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NS9 - Sensory Rs + Pathways (i) (Receptive field (vary in size (small…
NS9 - Sensory Rs + Pathways (i)
Sensory Rs
= transducers that convert ext/int stimuli to electric potentials, which get carried to CNS integrating centres via sensory pathways
can be on cell membrane, or in cytoplasm
Central Rs
eyes, nose, ears, tongue
Peripheral Rs
chemoRs
for olfaction (smell): olfactory Rs in olfactory mucosa
for taste: taste buds on tongue
for arterial PO2 in carotid + aortic body
for CSF PH in ventrolat medulla
osmoRs
thermoRs
for temp
cold/warm Rs on skin
baroRs
proprioRs (to know where your body is in space)
mechanoRs
for touch: pacninian corpuscles on skin
for audition: Hair cells in organ of corti
for vestibular (balance): Hair cells in macula + semicircular canal
part of SS system
PhotoRs
for vision
rods + cones on retina
nociceptors
for pain: Polymodal nociceptors on skin
for temp extremes: Thermal nociceptors on skin
Can be classified based on structure...
(a) free N endings (e.g. nociceptors)
(b) encased in connective tissue layers (e.g. mechanoRs)
(c) specialed R cell (e.g. hair cells)
Sensory Pathway
1) R -> 1st order neuron -> relay nucleus in cord
2) 2nd order neuron decussates + goes to brainstem
due to decussation, signal is interpreted by contra hemishere
3) 2nd order neuron then goes to thal - sends signal to appropriate part of SS cortex
All SS info goes to spinal cord apart from face + scalp
Rs in dermis
sub-cut tissue Rs
Hair Rs: sense direction + velocity
Merkel's discs: @ non-hairy sin, slow acting, sense vertical indentation
Pacninian corpuscles: fastest Skin Rs, encapsulated in connective tissue, sense vibrations + velocity
Dermal Rs
Ruffini endings: non-hairy skin, sense stretching
Meissner's corpuscle
abundant @ lips + fingertips
Receptive field
= area of body that when stimulated changes firing state of a sensory neuron
excitatory or inhibitory
exist for 1st, 2nd, 3rd + 4th order neurons
vary in size
small field: innervated by 1 neuron - large discrimatory index
large field: innervated by multiple neurons - small discrimatory index
can overlap with each other to allow interactions between sensory inputs
encodes stimulus location
each sensory neuron is dedicated to its specific stimulus mode