NERVOUS SYSTEM

Tetrodotoxin (TTX) is a potent neurotoxin that binds to and inhibits the action of voltage-gated sodium channels in neurons. Poisoning can be rapidly fatal, within 4-6 hours of ingestion. Which of the following is the most likely cause of death from TTX poisoning? Question 17 Answer Choices A. Respiratory failure B. Cardiac arrest C. Dehydration from excessive vomiting D. Increased blood pH due to hypoventilation

A. Tetrodotoxin (TTX) is a potent neurotoxin that binds to and inhibits the action of voltage-gated sodium channels in neurons. Poisoning can be rapidly fatal, within 4-6 hours of ingestion. Respiratory failure is the most likely cause of death from TTX poisoning. Blocking the action of voltage-gated sodium channels in neurons would prevent the occurrence of action potentials, leading to skeletal muscle paralysis. Because the diaphragm is made of skeletal muscle, it too would become paralyzed, leading to respiratory failure and death. According to the question text, cardiac muscle is not affected, and since heart contraction is not dependent on neural stimulation, TTX would not have a direct effect on the heart ("cardiac arrest" is wrong). Vomiting may occur, but death due to dehydration would take a few days, not a few hours ("dehydration from excessive vomiting" is wrong), and while hypoventilation probably occurs (remember diaphragm contraction depends on neural stimulation), hypoventilation would lead to decreased blood pH, not increased ("increased blood pH due to hypoventilation" is wrong).

When the bladder is full, neurons in the sacral spinal cord notify the brainstem of the need to urinate. Inhibitory signals from the brain prevent urination until the time is judged appropriate; then the inhibition is removed and urination is allowed to proceed under the control of neurons in the sacral spinal cord. Cutting the thoracic spinal cord would most likely cause: Question 15 Answer Choices A. automatic bladder, in which the entire bladder empties when it becomes full, whether the time is appropriate or not. B. inability to urinate. C. return of normal bladder function. D. stress incontinence, in which urine leaks from the bladder upon physical stress, as in climbing stairs.

A. When the bladder is full, neurons in the sacral spinal cord notify the brainstem of the need to urinate. Inhibitory signals from the brain prevent urination until the time is judged appropriate; then the inhibition is removed and urination is allowed to proceed under the control of neurons in the sacral spinal cord. Cutting the thoracic spinal cord would most likely cause automatic bladder, in which the entire bladder empties when it becomes full, whether the time is appropriate or not. The brain is required for the inhibition of urination, not the actual urination itself, which is controlled by the sacral neurons. If the brain is removed from the picture by severing the spinal cord between the sacral neurons and the brain (the thoracic region), then urination would simply become automatic. There is no reason to assume stress incontinence, and in any case, severing the spinal cord in the thoracic region would prevent lower body motor function, so climbing stairs would not be possible.

Which of the following neurotransmitters is most commonly used to conduct autonomic nervous system responses? Question 4 Answer Choices A. Acetylcholine B. Serotonin C. GABA D. Norepinephrine

A. Acetylcholine

What impact do the hormones aldosterone and ADH have on the nephron? Question 30 Answer Choices A. Aldosterone increases plasma osmolarity by increasing sodium reabsorption, and ADH increases water permeability in the distal tubule and collecting duct, allowing water reabsorption B. Aldosterone increases plasma osmolarity by increasing potassium reabsorption, and ADH increases water permeability in the distal tubule and collecting duct, allowing water reabsorption. C. Aldosterone increases plasma osmolarity by increasing sodium reabsorption, and ADH increases water permeability in the distal tubule and collecting duct, allowing water to dilute the filtrate. D. Aldosterone decreases plasma osmolarity by increasing potassium reabsorption, and ADH increases water permeability in the distal tubule and collecting duct, allowing water to dilute the filtrate.

A. Aldosterone increases sodium reabsorption from the filtrate, thus increasing plasma osmolarity (choices B and D are wrong). Antidiuretic hormone (ADH, or vasopressin) induces expression of water channels (aquaporins) on the cells that make up distal tubule and collecting duct. This makes these typically water-impermeable tubes now permeable to water. At the distal tubule this allows water to follow sodium out of the filtrate, and at the collecting duct water moves out of the filtrate due to the gradient previously established by the loop of Henle (choice C is wrong and choice A is correct).

Which of the following is NOT a function of antibodies? Question 13 Answer Choices A. Destroy antigen directly B. Crosslink antigen C. Activate complement system D. Stimulate macrophages to destroy antigen

A. Antibodies only bind to antigen and crosslink it to other antigen molecules to inactivate it (choice B is a function and can be eliminated), activate the complement system to destroy the pathogen that the antigen is a part of (choice C is a function and can be eliminated), or stimulate macrophages to ingest and destroy the antigen (choice D is a function and can be eliminated). However, antibody do not destroy antigen directly (choice A is not a function of antibodies and is the correct answer choice).

ADH (antidiuretic hormone, also called vasopressin) causes increased water retention by the kidneys, allowing a more concentrated urine to be produced. Which of the following is/are true about ADH? It is released when blood pressure is low. It is made in the posterior pituitary gland. Its release is controlled by ADH-RH from the hypothalamus. Question 10 Answer Choices A. I only B. I and II only C. II and III only D. I and III only

A. Item I is true: the release of ADH when blood pressure is low allows more water to be retained and urine to be concentrated (i.e., less water is eliminated in the urine). This water is returned to the bloodstream, increasing blood volume and subsequently, blood pressure (choice C can be eliminated). Item II is false: ADH is actually made in the hypothalamus, then transported to the posterior pituitary, where it is stored until release (choice B can be eliminated). Item III is false: the release of ADH is triggered by an action potential, not a releasing hormone (RH). Only the anterior pituitary hormones are controlled by releasing hormones (choice D can be eliminated and choice A is correct).

