Physio II: Neuro

1. At which point on the action potential shown in the figure below is the membrane closest to the Na+ equilibrium potential? a) Point A b) Point B c) Point C d) Point D e) Point E

**Not the same picture** Point A = repol. in picture

100. An 86-year-old woman develops unilateral vesicular eruption on the trunk in a T8 dermatomal pattern. Staining of the skin scrapings confirms a diagnosis of herpes zoster. The woman complains of significant pain, as well as increased sensitivity to touch. Which of the following receptors is responsible for measuring the intensity of a steady pressure on the skin surface? a. Krause ending b. Meissner corpuscle c. Merkel disk d. Pacinian corpuscle e. Ruffini ending

100. The answer is e. (Barrett, pp 158-160.) The Ruffini ending is a tonic receptor that produces a train of action potentials proportional to the intensity of pressure applied to the skin. The Pacinian corpuscle is a very rapidly adapting receptor that fires once or twice in response to skin deformation, but can produce a continuous train of action potentials if the stimulus is repetitively applied and withdrawn. Therefore, the Pacinian corpuscle is used to encode vibration.

101. A 41-year-old man complains to his physician about jet lag whenever he flies long distances to meetings. Melatonin is prescribed as a way to reset his circadian rhythm. The circadian rhythm is controlled by which of the following nuclei? a. Arcuate b. Lateral c. Paraventricular d. Suprachiasmatic e. Ventromedial

101. The answer is d. (Barrett, p 309. Le, p 62. Longo, p 214.) A variety of physiological functions, such as alertness (the sleep-wake cycle), body temperature, and secretion of hormones, exhibits cyclic activity that varies over a 24-hour period of time. These variations in activity are called circadian rhythms and are controlled by the suprachiasmatic nucleus of the hypothalamus. The paraventricular nucleus secretes oxytocin and vasopressin, the ventromedial and lateral nuclei control food intake, and the arcuate nucleus secretes gonadotropin-releasing hormone.

102. A 48-year-old woman with multiple sclerosis (MS) and increasing spasticity is treated with an intrathecal infusion of baclofen, a GABAB agonist that mediates presynaptic inhibition. Presynaptic inhibition in the central nervous system (CNS) affects the firing rate of α-motoneurons by which of the following mechanisms? a. Decreasing the frequency of action potentials by the presynaptic nerve ending b. Decreasing the potassium permeability of the α-motoneuron c. Hyperpolarizing the membrane potential of the α-motoneuron d. Increasing the amount of the neurotransmitter released by the presynaptic nerve ending e. Increasing the chloride permeability of the presynaptic nerve ending

102. The answer is e. (Barrett, pp 126-127. Widmaier, p 161.) Presynaptic inhibition is caused by interneurons that secrete a transmitter that increases the Cl − conductance of the presynaptic nerve ending. The increase in Cl − conductance causes a partial depolarization of the presynaptic nerve ending and a decrease in the magnitude of the action potential in the pre-synaptic nerve ending. Because the number of synaptic vesicles released from the presynaptic neuron is proportional to the magnitude of the action potential, fewer vesicles are released and magnitude of the postsynaptic potential is reduced. Reducing the magnitude of the postsynaptic potential decreases the probability that an action potential will be generated by the postsynaptic cell. Presynaptic inhibition does not change the membrane potential of the α-motoneuron.

104. A 24-year-old man complains of fatigue, increased daytime somnolence, and periodic sudden loss of muscle tone. Polysomnography confirms the diagnosis of narcolepsy. Narcolepsy is associated with which of the following? a. Decreased adenosine levels in the reticular formation b. Hypothalamic dysfunction with decreased CSF levels of orexins c. Increased discharge of noradrenergic neurons in the locus ceruleus d. Increased discharge of serotonergic neurons in the midbrain Raphé e. The presence of prions

104. The answer is b. (Barrett, p 276. Le, p 62. Longo, p 220.) Narcolepsy is associated with low CSF levels of the orexins and a defect in one of the receptors for orexins (hypocretins) in the hypothalamus. Adenosine induces sleep, and serotonin agonists suppress sleep. Fatal familial insomnia is a progressive prion disease, characterized by worsening insomnia, impaired autonomic and motor functions, dementia, and death.

117. A 59-year-old woman with bilateral glaucoma is treated with drops of the parasympathetic agent pilocarpine. Cholinergic stimulation of the pupil causes which of the following? a. Absence of the pupillary response to light b. Inequality of pupil size c. Pupillary constriction (miosis) d. Pupillary dilation (mydriasis) e. Tonic pupil (slow redilation after exposure to light)

117. The answer is c. (Barrett, p 260. Le, pp 233, 439, 449. Widmaier, p 205.) Parasympathetic stimulation or cholinergic muscarinic agonists used to treat glaucoma produce miosis, that is, pupillary constriction caused by contraction of the sphincter muscle of the iris. Anticholinergic agents (eg, atropine) or sympathetic stimulation produce mydriasis, that is, pupillary dilation, in which the increase in pupil size results from contraction of the radial muscle of the iris mediated by α1 -adrenergic receptors.

105. A 17-year-old boy is admitted to the hospital with a traumatic brain injury, sustained when he fell off his motorcycle. He develops a fever of 102.2°F (39°C), which is unrelated to an infection or inflammation. The fever is most likely due to a lesion of which of the following? a. Anterior hypothalamus b. Arcuate nucleus c. Lateral hypothalamus d. Paraventricular nucleus e. Posterior nucleus

105. The answer is a. (Barrett, p 309. Le, p 414.) The hypothalamus regulates body temperature. Core body temperature, the temperature of the deep tissues of the body, is detected by thermoreceptors located within the anterior hypothalamus. The anterior hypothalamus also contains neurons responsible for initiating reflexes, such as vasodilation and sweating, which are designed to reduce body temperature. Heat-producing reflexes, such as shivering, and heat-maintenance reflexes, such as vasoconstriction, are initiated by neurons located within the posterior hypothalamus. The posterior hypothalamus regulates catecholamine secretion. The paraventricular nucleus regulates TSH secretion. The lateral hypothalamus regulates thirst, and the arcuate nucleus exerts neuroendocrine control of prolactin secretion.

107. A 34-year-old woman, who has been immobilized with a sprained ankle for the past 4 days, develops a throbbing pain that has spread to her entire left leg. History reveals that she has been taking oral contraceptives for 15 years. Ischemic pain is associated with which of the following? a. A beta (Aβ) sensory fibers b. Afferent pathway in the neospinothalamic tract c. Overstimulation of somatic touch receptors d. Rapidly adapting receptors e. Sensory fibers terminating within the substantia gelatinosa of the dorsal horn of the spinal cord

107. The answer is e. (Barrett, p 15 Le, p 428. Longo, pp 93-97.) Activating nociceptors on the free nerve endings of C fibers produces ischemic pain. The C fibers synapse on interneurons located within the substantia gelatinosa (laminas II and III) of the dorsal horn of the spinal cord. The pathway conveying ischemic pain to the brain is called the paleospinothalamic system. In contrast, well-localized pain sensations are carried within the neospinothalamic tract. Ischemic pain does not adapt to prolonged stimulation. Pain is produced by specific nociceptors and not by intense stimulation of other mechanical, thermal, or chemical receptors.

108. A 42-year-old man sees his ophthalmologist because it is becoming increasingly difficult for him to read the newspaper. His vision problem most likely results from an inability to contract which of the following? a. Ciliary body b. Extraocular muscles c. Iris d. Pupils e. Suspensory ligaments

108. The answer is a. (Barrett, p 188. Le, pp 321, 439. Widmaier, pp 204-205.) The ciliary body contains the ciliary muscle, which changes the shape of the lens when your eyes focus on something, a process called accommodation. Contracting the ciliary body increases the refractive power of the eye for near vision. When the ciliary muscle contracts, it pulls the suspensory ligaments toward the cornea, which causes the lens surface to bulge, increasing its refractive power. Contraction of the ciliary muscle, which causes short-range focus, is mediated by M3 cholinergic muscarinic receptors, and relaxation of the ciliary muscle, which causes long-range focus, is mediated by β2 -adrenergic receptors. The muscles of the iris control the size of the pupils, and the extraocular muscles control the position of the eye in the socket. Sympathetic activation causes dilation of the pupil (mydriasis) by stimulating α1 -adrenergic receptors, which lead to contraction of the radial muscle in the iris of the eye. Parasympathetic stimulation causes constriction of the pupil (miosis) due to contraction of the circular muscle in the eye mediated by M3 cholinergic muscarinic receptors.

109. At a first-grade parent-teacher conference, the teacher of a 6-year-old boy indicates that the boy seems to have difficulty hearing. His parents take him to the pediatrician, who refers the boy to an otolaryngologist. The boy is found to have a significant hearing deficit accompanying a middle ear infection that also involves the middle ear bones. Which of the following is the primary function of the middle ear bones? a. Amplifying sounds b. Enhancing frequency discrimination c. Filtering high-frequency sounds d. Localizing sound e. Protecting the ear from load sounds

109. The answer is a. (Barrett, p 206. Widmaier, pp 213-215.) When sound waves pass from air to water, most of the energy contained in the sound stimulus is lost. Because the auditory receptors within the inner ear are bathed in liquid, most of the energy in the sound stimulus could be lost as the sound travels from air to water. The bones of the middle ear significantly reduce the amount of loss by amplifying the sound stimulus. Audiologists refer to this amplification phenomenon as impedance matching. Sound localization is carried out by the CNS, which integrates information from both ears. Frequency discrimination is a function of the basilar membrane. The stapedius and tensor tympani muscles protect the ear from loud sounds.

110. The morning after a rock concert, a 20-year-old college student notices difficulty hearing his professor during lecture. The physician at the student health center suspects possible damage to his hair cells by the loud music. Depolarization of the hair cells in the cochlea is caused primarily by the flow of which of the following? a. Ca2+ into the hair cell b. Cl− out of the hair cell c. K+ into the hair cell d. K+ out of the hair cell e. Na+ into the hair cell

110. The answer is c. (Barrett, pp 202-203. Widmaier, pp 215-216.) When the hair cells are bent, K+-selective channels open, K+ flows into the cell, and the cell depolarizes. This unusual situation occurs because the apical surface of the hair cells, on which the stereocilia are located, is bathed in endolymph, which contains a high concentration of K+. Moreover, the endolymph is positively charged with respect to the perilymph, which surrounds the basal lateral portion of the hair cell. Because the intracellular concentration of K+ is similar to the extracellular concentration of K+ , the electrical gradient determines the direction of K+ flow. Because the endolymph is positively charged and the intracellular fluid is negatively charged, K+ flows into the cell.

128. A 62-year-old man with COPD presents to the emergency room in respiratory distress. The attending physician uses succinylcholine to produce skeletal muscle relaxation prior to tracheal intubation. Soon after infusion of the succinylcholine, the patient develops a severe bradycardia. Which of the following drugs would counteract the bradycardia without affecting muscle relaxation? a. Acetylcholine b. Atropine c. Curare d. Dopamine e. Epinephrine

128. The answer is b. (Barrett, p 261.) Succinylcholine is a rapidly acting neuromuscular-blocking agent with a very short duration of action. Respiratory paralysis can be produced in less than 60 seconds and normal respiration typically returns within 15 minutes. Because succinylcholine can also stimulate autonomic postganglionic fibers, vagal fibers innervating the heart are stimulated. The vagal fibers release acetylcholine, which binds to muscarinic receptors on the SA node, slowing down the heart. The bradycardia can be prevented by administering atropine, which blocks the muscarinic receptors on the SA node.

