Final Flashcards
spinal reflexes and where the come from
automatic motor response to a reaction to a sensory stimulus
- stimuli from peripheral receptors
- circuitry enter within SC
components of a spinal reflex
- sensory neuron
- interneuron
- MN
what are they types of spinal mediated reflex (stretch reflex)
- autogenic excitation
- reciprocal inhibition
what is the spinal mediated reflex elicited by and mediated by and what is the goal
- elicited: stretch of muscle fibers
- mediated: muscle spindles va 1a afferent, ascend via dorsal column medial lemniscal tract
- goal: maintain muscle length
autogenic excitation and draw it
- 1a afferents diverge and project to all alpha motor neurons of the same muscle
- many MN of synergist
- monosynaptic reflex
reciprocal inhibition and draw it
- to facilitate the activation of the agonist /synergist muscle ( inhibit antagonist muscle)
- 1a afferents diverge onto 1a inhibitory IN
- 1a inhibitory IN project to alpha MN of the antagonist muscle
GTO mediated reflex types
- autogenic inhibition
- reciprocal excitation
GTO mediated reflex elicitation, mediation and goal
- elicited: active tension in muscle fibre
- mediated: Golgi tendon organs 1b afferent, ascend via dorsal column medial lemniscal tract
- goal: relax/inhibit muscle
autogenic inhibition and draw it
- 1b afferent projects to 1b inhibitory IN
- 1b inhibitory IN project to alpha MN of agonist muscle (inhibits agonist)
- disynaptic
reciprocal excitation and draw it
- to facilitate relaxation of agonist muscle (activate the antagonist)
- 1b inhibitory IN doverge onto other inhibitory IN
-second inhibitory IN project to alpha MN of antagonist
cutaneous mediated reflex parts
- flexor reflex
- crossed extensor reflex
cutaneous mediated reflex elicited, mediation and goal
- elicited: painful stimulus
- mediated: nociceptors via A or C fibres, ascended via spinothalamic tract
- goal: withdrawal form painful stimulus
flexor reflex and draw it
- coordinated response in limb flexor muscles (withdrawal from pain)
- a fibres project to excitatory IN and excited flexor alpha MN
- extensor MN inhibited all flexor to pull away
- a fibres project to inhibitory IN and inhibit extensor alpha MN
- poly synaptic
crossed extensor reflex and draw it
- function is to stabilize body to other limb can pull away
- a fibres project to excitatory IN and excite extensor alpha MN
- a fibres project to inhibitory IN and inhibit flexor alpha MN
- polysynaptic
recurrent inhibition and draw it
- negative feedback mechanism
- mediated by renshaw cells
- release glycine onto alpha MN
- activated by collateral from alpha MN (allows MN to stay informed)
- inhibition onto MN (acts as a limiter to prevent overactivity)
- rate of discharge is proportional to the rate of discharge of MN
c. tetani
- bacteria that causes tetanus (lockjaw)
- release toxin that prevents RC from releasing glycine (prevent recurrent inhibition)
- leads to hyperactivity of MN
presynaptic inhibition
- one presynaptic N inhibits another by releasing GABA
- leads to downstream decr in postsynaptic activity
- communication via axo-axonal synapse
what does the presynaptic inhibition prevent
- release Ca2+ channels from opening
- decr Ca2+ influx in presynaptic N
- decr in neurotransmitter release onto postsynaptic N
describe the monkey trial
Three conditions:
1. control: reward after every stimulation
2. Hreflex up: reward when reflex incr
3. Hreflex down: reward when reflex decr
- Can we train our reflexes through presynaptic inhibition –> able to train presynaptic inhibition to condition the H reflex depending on what task is required
vestibular reflex parts
- vestibular end organ:
- sense head motion (acceleration)
- project information regarding head motion to vestibular nucleus - vestibular nucleus:
- projects to muscles in the body to elicit reflexive witness compensate for head motion
vestibular reflex types
- vestibulo-ocular reflex
- vestibulocollic reflex
- vestibulospinal reflex
vestibulo-ocular reflex function and projection
- stabilize gaze
- projects from vestibular and organs to ocular muscles
vestibulocollic reflex function and projection
- stabilize head
- projections from vestibular and organs to muscles of the back of the neck to bring back to neutral position
vestibulospinal reflex function and projection
- maintain upright balance
- projections from vestibular and organs to muscles of the limbs
electrical vestibular stimulation what it is, what it does, and what reflex it stimulates
- small electrical currents activate vestibular afferents (mimics vestibular afferent activity)
- Central nervous system believes vestibular inference activities coming from actual head motion we think we’re falling
- stimulates vestibulospinal reflexes in lower limbs to counteract sensation of falling
when does standing balance occur and what is the goals
- quiet standing (maintain antigravity posture)
- unexpected perturbations (reactive balance)
- self initiated movements (anticipatory postural control)
postural control
Controlling body position in space to maintain stability in orientation
centre of mass (COM)
Location where all the mass of the bodies concentrated
centre of gravity (COG)
Vertical put projection of COM to ground
centre of pressure (COP)
Point of application of vertical ground reaction force exerted on body
base of support
Region bounded by body parts in contact with the support surface or surfaces
quiet standing
- there is still sway due to small physiological perturbations (HR, breathing, physiological tremor, muscle tone)
- can be stabilized
stability
- amount of sway is affected by body alignment
- stable when body is aligned with line of gravity
- minimizes energy required to maintain balance
- maximize stability
- line of action of COG is within base of support
biomechanisms of postural stability
- decr is the base of support is reduced
- decr is the line of COG is closer to the edge of the base of support
- decr if the height of COM is incr
standing balance (sway) trial
- why do we need to sway?
