W19-L8: Peripheral sensory mechanisms 2

Question 1

Where do sensory axons run in the spinal cord?

Answer 1

Dorsal columns, gracile (medial representing leg) and cuneate (lateral representing arm)

Question 2

Where is the first synapse in the main sensory mechanoreceptor pathway?

Answer 2

At the level of the pyramids on the gracile and cuneate nucleus

Question 3

How do the sensory fibres decussate?

Answer 3

Run from cuneate and gracile nucleus as internal arcuate fibres which synapse on medial lemniscus

Question 4

At the level of the pons in the medial lemniscus where is the lower limb represented?

Answer 4

Lateral

Question 5

Where is the second synapse in the main sensory mechanoreceptor pathway?

Answer 5

In the ventral posterolateral nucleus of the thalamus

Question 6

Where does the final (3rd) neurone in the main sensory mechanoreceptor pathway run?

Answer 6

From posterolateral nucleus of the thalamus to the postcentral gyrus (somatosensory cortex)

Question 7

How many sub-regions are there in the somatic sensory cortex and what are they?

Answer 7

4, they are region 1, 2, 3 a and 3b

Question 8

What is the difference between Primary somatosensory cortex (S1) and secondary somatosensory cortex (S2)?

Answer 8

S2 main input is from S1 rather than the thalamus (still receives some thalamic input)

Question 9

How many body maps are in each somatosensory hemisphere?

Answer 9

6, 4 in S1, 2 in S2

Question 10

T/ F: Neurons in the primary somatosensory cortex form functionally distinct columns

Answer 10

True

Question 11

Which region in the somatosensory cortex are most connections from the ventral posterolateral nucleus of the thalamus going?

Answer 11

Region 3 b

Question 12

What is somatosensory plasticity?

Answer 12

Functional changes in the somatic sensory cortex following changes eg amputation of digit so lost digit is no longer represented and other areas grow larger

Question 13

Can Stimulation cause somatosensory plasticity?

Answer 13

Yes, more stimulation to one digit over another changes the sensory distribution in the cortical territory accordingly or when lactating more cortex is given to nipple

Question 14

Erroneous peripheral nerve regeneration

Answer 14

nerves don’t always go to where they should (or where they were) and sensation is mislocalised (i.e the nerve that used to signal for pinky will re-grow and still signal for that finger regardless of where its re-grown into)

Question 15

When does somatosensory plasticity not help?

Answer 15

central plasticity doesn’t occur for area of skin (more for volume and size of information received) so when there is erroneous regrowth of nerves the sensation is mislocalised (same for all types of receptors)