two types of smooth muscle tissue are:

Accepted Answer

Visceral (single-unit) smooth muscle tissue is found in the walls of organs and helps organs like the stomach and bladder contract. Multiunit smooth muscle tissue is found in places like the eyes and blood vessels, where more precise control of muscle movement is needed.

Question 3

During an isotonic contraction of a muscle, the muscle shortens while the tension in the muscle increases, as in straightening the legs when rising from a sitting position to a standing position.

Accepted Answer

During an isotonic contraction, the tension in the muscle remains constant while the muscle changes length, allowing movement such as straightening the legs.

Question 4

Compared to skeletal muscle, cardiac muscle differs in that it:

Accepted Answer

Cardiac muscle cells are unique in that they have a branching structure, which allows them to interconnect with each other in a complex network. This is different from skeletal muscle cells, which are generally long, cylindrical, and arranged in parallel bundles.

Question 5

Which of the following is TRUE of myosin? 
1) It is located in the A band of the sarcomere.
2) It binds to tropomyosin during contraction.
3) It forms thick filaments.
4) The molecules are helix shaped.

Accepted Answer

1) Myosin is indeed located in the A band of the sarcomere, where it forms the thick filaments. 3) It forms thick filaments, which are crucial for muscle contraction by interacting with actin filaments. Myosin does not bind to tropomyosin; it binds to actin when the muscle contracts. Myosin molecules are not helix-shaped; instead, they have a tail and two heads, which are involved in binding to actin and ATP hydrolysis.

Question 6

The ability of muscular tissue to contract forcefully when stimulated is:

Accepted Answer

Contractility is the characteristic of muscle tissue that allows it to actively generate force to produce movement or tension.

Question 7

Neurotransmitter receptors are found where on the sarcolemma?

Accepted Answer

Neurotransmitter receptors are located on the motor end plate of the sarcolemma, which is the specialized region where the muscle fiber receives signals from the nerve ending.

Question 8

Which is a correct statement?

Accepted Answer

All of the statements are correct as they accurately describe the structure of muscle fibers and their components. Muscle fibers contain myofibrils, which in turn contain thick and thin filaments arranged into sarcomeres, the basic unit of muscle contraction.

Question 9

The protein has direct contact with actin in a muscle in the resting state, while the _____ protein has direct contact with actin in a muscle in the contracting state.

Accepted Answer

In the resting state of a muscle, tropomyosin covers the myosin-binding sites on actin filaments, preventing interaction between actin and myosin. During contraction, calcium ions bind to troponin, causing tropomyosin to move away from the binding sites, allowing myosin to bind to actin and initiate contraction.

Question 10

Place the following events in the correct order. 
1) ACh is released into the synaptic cleft.
2) Synaptic vesicles fuse with the plasma membrane.
3) A muscle action potential is triggered.
4) An action potential arrives at the synaptic end bulb.
5) ACh binds to receptors on the motor end plate.

Accepted Answer

The correct sequence starts with an action potential arriving at the synaptic end bulb (4), causing synaptic vesicles to fuse with the plasma membrane (2). This leads to the release of acetylcholine (ACh) into the synaptic cleft (1), which then binds to receptors on the motor end plate (5), ultimately triggering a muscle action potential (3).

Question 11

A somatic motor neuron is a nerve cell that stimulates a skeletal muscle fiber (cell) to contract.

Accepted Answer

Somatic motor neurons are responsible for conveying signals from the central nervous system to skeletal muscles, thereby causing them to contract.

Question 12

The ability of muscular tissue to be stretched without being damaged is:

Accepted Answer

Extensibility is the characteristic of muscle tissue that allows it to be stretched or extended without being damaged, enabling movements and flexibility.

Question 13

During contraction in a skeletal muscle fiber:

Accepted Answer

During contraction in a skeletal muscle fiber, myosin cross-bridges (heads) attach to actin in the thin filaments and pull them towards the center of the sarcomere, causing the thin filaments to slide past the thick filaments. This sliding filament mechanism is responsible for muscle contraction. The sarcomere shortens, bringing Z lines closer together, but the filaments themselves do not change in length; instead, they slide past each other.

Question 14

A bundle (fascicle) of skeletal muscle fibers (cells) is separated from neighboring bundles by perimysium.

Accepted Answer

Perimysium is the connective tissue that surrounds and separates bundles (fascicles) of skeletal muscle fibers from each other, providing structural support and facilitating the distribution of nerves and blood vessels to the muscle fibers.

Question 15

One sarcomere contains all of the following EXCEPT:

Accepted Answer

A sarcomere, the basic contractile unit of muscle fiber, contains the H zone, myosin, and the M line, but not myofibrils. Myofibrils are the larger structures within muscle cells that contain many sarcomeres aligned end to end.

Question 16

As skeletal muscle ages, after age 30, which of the following does NOT occur?

Accepted Answer

The relative number of slow oxidative fibers does not decrease with aging. Instead, there is a general decline in muscle mass and function, including a decrease in maximal strength, an increase in non-contractile tissue (fibrous connective tissue and adipose tissue), and a slowing of muscle reflexes. Slow oxidative fibers are more resistant to fatigue and are used for endurance activities; their proportion relative to other fiber types does not necessarily decrease with age.

Question 17

The skeletal muscle fibers that fatigue most easily are: 1. red muscle fibers.
2) slow oxidative (type I) fibers.
3) fast glycolytic (type IIb) fibers.

Accepted Answer

Fast glycolytic (type IIb) fibers fatigue most easily because they rely on anaerobic metabolism, which leads to quicker exhaustion compared to oxidative fibers that use aerobic pathways for energy.

Question 18

Which of the following is FALSE regarding skeletal muscle fibers (cells)?

Accepted Answer

The myofibrils in skeletal muscle fibers are arranged parallel to the long axis of the cell, not at right angles. This parallel arrangement contributes to the characteristic striated appearance of skeletal muscle under a microscope.

Question 19

An increase (hypertrophy) or decrease (atrophy) in muscle size is due to: 1. increased or decreased numbers of muscle cells.
2) increased or decreased deposition of adipose tissue.
3) increased or decreased size of skeletal muscle fibers.

Accepted Answer

Muscle hypertrophy or atrophy is primarily due to the increased or decreased size of skeletal muscle fibers, not a change in the number of muscle cells or the deposition of adipose tissue.

Question 20

The close association of a transverse (T) tubule and two terminal cisterns forms a:

Accepted Answer

The close association of a transverse (T) tubule and two terminal cisterns forms a triad, which is a structure found in skeletal muscle cells that plays a critical role in muscle contraction by facilitating the transmission of the action potential to the interior of the muscle cell.

Quiz 10: Muscular Tissue

In skeletal muscle, the sarcoplasmic reticulum (SR) :