3- somatosensory system Flashcards
which modalities carried by spinothalamic system
temperature, pain, pressure or crude touch
which modalities carried by dorsal column medial lemnisucs system
vibration, proprioception, fine touch, two point discrimination
what does strong receptor activation cause
high frequency of action potentials in primary sensory neurone
what are rapidly adaptive receptors
fire rapidly at start then adapt and fire slowly. eg. mechanoreceptors
what are slowly adaptive receptors
fire at steady rate. eg. nociceptors
what is a receptive field
an area of skin supplied by a single primary neurone
describe relationship between the size of receptive field and sensory acuity
as receptive field size increases, sensory acuity decreases
what is sensory acuity
the ability to have two point discrimination
why is topographical representation important
reduces the amount of building material eg. myelin needed
describe the dorsal column medial lemniscus system
- 1st order neurone ascend through gracile fasiculus (T7 below) or cuneate fasiculus (T7 above) to the cuneate nucleus in medulla
- the second order neurones cross the midline and project to contralateral thalamus in the medial lemniscus
- the third order neurones receive information from gracile nucleus (Lower half) project to medial part of primary sensory cortex. information from cruciate nucleus (upper half) project to the lateral part of primary sensory cortex.
describe the spinothalamic pathway
- first order neurones project onto second order in the dorsal horn at the segment that they enter the spinal cord (ie. before crossing over)
- second order neurones have cell bodies in dorsal horn. they cross over in the ventral white matter of the cord and enter the spinothalamic tract. this takes them to the thalamus
- third order neurones in thalamus receiving information from lower body project medially, and from upper body project laterally.
compare spinothalamic and dorsal column medial lemniscus system
-new axons are added medially in STT, and laterally in DCML. this means that a central cord lesion affects cervical first in STT and lumbar first in DCML
what is the purpose of lissaeurs tract
allows first order neurones in STT to ascend before synapsing with second order neurones in spinal cord. this means that if there is spinal cord damage, there is less damage to the STT as their neurones ascend more before synapsing. DCML will be more damaged.
what is brown-sequard syndrome and what is destroyed unilaterally
complete cord hemisection causing destruction of one lateral half of a single cord segment resulting from trauma or ischaemia. destroys dorsal and ventral horn, alll cord grey matter, all white matter pathways, dorsal and ventral rootsq
symptoms brown-sequard syndrome
ipsilateral complete segmental anaesthesia affecting a single dermatome, ipsilateral loss of dorsal column modalities below destroyed segment. contralateral loss of spinothalamic at or below destroyed segments ( may be lower due to lisseurs tract)
