Endocrine, Cardiovascular, Immunology MCAT Biology Diagnostic Exam 3B

Question 1

Question 1
Cardiac autorhythmic cells (and to some extent cardiac muscle cells) have the ability to trigger their own action potential independent of any neural input or other stimulation. Which of the following is responsible for this autorhythmic property?

A. K+ leak channels
B. Na+ leak channels
C. Na+/K+ ATPase
D. Slow voltage-gated Na+ channels

Answer 1

B. Cardiac autorhythmic cells contain Na+ leak channels that allow Na+ to enter the cell according to its gradient. As Na+ enters, the cell potential rises (depolarizes) until it reaches the threshold for slow voltage-gated Na+ channels; this triggers the action potential itself (choice D is wrong). K+ leak channels allow K+ to leave the cell, making it more negative (hyperpolarizing it) and less likely to fire an action potential (choice A is wrong). The Na+/K+ ATPase establishes the Na+ and K+ gradients necessary for heart function, but do not themselves trigger action potentials (choice C is wrong).

Concepts tested
Cardiovascular System: Cardiac Action Potential/Conduction System

Question 2

A bipolar neuron could be composed of which of the following?

A. A neuron with a soma and a single dendrite
B. A neuron with a soma and a single axon
C. A neuron with a soma, a single dendrite, and a single axon
D. A neuron with a soma, multiple dendrites, and a single axon

Answer 2

C. Bipolar neurons possess two extensions from the cell body (or soma); one dendrite and one axon (choice C is correct). Unipolar neurons possess only a single extension from the cell body (choices A and B are wrong), while multipolar neurons have multiple dendrites (or a dendritic arbor) extending from the cell body, but only a single axon (choice D is wrong).

Concepts tested
Nervous System: Neurons and Action Potentials

Question 3

Auditory hair cells would be classified as:

A. thermoreceptors.
B. nociceptors.
C. chemoreceptors.
D. mechanoreceptors

Answer 3

D. Auditory hair cells respond to vibrations of the basilar membrane and bend when vibrations occur. Thus they are classified as mechanoreceptors (choice D is correct). Thermoreceptors respond to temperature (choice A is wrong), nociceptors respond to pain (choice B is wrong), and chemoreceptors respond to chemicals (choices A, B, and C are wrong).

Concepts tested
Nervous System: Sensory Systems

Question 4

Question 4
A researcher records the membrane potential changes in a neuron in cell culture. Following excitation of a single nearby neuron, the membrane potential increases by 20 mV. If an additional nearby neuron is stimulated at the same time, an increase in membrane voltage of 32 mV is observed. Which of the following best explains this observation?

A. Long-term depression
B. Neural adaptation
C. Temporal summation
D. Spatial summation

Answer 4

D. The experiment describes two neurons synapsing with a third neuron from which membrane potential is recorded. When one neuron is excited, a depolarization is recorded, and when the second neuron is excited at the same time, a larger depolarization is recorded. This additive effect (two neurons synapsing on a single neuron and generating a larger response) is known as spatial summation (choice D is correct). Temporal summation involves the additive response due to repeated stimulation of a single neuron (choice C is wrong). Long-term depression is a decrease in neural excitability (choice A is wrong) and neural adaptation is a change in response over time (usually a decrease in firing) with a constant stimulus (choice B is wrong).

Concepts tested
Nervous System: Neurons and Action Potentials

Question 5

Question 5
T cells are involved in cell-mediated immunity, interacting directly with our own cells to help protect us from disease. MHC proteins assist T cells in their function. Which of the following statements is true about T cells?

A. Killer T cells bind to antigen displayed on MHC II and directly destroy abnormal cells.
B. Helper T cells bind to antigen displayed on MHC I and secrete chemicals to help killer T cells proliferate.
C. Killer T cells bind to antigen displayed on MHC I and directly destroy abnormal cells.
D. Helper T cells bind to antigen displayed on MHC II and assist killer T cells by directly destroying abnormal cells.

Answer 5

C. MHC proteins display intracellular antigen on the cell surface and interact with T cells. Killer T cells bind to antigen displayed on MHC I (choice A is wrong) and helper T cells bind to antigen displayed on MHC II (choice B is wrong). Killer T cells destroy abnormal cells directly, while helper T cells secrete chemicals (cytokines) to stimulate the proliferation of killer T cells and B cells (choice C is correct and choice D is wrong).

