NEURO 3000 MT 4 CH 12

Which of the following statements is false?

Warm receptors are coupled to Aδ and C fibers, whereas cold receptors are coupled only to C fibers. Cold receptors are coupled to Aδ and C fibers, whereas warm receptors are coupled only to C fibers. Given the organization of this system and its similarity to the pain pathway, damage to the spinal cord on one side will cause a loss of temperature sensitivity on the opposite side of the body.

When a dorsal root is cut, the corresponding dermatome on that side of the body does not lose all sensation. How many adjacent dorsal roots would need to be cut to result in a loss of sensation?

3 The residual somatic sensation is explained by the fact that the adjacent dorsal roots innervate overlapping areas. To lose all sensation in one dermatome, therefore, three adjacent dorsal roots must be cut.

Areas 1 and 2 of the postcentral gyrus receive inputs from area

3b The projections from 3b to area 1 send mainly texture information, while the projection to area 2 emphasizes size and shape. Small lesions in area 1 or 2 produce predictable deficiencies in discrimination of texture, size, and shape.

Which of the following will produce the most robust change in activity of temperature-sensitive receptors?

A decrease in temperature, from 37ºC to 32º With thermoreception, as with most other sensory systems, it is the sudden change in the quality of a stimulus that generates the most intense neural and perceptual responses.

Imagine skin temperature dropped from 37ºC to 32ºC. What would you expect in regard to the activity of a cold receptor over the course of the few seconds that followed?

A high rate of firing initially followed by adaptation. With thermoreception, as with most other sensory systems, it is the sudden change in the quality of a stimulus that generates the most intense neural and perceptual responses. Cold and warm receptors are most responsive to sudden changes in temperature, but they adapt over several seconds.

When a dorsal root is cut, the corresponding dermatome on that side of the body does not lose all sensation. Why?

Adjacent dorsal roots innervate overlapping areas. The residual somatic sensation is explained by the fact that the adjacent dorsal roots innervate overlapping areas. To lose all sensation in one dermatome, therefore, three adjacent dorsal roots must be cut.

Which axon from skin has the largest diameter?

Aα Aα fibers have a diameter of 13-20 µm, Aβ 6-12 µm, Aδ 1-5 µm, and C fibers 0.2-1.5 µm.

Which of the following afferent axons carries information from mechanoreceptors of the skin?

Aβ Aα carries information from proprioceptors of skeletal muscle, Aδ pain and temperature information, and C fibers pain, temperature and itch.

Which of the following afferent axons is myelinated and carries information regarding pain and temperature?

Aδ Aα carries information from proprioceptors of skeletal muscle, Aβ information from mechanoreceptors of the skin, and C fibers pain, temperature and itch.

The transduction of painful stimuli occurs in the free nerve endings of which of the following?

Aδ and C The transduction of painful stimuli occurs in the free nerve endings of unmyelinated C fibers and lightly myelinated Aδ fibers. The majority of nociceptors respond to mechanical, thermal, and chemical stimuli.

Which of the following is not a way in which mechanosensitive ion channels can be altered?

Biding of a ligand to a receptor site on the ion channel, causing a conformational change that opens an ion pore in the channel. By definition, ion movement following the binding of an extracellular molecule to a receptor site is ligand-gating. Forces applied to mechanosensitive channels alter gating and enhance or decrease channel opening.

Which of the following afferent axons is unmyelinated and carries information regarding pain and temperature?

C Aα carries information from proprioceptors of skeletal muscle, Aβ information from mechanoreceptors of the skin, and Aδ pain and temperature.

Which axon from skin has the slowest conduction velocity?

C C fibers have a conduction velocity of 0.5-2 m/sec, Aα fibers 80-120 m/sec, Aβ 35-75 m/sec, and Aδ 5-30 m/sec.

Individuals with amputation of a limb - say the arm at the elbow - often report sensations coming from the missing limb when other body parts like the face are touched. What appears to be the reason for these "phantom" sensations?

