Lecture 3 - Sensory Contribution Flashcards
What does sensory input do?
stimulus for reflex
modulate output of movement from pattern generators
modulate movement from signals originating from brainstem/cortex
How does the neuron convey info
frequency of signals? # of action potentials and time between them Duration of sensation = amount of time action potentials generated
What information is extracted from receptors
modality
intensity
duration
location
What is Weber’s law?
the just noticeable difference
minimal difference between reference stimulus and second stimulus that is just discriminated
larger stimulus intensity=larger difference needed
What is the sensory threshold?
lowest stimulus intensity an individual can detect
What is the difference between slow and rapid adapting receptors?
slow adapting are for slowly reduce firing frequency
rapid have a quick shut-off, used to detect fine textures/resolution
Need fast-adapting otherwise with skin contact with clothing would be inundated, overwhelmed with sensory info
What is the spatial resolution?
threshold for determining two different stimulus points
varies, highest in fingertips, face
lowest in shoulder, back
How is movement organized?
Feedback
closed-loop
nervous system monitors sensory signals, compared to desired state, then use relative error to modulate output
Feedforwards
open loop
entire movement planned prior to initation
Example of integration: catching a falling ball
Describe the composition of a muscle spindle
Part of the intrafusual muscle fibers, within the extrafusal (regular) muscle fibers
has nuclear bag (dynamic and static) and chain fibres
has 1a afferents conencted to all 3 fibres, has group 2 afferents connected to the static and chain fibres
has dynamic and static gamma neurons
What do muscle spindles do?
detect muscle length and change in length
feedback onto alpha motoneurons
What is the difference between group 1a and II afferents?
Group 1a show dynamic response to stretch (velocity/rate of change)
Group 2 shows static stretch, increases with amount of stretch
How to the group 1a and II afferents fire in regards to a muscle stretch, a tap, a sinusoidal stretch, and a release?
muscle stretch –> group 1a shows some increase btwn beginning and end, high frequency during change
group 2 shows change between beginning and end
tap –> group 1a shows high burst, group 2 shows nothing
sinusoidal stretch –> group 1a has bursts corresponding to stretching, group 2 stays fairly constant
release –> group 1a shows decrease between beginning and end, no frequency during change. group 2 shows decrease between beginning and end
Describe alpha-gamma coactivation
when alpha motor neurons fire and muscles contract, gamma motor neurons also fire to contract muscle spindles to remove slack and maintain sensitivity
What is the stretch reflex?
tendon tap, spindle group 1a fires, comes back down to agonist to fire to contract against the lengthening. has a 1a inhibitory interneuron to prevent antagonist from firing
Describe the golgi tendon organ
senses the load/force change in the muscle
tiny spindle shaped receptors at the muscle-tendon junction
sensory info via group 1b
has no efferent connections, therefore no CNS modulation
What do the GTOs do?
regulate muscle force
regulate muscle fatigue
active during stance phase
Describe the firing tendencies between when a muscle is passibely stretched and when it is lengthened for GTOs and muscle spindles
When muscle is passively stretched, muscle spindles pick up on this, GTOs show some increase
When muscle actively contracted, muscle spindles don’t sense this unless there is gamma coactivation, GTO’s pick up on this lots
How do joint receptors work?
provide info for small angles, or only at extremes, integrate from several receptors to provide better resolution
Provides proprioceptive info, but not totally necessary
What proprioceptive information do we receive?
