BIOD 102 Biology II Module 3 Exam
Portage Learning (2026/2027)
Section 1: Nervous System Organization & Neurons
Q1: Which region of a neuron contains the highest density of voltage-gated sodium channels and
serves as the primary trigger zone for action potentials?
A. Dendrites
B. Axon terminals
C. Axon hillock [CORRECT]
D. Myelin sheath
Correct Answer: C
Rationale: The axon hillock (and the adjacent initial segment) has the highest concentration of
voltage-gated Na+ channels, making it the critical integration zone where graded potentials
summate to reach threshold and fire an action potential.
Q2: A patient receives a local anesthetic injection before undergoing a dental procedure. The
anesthetic blocks voltage-gated sodium channels. How does this prevent the transmission of pain
signals?
A. It prevents the repolarization phase of the action potential in the sensory nerves.
B. It stops the opening of sodium channels, preventing depolarization from reaching
threshold. [CORRECT]
C. It increases the release of inhibitory neurotransmitters in the dental pulp.
D. It hyperpolarizes the sensory neuron by opening extra potassium channels.
Correct Answer: B
Rationale: Local anesthetics physically block the voltage-gated sodium channels, preventing
Na+ influx. Without depolarization, the membrane cannot reach threshold, and no action
potential is generated or propagated along the sensory nerve.
.
,Q3: Which transport mechanism is directly responsible for establishing the steep concentration
gradients of sodium and potassium across the neuronal membrane?
A. Facilitated diffusion through leak channels
B. Secondary active transport coupled to calcium
C. The sodium-potassium pump (Na+/K+ ATPase) [CORRECT]
D. Voltage-gated ion channels
Correct Answer: C
Rationale: The Na+/K+ ATPase uses ATP to actively pump 3 Na+ out of the cell and 2 K+ into
the cell against their concentration gradients, establishing the resting gradients necessary for
action potentials.
Q4: A Portage Learning clinical scenario describes a patient with an autoimmune disease that
destroys ligand-gated chloride channels on motor neurons. When an inhibitory neurotransmitter
binds to the remaining receptors, what is the expected postsynaptic result?
A. An excitatory postsynaptic potential (EPSP) due to sodium influx
B. No change in membrane potential due to complete receptor loss
C. A diminished inhibitory postsynaptic potential (IPSP) leading to potential
hyperexcitability [CORRECT]
D. An action potential due to direct activation of voltage-gated calcium channels
Correct Answer: C
Rationale: Normally, inhibitory neurotransmitters open chloride channels causing Cl- influx
(hyperpolarization/IPSP). Loss of these channels reduces the IPSP, meaning the neuron is less
inhibited, which can lead to hyperexcitability or spasticity.
Q5: A neurophysiologist observes that a neuron fires an action potential only when three separate
presynaptic neurons fire at the exact same time, but not when they fire individually. Which
neural coding mechanism is being demonstrated?
A. Temporal summation
B. Spatial summation [CORRECT]
.
, C. Presynaptic inhibition
D. Convergence without summation
Correct Answer: B
Rationale: Spatial summation occurs when multiple presynaptic neurons (different locations in
space) fire simultaneously, allowing their individual EPSPs to add up and reach threshold at the
axon hillock.
Q6: A patient in the emergency department is diagnosed with severe hyperkalemia. Based on the
physiological principles of the Nernst equation, how will this electrolyte imbalance affect the
resting membrane potential of neurons?
A. The membrane potential will become more negative (hyperpolarized).
B. The membrane potential will become less negative (depolarized). [CORRECT]
C. The membrane potential will remain unchanged because the Na+/K+ pump will compensate
instantly.
D. The membrane potential will shift to exactly 0 mV due to sodium equilibrium.
Correct Answer: B
Rationale: Hyperkalemia increases the extracellular concentration of potassium, which
decreases the concentration gradient driving K+ out of the cell. This reduces the outward K+
current, making the resting membrane potential less negative (closer to threshold).
Q7: During the absolute refractory period of an action potential, a second stimulus—no matter
how strong—is unable to trigger a new action potential. What is the specific cellular basis for
this?
A. Voltage-gated potassium channels are open and preventing sodium entry.
B. Voltage-gated sodium channels are inactivated and cannot be opened. [CORRECT]
C. The sodium-potassium pump is temporarily reversed.
D. The membrane's capacitance is maximized, blocking ion flow.
Correct Answer: B
Rationale: The absolute refractory period is caused by the inactivation gates of voltage-gated
Na+ channels closing and remaining locked shut until the membrane repolarizes. They cannot be
opened by any stimulus during this time.
