All Questions: 511-540

Correct answer: B

Inside the rod cell there is a substance called rhodopsin, which is made up of a protein called opsin and a molecule called retinal, which is capable of absorbing light. When retinal absorbs light, its configuration changes, an event that initiates the process of phototransduction.

Correct answer: D

Caudal means "towards the tail." At the level of the spinal cord in humans, rostral points up towards the head while caudal points down towards the end of the cord. In the brain, however, caudal points toward the posterior part of the brain.

Correct answer: B

The subiculum serves as the primary output structure of the hippocampal formation. Information processed through the hippocampal circuit is funneled into the subiculum, which then sends projections to a wide range of targets, including the entorhinal cortex and other cortical and subcortical areas.

Correct answer: C

The ganglion cells leaving the eye form the optic nerve. At the optic chiasm, about 60% of the axons from the optic nerve cross over to the other side of the brain, while the rest stay on the side they originated on. After the optic chiasm, the visual fibers are no longer called the optic nerve—they’re now called the optic tract.

Correct answer: C

Allosteric modulators bind to a receptor at a different site from where an agonist binds and influence the function of the receptor. Allosteric modulators can increase or decrease the likelihood of an agonist binding to a receptor, enhance or reduce the effects an agonist has when it does bind, or activate the receptor on their own.

Correct answer: B

Stage 2 sleep is characterized by the presence of phenomena on an EEG known as sleep spindles and K complexes. Sleep spindles are trains of high-frequency waves. A K complex involves a biphasic wave that stands out from the rest of the EEG.

Correct answer: B

Studies suggest that DMT’s action at the 5-HT2A serotonin receptor is especially important for producing its characteristically intense visual hallucinations.

Correct answer: C

Saltatory conduction is the propagation of an action potential along a myelinated axon by effectively "jumping" from one node of Ranvier to the next. This process greatly increases the speed of nerve impulse transmission compared to conduction along unmyelinated axons.

Correct answer: A

The most common type of color blindness is red-green color blindness, where individuals have difficulty distinguishing red and green hues.

Correct answer: D

Declarative memory is sometimes called explicit memory, and it refers to memories we can consciously access and describe. This includes episodic memory, which involves events from our own lives—such as what you did yesterday—or semantic memory, which consists of facts and general knowledge, like knowing what an axon is.

Correct answer: A

Serotonin is a monoamine neurotransmitter, a term that refers to its chemical structure and the fact that it is derived from an amino acid. To synthesize serotonin, the amino acid tryptophan is converted to 5-hydroxytryptophan, or 5-HTP, and 5-HTP is converted to serotonin, or 5-HT.

Correct answer: B

Myelination in parts of the prefrontal cortex involved in impulse control, long-term planning, and decision-making continues through adolescence and is not typically complete until adulthood. As a result, the neural circuits that support these functions may operate less efficiently in adolescents than in adults, potentially contributing to some stereotypical aspects of teen behavior.

Correct answer: C

Dopamine is often implicated in ADHD because medications that are commonly used to treat the condition, such as amphetamine and methylphenidate, cause increased transmission of dopamine and norepinephrine.

Correct answer: C

The active ingredients in kratom are thought to activate opioid receptors involved in pain relief to account for kratom’s analgesic and other opioid-like effects. Some refer to kratom alkaloids as "atypical opioids."

Correct answer: B

Because the superior oblique muscle helps to move the eye downwards, when the trochlear nerve is damaged the eye tends to deviate upwards since there is no opposing force coming from the superior oblique. This can result in diplopia, or double-vision. Some patients will adopt a head tilt as a compensatory mechanism to better align the eyes and reduce the diplopia.

Correct answer: C

Psilocybin itself is not thought to be very psychoactive, but soon after it is ingested it is metabolized into a substance called psilocin, which is highly psychoactive. We don't have a complete understanding of how psilocin produces its effects, but its action at serotonin receptors is thought to be critical to the effects of the drug.

Correct answer: D

Central sensitization is a rapid increase in the excitability of neurons in the dorsal horn of the spinal cord following high levels of nociceptor activity. This heightened excitability lowers the threshold for pain, increasing pain sensitivity.

Correct answer: B

When sound waves travel through the canal of our ear, they hit the tympanic membrane or 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: B

Mitral cells are one of the main output neurons of the olfactory bulb. They receive synaptic input from olfactory receptor neurons (within glomeruli) and send their axons through the olfactory tract to higher brain regions, including the olfactory cortex.

Correct answer: A

To do a PET scan, a patient is injected with a radioactive substance that emits positrons, which then emit gamma rays when they collide with electrons in brain tissue. These gamma rays are detected by the PET scanner. Detection of these rays can be used to determine blood flow to more active parts of the brain as well as the distribution of specific molecules, depending on the tracer that is used.

Correct answer: D

Frontotemporal dementia, or FTD, is a term used to describe a collection of related brain disorders that involve the neurodegeneration of the frontal and temporal lobes. The three main subtypes of FTD are: behavioral variant FTD, semantic variant primary progressive aphasia, and nonfluent variant primary progressive aphasia.

Correct answer: B

Despite popular conceptions, dopamine is not thought to directly produce feelings of pleasure. Instead, it seems to play a key role in motivation and reward learning—helping the brain recognize cues associated with rewards and driving behavior to seek them out again.

Correct answer: C

The pupillary light reflex is used to assess the function of the optic and oculomotor nerves and related structures. If light shined in the left eye causes only the left pupil to constrict, this indicates the sensory signal was received (since the left pupil constricted), but it may suggest a problem with the right oculomotor nerve (because the right pupil didn't constrict).

Correct answer: D

The vestibular system uses two organs, known as the otolith organs, to detect forward and backward movements and gravitational forces. The two otolith organs in the vestibular labyrinth are the utricle, which detects movement in the horizontal plane, and the saccule, which detects movement in the vertical plane.

Correct answer: C

Protein aggregates in Parkinson's disease are known as Lewy bodies, named after Fritz Lewy, who discovered them in 1910.

Correct answer: D

The anterior pituitary produces a number of hormones, and their secretion into the bloodstream is controlled by releasing hormones that are secreted by the hypothalamus.

Correct answer: C

The cingulate gyrus sits just above the corpus callosum. Its functions are not fully understood, but it is thought to play important roles in emotion and memory.

Correct answer: B

The subarachnoid space is a region between the arachnoid mater and pia mater that contains cerebrospinal fluid.

Correct answer: A

The striatum is often conceptualized a being divided into dorsal and ventral sections; the dorsal striatum contains the caudate and putamen while the ventral striatum contains the nucleus accumbens.

Correct answer: B

Damage to the oculomotor nerve often results in deviation of the affected eye to the side and downwards, impaired vertical and medial eye movements, and ptosis (drooping of the eyelid).