BIOL251 Human Anatomy & Physiology I w/Lab
2026 | Module 5 Exam Review | and Answers
Summary |LockDown Browser |Portage Learning
1. A researcher applies a voltage clamp to a neuron and observes that when the membrane
potential is stepped from -70 mV to -50 mV, an inward current is recorded that is blocked by
tetrodotoxin (TTX). Which of the following best explains the effect of TTX on the current-voltage
relationship?
A. TTX blocks the voltage-gated potassium channels, reducing outward current and prolonging the action
potential.
B. TTX blocks the voltage-gated sodium channels, eliminating the inward sodium current and preventing
depolarization.
C. TTX binds to the inactivation gate of sodium channels, causing them to remain open longer and increasing
inward current.
D. TTX enhances the activity of the sodium-potassium ATPase, hyperpolarizing the membrane and reducing
excitability.
Answer: B
Rationale: Tetrodotoxin specifically blocks voltage-gated sodium channels by binding to the pore. This
prevents the rapid influx of Na+ that normally occurs upon depolarization, thereby eliminating the
inward current observed in the voltage clamp. Options A, C, and D describe effects on potassium
channels, inactivation gate prolongation, or Na+/K+ pump activity, none of which are primary actions
of TTX.
2. In a study of synaptic transmission, a scientist applies a drug that irreversibly inhibits the
enzyme choline acetyltransferase. Which of the following immediate effects would be expected at a
cholinergic neuromuscular junction?
A. Increased acetylcholine release from the presynaptic terminal.
B. Enhanced degradation of acetylcholine in the synaptic cleft.
C. Reduced synthesis of acetylcholine, leading to decreased end-plate potential amplitude.
D. Blockade of acetylcholine receptors on the postsynaptic membrane.
Answer: C
Rationale: Choline acetyltransferase catalyzes the synthesis of acetylcholine from choline and
acetyl-CoA. Inhibition of this enzyme reduces acetylcholine production, leading to fewer
neurotransmitter molecules available for release. This results in smaller end-plate potentials. Option A
is incorrect because release is not directly affected; option B is incorrect because degradation is
mediated by acetylcholinesterase; option D is incorrect because the drug does not target receptors.
Page 1
,3. During a skeletal muscle contraction, a single twitch generates a force of 1 N. If the muscle is
stimulated repeatedly at a frequency of 50 Hz, the force increases to 4 N. Which of the following
mechanisms best explains this increase?
A. Recruitment of additional motor units due to higher stimulus intensity.
B. Summation of successive twitches because the muscle does not fully relax between stimuli.
C. Increased calcium release from the sarcoplasmic reticulum due to higher frequency.
D. Enhanced cross-bridge cycling rate due to increased ATP availability.
Answer: B
Rationale: At 50 Hz, the interval between stimuli is shorter than the duration of a single twitch, so the
muscle does not fully relax before the next stimulus arrives. This leads to temporal summation (or wave
summation) of forces, resulting in a greater total force. Option A refers to recruitment, which requires
increasing stimulus intensity, not frequency. Option C is plausible but secondary; the primary
mechanism is summation. Option D is incorrect because ATP availability is not directly affected by
stimulation frequency.
4. A patient presents with a lesion in the ventral horn of the spinal cord at the C5 level. Which of
the following clinical findings would most likely be observed?
A. Loss of pain and temperature sensation in the upper limb on the contralateral side.
B. Flaccid paralysis and muscle atrophy in the deltoid and biceps brachii.
C. Spastic paralysis and hyperreflexia in the lower limbs.
D. Loss of proprioception and vibration sense in the ipsilateral leg.
Answer: B
Rationale: The ventral horn contains lower motor neurons (LMNs) that innervate skeletal muscle. A
lesion here causes LMN signs: flaccid paralysis, atrophy, and areflexia in the myotomes supplied by the
damaged segment (C5 innervates deltoid and biceps). Option A describes a spinothalamic tract lesion
(sensory). Option C describes upper motor neuron signs (corticospinal tract). Option D describes dorsal
column lesion.
5. Which of the following best explains why the resting membrane potential of a typical neuron is
closer to the equilibrium potential for potassium (EK) than to that for sodium (ENa)?
A. The sodium-potassium pump actively transports three Na+ out for every two K+ in, creating a net negative
charge inside.
