somatosensory part 3 Flashcards
what are dermatomes
skin areas innervated by pairs of spinal nerves
how many different regions are there in the grey matter of the spinal cord
10
which sections are in the dorsal horn
laminae (layers) 1 to 6
which laminae is known as the intermediate zone
laminae 7
which laminae make up the ventral horn
8 - 10
different mechanoreceptors terminate in different
layers of the dorsal horn.
which fibres branch and carry information directly up the spinal cord to the medulla (they also project into the dorsal horn and terminate at layers 3 and 4)
the Abeta SA and RA LTMR
the C-LTMR and the Adelta-LTMR terminal in…
layer 2 predominantly
where do nociceptors and thermoreceptors fibres terminate
layer 2
where do the mechanoreceptors terminate
either on interneurons or projection neurons
interneurons
form short range connections just within the local regions of the spinal cord
projection neurons
contribute to the tract
project out of the spinal cord to the brain (output neurons from the dorsal horn)
how many output tracts are there
3
what are the 3 tracts
PSDC - post synaptic dorsal column
anterolateral tract
spinocervical tract
the anterolateral tract neurons start in what region of the dorsal horn
the superficial regions (layer 1 and 2)
where do the anterolateral neurons get their inputs from
nociceptors, thermoreceptors and the smaller mechanoreceptors
spinocervical neurons start in what region of the dorsal horn
layer 3 and 4
fibres going into the spinocervical tract are from…
hair follicles (not from glabrous skin)
Abeta RA and SA LTMR form collaterals that travel straight up to the dorsal column nuclei, as they do so they branch off creating endings in along the length of the cord.
interneurons means there can be segmental processing which means…
the input from one receptor might have an impact on the input from another receptor.
E.g interaction between mechanoreceptors and nociceptors (“rubbing something better” stimulates mechanoreceptors and it seems to have an inhibiting effect on the nociceptor input)
what are the three somatosensory pathways in the spinal cord that go to the brain
dorsal column lemniscal system
anterolateral system
spinocervical system
information coming in to the dorsal horn of the spinal cord can send collaterals into the dorsal column system. does this run up the spinal cord on the same side or opposite side that in information came in
the same side (homolateral)
is the spinocervical system homolateral
yes
is the anterolateral system homolateral?
no, the output neurons have to cross to reach the tract
dorsal column system contains…
fibres from the receptors themselves and the post synaptic dorsal column fibres (from the glabrous skin and the hairy skin)
where does the dorsal column system terminal
the dorsal column nuclei in the medulla
within the brain the dorsal column fibres cross over through a bundle of fibres called the…
medial lemniscus
they then terminate in the thalamus and then go to the…
somatosensory cortex on the opposite side to which the information entered
the spinocervical pathway receives its inputs from hair skin and they travel up to reach the…
lateral cervical nucleus
neurons from the lateral cervical nucleus project through the medulla and then cross over to reach the thalamus and the somatosensory cortex on other side.
what are most of the dorsal column fibres
collaterals of primary fibres
15-20% are secondary fibres (output of neurons in grey matter)
each dorsal column is divided in to what two fascicles
gracile fascicle
cuneate fascicle
cuneate fascicle carries information from the
forelimbs
gracile fascicle carries information from the…
trunk and hind limbs (runs more medially than the cuneate fascicle)
what nucleus in the thalamus is concerned with somatosensory information
the venteroposterior lateral nucleus
what is decussation
crossing over within the brain
the anterolateral pathway consists of what two tracts
the spinothalamic (STT) and spinoreticular (SRT) tracts
what laminae do the neurons of these tracts originate from
laminae 1,5 and 7
where is input from the nociceptors and thermoreceptors carried
in the lateral STT
where is input from mechanoreceptor and simple touch carried
in the anterior STT
the dorsal column pathway inputs from receptors in what type of skin
hairy and glabrous
in the DCN theres a distorted representation of stimulus emphasising…
boundaries and edges
important for control of hand movement
anterolateral system transmits information about…
pain and temperature
also carries information about coarse touch
whether the spinocervical system is in primates is questioned
but inputs information from…
hairy skin