Cortical regions originally devoted to the missing limb are now activated by stimulating the face. Functional brain imaging reveals that the cortical regions originally devoted to the missing limb are now activated by stimulating the face. While this plasticity may be adaptive in the sense that the cortex does not go unused, the mismatch between sensory stimulation and perception in amputees shows that it can lead to confusion on how signals from S1 should be interpreted.

If half of the spinal cord was damaged in a patient, which of the following would you expect given your knowledge of the ascending pathways for touch and pain/temperature?

Deficits in pain sensitivity on the contralateral side. The organization of ascending touch and pain/temperature pathways leads to a predictable group of deficits when the nervous system is impaired. If half the spinal cord is damaged, certain deficits of mechanosensitivity occur on the same side as the damage: insensitivity to light touch, the vibrations of a tuning fork on the skin, the position of a limb, etc. On the other hand, deficits in pain and temperature sensitivity will show up on the side of the body opposite the cord damage. Movements will be impaired on the ipsilateral side.

Individuals with congenital insensitivity to pain

Despite early training to avoid damaging situations, such individuals tend to develop progressive degeneration of joints and spinal vertebrae, leading to skeletal deformation, degeneration, infection, and finally death.

Which of the following statements is false?

False: Endorphins are lipid-derived molecules. True: Endorphins are relatively small proteins, or peptides. While receptors for endorphins are widely distributed in the CNS, they are particularly concentrated in areas that process or modulate nociceptive information.

The somatic sensory cortex, like other areas of the neocortex, is a layered structure. Thalamic inputs to S1 terminate mainly in layer

IV As is the case for visual and auditory cortex, the thalamic inputs to S1 terminate mainly in layer IV. The neurons of IV then project to cells in the other layers.

Large, myelinated Aβ axons conveying information about a touch to the skin enter the dorsal horn and branch. One branch synapses on second-order sensory neurons. What happens to the other branch?

It ascends straight to the brain. This ascending input is responsible for perception, enabling us to form complex judgments about the stimuli touching the skin.

Which of the following is characteristic of the pain pathway?

It has only free nerve endings in the The pain pathways has only free nerve endings in the skin, uses thin, lightly myelinated Aδ fibers and unmyelinated C fibers, has a slow conduction velocity, and its axons run within the zone of Lissauer and terminate within the substantia gelatinosa.

Which of the following is characteristic of the touch pathway?

It uses large diameter, myelinated Aβ fibers. The touch pathway is characterized by specialized structures in the skin, has a fast conduction velocity, and has axons that terminate deep in the dorsal horn of the spinal cord.

A mechanoreceptor that is slowly adapting

May respond quickly but generates a more sustained response. Merkel's disks and Ruffini's endings are examples of mechanoreceptors that are slowly adapting, generating a more sustained response during a long stimulus after perhaps responding quickly following stimulus application.

In which of the following places in the body will you find mechanoreceptors?

Mechanoreceptors are sensitive to physical distortion such as bending or stretching. They are present throughout the body, and monitor stimuli like skin contact, pressure in the heart or blood vessels, stretching of digestive organs, and force against the teeth. Photoreceptors detect light waves, chemoreceptors specific molecules, thermoreceptors changes in temperature, and nociceptors (a type of chemoreceptor) detect pain.

Which of the following can result in tissue damage?

Nociceptors are activated by stimuli that have the potential to cause tissue damage. The membranes of nociceptors contain ion channels that are activated by these types of stimuli. Oxygen deprivation, some chemicals, temperature extremes, mechanical stress

Area 3b is the primary somatic sensory cortex for each of the following reasons except

Not: its neurons are responsive to all sensory stimuli. Area 3b is the primary somatic sensory cortex because its neurons are very responsive to somatosensory stimuli but not to other sensory stimuli.