Concepts tested
Immunology: B-Cells, T-Cells, Immunity

Question 6

Which of the following statements is true about oxytocin?

A. It is released from the posterior pituitary and one of its functions is to induce uterine contractions during labor.
B. It is released from the anterior pituitary and one of its functions is to induce uterine contractions during labor.
C. It is released from the posterior pituitary and one of its functions is to induce milk production and ejection during lactation.
D. It is released from the anterior pituitary and one of its functions is to induce milk production and ejection during lactation.

Answer 6

A. Oxytocin is released from the posterior pituitary (choices B and D are wrong), and its functions include inducing uterine contractions during labor (choice A is correct) and milk ejection during lactation. The actual production of milk is triggered by prolactin (choice C is wrong).

Concepts tested
Endocrine System: Hormones and Hormone Functions

Question 7

Antibodies are made of two heavy chains and two light chains. There are five classes of antibody that differ in their tail (non-antigen binding) region. Which of the following statements about antibodies is true?

A. The antigen-binding region is made only of light chains and the tail region is made only of heavy chains.
B. The antigen-binding region is made of both heavy and light chains, but the tail region is made only of heavy chains.
C. The antigen-binding region is made of only light chains, but the tail region is made of both heavy and light chains.
D. The antigen-binding region is made only of heavy chains and the tail region is made only of light chains.

Answer 7

B. The tail region of the antibody molecule is known as the FC region. It determines the class of antibody (IgG, IgA, IgM, IgE, or IgD) and is made only of heavy chains (choices C and D are wrong). The antigen-binding region is the variable portion of the antibody molecule and is made of both heavy and light chains (choice A is wrong and choice B is correct).

Concepts tested
Immunology: Antibodies

Question 8

A neuroscientist develops a chemical that increases the permeability of neuron membranes to potassium. After administering this drug, she attempts to elicit action potentials, but notes the rates of firing have changed dramatically. Which of the following best explains this observation?

A. The resting membrane potential shifted in a more positive direction.
B. The resting membrane potential shifted in a more negative direction.
C. The Na+/K+ ATPase is unable to maintain concentration gradients.
D. The rapid depolarization phase of the action potential was most significantly impacted.

Answer 8

B. By increasing the permeability of the neuron membrane to potassium, the researcher shifted the resting membrane potential in a more negative direction. This pushes the neuron further from threshold and it would require more stimulation in order to generate action potentials, resulting in a probable decrease in firing rate (choice B is correct and choice A is wrong). The Na+/K+ ATPase is an active transporter, using ATP to move Na+ ions out of the cell and K+ ions into the cell; its action would be unaffected by an increase in membrane potassium permeability (choice C is wrong). The rapid depolarization seen in an action potential is due to the opening of voltage-gated sodium channels. Assuming the cell could get to threshold, the opening of these channels should not be affected by an increase in potassium permeability (choice D is wrong).

Concepts tested
Nervous System: Neurons and Action Potentials

Question 9

The function of the bicuspid AV (mitral) valve is to prevent reflux from the:

A. pulmonary artery to the right ventricle.
B. right ventricle to the right atrium.
C. aorta to the left ventricle.
D. left ventricle to the left atrium.

Answer 9

D. The bicuspid AV valve separates the left atrium and ventricle and closes during systole to prevent reflux into the left atrium (choice D is correct). The tricuspid AV valve does the same thing on the right side of the heart (choice B is wrong). The pulmonary semilunar valve closes during diastole to prevent reflux from the pulmonary artery into the right ventricle (choice A is wrong) and the aortic semilunar valve closes at the same time to prevent reflux from the aorta into the left ventricle (choice C is wrong).

Concepts tested
Cardiovascular System: Heart Anatomy

Question 10

Seizures, which result from foci of abnormal excessive brain activity, can spread to surrounding areas of the brain. In select patients, this activity can spread beyond the originating hemisphere. Severing which of the following structures would aid in limiting the spread of excessive activity?

