Question 1

Why is the innervation ratio in the ocular muscles one motor axon per 23 muscle fibers, whereas in the gastrocnemius muscle, it is one motor axon per 1,000 muscle fibers?
A) There are more nerves in the upper body than in the lower extremities.
B) The ocular muscles require finer control than moving the legs.
C) The innervation ratio has to do with the overall size of the muscle- the bigger the muscle, the fewer the muscle fibers per motor axon.
D) The gastrocnemius muscle contracts much harder than the ocular muscles do.
E) There are fewer muscle fibers in the gastrocnemius muscle than in the ocular muscles.

Accepted Answer

The ocular muscles require finer control for movements like tracking objects, whereas the gastrocnemius muscle is responsible for powerful movements like jumping or running. The finer control required for ocular movements necessitates a lower innervation ratio.

Question 2

When the nerve signal reaches the axon terminal, what happens next? A) The muscle contracts. B) The synaptic vesicles release neurotransmitter. C) An electrical signal is formed that jumps the synaptic cleft. D) H⁺ is pumped into the synaptic cleft. E) Myosin is released from the axon terminal.

Accepted Answer

When the nerve signal reaches the axon terminal, the synaptic vesicles present in the terminal release neurotransmitter into the synaptic cleft. This neurotransmitter then binds to receptors on the postsynaptic neuron, leading to the propagation of the signal.

Question 3

One sarcomere
A) extends from Z line to Z line.
B) is composed of many myofibrils.
C) contains only actin fibers.
D) is composed of many muscle fibers.
E) surrounds each muscle in the body.

Accepted Answer

A sarcomere is the basic unit of muscle contraction and extends from one Z line to the next Z line. It contains both actin and myosin fibers arranged in a specific pattern that allows for muscle contraction.

Question 4

Which of the following is not a phase of a single muscle twitch?
A) stimulation period
B) latent period
C) contraction period
D) relaxation period
E) None of these are phases of a muscle twitch.

Accepted Answer

A stimulation period is not a phase of a muscle twitch.

Question 5

What does the word sarco mean?
A) large
B) short
C) muscle
D) tubule
E) smooth

Accepted Answer

The word sarco comes from a Greek root meaning muscle, and is commonly used in scientific terms relating to muscles or muscle fibers.

Question 6

One motor neuron activates one muscle fiber.

Accepted Answer

One motor neuron can activate multiple muscle fibers, depending on the size and function of the muscle, which is known as motor unit recruitment.

Question 7

One motor unit obeys a principle called the all-or-none law.

Accepted Answer

The all-or-none law states that once a threshold stimulus is reached, all the muscle fibers in a motor unit will contract simultaneously and to their fullest extent. There is no partial contraction of motor units.

Question 8

What does troponin bind to, and what happens when it binds? A) Ca²⁺; tropomyosin shifts B) tropomyosin; the sarcomere relaxes C) acetylcholine; the sarcomere shortens D) ATP; tropomyosin returns to normal position E) T tubules; the sarcomere shortens

Accepted Answer

Troponin binds to calcium ions (Ca2+) and causes the tropomyosin to shift, exposing the binding sites on the actin filaments for myosin to bind to, leading to muscle contraction.

Question 9

Which way does the adductor longus move the thigh?
A) away from the midline
B) toward the midline
C) in a circle
D) in a cone
E) towards the back

Accepted Answer

The adductor longus muscle is named for its action of adduction, which means to move a body part toward the midline. Therefore, choice B is the correct answer.

Question 10

Which of the following does not attach to the sternocleidomastoid muscle?
A) rib
B) clavicle
C) sternum
D) mastoid process
E) skull

Accepted Answer

The sternocleidomastoid muscle attaches to the clavicle, sternum, mastoid process, and skull, but not to a rib.

Question 11

A muscle fiber is made up of many
A) muscle cells.
B) T tubules.
C) myofibrils.
D) fascicles.
E) bursa.

Accepted Answer

A muscle fiber is a single muscle cell that contains many myofibrils. Myofibrils are made up of sarcomeres, which are the basic contractile units of muscle.

Question 12

What ion is responsible for initiating muscle contraction? A) Mg²⁺ B) Ca²⁺ C) H⁺ D) Cl^- E) Na⁺

Accepted Answer

Calcium (Ca2+) ions are responsible for initiating muscle contraction by binding to proteins in muscle fibers and causing them to change shape, allowing for the contraction to occur.