A mechanoreceptor that is rapidly adapting

Responds quickly but then stops firing even though the stimulus continues. Meissner's and Pacinian corpuscles respond quickly at first but then stop firing even though the stimulus continues. These receptors are said to be rapidly adapting.

Which of the following is false concerning placebos or the placebo effect?

That the placebo effect occurs means that patients often only imagine their pain. The opioid receptor antagonist naloxone can block the analgesic effect of a placebo, just as it antagonized the effects of morphine, a true analgesic. Apparently, the belief that the treatment will work can be enough to cause activation of the endogenous pain-relief systems of the brain.

Why is the mouth so highly represented in the somatosensory cortex?

The importance of an input, and the size of its representation in cortex, are also reflections of how often it is used.

Which of the following statements is false?

The receptive fields of many S1 neurons produce a very disorderly map of the body on the cortex. Another way to map the somatosensory cortex is to record the activity of a single neuron and determine the site of its somatosensory receptive field on the body. The receptive fields of many S1 neurons produce an orderly map of the body on the cortex.

Which of the following is a somatic sensation?

The senses of temperature, touch, pain, and body position (proprioception) are all somatic senses, which can in turn be subdivided into many more.

statements is false!

There are no areas of skin that are insensitive to temperature. True: There are small areas of skin between the hot and cold spots that are relatively insensitive to temperature.

The posterior parietal cortex appears to be essential for which of the following?

These functions involve a complex integration of somatosensory information with that from other sensory systems, particularly the visual system.

A homunculus is

a somatotopic map. The somatotopic map is not scaled like the human body. Instead, it looks like a caricature: the mouth, tongue, and fingers are incongruously large, while the trunk, arms, and legs are tiny.

The type of drug most likely to suppress an itch is

an antihistamine. Histamine mediates itch by binding to histamine receptors, which then activate TRPV1 channels that are also stimulated by capsaicin and high temperatures.

In Melzack's and Wall's gate theory of pain, the relay of nociceptive signals by the projection neurons is gated by the activity of

an inhibitory interneuron. Activity in the non-nociceptive mechanoreceptor can suppress, or close the "gate" on, nociceptive signals before they can proceed to the spinothalamic tract.

Opioids like heroin, morphine, and codeine produce profound

analgesia. Under conditions of withdrawal from opioids, typically the opposite (hyperalgesia) results. In addition to affecting pain sensitivity, opioids have profound effects on mood, sleep, mental state, and activity of the gastrointestinal tract, to name a few.

Microinjections of morphine into the PAG, raphe nuclei, or dorsal horn all produce

analgesia. While receptors for endorphins are widely distributed in the CNS, they are particularly concentrated in areas that process or modulate nociceptive information. Activation of those receptors induces analgesia.

People with what condition cannot recognize common objects by feeling them?

astereognosia. Individuals with this condition may have a normal sense of touch and no trouble recognizing the object by sight or sound. Deficits are often limited to the side contralateral to the damage.

Clusters of cells in areas of S1 in a rodent that receive information from the vibrissae are known as

barrels. The brain of a rat has a highly evolved sense of touch to the face. Each barrel is specialized to receive input from a single whisker on the rat's face.

The axons of the spinothalamic tract and medial lemniscus

both terminate in the ventral posterior nucleus of the thalamus.

Which of the following molecules is formed from an extracellular peptide called kininogen and directly depolarizes nociceptors?

bradykinin

Nociceptors are notably absent in which of the following?

brain This explains the fact that brain operations can be performed in awake patients because brain tissue lacks receptors of somatic sensation, like those for pain detection.

What substance was used to identify the "hot" receptor protein?

capsaicin Capsaicin activates the thermal nociceptors that also signal painful elevations in temperature above 43ºC. It was the peculiar fact that these nociceptive neurons are selectively activated by capsaicin that led to the discovery of the transduction mechanism for the sensation of hot. TRP stands for transient receptor potential.

