Sensation and Perception Questions

Correct answer: B

The optic disc is a part of the retina where the axons of retinal ganglion cells leave the eye to form the optic nerve. The optic disc lacks photoreceptors, thus creating a small "blind spot" in our visual field. We do not typically notice the blind spot because the brain uses information from the other eye to make the visual scene appear intact. Go to this link for a quick demonstration of the existence of your blind spot:

Correct answer: C

The spinothalamic tract, which is part of the larger anterolateral pathway in the spinal cord, is the main pathway for carrying pain and temperature information to the brain. See this article for more info:

Correct answer: B

The small bumps that cover the tongue are sometimes mistakenly called taste buds, but the correct term for them is papillae. Taste buds are found in the walls of the papillae, with each papilla containing anywhere from a just a few to hundreds of taste buds. Each taste bud contains 50-150 taste receptor cells, which interact with the substances in the mouth through microvilli that extend into the mouth.

Correct answer: C

Hair cells get their name because they have small hair-like projections called stereocilia. The stereocilia deflect in response to mechanical forces, with the result being the production of electrochemical signals used to convey sensory information. Hair cells in the cochlea are responsible for creating signals to transmit information about sound waves, while those in the vestibular system are responsible for creating signals to transmit information about head movement.

Correct answer: A

Rods are sensitive to low levels of illumination, but cones do not function effectively at low light levels. In typical moonlight levels of illumination, rods would be the primary source of information for vision. Since rods don't allow for color perception, we typically see in grayscale in low levels of illumination. Often, we may believe we perceive color at these low light levels, but it is caused by our brain "applying" color based on the expected color due to previous experience.

Correct answer: B

Even though the brain is where we process (and become aware of) pain in the body, there are no pain receptors in brain tissue itself. This explains how brain surgery can be performed on awake patients---a procedure known as "awake craniotomy"---without them feeling pain from manipulation of their brain tissue. While brain tissue doesn't have pain receptors, however, there are structures in the cranium that are pain-sensitive, such as the meninges (particularly the dura mater).

Correct answer: B

The genetic mutations that commonly lead to color blindness are frequently found on the X chromosome. Because females have two X chromosomes, if there is a mutation on an X chromosome gene in a female, it is more likely to be balanced out by a "healthy" gene on the other X chromosome. In males, however, a mutation on an X chromosome gene is more likely to have an influence due to a lack of another X chromosome and thus a lack of a "healthy" gene to counteract the mutation.

Correct answer: B

The dorsal columns-medial lemniscus pathway is the main pathway that carries tactile sensations---including sensations of touch, pressure, and vibration---to the brain. It also carries information about proprioception. Neurons in the dorsal columns travel up the spinal cord and synapse in the brainstem on neurons that form the second part of the pathway: the medial lemniscus. This travels up to the somatosensory cortex, which is the main cortical area for processing touch sensations.

Correct answer: B

The semicircular canals consist of three tubes, positioned approximately at right angles to one another, that are each situated in a plane in which the head can rotate. This design allows each of the canals to detect one of the following head movements: nodding up and down, shaking side to side, or tilting left and right.

Correct answer: D

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. The result of this is that all of the information from the right visual field ends up traveling to the left side of the brain, and vice versa. After the optic chiasm, the visual fibers are no longer called the optic nerve; they’re now called the optic tract.

Correct answer: B

Olfaction, or smell, is unique in that olfactory information does not get sent to the thalamus before being sent to the cortex. Instead, it is sent to the olfactory cortex, where the initial processing of olfactory information occurs. It's unknown why exactly this unique pathway exists; some have hypothesized it is an evolutionary adaptation to enable faster processing of olfactory information.

Correct answer: B

The cochlea is a coiled structure that resembles a snail shell (cochlea comes from the Greek kochlos, which means "snail"); it is found within the inner ear. It contains the organ of Corti, which is the main receptor organ for hearing.

Correct answer: C

Nociceptors are cutaneous receptors that are specialized to detect noxious stimuli like extreme pressure, very hot or cold temperatures, or tissue damage. When activated, nociceptors convey information regarding a painful stimulus to the spinal cord, and from there it gets sent up to the brain.