A. Brainstem
B. Cerebral cortex
C. Thalamus
D. Corpus callosum

Answer 10

D. The corpus callosum connects the left and right hemispheres of the brain and in select patients, severing this connection can decrease the severity of recurrent seizures (choice D is correct). Severing the brain stem, which is critical for numerous basic vital functions (e.g. breathing), would kill the patient (choice A is wrong). The cerebral cortex, which is the outer layer of the brain, is critical for higher level thought and self-awareness (choice B is wrong), and the thalamus is involved in relaying sensory and motor information to and from the brain (choice C is wrong).

Concepts tested
Nervous System: Central Nervous System

Question 11

Action potentials can involve voltage-gated calcium channels. Intracellular Ca2+ concentration is typically several fold below extracellular Ca2+ concentration. In which of the following processes might calcium play a role?

A. Depolarization
B. Repolarization
C. Polarization
D. Hyperpolarization

Answer 11

A. From the stem of the question, voltage-gated calcium channels are similar to voltage-gated sodium channels. When membrane potential reaches the threshold for a voltage-gated channel, the channel opens. In this case, calcium would flow into the cell (down its concentration gradient) causing membrane potential to move in the positive direction, i.e., depolarization (choice A is correct). Repolarization is a return to rest potential (choice B is wrong) and hyperpolarization is a movement from rest potential to more negative values (choice D is wrong). Polarization simply describes the cell at rest potential, i.e., negative inside with respect to the outside (choice C is wrong).

Concepts tested
Nervous System: Neurons and Action Potentials

Question 12

Which of the following represents the correct order of structures through which a red blood cell, starting in the lungs, would travel?

A. Pulmonary veins Right arrow left atrium Right arrow bicuspid valve Right arrow left ventricle Right arrow aorta
B. Pulmonary veins Right arrow left atrium Right arrow tricuspid valve Right arrow left ventricle Right arrow aorta
C. Pulmonary arteries Right arrow left atrium Right arrow bicuspid valve Right arrow left ventricle Right arrow aorta
D. Pulmonary arteries Right arrow left atrium Right arrow tricuspid valve Right arrow left ventricle Right arrow aorta

Answer 12

A. Pulmonary veins carry the blood from the lungs back to the heart (choices C and D can be eliminated). The bicuspid valve is found on the left side of the heart, and the tricuspid valve is on the right (choice B can be eliminated and choice A is correct).

Concepts tested
Cardiovascular System: Heart Anatomy

Question 13

Auditory transduction occurs inside the cochlea. Pitch and loudness are determined by the location of maximal vibration and amplitude of vibration of the basilar membrane, respectively. Which of the following is a true statement?

A. Loud, high-pitched sounds would produce large amplitude vibrations near the flexible apex of the basilar membrane.
B. Loud, low-pitched sounds would produce large amplitude vibrations near the flexible apex of the basilar membrane.
C. Loud, high-pitched sounds would produce small amplitude vibrations near the stiffer region of the basilar membrane near the oval window.
D. Loud, low-pitched sounds would produce small amplitude vibrations near the stiffer region of the basilar membrane near the oval window.

Answer 13

B. Loud sounds produce large amplitude vibrations (choices C and D can be eliminated). High pitched (high frequency) sounds vibrate the stiffer region of the basilar membrane near the oval window, while low pitched (low frequency) sounds vibrate the more flexible apex of the basilar membrane (choice B is correct and choice A is wrong).

Concepts tested
Nervous System: Sensory Systems

Question 14

Lymphatic vessels are most like:

A. arteries, because they are very elastic and have muscular walls.
B. arteries, because they are large and carry fluid at low pressure.
C. veins, because they carry fluid toward the heart and are at low pressure.
D. veins, because the fluid they carry is low in oxygen and at low pressure.

Answer 14

C. Lymphatic vessels are more like veins than arteries. They carry fluid toward the heart, are very thin, non-elastic, and do not have a muscle layer (choice A is wrong), have valves, and are at low pressure (choice C is correct and choice B is wrong). The fluid in lymphatic vessels is low in oxygen, but not all veins carry low-oxygen blood. The pulmonary veins carry blood rich in oxygen toward the heart (choice D is wrong).

Concepts tested
Immunology: Lymphatic System

Question 15

Varicose veins are swollen, twisted vessels typically found in the legs. They are the result of poorly functioning venous valves combined with increased pressure in the vein that limits blood flow. This causes a pooling of blood in the vessel. Which of the following is the most likely reason that veins become varicose, but not arteries?