Which of the following is not a division of the spinal gray matter?

caudal horn The dorsal horn receives sensory information from incoming dorsal root axons, cells of the intermediate zone contain primarily interneurons, and cell bodies in the ventral horn initiate muscle contraction in the periphery.

The dorsal root ganglion contains

cell bodies of sensory neurons. Axons bringing information from the somatic sensory receptors to the spinal cord or brain stem are the primary afferent axons of the somatic sensory system. The primary afferent axons enter the spinal cord through the dorsal roots; their cell bodies lie in the dorsal root ganglia.

In humans, primary somatosensory cortex lies right behind which sulcus?

central The somatosensory cortex lies on the postcentral gyrus, which sits directly behind the central sulcus. The primary motor cortex lies on the precentral gyrus, directly in front of the central sulcus.

Nociceptors that respond to histamine are

chemical nociceptors. The majority of nociceptors respond to mechanical, thermal, and chemical stimuli and are known as polymodal nociceptors. Mechanical nociceptors show selective responses to strong pressure. Thermal nociceptors show selective responses to burning heat or extreme cold. Chemical nociceptors show selective responses to histamine and other chemicals.

The spinal cord is composed of an inner core of gray matter, surrounded by a thick covering of white matter tracts called

columns The spinal cord is composed of an inner core of gray matter, surrounded by a thick covering of white matter tracts that are often called columns. There are a number of columns in the spinal cord named for their position and that carry sensory and motor information to and from the brain and other spinal cord regions.

The amplification of differences in the activity of neighboring neurons is known as

contrast enhancement. Information is usually transformed as it is passed from one neuron to the next in a sensory pathway. One common transformation is the amplification of differences in the activity of neighboring neurons, also known as contrast enhancement.

The relative size of somatosensory cortex devoted to each body part is

correlated with the density of sensory input received from that part. The somatotopic map is not scaled like the human body. Instead, it looks like a caricature: the mouth, tongue, and fingers are incongruously large, while the trunk, arms, and legs are tiny. As information from your index finger is more useful than that from your elbow, the amount of somatosensory cortex devoted to each body part is correlated with the density of sensory input received from that part.

Elevation of extracellular concentrations of potassium will causes nociceptor membranes to

depolarize. Elevations of extracellular concentrations of potassium will prevent intracellular potassium from moving out of the cell, thus keeping the cell depolarized longer and preventing repolarization.

The substantia gelatinosa is located in the

dorsal horn. Small-diameter pain fibers have their cell bodies in the segmental dorsal root ganglia, and they enter the dorsal horn of the spinal cord. The fibers branch immediately, then travel a short distance up and down the spinal cord in a region called the zone of Lissauer, and then synapse on cells in the outer part of the dorsal horn in a region known as the substantia gelatinosa.

Like the Aβ mechanosensory fibers, the small-diameter Aδ and C fibers have their cell bodies in the

dorsal root ganglia. Small-diameter pain fibers have their cell bodies in the segmental dorsal root ganglia, and they enter the dorsal horn of the spinal cord. The fibers branch immediately, then travel a short distance up and down the spinal cord in a region called the zone of Lissauer.

The outer layer of the skin is known as the

epidermis The epidermis consists of epithelial tissue and mostly dead cells, is dozens of cell layers thick, and sheds itself about once every 45 days. The dermis, underneath the epidermis, consists of primarily connective tissues. The hypodermis, not part of the skin proper, is primarily adipose tissue connecting the skin to underlying structures like muscle and bone. Glabrous is another term for "hairless."

In an owl monkey, when activity from a digit in the hand is experimentally increased, the area of the cortex that responds to that digit

expands. These experiments reveal that cortical maps are dynamic and adjust depending on the amount of sensory experience. Subsequent experiments in other areas of the cortex (visual, auditory, motor) have shown that this type of map plasticity is widespread in the brain.

