Question 1

The role of enkephalins in the spinal cord is:

Accepted Answer

Enkephalins bind with receptor sites on both the primary afferents and interneurons of the pain system.Enkephalin binding depresses the release of substance P and hyperpolarizes the interneurons,thus inhibiting the transmission of nociceptive signals.

Question 2

If only one sensory root is severed,does a complete loss of sensation result in that area?

Accepted Answer

The results of somatosensory testing procedures can be used to map a person's pattern of sensory loss.The resulting map can be compared with standardized maps of peripheral nerve distribution and of dermatome distributions to determine whether the person's pattern of sensory loss is consistent with a peripheral nerve or a spinal region pattern.Because every individual is unique and adjacent dermatomes overlap one another,the maps presented represent common but not definitive nerve distributions.The overlap of adjacent dermatomes also ensures that if only one sensory root is severed,then a complete loss of sensation does not occur in any area.

Question 3

Which of the following is(are)part of the pain matrix?

Accepted Answer

The pain matrix includes parts of the brainstem,amygdala,hypothalamus,thalamus,and cerebral cortex.

Question 4

Which of the following is not measured during a complete sensory evaluation?

Accepted Answer

A complete sensory evaluation includes measuring sensitivity and thresholds for stimulation of each conscious sensation,except proprioceptive thresholds,which are not measured.For example,a measure of conscious touch sensitivity is the ability to distinguish between two closely applied points on the skin;threshold is the lowest intensity of a stimulus that can be perceived,similar to when the person barely perceives being touched.

Question 5

Sensory extinction is the:

Accepted Answer

In cases of sensory extinction (also called sensory inattention),the loss of sensation is only evident when symmetrical body parts are tested bilaterally.

Question 6

When the raphespinal tract is active,which neurotransmitter is released at the axon terminal in the dorsal horn of the spinal cord?

Accepted Answer

When the rostral ventromedial medulla is electrically stimulated,the raphespinal tracts (i.e.,the axons projecting to the spinal cord)release the neurotransmitter,serotonin,in the dorsal horn,inhibiting the tract neurons via enkephalin interneurons and thus interfering with the transmission of nociceptive messages.

Question 7

What does the counterirritant theory hypothesizes a mechanism affecting:

Accepted Answer

A theory that has incorporated findings from research stimulated by the gate theory is the counterirritant theory.According to the counterirritant theory,inhibition of nociceptive signals by stimulation of non-nociceptive receptors occurs in the dorsal horn of the spinal cord.

Question 8

The locus coeruleus is located in which one of the following?

Accepted Answer

The locus coeruleus is located in the pons.

Question 9

Which of the following are not endorphins?

Accepted Answer

Antinociception is the suppression of pain in response to stimulation that would normally be painful.The endogenous or natural-occurring substances that activate antinociceptive mechanisms are called endorphins.Endorphins include enkephalins,dynorphins,and ẞ-endorphins.

Question 10

Which of the following are NOT characteristics of acute pain?

Accepted Answer

Acute pain is typically associated with a clear cause, such as tissue damage, and can usually be localized. It is not characterized by dysfunction of endogenous pain control systems; this is more associated with chronic pain conditions.

Question 11

If sitting with the legs crossed,sensory loss will eventually occur.(Part of the limb will "fall asleep.")In what order will this loss occur? (Hint: compression of a nerve affects function in order according to axon diameter and myelination;largest diameter myelinated axons are affected first)

Accepted Answer

When a person stands up after prolonged sitting with the legs crossed,occasionally,the person finds that part of the limb has "fallen asleep." The sensory loss proceeds in the following order: 1.conscious proprioception and discriminative touch;2.cold;3.fast pain;4.heat;and 5.slow pain.

Question 12

The periaqueductal gray is located in which one of the following?

Accepted Answer

The periaqueductal gray is located in the midbrain.

Question 13

What numerical value(s)is (are)involved in determining whether the results of a nerve conduction study are normal?

Accepted Answer

To determine whether a nerve conduction study is normal,three numerical values are compared: (1)distal latency, (2)amplitude of the evoked potential,and (3)conduction velocity.

Question 14

Which of the following guidelines will improve the reliability of sensory testing?

Accepted Answer

The following guidelines serve to improve the reliability of sensory testing: (1)administer the tests in a quiet,distraction-free setting;(2)position the patient seated or lying and supported by a firm,stable surface to avoid challenging balance during the test;(3)explain the purpose of the test;(4)demonstrate each test before administering it;during the demonstration,allow the patient to see the stimulus;(5)during testing,block the patient's vision by having the patient close the eyes or wear a blindfold or by placing a barrier between the part being tested and the patient's eyes;and (6)apply stimuli near the center of the dermatomes being tested.

Question 15

Lesions in what location(s)will result in decreased or lost sensation from the contralateral body or face?

Accepted Answer

Lesions in the VPL or VPM nucleus of the thalamus result in decreased or lost sensation from the contralateral body or face because all somatosensory information has crossed the midline before reaching the thalamus.Rarely,people who have strokes that affect the VPL or VPM nucleus have severe pain in the contralateral body or face.

Question 16

Which of the following is a site in the nervous system where the transmission of nociceptive information can be altered?

Accepted Answer

The transmission of nociceptive information can be altered at several locations in the nervous system.The phenomenon of antinociception is summarized with a five-level model: Level 1 occurs in the periphery;level II occurs in the dorsal horn;level III is the fast-acting neuronal descending system;level IV is the hormonal system;and level V is the cortical level.

Question 17

Loss of pain and temperature information from the left lower limb below the L4 dermatome,complete loss of discriminative touch and conscious proprioception information from the right lower limb below the L2 dermatome,and loss of voluntary control of the right lower limb below the L2 dermatome indicates which one of the following?

Accepted Answer

A hemisection (i.e.,damage to the right or left half of the cord)interrupts pain and temperature sensation from the contralateral body because the axons transmitting nociceptive and temperature information cross to the opposite side of the cord soon after entering the cord.As a result of collateral branching of nociceptive axons in the dorsolateral tract,the complete loss of pain sensation occurs two to three dermatomes below the level of the lesion.Because discriminative touch and conscious proprioception information ascends on the same side of the cord as it entered,these sensations are lost ipsilateral to the lesion.Paralysis also occurs ipsilaterally.The pattern of loss is called Brown-Séquard syndrome.

Question 18

Which of the following is(are)part of the fast-descending neuronal system for pain inhibition?

Accepted Answer

The brainstem areas that provide intrinsic antinociception form a neuronal descending system,arising in the following: rostral ventromedial medulla,periaqueductal gray (PAG)in the midbrain,and locus coeruleus in the pons.

Quiz 7: Somatosensation: Clinical Application