A. Arterial valves are much stronger than venous valves and are less likely to fail, leading to less pooling of arterial blood.
B. The pressure in the arteries never becomes high enough to lead to varicosities.
C. The walls of veins are much less elastic than arteries, preventing the vein from regaining its shape after being stretched by the pooled blood.
D. The blood in the leg arteries flows downward, while the blood in the leg veins flows upward, against gravity.

Answer 15

C. Veins are far more likely to become swollen and enlarged because they lack the elasticity that arteries have. The elastic walls of the arteries are what allow arteries to stretch and expand, and then regain their shape. When veins expand due to the pooling of blood, they cannot regain their shape as easily. Over time, the vein becomes permanently enlarged (choice C is correct). Arteries do not contain valves (choice A is wrong). The pressure in the arteries is very high; much higher than venous pressure. However, the muscular wall of the artery helps to resist that pressure, plus the elasticity of artery wall ensures that even if it enlarges, it can regain its shape (choice B is wrong). While it is true that blood in the leg generally flows upward against gravity, this fact alone is not enough to explain why veins become varicose and not arteries. There are places in the body where blood in arteries flows upward, against gravity (the carotid arteries) and these do not become varicose (choice D is true but irrelevant).

Concepts tested
Cardiovascular System: Blood Vessels

Question 16

Which of the following neurotransmitters stimulates autonomic postganglionic neurons?

A. Acetylcholine
B. Norepinephrine
C. Epinephrine
D. Serotonin

Answer 16

A. Acetylcholine is used as the neurotransmitter at the ganglia in both the sympathetic and parasympathetic divisions of the autonomic nervous system (choice A is correct). The sympathetic division then utilizes norepinephrine at its effector organs (choice B is wrong) and the parasympathetic division continues to use acetylcholine. Epinephrine is a hormone; its release is triggered by activation of the sympathetic nervous system and it can stimulate similar receptors as norepinephrine (choice C is wrong). Serotonin is a neurotransmitter used in the brain; it is not found at autonomic ganglia (choice D is wrong).

Concepts tested
Nervous System: PNS/Autonomic Nervous System

Question 17

Non-specific defense systems include barriers to pathogen entry, chemicals that kill pathogens or destroy antigen, and phagocytic cells that ingest pathogens and antigens. Which of the following non-specific defense mechanisms is LEAST likely to be classified as a chemical method of defense?

A. Complement
B. Mucus

C. Lysozyme
D. Stomach acid

Answer 17

B. Mucus is best classified as a barrier; it is a sticky fluid that traps pathogens, dust, etc. and keeps them from entering the body (choice B is least likely to be classified as a chemical method of defense and is the correct answer choice). Complement is a set of proteins (effectively chemicals) that interacts with pathogens to destroy them (choice A can be classified as a chemical method and can be eliminated). Lysozyme is an enzyme in saliva and tears that kills bacteria non-specifically (choice C can be classified as a chemical method and can be eliminated). Stomach acid is a chemical that kills many swallowed pathogens (choice D can be classified as a chemical method and can be eliminated).

Concepts tested
Immunology: Non-specific Defense

Question 18

Voltage-gated sodium channels inactivate via a “ball-and-chain” mechanism, where a peptide “ball” tethered to the channel blocks the channel, preventing sodium influx. Increasing the length of the tether on the inactivation peptide increases the time required for inactivation. Which of the following would be observed?

A. Decreased time required between action potentials
B. Decreased maximal rate (frequency) of firing
C. Increased maximal sodium conductance rate
D. Increased maximal rate (frequency) of firing

Answer 18

B. Increased time required for inactivation would result in a lengthened absolute refractory period which could decrease the maximal rate, or frequency, of firing (choice B is correct and choices A and D are wrong). Increasing the time required for inactivation would not alter the maximal sodium conductance rate (choice C is wrong). Note that answer choices A and D are identical and both cannot be correct.