What type of receptor is represented by the hair cells of the ear? Question 5 Answer Choices A. Mechanoreceptor B. Baroreceptor C. Nociceptor D. Chemoreceptor

A. Mechanoreceptor

Auditory transduction occurs inside the cochlea. How is the pitch of a sound determined? Question 18 Answer Choices A. Pitch is determined by the location of maximal vibration along the basilar membrane. 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 B. Pitch is determined by the location of maximal vibration along the basilar membrane. High pitched (high frequency) sounds vibrate the more flexible apex of the basilar membrane, while low pitched (low frequency) sounds vibrate the stiffer region of the basilar membrane near the oval window. C. Pitch is determined by the amplitude of vibration; high pitched (high frequency) sounds produce large amplitude vibrations, which low pitched (low frequency) sounds produce smaller amplitude vibrations. D. Pitch is determined by the amplitude of vibration; high pitched (high frequency) sounds produce smaller amplitude vibrations, which low pitched (low frequency) sounds produce large amplitude vibrations.

A. Pitch is determined by location, and loudness is determined by amplitude (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 A is correct and choice B is wrong).

Which of the following would have the greatest impact on the resting membrane potential? Question 20 Answer Choices A. Increasing membrane permeability to sodium B. Increasing membrane permeability to potassium C. Increasing extracellular calcium concentration D. Decreasing extracellular calcium concentration

A. Resting membrane potential is dictated by the relative ion concentrations inside and outside of the cell as well as by their relative permeabilities. At rest, the resting membrane potential of a typical neuron is -70 mV which arises primarily from the potassium leak channels present in the membrane (the equilibrium potential of potassium is -90 mV). There is relatively little sodium permeability across the membrane under resting conditions and an increase would significantly depolarize the membrane (bringing it closer to sodium's equilibrium potential of +40 mV, choice A is correct). An increase in potassium permeability may hyperpolarize the membrane, but this would have a less significant effect than an increase in sodium permeability (choice B is wrong). Calcium cannot cross the plasma membrane; simply altering its concentration without changing membrane permeability to calcium would not affect resting membrane potential (choices C and D are wrong).

The cardiac muscle cell action potential is approximately 100 times longer than the neural action potential due to a long plateau phase. Which channel is responsible for the plateau in the cardiac action potential? Question 3 Answer Choices A. Voltage-gated Ca2+ B. Fast voltage-gated Na+ C. Voltage-gated K+ D. Slow voltage-gated Na+

A. The plateau phase in the cardiac muscle cell action potential is due to the influx of calcium through voltage-gated Ca2+ channels. Fast Na+ channels are responsible for the initial depolarization (choice B is wrong), voltage-gated K+ channels are responsible for the repolarization (choice C is wrong), and slow Na+ channels are not found in cardiac muscle cells (choice D is wrong).

All of the following statements about oxygen transport and hemoglobin are true EXCEPT: Question 19 Answer Choices A. 2,3-BPG, made by red blood cells in low-oxygen environments, increases hemoglobin's affinity for oxygen so that more O2 can be delivered to the tissues. B. Hemoglobin is almost fully saturated in the lungs and is less saturated in the tissues. C. The Bohr shift is triggered by exercise conditions (increased CO2, decreased pH, and increased temperature), and reduces hemoglobin's affinity for oxygen, facilitating oxygen delivery to the tissues. D. Fetal hemoglobin has an increased affinity for oxygen compared to adult hemoglobin so that it can "steal" oxygen from maternal hemoglobin.

A. While it is true that 2.3-BPG is made in low O2 environments, it decreases hemoglobin's affinity so that more oxygen can be delivered to the tissues. Hemoglobin with an increased O2 affinity would tend to hang on to its oxygen, which is the exact opposite of what is needed in low-oxygen environments (choice A is false and is the correct answer choice). All other statements are true. Hemoglobin is 98% saturated in the high-oxygen environment of the lungs and releases that oxygen as it enters the lower-oxygen environment of the tissues (choice B is true and can be eliminated). The Bohr shift reduces hemoglobin's affinity for oxygen, allowing more O2 to be delivered to the tissues under exercise conditions (choice C is true and can be eliminated). Fetal hemoglobin has a high affinity for oxygen so that when maternal hemoglobin releases O2, the baby's hemoglobin can bind it (choice D is true and can be eliminated).

A patient suffering from menopause experiences decreased levels of estrogen due to decreased ovarian production. Which of the following lab results would be expected? Question 26 Answer Choices A. Increased FSH, increased GnRH B. Increased FSH, decreased GnRH C. Decreased LH, increased GnRH D. Decreased LH, decreased GnRH

A. With menopause, the ovaries begin to degenerate and fail to produce appropriate levels of estrogen. This decrease in estrogen impacts the hormone feedback loop to GnRH and FSH/LH; the lack of negative feedback by estrogen triggers an increase in GnRH (and subsequently FSH and LH) in an attempt to generate more estrogen (choice A is correct and choices B, C, and D are wrong). In fact, a common diagnostic test for menopause is measuring FSH levels.

Which of the following neurons could directly stimulate the relaxation of bronchial smooth muscle? Question 11 Answer Choices A. Parasympathetic postganglionic neurons B. Sympathetic postganglionic neurons C. Sympathetic preganglionic neurons D. Somatic motor neurons

B. Sympathetic postganglionic neurons could directly stimulate the relaxation of bronchial smooth muscle. Relaxation of bronchial smooth muscle is an involuntary process that is triggered by activation of the sympathetic nervous system. Postganglionic neurons directly stimulate target tissues; preganglionic neurons stimulate postganglionic neurons.

