Somatosensory System

Question 1

What does the spinothalmic system detect?

Answer 1

Pain (nociceptors), Temperature, Pressure/crude touch

Question 2

What does the dorsal column-medial lemniscus system detect ?

Answer 2

Vibration , proprioception , fine touch and 2 point discrimination

Question 3

Where is the cell body of primary sensory neurones ?

Answer 3

the dorsal root ganglion

Question 4

where does a primary neurone get its input?

Answer 4

single receptor type on a single dermatome

Question 5

how does the primary neurone get into the spinal cord?

Answer 5

via their central axon on the ipsilateral side

Question 6

how is strong receptor activation translated in the the neurone?

Answer 6

by increasing frequency of action potentials

Question 7

Explain how adaptation in receptors affects action potentials

Answer 7

fast adaptation = they respond best to changes of stimulation but also decrease frequency of APs after initial stimulus
Slow adapting = frequency of APs stays fairly even after initial stimulus

Question 8

What receptor type is slow adapting ?

Answer 8

Nociceptors = pain

Question 9

what is a receptive field ?

Answer 9

the area of skin a single primary neurone supplies

Question 10

how can skin be low or high acuity?

Answer 10

skin that has supply from primary neurones that have small receptive fields = high acuity . vice versa (good 2 point discrimination

Question 11

why do dermatomes have fuzzy boundaries ?

Answer 11

due to overlap of receptive fields of adjancent primary neurones from adjacent dermatomes

Question 12

where are secondary order sensory neurones cell body?

Answer 12

dorsal horn or medulla

Question 13

where are third order sensory neurones cell body and where do they project to ?

Answer 13

Thalamus

primary sensory cortex (post central gyrus)

Question 14

how is the body projected on the sensory cortex and why is it this way ?

Answer 14

homculular pattern where adjacent structures are next to each other in the sensory cortex
This reduces the amount of wiring needed . also the modalities converge into the area of the homoculus it is suppling .

Question 15

Which neurone desiccates in the DCML and in which tract does it happen in ?

Answer 15

second order neurone 
medial lemniscus (in medulla)

Question 16

Where does the lower DCML neuornes start ? where do they go to in the spinal cord ?

Answer 16

T7 and below

up ipsilaterally via gracile fasciculus to nucleus in medulla

Question 17

Where does the upper DCML neuornes start ? where do they go to in the spinal cord ?

Answer 17

T6 and above

up ipsilaterally via cuneate fasciculus to nucleus in medulla

Question 18

how do thalamic neurones (3rd order) organise themeselves?

Answer 18

lower body goes to medial side of the bundle of nerves

upper body goes to lateral side

Question 19

where does the DMCL desiccate ?

Answer 19

medulla in the medial leminicus tract

Question 20

Where does the primary neurone in the spinothalmic tract project to ?

Answer 20

the ipsilateral second order neurone at the dorsal horn

Question 21

Where does the spinothalmic tract desiccate ?

Answer 21

Second order neurone - ventral white commissure of the cord

Question 22

Where are the cell bodies of the second order neurones of the spinothalmic tract ?

Answer 22

dorsal horn

Question 23

what is the topographical organisation of the spinothalmic tract ? why does this occur?

Answer 23

axons from inferior = lateral and superior = medial

due to desscuation at the second neurone

Question 24

what happens to the spinal cord in Brown - Sequard syndrome ?

Answer 24

one laterla half of the spinal cord is destroyed?

Question 25

What are the symptoms of B-S syndrome

Answer 25

Ispliaterally = loss of DCML modalities at and below lesion
loss of sensation at the affected dermatome
contralateral = loss of STT modalities at and below segment

Question 26

how are second order neurones in the STT inhibited when pain is present ?

Answer 26

the have a dual input from the primary and alss inhibitory interneurones that relase endorphins such as encephalin

Question 27

how can interneurones in the STT be activated ?

Answer 27

certain mechanoreceptors can cause activation

also descending inputs from higher centres e.g periaqueductal grey matter .