Concepts tested
Nervous System: Neurons and Action Potentials

Question 19

The brain contributes to sex hormone secretion in males by:

A. secreting FSH and LH from the posterior pituitary, in response to GnRH.
B. secreting LH (which affects interstitial cells in the testes), and FSH (which stimulates sustentacular cells).
C. inhibiting FSH and LH production in the testes, thereby increasing systemic testosterone.
D. increasing testosterone secretion, primarily from sustentacular cells in the testes.

Answer 19

B. GnRH is released from the hypothalamus and induces FSH and LH secretion from the anterior pituitary (choices A and C are wrong). FSH stimulates the sustentacular (Sertoli) cells in the testes to produce many secretions that affect spermatogenesis (primarily). LH stimulates interstitial (Leydig) cells to produce testosterone (choice B is correct and choice D is wrong).

Concepts tested
Endocrine System: Hormones and Hormone Functions

Question 20

Heart murmurs are extra, abnormal sounds (beyond the normal closure of the valves) produced during the cardiac cycle. They can be caused by stenotic (stiffened) valves, or by valves that do not close properly and allow regurgitation. Murmurs are classified as diastolic or systolic depending on when the additional sound is produced. A heart murmur caused by a failure of the AV valves to close properly would most likely be classified as a:

A. diastolic murmur, because this would allow flow from the atria to the ventricles during diastole.
B. systolic murmur, because this would allow regurgitation of blood from the ventricles to the atria during systole.
C. diastolic murmur, because this would allow regurgitation of blood from the arteries to the ventricles during diastole.
D. systolic murmur, because this would allow additional blood to flow from the atria to the ventricles during systole.

Answer 20

B. The AV valves close at the beginning of systole to prevent regurgitation of blood into the atria while the ventricles are contracting. If the AV valves failed to close properly, blood from the high-pressure ventricles would flow back into the low-pressure atria during systole and would produce an abnormal murmur (choice B is correct). Flow from the atria to the ventricles during systole would be prevented by the pressure gradient (choice D is wrong). Blood normally flows from the atria to the ventricles during diastole, through the open AV valves; this would not produce a murmur (choice A is wrong), and these valves do not separate the ventricles and the arteries so this would not affect blood flow between those regions (choice C is wrong).

Concepts tested
Cardiovascular System: Heart Anatomy

Question 21

A professional body builder purchases recombinant HGH (human growth hormone) online and proceeds to mix it into a morning energy shake each day. After four months, he still is not seeing the results he wanted. What was the likely cause in the failure of the body builder to build more muscle?

A. HGH does not increase muscle mass.
B. HGH cannot enter the cell to bind to its intracellular receptor.
C. Increased levels of the functional hormone have not been achieved in the blood.
D. Steroid hormones cannot be administered orally.

Answer 21

C. The body builder is attempting to use human growth hormone to increase muscle mass by taking the hormone orally. Growth hormone, which is produced in the pituitary gland, is a peptide hormone that binds to extracellular receptors (choices B and D are wrong) and would be subject to degradation in the stomach and small intestine. This degradation could explain the observed lack of effect as the hormone is not absorbed in a functional form (choice C is correct). Growth hormone has numerous effects including increasing height in children/adolescents, increasing calcium retention, and increasing muscle mass (choice A is not correct).

Concepts tested
Endocrine System: Endocrine System Basics

Question 22

Which of the following hormones increases blood glucose and is released from the pancreatic islets of Langerhans?

A. Glucagon
B. Insulin
C. Epinephrine
D. Cortisol

Answer 22

A. Glucagon is made by the α cells within the islets of Langerhans and stimulates the breakdown of glycogen stores in the liver to increase circulating glucose levels (choice A is correct). Insulin is made by the β cells of the pancreas, but it decreases the circulating levels of glucose (choice B is wrong). Epinephrine and cortisol both increase glucose, but they are released by the adrenal medulla and adrenal cortex, respectively (choices C and D are wrong).

Concepts tested
Endocrine System: Hormones and Hormone Functions

Question 23

An increase in heart rate will have what effect on cardiac output and blood pressure?

A. Increase cardiac output and increase blood pressure.
B. Increase cardiac output and decrease blood pressure
C. Decrease cardiac output and increase blood pressure
D. Decrease cardiac output and decrease blood pressure

Answer 23

A. Cardiac output is the volume of blood pumped out of the heart in one minute, and is the product of the stroke volume (volume pumped in one beat) and the heart rate (beats per minute). Increases in either of these two values will increase cardiac output (choices C and D are wrong). Cardiac output and blood pressure are directly proportional; if cardiac output increases, blood pressure will increase (choice A is correct and choice B is wrong).

