,SCI 221 Exam 4 | Human Physiology (2026) Q&A |
Nightingale College
1. Which mechanism primarily maintains the resting membrane potential of a
neuron?
A) Sodium-potassium pump and potassium leak channels
B) Voltage-gated sodium channels
C) Calcium pumps
D) Chloride transporters
Correct Answer: Sodium-potassium pump and potassium leak channels
Rationale: The resting membrane potential is established by the electrogenic
sodium-potassium pump, which exports three Na⁺ ions for every two K⁺ ions
imported, and by the high permeability of potassium leak channels that allow K⁺
to exit the cell down its concentration gradient. Voltage-gated sodium channels are
closed at rest, calcium pumps regulate intracellular calcium, and chloride
transporters play a minor role.
2. During the depolarization phase of an action potential, which ion movement
occurs?
A) Potassium efflux
B) Sodium influx
C) Chloride influx
D) Calcium efflux
Correct Answer: Sodium influx
,Rationale: Depolarization is triggered when voltage-gated sodium channels
open, allowing Na⁺ to rush into the cell along its electrochemical gradient. This
influx of positive charge shifts the membrane potential from approximately −70
mV toward a positive value. Potassium efflux drives repolarization, chloride influx
causes hyperpolarization, and calcium efflux is not a primary event in the action
potential upstroke.
3. What is the primary function of the myelin sheath?
A) To generate action potentials
B) To release neurotransmitters
C) To insulate the axon and increase conduction velocity
D) To receive incoming signals
Correct Answer: To insulate the axon and increase conduction velocity
Rationale: Myelin is a lipid-rich insulating layer produced by oligodendrocytes
in the central nervous system and Schwann cells in the peripheral nervous system.
It prevents ion leakage across the axonal membrane and forces action potentials to
jump between nodes of Ranvier (saltatory conduction), greatly increasing
conduction speed. Action potentials are generated at the axon hillock,
neurotransmitters are released at axon terminals, and signals are received by
dendrites.
4. Which neurotransmitter is released at the neuromuscular junction 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 and triggers calcium release from the
sarcoplasmic reticulum. Norepinephrine is primarily sympathetic, dopamine is a
central neurotransmitter, and GABA is inhibitory.
5. 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.
6. What is the primary role of the sarcoplasmic reticulum in skeletal muscle
fibers?
A) Synthesis of ATP
B) Storage and release of calcium ions
Nightingale College
1. Which mechanism primarily maintains the resting membrane potential of a
neuron?
A) Sodium-potassium pump and potassium leak channels
B) Voltage-gated sodium channels
C) Calcium pumps
D) Chloride transporters
Correct Answer: Sodium-potassium pump and potassium leak channels
Rationale: The resting membrane potential is established by the electrogenic
sodium-potassium pump, which exports three Na⁺ ions for every two K⁺ ions
imported, and by the high permeability of potassium leak channels that allow K⁺
to exit the cell down its concentration gradient. Voltage-gated sodium channels are
closed at rest, calcium pumps regulate intracellular calcium, and chloride
transporters play a minor role.
2. During the depolarization phase of an action potential, which ion movement
occurs?
A) Potassium efflux
B) Sodium influx
C) Chloride influx
D) Calcium efflux
Correct Answer: Sodium influx
,Rationale: Depolarization is triggered when voltage-gated sodium channels
open, allowing Na⁺ to rush into the cell along its electrochemical gradient. This
influx of positive charge shifts the membrane potential from approximately −70
mV toward a positive value. Potassium efflux drives repolarization, chloride influx
causes hyperpolarization, and calcium efflux is not a primary event in the action
potential upstroke.
3. What is the primary function of the myelin sheath?
A) To generate action potentials
B) To release neurotransmitters
C) To insulate the axon and increase conduction velocity
D) To receive incoming signals
Correct Answer: To insulate the axon and increase conduction velocity
Rationale: Myelin is a lipid-rich insulating layer produced by oligodendrocytes
in the central nervous system and Schwann cells in the peripheral nervous system.
It prevents ion leakage across the axonal membrane and forces action potentials to
jump between nodes of Ranvier (saltatory conduction), greatly increasing
conduction speed. Action potentials are generated at the axon hillock,
neurotransmitters are released at axon terminals, and signals are received by
dendrites.
4. Which neurotransmitter is released at the neuromuscular junction 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 and triggers calcium release from the
sarcoplasmic reticulum. Norepinephrine is primarily sympathetic, dopamine is a
central neurotransmitter, and GABA is inhibitory.
5. 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.
6. What is the primary role of the sarcoplasmic reticulum in skeletal muscle
fibers?
A) Synthesis of ATP
B) Storage and release of calcium ions
