NS 3: Somatic sensation and the Sensory pathway Flashcards
2 main functions of neuronal cell bodies of SC?
- serving local functions of a neuronal segment: local reflexes, sensory functions of neuronal segment to which they belong (dermatomes- area of skin supplied by sensory nerve fibres of a single spinal nerve root), motor functions of neuronal segment to which they belong (myotomes- muscles supplied by motor nerve fibres of a single spinal nerve root).
- relaying sensory information to the brain: ‘ascending axons’ as transmitting information to higher levels of neuraxis.
2 main functions of axonal fibres of SC?
- carry sensory information from surface of body and muscles to brain (ascending tracts)
- carry motor commands from brain to cell bodies of spinal motor neurones (descending tracts.)
how are cell bodies arranged in the grey matter of the SC?
in layers of cell bodies with similar functions, that stretch horizontally, arranged from dorsal to ventral
name given to each of the discrete layers of cell bodies forming the grey matter of the SC?
Rexed laminae
numbered I to X
each lamina is equivalent to a neuronal nucleus
where might cell bodies of axons of white matter be found?
SC
brain
dorsal root ganglion (PNS)
what is the propriospinal system of the SC?
soma axons have cell bodies in the SC but don’t project to the brain, axons instead sent to neighbouring spinal segments to help share info. locally.
define a fasciculus
a clump of axonal fibres of SC which travel together with a common origin or destination
tracts/fasciculi are grouped in anterior, posterior and lateral columns= funiculi
where is the destination of ascending tracts for conscious sensations?
postcentral gyrus- primary sensory cortex in parietal lobe
which tract carries pain fibres from the SC to the thalamus?
spinothalamic tract
what does the corticospinal tract do?
carries motor fibres from cortex dward to spine
how is the gray matter on either side of the SC connected?
by comissures- contain bundles of fibres that allow info flow across midline
what is sensory acuity?
the precision by which a stimulus can be located
what 3 things determine sensory acuity?
lateral inhibition in CNS
2 point discrimination- determined by density of sensory receptors, size of neuronal receptive fields and psychological factors
synaptic convergence- decreases acuity and divergence- amplifies signal
what type of sensation is the dorsal column associated with?
(medial lemniscal tract)
fine touch
conscious proprioception
course of SC?
lies within vertebral canal, extends from foramen magnum to lower border of 1st lumbar vertebra (or upper border of 2nd)
where is cell body of all 1st order neurones of the tracts carrying sensation from the trunk and limbs located?
dorsal root ganglion
where is the 1st point that a stimulus is perceived?
thalamus
where are the cell bodies of 2nd order neurones of the dorsal column located?
nucleus gracilis or nucleus cuneatus
where are cell bodies of 2nd order neurones of anterior and lateral spinothalamic tracts located?
dorsal horn
where are cell bodies of 2nd order neurones of spinocerebellar tracts located?
spinal grey matter
where are cell bodies of 2nd order neurones of cuneocerebellar tracts located?
nucleus cuneatus
where are cell bodies of 3rd order neurones of spinothalamic tracts and dorsal column located?
thalamus
where are cell bodies of 3rd order neurones of spinocerebellar and cuneocerebellar tracts located?
NO cell bodies
function of anterior spinothalamic tract?
crude touch
pressure
function of anterior and posterior spinocerebellar tracts?
unconscious proprioception
function of cuneocerebellar tract?
unconscious proprioception
function of cuneocerebellar tract?
unconscious proprioception
where is there decussation of spinothalamic tracts?
spinal cord
where is there decussation of dorsal column?
medulla
where is there decussation of spinocerebellar tracts?
anterior= spinal cord posterior= none
where does the dorsal column, and spinothalamic tracts terminate?
somatosensory/primary sensory cortex/ postcentral gyrus
where do the spinocerebellar and cuneocerebellar tracts terminate?
cerebellum