BIO 256 EXAM 3: ULTIMATE MUSCLE PHYSIOLOGY
STUDY GUIDE | 200 COMPREHENSIVE MCQS WITH
RATIONALES
1. Which of the following best describes the function of the
sarcoplasmic reticulum in skeletal muscle fibers?
A) It synthesizes ATP for muscle contraction.
B) It stores and releases calcium ions.
C) It produces acetylcholine for synaptic transmission.
D) It anchors the myofilaments to the sarcolemma.
Correct Answer: B) It stores and releases calcium ions.
Rationale: The sarcoplasmic reticulum is a modified endoplasmic
reticulum that surrounds the myofibrils and acts as a calcium reservoir.
Upon stimulation, it releases calcium into the sarcoplasm to trigger
contraction.
2. A motor neuron and all the muscle fibers it innervates are
collectively referred to as a:
A) Sarcomere
B) Motor unit
C) Myofibril
D) Neuromuscular junction
Correct Answer: B) Motor unit
Rationale: A motor unit is the functional unit of muscle contraction,
consisting of a single motor neuron and the specific group of muscle
fibers it stimulates.
,3. The role of calcium ions in skeletal muscle contraction is to:
A) Bind to myosin and energize the power stroke.
B) Break down acetylcholine in the synaptic cleft.
C) Bind to troponin, causing tropomyosin to shift and expose active
sites.
D) Depolarize the T-tubules.
Correct Answer: C) Bind to troponin, causing tropomyosin to shift and
expose active sites.
Rationale: Calcium binds to the troponin complex on the actin filament,
inducing a conformational change that moves tropomyosin away from
the myosin-binding sites, allowing cross-bridge formation.
4. In an isotonic contraction, the muscle:
A) Generates tension but does not change in length.
B) Changes in length and moves a load.
C) Is unable to relax after contraction.
D) Shortens with a constant velocity against no load.
Correct Answer: B) Changes in length and moves a load.
Rationale: Isotonic contractions involve a change in muscle length while
the tension remains relatively constant, allowing the muscle to move a
load. Isometric contractions generate tension without changing length.
5. Which of the following is the primary neurotransmitter released at
the neuromuscular junction?
A) Norepinephrine
B) Dopamine
C) Acetylcholine
D) Serotonin
Correct Answer: C) Acetylcholine
Rationale: Acetylcholine (ACh) is the neurotransmitter released from
,the synaptic vesicles of the motor neuron into the synaptic cleft to bind
to receptors on the motor end plate.
6. The elaborate network of membranes in skeletal muscle cells that
functions in calcium storage is the:
A) Mitochondria
B) Sarcoplasmic reticulum
C) Myofibril
D) Sarcolemma
Correct Answer: B) Sarcoplasmic reticulum
Rationale: The sarcoplasmic reticulum is the specialized smooth
endoplasmic reticulum in muscle cells that sequesters and stores
calcium ions.
7. The first thing that stops a muscle contraction after a motor neuron
stops releasing acetylcholine is:
A) Calcium is reabsorbed by the sarcoplasmic reticulum.
B) Acetylcholinesterase destroys the acetylcholine at the membrane
receptors.
C) The sarcomere reaches its maximum shortening length.
D) ATP is depleted in the muscle fiber.
Correct Answer: B) Acetylcholinesterase destroys the acetylcholine at
the membrane receptors.
Rationale: Acetylcholinesterase is an enzyme located in the synaptic
cleft that rapidly breaks down acetylcholine, terminating the signal and
preventing continuous muscle stimulation.
8. The number of muscle fibers in a contracted state in an otherwise
relaxed muscle is known as its:
A) Muscle tone
, B) Threshold stimulus
C) Tetanus
D) Recruitment
Correct Answer: A) Muscle tone
Rationale: Muscle tone is the continuous, passive partial contraction of
muscles. It is maintained by the alternating activation of different motor
units in a relaxed muscle.
9. Which protein component of the thin filament covers the myosin-
binding sites when the muscle is relaxed?
A) Actin
B) Myosin
C) Tropomyosin
D) Troponin
Correct Answer: C) Tropomyosin
Rationale: In a relaxed muscle, tropomyosin physically blocks the active
binding sites on the actin molecules, preventing myosin from attaching.
10. What is the major function of the sarcoplasmic reticulum in muscle
contraction?
A) Regulates intracellular calcium levels
B) Synthesizes actin and myosin
C) Generates the action potential
D) Stores glycogen for ATP production
Correct Answer: A) Regulates intracellular calcium levels
Rationale: The primary function of the sarcoplasmic reticulum is to
regulate intracellular calcium levels by storing calcium when the muscle
is relaxed and releasing it upon stimulation.