111. A 62-year-old man with a history of hypertension and hyperlipidemia is admitted to the hospital for evaluation after demonstrating signs and symptoms of a stroke. Subsequent CT scans, perceptual tests, and a neurological examination provide evidence for impairment of the otolith pathways. The otolith organs (utricle and saccule) are responsible for which of the following? a. Detecting angular acceleration b. Detecting the position of the head in space c. Producing rotary nystagmus d. Producing the stretch reflex e. Producing the vestibulo-ocular reflex

111. The answer is b. (Barrett, pp 211-212, 183-184. Widmaier, p 201.) The otolith organs provide information about the position of the head with respect to gravity. When the head is bent away from its normal upright position, otoliths (small calcium carbonate crystals within the utricle and saccule) are pulled downward by gravity. The crystals bend the stereocilia on the hair cells, causing the hair cells to depolarize. Depolarization of the hair cells stimulates the vestibular nerve fibers. Bending the head in different directions causes different otoliths to move. Therefore, the particular group of vestibular nerve fibers that is stimulated signals the direction in which the head bends.

112. A 27-year-old man with severe epilepsy, characterized by major convulsions and lapses of consciousness every few minutes, underwent experimental neurosurgery to help relieve his seizures. The operation had a significant, beneficial effect on the epilepsy, but led to a devastating memory deficit. He had normal procedural memory, maintained long-term memory for events that occurred prior to surgery, and his short-term memory was intact, but he could not commit new events to long-term memory (loss of declarative memory). Which of the following areas of the brain was bilaterally resected in this patient? a. Cerebral cortex b. Cingulate gyrus c. Hypothalamus d. Parietal lobe e. Temporal lobe

112. The answer is e. (Barrett, pp 283-285.) The patient underwent bilateral surgical removal of the amygdala, large portions of the hippocampal formation, and portions of the association area of the temporal cortex. He died in 2008. His case was the first to bring attention to the critical role of the temporal lobes in formation of long-term declarative memories and to implicate this region in the conversion of short- to long-term memories. Later work showed that the hippocampus is the primary structure within the temporal lobe involved in this conversion. Because the patient retained memories from before surgery, his case also shows that the hippocampus is not involved in the storage of declarative memory.

113. A 68-year-old man with avitaminosis A presents with a chief complaint of night blindness (nyctalopia). Which of the following reactions in the retinal rods is caused directly by the absorption of light energy? a. Decomposition of scotopsin b. Dissociation of scotopsin and metarhodopsin c. Transformation of 11-cis retinal to all-trans retinal d. Transformation of metarhodopsin to lumirhodopsin e. Transformation of vitamin A to retinene

113. The answer is c. (Barrett, pp 183-184.) The light-sensitive chemical in the retinal rods is called rhodopsin. It is a combination of 11-cis retinal and opsin. The photoisomerization of 11-cis retinal to all-trans retinal activates rhodopsin. The subsequent separation of opsin and retinal and the reformation of 11-cis rhodopsin are not necessary for the activation of the visual receptors. Rhodopsin cannot absorb another photon of light, however, until it is enzymatically isomerized back to its 11-cis conformation.

114. A 20-year-old boxer presents at a neurologist's office complaining of dizziness and a problem with his balance. He indicates that in a recent match, he suffered several blows to the ears. Which of the following normally happens when a person slowly rotates toward the right? a. Both the left and right eyes deviate toward the left b. The endolymph in the left and right horizontal semicircular canals moves in opposite directions c. The hair cells in the left horizontal semicircular canal become depolarized d. The stereocilia on the hair cells in the right horizontal semicircular canal bend away from the kinocilium e. The visual image on the retina becomes unfocused

114. The answer is a. (Barrett, pp 211-212.) When the head rotates in one direction, the hair cells mounted on the cristae rotate along with the head. However, the flow of endolymph is delayed and as a result, the cupula is moved in a direction opposite to the movement of the head. When the head moves to the right, the cupula moves toward the left; this bends the stereo-cilia on the hair cells in the right horizontal canal toward the kinocilium and bends the stereocilia on the hair cells in the left horizontal canal toward the kinocilium. As a result, the hair cells in the right horizontal canal depolarize and those in the left horizontal canal hyperpolarize. The depolarization of the hair cells in the right horizontal canal stimulates the right vestibular nerve, which in turn causes the eyes to deviate toward the left. The movement of the eyes toward the left as the head deviates toward the right keeps the image on the retina in focus.

115. A 58-year-old woman goes to her physician because she is having difficulty threading needles. An eye examination leads to the diagnosis of presbyopia (old eyes). Her condition is most likely caused by which of the following? a. Ciliary muscle paralysis b. Clouding of the vitreous c. Degeneration of the macula d. Retinal detachment e. Stiffening of the lens

115. The answer is e. (Barrett, p 188. Longo, p 224. Widmaier, pp 204-205.) The increase in lens power that normally occurs when objects are placed close to the eye (the accommodation reflex) does not take place in presbyopia. The failure of the accommodation reflex occurs because the lens and lens capsule stiffen with age. There are some reports of ciliary muscle weakness accompanying presbyopia, but there are none indicating that presbyopia is caused by ciliary muscle paralysis.

116. An 8-year-old boy is hit in the head by a baseline drive during a little league game. His father, a doctor, rushes out on the field to do a neurological assessment, including use of his penlight to check reactivity of the pupils. When light strikes the eye, which of the following normally increases? a. The activity of transducin b. The amount of transmitter released from the photoreceptors c. The concentration of all-trans retinal within the photoreceptors d. The concentration of calcium within the photoreceptors e. The activity of guanylyl cyclase

116. The answer is a. (Barrett, p 184.) Transducin is the G protein activated by rhodopsin when light strikes the eye. Transducin activates a phosphodiesterase that hydrolyzes cGMP. When cGMP concentrations within the rods or cones decrease, sodium channels close, sodium conductance decreases, and the cell membrane potential becomes more negative (hyper-polarizes). Hyperpolarization of the cell causes a decrease in the release of neurotransmitter. Eventually, the all-trans retinal dissociates from opsin and reduces the concentration of rhodopsin in the cell.

Administration of which of the following drugs is contraindicated in a 10-year-old child with a history of asthma? A. Albuterol B. Epinephrine C. Isoproterenol D. Norepinephrine E. Propranolol

E. Propranolol

118. A 20-year-old woman complains of altered taste following extraction of her wisdom teeth. Which of the following is the most likely cause of the dysgeusia? a. A disturbed salivary milieu b. Damage to the central gustatory pathways c. Damage to the gustatory afferent nerves d. Impaired transport of the tastant to the receptor cells in the taste bud e. Injury to the taste receptor cells

118. The answer is c. (Barrett, p 222. Longo, pp 244-246.) Trauma to the chorda tympani branch of the facial nerve during third molar extractions or middle ear surgery is relatively common and can cause dysgeusia. Other mechanisms of disorders of the sense of taste, besides damage to the gustatory afferent nerves, include damage to central gustatory pathways (trauma, diabetes mellitus, hypothyroidism, stroke, CNS disorders), sensory losses (aging, Candidiasis, viral infections, many drugs especially those that interfere with cell turnover such as antineoplastic and antithyroid agents), and transport gustatory losses (interference with access of tastant to receptor cells, such as with xerostomia, Sjögren syndrome, heavy metal intoxication, oral radiation therapy). No effective therapies exist for the sensorineural disorders of taste. Altered taste due to surgical stretch of the chorda tympani nerve usually improves within 3 to 4 months.

119. A 52-year-old man has a motor vehicle accident and closed head injury, after which he notes decreased sense of smell. Anosmia after head injury is most likely associated with which of the following? a. Direct injury to the olfactory bulbs b. Fractures of the cribriform plate c. Low Glasgow coma scale d. Recovery of olfaction over time to baseline e. Shearing of the olfactory fila as they pass through the cribriform plate

119. The answer is e. (Longo, p 244.) "The physiologic basis for most head trauma-related smelling losses is the shearing and subsequent scarring of the olfactory fila as they pass from the nasal cavity into the brain cavity. The cribriform plate does not have to be fractured or show pathology for smell loss to be present. Severity of trauma, as indexed by a poor Glasgow Coma Rating on presentation, and the length of posttraumatic amnesia, is associated with a higher risk of olfactory impairment. Fewer than 10% of posttraumatic anosmic patients recover age-related normal function over time."

120. A Jewish couple present at the pediatrician's office with concerns about their 6-month-old child. They report that the infant was perfectly fine for the first few months of life, but lately he is very easily startled by noise, he has difficulty swallowing, he can no longer hold his head up, and he had a seizure earlier in the day. On physical examination, the doctor also notes "cherry-red" spots in the child's eyes. These symptoms are due to the accumulation of harmful quantities of which of the following substances in the brain? a. Beta-amyloid b. Beta-hexosaminidase A c. Ganglioside GM2 d. Sphingomyelin e. Tau protein

120. The answer is c. (Le, pp 112, 566. http://www.ninds.nih.gov/disorders/taysachs/taysachs.htm. http://www.ninds.nih.gov/disorders/niemann/niemann.htm.) Tay- Sachs disease is a fatal autosomal recessive lipid storage disorder in which harmful quantities of a fatty substance called ganglioside GM2 build up in tissues and nerve cells in the brain. The condition is caused by insufficient activity of the enzyme beta-hexosaminidase A, which catalyzes the biodegradation of acidic fatty materials known as gangliosides. Gangliosides are made and biodegraded rapidly in early life as the brain develops. Infants with Tay-Sachs disease appear to develop normally for the first few months of life. Then, as nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. The child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in. Other neurological symptoms include dementia, seizures, and an increased startle reflex to noise. A much rarer form of the disorder occurs in patients in their 20s and early 30s and is characterized by an unsteady gait and progressive neurological deterioration. Persons with Tay-Sachs also have "cherry-red" spots in their eyes. The incidence of Tay-Sachs is particularly high among people of Eastern European and Ashkenazi Jewish descent. Patients and carriers of Tay-Sachs disease can be identified by a simple blood test that measures beta- hexosaminidase A activity. Both parents must carry the mutated gene in order to have an affected child. In these instances, there is a 25% chance with each pregnancy that the child will be affected with Tay-Sachs disease. Prenatal diagnosis is available if desired. Another inherited lipid storage disease is Niemann-Pick (NP) disease. NP has four types. In types A and B, insufficient activity of the enzyme sphingomyelinase causes the buildup of toxic amounts of sphingomyelin, a fatty substance present in every cell of the body. Types C and D are characterized by a defect that disrupts the transport of cholesterol between brain cells and are caused by a lack of the NPC1 or NPC 2 proteins. Beta-amyloid plaques and neurofibrillary tangles of tau protein accumulate in the brains of patients with Alzheimer disease.