Question 13

When a muscle contracts, the H band almost disappears.

Accepted Answer

When a muscle contracts, the sarcomeres, which are the basic units of muscle tissue, shorten, causing the Z lines to move closer together. This causes the H band, which is the region in the middle of the A band that contains only myosin filaments, to almost disappear as the actin and myosin filaments overlap.

Question 14

What supplies the energy for muscle contraction? A) actin B) myosin C) tropomyosin D) ATP E) Ca²⁺

Accepted Answer

ATP supplies the energy for muscle contraction.

Question 15

Each actin molecule is shaped like a golf club, with a straight portion ending in a globular head.

Accepted Answer

Each myosin molecule is shaped like a golf club.

Question 16

What happens to the actin and myosin filaments when a muscle contracts?
A) Both of them shorten.
B) Both of them lengthen.
C) Both stay the same length.
D) Actin shortens, while myosin lengthens.
E) Myosin shortens, while actin lengthens.

Accepted Answer

The actin and myosin filaments stay the same length when a muscle contracts. They just slide past each other.

Question 17

Several of the structures in the muscle cell are given special names. For example, the cytoplasm of a muscle fiber is called the sarcoplasm. Which of the following is truly a unique structure to muscle cells not just a renamed one)?
A) cytoplasm
B) nucleus
C) endoplasmic reticulum
D) transverse T) system
E) plasma membrane

Accepted Answer

The transverse (T) system is unique to muscle cells and is responsible for transmitting the action potential deep into the muscle fiber, allowing for synchronized contraction of the entire cell. The other structures listed (cytoplasm, nucleus, endoplasmic reticulum, plasma membrane) are found in many types of cells and are not unique to muscle cells.

Question 18

What is the biggest muscle in terms of mass) in the body?
A) gluteus maximus
B) sartorius
C) stapedius
D) quadriceps femoris
E) latissimus dorsi

Accepted Answer

The gluteus maximus is the largest muscle in terms of mass in the body. It is responsible for hip extension and external rotation, as well as thigh abduction and adduction.

Question 19

What information does the word rectus give you about a muscle?
A) the size of the muscle fibers
B) the attachment of the muscle fibers
C) the action of the muscle fibers
D) the shape of the muscle fibers
E) the direction of muscle fibers

Accepted Answer

The word "rectus" indicates the direction of the muscle fibers, as it comes from the Latin word for "straight". This suggests that the muscle fibers are arranged in a linear or straight fashion.

Question 20

What is the name of the small gap that separates the axon terminal of a nerve from the sarcolemma?
A) T tubule
B) sliding filament
C) synaptic cleft
D) synaptic vesicle
E) sarcoplasmic reticulum

Accepted Answer

The small gap that separates the axon terminal of a nerve from the sarcolemma is called the synaptic cleft. It is the space where chemical signals called neurotransmitters are released from the axon terminal and diffuse across to bind to receptors on the sarcolemma, initiating muscle contraction. The other answer choices are not relevant to the synaptic cleft.

Quiz 13: Muscular System

Why is the innervation ratio in the ocular muscles one motor axon per 23 muscle fibers, whereas in the gastrocnemius muscle, it is one motor axon per 1,000 muscle fibers?

When the nerve signal reaches the axon terminal, what happens next?

One sarcomere

Which of the following is not a phase of a single muscle twitch?

What does the word sarco mean?

One motor neuron activates one muscle fiber.

One motor unit obeys a principle called the all-or-none law.

What does troponin bind to, and what happens when it binds?

Which way does the adductor longus move the thigh?

Which of the following does not attach to the sternocleidomastoid muscle?

A muscle fiber is made up of many

What ion is responsible for initiating muscle contraction?

When a muscle contracts, the H band almost disappears.

What supplies the energy for muscle contraction?

Each actin molecule is shaped like a golf club, with a straight portion ending in a globular head.

What happens to the actin and myosin filaments when a muscle contracts?

Several of the structures in the muscle cell are given special names. For example, the cytoplasm of a muscle fiber is called the sarcoplasm. Which of the following is truly a unique structure to muscle cells not just a renamed one) ?

What is the biggest muscle in terms of mass) in the body?

What information does the word rectus give you about a muscle?

What is the name of the small gap that separates the axon terminal of a nerve from the sarcolemma?