The neurotransmitter of pain afferents is

glutamate. The neurotransmitter of pain afferents is glutamate. However, these neurons also contain the peptide substance P, which is contained within storage granules in the axon terminals and can be released by high-frequency trains of action potentials.

A patient recovering from an automobile accident is unable to feel the vibrations of a tuning fork applied to her skin on the right side only. This suggests that she

has damage to her dorsal column on her right side. The organization of ascending touch and pain/temperature pathways leads to a predictable group of deficits when the nervous system is impaired. If half the spinal cord is damaged, certain deficits of mechanosensitivity occur on the same side as the damage: insensitivity to light touch, the vibrations of a tuning fork on the skin, the position of a limb, etc. On the other hand, deficits in pain and temperature sensitivity will show up on the side of the body opposite the cord damage.

In response to activation by a foreign substance (like venom from a bee sting, for example), mast cells release a molecule called ________ that depolarizes nociceptor membranes and dilates blood capillaries.

histamine Bradykinin is formed from an extracellular peptide called kininogen and directly depolarizes nociceptors. Prostaglandins are chemicals generated by the enzymatic breakdown of phospholipids. Substance P is a peptide synthesized by nociceptors and causes vasodilation and the release of histamine from mast cells.

The natural itch-producing substance released by mast cells in the skin during inflammation is

histamine. Histamine mediates itch by binding to histamine receptors, which then activate TRPV1 channels that are also stimulated by capsaicin and high temperatures.

The excruciating dull ache associated with very hard exercise is due to

hydrogen ions as a result of lactic acid buildup activating H+-gated ion channels on nociceptors. When tissue oxygen levels do not meet the oxygen demand, muscle cells use anaerobic metabolism (such as lactic acid fermentation) to generate ATP. A consequence of this is the buildup of lactic acid in cells, leading to the dull ache through decreases in pH.

A heightened sensitivity to pain is known as

hyperalgesia. The phenomenon of hyperalgesia is the most familiar example of our body's ability to control its own pain. Primary hyperalgesia occurs within the area of damaged tissue, whereas secondary hyperalgesia refers to the increased sensitivity from tissues surrounding that area.

A common measure of pain sensitivity in rodents is the tail flick test, in which the tail of an anesthetized rodent is placed over a heat source, and the time to reflexively move the tail in response to increasing heat (indicating pain detection by the CNS) is measured. Electrical stimulation of the periaqueductal gray while increasing the heat would likely

increase the latency for the tail to flick. The periaqueductal gray is well studied for its role in pain suppression. The PAG normally receives input from several brain structures, many of them appropriate for transmitting signals related to emotional status.

Prostaglandins do not elicit overt pain, but instead

increase the sensitivity of nociceptors to other stimuli. Prostaglandins are chemicals generated by the enzymatic breakdown of phospholipids. Aspirin and other nonsteroidal anti-inflammatory drugs inhibit the enzyme required for prostaglandin synthesis.

Based on results of the two-point discrimination test, which area of the body is the most sensitive?

index finger The index finger and thumb are the most sensitive, followed by the lip, big toe, sole of the foot, forearm, back, and calf.

Aspirin and other nonsteroidal anti-inflammatory drugs are a useful treatment for hyperalgesia because they

inhibit the enzyme required for prostaglandin synthesis.

In Melzack's and Wall's gate theory of pain, activity of an Aα or Aβ axon will

inhibit the projection neuron. Activity in the non-nociceptive mechanoreceptor can suppress, or close the "gate" on, nociceptive signals before they can proceed to the spinothalamic tract.

Contrast enhancement via lateral inhibition is due primarily to

inhibitory interneurons between cells. Inhibitory interneurons greatly amplify the activity of a cell with increased firing rates and its neighbors, leading to significant contrast enhancement.

In addition to the ventral posterior nucleus, other spinothalamic tract axons end in the ________ nucleus of the thalamus.

intralaminar The intralaminar nuclei of the thalamus is divided into anterior and posterior groups, and further subdivided into smaller nuclei named by their position or relationship to adjacent structures.