121. A 24-year-old male medical student develops apprehension, restlessness, tachycardia, and tachypnea as he enters the testing center for his initial licensure examination. Activation of which of the following receptors would be expected to decrease his anxiety? a. GABAA b. Glutamate c. Histamine d. Neurokinin 1 (NK-1, substance P) e. Neuropeptide Y

121. The answer is a. (Barrett, pp 143, 149-151.) Gamma-aminobutyric acid (GABA) is the major inhibitory mediator in the brain. GABAA receptors are pentameric Cl − ion channels that are widely distributed in the CNS. The increase in Cl − conductance produced by GABAA receptors is potentiated by the anxiolytic drug, diazepam, and other benzodiazepines. Gluta-mate is the major excitatory transmitter in the brain. Neuropeptide Y is an excitatory neurotransmitter that has a stimulatory effect on food intake. CNS actions of histamine have been implicated in arousal, sexual behavior, drinking, pain thresholds, and the sensation of itch. Antagonism of central NK-1 receptors has antidepressant activity in humans.

122. A 26-year-old African American female medical student goes to the emergency department when she sees flashes of light, moving spots, and has reduced visual acuity. An ophthalmology consult reveals that she is myopic, does not have eye pain, and has a scotoma in the peripheral vision field of her right eye. There is no cherry red spot on the fovea. Which of the following is the most likely cause for her acute vision loss? a. Central retinal artery embolism b. Glaucoma c. Macular degeneration d. Optic neuritis e. Retinal detachment

122. The answer is e. (Kaufman, p 348. Le, p 441. Longo, pp 230, 232-235.) Among the causes of acute vision loss, detachment of the retina is painless, and accompanied by floaters, flashing lights, and a scotoma in the peripheral visual field corresponding to the detachment. The diagnosis is confirmed by ophthalmoscopic examination of the dilated eye. Patients with a history of myopia, trauma, or prior cataract extraction are at greatest risk for retinal detachment. Another cause of sudden painless vision loss is a transient ischemic attack of the retina, also called amaurosis fugax. Amaurosis fugax usually results from an embolus that lodges in a retinal arteriole. Complete occlusion of the central retinal artery produces arrest of blood flow and a milky retina with a cherry red spot on the fovea. Optic neuritis is a common inflammatory disease of the optic nerve that is accompanied by eye pain, especially with eye movements. It is caused by demyelination, and often progresses to MS. Glaucoma and macular degeneration cause chronic vision loss. Glaucoma is the leading cause of blindness in African Americans; it is a slowly progressive, insidious optic neuropathy. Macular degeneration is the major cause of gradual, painless, bilateral central blindness in the elderly.

129. A fireman suffers extensive burns, resulting in a fluid and electrolyte imbalance. Which of the following electrolyte imbalances will produce a decrease in the magnitude of a nerve membrane action potential? a. Hyperkalemia b. Hypernatremia c. Hypocalcemia d. Hypokalemia e. Hyponatremia

129. The answer is e. (Barrett, pp 87-89. Kaufman, pp 246-247.) The upstroke of the action potential is caused by an inward flow of sodium ions, and therefore its magnitude depends on the extracellular sodium concentration. Decreasing the external Na+ concentration decreases the size of the action potential, but has little effect on the resting membrane potential because the permeability of the membrane to Na+ at rest is low. Conversely, increasing the external K+ concentration decreases the resting membrane potential. Changes in external Ca2+ concentration affect the excitability of nerve and muscle cells, but not the magnitude of the resting potential or the action potential.

123. After sitting with one leg crossed under the other for several hours while working on a document at her computer terminal, a 52-year-old woman tries to stand up, but is unable to walk on the crossed leg, and feels tingling and pain. Which of the following explains the loss of motor function without the loss of pain sensation in the peripheral nerves? a. A fibers are more susceptible to local anesthetics than C fibers b. Aβ fibers are more sensitive to pressure than C fibers c. C fibers are more sensitive to pressure than Aβ fibers d. C fibers are more susceptible to hypoxia than B fibers e. C fibers have higher conduction velocities than A fibers

123. The answer is b. (Barrett, pp 92-93.) Mammalian nerve fibers are classified into A, B, and C groups, and A fibers are further subdivided into α, β, γ, and δ fibers, each of which has different histologic characteristics and functions. Aβ fibers have touch, pressure, and motor functions. The dorsal root C fibers conduct some impulses generated by touch and other cutaneous receptors, as well as impulses generated by pain and temperature receptors. Aβ fibers are most susceptible to pressure and C fibers are least susceptible to pressure, which explains why a limb with a transiently compressed nerve loses motor function, but not pain sensation. B fibers are preganglionic autonomic nerves; they are most susceptible to hypoxia, whereas C fibers are least susceptible to hypoxia. Local anesthetics depress transmission in the group C fibers before they affect the touch fibers in the A group. C fibers are unmyelinated, whereas A and B fibers are myelinated. In addition, C fibers generally have smaller diameters than A or B fibers. For both reasons, C fibers have lower conduction velocities than A fibers.

124. Three weeks following a gastrointestinal (GI) infection with Campylobacter jejuni, a 60-year-old man develops weakness and tingling in his legs. Over the next few days, his legs and face become paralyzed, and he is hospitalized for Guillain-Barré syndrome (GBS). Which of the following is the most likely underlying cause of his motor paralysis? a. Antibodies against nerve growth factor b. Antibodies against oligodendrogliocytes c. Demyelination of Aβ fibers d. Demyelination of B fibers e. Demyelination of C fibers

124. The answer is c. (Barrett, pp 92-93. Kaufman, pp 343-344. Le, pp 136, 412, 444, 569. Longo, pp 3473-3477.) GBS is an acute, rapidly evolving inflammatory demyelinating polyradiculopathy that generally manifests as an areflexic ascending motor paralysis and is autoimmune in nature. The basis for the flaccid paralysis and sensory disturbance is conduction block in the Aβ fibers; axonal conduction remains intact unless there is secondary axonal degeneration. Most cases are preceded by a viral upper respiratory infection or a GI infection. Twenty to thirty percent of all cases occurring in North America, Europe, and Australia are preceded by infection or reinfection with C. jejuni. A similar proportion is preceded by a herpes virus infection, often CMV or Epstein-Barr virus. The postulated immunopathogenesis of GBS associated with C. jejuni infection involves production of autoantibodies against gangliosides present on the surface of Schwann cells, causing widespread myelin damage. The widespread administration of the swine influenza vaccine in the United States in 1976 was associated with an increased occurrence of GBS, but influenza vaccines in use from 1992 to 1994 resulted in only one additional case of GBS per million persons vaccinated. Older-type rabies vaccines prepared in nervous system tissue are still used in developing countries and are thought to be a trigger for GBS, presumably via immunization of neural antigens. Nerve growth factor is necessary for the growth and maintenance of sympathetic neurons and some sensory neurons, not motoneurons. Experimental injection of antiserum against nerve growth factor in newborn animals produces immunosympathectomy. Oligodendrocytes are involved in myelin formation in the CNS, whereas Schwann cells are involved in myelin formation in peripheral nerves.

126. A 26-year-old woman presents with unilateral facial weakness. She states that whenever she tries to close her eyes, the upper eyelid on the affected side rolls upward. Electromyography on the affected side shows evidence of axonal degeneration. Which of the following characteristics of an axon is most dependent on its diameter? a. The magnitude of its resting potential b. The duration of its refractory period c. The conduction velocity of its action potential d. The overshoot of its action potential e. The activity of its sodium-potassium pump

126. The answer is c. (Barrett, pp 87-92. Longo, pp 3362-3363.) The conduction velocity of an action potential along an axon is proportional to the axon's diameter for both nonmyelinated and myelinated axons. For any given axon diameter, conduction velocity is greater in myelinated than in nonmyelinated fibers. Propagation via saltatory conduction in myelinated fibers is faster than propagation in nonmyelinated fibers of the same axon diameter because less charge leaks out through the myelin-covered sections of the membrane. Conduction velocities range from about 0.5 m/s for small-diameter unmyelinated fibers to about 100 m/s for large-diameter myelinated fibers. The resting membrane potential, the duration of the relative refractory period, and the magnitude of the action potential are dependent on the type and density of electrically excitable gates and the ability of the Na + -K + -ATPase to establish and maintain the concentration gradients. These characteristics are not related in any systematic way to the axon diameter. Bell palsy is the most common form of facial paralysis. This idiopathic disorder has a fairly abrupt onset with maximal weakness attained within about 48 hours. MRI may reveal swelling of the geniculate ganglion and facial nerve. If denervation is evident on electromyography indicating axonal degeneration, it can take up to 3 months or longer for regeneration and recovery to occur.

127. An 80-year-old farmer presented with complaints of weakness and fatigue, aching, orthostatic hypotension, constipation, and sleep disturbances. His family physician told him that he was just getting old, and would have to get used to it. His bradykinesia worsened and he couldn't pick up his feet when he walked. When he was no longer able to plow his own fields, he got depressed, and his wife said he would just sit at the table and rub his thumb along his fingers. She called her son-in- law, a neurologist, and asked him if he'd come out to the country to evaluate "Pops." The pathophysiology of Parkinson disease can be attributed to a paucity of which of the following neurotransmitters? a. Acetylcholine b. Dopamine c. Glutamate d. Neuropeptide Y e. Serotonin

127. The answer is b. (Barrett, pp 245-248. Le, pp 413, 416-417, 569-571. Longo, pp 3317-3321.) Parkinson disease results from a reduction of dopaminergic transmission within the basal ganglia, generally due to degeneration of nigrostriatal dopaminergic neurons. The fibers going to the putamen are most severely affected. Dopaminergic neurons and receptors are steadily lost with age in the basal ganglia, but an abnormal acceleration of that process results in Parkinson disease. The diagnosis of Parkinson disease can generally be made with at least two of the cardinal signs of parkinsonism, which are resting tremor, paucity and slowness of movement (bradykinesia), rigidity, and postural instability (falls).

130. A 19-year-old woman with a history of diplopia and paresthesia is diagnosed with MS. Immersion of an affected limb in a cold bath restores nerve conduction in many MS patients. The explanation often cited for this effect is that cold increases the duration of the action potential. Which of the following best explains why increasing the duration of the action potential can restore nerve conduction in patients with MS? a. The amount of sodium entering the nerve with each action potential increases b. The capacitance of the nerve fiber membrane is increased c. The duration of the refractory period is increased d. The potassium conductance of the membrane is increased e. The membrane potential becomes more positive

130. The answer is a. (Barrett, pp 87-92. Le, p 444.) In order for propagation of an action potential to occur, the depolarization produced by one action potential must depolarize the adjacent patch of excitable membrane to the threshold level. In demyelinating diseases, such as MS, too much charge leaks from the membrane and as a result, not enough charge is available to bring the next patch of membrane to threshold. Increasing the duration of the action potential increases the amount of charge entering the cell, and therefore increases the probability that the next patch of excitable membrane will be depolarized to threshold. Increasing the duration of the refractory period will not affect the amount of charge entering the cell. Depolarizing the membrane and increasing potassium conductance will make it more difficult to produce an action potential. If membrane capacitance is increased, the amount of charge required to excite the next patch of membrane will be increased.

131. A 37-year-old woman presents with severe migraine headaches that are accompanied by hemiparalysis. Genetic analysis confirms the suspicion of an inherited channelopathy. The membrane potential will depolarize by the greatest amount if the membrane permeability increases for which of the following ions? a. Chloride b. Potassium c. Sodium d. Chloride and potassium e. Sodium and potassium

131. The answer is c. (Barrett, pp 87-92. Longo, p 3325. Widmaier, pp 142-156.) When the permeability of a particular ion is increased, the membrane potential moves toward the equilibrium potential for that ion. The equilibrium potential for sodium (+60 mV) is much greater than the resting membrane potential. Thus, increasing the permeability for sodium causes a large depolarization. The equilibrium potentials for chloride (−80 mV) and potassium (−92 mV) are close to the resting membrane potential, so increases in their permeability have little effect on the resting membrane potential. The resting potentials of neurons and the action potentials responsible for impulse conduction are generated by ion currents and ion channels. Disorders of ion channels, that is, channelopathies, are responsible for a growing number of neurologic diseases. Mutations in Na + , K + , and Ca ++ channels that alter ion permeability are associated with migraine and epilepsy.

