All Questions: 571-600
571. The inhibitory neurotransmitter GABA is synthesized directly from which of the following amino acids?
- A. glutamate
- B. aspartate
- C. glutamine
- D. tyrosine
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Correct answer: A
GABA is synthesized from another amino acid neurotransmitter, glutamate, in a reaction catalyzed by the enzyme glutamic acid decarboxylase.
572. Most antipsychotic drugs share which of the following as a primary mechanism of action?
- A. antagonism of norepinephrine receptors
- B. antagonism of dopamine receptors
- C. antagonism of glutamate receptors
- D. antagonism of GABA receptors
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Correct answer: B
Although newer antipsychotics vary more in their pharmacology, most drugs in the class work at least in part by blocking dopamine receptors.
573. Which cranial nerve innervates four of the six extraocular muscles and is primarily responsible for moving the eye upward, downward, and medially?
- A. optic nerve (CN II)
- B. oculomotor nerve (CN III)
- C. trochlear nerve (CN IV)
- D. abducens nerve (CN VI)
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Correct answer: B
The oculomotor nerve is responsible for supplying 4 of the 6 extraocular muscles: the medial rectus, which moves the eye towards the nose; the superior rectus, which moves the eye upwards; the inferior rectus, which moves the eye downwards; and the inferior oblique, which moves the eye up and out.
574. Which of the following findings is most consistent with upper motor neuron damage?
- A. weakness or paralysis with decreased or absent muscle tone
- B. weakness or paralysis with decreased or absent reflexes
- C. weakness or paralysis with spasticity
- D. weakness or paralysis with muscle atrophy
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Correct answer: C
Symptoms of upper motor neuron damage, which are collectively called upper motor neuron syndrome, can include weakness or paralysis, spasticity, increased muscle tone, over-responsive reflexes, and a positive Babinski sign, which occurs when the bottom of the foot is stroked and---instead of the toes curling down---the big toe extends up and the other toes fan out.
575. The cochlea contains three fluid-filled cavities. Which of the following correctly names these three cavities?
- A. scala vestibuli, scala media, and scala tympani
- B. scala vestibuli, vestibular duct, and tympanic duct
- C. scala vestibuli, scala cochlearis, and scala tympani
- D. scala media, vestibular canal, and tympanic canal
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Correct answer: A
The interior of the cochlea consists of three fluid-filled canals that run parallel to one another: the scala vestibuli, the scala media, and the scala tympani.
576. Which of the following serves as the major input pathway to the hippocampal formation?
- A. fornix
- B. anterior commissure
- C. Schaffer collaterals
- D. perforant pathway
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Correct answer: D
Information enters the hippocampal formation mainly through an adjacent area called the entorhinal cortex, which serves as a primary interface between the hippocampus and much of the rest of the cerebral cortex. The major pathway from the entorhinal cortex to the hippocampal formation is the perforant pathway, which carries information to the dentate gyrus and other parts of the hippocampal formation.
577. At the neuromuscular junction, acetylcholine receptors are concentrated within the:
- A. active zones of the presynaptic terminal
- B. basal lamina of the synaptic cleft
- C. junctional folds of the motor end plate
- D. presynaptic membrane of the axon terminal
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Correct answer: C
When a motor neuron approaches a muscle, it branches out into several extensions that end in areas called synaptic boutons, which are situated over a specialized region of muscle called the end-plate. The end-plate beneath each synaptic bouton contains several deep indentations called junctional folds. These junctional folds contain high numbers of acetylcholine receptors.
578. Varenicline (Chantix) is a medication used to help people stop smoking. It binds to acetylcholine receptors, producing enough receptor activation to reduce nicotine cravings and withdrawal symptoms, but not the maximal response possible at those receptors. Which of the following terms best describes this mechanism of action?
- A. full agonism
- B. partial agonism
- C. inverse agonism
- D. antagonism
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Correct answer: B
Agonists that can generate a maximal response at a receptor are called full agonists. Partial agonists are only able to generate a fraction of the possible response at a receptor. Varenicline is a partial agonist.
579. During REM sleep, neurons in which of the following brain regions project to the medulla and spinal cord to produce the muscle paralysis characteristic of REM sleep?
- A. cerebellum
- B. thalamus
- C. pons
- D. basal ganglia
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Correct answer: C
During REM sleep, certain neurons in the pons drive activation of the cortex, while others project to the medulla and spinal cord to inhibit motor neurons and cause the paralysis characteristic of REM sleep.
580. Although the trigeminal nerve (CN V) is the main sensory nerve of the head, it also provides motor innervation to muscles involved in:
- A. facial expression
- B. tongue movement
- C. eye movement
- D. mastication (chewing)
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Correct answer: D
Although the trigeminal nerve is the main sensory nerve of the head, it also controls the muscles involved with chewing.
581. Which type of seizure involves abnormal electrical activity that develops simultaneously in widespread areas of both cerebral hemispheres?