The zone of Lissauer

is a tract adjacent to the dorsal horn of the spinal cord. Small-diameter pain fibers have their cell bodies in the segmental dorsal root ganglia, and they enter the dorsal horn of the spinal cord. The fibers branch immediately, then travel a short distance up and down the spinal cord in a region called the zone of Lissauer.

Violinists must continually finger the strings with their left hand while the other hand, holding the bow, receives considerably less stimulation. In such individuals, the area of S1 devoted to the fingers of the left hand

is greatly enlarged. These experiments reveal that cortical maps are dynamic and adjust depending on the amount of sensory experience. Subsequent experiments in other areas of the cortex (visual, auditory, motor) have shown that this type of map plasticity is widespread in the brain.

Area 3a is not the primary somatic sensory cortex because

it is concerned more with body position than touch. Area 3a is on the postcentral gyrus of the parietal lobe, directly posterior to the central sulcus.

One general mechanism underlying contrast enhancement in sensory systems involves neighboring cells affecting the activity of one another. This is known as

lateral inhibition. Information is usually transformed as it is passed from one neuron to the next in a sensory pathway. One common transformation is the amplification of differences in the activity of neighboring neurons, also known as contrast enhancement.

Nociceptors that respond to intense compression of the skin are known as

mechanical nociceptors. The majority of nociceptors respond to mechanical, thermal, and chemical stimuli and are known as polymodal nociceptors. Mechanical nociceptors show selective responses to strong pressure. Thermal nociceptors show selective responses to burning heat or extreme cold. Chemical nociceptors show selective responses to histamine and other chemicals.

In Melzack's and Wall's gate theory of pain, the interneuron is both excited by the ________ and inhibited by the ________.

mechanoreceptor axon; nociceptive signals By this arrangement, activity in the pain axon alone maximally excited the projection neuron, allowing nociceptive signals to rise to the brain. However, if the large mechanoreceptive axon fires concurrently, it activates the interneuron and suppresses nociceptive signals.

Most of the sensory receptors in the somatic sensory system are

mechanoreceptors. Mechanoreceptors are sensitive to physical distortion such as bending or stretching. They are present throughout the body, and monitor stimuli like skin contact, pressure in the heart or blood vessels, stretching of digestive organs, and force against the teeth. Photoreceptors detect light waves, chemoreceptors detect specific molecules, thermoreceptors detect changes in temperature, and nociceptors (a type of chemoreceptor) detect pain.

What substance was used to identify the "cold" receptor protein?

menthol Menthol, which produces a sensation of cold, was found to stimulate a receptor called TRPM8, which is also activated by nonpainful decreases in temperature below 25 ºC.

Several brain regions have been implicated in pain suppression. The most well studied is the periaqueductal gray matter of the

midbrain. The periaqueductal gray wraps around (peri = "around") the cerebral aqueduct (or mesencephalic duct) that connects the third ventricle to the fourth ventricle.

What would you expect in regard to serotonin release onto dorsal horn cells following electrical stimulation of and simultaneous naloxone injections into the periaqueductal gray?

no effect Electrical stimulation of the periaqueductal gray normally stimulates cells of the raphe nuclei in the brainstem, increasing serotonin release onto nociceptive cells of the dorsal horn, inhibiting them. Simultaneous infusions of naloxone (an opioid receptor antagonist) would block the analgesic effects induced by electrical stimulation of the PAG (thus, serotonin release from the raphe would be decreased).

The branching, unmyelinated nerve endings that signal that body tissue is being damaged or is at risk of being damaged are called

nociceptors. The word comes from the Latin nocere, which means "to hurt." Information from nociceptors takes a path to the brain that is largely distinct from the path taken by mechanoreceptors, and thus the subjective experience elicited by activation of these two pathways is different.