Damage to which one of the following would be most likely to hinder the detection of high-frequency, but not mid-frequency sound by the ear? Question 19 Answer Choices A. Outer ear B. Cochlea C. Auditory nerve D. Malleus, incus, or stapes

B. Damage to the cochlea would be most likely to hinder the detection of high-frequency, but not mid-frequency sound by the ear. Damage to the auditory nerve or to the auditory ossicles (malleus, incus, and stapes) would hinder the detection of all frequencies since the nerve would be unable to send impulses to the brain and the ossicles would be unable to transmit sound waves to the inner ear, and neither of these functions is pitch-specific. Damage to the outer ear would not hinder pitch-specificity at all. The cochlea is a large, curled structure in the inner ear, along which the basilar membrane is stretched. The basilar membrane supports the hair cells of the ear (the sound receptors), and vibrates in sound waves. However, since one end of the basilar membrane is considerably thicker than the other, maximum vibration of a particular area depends of the frequency of the wave stimulating the membrane. Damage to the cochlea is the most likely injury to hinder the detection of particular frequencies.

Both the sympathetic and parasympathetic divisions of the ANS can affect the cardiovascular system. Which of the following statements regarding sympathetic activation is/are true? I. Activation causes the heart to contract II. Activation relaxes smooth muscle in blood vessels serving skeletal muscle III. Activation relaxes smooth muscle in blood vessels serving skin and digestive organs Question 10 Answer Choices A. I only B. II only C. I and II only D. I and III only

B. I. Activation causes the heart to contract II. Activation relaxes smooth muscle in blood vessels serving skeletal muscle III. Activation relaxes smooth muscle in blood vessels serving skin and digestive organs Both the sympathetic and parasympathetic divisions of the ANS can affect the cardiovascular system. Regarding sympathetic activation, Item II only is true. Activation of the sympathetic division of the ANS leads to the "fight or flight" stress response. Item I is false: The heart is autorhythmic and can generate its own contraction without input from the nervous system. However, activation of the sympathetic division can make the heart contract more frequently (i.e., increase the heart rate). Item II is true: It is helpful to have increased blood flow to skeletal muscles during times of stress to provide adequate oxygen and nutrients to the working muscles. Relaxing the smooth muscle in the blood vessels serving the skeletal muscle would cause dilation of the vessels and increased blood flow. Item III is false: during stress situations, blood is diverted from skin and digestive organs by constricting those vessels (i.e., contracting the smooth muscle)

Which of the following senses relies on chemoreceptors? I. Touch II. Taste III. Olfaction Question 18 Answer Choices A. III only B. II and III only Correct Answer (Blank) C. I only D. I and II only

B. II and III only rely on chemoreceptors. I. Touch II. Taste III. Olfaction Item I is false: The sense of touch relies primarily on mechanoreceptors, and somewhat on nociceptors (pain) and thermoreceptors (temperature), but not chemoreceptors. Items II and III are true: Both taste and smell rely on chemoreceptors.

In the condition myopia the inverted image formed by the lens falls: Question 3 Answer Choices A. on the retina. B. in front of the retina. C. behind the retina. D. on the optic nerve.

B. In the condition myopia the inverted image formed by the lens falls in front of the retina. In myopia, the image is formed in front of the retina, generally due to the shape of the eye being too long.

Hair cells used to detect motion are found in which of the following structures? I. The organ of Corti II. The skin III. The semicircular canals Question 23 Answer Choices A. I only B. I and III only C. III only D. I, II, and III

B. Items I and III are true: Both the organ of Corti and the semicircular canals contain hair cells with small "hairs" that project from the apical surface of the cell into the surrounding fluid. Movement of the fluid around the hair cells detects sound in the organ of Corti and a change in body orientation in the semicircular canals. Item II is incorrect: Hair in the skin is different; it is not made up of "hair cells" but is made up of dead epithelial cells.

Nerve cells that control thermoregulation are concentrated in which portion of the brain? Question 4 Answer Choices A. Cerebrum B. Hypothalamus C. Medulla D. Cerebellum

B. Nerve cells that control thermoregulation are concentrated in the hypothalamus. The hypothalamus is a key regulator in many different processes, including food intake, blood pressure, and neuroendocrine control, as well as temperature regulation.

Which of the following would be an appropriate example of difference threshold? Question 16 Answer Choices A. Recognizing a family member based on his/her pattern of walking without being able to see his/her face B. Picking up two cantaloupes one after the other to determine which is heavier since each costs the same C. No longer perceiving the sound of a television after being in a room with it for an extended period of time D. Creating a list of pros and cons to aid in decision making processes

B. Picking up two cantaloupes one after the other to determine which is heavier since each costs the same is an appropriate example of difference threshold. Difference threshold is the minimum difference needed between two stimuli to be able to detect that there is in fact a difference at least 50% of the time. The "weighing" of the cantaloupes best describes this, as perceiving a difference in their size would require them to be proportionally distinct in their mass. Adaptation stops us from perceiving a constant sound if exposed to it long enough and top-down processing allows us to make a specific connection or recognition based on prior experience. Decision making strategies are not part of the difference threshold.

Shapes, patterns, and movement are perceived by the retina and a complex network of pattern-recognition circuits in the brain. Colors, however, are identified: Question 21 Answer Choices A. by selective filtering of light in the retina. B. by the relative stimulation of cones in the retina, of which there are only three types with regard to color perception. C. by the activation of all cones, which is different for every different wavelength of light. D. by the relative stimulation of rods in the retina, of which there are only three types with regard to color perception.

B. Shapes, patterns, and movement are perceived by the retina and a complex network of pattern-recognition circuits in the brain. Colors, however, are identified by the relative stimulation of cones in the retina, of which there are only three types with regard to color perception. Cones transduce color for the brain, while rods respond to black and white images. There are only three types of cones, and they are specific for different wavelengths of light. There is no selective filtering of light in the retina.