132. A 65-year-old postgastrectomy patient presents to his gastroenterologist's office with fatigue, weakness in his legs, and frequent falls over the past several months. His physical examination demonstrates increased deep tendon reflexes and decreased vibratory sense in his toes. Laboratory analysis reveals megaloblastic anemia and vitamin B12 deficiency. Which of the following mechanisms cause the neurological deficits characteristic of vitamin B12 deficiency? a. Decreased folate concentration b. Decreased myelin synthesis c. Decreased Na+-K+ pump activity d. Increased hyperphosphorylated microtubule protein tau e. Production of antinerve antibodies (ANA)

132. The answer is b. (Le, pp 93, 354. Longo, pp 3374, 3467. Widmaier, pp 418-419, 527.) Vitamin B12 is necessary for normal neurological function because it is involved in myelin synthesis and repair. Vitamin B12 deficiency causes damage to the white matter of the spinal cord and peripheral neuropathy. Treatment consists of vitamin B12 administration. Although folate may be an adequate substitute for treatment of the megaloblastic anemia characteristic of vitamin B12 deficiency, folate should not be used instead of vitamin B12 because the neurological deficits will persist and progress. Vitamin B12 does not modulate the sodium/potassium pump. Tau hyper-phosphorylation causes neuritic tangles, as seen in the brains of dementia patients. Vitamin B12 or its deficiency does not stimulate formation of ANA.

133. A 52-year-old man presents at the oral surgeon's office with an abscessed tooth. Prior to surgery to extract the tooth, the patient is given a shot of procaine. Preventing the inactivation of sodium channels by local anesthetics will decrease which of the following? a. Downstroke velocity of nerve cell action potentials b. Duration of nerve cell action potentials c. Magnitude of the overshoot in nerve cell action potentials d. Relative refractory period of nerve cells e. Upstroke velocity of nerve cell action potentials

133. The answer is a. (Barrett, pp 87-91. Widmaier, p 152.) The repolarization phase of the action potential is produced by a decrease in Na+ conductance caused by the inactivation of Na+ channels, and the increase in K+ conductance due to the activation of K+ channels. Preventing the inactivation of Na+ channels will decrease the downstroke velocity of the action potential. This will slow down the normal repolarization phase of the action potential and thereby prolong the duration of the action potential. The relative refractory period is prolonged because of the prolonged duration of the action potential. The upstroke velocity and the magnitude depend on how rapidly and how long the sodium channels are opened. By preventing inactivation of the Na+ channel, the rate of the upstroke and the magnitude of the overshoot may be increased.

134. A 13-year-old boy on the junior high wrestling team experienced attacks of proximal muscle weakness that lasted from 30 minutes to as long as 4 hours following exercise and fasting. The trainer attributed it to the symptoms of fatigue, but his mother recalled having similar symptoms when she was on a diet and exercise regime. Genetic testing revealed an inherited channelopathy. Electrically excitable gates are normally involved in which of the following? a. Depolarization of the end-plate membrane by acetylcholine b. Hyperpolarization of rods by light c. Increase in nerve cell potassium conductance caused by membrane depolarization d. Release of calcium from ventricular muscle sarcoplasmic reticulum e. Transport of glucose into cells by a sodium-dependent, secondary active transport system

134. The answer is d. (Barrett, pp 49, 54. Longo, p 3325.) Electrically excitable gates are those that respond to a change in membrane potential. The most notable electrically excitable gates are those on the sodium and potassium channels that produce the nerve action potential. The potassium channel gate is opened by depolarization. Ventricular muscle sarcoplasmic reticulum releases its calcium in response to an increase in intracellular calcium. The gates opened by ACh are chemically excitable gates. In rods, sodium channels are closed when cGMP is hydrolyzed. Electrically excitable gates do not regulate the active transport of glucose.

135. A 58-year-old man with a history of hypertension and renal disease presents at his physician's office with a complaint of headaches. His blood pressure is 190/115 mm Hg and laboratory results show an elevated plasma renin activity with hypernatremia. Which of the following best describes the sodium gradient across the nerve cell membrane? a. It is a result of the Donnan equilibrium b. It is maintained by a Na+/Ca2+ exchanger c. It is significantly changed during an action potential d. It is the primary determinant of the resting membrane potential e. It is used as a source of energy for the transport of other ions

135. The answer is e. (Barrett, pp 8, 51-53, 87-91. McPhee and Hammer, pp 615-618. Widmaier, pp 100-104.) The sodium-potassium pump uses the energy contained in ATP to maintain the sodium gradient across the membrane. The sodium gradient, in turn, is used to transport other substances across the membrane. For example, the Na/Ca exchanger uses the energy in the sodium gradient to help maintain the low intracellular calcium required for normal cell function. Although sodium enters the cell during an action potential, the quantity of sodium is so small that no significant change in intracellular sodium concentration occurs. Because the sodium transference is so low, the sodium equilibrium potential is not an important determinant of the resting membrane potential. Recall that transference is a measure of an ion's relative conductance: where T is the transference and g is the conductance.

136. A 19-year-old sexually active woman presents with lower abdominal pain for 1 week. Physical examination reveals a temperature of 101°F (38.33°C), tenderness on pelvic examination, and a mucopurulent vaginal discharge. Synaptic transmission between pain fibers from the pelvis and spinal cord neurons is mediated by which of the following? a. Acetylcholine b. Endorphins c. Serotonin d. Somatostatin e. Substance P

136. The answer is e. (Barrett, p 150. Le, pp 173. Longo, pp 1104-1107.) Pain is the most common presenting symptom, and thus understanding pain is essential to the goals of relieving suffering, as well as preserving and restoring health. The function of the pain sensory system is to protect the body by detecting, localizing, and identifying tissue-damaging processes. Different diseases produce characteristic patterns of tissue damage; the resultant manifestations of pain and tenderness can provide important diagnostic clues and can also be used to evaluate treatment regimens. Pelvic inflammatory disease is an infection of the upper genital structures in women (uterus, ovaries, oviducts) often with involvement of neighboring organs, which is generally accompanied by lower abdominal pain with pelvic, adnexal, and cervical motion tenderness. Peripheral nerves consist of primary sensory afferent axons, motoneurons, and sympathetic post-ganglionic neurons. Primary sensory afferent nerves include those with large-diameter A-beta (Aβ), which normally are not involved in pain, as well as two populations of primary afferent nociceptors, the small-diameter myelinated A-delta (Aδ) and unmyelinated (C fiber) axons, both of which are present in nerves to the skin and to deep somatic and visceral structures. Many Aδ and C fibers innervating viscera are completely insensitive in normal, uninjured, noninflamed tissue, but become sensitive to mechanical stimuli in the presence of inflammatory mediators. An important concept to emerge in recent years is that afferent nociceptors also have a neuroeffector function, in that they contain polypeptide mediators that are released from their nerve terminals when activated. Most notably, substance P, an 11-amino acid polypeptide found in neurons within the hypothalamus and spinal cord, is released from small Aδ and C fibers that relay information from nociceptors to neurons within the substantia gelatinosa of the spinal cord. The biologic actions of substance P include vasodilation, neurogenic edema and the accumulation of bradykinin, the release of histamine from mast cells, and the release of serotonin from platelets. Endorphins and other opioid peptides such as the enkephalins may partially inhibit the perception of pain by presynaptically inhibiting the release of substance P from nociceptor afferent fibers.

137. A 16-year-old, highly allergic girl who is stung by a bee gives herself a shot of epinephrine prescribed by her physician. Because epinephrine activates β- adrenergic receptors, it will relieve the effects of the bee sting by decreasing which of the following? a. Contraction of airway smooth muscle b. Rate of depolarization in the SA node c. Rate of glycogenolysis in the liver d. Strength of ventricular muscle contraction e. Transport of calcium into skeletal muscle fibers

137. The answer is a. (Barrett, pp 145-147, 357-358, 447. Longo, pp 2709-2710.) Epinephrine (adrenalin) acts on both α-and β-adrenergic receptors, but has a greater affinity for β-adrenergic receptors. Activation of β2 -adrenergic receptors leads to relaxation of smooth muscle in the bronchi, vasculature, intestine, uterus, and bladder; to increased pancreatic insulin and glucagon secretion; and an increase in liver glycogenolysis. The bronchodilator effects of epinephrine are key in the treatment of the life-threatening effects of anaphylactic shock. Activation of β1 - and β-2 -adrenergic receptors in the heart leads to an increase in the rate of SA nodal phase 4 depolarization and thus heart rate (positive chronotropic response), an increase in contractility (positive inotropic response), an increase in conduction velocity (positive dromotropic response), and an increase in cardiac excitability/irritability. The transport of Ca 2+ into skeletal muscle fibers is not affected by β-receptors. The effects of epinephrine-induced β-adrenergic receptor activation are due to G-protein-mediated activation of adenylate cyclase, which catalyzes the formation of cyclic adenosine monophosphate and activation of protein kinase A.

138. A 10-year-old girl with type I diabetes develops a neuropathy of sensory neurons with free nerve endings. As a result, quantitative sensory testing will reveal higher-than-normal thresholds for detection of which of the following stimuli? a. Fine touch b. Muscle length c. Pressure d. Temperature e. Vibration

138. The answer is d. (Barrett, pp 92-93, 158-160.) Free nerve endings are small diameter nerves that contain receptors for temperature, pain, and crude touch. Fine touch, pressure, and vibration are detected by nerve endings contained within specialized capsules that transmit the stimulus to the sensory receptors. Muscle length is encoded by the primary nerve endings of Ia fibers, which are located on intrafusal fibers within the muscle spindle.

139. An 85-year-old man is brought to his doctor by his daughter. She reports that he has memory loss, is often confused, and has been having increasing difficulty with routine activities that he used to do on his own, such as paying bills and going grocery shopping. She wonders if this is just because of old age or a more serious problem. Which of the following would provide the definitive diagnosis of Alzheimer disease? a. Cerebral cortical atrophy on CT or MRI b. Improved symptoms with cholinesterase inhibitors c. Neuritic plaques containing A-beta (Aβ) amyloid bodies d. Nonspecific slowing of the EEG e. Presence of an apolipoprotein ε4 allele on chromosome 19

139. The answer is c. (Kaufman, pp 324-325. Longo, pp 3305-3309. McPhee and Hammer, pp 178-181.) The presence of an apolipoprotein ε4 allele on chromosome 19, especially in the homozygous 4/4 state, is an important risk factor for Alzheimer disease, and cortical atrophy on CT or MRI is a diagnostic sign of Alzheimer disease. Also, cholinesterase inhibitors may be used to improve memory in Alzheimer disease by increasing available levels of acetylcholine. However, the definitive diagnosis of Alzheimer disease is only obtained by tissue examination on autopsy, with the presence of amyloid plaques and neurofibrillary tangles in the neurons of the cerebral cortex, primarily in the temporal lobe, hippocampus, and nucleus basalis of Meynert (lateral septum). Short of autopsy, diagnosis is mainly clinical. Alzheimer disease is the most common cause of dementia. It is a slowly progressive dementia, and a clinical diagnosis must rule out other causes of dementia, including other major common causes such as vascular disease, Parkinson disease, alcohol dependence, alcoholism, or other drug/medication intoxication.