All but which of the following sensory stimuli synapse in the thalamus first before making their way to the neocortex for higher order processing?

olfactory, do not. Olfactory information from the olfactory bulbs travels to olfactory cortex (frontal and temporal lobe cortices) before making its way to the thalamus and eventually the amygdala.

Which of the following is a somatic sensation?

pain The senses of temperature, touch, pain, and body position (proprioception) are all somatic senses, which can in turn be subdivided into many more. The somatic sensory system is a catch-all name for all the sensations that are not seeing, hearing, tasting smelling, and balance.

Most of the cortex concerned with the somatic sensory system is located in which lobe?

parietal As with all other sensory systems, the most complex levels of somatosensory processing occur in the cerebral cortex, and most of the cortex concerned with the somatic sensory system is located in the parietal lobe, Brodmann's area 3b, now regarded as the primary somatosensory cortex (S1).

Nociceptors that respond to mechanical, thermal, and chemical stimuli are known as

polymodal nociceptors. The majority of nociceptors respond to mechanical, thermal, and chemical stimuli and are known as polymodal nociceptors. Mechanical nociceptors show selective responses to strong pressure. Thermal nociceptors show selective responses to burning heat or extreme cold. Chemical nociceptors show selective responses to histamine and other chemicals.

What region of the parietal lobe appears to be the site where simple, segregated streams of sensory information converge to generate particularly complex neural representations?

posterior parietal cortex Neurons of the posterior parietal cortex have large receptive fields with stimulus preferences that are a challenge to characterize because they are so elaborate. The area is concerned not only with somatic sensation but also with visual stimuli, movement planning, and even a person's state of attentiveness.

Referred pain can be explained by the fact that

primary afferent axons from the skin and viscera enter the spinal cord through the same dorsal root. In the phenomenon of referred pain, visceral nociceptor activation is perceived as a cutaneous sensation. The classic example of referred pain is angina or chest pain that radiates down the left arm, occurring when the heart fails to receive sufficient oxygen.

Dorsal column nuclei

process information from the ipsilateral side of the body. Information in the dorsal column nuclei is still represented ispilaterally; that is, touch information from the right side of the body is represented in the activity of cells in the right dorsal column nuclei.

The periaqueductal gray decreases pain through via efferent projections to the ________ nuclei of the ________.

raphe; medulla oblongata The PAG can influence the raphe nuclei of the medulla, which in turn can modulate the flow of nociceptive information through the dorsal horns of the spinal cord.

When digit 3 from an owl monkey was surgically removed, neurons in the S1 cortex that responded to sensations from that finger

respond to stimulation of adjacent digits. Such amputation causes a major rearrangement of the circuitry underlying cortical somatotopy. Experiments such as these have important implications for the recovery of function after peripheral nerve injury.

The neurons that receive sensory input from primary afferents are called

second-order sensory neurons. After receiving sensory information from large, myelinated Aβ axons that convey information about touch to the skin, these cells send information up the spinal cord to the thalamus, the brain's sensory relay station, after crossing over to the other side of the spinal cord.

Area 2 of the postcentral gyrus processes information related mainly to

size. The projections from 3b to area 1 send mainly texture information, while the projection to area 2 emphasizes size and shape. Small lesions in area 1 or 2 produce predictable deficiencies in discrimination of texture, size and shape.

The largest sensory organ in humans is the

skin. The skin, which consists of the outer epidermis and inner dermis, performs essential protective functions and prevents the loss of body fluids and heat to the environment in which we live. The organ is approximately 9 pounds and covers about 20 square feet in the average human.

The mapping of the body's surface sensations onto a structure in the brain is called

somatotopy. The brain has maps of other sensory surfaces, such as the light-sensitive retina in the eye (retinotopy) and the sound frequency-sensitive cochlea in the inner ear (tonotopy).

Which of the following molecules causes histamine release from mast cells?

substance P Bradykinin is formed from an extracellular peptide called kininogen and directly depolarizes nociceptors. Prostaglandins are chemicals generated by the enzymatic breakdown of phospholipids. Substance P is a peptide synthesized by nociceptors and causes vasodilation and the release of histamine from mast cells.

