All Questions: 481-510

Correct answer: A

In the peripheral nervous system, glial cells called Schwann cells form myelin. Each Schwann cell wraps around one segment of an axon many times to form one myelinated internode.

Correct answer: B

It is thought that the central components of the structure of the blood-brain barrier are the tight junctions of endothelial cells, the cells that make up the interior surface of blood vessels. The endothelial cells that make up the blood-brain barrier are fused tightly together to form tight junctions that restrict diffusion across the blood vessel lining.

Correct answer: C

The transition to sleep is thought to be controlled to a large degree by the inhibition of ascending arousal systems. For example, neurons in a nucleus of the hypothalamus called the ventrolateral preoptic nucleus, or VLPO, project to most parts of the ascending arousal system and release the inhibitory neurotransmitters GABA and galanin onto those wake-promoting regions.

Correct answer: A

The knee-jerk reflex causes immediate contraction of the quadriceps muscle to produce movement of the leg. Additionally, the sensory neurons traveling from muscle spindles stimulate interneurons that inhibit the activity of motor neurons that supply opposing muscles like the hamstring muscle. The stimulation of these inhibitory interneurons causes the action of the quadriceps muscle to be unopposed.

Correct answer: C

After neurotransmitters have communicated with a postsynaptic neuron, they must be removed from the synaptic cleft. To accomplish this, many synapses rely primarily on proteins called transporter proteins, which remove neurotransmitters from the synaptic cleft and typically shuttle them back into the neuron that released them in a process called reuptake.

Correct answer: B

Deep brain stimulation is a neurosurgical approach that involves the use of brain-implanted electrodes to treat a variety of neurological and psychiatric conditions. It is primarily used to treat Parkinson’s disease, but has also been approved by the FDA for use in treating epilepsy and obsessive-compulsive disorder, and is being studied as a potential treatment for a number of other disorders.

Correct answer: D

Serotonin neurons are primarily found in the brainstem in clusters of neurons called the raphe nuclei. Serotonin neurons from the raphe nuclei project throughout the brainstem and brain, and provide serotonin to the rest of the central nervous system.

Correct answer: B

Narcolepsy type 1 is linked to a loss of orexin-producing neurons in the hypothalamus, leading to low orexin levels. Orexin neurons have an excitatory effect on several regions of the brain that are involved in promoting wakefulness and suppressing REM sleep. Thus, the loss of these neurons leads to deficiencies in maintaining wakefulness and is linked to the dysregulation of REM sleep.

Correct answer: C

Similar to the benzodiazepines, zolpidem exerts its effects by increasing activity at receptors for the neurotransmitter GABA. GABA is primarily an inhibitory neurotransmitter, and increasing GABA activity can promote sleep as GABA can decrease activity in parts of the brain that promote wakefulness.

Correct answer: B

Fatal insomnia is a very rare terminal condition characterized by difficulty sleeping that becomes progressively worse over time. Although the disease is typically genetic in origin, sporadic cases without a clear genetic basis have also been documented. Thus, the statement is false.

Correct answer: A

When light hits photoreceptors, it interacts with a molecule called photopigment, which begins a chain of events that serves to propagate the visual signal. The signal is transmitted to cells called bipolar cells, which connect photoreceptors to ganglion cells. Bipolar cells pass the signal on to ganglion cells, which leave eye in a large cluster at an area called the optic disc.

Correct answer: B

Sodium entering the neuron brings positive charge into the cell, making the membrane potential less negative and moving it closer to threshold.

Correct answer: D

When sound waves travel through the canal of our ear, they hit the tympanic membrane (eardrum) and cause it to vibrate. This vibration prompts movement in the ossicles, a trio of tiny bones that transmit the vibration to a structure called the oval window, which sits in the wall of the cochlea.

Correct answer: C

The primary somatosensory cortex is responsible for processing somatic sensations, or sensations from the body that include touch, proprioception or the position of the body in space, nociception or pain, and temperature.

Correct answer: B

Most neurotransmitters are packaged in small membranous sacs called vesicles.

Correct answer: D

Ketamine and its metabolite norketamine both act at a receptor for the neurotransmitter glutamate called the NMDA receptor. Glutamate is the primary excitatory neurotransmitter in the brain, and ketamine and norketamine act as antagonists at the NMDA receptor, which means that they block the receptor and inhibit activity there.

Correct answer: C

There are 3 identified ionotropic glutamate receptors, named for substances that activate them: NMDA, AMPA, and kainate receptors. mGluR1 through mGluR8 are metabotropic glutamate receptors.

Correct answer: A

Tricyclic antidepressants are thought to work to treat depression by blocking the reabsorption, or reuptake, of neurotransmitters like serotonin and norepinephrine.

Correct answer: B

NMDA receptors are not activated by low levels of glutamate release because the ion channel of an NMDA receptor is blocked by a magnesium ion. If frequent action potentials cause greater stimulation of AMPA receptors, however, this will cause the postsynaptic neuron to depolarize, which eventually causes the voltage-dependent magnesium blockage of the NMDA receptor to be removed.

Correct answer: B

The white matter of the spinal cord consists of bundles of ascending and descending fibers that carry sensory information to the brain and motor information to the body, respectively.

Correct answer: C

Oxytocin is primarily produced in the hypothalamus and transported through axons to the posterior lobe of the pituitary gland. From there it is secreted into the bloodstream of the body.

Correct answer: A

Tau protein is normally found inside neurons and involved in maintaining neuronal structure. It is found in a misfolded state in Alzheimer’s, and it accumulates inside neurons in clusters called neurofibrillary tangles.

Correct answer: D

The anterior cerebral arteries supply the medial frontal and parietal lobes, and they are connected by the anterior communicating artery.

Correct answer: C

Although GABA’s primary functions are as a neurotransmitter, it has the structure of an amino acid and thus is referred to as an amino acid neurotransmitter. It is synthesized from another amino acid neurotransmitter, glutamate, in a reaction catalyzed by the enzyme glutamic acid decarboxylase.

Correct answer: C

The pathology of Huntington’s disease can be traced back to a mutation in a single gene called huntingtin. The mutation that causes Huntington’s disease is a dominant mutation. Thus, if one parent has the disease-causing mutation, their child has a 50% chance of inheriting it.

Correct answer: D

The ventricles are a network of cavities distributed throughout the brain. Their primary role is in the production and circulation of cerebrospinal fluid.

Correct answer: B

After the falling phase of the action potential, the neuron returns to resting membrane potential but actually to overshoots it, and the cell becomes more negative than resting membrane potential. This is referred to as hyperpolarization. During this phase, known as the refractory period, it is very difficult to cause the neuron to fire again.

Correct answer: A

The abducens nerve is a motor nerve responsible for moving the eye laterally toward the side of the head. Damage to the abducens nerve causes impairment in the ability of the eye the nerve supplies to to move laterally, and a condition called esotropia in which the eye that’s affected deviates medially. This also leads to diplopia, or double vision.

Correct answer: A

The ventral tegmental area is a major source of dopamine neurons in the brain. In the mesolimbic pathway, these neurons project to the nucleus accumbens, a key structure in the ventral striatum involved in motivation and reward. Therefore, the cell bodies of these neurons are located in the VTA.