B. The membrane at rest is highly permeable to K+ but only slightly permeable to Na+, allowing K+ to diffuse
out and dominate the potential.
C. Large intracellular anions such as proteins and organic phosphates are impermeant and contribute a negative
fixed charge.
D. Voltage-gated sodium channels are inactivated at rest, preventing any sodium movement.
Answer: B
Rationale: The resting membrane potential is determined by the relative permeabilities of ions. At rest,
K+ channels are open, making the membrane highly permeable to K+, which diffuses out and brings the
potential near EK (~ -90 mV). Na+ permeability is very low, so ENa (~ +60 mV) has little influence.
Option A is true but contributes a small direct effect; option C is true but secondary; option D is false
because voltage-gated Na+ channels are closed, not inactivated, at rest.
Page 2
,6. A researcher measures the cardiac output of a subject at rest and during exercise. At rest, heart
rate is 70 bpm and stroke volume is 70 mL. During exercise, heart rate increases to 150 bpm and
stroke volume increases to 110 mL. What is the percent increase in cardiac output from rest to
exercise?
A. 136%
B. 237%
C. 57%
D. 171%
Answer: B
Rationale: Cardiac output (CO) = heart rate × stroke volume. At rest: CO = 70 × 70 = 4900 mL/min.
During exercise: CO = 150 × 110 = 16500 mL/min. Increase = (16500 - 4900)/4900 × 100% =
(11600/4900) × 100% 237%. Option A (136%) might come from adding percentages incorrectly; option
C (57%) is the percent increase in HR alone; option D (171%) is close but incorrect.
7. A patient with chronic obstructive pulmonary disease (COPD) has an arterial blood gas showing
pH 7.32, PaCO2 60 mmHg, and HCO3- 30 mEq/L. Which of the following best describes the
acid-base status?
A. Uncompensated respiratory acidosis
B. Partially compensated respiratory acidosis
C. Fully compensated respiratory acidosis
D. Metabolic alkalosis with respiratory compensation
Answer: B
Rationale: The low pH (7.32) indicates acidosis. The elevated PaCO2 (60 mmHg) indicates a respiratory
cause. The HCO3- is elevated (30 mEq/L), suggesting renal compensation (increased bicarbonate
reabsorption). However, the pH is still acidic, so compensation is partial. Full compensation would
return pH to normal (7.35-7.45). Option A would have normal HCO3-; option C would have normal pH;
option D is incorrect because the primary disturbance is respiratory.
8. Which of the following correctly describes the effect of a rightward shift in the
oxygen-hemoglobin dissociation curve?
A. Increased affinity of hemoglobin for oxygen, promoting oxygen loading in the lungs.
B. Decreased affinity of hemoglobin for oxygen, promoting oxygen unloading in the tissues.
C. Increased oxygen-carrying capacity of blood due to higher hemoglobin concentration.
D. Decreased oxygen delivery to tissues because hemoglobin holds oxygen more tightly.
Answer: B
Rationale: A rightward shift indicates decreased affinity of hemoglobin for O2, meaning O2 is more
readily released to tissues. This is caused by factors such as increased temperature, acidosis, and
increased 2,3-BPG. Option A describes a leftward shift; option C is unrelated to the curve shift; option
D is opposite of the actual effect.
9. A patient with renal failure has a glomerular filtration rate (GFR) of 20 mL/min. Which of the
following would be the most direct consequence for creatinine clearance?
Page 3
, A. Creatinine clearance will be greater than GFR due to tubular secretion.
B. Creatinine clearance will be approximately equal to GFR, indicating reduced renal function.
C. Creatinine clearance will be less than GFR due to tubular reabsorption.
D. Creatinine clearance will be zero because creatinine is not filtered in renal failure.
Answer: B
Rationale: Creatinine is freely filtered at the glomerulus and not reabsorbed; a small amount is secreted,
but clearance approximates GFR. In renal failure with low GFR, creatinine clearance is similarly
reduced. Option A is incorrect because secretion does not make clearance exceed GFR significantly;
option C is incorrect because reabsorption is negligible; option D is false because filtration still occurs.
10. A researcher administers a drug that blocks the action of antidiuretic hormone (ADH) on the
collecting ducts. Which of the following changes in urine composition would most likely occur?