The cell bodies of a somatic sensory nerve are located in the: Question 5 Answer Choices A. ventral horn. B. dorsal root ganglion C. brain. D. spinal cord.

B. The cell bodies of a somatic sensory nerve are located in the dorsal root ganglion. The other answer choices are wrong since the cell bodies of somatic sensory neurons are not located in the CNS. They are located in dorsal root ganglia just behind and along the length of the spinal cord.

The myelin sheath of many axons is produced by the: Question 9 Answer Choices A. nerve cell body. B. Schwann cells. C. nodes of Ranvier. D. axon hillock.

B. The myelin sheath of many axons is produced by the Schwann cells. The myelin sheath is not produced by the neuron it is associated with. Instead, it is produced by a different type of cell, the Schwann cell, that wraps around the axon to create layers of insulating myelin. (Note that this is only the case in the PNS. A different cell, an oligodendrocyte, is responsible for myelination in the CNS.)

How do the photoreceptors of the eye respond to stimulation by light? Question 6 Answer Choices A. Light closes Na+ channels, the cells become depolarized and the optic nerve is stimulated. B. Light closes Na+ channels, the cells become hyperpolarized and the optic nerve is stimulated. C. Light opens Na+ channels, the cells become hyperpolarized and the stimulation of the optic nerve stops. D. Light opens Na+ channels, the cells become depolarized and the stimulation of the optic nerve stops.

B. When the photoreceptors of the eye are stimulated by light, light closes Na+ channels, the cells become hyperpolarized and the optic nerve is stimulated. Stimulation by light causes Na+ channels in the photoreceptors to close. This causes the cells to hyperpolarize and to stop releasing an inhibitory neurotransmitter onto the bipolar cells. Removal of the inhibition causes the bipolar cells to fire action potentials, ultimately transmitted to the optic nerve.

A red blood cell leaving the heart on its way to the lungs would travel through the: Question 27 Answer Choices A. aorta. B. pulmonary artery C. pulmonary vein. D. superior vena cava.

B. Arteries always carry blood away from the heart, and veins carry blood toward the heart (choices C and D can be eliminated). The aorta carries blood to the body and the pulmonary artery carries blood to the lungs (choice A can be eliminated and choice B is correct).

Which of the following do peptide and steroid hormones have in common? Question 12 Answer Choices A. They function on a similar timescale. B. Both bind to protein effectors C. They are both synthesized at the rough endoplasmic reticulum. D. Both travel through the blood bound to a protein.

B. Both peptide and steroid hormones bind to protein receptors to impact a given cell (choice B is correct). Peptide hormones function on a much shorter time scale than steroid hormones (choice A is wrong) and only peptide hormones are synthesized at the RER (choice C is wrong). Steroid hormones, because they are hydrophobic, travel through the blood bound to protein (generally albumin) while peptides generally do not require a carrier (choice D is wrong).

An individual with blood type B- has: Question 7 Answer Choices A. type B antigen, anti-B antibodies, and will make anti-Rh antibodies if exposed to Rh positive blood. B. type B antigen, anti-A antibodies, and will make anti-Rh antibodies if exposed to Rh positive blood C. type B antigen, anti-B antibodies, and anti-Rh antibodies. D. type B antigen, anti-A antibodies, and anti-Rh antibodies.

B. For the A and B antigens, the blood type specifies the antigen, and the individual automatically makes antibodies to the opposite antigen. Thus, an individual with blood type B- would have type B antigen on the surface of the red cells, and would automatically make anti-A antibodies (choices A and C can be eliminated). The Rh factor works a little bit differently; anti-Rh antibodies are only made if the individual gets exposed to Rh+ blood (choice B is correct and choice D is wrong).

Myelination facilitates in which of the following? Increasing action potential rate of travel Increasing action potential strength Restricting ion flow across the membrane Question 24 Answer Choices A. I only B. I and III only C. II and III only D. I, II, and III

B. Item I is true: myelination results in significantly increased rates of action potential conductance along an axon (choice C can be eliminated). Item II is false: action potential "strength" (or size) does not change as it is an all-or-none process (choice D can be eliminated). Item III is true: myelination prevents ion flow across the membrane, effectively allowing the action potential to "jump" from one Node of Ranvier to the next (nodes are breaks in the myelin sheath, choice A can be eliminated and choice B is correct).

Depletion of extracellular calcium would have which of the following effects on synaptic transmission? Question 8 Answer Choices A. Increased neurotransmitter release B. Decreased neurotransmitter release C. Increased EPSPs D. Increased IPSPs

B. Synaptic transmission depends on calcium influx through voltage-gated calcium channels at the axon terminal. Calcium influx triggers neurotransmitter release and subsequent changes in the postsynaptic membrane potential. A decrease in extracellular calcium would lead to a significant decrease in neurotransmitter release (choice B is correct and choice A is wrong). This decrease in neurotransmitter release would result in a decrease in either EPSPs (excitatory postsynaptic potentials) or IPSPs (inhibitory postsynaptic potentials), depending on the synapse in question (choices C and D are wrong).

Temporal summation relies upon which of the following? Question 4 Answer Choices A. The rate of recovery must be more rapid than the excitation rate. B. The rate of excitation must be more rapid than the recovery rate. C. The synaptic inputs must be in close proximity to one another. D. The synaptic inputs may be distant, but must still be additive.

B. Temporal summation is the repeated activation of a given synapse resulting in a response of greater magnitude. In order to accomplish this, the rate of excitation must outpace the rate of recovery or else the postsynaptic neuron will have returned to its resting state before the second stimulation arrives (choice B is correct and choice A is wrong). As temporal summation results from the repeated stimulation of a single postsynaptic neuron, proximity is not an issue (choice C and D are wrong).