- A. focal seizure
- B. generalized seizure
- C. nonepileptic seizure
- D. focal-to-bilateral tonic-clonic seizure
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Correct answer: B
In generalized seizures, abnormal electrical activity arises simultaneously in widespread areas of both cerebral hemispheres. This contrasts with focal seizures, in which abnormal electrical activity originates in a localized area of one cerebral hemisphere but may spread to other regions of the brain.
582. Wernicke-Korsakoff syndrome most commonly develops as a result of thiamine deficiency associated with chronic use of which of the following substances?
- A. heroin or other opioids
- B. alcohol
- C. nicotine
- D. methamphetamine
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Correct answer: B
Although alcohol consumption is not always a factor in Wernicke-Korsakoff syndrome, the condition is typically linked to alcoholism. Wernicke-Korsakoff syndrome is caused by a deficiency in thiamine, also known as vitamin B1. Alcohol consumption can interfere with thiamine in a number of ways, such as by impairing its absorption from the small intestine, affecting its transport into the brain, and disrupting its utilization.
583. The withdrawal reflex involves activation of the ______ muscle and inhibition of the ______ muscle in the limb that contacts a painful stimulus.
- A. extensor; flexor
- B. flexor; flexor
- C. flexor; extensor
- D. extensor; extensor
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Correct answer: C
The withdrawal reflex is an automatic response enacted to withdraw a limb from a painful stimulus. It involves activation of the flexor muscle in the limb, which causes the limb to withdraw from the painful stimulus. The extensor muscle is inhibited to prevent the muscle from counteracting the efforts of the flexor muscle.
584. Association areas of the cerebral cortex are best described as regions that:
- A. integrate sensory, motor, and cognitive information to support complex behaviors
- B. are devoted primarily to one type of sensory information, such as vision
- C. generate reflexive motor responses without input from other brain regions
- D. relay information between the cerebral cortex and the spinal cord
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Correct answer: A
Association areas are involved in the integration of information from multiple brain regions. This integration can do things like add complexity to sensory perceptions or facilitate higher cognitive processes.
585. A neuron is exposed to a substance that selectively blocks voltage-gated potassium channels. Which of the following would be the most likely effect on a typical action potential?
- A. the action potential will fail to reach threshold
- B. the peak of the action potential will be substantially reduced
- C. the action potential will reach threshold more quickly
- D. repolarization will be prolonged
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Correct answer: D
TEA (tetraethylammonium) blocks voltage-gated potassium channels, which normally help repolarize the membrane after depolarization. As a result, repolarization is slower, causing the action potential to have a longer duration.
586. A person has damage to the left optic tract. Which visual deficit would you expect?
- A. blindness in the left eye
- B. blindness in the right eye
- C. loss of the left visual field in both eyes
- D. loss of the right visual field in both eyes
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Correct answer: D
After information from the two eyes reaches the optic chiasm, visual information is organized by visual field, not by eye. The left optic tract carries information from the right visual field of both eyes to the left side of the brain. So damage to the left optic tract would cause a loss of the right visual field in both eyes, also called a right homonymous hemianopia.
587. Which of the following is true about the molecular clock in neurons of the suprachiasmatic nucleus (SCN)?
- A. PER and CRY proteins inhibit the activity of CLOCK and BMAL1
- B. CLOCK and BMAL1 inhibit transcription of the PER and CRY genes
- C. PER and CRY proteins activate their own gene transcription
- D. SCN rhythms are generated by melatonin released within the SCN
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Correct answer: A
CLOCK and BMAL1 stimulate production of PER and CRY proteins. As PER and CRY accumulate, they inhibit the activity of CLOCK and BMAL1, reducing their own production. This negative feedback loop helps generate the brain's approximately 24-hour circadian rhythm.
588. Which of the following arteries is formed by the union of the two vertebral arteries?
- A. internal carotid artery
- B. middle cerebral artery
- C. anterior communicating artery
- D. basilar artery
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Correct answer: D
The two vertebral arteries come together to form the basilar artery.
589. Which region of the substantia nigra contains a high density of GABA neurons?
- A. substantia nigra pars compacta
- B. substantia nigra pars reticulata
- C. GABA neurons are not prevalent in any part of the substantia nigra
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Correct answer: B
The substantia nigra is made up of two distinct regions: the substantia nigra pars compacta and the substantia nigra pars reticulata. The dopamine neurons in the substantia nigra are primarily found in the substantia nigra pars compacta, and the substantia nigra pars reticulata is more heavily populated with GABA neurons.
590. Which of the following sequences correctly describes the flow of information through a neuron?
- A. soma → dendrites → axon → axon terminals
- B. dendrites → axon terminals → soma → axon
- C. axon terminals → soma → dendrites → axon
- D. dendrites → soma → axon → axon terminals
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Correct answer: D
Typically, dendrites receive information from other neurons, the soma integrates those signals, and if the combined input is strong enough, an action potential is generated. The action potential then travels down the axon to the axon terminals, where it can trigger the release of neurotransmitters.
