8 - ascending pathways for the body Flashcards
each modality is detected by ..
specific receptos/specialised nerve endings
can you have a dermatome for cranial nerves?
no - by definition dermatomes are regions of skin supplied by SPINAL neves - can do same for CN but not called dermatome
what dermatome is the nipple?
T4
what infection recurs and is characterised by vesicles confined to one dermatome?
Herpes Zoster - reactivation = shingles
why is synaptic transmission between the 3 neurones in this chain not just a simple relay mechanism?
transmission modified by convergence (many to one) and divergence (one to many), descending pathways can also modify
modalities for spinothalamic pathway?
pain, temperature, crude touch, some pressure
what sort of fibres from receptors in spinothalamic?
thin, slow, little/no myelination (think: don’t want to feel pain all the time - sharp pain = lots of fibres to brain)
where does the spinothalamic pathway cross the midline?
level of spinal cord
the tracts change names once reach brainstem, what are they called now?
spinothlamic tract > spinal lemniscus
dorsal tract > medial lemniscus
where do pain and temp fibres (spinothalamic) synapse?
substantia gelatinosa (Rexed lamina II)
where do the cell bodies of the first, second and third order neurons lie for all general sensory pathways?
first order - peripheral ganglia (e.g. DRG) = pseudounipolar
second order - reside in ipsilateral grey matter. Axons ascend to VPL in thalamud
third order - reside in thalamus and ascend to somato-sesory cortex
which modalities are ipsi and contralateral?
fine touch, vibration, pressure, proprioception
crude touch, pain, temperature
ipsi - fine touch, vibration, pressure, proprioception
contra -crude touch, pain, temperature
describe the general sensory pathway for crude touch, pain and temperature.
spinothalamic
- thin. slow fibre from receptor, cell body in DRG, enter SC via Lissauer’s tract
- fibres may synapse 2nd cell body immediately, or ascenf 1-2 segments in DRH. Once synapsed, crosses midline immediately via VENTRAL WHITE COMMISSURE. Then ascend in spinothalamic tract until thalamus - here somatotopic organisation
- synapse 3rd cell body in VPL of thalamus –> post central gyrus
how is the spinothalamic tract somatotopically organised?
more superior body (arm) is more anterior in the tract
how do you differentiate between crude touch, pain and crude touch due to pain?
pain and temp - synapse in sub gel and cross midline immediately
crude touch - reach DRG, ascend LT, synapse and only then cross
if someone pinched you, both these pathways would fire
where does the spinothalamic pathway cross? And what is it called past the medulla?
cross at level of spinal cord
called spinal lemniscus
describe the pathway for discriminative touch, vibration, pressure, proprioception
DORSAL COLUMN PATHWAY
thick, fast fibres of these modalities have their primary cell bodies in DRG, then enter DGH. The primary neurones travel up one of the dorsal columns (gracile if LL, cuneate if above T6)
synapse with secondary at the respective tubercle. Here they cross the midline and somatopically organise in the medial lemniscus –>
travels to thalamus, synapse in VPL, then to SSC
where do the secondary neurones cross the midline for either general sensory pathway?
ST - immediately, after synapsing in DGH
DC - immediately, after synapsing in the tubercles
how is the medial lemniscus somatotopically organised?
more superior (arm) = more posterior
what do the secondary neurones cross the midline via, in either pathway?
ST - ventral white commissure
DC - internal arcuate fibres (in
closed medulla)
the cuneate fascile only appears above what level?
T6
where do fibres for leg, arm and face get somatotopically organised to on the somatosensory cortex?
Leg - close to the longitudinal fissure
arm - middle
face - lateral side
what type of fibres in dorsal column pathway?
large diameter, heavily myelinated, fast