Concepts tested
Cardiovascular System: Blood Pressure

Question 24

Continuous myelination of the axon would most likely result in which of the following?

A. Increased ion flow across the plasma membrane
B. Increased membrane depolarization required to fire an action potential
C. Decreased membrane resistance
D. Decreased reliable signal transduction to the axon terminus

Answer 24

D. Continuous myelination of the axon would decrease the ability of an action potential to reach the axon terminus (choice D is correct). Under normal conditions, myelin surrounds the plasma membrane and prevents ion flow, resulting in an increase in membrane resistance (choices A and C are wrong). Breaks in the myelin sheath along the axon, known as nodes of Ranvier, are where voltage-gated sodium channels exist at high concentrations. These nodes effectively boost the signal as the action potential travels along the axon. Without these nodes, the ability of that initial action potential to reach the axon terminus would be greatly impaired. The threshold of voltage-gated sodium channels is unlikely to change with myelination (choice B is wrong).

Concepts tested
Nervous System: Neurons and Action Potentials

Question 25

POMC is a precursor peptide generated in the anterior pituitary gland that is subject to proteolytic cleavage to generate several functional hormone derivatives. Which of the following pairs of hormones are likely derived from POMC?

A. ACTH and MSH
B. ACTH and oxytocin
C. TSH and ADH
D. FSH and ADH

Answer 25

A. The pituitary gland, a commonly discussed endocrine gland, is responsible for producing numerous hormones including FSH, LH, ACTH, TSH, prolactin, GH, and MSH (choice A is correct). ADH and oxytocin are produced in the hypothalamus (choices B, C, and D are not correct). Note: to answer this question, you must know that ACTH is produced in the anterior pituitary and that oxytocin and ADH are not.

Concepts tested
Endocrine System: Hormones and Hormone Functions

Question 26

Which of the following methods does carbon dioxide employ in order to be transported through the blood?

Converted into bicarbonate and dissolved in the plasma
Directly dissolved in the plasma
Bound to hemoglobin
  	A.  I only
  	B.  II only
  	C.  I and III only
  	D.  I, II, and III

Answer 26

D. Item I is true: the majority of carbon dioxide in the blood (about 73%) is found as bicarbonate ion. Carbon dioxide and water combine to form carbonic acid (H2CO3), which then dissociates into H+ and bicarbonate (HCO3–, choice B can be eliminated). Item II is true: some carbon dioxide, about 7%, dissolves directly in the plasma (choices A and C can be eliminated and choice D is correct). Item III is true: about 20% of the carbon dioxide in the blood is bound to hemoglobin to form carbaminohemoglobin.

Concepts tested
Cardiovascular System: Gas Transport

Question 27

Question 27
Which of the following is the first event in transduction of light by rod cells?

A. A sodium channel opens and the cell depolarizes.
B. A sodium channel closes and the cell hyperpolarizes.
C. A potassium channel opens and the cell hyperpolarizes.
D. A potassium channel closes and the cell depolarizes.

Answer 27

B. Rod cells are unique in that they are depolarized at rest by the constant influx of Na+. Stimulation by light causes the Na+ channel to close (choices C and D are wrong) and the rod cell to hyperpolarize (choice B is correct and choice A is wrong).

Concepts tested
Nervous System: Sensory Systems

Question 28

A woman with blood type A+ has four children. The blood types of her children are O+, AB–, A+, and AB+. Which of the following statements is true?

A. Her husband cannot have type AB blood.
B. Her husband must have type B– blood.
C. Her husband is homozygous for the IB allele.
D. Her husband must be heterozygous for the Rh allele.

Answer 28

A. In order to produce children with blood type O, both parents must donate a recessive i allele, thus the husband cannot have type AB blood (choice A is true), and he cannot be homozygous for IB (choice C is wrong). In order to produce children that are Rh–, both parents must donate the recessive r allele. Since she is A+, then she must be heterozygous for the Rh factor (Rr), but the husband could be Rh– (homozygous recessive rr) or Rh+ and heterozygous (Rr, choices B and D are wrong).

