,SCI 221 Exam 2 | Human Physiology (2026) Q&A |
Nightingale College
1. During the depolarization phase of a neuronal action potential, which event
occurs first?
A) Voltage-gated potassium channels open and K⁺ exits the cell.
B) Voltage-gated sodium channels open and Na⁺ enters the cell.
C) The sodium-potassium pump actively extrudes three Na⁺ ions.
D) Calcium ions diffuse into the axon terminal.
Correct Answer: Voltage-gated sodium channels open and Na⁺ enters the cell.
Rationale: Depolarization is initiated when a threshold stimulus opens voltage-
gated sodium channels, allowing a rapid influx of Na⁺ that makes the membrane
potential more positive. Potassium efflux drives repolarization, the sodium-
potassium pump restores ion gradients over a longer timeframe, and calcium entry
occurs at the axon terminal to trigger neurotransmitter release.
2. Which neuroglial cell is responsible for myelinating axons within the central
nervous system?
A) Schwann cell
B) Astrocyte
C) Oligodendrocyte
D) Microglial cell
Correct Answer: Oligodendrocyte
,Rationale: Oligodendrocytes extend processes that wrap multiple axons in the
brain and spinal cord with myelin, enabling saltatory conduction. Schwann cells
perform the same function in the peripheral nervous system, astrocytes regulate
the extracellular environment, and microglia act as resident immune cells.
3. At the neuromuscular junction, which neurotransmitter is released to stimulate
skeletal muscle contraction?
A) Norepinephrine
B) Acetylcholine
C) Dopamine
D) Gamma-aminobutyric acid
Correct Answer: Acetylcholine
Rationale: Motor neurons release acetylcholine, which binds to nicotinic
receptors on the motor end plate, generating an end-plate potential that
propagates along the sarcolemma. Norepinephrine is primarily sympathetic,
dopamine is a central neurotransmitter, and GABA is inhibitory.
4. In the sliding filament model, which protein blocks myosin-binding sites on
actin in a relaxed muscle?
A) Troponin
B) Myosin
C) Tropomyosin
D) Titin
Correct Answer: Tropomyosin
, Rationale: Tropomyosin wraps around actin and physically covers the myosin-
binding sites when intracellular calcium is low. Calcium binding to troponin shifts
tropomyosin aside to permit cross-bridge formation. Myosin is the motor protein,
and titin provides elastic recoil.
5. What is the primary role of the sarcoplasmic reticulum in skeletal muscle
fibers?
A) Synthesis of ATP
B) Storage and release of calcium ions
C) Conduction of action potentials to the interior of the cell
D) Production of contractile proteins
Correct Answer: Storage and release of calcium ions
Rationale: The sarcoplasmic reticulum is a modified endoplasmic reticulum that
sequesters calcium. An action potential traveling down the T-tubules triggers
calcium release from the sarcoplasmic reticulum into the sarcoplasm, initiating
contraction; calcium is then actively pumped back to allow relaxation.
6. Which part of the brain coordinates complex voluntary movements and
maintains balance?
A) Cerebellum
B) Hypothalamus
C) Cerebrum
D) Medulla oblongata
Correct Answer: Cerebellum
Nightingale College
1. During the depolarization phase of a neuronal action potential, which event
occurs first?
A) Voltage-gated potassium channels open and K⁺ exits the cell.
B) Voltage-gated sodium channels open and Na⁺ enters the cell.
C) The sodium-potassium pump actively extrudes three Na⁺ ions.
D) Calcium ions diffuse into the axon terminal.
Correct Answer: Voltage-gated sodium channels open and Na⁺ enters the cell.
Rationale: Depolarization is initiated when a threshold stimulus opens voltage-
gated sodium channels, allowing a rapid influx of Na⁺ that makes the membrane
potential more positive. Potassium efflux drives repolarization, the sodium-
potassium pump restores ion gradients over a longer timeframe, and calcium entry
occurs at the axon terminal to trigger neurotransmitter release.
2. Which neuroglial cell is responsible for myelinating axons within the central
nervous system?
A) Schwann cell
B) Astrocyte
C) Oligodendrocyte
D) Microglial cell
Correct Answer: Oligodendrocyte
,Rationale: Oligodendrocytes extend processes that wrap multiple axons in the
brain and spinal cord with myelin, enabling saltatory conduction. Schwann cells
perform the same function in the peripheral nervous system, astrocytes regulate
the extracellular environment, and microglia act as resident immune cells.
3. At the neuromuscular junction, which neurotransmitter is released to stimulate
skeletal muscle contraction?
A) Norepinephrine
B) Acetylcholine
C) Dopamine
D) Gamma-aminobutyric acid
Correct Answer: Acetylcholine
Rationale: Motor neurons release acetylcholine, which binds to nicotinic
receptors on the motor end plate, generating an end-plate potential that
propagates along the sarcolemma. Norepinephrine is primarily sympathetic,
dopamine is a central neurotransmitter, and GABA is inhibitory.
4. In the sliding filament model, which protein blocks myosin-binding sites on
actin in a relaxed muscle?
A) Troponin
B) Myosin
C) Tropomyosin
D) Titin
Correct Answer: Tropomyosin
, Rationale: Tropomyosin wraps around actin and physically covers the myosin-
binding sites when intracellular calcium is low. Calcium binding to troponin shifts
tropomyosin aside to permit cross-bridge formation. Myosin is the motor protein,
and titin provides elastic recoil.
5. What is the primary role of the sarcoplasmic reticulum in skeletal muscle
fibers?
A) Synthesis of ATP
B) Storage and release of calcium ions
C) Conduction of action potentials to the interior of the cell
D) Production of contractile proteins
Correct Answer: Storage and release of calcium ions
Rationale: The sarcoplasmic reticulum is a modified endoplasmic reticulum that
sequesters calcium. An action potential traveling down the T-tubules triggers
calcium release from the sarcoplasmic reticulum into the sarcoplasm, initiating
contraction; calcium is then actively pumped back to allow relaxation.
6. Which part of the brain coordinates complex voluntary movements and
maintains balance?
A) Cerebellum
B) Hypothalamus
C) Cerebrum
D) Medulla oblongata
Correct Answer: Cerebellum
