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
