Somatosensory System Flashcards
What does the spinothalmic system detect?
Pain (nociceptors), Temperature, Pressure/crude touch
What does the dorsal column-medial lemniscus system detect ?
Vibration , proprioception , fine touch and 2 point discrimination
Where is the cell body of primary sensory neurones ?
the dorsal root ganglion
where does a primary neurone get its input?
single receptor type on a single dermatome
how does the primary neurone get into the spinal cord?
via their central axon on the ipsilateral side
how is strong receptor activation translated in the the neurone?
by increasing frequency of action potentials
Explain how adaptation in receptors affects action potentials
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
What receptor type is slow adapting ?
Nociceptors = pain
what is a receptive field ?
the area of skin a single primary neurone supplies
how can skin be low or high acuity?
skin that has supply from primary neurones that have small receptive fields = high acuity . vice versa (good 2 point discrimination
why do dermatomes have fuzzy boundaries ?
due to overlap of receptive fields of adjancent primary neurones from adjacent dermatomes
where are secondary order sensory neurones cell body?
dorsal horn or medulla
where are third order sensory neurones cell body and where do they project to ?
Thalamus
primary sensory cortex (post central gyrus)
how is the body projected on the sensory cortex and why is it this way ?
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 .
Which neurone desiccates in the DCML and in which tract does it happen in ?
second order neurone medial lemniscus (in medulla)
Where does the lower DCML neuornes start ? where do they go to in the spinal cord ?
T7 and below
up ipsilaterally via gracile fasciculus to nucleus in medulla
Where does the upper DCML neuornes start ? where do they go to in the spinal cord ?
T6 and above
up ipsilaterally via cuneate fasciculus to nucleus in medulla
how do thalamic neurones (3rd order) organise themeselves?
lower body goes to medial side of the bundle of nerves
upper body goes to lateral side
where does the DMCL desiccate ?
medulla in the medial leminicus tract
Where does the primary neurone in the spinothalmic tract project to ?
the ipsilateral second order neurone at the dorsal horn
Where does the spinothalmic tract desiccate ?
Second order neurone - ventral white commissure of the cord
Where are the cell bodies of the second order neurones of the spinothalmic tract ?
dorsal horn
what is the topographical organisation of the spinothalmic tract ? why does this occur?
axons from inferior = lateral and superior = medial
due to desscuation at the second neurone
what happens to the spinal cord in Brown - Sequard syndrome ?
one laterla half of the spinal cord is destroyed?
What are the symptoms of B-S syndrome
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
how are second order neurones in the STT inhibited when pain is present ?
the have a dual input from the primary and alss inhibitory interneurones that relase endorphins such as encephalin
how can interneurones in the STT be activated ?
certain mechanoreceptors can cause activation
also descending inputs from higher centres e.g periaqueductal grey matter .