81. An 82-year-old woman with end-stage renal disease is brought to the emergency department complaining of nausea, vomiting, muscle cramps, and generalized weakness. Laboratory analysis reveals significant hyper-kalemia. Elevations of extracellular potassium ion concentration will have which of the following effects on nerve membranes? a. The activity of the Na+-K+ pump will decrease b. The membrane potential will become more negative c. The membrane will become more excitable d. Potassium conductance will increase e. Sodium conductance will increase

81. The answer is d. (Barrett, pp 88-89. Longo, pp 355-359.) Because the resting membrane potential is related to the ratio of ICF to ECF K+ concentration, an increase in extracellular K+ partially depolarizes the cell membrane, that is, makes the membrane potential more positive. Depolarizing the membrane opens K+ channels, causing an increase in membrane conductance to potassium. Prolonged depolarization, whether caused by an increase in extracellular K+ or by an action potential, inactivates Na+ channels and decreases the excitability of the nerve membrane, which manifests as weakness, and which may progress to flaccid paralysis. The activity of the Na -K+ pump is reduced in hypokalemia, not in hyperkalemia.

82. A 16-year-old adolescent boy is brought to the emergency room by ambulance after suffering a concussion during a football game. When he awoke, he was able to understand and follow commands, including repeating language spoken to him, but he had difficulty with spelling, mild word-finding difficulty, and difficulty understanding written language and pictures. His condition is most likely caused by damage to which of the following? a. Angular gyrus in the categorical hemisphere b. Arcuate fasciculus connectingBroca and Wernicke areas c. Broca area in the frontal lobe d. Hippocampus e. Wernicke area at the posterior end of the superior temporal gyrus

82. The answer is a. (Barrett, p 293. Le, p 420. Longo, pp 202-206.) Aphasias are language disorders in which a person is unable to properly express or understand certain aspects of written or spoken language. Aphasias are caused by lesions to the language centers, which are located in the categorical hemisphere of the neocortex. There are a number of different classifications of aphasias, but one divides them into fluent, nonfluent, and anomic aphasias. In this case, the boy developed an anomic aphasia, in which he was able to understand and follow commands, but he had difficulty understanding written language and pictures. There may be mild word-finding difficulty with this aphasia as well. Anomic aphasia is the single most common language disturbance seen in head trauma, metabolic encephalopathy, and Alzheimer disease. Anomic aphasia can be caused by lesions anywhere within the language network, but often is caused by damage to the angular gyrus without damage to Broca or Wernicke areas. A lesion in Broca area leads to nonfluent aphasia, and would have resulted in a severe impairment in expressive language. Fluent aphasias are due to lesions in Wernicke area or to lesions in and around the auditory cortex. Language disorders caused by memory loss, which could be the result of a hippocampal lesion, are not classified as aphasias, nor are language disorders caused by vision or hearing abnormalities or motor paralysis. Damage to the arcuate fasciculus would be incorrect because the patient was able to verbally repeat language spoken to him.

83. A 13-year-old adolescent boy has no movement in his legs after falling out of a tree. Neurological examination shows the absence of both the myotatic (stretch) and reverse myotatic reflexes in the lower extremities. Which of the following is the most important role of the γ-motoneurons? a. Detect the length of resting skeletal muscle b. Generate activity in Ib afferent fibers c. Maintain Ia afferent activity during contraction of muscle d. Prevent muscles from producing too much force e. Stimulate skeletal muscle fibers to contract

83. The answer is c. (Barrett, pp 229-232.) The γ-motoneurons innervate the intrafusal fibers of the muscle spindle. When a skeletal muscle contracts, the intrafusal muscle fiber becomes slack and the Ia afferents stop firing. By stimulating the intrafusal muscle fibers during a contraction, the γ-motoneurons prevent the intrafusal muscle fibers from becoming slack and thus maintain Ia firing during the contraction. Golgi tendon organs generate Ib afferents, and prevent excessive force of contraction. Alpha motoneurons cause skeletal muscle contraction.

84. A 72-year-old man visits his physician because he finds it difficult to hold his hand steady when painting. Examination reveals a resting tremor and rigidity. The symptoms are relieved by a single dose of levodopa. This patient's neurological signs are most likely related to a lesion within which of the following? a. Caudate nucleus and putamen b. Cerebellum c. Hippocampus d. Premotor area e. Substantia nigra

84. The answer is e. (Barrett, pp 245-248. Le, pp 234, 416-417, 455-456, 569-571. Longo, pp 3317-3335.) These findings are consistent with the presence of Parkinson disease, which is characterized by resting tremor rigidity and bradykinesia. It is caused by destruction of the dopa-mine-secreting neurons within the substantia nigra pars compacta. Levo (L)-dopa is a precursor for dopamine. L-dopa, rather than dopamine, is administered because it can cross the blood-brain barrier, but dopamine cannot. In contrast to the resting tremor of Parkinson disease, cerebellar disease is characterized by an intention tremor. In contrast to damage to the nigrostriatal dopaminergic system in Parkinson disease, Huntington disease results in a loss of the intrastriatal GABAergic and cholinergic neurons in the caudate nucleus and putamen of the basal ganglion, and is not responsive to treatment with L-dopa. Hippocampal lesions do not cause Parkinson disease.

86. A 72-year-old man develops selective loss of the large pyramidal cells in the precentral gyrus and degeneration of the corticospinal and corticobulbar projections. Other neuronal systems are spared. He is told that the progression of the disease is variable, and that the worst prognosis is about a 3-year survival. The precentral gyrus and corticospinal and corticobulbar tracts are essential for which of the following? a. Auditory identification b. Kinesthesia c. Olfaction d. Vision e. Voluntary movement

86. The answer is e. (Barrett, pp 236-237. Longo, p 3350.) The precentral gyrus is the motor area of the cortex that contains the cell bodies of the neurons that form the corticospinal tract (also referred to as the pyramidal tract). The corticospinal tract contains axons that cross to the contralateral side of the brain within the pyramids and end within the motor areas of the spinal cord. These structures are essential for the generation of fine voluntary movements. Kinesthesia, the sense of movement and position of the limbs, is handled primarily by the Ia and Ib afferents that innervate the muscle spindles and Golgi tendon organs, respectively, and by the parietal lobe. Olfaction is processed in the frontal lobe. Cortical localization of visual function is within the occipital lobes, and the optic tracts. Primary lateral sclerosis (PLS) is a rare disorder arising sporadically in midto-late life. PLS is characterized clinically by progressive spastic weakness of the limbs, preceded or followed by spastic dysarthria and dysphagia, indicating combined involvement of corticospinal and corticobulbar tracts. Sensory changes are absent and neither EMG nor muscle biopsy shows denervation.

87. A 62-year-old woman with a history of multiple head injuries in the past becomes progressively more confused, and develops urinary incontinence and a gait disorder. An MRI of the brain (shown below) and lumbar puncture are performed. Intracranial pressure is found to be within normal limits. The patient's symptoms improved after ventriculoperitoneal shunting. Under normal conditions, which of the following statements correctly describes the cerebrospinal fluid (CSF)? a. It is absorbed into the choroid plexus b. It circulates in the epidural space c. It has a higher protein concentration than plasma d. It has a lower glucose concentration than plasma e. Its absorption is independent of CSF pressure

87. The answer is d. (Barrett, p 603. Le, p 426. Longo, p 3313.) The concentrations of glucose and protein within the CSF are much lower than those of plasma. Changes in the CSF concentrations of these substances are helpful in detecting pathologic processes, such as tumor or infection, in which the blood-brain barrier is disrupted. CSF, which is in osmotic equilibrium with the extracellular fluid of the brain and spinal cord, is formed primarily in the choroid plexus by an active secretory process. It circulates through the subarachnoid space (not the epidural space) between the arachnoid mater and pia mater and is absorbed into the circulation by the arachnoid villi. Disturbances in CSF circulation or absorption result in hydrocephalus. Normal pressure hydrocephalus is characterized by dementia, urinary urgency and/or incontinence, and gait changes. It is important to recognize because it may be reversible with a removal of CSF via permanent shunt.

88. A 78-year-old man is evaluated by a physiatrist after a stroke. The patient is observed to suffer from dysmetria, ataxia, and an intention tremor. These neurological signs are most likely related to a lesion within which of the following regions of the brain? a. Basal ganglia b. Cerebellum c. Cortical motor strip d. Eighth cranial nerve e. Medulla

88. The answer is b. (Barrett, pp 251-252. Le, pp 415, 417. Longo, p 193.) Ataxia, dysmetria, and an intention tremor all are classic findings in a patient with a lesion involving the cerebellum. Affected persons also exhibit adiadochokinesia, which is a loss of ability to accomplish a swift succession of oscillatory movements, such as moving a finger rapidly up and down. Lesions in the basal ganglia more commonly present with a resting tremor, such as seen in Parkinson disease. Lesions in the cortical motor strip would cause contralateral hemiparesis. Damage to the eighth (vestibulocochlear) nerve can result in symptoms such as hearing loss, nystagmus, and vertigo. Lesions in the medulla may compromise respiration and other autonomic functions.

89. A 41-year-old man is seen by his physician complaining of "always feeling tired" and having "vivid dreams when he is sleeping." He is referred to the hospital's sleep center for evaluation. He is diagnosed with narcolepsy based on his clinical history and the presence of rapid eye movements (REM) as soon as he falls asleep. Which of the following signs will be observed when the patient is exhibitingREM sleep? a. High-amplitude electroencephalogram (EEG) waves b. Hyperventilation c. Low frequency EEG waves d. Periods of loss of skeletal muscle tone e. Slow but steady heart rate

89. The answer is d. (Barrett, pp 274-276. Le, pp 61-62. Longo, pp 213-223.) In a normal sleep cycle, a person passes through the three stages of non-REM sleep before enteringREM sleep. In narcolepsy, a person may pass directly from the waking state to REM sleep. REM sleep is characterized by irregular heartbeats and respiration and atonia (loss of muscle tone). Hypoventilation is characteristic of both REM and non-REM sleep because sleep depresses the central chemoreceptors. It is also the state of sleep in which dreaming occurs. High-amplitude EEG waves occur in the late stages of slow-wave sleep. EEG duringREM sleep is low amplitude, high frequency.

90. A 43-year-old woman has a chief complaint of muscle weakness. The distribution of muscle weakness and the presence of hyperactive tendon reflexes is consistent with pyramidal tract disease. Tapping the patella tendon elicits a reflex contraction of the quadriceps muscle. Which of the following occurs during the contraction of the quadriceps muscle? a. The α-motoneurons innervating the extrafusal muscle fibers decrease their rate of firing b. The α-motoneurons to the antagonistic muscles increase their rate of firing c. The γ-motoneurons innervating the intrafusal muscle fibers increase their rate of firing d. The Ia afferents from the muscle spindle increase their rate of firing e. The Ib afferents from the Golgi tendon organ increase their rate of firing

90 The answer is e. (Barrett, pp 229-232.) The Ib afferents innervating the quadriceps muscles are activated when the quadriceps contracts in response to tapping the patella tendon. Stretching the patella tendon stretches the intrafusal muscle fibers within the quadriceps muscle and causes an increase in Ia afferent activity. The increase in Ia afferent activity causes an increase in α-motoneuron activity, which results in contraction of the quadriceps muscle. When the muscle contracts, the intrafusal muscle fibers are unloaded and the Ia afferent activity is reduced.