STUDY GUIDE | 200 COMPREHENSIVE MCQS WITH
RATIONALES
1. Which of the following best describes the function of the
sarcoplasmic reticulum in skeletal muscle fibers?
A) It synthesizes ATP for muscle contraction.
B) It stores and releases calcium ions.
C) It produces acetylcholine for synaptic transmission.
D) It anchors the myofilaments to the sarcolemma.
Correct Answer: B) It stores and releases calcium ions.
Rationale: The sarcoplasmic reticulum is a modified endoplasmic
reticulum that surrounds the myofibrils and acts as a calcium reservoir.
Upon stimulation, it releases calcium into the sarcoplasm to trigger
contraction.
2. A motor neuron and all the muscle fibers it innervates are
collectively referred to as a:
A) Sarcomere
B) Motor unit
C) Myofibril
D) Neuromuscular junction
Correct Answer: B) Motor unit
Rationale: A motor unit is the functional unit of muscle contraction,
consisting of a single motor neuron and the specific group of muscle
fibers it stimulates.
,3. The role of calcium ions in skeletal muscle contraction is to:
A) Bind to myosin and energize the power stroke.
B) Break down acetylcholine in the synaptic cleft.
C) Bind to troponin, causing tropomyosin to shift and expose active
sites.
D) Depolarize the T-tubules.
Correct Answer: C) Bind to troponin, causing tropomyosin to shift and
expose active sites.
Rationale: Calcium binds to the troponin complex on the actin filament,
inducing a conformational change that moves tropomyosin away from
the myosin-binding sites, allowing cross-bridge formation.
4. In an isotonic contraction, the muscle:
A) Generates tension but does not change in length.
B) Changes in length and moves a load.
C) Is unable to relax after contraction.
D) Shortens with a constant velocity against no load.
Correct Answer: B) Changes in length and moves a load.
Rationale: Isotonic contractions involve a change in muscle length while
the tension remains relatively constant, allowing the muscle to move a
load. Isometric contractions generate tension without changing length.
5. Which of the following is the primary neurotransmitter released at
the neuromuscular junction?
A) Norepinephrine
B) Dopamine
C) Acetylcholine
D) Serotonin
Correct Answer: C) Acetylcholine
Rationale: Acetylcholine (ACh) is the neurotransmitter released from
,the synaptic vesicles of the motor neuron into the synaptic cleft to bind
to receptors on the motor end plate.
6. The elaborate network of membranes in skeletal muscle cells that
functions in calcium storage is the:
A) Mitochondria
B) Sarcoplasmic reticulum
C) Myofibril
D) Sarcolemma
Correct Answer: B) Sarcoplasmic reticulum
Rationale: The sarcoplasmic reticulum is the specialized smooth
endoplasmic reticulum in muscle cells that sequesters and stores
calcium ions.
7. The first thing that stops a muscle contraction after a motor neuron
stops releasing acetylcholine is:
A) Calcium is reabsorbed by the sarcoplasmic reticulum.
B) Acetylcholinesterase destroys the acetylcholine at the membrane
receptors.
C) The sarcomere reaches its maximum shortening length.
D) ATP is depleted in the muscle fiber.
Correct Answer: B) Acetylcholinesterase destroys the acetylcholine at
the membrane receptors.
Rationale: Acetylcholinesterase is an enzyme located in the synaptic
cleft that rapidly breaks down acetylcholine, terminating the signal and
preventing continuous muscle stimulation.
8. The number of muscle fibers in a contracted state in an otherwise
relaxed muscle is known as its:
A) Muscle tone
, B) Threshold stimulus
C) Tetanus
D) Recruitment
Correct Answer: A) Muscle tone
Rationale: Muscle tone is the continuous, passive partial contraction of
muscles. It is maintained by the alternating activation of different motor
units in a relaxed muscle.
9. Which protein component of the thin filament covers the myosin-
binding sites when the muscle is relaxed?
A) Actin
B) Myosin
C) Tropomyosin
D) Troponin
Correct Answer: C) Tropomyosin
Rationale: In a relaxed muscle, tropomyosin physically blocks the active
binding sites on the actin molecules, preventing myosin from attaching.
10. What is the major function of the sarcoplasmic reticulum in muscle
contraction?
A) Regulates intracellular calcium levels
B) Synthesizes actin and myosin
C) Generates the action potential
D) Stores glycogen for ATP production
Correct Answer: A) Regulates intracellular calcium levels
Rationale: The primary function of the sarcoplasmic reticulum is to
regulate intracellular calcium levels by storing calcium when the muscle
is relaxed and releasing it upon stimulation.
