sensory input lost, control affected
- 5 general receptors
3 specific skin receptors
- skin - pressure
- viscera - stretch of tissue
- proprioception - in muscle joints
- thermoreceptors in skin
- nociceptors in skin,viscera
a. bare nerve ending - temp
b. hair receptor: flow of air, change in position
c. pacinian corpuscle - respond rapidly, adapt quickly.
measuring nerve conduction velocity
electrode pairs at 2 stimulating points. measure time it takes for each to get to recording electrode. measure distance btw points and distance in time
sensory axon types - myelin? conduction velocity? associated sensory endings?
1a
IV
A
Ia = Aa, yes, 80-120 m/s, muscle spindle primary endings IV = C, no, 0.5-2.0 m/s, nociceptors, warmth thermoreceptors A = Aa, yes, 80-120 m/s, extrafusal muscle fibers
spinal cord anatomy
central grey matter =
white matter =
spinal nerves =
c: motoneurons, interneurons
w: axonal tracts from brain or ascending to brain
s: dorsal root (sensory), ventral root (motor)
interface between PNS and CNS
- sensory afferents enter spinal cord where?
- sensory afferents bifurcate discuss.
- descending axons travel how far?
- how many segments of axons synapse on what?
- motoneuron cell bodies where?
- motor efferent axons leave from where?
- dorsal root.
- one ascending, one descending branch. carry sensory info to brain.
- 2-3 spinal segments
- 2-3 segments of azons synapse on motoneurons and interneurons
- cell bodies = ventral horn
- axons leave from ventral roots
pathway from peripheral mechanoreceptors to somatosensory cortex
mechanoreception, ascend in dorsal columns. synapse on 2nd-order neurons and decussate in dorsal column nuclei, cross to contralateral thalamus and S1
neural coding - based on 3 things
frequency code - rate of firing
population code - pressure causes more receptors fired
temporal pattern code: variability of firing rate mayencode sensory info.
divergence - neuron
convergence
d: each interneuron gets and gives various inputs
C: inputs from multiple receptors to 1 interneuron
coincidence detection
hypothesis?
2nd order neurons in Dorsal column nuclei, detect coincidence of AP from tactile afferents.
- activated at different times, depending on shape touched.
- time of arrival of afferent AP vary w conductio velocity
lateral inhibition:
sharpen contrast by focussing activation of CNS neurons. enhance highest activated, inhibited adjacent - lower firing.
2 -point discrimination
- depends on 3 things
- receptor density in skin
- contrast enhancement by lateral inhibition
- number of receiving neurons in CNS
proprioception
kinesthesia
mediated by?
position sense
movement sense
by skin afferents and muscle spindle afferents
goodwin experiment on muscle spindles
vibrate one arm, subject indicates with left arm where perception of right arm is.
= muscle spindle activity elicited illusions of movement and changes in position.
gelfan & carter - pulled surgically exposed tendons of finger flexor
moberg’s repitition
moberg - said yes, but when skin anesthetized, couldnt feel anything.
mccloskey: reproduce moberg and gelfan
tendon in toe exposed & cut - felt it move.
collins - finger flexion controlled by ?
stretching of skin
edin - human skin afferents signal?
joint movement
somatosensory cortex
- dorsal column ?
- “private lines” to S1
- alternating columns of neurons
- receptive fields of single neurons from S1 to S2 (etc)
- feature detecting in S2 respond to specific features of stimuli. ie?
- DC mediate touch, pressure, vibration, kinesthesia.
- private line from skin to S1 respond in mocality-specific way.
- alternating, receive input from Merkel’s, Meissner’s
- become pregressily larger
- ie directional tuning - neuron attune to specific direction of stimulus firing
multisensory object recognition
if hand is holding object, and when hand is in the same position without object = same tactile and proprioceptive respoonses.
perception of touch in bodily areas not involved in task reduced during movement.
- reduction of responses when not involved in muscle activty. progressive, greated reduction at S1 - when not relevant.
BUT augments behaviourally important.
peripheral nerve injury and repair
5 steps
3 facts
- nerve severed, wallerian degeneration (myein in distal nerve degenerates
- schwann and macrophage clean up
- chromatolysis : nucleus migrate
- more molecules for growth and repair.
- schwann grow, proliferate. growth cone forms, send axons along phyllopodia - attracted toguidance molecules
- rate = 2-5 mm/day
- more proximal = worse re-innervation
- surgical reconnection may help