A. Increased urine osmolarity and decreased urine volume.
B. Decreased urine osmolarity and increased urine volume.
C. Increased urine osmolarity and increased urine volume.
D. No change in urine osmolarity or volume because ADH primarily affects the loop of Henle.
Answer: B
Rationale: ADH increases water permeability of the collecting duct, allowing water reabsorption and
concentrating urine. Blocking ADH prevents water reabsorption, leading to dilute urine (low
osmolarity) and large volume (diuresis). Options A and C describe opposite effects; option D is
incorrect because ADH acts on collecting ducts, not the loop of Henle.
11. A researcher is investigating the role of the autonomic nervous system in maintaining blood
pressure during orthostatic stress. Which of the following neural pathways is primarily responsible
for the rapid compensatory increase in heart rate and vasoconstriction upon standing?
A. Activation of the baroreflex via increased firing of glossopharyngeal nerve afferents from carotid sinus
baroreceptors
B. Direct sympathetic preganglionic input from the nucleus ambiguus to the sinoatrial node
C. Inhibition of parasympathetic outflow from the dorsal motor nucleus of the vagus to the heart
D. Activation of sympathetic postganglionic fibers from the celiac ganglion to peripheral arterioles
Answer: A
Rationale: Upon standing, decreased blood pressure reduces baroreceptor stretch, leading to decreased
afferent firing from carotid sinus baroreceptors via the glossopharyngeal nerve. This reduces inhibition
of the medullary cardiovascular centers, increasing sympathetic outflow and decreasing
parasympathetic outflow, which increases heart rate and vasoconstriction. Option B is incorrect because
the nucleus ambiguus is primarily associated with parasympathetic input to the heart. Option C is
partially true but is not the primary afferent pathway; the reflex is initiated by decreased baroreceptor
afferent firing. Option D describes sympathetic efferents but not the initiating reflex pathway.
12. During a graded exercise test, a subject's oxygen consumption (VO2) plateaus despite
increasing workload. Which of the following physiological mechanisms most likely explains this
plateau?
A. Maximal activation of oxidative phosphorylation in skeletal muscle mitochondria
Page 4
2026 | Module 5 Exam Review | and Answers
Summary |LockDown Browser |Portage Learning
1. A researcher applies a voltage clamp to a neuron and observes that when the membrane
potential is stepped from -70 mV to -50 mV, an inward current is recorded that is blocked by
tetrodotoxin (TTX). Which of the following best explains the effect of TTX on the current-voltage
relationship?
A. TTX blocks the voltage-gated potassium channels, reducing outward current and prolonging the action
potential.
B. TTX blocks the voltage-gated sodium channels, eliminating the inward sodium current and preventing
depolarization.
C. TTX binds to the inactivation gate of sodium channels, causing them to remain open longer and increasing
inward current.
D. TTX enhances the activity of the sodium-potassium ATPase, hyperpolarizing the membrane and reducing
excitability.
Answer: B
Rationale: Tetrodotoxin specifically blocks voltage-gated sodium channels by binding to the pore. This
prevents the rapid influx of Na+ that normally occurs upon depolarization, thereby eliminating the
inward current observed in the voltage clamp. Options A, C, and D describe effects on potassium
channels, inactivation gate prolongation, or Na+/K+ pump activity, none of which are primary actions
of TTX.
2. In a study of synaptic transmission, a scientist applies a drug that irreversibly inhibits the
enzyme choline acetyltransferase. Which of the following immediate effects would be expected at a
cholinergic neuromuscular junction?
A. Increased acetylcholine release from the presynaptic terminal.
B. Enhanced degradation of acetylcholine in the synaptic cleft.
C. Reduced synthesis of acetylcholine, leading to decreased end-plate potential amplitude.
D. Blockade of acetylcholine receptors on the postsynaptic membrane.
Answer: C
Rationale: Choline acetyltransferase catalyzes the synthesis of acetylcholine from choline and
acetyl-CoA. Inhibition of this enzyme reduces acetylcholine production, leading to fewer
neurotransmitter molecules available for release. This results in smaller end-plate potentials. Option A
is incorrect because release is not directly affected; option B is incorrect because degradation is
mediated by acetylcholinesterase; option D is incorrect because the drug does not target receptors.
