3- Somatosensory System

Question 1

What classification can sensation be split into?

Answer 1

General (somatic and visceral)
Special sensation

Question 2

What is a modality?

Answer 2

A basic unit of sensation e.g temperature or pain

Question 3

What modalities does the spinothalamic system cover?

Answer 3

Temperature, pain, pressure/crude touch

Question 4

What are the receptors called which detect pain?

Answer 4

Nociceptors

Question 5

What receptors detect pressure?

Answer 5

Mechanoreceptors

Question 6

Which modalities does the dorsal column medial lemiscus system cover?

Answer 6

Vibration, proprioception, two-point discrimination and fine touch

Question 7

How will the strength of activation of a receptor affect frequency of action potentials in the primary sensory neurone?

Answer 7

Stronger receptor activation increases frequency of action potentials in primary sensory neurone

Question 8

What feature of mechanoreceptors explains why you are not aware of your clothes on your skin after wearing them for a little while?

Answer 8

They are rapidly adapting receptors

Question 9

What is an example of a type of receptor that would be slow adapting?

Answer 9

Nociceptors

Question 10

Where are the cell bodies of primary sensory neurones located?

Answer 10

In the dorsal root ganglia

Question 11

What is a receptive field?

Answer 11

The area of skin supplied by a single primary sensory neurone

Question 12

Where does skin on the body have a relatively low sensory acuity?

Answer 12

Skin on the back and elbow

Question 13

How does size of receptive field affect sensory acuity?

Answer 13

The smaller the receptive field the higher the acuity

Question 14

Where are the cell bodies of second order sensory neurones of the spinothalamic pathway located?

Answer 14

In dorsal horn of spinal cord or medulla

Question 15

Which of the sensory neurones in the somatosensory system decussate?

Answer 15

Second order sensory neurones

Question 16

Where are the cell bodies of third order sensory neurones found?

Answer 16

In the thalamus

Question 17

How does the organisation of information differ between the level of the spinal nerves compared to level of the thalamus and above?

Answer 17

Starts as dermatomal organisation and at thalamus and after there is a homuncular pattern

Question 18

Through which tract do DCML system neurones from T7 and below travel up the spinal cord?

Answer 18

Gracile fasciculus

Question 19

Through which tract do neurones of the DCML from the upper body travel up the spinal cord?

Answer 19

Cuneate fasciculus

Question 20

Where are the second order neurone cell bodies of the DCML found?

Answer 20

Gracile nucleus and cuneate nucleus

Question 21

Are axons are added to the dorsal columns from superior parts medially or laterally?

Answer 21

Axons from progressively superior body parts are added laterally to the dorsal columns

Question 22

Where along the spinal cord do neurones of the spinothamalmic pathway decussate?

Answer 22

Around the level that they entered the spinal cord in ventral white commissure

Question 23

What is the significance of Lissauer’s Tract?

Answer 23

It allows sensory neurones to ascend a few levels before crossing over

Question 24

What effect do encephalinergic interneurones have on pain transmission?

Answer 24

These exert an inhibitory effect on the second sensory neurone receiving information from C fibres

Question 25

Why does rub a sore area help to relieve the pain?

Answer 25

Inhibitory (encephalinergic) interneurones can be activated by impulses from incoming mechanoreceptors

Question 26

Inputs from which higher centres act to activate encephalinergic interneurones and help with pain regulation?

Answer 26

Periaqueductal grey matter and nucleus raphe Magnus