Session 3 - Somatosensory System

Question 1

What are the two divisions of general sensation?

Answer 1

Somatic (conscious)

Visceral (unconscious)

Question 2

Name the ascending tracts of the spinal cord.

Answer 2

Dorsal column 
Spinothalamic tract 
Spinorecticular tract 
Dorsal spinocerebellar tract 
Ventral spinocerebellar tract

Question 3

Name the two fasciculi of the dorsal column.

Answer 3

Fasciculus gracilis

Fasciculus cuneatus

Question 4

Name all the modalities.

Answer 4

Temperature
Pain 
Pressure/crude touch
Vibration 
Proprioception 
Fine touch/discriminative touch 
Two point discrimination

Question 5

Which modalities are conducted through the spinothalamic system?

Answer 5

Temperature
Pain
Pressure/crude touch

Question 6

Which modalities are conducted through the dorsal column system?

Answer 6

Vibration
Proprioception
Fine touch/discriminative touch
Two point discrimination

Question 7

What are rapidly adapting receptors?

Answer 7

Receptors that initially create a high frequency train of action potentials when there is high receptor activation, but which then decrease the action potential firing over time.

Question 8

What are slowly adapting receptors?

Answer 8

Receptors which don’t reduce their action potential frequency when subjected to high receptor activation, or which do so very slowly.

Question 9

Give an example of a type of slowly adapting receptor.

Answer 9

Nociceptor (pain receptor)

Question 10

What is a receptive field?

Answer 10

An area of skin supplied by a sensory neurone.

Question 11

What is meant by low acuity with regards to sensory innervation of skin?

Answer 11

If the region of skin supplied by a single sensory neurone is very large, it is said to have low acuity.

Question 12

What creates the poorly defined boundaries of dermatomes?

Answer 12

Overlap of receptive fields

Question 13

Where is the cell body of a primary sensory neurone found?

Answer 13

In the dorsal root ganglia

Question 14

Where is the cell body of a secondary sensory neurone found?

Answer 14

In the dorsal horn of the spinal cord or the medulla

Question 15

Where is the cell body of a tertiary sensory neurone found?

Answer 15

In the thalamus

Question 16

Where does the axon of a primary sensory neurone run in relation to its cell body?

Answer 16

Axon runs ipsilateral to the cell body

Question 17

Which type of sensory neurone decussates?

Answer 17

Secondary sensory neurone

Question 18

Which type of sensory neurone projects into the primary sensory cortex?

Answer 18

Tertiary sensory neurone

Question 19

In the dorsal column pathway, the lower body maps on to which portion of the tract?

Answer 19

The medial portion of the tract.

Question 20

In the spinothalamic pathway, the lower body maps on to which portion of the tract?

Answer 20

Lateral/superficial parts of the tract

Question 21

In the dorsal column pathway, primary sensory neurones coming from the upper body synapse in which nucleus?

Answer 21

Cuneate nucleus

Question 22

In the dorsal column pathway, primary sensory neurones coming from the lower body synapse in which nucleus?

Answer 22

Gracile nucleus

Question 23

In the dorsal column pathway, where are the cell bodies of secondary sensory neurones found?

Answer 23

Medulla

Question 24

In the spinothalamic pathway, where are the cell bodies of secondary sensory neurones found?

Answer 24

Dorsal horn

Question 25

Isolated lesions of the dorsal column pathway lead to what signs?

Answer 25

Ipsilateral loss of dorsal column modalities below the lesion.

Question 26

Isolated lesions of the spinothalamic pathway lead to what signs?

Answer 26

Contralateral loss of spinothalamic modalities below the lesion.

Question 27

Describe the pattern of sensory loss seen in Brown-Sequard syndrome.

Answer 27

Ipsilateral complete segmental anaesthesia of a single dermatome.

Ipsilateral loss of dorsal column modalities below the lesion.

Contralateral loss of spinothalamic modalities below the lesion.

Question 28

What is the role of A fibres?

Answer 28

Carry impulses from mechanoreceptors in the skin.

Question 29

What is the role of C fibres?

Answer 29

Carry pain from nociceptors.

Question 30

How does rubbing a painful area alleviate pain?

Answer 30

Rubbing an area activates mechanoreceptors, which activates A frisbees. The A fibres then excite inhibitory enkephalinergic interneurones in the cord. This inhibits the transmission of pain sensation.