91. A 64-year-old female patient is referred to a neurologist because her sister and brother both suffered recent strokes. She is diagnosed with an antiphospholipid antibody syndrome, and placed on warfarin. Despite the anticoagulation therapy, she develops a thrombotic cerebral infarct, which leads to spasticity of her left wrist, elbow, and knee. The infarction most likely affected which of the following? a. Ia afferent fibers b. Corticoreticular fibers c. Corticospinal fibers d. Reticulospinal fibers e. Vestibulospinal fibers

91. The answer is b. (Barrett, p 240. Le, p 428. Longo, pp 181-182.) Spasticity results from overactivity of the α-motoneurons innervating the skeletal musculature. Under normal circumstances, these α-motoneurons are tonically stimulated by reticulospinal and vestibulospinal fibers originating in the brain stem. These brain stem fibers are normally inhibited by fibers originating in the cortex. Cutting the corticoreticular fibers releases the brain stem fibers from inhibition and results in spasticity. Cutting the fibers from the reticular formation, vestibular nuclei, or the Ia afferents will reduce the spasticity.

Which of the following is the most common action of γ-aminobutyric acid (GABA): A) Opening channels permeable to Cl− B) Opening channels permeable to Ca2+ C) Opening channels permeable to Na+ and K+ D) Closing channels permeable to Na+ E) Closing channels permeable to Cl− and K+

A) Opening channels permeable to Cl−

92. A 27-year-old patient with a chief complaint of mild vertigo of 3-month duration is seen by a neurologist. Examination reveals a positional (horizontal and vertical) nystagmus that is bidirectional. The patient reports the absence of tinnitus. Which of the following is the most likely etiology of the vertigo? a. Labyrinthitis b. Lesion of the flocculonodular lobe of the cerebellum c. Lesion of the spinocerebellum d. Ménière syndrome e. Psychogenic

92. The answer is b. (Barrett, pp 212, 250. Le, p. 446. Longo, pp 4178-4179. Widmaier, pp 219-220.) The flocculonodular lobe, or vestibulocerebellum, is connected to the vestibular nuclei and participates in the control of balance and eye movements, particularly changes in the vestibulo-ocular reflex, which serves to maintain visual stability during head movement; a lesion of this area of the cerebellum may result in vertigo and nystagmus. In contrast, the spinocerebellum is involved in the coordination of limb movement. Pathologic vertigo is generally classified as peripheral (labyrinthine) or central (brain stem or cerebellum). The clinical presentation in this case is most consistent with central vertigo. Positional (especially horizontal) nystagmus (to-and-fro oscillation of the eyes) is common in vertigo of central origin, but absent or uncommon in peripheral vertigo. The chronicity of the vertigo is characteristic of central vertigo, whereas the symptoms of peripheral vertigo generally have a finite duration and may be recurring. Tinnitus and/or deafness is often present in peripheral vertigo, but absent in central vertigo. Labyrinthitis and Méniére syndrome are examples of vertigo of peripheral origin. In psychogenic versus organic vertigo, nystagmus is absent during a vertiginous episode.

93. A 16-year-old adolescent girl with epilepsy has an EEG recording done during a routine visit to her neurologist. The α-rhythm appearing on an EEG has which of the following characteristics? a. It disappears when a patient's eyes open b. It is associated with deep sleep c. It is replaced by slower, larger waves duringREM sleep d. It produces 20 to 30 waves per second e. It represents activity that is most pronounced in the frontal region of the brain

93. The answer is a. (Barrett, pp 272-273. Le, p 445. Longo, pp e45-1-e45-3.) As shown in the EEG below, in a totally relaxed adult with eyes closed, the major component of the EEG will be a regular pattern of 8 to 12 waves per second observed over the posterior (occipital) brain regions, called the α-rhythm or posterior dominant rhythm. The α-rhythm disappears when the eyes are opened. It is most prominent in the occipital region. In deep sleep, the α-rhythm is replaced by larger, slower waves called delta waves. In REM sleep, the EEG will show fast, irregular activity.

94. A 29-year-old woman presents at the ophthalmologist's office complaining of slowly progressive loss of vision. Based on the visual field defect shown here, the ophthalmologist determines that the patient has a right-sided homonymous hemianopia. She refers the patient to a neurologist who orders a CT scan of the head. The CT scan demonstrates a high-density, space-occupying lesion, which is compressing which area of the brain? a. Left optic nerve b. Left optic tract c. Optic chiasm d. Right lateral geniculate nucleus e. Right visual cortex

94. The answer is b. (Barrett, pp 189-191. Le, p 441.) The loss of vision on the right half of the visual field of both eyes (right-sided homonymous hemianopia) occurs because neurons from the left half of each of the retinas do not reach the visual cortex. This would result from a lesion of the left visual pathway distal to the optic chiasm, that is, the left optic tract, where the visual information from the nasal portion of the left retina (the right hemifield of the left eye's visual field) and the temporal portion of the right retina (the right hemifield of the right eye's visual field) are carried within the same nerve tract.

96. On physical examination, stroking the plantar surface of her foot produces a reflex extension of the large toe rather than the expected flexion, which indicates damage to which of the following? a. Basal ganglia b. Brain stem c. Cerebellum d. Lower motoneurons e. Upper motoneurons

96. The answer is e. (Barrett, p 240. Le, p 432. Longo, pp 182, 3237.) The plantar reflex is a cutaneous reflex elicited by stroking the lateral surface of the sole of the foot with a noxious stimulus such as a tongue blade, beginning near the end of the heel and moving across the ball of the foot to the great toe. The normal reflex consists of plantar flexion of the toes. With upper motoneuron lesions above the S1 level of the spinal cord, a paradoxical extension of the toe is observed, associated with fanning and extension of the other toes; this is termed an extensor plantar reflex or the Babinski sign. Other signs of pyramidal tract lesions include loss of the hopping and placing reaction, the cremasteric reflex, and the abdominal scratch reflex. Damage confined to the pyramidal tract results in distal muscular weakness and loss of fine motor control. Damage to other areas of the cortical motor control system is referred to as upper motoneuron disease and produces spasticity. Damage to the basal ganglia produces a variety of signs, including dystonia (striatum), ballism (subthalamic nucleus), and tremor at rest (substantia nigra). Damaging the cerebellum causes uncoordinated movements (dysmetria, ataxia, intention tremor).

97. A 59-year-old woman with an inherited neurodegenerative disease is admitted to the hospital because of agitation and aggression. Three years prior to admission, her irregular, flinging movements had become so severe that she could not walk or assist in her own care. Within which of the following areas of the brain the neuronal degeneration results in this presentation? a. Anterior cerebellum b. Limbic system c. Striatum d. Substantia nigra e. Subthalamus

97. The answer is c. (Barrett, pp 5245-5246. Le, pp 417, 556. Longo, pp 3330-3331.) Huntington chorea is an inherited genetic defect leading to the degeneration of neurons with the striatum (the caudate nucleus and putamen). It is progressive disease characterized by uncontrolled movements, irritability, depression, and ultimately dementia and death. Lesions of the subthalamic nucleus produce wild flinging movements called ballism; those within the anterior cerebellum produce ataxia; those within the substantia nigra produce Parkinson disease; and those within the limbic system yield emotional disorders.

Most axons in the superior, middle, and inferior peduncles are which of the following? A. Afferent to the cerebellum B. Axons of Golgi cells C. Axons of Purkinje cells D. Parallel fibers of granule cells E. Projections from neurons in the deep cerebellar nuclei

A. About 97% of the axons in the peduncles connecting the cerebellum to the rest of the brain are afferent to the cerebellum. The output of the cerebellar cortex is conveyed exclusively by the Purkinje cells, which although large and powerful are not numerous.

98. A 22-year-old woman presents at the student medical center with tachycardia and palpitations. She reports that she has been taking a diet supplement containing ephedrine that she purchased from an Internet site. Activation of the sympathetic nervous system by ephedrine causes smooth muscle contraction in which of the following? a. Arterioles b. Bronchioles c. Ciliary bodies d. Intestines e. Pupils

98. The answer is a. (Barrett, pp 259-261.) The catecholamine, norepinephrine (and epinephrine), activates both α- and β-adrenergic receptors. When the α1 - adrenergic receptors are stimulated, they activate a G protein, which in turn activates phospholipase C, which hydrolyzes PIP2 and produces IP3 and DAG. The IP3 causes the release of Ca 2 from the sarcoplasmic reticulum, which in turn increases muscle contraction. α1 -Adrenergic receptors predominate on arteriolar smooth muscle, so these muscles contract when stimulated with norepinephrine. Ephedrine is both a direct and indirectly acting sympathomimetic amine. Its direct action to activate postsynaptic α-receptors and β-receptors is weak. Ephedrine's actions are primarily due to its effects as an indirect sympathomimetic, which involves its uptake into the presynaptic nerve terminal, where it is packaged and released with norepinephrine from the sympathetic nerve terminals. The effect of adding ephedrine is to increase the number of vesicles released during each action potential and possibly to extend the duration of action of norepinephrine by prolonging its inactivation via the neuronal reuptake process. Therefore, the actions of norepinephrine are enhanced in the presence of ephedrine. There are no α-receptors in the bronchioles, pupils, or ciliary smooth muscles in the ciliary body of the eye, so norepinephrine does not cause contraction in these areas, but rather smooth muscle relaxation caused by activation of β-receptors in these tissues. Intestinal smooth muscles have α2 -adrenergic receptor, which mediates relaxation when bound to norepinephrine.

99. A 27-year-old musician visits an otolaryngologist complaining of ringing in his ear. An audiometry test reveals a high-frequency hearing loss in which the threshold for hearing high-frequency sounds is raised by 1000 times. If a patient is unable to hear high-frequency sounds, the damage to the basilar membrane is closest to which of the following structures? a. Helicotrema b. Modiolus c. Oval window d. Spiral ganglion e. Stria vascularis

99. The answer is c. (Barrett, pp 206-207. Longo, pp 248-250.) The portion of the basilar membrane vibrated by a sound depends on the frequency of the sound. High-frequency sounds produce a vibration of the basilar membrane at the base of the cochlea (near the oval and round windows); low-frequency sounds produce a vibration of the basilar membrane at the apex of the cochlea (near the helicotrema). The modiolus is the bony center of the cochlea from which the basilar membrane emerges, the spiral ganglion contains the cell bodies of the auditory nerve fibers, and the stria vascularis is the vascular bed located on the outer wall of the scala media of the cochlea responsible for endolymph secretion.

Which of the following is the most common action of γ-aminobutyric acid (GABA): A. Opening channels permeable to Cl− B. Opening channels permeable to Ca2+ C. Opening channels permeable to Na+ and K+ D. Closing channels permeable to Na+ E. Closing channels permeable to Cl− and K+

A. GABA and glycine are the most important inhibitory neurotransmit- ters and produce their most common inhibitory effects by opening Cl− channels and producing a current that often causes a slight hyperpolar- ization and always tends to clamp the neuron close to its resting potential.