Which of the following neurotransmitters is released by sympathetic neurons onto the heart? Question 31 Answer Choices A. Acetylcholine B. Norepinephrine C. Epinephrine D. Serotonin

B. The sympathetic division of the ANS primarily releases norepinephrine (NE) at the organ level; the only significant exception is the sweat glands, where it releases acetylcholine (ACh; choice B is correct). ACh is the primary neurotransmitter of the parasympathetic division (choice A is wrong). Epinephrine is a hormone; its release into the blood is triggered by 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 secreted by autonomic neurons (choice D is wrong).

Question 20 Which of the following is NOT true of the sympathetic nervous system? Question 20 Answer Choices A. Epinephrine prolongs and enhances its effects. B. It increase heart rate, dilates bronchial tubes, and increases blood flow to skeletal muscle. C. It increases pupil diameter to enhance near-object vision. D. ACh stimulates the adrenal medulla.

C. It is NOT true of the sympathetic nervous system that it increases pupil diameter to enhance near-object vision. All of the other answer choices are true. One of the first effects of the sympathetic system is to release ACh onto the adrenal medulla; this triggers the release of epinephrine into the blood to enhance and prolong the overall effects of the system. Among those effects are increased rate and force of cardiac contraction, dilation of bronchial tubes to increase the volume of air that can enter the lungs, and increased blood flow to skeletal muscles to ensure adequate delivery of glucose and oxygen during stress situations. However, while it is true that the sympathetic system increases pupil dilation, this increases distance vision, not near-object vision. Distance vision is an advantage in a stress situation.

Damage to which component of the ear would be most likely to alter a person's perception of pitch? Question 24 Answer Choices A. Cochlea B. Tympanic membrane C. Basilar membrane D. Semicircular canals

C. Sound waves are transmitted to the basilar membrane, causing it to vibrate. The location along the basilar membrane that experiences maximal vibration determines a person's perception of pitch. The cochlea does contain the basilar membrane, but it is this membrane specifically that is involved in pitch transduction. The tympanic membrane and semicircular canals are not part of this process.

Which of the following processes always result(s) in a negative membrane potential? I. Repolarization II. Depolarization III. Hyperpolarization Question 22 Answer Choices A. II and III only B. I, II, and III C. I and III only D. I only

C. The processes I and III only always result in a negative membrane potential. I. Repolarization II. Depolarization III. Hyperpolarization Item I is true: repolarization is defined as a return to resting membrane potential (RMP). Since the RMP is negative (-70 mV), repolarization always results in a negative membrane potential (choice "II and III only" can be eliminated). Item II is false: depolarization is defined as "the movement of membrane potential away from resting potential in the positive (less negative) direction". For example, a change in membrane potential from -70 mV to -60 mV is a depolarization. However, if the change to a less negative potential is enough to cause the voltage-gated sodium channels to open, then membrane potential can spike to positive values. Keep in mind that the question uses the word "always"; sometimes depolarization can lead to a negative potential, and sometimes to a positive potential (choice "I, II, and III" can be eliminated). Item III is true: hyperpolarization is defined as "the movement of membrane potential away from resting potential in the negative direction". Since resting membrane potential is already negative, hyperpolarization will always result in a negative potential (choice "I only" can be eliminated).

Which description below correctly identifies the role of the myelin sheath in action potential transmission? Question 8 Answer Choices A. Protein fibers assemble along the axon of neurons, preventing leakage of current across the membrane. B. Convolutions in the axons of neurons dissipate current through specialized leakage channels. C. Schwann cells insulate the axons of neurons, causing membrane depolarization to jump from node to node. D. Glial cells cover the nodes of Ranvier to prevent backflow of current along the axon of neurons.

C. The role of the myelin sheath in action potential transmission is correctly identified by the following description: Schwann cells insulate the axons of neurons, causing membrane depolarization to jump from node to node. The myelin sheath insulates the neuronal axon except for small gaps (nodes of Ranvier) through which ions can traverse the membrane, causing the action potential to leap from node to node (saltatory conduction).

Blood pressure is affected by many factors. Which of the following would increase blood pressure? An increase in peripheral blood vessel diameter An increase in heart rate due to physical exertion An increase in blood volume due to aldosterone Question 5 Answer Choices A. I only B. II only C. II and III only D. I, II, and III

C. Item I is false: an increase in vessel diameter would reduce peripheral resistance. Since peripheral resistance and blood pressure are directly proportional, this would lead to a decrease in blood pressure (choices A and D can be eliminated). Since both remaining answer choices include Item II, it must be true: an increase in heart rate would lead to an increase in cardiac output. Cardiac output and blood pressure are directly proportional, so this would increase blood pressure. Item III is true: consider the heart and blood vessels as a "container" for blood in the body. If the volume of blood in the "container" increases but the container size remains the same, the pressure inside the container must increase (choice B can be eliminated and choice C is correct)

Olfactory receptors would be classified as: Question 32 Answer Choices A. nociceptors. B. mechanoreceptors. C. chemoreceptors. D. thermoreceptors.

C. Olfactory receptors are found in the nose and respond to odor chemicals, so are classified as chemoreceptors (choice C is correct). Nociceptors respond to pain, mechanoreceptors to physical movement, and thermoreceptors to temperature (choices A, B, and D are wrong).

