,BIOL 251 Module 5 | Human Anatomy & Physiology I w/Lab
Exam Q&A | Portage Learning
1. A patient presents with extreme muscle weakness and flaccid paralysis. Laboratory
results reveal severe hypokalemia. How does this state affect the resting membrane
potential of somatic motor neurons?
A) It causes hyperpolarization by increasing the efflux of potassium, moving the
resting membrane potential further from threshold
B) It causes depolarization by driving sodium influx, keeping the cell above threshold
continuously
C) It inactivates voltage-gated sodium channels completely, preventing any electrical
conduction
D) It increases the threshold potential required to trigger an action potential
Correct Answer: It causes hyperpolarization by increasing the efflux of potassium,
moving the resting membrane potential further from threshold
Rationale: Hypokalemia increases the concentration gradient for potassium across
the plasma membrane, causing more potassium to diffuse out of the neuron. This
loss of positive ions hyperpolarizes the resting membrane potential, moving it further
from threshold and reducing excitability.
2. During a laboratory experiment, a researcher applies a neurotoxin to an isolated
nerve axon that specifically blocks voltage-gated potassium channels. What specific
phase of the neuronal action potential will be primarily impaired?
A) Depolarization phase
B) Absolute refractory period initiation
C) Repolarization phase
D) Resting membrane potential setup
,Correct Answer: Repolarization phase
Rationale: Voltage-gated potassium channels open in response to threshold
depolarization to allow potassium efflux, which returns the membrane potential to its
negative resting state. Blocking these channels prevents repolarization, causing
prolonged depolarization.
3. An anatomical slice reveals a cross-section of the human spinal cord. Which
structural feature contains the cell bodies of somatic motor neurons whose axons
innervate skeletal muscles?
A) Posterior (dorsal) horn
B) Anterior (ventral) horn
C) Lateral horn
D) Dorsal root ganglion
Correct Answer: Anterior (ventral) horn
Rationale: The anterior gray horn of the spinal cord contains the cell bodies of
somatic motor neurons. The posterior horn processes sensory information, and the
lateral horn houses autonomic motor cell bodies.
4. A patient involved in a motor vehicle accident experiences loss of pain and
temperature sensations in the left leg, while tactile discrimination remains intact.
Which spinal tract is most likely damaged?
A) Left lateral corticospinal tract
B) Right spinothalamic tract
C) Right posterior column
D) Left spinothalamic tract
, Correct Answer: Left spinothalamic tract
Rationale: Pain and temperature fibers enter the spinal cord, cross over at or near
the level of entry, and ascend via the contralateral spinothalamic tract. Sensory loss in
the left leg corresponds to injury of the ascending spinothalamic pathway from that
side.
5. A histology slide shows neuroglial cells in the central nervous system with small,
elongated processes wrapping tightly around multiple axons to form myelin sheaths.
Which cell type is being observed?
A) Schwann cell
B) Oligodendrocyte
C) Astrocyte
D) Microglia
Correct Answer: Oligodendrocyte
Rationale: Oligodendrocytes are the myelin-producing glial cells within the CNS,
capable of myelinating segments of multiple adjacent axons. Schwann cells perform
a similar function but exclusively within the PNS.
6. Which of the following is NOT a function of the nervous system?
A) Receiving sensory input
B) Integrating information
C) Producing red blood cells
D) Responding to stimuli with motor output
Exam Q&A | Portage Learning
1. A patient presents with extreme muscle weakness and flaccid paralysis. Laboratory
results reveal severe hypokalemia. How does this state affect the resting membrane
potential of somatic motor neurons?
A) It causes hyperpolarization by increasing the efflux of potassium, moving the
resting membrane potential further from threshold
B) It causes depolarization by driving sodium influx, keeping the cell above threshold
continuously
C) It inactivates voltage-gated sodium channels completely, preventing any electrical
conduction
D) It increases the threshold potential required to trigger an action potential
Correct Answer: It causes hyperpolarization by increasing the efflux of potassium,
moving the resting membrane potential further from threshold
Rationale: Hypokalemia increases the concentration gradient for potassium across
the plasma membrane, causing more potassium to diffuse out of the neuron. This
loss of positive ions hyperpolarizes the resting membrane potential, moving it further
from threshold and reducing excitability.
2. During a laboratory experiment, a researcher applies a neurotoxin to an isolated
nerve axon that specifically blocks voltage-gated potassium channels. What specific
phase of the neuronal action potential will be primarily impaired?
A) Depolarization phase
B) Absolute refractory period initiation
C) Repolarization phase
D) Resting membrane potential setup
,Correct Answer: Repolarization phase
Rationale: Voltage-gated potassium channels open in response to threshold
depolarization to allow potassium efflux, which returns the membrane potential to its
negative resting state. Blocking these channels prevents repolarization, causing
prolonged depolarization.
3. An anatomical slice reveals a cross-section of the human spinal cord. Which
structural feature contains the cell bodies of somatic motor neurons whose axons
innervate skeletal muscles?
A) Posterior (dorsal) horn
B) Anterior (ventral) horn
C) Lateral horn
D) Dorsal root ganglion
Correct Answer: Anterior (ventral) horn
Rationale: The anterior gray horn of the spinal cord contains the cell bodies of
somatic motor neurons. The posterior horn processes sensory information, and the
lateral horn houses autonomic motor cell bodies.
4. A patient involved in a motor vehicle accident experiences loss of pain and
temperature sensations in the left leg, while tactile discrimination remains intact.
Which spinal tract is most likely damaged?
A) Left lateral corticospinal tract
B) Right spinothalamic tract
C) Right posterior column
D) Left spinothalamic tract
, Correct Answer: Left spinothalamic tract
Rationale: Pain and temperature fibers enter the spinal cord, cross over at or near
the level of entry, and ascend via the contralateral spinothalamic tract. Sensory loss in
the left leg corresponds to injury of the ascending spinothalamic pathway from that
side.
5. A histology slide shows neuroglial cells in the central nervous system with small,
elongated processes wrapping tightly around multiple axons to form myelin sheaths.
Which cell type is being observed?
A) Schwann cell
B) Oligodendrocyte
C) Astrocyte
D) Microglia
Correct Answer: Oligodendrocyte
Rationale: Oligodendrocytes are the myelin-producing glial cells within the CNS,
capable of myelinating segments of multiple adjacent axons. Schwann cells perform
a similar function but exclusively within the PNS.
6. Which of the following is NOT a function of the nervous system?
A) Receiving sensory input
B) Integrating information
C) Producing red blood cells
D) Responding to stimuli with motor output