Correct answer: B

Most of the neurons in the optic tracts terminate in the lateral geniculate nucleus of the thalamus. Here, the optic tracts synapse on neurons that leave the lateral geniculate nucleus and extend toward the back of the brain as bundles of fibers called the optic radiations. The optic radiations travel back to the primary visual cortex.

Correct answer: C

The visual signal travels from photoreceptors to bipolar cells to ganglion cells. The ganglion cells carry the signal out of the eye, forming the optic nerve.

Correct answer: D

Cochlear implants involve a microphone that detects sound, as well as a sound processor that converts the sound into a radio frequency signal. The signal is transmitted to a receiver implanted under the skin behind the ear. The receiver decodes the signal, then converts it into electrical currents. The currents are sent along wires to stimulate the auditory nerve, which sends auditory information to the brain.

Correct answer: D

The periaqueductal gray, or PAG, is an area of gray matter found in the brainstem. Although the functions of the PAG are complex and not fully understood, it is best known for its role in the inhibition of pain.

Correct answer: C

The dorsal columns-medial lemniscus pathway (also called the posterior columns-medial lemniscus) is the main pathway that carries tactile information to the brain. It carries information about fine touch, vibration, pressure, and proprioception (the sense of body position).

Correct answer: D

The fovea is a small, specialized area in the center of the retina. It's the area responsible for our sharpest, most detailed vision. The fovea contains mostly cone photoreceptors, which are responsible for color vision and fine detail. It has virtually no rods, which are more sensitive to low light but less precise.

Correct answer: D

Pacinian corpuscles are rapidly-adapting touch receptors with very large receptive fields. They are thought to be most effective at transmitting information about vibrations objects cause when they are contacted or grasped by the hand. This information may be important for the use of tools.

Correct answer: B

The basilar membrane moves in response to fluid vibrations in the cochlea. This movement causes the hair cells' stereocilia to bend, which leads to their activation and the transmission of sound signals to the brain.

Correct answer: D

The dorsal columns-medial lemniscus pathway carries conscious proprioception (and fine touch, vibration, etc.) to your cerebral cortex for conscious awareness. Other pathways like spinocerebellar tracts handle unconscious proprioception, feeding it to the cerebellum for coordination (not conscious perception).

Correct answer: B

Olfactory receptors are located in the olfactory epithelium—a specialized area of tissue at the top of the nasal cavity. This is where odorant molecules first bind, initiating the sense of smell.

Correct answer: B

In darkness, rod photoreceptors are depolarized and continuously release the neurotransmitter glutamate. When exposed to light, a phototransduction cascade is triggered that leads to the closure of sodium channels, causing the cell to hyperpolarize. This hyperpolarization reduces glutamate release, which is the key signal that initiates changes in downstream retinal cells and ultimately leads to visual perception.

Correct answer: B

The vestibular system, which includes structures in the inner ear and their connections to the brain, plays a key role in balance and a sense of stability. Vertigo is typically associated with a disruption in function of either the vestibular system or one of the regions it communicates with to maintain our sense of balance.

Correct answer: D

At the optic chiasm, fibers from the nasal (medial) half of each retina cross to the opposite side, while fibers from the temporal (lateral) halves stay on the same side. This partial crossing allows visual information from the same visual field to be processed together in the opposite hemisphere of the brain.

Correct answer: C

The ampullae of the semicircular canals contain hair cells that respond to rotational movements of the head. The utricle and saccule detect linear acceleration, and the cochlear duct is involved in hearing.

Correct answer: C

A-delta fibers are thinly myelinated and conduct signals relatively quickly, carrying information about fast, sharp, well-localized pain.

Correct answer: D

Photoreceptors (rods and cones) synapse directly onto bipolar cells, initiating the flow of visual information that will eventually reach the brain and form a visual scene.

Correct answer: B

Allodynia is pain triggered by a stimulus that does not normally cause pain, such as light touch, mild pressure, or gentle temperature changes. It often occurs in conditions where the nervous system becomes sensitized and misinterprets non-painful input as painful.