Which of the following represents the correct order of events? Question 11 Answer Choices A. Light stimulates rod cells, rod cells depolarize and stimulate biopolar cells, which stimulate ganglion cells, a signal is sent along the optic nerve. B. Light stimulates rod cells, rod cells depolarize and stimulate ganglion cells, which stimulate bipolar cells, a signal is sent along the optic nerve. C. Light stimulates rod cells, rod cells hyperpolarize and release the inhibition on biopolar cells, which stimulate ganglion cells, a signal is sent along the optic nerve D. Light stimulates rod cells, rod cells hyperpolarize and release the inhibition on ganglion cells, which stimulate bipolar cells, a signal is sent along the optic nerve.

C. 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 and the rod cell to hyperpolarize (choices A and B are wrong). Rod cells synapse with bipolar cells, which synapse with ganglion cells (choice C is correct and choice D is wrong).

Which of the following is not a component of the Organ of Corti? Question 6 Answer Choices A. Hair cells B. Tectorial membrane C. Tympanic membrane D. Basilar membrane

C. Tympanic membrane

Sodium plays the principle role in rapid depolarization during action potentials due to which of the following? Question 25 Answer Choices A. The rapid inactivation of voltage-gated sodium channels B. The rapid efflux of sodium from the neuron C. Sodium conductance results in a positive membrane potential D. Sodium conductance results in a negative membrane potential

C. Sodium conductance is responsible for the rapid depolarization observed during the action potential. This is due to the fast opening of voltage-gated sodium channels which allow the flow of sodium across the membrane. Sodium flows into the cell down its electrochemical gradient resulting in depolarization of the cell (choice C is correct and choices B and D are wrong). While inactivation of the voltage-gated sodium channels does occur, this occurs after the rapid depolarization observed and thus cannot be the cause of the depolarization (choice A is wrong).

Brain damage due to head trauma can be seen as lesions in different areas of the brain. A patient recently involved in a car accident presents with severely unsteady gait (difficulty walking), uncoordinated eye movements, and poor motor control in general . Which of the following regions of the brain is the likely location of the lesion afflicting this patient? Question 16 Answer Choices A. Cerebrum B. Hypothalamus C. Cerebellum D. Corpus callosum

C. The cerebellum plays an important role in motor control and coordination (choice C is correct), which are impaired in this patient. The cerebrum is involved in many functions, typically associated with a particular lobe. For example, the frontal lobe controls voluntary movement and problem solving, the parietal lobe controls general sensation, the temporal lobe controls hearing and memory, and the occipital lobe controls vision. The frontal lobe is involved in movement, but it generates the signal for movement to occur, while the cerebellum smooths and coordinates the movement. Since the movement is occurring, although in a less coordinated manner, the cerebellum is more likely to be the problem than the cerebrum (choice A is wrong). The hypothalamus is involved in many processes to maintain body homeostasis, including body temperature, hunger/thirst, and sleep (choice B is wrong), and the corpus callosum is the bridge between the two hemispheres of the brain (choice D is wrong).

Which of the following valves prevents backflow of blood into the right ventricle? Question 17 Answer Choices A. Tricuspid AV valve B. Bicuspid AV (mitral) valve C. Pulmonary semilunar valve D. Aortic semilunar valve

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

B cells participate in: Question 2 Answer Choices A. cell-mediated immunity. B. innate immunity. C. humoral immunity D. non-specific immunity.

C. When stimulated by an antigen (usually a foreign protein), B cells secrete antibodies into the blood (choice A is wrong and choice C is correct). Antibodies are highly specific markers for antigen (choice D is wrong) and when bound, target that antigen for destruction. Innate immunity is non-specific and includes things like the skin, lysozyme, stomach acid, etc. (choice B is wrong).

The first heart sound is produced by the: Question 29 Answer Choices A. closure of the semilunar valves at the beginning of systole. B. closure of the semilunar valves at the beginning of diastole. C. closure of the AV valves at the beginning of systole. D. closure of the AV valves at the beginning of diastole.

C. When the ventricles begin to contract (the beginning of systole), pressure inside those chambers rises dramatically. Blood would like to flow backwards, into the lower pressure atria, but pushes up against the AV valves, closing them to prevent backflow and producing the first heart sound (choice C is correct and choice A is wrong). Pressure continues to rise in the ventricles and eventually exceeds arterial pressure, at which point blood is ejected from the heart. When the ventricles begin to relax (at the beginning of diastole), pressure inside immediately drops below arterial pressure; blood would like to backflow into the ventricles but pushes up against the semilunar valves and closes them, producing the second heart sound (choices B and D are wrong).

How does absolute threshold function as a measure of sensory perception? Question 2 Answer Choices A. As the minimum stimulus needed to activate sensory receptors at least 50% of the time, this measure of perception has a well-established profile that differs between men and women. B. As the maximum stimulus which can be tolerated by sensory receptors before incurring damage, this measure of perception varies with age and by person. C. As the maximum stimulus which can be tolerated by sensory receptors before incurring damage, this measure of perception has a well-established profile that differs between men and women. D. As the minimum stimulus needed to activate sensory receptors at least 50% of the time, this measure of perception varies with age and by person.

D. Absolute threshold is the minimum amount of stimulation needed to achieve activation of sensory receptors 50% of the time; this is not a measure of maximum stimulation or capacity. This measure does vary by age and between people, but does not have established values based on the sex of an individual.

A researcher isolates a squid giant axon and places it into an electrolyte bath that mimics its normal conditions. She stimulates the axon and normal action potentials occur. She then introduces a drug into the electrolyte bath that blocks voltage-gated potassium channels, and again attempts to elicit action potentials. Which of the following is most likely to occur? Question 12 Answer Choices A. Since the voltage-gated channels are blocked, the action potential will not occur. B. The resting potential will become more positive since potassium is unable to exit the cell normally through leak channels. C. Since the cell remains depolarized for a longer period of time, subsequent action potentials will be easier to elicit and the frequency of action potentials will increase. D. The axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long.

