Histology Testbank: Muscle 5a

Instructions: For each histology question, pick the one best answer. This histology test bank is also useful for the histology questions on the USMLE (USMLE step 1).

1.
What is the cytoplasm of a muscle cell?
a. Epimysium
b. Sarcolemma
c. Endomysium
d. Sarcoplasm
e. Perimysium

Answer: d

The outer connective tissue covering of a muscle is the epimysium. Within the muscle, there are subdivisions called fascicles. The perimysium surrounds these muscle fascicles. The endomysium is the covering around an individual muscle fiber. The sarcolemma is the plasma membrane of a muscle cell. The sarcoplasm is the cytoplasm of a muscle cell.

2.
What is another term for muscle cells?
a. Myofilaments
b. Myosin
c. Muscle fibers
d. Myofibrils
e. Myocardium

Answer: c

Myofilaments are the contractile protein within a muscle cell. The myofilaments are actin and myosin. The thin filaments are actin and the thick filaments are myosin. The muscle cell is a muscle fiber. The term "muscle cell" and "muscle fiber" are synonymous. A myofibril is a longitudinal bundle of myofilaments within a muscle cell. Myocardium is the muscular layer of the heart. Thus, the myocardium is composed of cardiac muscle.

3.
Which of the following contains a substantial amount of smooth muscle?
a. Upper esophagus
b. Blood vessels
c. Heart
d. Biceps muscle
e. Tongue

Answer: b

There are two chief categories of muscle: striated and non striated muscle (smooth muscle).

Striated muscle can be sub-categorized into cardiac muscle and skeletal muscle. The tongue, biceps muscle, and upper esophagus are made of striated muscle. The heart is composed of cardiac muscle.

Non striated muscle is also called smooth muscle. Smooth muscle is involuntary muscle. It is found in viscera and blood vessels.

4.
What type of muscle contains actin and myosin?
a. Skeletal muscle
b. Cardiac muscle
c. Smooth muscle
d. Both "a" and "b"
e. "a" "b" and "c"

Answer: e

All types of muscle contain actin and myosin.

5.
What is a single neuron and the aggregation of muscle fibers innervated by that single neuron called?
a. Motor unit
b. Motor neuron
c. Motor end plate
d. Neuromuscular spindle
e. Neurotransmitter

Answer: a

A single motor neuron and the aggregation of muscle fibers innervated by that single neuron is called the motor unit. A motor neuron is a neuron which innervates a muscle cell. The point of contact where a neuron contacts a muscle is the motor end plate. A neuromuscular spindle is a receptor which is sensitive to stretching of the muscle. A neurotransmitter is the chemical released by a nerve at a synapse.

6.
Which fiber type has a lot of mitochondria?
a. Red fibers
b. White fibers
c. Intermediate fibers
d. All of the above
e. None of the above

Answer: a

Skeletal muscle fibers can be classified as red fibers, white fibers or intermediate fibers. Red fibers are smaller in diameter; white fibers are larger in diameter. Red fibers have more mitochondria than white fibers. Red fibers make up slow-twitch muscle; white fibers make up fast-twitch muscle. Red fibers are more resistant to fatigue than are white fibers. Red fibers have more myoglobin (oxygen binding pigment) than white fibers. White fibers store glycogen and use anaerobic metabolism.

7.
Which fiber type uses more aerobic metabolism?
a. Red fibers
b. White fibers
c. Intermediate fibers
d. All of the above
e. None of the above

Answer: a

Skeletal muscle fibers can be classified as red fibers, white fibers or intermediate fibers. Red fibers are smaller in diameter; white fibers are larger in diameter. Red fibers have more mitochondria than white fibers. Red fibers make up slow-twitch muscle; white fibers make up fast-twitch muscle. Red fibers are more resistant to fatigue than are white fibers. Red fibers have more myoglobin (oxygen binding pigment) than white fibers. White fibers store glycogen and use anaerobic metabolism.

Red fiber and slow twitch muscle is for endurance.

White fiber and fast twitch muscle is for a burst of power.

8.
What is the light band in muscle?
a. A band
b. I band
c. Z line
d. H band
e. M line

Answer: b

The A band is the darker staining band. The I band is the light band. The I band is made of thin filaments. The Z line runs through the I band. The H band bisects the A band. The M line runs through the H band.

A sarcomere is the segment that runs from Z line to Z line.

9.
What type of muscle contains sarcomeres?
a. Skeletal muscle
b. Cardiac muscle
c. Smooth muscle
d. Both "a" and "b"
e. "a" "b" and "c"

Answer: d

Both skeletal muscle and cardiac muscle have sarcomeres. Smooth muscle has no sarcomeres.

10.
What type of muscle has branching cells?
a. Skeletal muscle
b. Cardiac muscle
c. Smooth muscle
d. Both "a" and "b"
e. "a" "b" and "c"

Answer: b

Branching cells are seen in cardiac muscle.

Histology hint from Sarah Bellham: This is an important point, as both skeletal muscle and cardiac muscle are striated. The branching seen with cardiac muscle is one of the things that can be used to distinguish between the two.