Concepts tested
Genetics: Mendelian Genetics/Probability Cardiovascular System: Blood

Question 29

Landmark studies establishing the quantal nature of synaptic transmission utilized curare to block postsynaptic receptors and prevent action potential transmission. Which of the following best explains the impact of curare on the synapse?

A. Decreases neurotransmitter release
B. Increases calcium influx into the presynaptic terminal
C. Decreases cation flow into the postsynaptic neuron
D. Blocks voltage-gated calcium channels

Answer 29

C. The stem of the question informs us that curare has an impact on postsynaptic receptors. This makes it unlikely to have any effect presynaptically, such as neurotransmitter release (choice A can be eliminated) or calcium influx into the presynaptic terminal (choice B can be eliminated). Voltage-gated calcium channels are present on the presynaptic neuron and are also not likely to be affected by a compound which blocks postsynaptic receptors (choice D can be eliminated). The only answer choice which clearly has a postsynaptic action is choice C; often neurotransmitter receptors on postsynaptic neurons are linked to ion channels. The opening of these ion channels impacts ion flow into the postsynaptic cell. If curare blocked the receptors from binding neurotransmitter, the ion channels could not be opened, leading to a decrease in cation flow into the postsynaptic neuron and ultimately, prevention of action potential transmission (choice C is correct). Curare is a competitive inhibitor of acetylcholine which is a neurotransmitter that acts, among other places, at the neuromuscular junction. Note that you did not have to know anything about curare specifically to answer this question.

Concepts tested
Nervous System: Synaptic Transmission

Question 30

A patient presents with an accelerated heart rate, excessive sweating, and heat intolerance. He is subsequently diagnosed with acute toxicity of an iodide-containing hormone present in a weight-loss supplement he recently began taking. Which of the following lab results matches the described scenario?

A. Increased T4 (thyroid hormone), increased TSH
B. Increased T4 (thyroid hormone), decreased TSH
C. Decreased T4 (thyroid hormone), increased TSH
D. Decreased T4 (thyroid hormone), decreased TSH

Answer 30

B. This patient is suffering from acute thyroid hormone toxicity and is experiencing symptoms of hyperthyroidism including accelerated heart rate, excessive sweating, and heat intolerance. The elevated levels of T4 (choices C and D are wrong) will result in feedback to the hypothalamus and anterior pituitary, causing a decrease in TSH (choice B is correct and choice A is wrong). Note that these symptoms could also be explained if the patient were ingesting TSH, however the stem of the question informs us that the substance being ingested contained iodide, indicating he was consuming thyroid hormone directly.

Concepts tested
Endocrine System: Hormones and Hormone Functions

Question 31

Which of the following physiological responses is LEAST likely to occur upon stimulation of the parasympathetic division of the ANS?

A. Increased digestive secretion and motility
B. Constricted bronchial tubes
C. Enhanced distance vision
D. Reduced heart rate

Answer 31

C. The parasympathetic division is also known as the “rest and digest” division, and leads to effects in the body such as increased digestive activity (choice A Is likely to occur and can be eliminated), reduced air flow (choice B is likely to occur and can be eliminated), and reduced heart rate (choice D is likely to occur and can be eliminated). However distance vision is a feature of the sympathetic nervous system; the parasympathetic division enhances near-object vision (choice C is least likely to occur and is the correct answer choice).

Concepts tested
Nervous System: PNS/Autonomic Nervous System

Question 32

A decrease in blood pH can lead to a decrease in CSF pH, which can trigger an increase in ventilation rate. Which region of the brain contains the respiratory center that can alter the rate of ventilation?

A. Medulla oblongata
B. Hypothalamus
C. Cerebellum
D. Corpus callosum

Answer 32

A. The medulla contains the main respiratory rhythmicity centers that control ventilation rate, and also contains the central chemoreceptors that would monitor CSF pH (choice A is correct). The hypothalamus maintains body homeostasis, including body temperature, ion balance, hunger/thirst, etc., primarily by controlling the pituitary gland (choice B is wrong). The cerebellum helps to smooth and coordinate body movement (choice C is wrong), and the corpus callosum is the bridge between the two hemispheres of the brain (choice D is wrong).

Concepts tested
Nervous System: Central Nervous System