D. If a drug is introduced that blocks voltage-gated potassium channels, the most likely occurrence is that the axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long. Since the voltage-gated sodium channels are not affected, the cell should still be able to depolarize normally. However, the voltage-gated potassium channels are critical for repolarizing the cell; if these are blocked, the cell will remain in a depolarized state for much, much longer than normal. This would prevent the firing of subsequent action potentials (decrease the action potential frequency) since when depolarized, the cell is in an absolute refractory period, unable to fire additional action potentials. The resting potential of the cell should not be affected since it does not depend on voltage-gated channels (only on the Na+/K+ ATPase and the potassium leak channels).

How does the auditory cortex in the temporal lobe receive stimulation from the ear? Question 1 Answer Choices A. Sound waves flex the tectorial membrane to trigger release of neurotransmitter B. Hair cells directly trigger bipolar auditory neurons via mechanical stimulation C. Sound waves stimulate baroreceptors to open ion channels in hair cells D. Hair cells contacting the tectorial membrane open ion channels to trigger release of neurotransmitter

D. The auditory cortex in the temporal lobe receives stimulation from the ear when hair cells contacting the tectorial membrane open ion channels to trigger release of neurotransmitter. Perception of sound begins with sound waves vibrating the basilar membrane. This causes hair cells (mechanoreceptors) to come in contact with the tectorial membrane, and this contact opens ion channels in the hair cells. The cells depolarize and release neurotransmitter to stimulate the bipolar auditory neurons that run to the auditory cortex in the temporal lobe. Baroreceptors are not involved in this process.

Which of the following is the correct pathway of light entering the anterior surface of the eye leading to stimulation of the optic nerve? Question 7 Answer Choices A. Choroid cornea vitreous chamber anterior chamber retina B. Cornea vitreous chamber anterior chamber choroid C. Cornea pupil sclera anterior chamber optic disk fovea D. Cornea anterior chamber lens retina

D. The correct pathway of light entering the anterior surface of the eye leading to stimulation of the optic nerve is cornea anterior chamber lens retina. The cornea is the first structure that light must pass through ("choroid cornea vitreous chamber anterior chamber retina" is wrong). The anterior chamber is before the vitreous chamber ("cornea vitreous chamber anterior chamber choroid" is wrong). The sclera is the tough, outer, white covering of the eyeball; light cannot pass through this layer. This is why the cornea exists in the first place—to have a transparent outer layer for light to pass through. In any case, once light has passed through the cornea and the pupil, it can't reach the sclera until it passes through the lens, the vitreous humor, and the retina ("cornea pupil sclera anterior chamber optic disk fovea" is wrong).

Which of the following best characterizes the difference between the soma and axon hillock? Question 13 Answer Choices A. Increased ribosomal activity in the axon hillock B. Axon hillocks are denoted by demyelinated areas between myelin sheets along the axon C. Decreased myelination surrounding the soma D. Decreased voltage-gated sodium channel density in the soma

D. The difference between the soma and axon hillock is that there is decreased voltage-gated sodium channel density in the soma. The axon hillock, the area linking the soma to the axon, possesses an increased voltage-gated sodium channel density, allowing it to fire action potentials. In the soma, the decreased density allows for local depolarization which degrades exponentially over the distance of the soma. Neither the soma nor axon hillock are myelinated, and biosynthetic activity takes place in the soma, not the axon hillock. Nodes of Ranvier are the demyelinated areas between myelin sheets along the axon; the hillock is only at the area connecting the axon and soma.

On what part of the retina does the image focus on when you stare directly at something? Question 14 Answer Choices A. Optic disk B. Pupil C. Lens D. Fovea centralis

D. The image focuses on the fovea centralis when you stare directly at something. The fovea centralis, also known as the focal point, is responsible for extreme visual acuity. When you stare directly at something, the image is focused on the fovea centralis part of the retina to maximize the visual acuity. The lens is not part of the retina, but rather it is in front of the retina. Its role is to focus incoming light beams onto the retina. The pupil is also not part of the retina. Its role is to control the amount of light that enters the eye. While the optic disk is part of the retina, it has no photoreceptors. For this reason, it is also called the blind spot.

Testosterone is a steroid hormone that does each of the following EXCEPT: Question 23 Answer Choices A. create negative feedback to the anterior pituitary and hypothalamus in the brain. B. induce male sex characteristics such as a deep voice, broad shoulders and body hair. C. stimulate sustentacular cells, thereby indirectly stimulating spermatogenesis. D. create negative feedback to the interstitial cells, keeping systemic hormone levels low during certain developmental stages.

D. Choices A, B, and C are true statements about testosterone, and can be eliminated. Choice D is false (and thus the correct answer choice); testosterone is made by interstitial cells, but does not feedback significantly to these cells.

Which of the following statements is true about cortisol? Question 1 Answer Choices A. It is released from the adrenal medulla in a stress situation and helps mobilize fats for energy. B. It is released from the adrenal cortex in a stress situation and binds to an extracellular receptor to mediate its effect. C. It is released from the adrenal medulla in a stress situation and reduces inflammation. D. It is released from the adrenal cortex in a stress situation and modifies transcription to exert its effect.

D. Cortisol is released from the adrenal cortex (choices A and C are wrong), and because it is a steroid hormone, enters cells, binds to an intracellular receptor (choice B is wrong), and modifies transcription. Note that mobilizing fats for energy and reducing inflammation are among cortisol's effects, but it is not released from the adrenal medulla. Thus, choice D is correct.