591. Which of the following structures is considered a circumventricular organ?
- A. posterior pituitary
- B. corpus callosum
- C. hippocampus
- D. thalamus
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Correct answer: A
The circumventricular organs are a group of structures that lack a typical blood-brain barrier, allowing communication between the blood and the brain. The posterior pituitary is one of these organs; its lack of a typical blood-brain barrier allows hormones such as oxytocin and vasopressin to be released directly into the bloodstream.
592. The spinal cord contains two regions that are enlarged because they contain additional neurons needed to innervate the limbs. In which regions of the spinal cord do these enlargements occur?
- A. thoracic and sacral regions
- B. cervical and thoracic regions
- C. cervical and lumbar regions
- D. lumbar and sacral regions
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Correct answer: C
There are two locations along the cord that are slightly enlarged---the cervical and lumbar enlargements---because these parts of the spinal cord contain more neurons in order to supply the limbs. The lower enlargement is often referred to as the lumbosacral enlargement because it also includes several sacral segments.
593. After entering the spinal cord, pain fibers often travel up or down one or more spinal segments before synapsing in the dorsal horn. These ascending and descending fibers travel in:
- A. Lissauer's tract
- B. fasciculus gracilis
- C. corticospinal tract
- D. Clarke's column
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Correct answer: A
The sensory neurons carrying pain signals enter the spinal cord through the dorsal root and branch off into ascending and descending collaterals that travel up or down the spinal cord for one or more segments in a collection of fibers known as Lissauer’s tract before synapsing in the dorsal horn, an area of gray matter in the spinal cord.
594. The recognizable psychostimulant effects of methamphetamine are thought to be most directly caused by:
- A. increased release of dopamine, norepinephrine, and serotonin
- B. antagonism of GABA receptors
- C. activation of nicotinic acetylcholine receptors
- D. inhibition of serotonin synthesis
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Correct answer: A
The main mechanism of action of methamphetamine in the central nervous system is similar to that of amphetamine and involves the increased release of dopamine, norepinephrine, and serotonin.
595. Which of the following is a primary effect of the hormone ghrelin?
- A. it suppresses appetite and promotes feelings of satiety
- B. it promotes appetite and helps stimulate food intake
- C. it increases insulin secretion to lower blood glucose
- D. it decreases activity in hunger-related brain regions
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Correct answer: B
Ghrelin is produced mainly by the stomach and is released when energy availability is low, such as during a period of fasting. Ghrelin levels typically rise before meals and fall after eating, and thus may play an important role as a short-term driver of hunger and feeding. Ghrelin is sometimes referred to as the "hunger hormone."
596. Satellite glial cells are found in the:
- A. central nervous system
- B. peripheral nervous system
- C. central and peripheral nervous systems
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Correct answer: B
Satellite cells surround neurons in some parts of the peripheral nervous system, playing a protective and supportive role. They are thought to help regulate the local environment around neurons and may play a role in pain signaling.
597. Huntington's disease is caused by which of the following genetic mechanisms affecting the huntingtin (HTT) gene?
- A. single-nucleotide substitution in the HTT gene
- B. deletion of the HTT gene
- C. duplication of the HTT gene
- D. an excess of trinucleotide repeats in the HTT gene
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Correct answer: D
The huntingtin gene contains a DNA sequence that consists of three nucleotides in repetition---a pattern known as a trinucleotide repeat. When the gene is mutated, an excess number of repeats can occur, and a mutated form of huntingtin protein is created. The higher the number of repeats, the greater the risk of disease, and all people with 40 or more repeats in the huntingtin gene will develop Huntington’s disease.
598. Current evidence suggests that sleepwalking may occur because:
- A. the entire brain abruptly transitions from sleep to wakefulness
- B. REM sleep intrudes into slow-wave sleep
- C. wake- and sleep-like activity occur in different brain regions at the same time
- D. there is complete activation of the prefrontal cortex during slow-wave sleep
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Correct answer: C
Although the exact cause of sleepwalking remains uncertain, evidence suggests it may result from some brain regions, such as those involved in movement, showing wake-like activity while other regions involved in conscious awareness and complex cognition remain in a sleep-like state.
599. According to traditional models of basal ganglia function, what is the primary role of the indirect pathway?
- A. it facilitates voluntary movement
- B. it inhibits unwanted movement
- C. it increases dopamine release
- D. it directly activates the cortex
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Correct answer: B
Activity in the indirect pathway is thought to antagonize the activity of the direct pathway and act to keep unwanted movements from occurring.
600. Which of the following structures is found in the midbrain?
- A. locus coeruleus
- B. inferior olivary nucleus
- C. nucleus gracilis
- D. superior colliculus
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Correct answer: D
The superior colliculi are found in the midbrain. Along with the inferior colliculi, they form four bumps on the posterior surface of the brainstem. Among other things, the superior colliculi are thought to be involved with directing behavioral responses toward stimuli in the environment.