Page 1
,3. During a skeletal muscle contraction, a single twitch generates a force of 1 N. If the muscle is
stimulated repeatedly at a frequency of 50 Hz, the force increases to 4 N. Which of the following
mechanisms best explains this increase?
A. Recruitment of additional motor units due to higher stimulus intensity.
B. Summation of successive twitches because the muscle does not fully relax between stimuli.
C. Increased calcium release from the sarcoplasmic reticulum due to higher frequency.
D. Enhanced cross-bridge cycling rate due to increased ATP availability.
Answer: B
Rationale: At 50 Hz, the interval between stimuli is shorter than the duration of a single twitch, so the
muscle does not fully relax before the next stimulus arrives. This leads to temporal summation (or wave
summation) of forces, resulting in a greater total force. Option A refers to recruitment, which requires
increasing stimulus intensity, not frequency. Option C is plausible but secondary; the primary
mechanism is summation. Option D is incorrect because ATP availability is not directly affected by
stimulation frequency.
4. A patient presents with a lesion in the ventral horn of the spinal cord at the C5 level. Which of
the following clinical findings would most likely be observed?
A. Loss of pain and temperature sensation in the upper limb on the contralateral side.
B. Flaccid paralysis and muscle atrophy in the deltoid and biceps brachii.
C. Spastic paralysis and hyperreflexia in the lower limbs.
D. Loss of proprioception and vibration sense in the ipsilateral leg.
Answer: B
Rationale: The ventral horn contains lower motor neurons (LMNs) that innervate skeletal muscle. A
lesion here causes LMN signs: flaccid paralysis, atrophy, and areflexia in the myotomes supplied by the
damaged segment (C5 innervates deltoid and biceps). Option A describes a spinothalamic tract lesion
(sensory). Option C describes upper motor neuron signs (corticospinal tract). Option D describes dorsal
column lesion.
5. Which of the following best explains why the resting membrane potential of a typical neuron is
closer to the equilibrium potential for potassium (EK) than to that for sodium (ENa)?
A. The sodium-potassium pump actively transports three Na+ out for every two K+ in, creating a net negative
charge inside.
B. The membrane at rest is highly permeable to K+ but only slightly permeable to Na+, allowing K+ to diffuse
out and dominate the potential.
C. Large intracellular anions such as proteins and organic phosphates are impermeant and contribute a negative
fixed charge.
D. Voltage-gated sodium channels are inactivated at rest, preventing any sodium movement.
Answer: B
Rationale: The resting membrane potential is determined by the relative permeabilities of ions. At rest,
K+ channels are open, making the membrane highly permeable to K+, which diffuses out and brings the
potential near EK (~ -90 mV). Na+ permeability is very low, so ENa (~ +60 mV) has little influence.
Option A is true but contributes a small direct effect; option C is true but secondary; option D is false
because voltage-gated Na+ channels are closed, not inactivated, at rest.
Page 2
,6. A researcher measures the cardiac output of a subject at rest and during exercise. At rest, heart
rate is 70 bpm and stroke volume is 70 mL. During exercise, heart rate increases to 150 bpm and
stroke volume increases to 110 mL. What is the percent increase in cardiac output from rest to
exercise?
A. 136%
B. 237%
C. 57%
D. 171%
Answer: B
Rationale: Cardiac output (CO) = heart rate × stroke volume. At rest: CO = 70 × 70 = 4900 mL/min.
During exercise: CO = 150 × 110 = 16500 mL/min. Increase = (16500 - 4900)/4900 × 100% =
(11600/4900) × 100% 237%. Option A (136%) might come from adding percentages incorrectly; option
C (57%) is the percent increase in HR alone; option D (171%) is close but incorrect.
7. A patient with chronic obstructive pulmonary disease (COPD) has an arterial blood gas showing
pH 7.32, PaCO2 60 mmHg, and HCO3- 30 mEq/L. Which of the following best describes the
acid-base status?