How does myelin increase the efficiency with which an action potential is conducted in a neuron? Question 1 Answer Choices A. Decreasing the amount of Na+ allowed into the cell B. Increasing the amount of neurotransmitter released C. Increasing the number of K+ channels D. Decreasing the surface area to be depolarized

D. Decreasing the surface area to be depolarized

When is a neuron in its relative refractory period? Question 2 Answer Choices A. During depolarization B. During the transmission of an action potential C. During repolarization D. During hyperpolarization

D. During hyperpolarization

What area of the brain is responsible for primary regulation of the endocrine system? Question 3 Answer Choices A. Thalamus B. Pons C. Epithalamus D. Hypothalamus

D. Hypothalamus

Which of the following is/are a function of the lymphatic system? Recover excess tissue fluid and return it to the circulatory system Absorb and transport fats from the intestines Filter fluid to remove antigens and other potentially harmful substances Question 9 Answer Choices A. I only B. II only C. I and III only D. I, II, and III

D. Item I is true: there is a net outward flow of fluid to the tissues as more fluid is lost at the arterial end of capillary beds (due to pressure) than is regained at the venous end of capillary beds (by osmosis). Lymphatic vessels pick up this excess tissue fluid and return it to the circulatory system (choice B can be eliminated). Item II is true: specialized lymphatic vessels in the digestive system called lacteals absorb and transport digested fats (choices A and C can be eliminated, and choice D is correct). Item III must be true: as the excess tissue fluid is transported, it passes through hundreds of lymph nodes (concentrated areas of white blood cells) which help to filter the fluid of any harmful material it may have picked up.

All of the following are examples of non-specific body defense mechanisms EXCEPT: Question 15 Answer Choices A. the complement system. B. lysozyme. C. the skin. D. lymphocytes.

D. Lymphocytes are B cells and T cells and participate in the adaptive immune response, a highly specific defense response (choice D is not a non-specific defense mechanism and is the correct answer choice). Choices A, B, and C are all examples of non-specific defense and can be eliminated: the complement system destroys bacteria non-specifically, lysozyme is an enzyme found in saliva and tears that kills bacteria, and the skin is a great non-specific barrier.

A researcher treats cultured neurons with an RNA polymerase II inhibitor. Which of the following areas of the neuron will be most directly impacted? Question 22 Answer Choices A. Axon terminal B. Axon hillock C. Dendrites D. Soma

D. RNA polymerase II is responsible for the production of mRNA in the nucleus of eukaryotic cells. In neurons, the cell body (or soma) houses the nucleus and the majority of metabolic activity (choice D is correct). The axon terminal is the end of an axon which frequently forms a synapse with another neuron or effector organ (choice A is wrong). The axon hillock is the region where the axon and soma meet and is important in action potential initiation (choice B is wrong). Dendrites are offshoots from the soma which receive input from other neurons (choice C is wrong).

A man on a hunting trip sustains an accidental gunshot wound. The bullet penetrates the skull and travels a short way into the cerebral cortex. Shortly after the accident, the man finds that his sense of smell has been impaired. Which of the following brain regions was most likely damaged? Question 6 Answer Choices A. Parietal lobe B. Occipital lobe C. Frontal lobe D. Temporal lobe

D. The region of the brain that processes olfactory sensation (smell) is the temporal lobe. The parietal lobe is for general sensations of pain, pressure, and touch (choice A is wrong), the occipital lobe processes visual sensation (choice B is wrong), and the frontal lobe controls voluntary movement and problem solving (choice C is wrong).

The relative refractory period of an action potential could be extended by which of the following? Question 28 Answer Choices A. Increasing the rate of voltage-gated Na+ channel inactivation B. Increasing the rate of voltage-gated K+ channel deactivation C. Decreasing the rate of voltage-gated Na+ channel inactivation D. Decreasing the rate of voltage-gated K+ channel deactivation

D. The relative refractory period results from the hyperpolarization of the membrane due to the slow deactivation of voltage-gated potassium channels. To extend the relative refractory period, we would need to decrease the rate of deactivation of these channels (i.e., make them deactivate even more slowly). This would result in an extended period of hyperpolarization where a greater stimulus would be required in order to fire an action potential (choice D is correct and choice B is wrong). Changing the rate of voltage-gated sodium channel inactivation would change the absolute refractory period, not the relative refractory period (choices A and C are wrong).

Which of the following statements is true about arteries but not about veins? Question 21 Answer Choices A. They have valves to maintain flow in a single direction. B. They carry only oxygen-rich blood. C. They are a low-pressure system of vessels. D. They have a muscle layer to regulate blood flow.

D. The walls of arteries contain a layer of muscle that can adjust the diameter of the artery to regulate blood flow to different regions of the body. Veins lack this muscle layer (choice D is true about arteries but not about veins and is the correct answer choice). Veins have valves, but arteries do not (choice A is true about veins, not arteries and can be eliminated). Most arteries carry oxygen-rich blood, but the pulmonary arteries carry oxygen-poor blood; likewise, most veins carry oxygen-poor blood, but the pulmonary veins carry oxygen rich blood (choice B is true of neither arteries nor veins and can be eliminated). Arteries are a high-pressure system and veins are a low pressure system (choice C is true about veins and can be eliminated).

A resident is asked to assist on his first surgery and starts to panic. Which of the following would be the LEAST likely response? Question 14 Answer Choices A. Increased heart rate B. Bronchial dilation C. Increased blood flow to skeletal muscle D. Pupillary constriction

D. When the resident is asked to assist on his first surgery, it triggers a fight-or-flight response, i.e., activates the sympathetic division of the autonomic nervous system. Increased heart rate, bronchial dilation, and increased blood flow to skeletal muscle are all typical responses of sympathetic activity (choices A, B and C are sympathetic responses and can be eliminated). Pupillary constriction is typical of a parasympathetic response (choice D is not a sympathetic response and is the correct answer choice).