Flashcards in Central Processing of Somatosensory Input Deck (23):
what is the grey matter subdivided into?
dorsal (posterior) and ventral (anterior) horns and ten distinct laminae of rexed
what is the fibre class of nociceptors and where do they terminate?
terminate in laminae I and II
what is the fibre class of LTMs and where do they terminate?
terminate in laminae III to VI
what is the fibre class of proprioceptors and where do they terminate?
terminate in laminae VII to IX
describe the changes in grey and white matter as you move up the spinal cord and why is this change required?
more white matter and less grey matter as you move up from sacral to cervical
this is due to more afferent fibres joining further up and more white matter is needed to carry all these axons
how is the grey matter in the ventral and dorsal horns of spinal cord divided?
into 10 laminae of rexed
what laminae are found in the dorsal horn and what afferent signals terminate there?
I and II most posterior in dorsal horn - nociceptors found here
III to VI found in anterior of dorsal horn - low threshold mechanoreceptors found here
VII to IX found in ventral horn - proprioceptors found here
using the dorsal column / medial leminiscus tract and the spinothalamic tract, explain what symptoms a patient with brown-sequard syndrome would experience if there was a hemisection of spinal cord?
dorsal column tract = touch, vibration
this would be lost on ipsilateral side of hemisection as sensory input does not cross until brainstem
spinothalamic tract = pain and temperature
this would be lost on the contralateral side to the hemisection as the sensory fibres cross segmentally in this tract
what are the two sections of the dorsal column called and what levels do they extend to/from in spinal cord?
gracile = medial section (extends whole way up spinal cord)
cuneate = lateral section (extends from T6 upwards - deal with info from upper limbs)
what can the dorsal column/medial leminscus pathway be used for?
stereognosis - recognise object by feeling it
fine touch - two point discrimination
conscious proprioception - awareness of body position and movement
what is lateral inhibition and why/where does it occur?
active neurone inhibits the activity of its neighbours via stimulating inhibitory interneurones lateral to it
this sharpens stimulus perception (eliminates background noise)
this happens in synapses of DCML pathway
the DCML pathway does not exist for sensory information from anterior head - what picks up this information instead?
trigeminal divisions which feedback to the trigeminal ganglion and different nuclei in brainstem
where is the primary somatosensory cortex located?
post central gyrus of the parietal cortex immediately posterior to central sulcus (SI)
adjacent to posterior parietal cortex (SII)
what areas are found in the primary somatosensory cortex?
brodmann areas (BA) 1, 2, 3a and b
what areas of the primary somatosensory cortex receive most information from thalamus?
areas 3a and b receive around 70%
what sensations do each of the brodmann areas deal with?
3a = proprioception
2b = touch (texture, shape, size)
1 = texture (as this receives input from 3b)
2 = pressure and joint position, distinguishing objects
describe the organisation of the body parts in the primary somatosensory cortex?
the toes are at the top of the post central gyrus with tongue at lower end, but the hand separates the head from the face
describe the organisation of the columns in the sensory cortex?
alternating columns of cells with rapidly adapting and slowly adapting sensory responses
are each of the brodmann areas using the same somatotropic map?
yes - adjacent strips of cortex have the same parts of the body in parallel to each other
but maps are not identical, they are mirror images of each other
what happens if the sensory input from a particular area of the body increases?
cortical space for that digit increases
(relative to other inputs generating less activity)
describe a condition where cortical remapping can become an issue?
phantom limb pain
if a limb is amputated and other parts of the body take over that area of cortex, a pain stimulation in these areas can cause the brain to feel it as pain from non-existent limb
what is the job of the posterior parietal cortex?
receives and integrates information from SI and other cortical areas (visual, auditory) and sub-cortical areas (thalamus)