Which of the following is a property of C fibers? A. Have the slowest conduction velocity of any nerve fiber type B. Have the largest diameter of any nerve fiber type C. Are afferent nerves from muscle spindles D. Are afferent nerves from Golgi tendon organs E. Are perpendicular autonomic fibers

A. Have the slowest conduction velocity of any nerve fiber type

Patients are enrolled in trials of a new atropine analog. Which of the following would be expected? A. Increased AV node conduction velocity B. Increased gastric acidity C. Pupillary constriction D. Sustained erection E. Increased sweating

A. Increased AV node conduction velocity

Which reflex is responsible for monosynaptic excitation of ipsilateral homonymous muscle? A. Stretch reflex (myotatic) B. Golgi tendon reflex (inverse myotatic) C. Flexor withdrawal reflex D. Subliminal occlusion reflex

A. Stretch reflex (myotatic)

Which of the following statements best describes the basilar membrane of the organ of Corti? A. The apex responds better to low frequencies than the base does B. The base is wider than the apex C. The base is more compliant than the apex D. High frequencies produce maximal displacement of the basilar membrane near the helicotrema E. The apex is relatively stiff compared to the base

A. The apex responds better to low frequencies than the base does

Which adrenergic receptor produces its stimulatory effects by the formation of inositol 1,4,5-triphosphate (IP3) and an increase in intracellular [Ca2+]? A. alpha 1 receptors B. alpha 2 receptors C. beta 1 receptors D. beta 2 receptors E. muscarinic recepetors F. nicotinic receptors

A. alpha 1 receptors

When compared with the cones of the retina, the rods A. are more sensitive to low-intensity light B. adapt to darkness before the cones C. are most highly concentrated on the fovea D. are primarily involved in color vision

A. are more sensitive to low-intensity light

Complete transection of the spinal cord at the level of T1 would most likely result in A. temporary loss of stretch reflexes below the lesion B. temporary loss of conscious proprioception below the lesion C. permanent loss of voluntary control of movement above the lesion D. permanent loss of consciousness above the lesion

A. temporary loss of stretch reflexes below the lesion

Activity in climbing fibers will do which of the following? A. Cause release of GABA from climbing fiber terminals B. Evoke complex spikes in Purkinje cells C. Have no effect in the flocculonodular lobe D. Strongly excite neurons in deep cerebellar nuclei E. Weakly depolarize Purkinje cells

B. A single action potential in a single climbing fiber evokes a complex spike in each of the Purkinje fibers (1-20) on which the climbing fiber synapses. The complex spike, which is activated by glutamate released from the climbing fiber, is an overshooting action potential generated simultaneously in the soma and dendrites. This is the strongest synaptic connection known in the central nervous system (CNS). In contrast, synapses from the climbing fibers to neurons in deep cerebellar nuclei are very weak. Climbing fibers strongly excite Purkinje cells in all regions of the cerebellar cortex.

Which autonomic recpetor mediates an increase in heart rate? A. Adrenergic alpha receptors B. Adrenergic beta 1 receptors C. Adrenergic beta 2 receptors D. Cholinergic muscarinic receptors E. Cholinergic nicotinic receptors

B. Adrenergic beta 1 receptors

The velocity of action potential conduction is noted to be affected byvarious parameters. If the conduction velocity were found to be augmented, which of the following characteristics would most likely be decreased? A. Action potential amplitude B. Effective membrane capacitance C. The concentration gradient for Na+ D. The rate at which Na+ channels open in response to depolarization E. Na+ channel density uniformly along a fiber

B. Effective membrane capacitance is decreased in many mammalian axons by myelination—the tight wrapping of many glial membranes around the axon, which is functionally equivalent to increasing the thickness of the membrane. Because conduction velocity is inversely related to membrane capacitance, which is related inversely to effective membrane thickness, a decrease in membrane capacitance increases conduction velocity. Decreasing action potential amplitude (answer A) will decrease rather than increase action potential velocity (see Case 8), as will decreasing the concentration gradient for Na+ (because this will reduce action potential amplitude). In addition, decreases in the opening rate or density of Na+ channels will decrease conduction velocity.

Which of the following responses is mediated by parasympathetic muscarinic receptors? A. Dilation of bronchiolar smooth muscle B. Miosis C. Ejaculation D. Constriction of gastrointestinal sphincters E. Increased cardiac contractility

B. Miosis

Hyperkalemia reduces the excitability of neurons and muscle cells. Which of the following best describes the effect of increased extracellular potassium K+? A. Depolarizes the cell, thus reducing action potential amplitude B. Depolarizes the cell, thus inactivating voltage-gated Na+ channels C. Hyperpolarizes the cell, which increases the action potential threshold D. Increases the activity of the Na-K-ATPase, which hyperpolarizes the cell E. Stimulates endocytosis of Na+ channels

B. Sustained depolarization, as occurs with hyperkalemia, inacti- vates voltage-gated Na+ channels, which remain inactivated until the membrane repolarizes, thus blocking action potential generation. If action potentials are generated, their amplitude will be reduced (answer A), but this is a consequence rather than a cause of reduced excitability. Hyperpolarization also can reduce excitability by increasing the depolarization needed to reach action potential threshold (answers C and D), but this would be produced by hypokalemia, not by hyperkalemia. There is no evidence that pro- longed hyperkalemia decreases the number of Na+ channels in the membrane (answer E).

Which of the following is a characteristic of nuclear bag fibers? A. They are one type of extrafusal muscle fiber B. They detect dynamic changes in muscle length C. They give rise to group Ib afferents D. They are innervated by alpha-motorneurons

B. They detect dynamic changes in muscle length

The excessive muscle tone produced in decerebrate rigidity can be reversed by A. stimulation of group 1a afferents B. cutting the dorsal roots C. transection of cerebellar connections to the lateral vestibular nucleus D. stimulation of alpha-motoneurons E. stimulation of gamma-motoneurons

B. cutting the dorsal roots

Which autonomic receptor is activated by low concentrations of epinephrine released from the adrenal medulla and causes vasodilation? A. Adrenergic alpha receptors B. Adrenergic beta 1 receptors C. Adrenergic beta 2 receptors D. Cholinergic muscarinic receptors E. Cholinergic nicotinic receptors

C. Adrenergic beta 2 receptors

Which of the following parts of the body has cortical motorneurons with the largest representation on the primary motor cortex (area 4)? A. Shoulder B. Ankle C. Fingers D. Elbow E. Knee

C. Fingers

Which reflex is responsible for polysnaptic excitation of contralateral extensors? A. Stretch reflex (myotatic) B. Golgi tendon reflex (inverse myotatic) C. Flexor withdrawal reflex D. Subliminal occlusion reflex

C. Flexor withdrawal reflex

Muscle stretch leads to a direct increase in firing rate of which type of nerve? A. alpha-Motorneurons B. gamma-Motorneurons C. Group Ia fibers D. Group Ib fibers

C. Group Ia fibers

Which of the following provide, respectively, the predominant input to, the output from, and the direct synaptic target of the basal ganglia? A. Cerebellum, globus pallidus, substantia nigra B. Cerebral cortex, globus pallidus, cerebral cortex C. Cerebral cortex, globus pallidus, thalamus D. Cerebral cortex, putamen, substantia nigra E. Thalamus, globus pallidus, cerebral cortex

C. The basal ganglia and thalamus form a motor loop with the cerebral cortex. Input to the basal ganglia comes from prefrontal and sensory association areas of the cerebral cortex and leaves the basal ganglia via the internal segment of the globus pallidus. The immediate target of these neurons is the thalamus (ventral anterior, ventral lateral, and centromedian nuclei). These thalamic nuclei then project to motor areas in the cerebral cortex.

Which of the following is the major neurotransmitter released by most neurons within the basal ganglia? A. Acetylcholine B. Dopamine C. GABA D. Glycine E. Glutamate

C. The majority of synapses from neurons in the basal ganglia are inhibitory and release GABA. The other major inhibitory neurotrans- mitter, glycine, is not important in the basal ganglia and is released primarily from inhibitory interneurons in the spinal cord. Dopamine is an important neurotransmitter that is released by neurons in the substantia nigra, but these neurons account for only a small fraction of the total number of neurons in the basal ganglia. In addition, other neurotransmitters (eg, acetylcholine, NO, various neuropeptides) are released from some neurons in the basal ganglia, but the largest num- ber of synapses are GABAergic.

The inability to perform rapidly alternating movements (dysdiadochokinesia) is associated with lesions of the A. premotor cortex B. motor cortex C. cerebellum D. substantia nigra E. medulla

C. cerebellum

Pathogens that produce fever cause A. decreased production of interleukin-1 (IL-1) B. decreased set-point temperature in the hypothalamus C. shivering D. vasodilation of blood vessels in the skin

C. shivering

Which tracts are responsible for direct cortical control of spinal motor systems?

Cortical control of motor neurons: By the lateral and ventral corticospinal tracts.

Which one of the followings is considered as the mechanism of "synaptic fatigue"? A) exhaustion of the stores of transmitters in the presynaptic terminal B) progressive inactivation of the postsynaptic membrane receptors C) development of abnormal concentrations of ions inside the postsynaptic cell D) All of them

D) All of them

The resting transmembrane potential (Vm ) of a nerve axon is essential for signal generation. Instantaneous elimination of which of the following would most rapidly bring Vm close to 0 mV? A) Active transport of K+ out of the cell B) Active transport of Na+ out of the cell C) Concentration gradient for Na+ D) High membrane permeability to K+ E) High membrane permeability to Na+

D) High membrane permeability to K+

Which set of the following receptors helps us to detect the texture of the object by touch? A) Ruffini's endings & Pacinian corpuscles B) Merkel's discs & Free nerve endings C) Pacinian corpuscles & Hair end-organ D) Meissner's corpuscles & Merkel's discs

D) Meissner's corpuscles & Merkel's discs

Which of the following causes synapse stability? A) Divergence circuits B) Intrinsic neuronal discharge C) Reverberatory circuits D) Synaptic fatigue

D) Synaptic fatigue

Compared with the intracellular fluid, the extracellular fluid has __________ sodium ion concentration, __________ potassium ion concentration, __________ chloride ion concentration, and __________ phosphate ion concentration. A) Lower, lower, lower, lower B) Lower, higher, lower, lower C) Lower, higher, higher, lower D) Higher, lower, higher, lower E) Higher, higher, lower, higher F) Higher, higher, higher, higher

D) The extracellular fluid has relatively high concen- trations of sodium and chloride ions but lower concen- trations of potassium and phosphate compared with the intracellular fluid.

A 42-year-old woman with elevated blood pressure, visual disturbances, and vomiting has increased urinary excretion of 3-methoxy-4-hydroxymandelic acid (VMA). A computerized tomographic scan shows an adrenal mass that is consistent with a diagnosis of pheochromocytoma. While awaiting surgery to remove the tumor, she is treated with phenoxybenzamine to lower her blood pressure. What is the mechanism of this action of the drug? A. Increasing cyclic adenosine monophosphate (cAMP) B. Decreasing cAMP C. Increasing inositol 1,4,5 triphosphate (IP3)/Ca2+ D. Decreasing IP3/Ca2+ E. Opening Na+/K+ channels F. Closing Na+/K+ channels

D. Decreasing IP3/Ca2+

Which of the following statements distinguishes excitatory chemical synapses in the brain from the neuromuscular junction? A. Excitation is produced by ligand-gated channels. B. Ligand-gated channels increase permeability to both Na+ and K+ C. Postsynaptic action potentials are triggered when a sufficient number of voltage-gated Na+ channels are opened by an EPP or by summating EPSPs. D. Temporal summation and spatial summation onto the postsynaptic cell increase the likelihood that a postsynaptic action potential will be evoked. E. The synaptic reversal potential is close to 0 mV.

