Somatic Sensation

Question 1

Which modalities are associated with the Spinothalamic pathway?

Answer 1

Temperature,
Pain,
Pressure/crude touch.

Question 2

Which modalities are associated with the Dorsal column?

Answer 2

Fine touch,
Proprioception,
2 point discrimination,
Vibration.

Question 3

Give an example of a rapidly adapting receptors.

Answer 3

Mechanoreceptor in skin,

Baroreceptors in skin.

Question 4

Give an example of a slowly adapting receptor.

Answer 4

Nociceptors in skin (pain receptors).

Question 5

Where do second order sensory neurones synapse to their third order counterparts?

Answer 5

Thalamus (3 order are thalamocortical neurones)

Question 6

What is Somatotopy?

What is its advantage?

Answer 6

Point for point correspondence of an area of the body to a specific point within the central nervous system.
The parallel topographical layout saves resources as it provides a quick route to each part of the body.

Question 7

What is the relationship between acuity and receptive field?

Answer 7

Acuity is inversely proportional to the size of a receptive field

Question 8

What is the area where second order neurones in the dorsal column cross called?

Answer 8

Medial leminiscus.

Question 9

What is the purpose of Lissauers tract?

Answer 9

Enables the first order neurones of the spinothalamic system to ascend 2-3 spinal segments before synapse goes onto their second order neurone, as such avoiding possible hemisections and nerve lesions.

Question 10

Why might central lesions in the spinothalamic pathway result in bilateral signs?

Answer 10

May compress decussating fibres on both sides as they cross over.

Question 11

How might a central nerve lesion result in Dissociation (sensory damage in both upper body and lower body modalities)?

Answer 11

Grow to compress the spinothalamic system located centrally and the Dorsal column system dorsally. As these are arranged in opposite directions, different parts of the body are affected in each.

Question 12

How does rubbing an injury help alleviate pain?

Answer 12

Stimulates ABeta neurones that stimulate inhibitory interneurones to prevent the spread of pain signal to the second order neurone.

Question 13

How might hypnosis be able to modulate pain?

Which areas of the brain are involved?

Answer 13

Stimulation of cortical neurones that excite the periacqueductal grey area of the brain. This then stimulates the nucleus raphe mag is found in the medulla, which in turn stimulates the inhibitory interneurones.

Question 14

What would strong receptor activation lead to in terms of action potential?

Answer 14

Hih frequency action potentials.

Question 15

Name an area of the body with high sensory acuity.

What about low sensory acuity?

Answer 15

Skin of the fingertips.

Skin of the back.

Question 16

Why do dermatomes have ‘fuzzy’ boundaries?

Answer 16

Overlap of sensory receptive fields that supply them. Particularly noticeable over the trunk of the body.

Question 17

The gracile fasciculus facilitates ascension of which nerve roots?

Answer 17

T7 and below of the dorsal column system.

Question 18

In the dorsal column system, T6 and above first order neurones ascend in which structure?

Answer 18

Cuneate fasciculus

Question 19

Where do the second order neurones of the spinothalamic system decussate?

Answer 19

In the ventral white commisure of the cord (at the level of the entry of first order neurones)

Question 20

In the spinothalamic tract, where do axons from the lower part of the body run?

Answer 20

Most laterally/superficially. As you ascend, fobres are added medially.

Question 21

In the dorsal column, where do the axons from the lower body run?

Answer 21

Most medially. As you ascend, axons are added laterally.

Question 22

Brown-Sequard syndrome (complete hemisection) leads to what sensory distrubances?

Answer 22

Ipsilateral complete segment anaesthesia of the affected dermatome,
Ipsilateral loss of dorsal column modalities below the hemisection,
Contralateral loss of spinothalamic modalities below the hemisection (note 1 or 2 levels may ascend in Lissauers tract and remain intact)

Question 23

Which descending input centres of the brain can activate encephalinergic neurones that regulate pain?

Answer 23

Periacqueductal grey,

Nucleus raphe magnus.