Kinetic, kinematic: velocity, force, distance, accuracy
Coordination of body/limb: postural control, adaption to movement constraints
What are the 2 ascending sensory pathways
dorsal column –> touch, vibration, conscious proprioceptive info to somatosensory cortex
Spinocerebellar tracts –> unconscious proprioceptive info to cerebellum. includes ventral/dorsal pathway, GTOs, muscle spindles
4 ways to study proprioception
1) surgical deafferentation –> surgically remove afferent pathways
2) sensory neuropathy –> clinical, where afferent pathways don’t function normally
3) Nerve block –> blood pressure cuff or anesthetic, cut off afferent pathways
4) muscle-tendon vibration –> distorts muscle spindle firing patterns, distorts feedback
What are the different cutaneous receptors
1) Meissner corpuscles: stroking, vibration
2) Pacinian corpuscles: vibration
3) Ruffinian corpuscles: skin stretch
4) Merkel’s disks: pressure
5) free nerve endings: pain
6) hair follicles: sense movement of air
How do you prevent wine glass from slipping?
skin stretch receptors rely loss of control, finger muscles fire, other muscles not actively involved decrease firing rate to cushion glass
What are the different components of the vestibular system and what does it do?
signals head acceleration
stabilize head
maintain balance
perception of self-motion
otolith organs: linear acceleration saccule (vertical) and utricle (horizontal)
semicircular canals: angular acceleration: superior, posterior, horizontal
How do the otolith organs and semicircular canals work?
otolith organs: have otolithic membrane with otoconia (calcium carbonate stones) this membrane shifts with movement to deflect the cilia
semicircular canals: cilia within gelatinous cupule, canal filled with viscous endolymph, movement of head moves endolymph and deflects cilia
What movement of the kinocilium results in depolarization?
When the head turns to the right, which side experiences depolarization?
Kinocilium bending away from the others.
Left side, so increased firing on left, decreased firing on right
What is the vestibular-ocular reflex?
decoupling of head from eye movement
when head moves, eyes stay still to maintain fixation
What is the Galvanic Vestibular Stimulation?
anode and cathode attached, afferents decrease firing on anode side and causes sway towards the anode
What happens to light when it hits the eye?
Light passes through cornea and focused by lens (controlled by ciliary muscles) and focused onto retina (specifically fovea)
It hits the retinal pigment epithelium, and then moves through the bipolar cells to the retinal ganglion cells to the optic nerve
Where are rods and cones? What do they do?
cones in fovea, rods in the rest of the photoreceptors
transduce light into electric signals
What is the optic chiasm
crossing point between the optic tracts. If light hits the retina on the nasal hemiretina portion, then it will cross over at the optic chiasm. If it hits the temporal hemiretina, then it won’t transfer over.
What do the different neurons see?
Lateral geniculate nucleus neurons see spots of light
simple V1 neurons see bars of light
complex V1 neurons see moving bars of light
v2 neurons respond to shape and colour
What is the difference between the striate and the extrastriate visual cortex
striate=v1
What is the MT?
medial temporal region (V5)
processes motion
What is the MST?
medial temporal superior region
also processes motion (object or self)
What is visual proprioception?
exproprioception: limb position, visual info of body relative to environment
exteroception: environmental characteristics
Describe the ventral and dorsal streams
Ventral (vision for perception): uses P-pathway: V1 (layer 4) > V2 > V4 > temporal lobe
senses shapes, colours
Dorsal (vision for action): uses M-pathway: V1 (layer 4) > V2 > MT > MST > posterior parietal cortex
senses movement
egocentric frame of reference
What is the evidence for the 2 streams?
picking up and interacting with and differentiating between the egg shapes
What is optic flow?
change in the spatial pattern of light
allows retina to perceive motion, position, timing
abrupt changes = edges, sharp contrast
What are the 2 parts of image flow?
translational flow: eye moves through environment
rotational flow: eye turning within environment
What is the binocular retinal disparity?
way to calculate TTC
as fixation point changes, it hits different parts of the retina, so depth is perceived, so we can identify object motion
What is the Woodworth concept on vision and reaching?
two components, initial impulse and current-control phase
initial impulse is feedforward, planned
current-control allows for feedback, correction of movement
current-control only occurs if there is enough time for visual feedback to be acted upon
How does vision affect performance?
Takes time for processing visual feedback (slows processing), used as substitute for touch/proprioceptive information