.
Portage Learning (2026/2027)
Section 1: Nervous System Organization & Neurons
Q1: Which region of a neuron contains the highest density of voltage-gated sodium channels and
serves as the primary trigger zone for action potentials?
A. Dendrites
B. Axon terminals
C. Axon hillock [CORRECT]
D. Myelin sheath
Correct Answer: C
Rationale: The axon hillock (and the adjacent initial segment) has the highest concentration of
voltage-gated Na+ channels, making it the critical integration zone where graded potentials
summate to reach threshold and fire an action potential.
Q2: A patient receives a local anesthetic injection before undergoing a dental procedure. The
anesthetic blocks voltage-gated sodium channels. How does this prevent the transmission of pain
signals?
A. It prevents the repolarization phase of the action potential in the sensory nerves.
B. It stops the opening of sodium channels, preventing depolarization from reaching
threshold. [CORRECT]
C. It increases the release of inhibitory neurotransmitters in the dental pulp.
D. It hyperpolarizes the sensory neuron by opening extra potassium channels.
Correct Answer: B
Rationale: Local anesthetics physically block the voltage-gated sodium channels, preventing
Na+ influx. Without depolarization, the membrane cannot reach threshold, and no action
potential is generated or propagated along the sensory nerve.
.
,Q3: Which transport mechanism is directly responsible for establishing the steep concentration
gradients of sodium and potassium across the neuronal membrane?
A. Facilitated diffusion through leak channels
B. Secondary active transport coupled to calcium
C. The sodium-potassium pump (Na+/K+ ATPase) [CORRECT]
D. Voltage-gated ion channels
Correct Answer: C
Rationale: The Na+/K+ ATPase uses ATP to actively pump 3 Na+ out of the cell and 2 K+ into
the cell against their concentration gradients, establishing the resting gradients necessary for
action potentials.
Q4: A Portage Learning clinical scenario describes a patient with an autoimmune disease that
destroys ligand-gated chloride channels on motor neurons. When an inhibitory neurotransmitter
binds to the remaining receptors, what is the expected postsynaptic result?
A. An excitatory postsynaptic potential (EPSP) due to sodium influx
B. No change in membrane potential due to complete receptor loss
C. A diminished inhibitory postsynaptic potential (IPSP) leading to potential
hyperexcitability [CORRECT]
D. An action potential due to direct activation of voltage-gated calcium channels
Correct Answer: C
Rationale: Normally, inhibitory neurotransmitters open chloride channels causing Cl- influx
(hyperpolarization/IPSP). Loss of these channels reduces the IPSP, meaning the neuron is less
inhibited, which can lead to hyperexcitability or spasticity.
Q5: A neurophysiologist observes that a neuron fires an action potential only when three separate
presynaptic neurons fire at the exact same time, but not when they fire individually. Which
neural coding mechanism is being demonstrated?
A. Temporal summation
B. Spatial summation [CORRECT]
.
, C. Presynaptic inhibition
D. Convergence without summation
Correct Answer: B
Rationale: Spatial summation occurs when multiple presynaptic neurons (different locations in
space) fire simultaneously, allowing their individual EPSPs to add up and reach threshold at the
axon hillock.
Q6: A patient in the emergency department is diagnosed with severe hyperkalemia. Based on the
physiological principles of the Nernst equation, how will this electrolyte imbalance affect the
resting membrane potential of neurons?
A. The membrane potential will become more negative (hyperpolarized).
B. The membrane potential will become less negative (depolarized). [CORRECT]
C. The membrane potential will remain unchanged because the Na+/K+ pump will compensate
instantly.
D. The membrane potential will shift to exactly 0 mV due to sodium equilibrium.
Correct Answer: B
Rationale: Hyperkalemia increases the extracellular concentration of potassium, which
decreases the concentration gradient driving K+ out of the cell. This reduces the outward K+
current, making the resting membrane potential less negative (closer to threshold).
Q7: During the absolute refractory period of an action potential, a second stimulus—no matter
how strong—is unable to trigger a new action potential. What is the specific cellular basis for
this?
A. Voltage-gated potassium channels are open and preventing sodium entry.
B. Voltage-gated sodium channels are inactivated and cannot be opened. [CORRECT]
C. The sodium-potassium pump is temporarily reversed.
D. The membrane's capacitance is maximized, blocking ion flow.
Correct Answer: B
Rationale: The absolute refractory period is caused by the inactivation gates of voltage-gated
Na+ channels closing and remaining locked shut until the membrane repolarizes. They cannot be
opened by any stimulus during this time.
.