Which of the following molecules is synthesized by nociceptors and causes swelling of blood capillaries?

substance P Bradykinin is formed from an extracellular peptide called kininogen and directly depolarizes nociceptors. Prostaglandins are chemicals generated by the enzymatic breakdown of phospholipids. Substance P is a peptide synthesized by nociceptors and causes vasodilation and the release of histamine from mast cells.

While the primary neurotransmitter of afferent pain neurons is glutamate, what other molecule, released in response to high-frequency trains of action potentials, can also serve as a nociceptive signal?

substance P Recent experiments have shown that synaptic transmission mediated by substance P is required to experience moderate to intense pain.

Capsaicin, in addition to producing the "hot and spicy" feeling, can actually cause analgesia in large quantities by depleting which of the following from nerve terminals of pain fibers?

substance P. This paradoxical effect of capsaicin is due to the depletion of substance P from nerve terminals of pain fibers. Capsaicin ointments, sprays, and patches are useful treatments for pain associated with arthritis, psoriasis, shingles, and other conditions.

At the cellular level, endorphins exert effects by

suppressing the release of glutamate from synaptic terminals. These effects at the cellular level lead to endorphin-containing neurons in the spinal cord and brain stem preventing the passage of nociceptive signals through the dorsal horn and into higher levels of the brain where the perception of pain is generated.

The dorsal columns carry information to the brain regarding which of the following combinations of stimuli?

tactile and proprioceptive Information about touch or vibration of the skin takes a path to the brain that is entirely different from that taken by information about pain and temperature. The dorsal column-medial lemniscal pathway is the major route by which touch and proprioceptive information ascend to the cerebral cortex.

Area 1 of the postcentral gyrus processes information related mainly to

texture. The projections from 3b to area 1 send mainly texture information, while the projection to area 2 emphasizes size and shape. Small lesions in area 1 or 2 produce predictable deficiencies in discrimination of texture, size and shape.

Axons of the spinothalamic tract synapse in the

thalamus. The spinothalamic fibers project up the spinal cord and through the medulla, pons, and midbrain without synapsing, until they reach the thalamus. As the spinothalamic axons make their way through the brain stem, they eventually come to lie alongside the medial lemniscus, but the two groups of axons remain distinct from each other.

A dermatome is

the area of skin innervated by the right and left dorsal roots of a single spinal segment. When mapped, the dermatomes delineate a set of bands on the body surface. The organization of the dermatomes is best revealed when one bends over to stand on both hands and feet; this organization presumably reflects our distant quadrupedal ancestry.

The sensitivity of a sensory neuron to a change in temperature depends on

the type of ion channels it expresses. Discovery of the channels responsive to painful increases in temperature above 43ºC led researchers to wonder if other, closely related channels might be tuned to sense other temperature ranges.

The dorsal column-medial lemniscal pathway carries information to the brain regarding

touch. Information about touch or vibration of the skin takes a path to the brain that is entirely different from that taken by information about pain and temperature. The dorsal column-medial lemniscal pathway is the major route by which touch and proprioceptive information ascend to the cerebral cortex.

Somatic sensation of the face is supplied mostly by which cranial nerve?

trigeminal s

A variety of ion channel types have been implicated in mechanosensation, but the specific types of channels in most of the somatic sensory receptors are

unidentified. Recent work on Merkel's disks reveal mechanosensitive channels called Piezo2 that open in response to pressure and depolarize the cell, which triggers release of an unknown neurotransmitter, which in turn activates the nearby nerve ending through a second and unknown ion channel.

Aδ and C fibers would send information to the brain

via the lateral spinothalamic tract. The spinothalamic fibers project up the spinal cord contralaterally and through the medulla, pons, and midbrain without synapsing, until they reach the thalamus.