A. Uncompensated respiratory acidosis
B. Partially compensated respiratory acidosis
C. Fully compensated respiratory acidosis
D. Metabolic alkalosis with respiratory compensation
Answer: B
Rationale: The low pH (7.32) indicates acidosis. The elevated PaCO2 (60 mmHg) indicates a respiratory
cause. The HCO3- is elevated (30 mEq/L), suggesting renal compensation (increased bicarbonate
reabsorption). However, the pH is still acidic, so compensation is partial. Full compensation would
return pH to normal (7.35-7.45). Option A would have normal HCO3-; option C would have normal pH;
option D is incorrect because the primary disturbance is respiratory.
8. Which of the following correctly describes the effect of a rightward shift in the
oxygen-hemoglobin dissociation curve?
A. Increased affinity of hemoglobin for oxygen, promoting oxygen loading in the lungs.
B. Decreased affinity of hemoglobin for oxygen, promoting oxygen unloading in the tissues.
C. Increased oxygen-carrying capacity of blood due to higher hemoglobin concentration.
D. Decreased oxygen delivery to tissues because hemoglobin holds oxygen more tightly.
Answer: B
Rationale: A rightward shift indicates decreased affinity of hemoglobin for O2, meaning O2 is more
readily released to tissues. This is caused by factors such as increased temperature, acidosis, and
increased 2,3-BPG. Option A describes a leftward shift; option C is unrelated to the curve shift; option
D is opposite of the actual effect.
9. A patient with renal failure has a glomerular filtration rate (GFR) of 20 mL/min. Which of the
following would be the most direct consequence for creatinine clearance?
Page 3
, A. Creatinine clearance will be greater than GFR due to tubular secretion.
B. Creatinine clearance will be approximately equal to GFR, indicating reduced renal function.
C. Creatinine clearance will be less than GFR due to tubular reabsorption.
D. Creatinine clearance will be zero because creatinine is not filtered in renal failure.
Answer: B
Rationale: Creatinine is freely filtered at the glomerulus and not reabsorbed; a small amount is secreted,
but clearance approximates GFR. In renal failure with low GFR, creatinine clearance is similarly
reduced. Option A is incorrect because secretion does not make clearance exceed GFR significantly;
option C is incorrect because reabsorption is negligible; option D is false because filtration still occurs.
10. A researcher administers a drug that blocks the action of antidiuretic hormone (ADH) on the
collecting ducts. Which of the following changes in urine composition would most likely occur?
A. Increased urine osmolarity and decreased urine volume.
B. Decreased urine osmolarity and increased urine volume.
C. Increased urine osmolarity and increased urine volume.
D. No change in urine osmolarity or volume because ADH primarily affects the loop of Henle.
Answer: B
Rationale: ADH increases water permeability of the collecting duct, allowing water reabsorption and
concentrating urine. Blocking ADH prevents water reabsorption, leading to dilute urine (low
osmolarity) and large volume (diuresis). Options A and C describe opposite effects; option D is
incorrect because ADH acts on collecting ducts, not the loop of Henle.
11. A researcher is investigating the role of the autonomic nervous system in maintaining blood
pressure during orthostatic stress. Which of the following neural pathways is primarily responsible
for the rapid compensatory increase in heart rate and vasoconstriction upon standing?
A. Activation of the baroreflex via increased firing of glossopharyngeal nerve afferents from carotid sinus
baroreceptors
B. Direct sympathetic preganglionic input from the nucleus ambiguus to the sinoatrial node
C. Inhibition of parasympathetic outflow from the dorsal motor nucleus of the vagus to the heart
D. Activation of sympathetic postganglionic fibers from the celiac ganglion to peripheral arterioles
Answer: A
Rationale: Upon standing, decreased blood pressure reduces baroreceptor stretch, leading to decreased
afferent firing from carotid sinus baroreceptors via the glossopharyngeal nerve. This reduces inhibition
of the medullary cardiovascular centers, increasing sympathetic outflow and decreasing
parasympathetic outflow, which increases heart rate and vasoconstriction. Option B is incorrect because
the nucleus ambiguus is primarily associated with parasympathetic input to the heart. Option C is
partially true but is not the primary afferent pathway; the reflex is initiated by decreased baroreceptor
afferent firing. Option D describes sympathetic efferents but not the initiating reflex pathway.
12. During a graded exercise test, a subject's oxygen consumption (VO2) plateaus despite
increasing workload. Which of the following physiological mechanisms most likely explains this
plateau?
A. Maximal activation of oxidative phosphorylation in skeletal muscle mitochondria
Page 4