D. In contrast to other neuronal synapses, the individual EPSPs (or EPPs) at the neuromuscular junction are normally much larger than is required to evoke an action potential, and so temporal summation does not increase the probability of firing (although high-frequency firing of the motor neuron does lead to summation of twitches and to tetaniza- tion). All the other features listed are shared by the neuromuscular junction and excitatory chemical synapses in the brain.

Which of the following autonomic drugs acts by stimulating adenylate cyclase? A. atropine B. Clonidine C. Curare D. Norepinephrine E. Phentolamine F. Phenylephrine G. Propranolol

D. Norepinephrine

Major functions of cerebellar cortex include which of the following? A. Directly exciting alpha motor neurons B. Exciting deep cerebellar nuclei C. Generating motor patterns that subserve the scratch reflex D. Learning and controlling novel movement patterns E. Recognizing emotionally potent stimuli

D. One of the most important functions of the cerebellar cortex is to learn and control novel patterns of movement and posture. Cerebellar learning and other cerebellar functions are not implemented by direct actions on motor neurons (answer A) or spinal pattern generators (answer C) but instead modulate activity in the motor cortex by patterned inhibition (not excitation, as in answer B) of deep cerebellar nuclei, which excite thalamic neurons, which in turn excite neurons in motor cortex. The cerebellum is much less important for processing emotional information (answer E) than for controlling the spatial accuracy and temporal coordination of movement.

Which of the following has a much lower concentration in the cerebrospinal fluid (CSF) than in cerebral capillary blood? A. Na+ B. K+ C. Osmolarity D. Protein E. Mg2+

D. Protein

Which of the following would produce maximum excitation of the hair cells in the right horizontal semicircular canal? A. Hyperpolarization of hair the hair cells B. Bending the stereocilia away from the kinocilia C. Rapid ascent in an elevator D. Rotating the head to the right

D. Rotating the head to the right

Sensory receptor potentials A. are action potentials B. always bring the membrane potential of a receptor cell toward threshold C. always bring the membrane potential of a receptor cell away from the threshold D. are graded in size, depending on stimulus intensity E. are all-or-none

D. are graded in size, depending on stimulus intensity

A lesion of the chorda tympani nerve would most likely result in A. impaired olfactory function B. impaired vestibular function C. impaired auditory function D. impaired taste function E. nerve deafness

D. impaired taste function

Which of the following effects is caused by activation of gamma motor neurons during active contraction of extrafusal muscle fibers? A. Decreased magnitude of the stretch reflex B. Increased force developed by the extrafusal muscle fibers C. Increased sensitivity of Ib afferents D. Increased summation of motor units E. Maintained sensitivity of the Ia afferents during unexpected stretch

E. Coactivation of gamma motor neurons with alpha motor neurons shortens the intrafusal muscle fibers during contraction of extrafusal fibers so that sensitivity of the Ia stretch receptors in the intrafusal fibers is maintained when unexpected stretch occurs during the extra- fusal muscle contraction. This would increase rather than decrease the magnitude of any stretch reflex evoked during contraction (answer A) and would have no direct effect on extrafusal force devel- opment, the sensitivity of Ib afferents, or the summation of motor units (answers B, C, and D).

Which of the following structures has a primary function to coordinate rate, range, force, and direction of movement? A. Primary motor cortex B. Premotor cortex and supplementary motor cortex C. Prefrontal cortex D. Basal ganglia E. Cerebellum

E. Cerebellum

Which of the following enzymes catalyzes the synthesis of ACh? A. Acetyl-coenzyme A B. Acetylcholinesterase (AChE) C. Acetylcholine-H+ (ACh-H+) exchanger D. Amino acid decarboxylase E. Choline acetyltransferase

E. Choline acetyltransferase synthesizes ACh from choline and acetyl- coenzyme A. The ACh is transported into the vesicle by the ACh-H+ exchanger, and after release it is hydrolyzed by AChE to acetate and choline.

Which autonomic receptor is blocked by hexamethonium at the ganglia, but not at the neuromuscular junction? A. Adrenergic alpha receptors B. Adrenergic beta 1-receptors C. Adrenergic beta 2-receptors D. Cholinergic muscarinic receptors E. Cholinergic nicotinic receptors

E. Cholinergic nicotinic receptors

Which autonomic receptor mediates secretion of epinephrine by the adrenal medulla? A. Adrenergic alpha receptors B. Adrenergic beta 1 receptors C. Adrenergic beta 2 receptors D. Cholinergic muscarinic receptors E. Cholinergic nicotinic receptors

E. Cholinergic nicotinic receptors

A motor unit that innervates only three muscle fibers is likely to innervate muscle in which of the following? A. Back B. Biceps C. Bladder D. Thigh E. Thumb

E. Motor units are smallest in the parts of the body that have the most precise motor control, such as the thumb, fingers, and tongue.

Which of the following is a feature of the sympathetic, but not the parasympathetic nervous system? A. Ganglia located in the effector organs B. Long preganglionic neurons C. Preganglionic neurons release norepinephrine D. Preganglionic neurons release ACh E. Preganglionic neurons originate in the thoracolumbar spinal cord F. Postganglionic neurons synapse on effector organs G. Postganglionic neurons release epinephrine H. Postganglionic neurons release ACh

E. Preganglionic neurons originate in the thoracolumbar spinal cord

A 62-year-old nursing home patient is brought into the emergency department for evaluation of altered mental status. Magnetic resonance imaging indicates degeneration of dopamine-containing neurons in the substantia nigra. This loss is most likely to do which of the following? A. Decrease activity in basal ganglia output nuclei B. Produce dyskinesias such as choreiform movements C. Produce hemiballism D. Suppress activity in the subthalamic nucleus E. Suppress the direct pathway and facilitate the indirect pathway from the striatum to the basal ganglia output nuclei

E. Under normal conditions, dopamine released by neurons in the substantia nigra affects both the direct and indirect pathways in the motor loop to the cerebral cortex, exciting the direct, stimulatory pathway to the thalamus and inhibiting the indirect, inhibitory pathway to the thalamus. Thus, if the dopamine-containing neurons degenerate (as occurs in Parkinson disease), the excitatory actions on the thalamus are inhibited and there is less disinhibition of the inhibitory actions, with the consequence that excitation from the thalamus to motor areas in the cortex is decreased and it becomes more difficult to initiate movements. The other effects listed (answers A-D) would not be produced by selective loss of dopaminergic neurons, but instead by lesions of the subthalamic nucleus or early stages of striatal neuron loss.

Which of the following observations would suggest that an upper motor neuron lesion rather than a lower motor neuron lesion is present? A. Fasciculations B. Hyporeflexia C. Profound weakness D. Pronounced atrophy E. Spasticity

E. Upper motor neuron lesions produce spasticity, involving hyper- active stretch reflexes. Lower motor neuron lesions do not produce spasticity. Fasciculations are not induced by upper motor neuron lesions, and compared with lower motor neuron lesions, there is less dramatic weakness and muscle atrophy.

What effect would an AChE inhibitor have at the neuromuscular junction?

Effect of AChE inhibitor: Blocks the degradation of ACh, causing an increase in the endplate potential, and prolongs the action of ACh at the motor endplate.

How would a large reduction in extracellular [Ca2+] affect synaptic transmission at the neuromuscular junction?

Effect of reducing Ca2+: Reduces Ca2+-dependent exocytosis of ACh from vesicles in the presynaptic terminal.

What do group Ia afferents detect?

Group Ia afferents detect: Muscle stretch.

What is the ionic mechanism that underlies the endplate potential (EPP) produced by acetylcholine (ACh) release?

Ionic mechanism of EPP: ACh opens ligand-gated channels that are equally permeable to Na+ and K+ . The net effect is depolarization that reaches action potential threshold in the muscle cell.

A 66-year-old man with chronic hyper-tension is treated with prazosin by his physician. The treatment successfully decreases his blood pressure to within the normal range. What is the mechanism of the drug's action? A. Inhibition of beta 1 receptors in the sinoatrial (SA) node B. Inhibition of beta 2 receptors in the SA node C. Stimulation of muscarinic receptors in the SA node D. Stimulation of nicotinic receptors in the SA node E. Inhibition of beta 1 receptors in ventricular muscles F. Stimulation of beta 1 receptors in ventricular muscle G. Inhibition of alpha 1 receptors in the SA node H. Stimulation of alpha 1 receptors in ventricular muscle I. Inhibition of alpha 1 receptors in the SA node J. Inhibition of alpha 1 receptors on vascular smooth muscle K. Stimulation of alpha 1 receptors on vascular smooth muscle L. Stimulation of alpha 2 receptors on vascular smooth muscle

J. Inhibition of alpha 1 receptors on vascular smooth muscle

Where is the lesion for Parkinson disease located?

Location of lesion in Parkinson disease: Substantia nigra.

What would be the location of the lesion in a patient with hemiballismus?

Location of lesion in patient with hemiballismus: Subthalamic nucleus.

What is the neurotransmitter for Purkinje cells?

Neurotransmitter for Purkinje cells: Gamma-aminobutyric acid (GABA).

Which nuclei compose the basal ganglia?

Nuclei composing basal ganglia: Caudate, putamen, globus pallidus, subthalamic, substantia nigra.

Is the output of the cerebellar cortex excitatory, inhibitory, or both?

Output from cerebellar cortex: Inhibitory.

What part of the cerebellum is responsible for planning and initiation of movement?

Part of cerebellum responsible for planning and initiation of movement: Cerebrocerebellum (neocerebellum).

What is the muscle response during the reverse myotatic reflex?

Response during reverse myotatic reflex: Relaxation of muscle that had been strongly contracting.

10. Which one of the following neurotransmitters is found in the neuromuscular junction? a) Dopamine b) Serotonin c) Epinephrine d) Acetylcholine

d) Acetylcholine

12. An excitable cell has an intracellular concentration of 14 mEq/Lit for a monovalent anion and extracellular concentration of 1.4 mEq/Lit. Assuming that resting membrane potential is - 80 mv, what would the membrane potential be if the cell membrane were permeable only to this ion? and how would the permeability to this ion change the membrane potential? a) Depolarization, + 61 mv b) Hyperpolarization, - 61 mv c) Depolarization, + 122 mv d) Hyperpolarization, -122 mv

a) Depolarization, + 61 mv

7. Deficiency of which one of the following neurotransmitters causes Parkinson's disease? a) Dopamine b) Serotonin c) Epinephrine d) Acetylcholine e) Bradykinin

a) Dopamine

9. Which one of the following neurotransmitters has a role in analgesia and is made in the hypophysis? a) Enkephalin b) Endorphin c) Dynorphin d) Serotonin

b) Endorphin

6. Which one of the following neurotransmitters is a gas? a) Bradykinin b) Nitric oxide c) Epinephrine d) Acetylcholine

b) Nitric oxide

8. Which one of the following neurotransmitters contributes to the analgesic system of brain and spinal cord? a) Dopamine b) Serotonin c) Epinephrine d) Acetylcholine

b) Serotonin

11. Which one of the following neurotransmitters can cause presynaptic inhibition? a) Serotonin b) Epinephrine c) Acetylcholine d) GABA e) Cholecystokinin

d) GABA