Somatosensory I I

Question 1

Pain is an unpleasant sensation and an emotional experience.

True

False

Answer 1

True

Explanation

This statement is true: pain is an unpleasant sensation that occurs in a part/parts of the body, but it is also an emotional experience.

Question 2

Pain, temperature and crude touch receptors are encapsulated nerve endings.

True

False

Answer 2

False

Explanation

This statement is false: the receptors of the anterolateral system are free nerve endings.

Question 3

Which of the following receptors will encode pain related to tissue damage that is well localized and contributes to the primary pain response?

thermoreceptors

mechanonociceptors

C-poly modal nociceptors

Answer 3

mechanonociceptors

Explanation

Mechanonociceptors (group III fibers) respond to mechanical stimulation that results in tissue damage and because they conduct at a higher rate and have smaller receptive field that C-poly modal fibers they encode pain that is well localized and considered our primary pain response. Thermoreceptors are not nociceptors they respond to ambient temperature changes; thermonociceptors are the receptors that respond to extreme temperature changes that damage the skin.

Question 4

A potential consequence of peripheral sensitization is that a person may interpret non-noxious stimuli as painful.

True

False

Answer 4

False

Explanation

This statement is false: this is a potential consequence of central sensitization as is called allodynia (see clinical terms at end of lecture).

Question 5

Which of the following statements reflect changes associated with peripheral sensitization? Select all that apply.

nociceptors have a lower threshold for activation

nociceptors are more responsive to stimuli (higher firing rate when activated)

posterior horn cells have larger receptive fields

over activity of nociceptors results in an exaggerated response to painful stimuli in the area of tissue damage

Answer 5

nociceptors have a lower threshold for activation, nociceptors are more responsive to stimuli (higher firing rate when activated), over activity of nociceptors results in an exaggerated response to painful stimuli in the area of tissue damage

Explanation

Peripheral sensitization results from receptors becoming more sensitive (lower threshold for activation) and more responsive (increased firing rate when stimulated) to noxious stimuli in the receptive fields. This will result in an exaggerated response to painful stimuli in the area of tissue damage (primary hyperalgesia). Increase receptive field sizes of posterior horns cells is related to central sensitization.

Question 6

You are administering a pin prick test to assess Jasper’s ability to sense sharp/painful stimuli on Jasper’s upper limb. Which system are you activating?

Direct pathway of the ALS

Indirect pathway of the ALS

Trigeminal system

Answer 6

Direct pathway of the ALS

Explanation

A pin prick test is used to assess the integrity of the ALS and this type of sensation will be mediated by the direct pathway of the ALS. Jasper should be able to precisely localize this stimuli. The indirect pathway (originating from predominantly group IV fibers which have larger receptive fields and conduct at a slower rate) gives rise to pain sensations that are more poorly localized. The trigeminal system conveys pain/temp information from the face NOT the body.

Question 7

The indirect pathway of the ALS projects to multiple brain regions, including the brainstem, hypothalamus, thalamus, and frontal and limbic cortices.

True

False

Answer 7

True

Explanation

This statement is true: the indirect pathway (paleospinothalamic pathway) consists of multiple tracts that project to the brainstem, hypothalamus, association nuclei in the thalamus, & cotrical areas (frontal and limbic cortices). This pathway is important in mediating our visceral, emotional, and behavioral responses to pain. It will also play a role in the modulation of pain by higher centers.

Question 8

The central processes of the primary afferents of the trigeminal system will descend as which tract to reach second order neurons in the spinal trigeminal nucleus?

anterior trigeminothalamic

spinal trigeminal

spinothalamic

Answer 8

spinal trigeminal

Explanation

The spinal trigeminal tract contains the central processes of the primary afferents of the trigeminal tract. It is considered a descending tract because the sensory fibers are entering at the level of the pons and must reach the spinal trigeminal nucleus which is located in the medulla. The anterior trigeminothalamic tract (coming from the trigeminal system of nuclei and reaching VPM of the thalamus) is an ascending tract. The spinothalamic tract is part of the ALS and connects the posterior horn cells with the thalamus.