Unit 7 - Somatosensory Pathway Flashcards
somatosensory pathway
min of 3 neurons in transmission from periphery to cerebral cortex
1°, 2°, 3°
at each synapse, modification of signal can occur
most sensory stimuli do not reach our consciousness - 99%
conscious perception occurs at the level of the cerebral cortex
ascending tracts - dorsal column - medial lemniscal system
type of sensation
difference between 1st, 2nd and 3rd order
dorsal column - medial lemniscal system
tactile sensation and propriocepton
1st order - mainly Aβ (main mechanoreceptors) that terminte in dorsal column nuclei, also Ia and type II
2nd order - crossover and project to thalamus
3rd order - somatosensory cortex
path of ascending tracts
Ascends from dorsal horn on IPSILATERAL side to medulla and synapse at that point with the second order neuron
Crosses to contralateral side and ascends to the midbrain to contralateral thalamus
Filtering out of unnecessary info - if it is necessary it goes to 3rd order neuron
anterolateral/spinothalamic ascending tract
senses
temperature and pain
1st order terminate in spinal cord (Aδ and C)
2nd order cross, terminate in thalamus (ventral posterior complex - VP)
3rd order to somatosensory cortex
Wherever they enter, they synapse - contralateral side
ascending tracts that don’t connect with somatosensory system
spinoreticular
spinocerebellar
spino-olivary
where does most sensory info project to
thalamus
EXCEPTIONS
olfactory
equilibrium
structure of VP complex
gyrus of somatosensory cortex (SI)
post central gyrus of parietal lobe
function of SI
arrangement of SI
what do neurons in SI form
conscious awareness of somatic sensory signals - intensity and location
somatotopic map - homunculus
greater representation to functions that are critical e.g. facial expression - More sensation you have in your body, the more cortical space is dedicated to the area
neurons in SI form functionally distinct columns
fast and slow adapting in different areas
pathway to SI
Sensory receptors become activated - transmit info via Aδ and C fibres
Info travels via spinothalamic tract
To cortex - primary somatosensory cortex
somatotopic order in the human primary somatic sensory cortex
3b and 1
cutaneous stimuli (pain and temp)
area 3a
proprioception
area 2
tactile (mechanoreceptors) and proprioception
SI sends projections to
SII - lateral sulcus
SII projects to
limbic structures (e.g. amygdala and hippocampus)
learning and memory of stimulus
Emotional response etc to sensory stimulus
Painful stimulus - you cry
Hippocampus - don’t touch hot surface again
SI projections that integrate sensory and motor info
parietal area to motor and premotor area
integration of sensory and motor info - proprioception
SI projections - that fine tune ascending projections
SI to thalamus, brainstem and spinal cord
overview of projections
3b and 1
cutaneous stimuli
3a
proprioception
2
tactile and proprioception
