Somatosensory System 2 Flashcards Preview

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Flashcards in Somatosensory System 2 Deck (24)
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1
Q

what is contained within grey and white matter of the spinal cord?

A

grey matter = cell bodies and sensory afferent terminals

white matter = ascending and descending tracts

2
Q

what are the divisions of grey matter in the spinal cord?

A

dorsal and ventral horns
10 distinct laminae of rexed
- laminae 1 and 2 = where nociceptors terminate
- laminae 3-6 = where LTMs terminate
- laminae 7-9 = where proprioceptors terminate

3
Q

what is the dorsal column/medial lemniscus pathway?

A

major route by which touch and proprioception ascends to the cerebral cortex (apart from anterior head)

4
Q

what are the 1st, 2nd and 3rd order neurones of the dorsal column pathway?

A
1st = enters dorsal horn and synapses on 2nd order neurones in deep dorsal horn/forms long ascending axon synapsing in gracile/cuneate nucleus in medulla
2nd = cross in great sensory decussation to other side of medulla and ascend in medial lemniscus to ventral posterior lateral (VPL) nucleus of thalamus
3rd = project to primary somatosensory cortex (S1) via posterior internal capsule
5
Q

what are the 5 abilities of the dorsal column pathway?

A

stereogenesis (ability to recognise objects by feeling them)
vibration detection (tested via tuning fork)
conscious proprioception
fine touch
weight discrimination

6
Q

what is lateral inhibition?

A

functions to remove the “noise” in sensory neuronal system (extra non-important sensory information which isn’t needed and gives false positives)
this sharpens up the sensation of the important information
collateral inhibitory interneurons branch from the neurone carrying the important information and synapse on adjacent/parallel nerves carrying “noise”, inhibiting these signals giving a simpler, sharper stimulus perception

7
Q

somatic information from the anterior head is mediated by what?

A

two trigeminothalamic pathways

8
Q

1st, 2nd and 3rd order neurones of sensory divisions of trigeminal nerve?

A
1st = area of sensation > trigeminal sensory ganglion in pons
2nd = pons > chief sensory nucleus/spinal nucleus > decussate and project via trigeminal lemniscus > VPM nucleus of thalamus
3rd = VPM of thalamus > thalamocortical neurones > cortex
9
Q

where on the thalamus do the dorsal column and trigeminal nerve synapse on the thalamus?

A

dorsal column = lateral

trigeminal = medial (VPM)

10
Q

what are the 2 parts of the somatosensory cortex?

A

both in post central gyrus

  • S1 = posterior to central sulcus (primary somatosensory cortex)
  • S2 = adjacent to posterior parietal cortex
11
Q

S1 somatosensory cortex is divided into what?

A

brodmann areas (BA)

  • 1
  • 2
  • 3a
  • 3b
12
Q

function of BA 1?

A

receives input from BA 3b and cutaneous mechanoreceptors

involved in texture discrimination

13
Q

function of BA 2 and what can damage here cause?

A

input from joint afferents, Golgi tendon organs, deep tissues, 3a and 3b
involved in pressure, joint position and object perception
damage causes impaired grasping and impaired size/shape discrimination (astereognosis)

14
Q

function of BA 3a?

A

receives information from proprioceptors (muscle spindles)

involved in body position sensation

15
Q

function of BA 3b?

A

receives input from 3rd order neurones which are associated with merkel cells and Meissner’s corpuscles and from 3a
involved in texture and shape perception

16
Q

how is the primary somatosensory cortex organised in terms of receptive fields?

A

receptive fields from S1 neurones form a somatotopic map (different parts of cortex relate to different parts of body)
= homunculus
(map isn’t proportional to size of body area or in order of body positions - i.e feet > face > hand > tongue etc)

17
Q

the somatosensory cortex is divided in which 2 ways?

A

divided into layers and columns

  • 6 cell layers (I-VI)
  • vertical columns extend across all 6 layers (each column = neurones with similar inputs and responses)
18
Q

thalamic inputs to S1 terminate mainly on neurones within which layer of the somatosensory cortex?

A

layer IV

cells in this layer then project to cell towards the surface of the cortex and also deeper layers

19
Q

there are multiple maps in the somatosensory system, where are these found?

A

adjacent somatotopic maps in BAs 1 and 3b
adjacent strips of cortex map the same parts of the body in parallel to each other
maps aren’t identical but are mirror images of each other

20
Q

what happens to the relevant area of S1 if a digit/limb etc is lost in an accident or is amputated?

A

cortical remapping - it becomes utilized by other sensory inputs

  • after months the area now responds to stimulation from adjacent digits/limb
  • involved in phantom limb pain
21
Q

what happens to the relevant area of S1 if the sensory input from a finger increases?

A

cortical representation of the digit in the cortex expands over time
common in string musicians etc

22
Q

what is the function of S2 (posterior parietal cortex area of somatosensory cortex)?

A

receives and integrates information from S1 and other cortical areas (visual/auditory etc) and sub-cortical areas (thalamus)
deciphers meaning from the information in S1 (e.g attaches meaning to visual information - attaching name to recognisable face)

23
Q

what can damage to S2 cause?

A

bizarre neurological symptoms with simple sensory skills in tact
e.g hemispatial neglect syndrome

24
Q

what is hemispatial neglect syndrome?

A

damage to the right parietal cortex causing patient to believe that the left side of the world does not exist and may even disclaim the existence of the left side of their body