- in the absence of COM displacement (no sway) we drive our bodies to try to sway
- allows us to gather sensory info we need to balance
- sway is an exploratory mechanism
- driven by subcortical activity
corticomuscular coherence in regards to standing balance
how similar are the signals measured in your motor cortex to the signals measured in muscles
what is the study of balance
- maintenance of balance/equilibrium and boyd orientation in the standing position is essential for the performance of activities
what is the factors that affect posture
- medication
- pain
- aging
- neurological disorders
how are the sensory systems contributing to standing balance assessed
- removing or altering the sensory information available
- using patient populations where the sensory info is absent or distorted
what are the two parts the standing balance for sensory contribution
- quite standing (COM or COP)
- external perturbation
what are the sensory contributions of standing balance
- vision
- vestibular (otoliths and semi-circular canals)
- proprioception (muscle spindles, GTO, joint receptors, cutaneous receptors)
standing balance - vision (physical and visual perturbations)
- when no visual input sway increase 30-40%
- physical pert: when eyes closed, COM displacement is greater following a liner translation
- visual pert: linear vection (sitting in a car and the car next to you moves, you think your moving)
moving room paradigm
- optic flow, toddlers
move the visual surrounding and they fall over - moving lines to create illusions that person is moving forward shift COM backward
how do you know vision is involved in quiet standing
- remove vision –> great sway as indicated by greater movement of COM/COP
- alter optic flow to give illusion that a person is swaying in one direction –> they will move the COM in the opposite direction
standing balance - vestibular
- head tilting –> COP root mean square (measure of total COP displacement) incr with head tilt even when visual input remains constant
standing balance - proprioception and three ways it is affected
- reduced sensory feedback from legs and feet (incr postural sway)
1. vibration to muscle used in postural control causes an illusion of change in body sway
2. cooling feet or applying topical anesthetic causes an incr in postural sway
3. loss of lower limb somatosensory inputs leads to incr sway
standing balance proprioception test
- add proprioceptive feedback with touch
how is proprioception involved in quiet standing
- remove/alter proprioception –> greater sway, as indicated by greater movement of COM/COP
- add proprioceptive feedback with a finger –> decr movement of COP/COM
sensory dysfunction in blind individuals
- blind individuals have smaller COP/COM displacement compared to sighted with eyes closed
- if a deficit is postural control due to loss of vision remained it should stay the same
sensory dysfunction in vestibular loss individuals
- immediate after a unilateral/bilateral loss of vest info, indiv adopt abnormal alignment and incr in sway
- if closing eyes or adopt a challenging posture, sway is incr
dark room experiment in vest loss individuals
- incr proprioception with touch can incr vest function in loss of vision
standing balance in deafferented individuals
- cant stand unsupported (when complete absence)
- can stand but only with vision and conscious control (slight deficit
standing balance in older indiv (falls)
- growing rate of falls
- leading cause of injury
- reduced muscle strength
- reduced sensory function
- incr postural sway
- responds to perturbations slower and greater
reactive balance
- how does the postural control system maintain a desired orientation and stability if there is an external pert
- response to destabilizing external force
- utilizes feedback mechanisms to restore stability
- automatic reactive response that involves a pattern of muscle activation (muscle synergy)
muscle synergy
particular muscles work together to achieve the task
- muscles involved depend on task
types of strategies to reactive balance
- ankle: distal to proximal (smaller pert)
- hip: proximal to distal (larger pert)
- suspensory: crouch down (young children)
- step: taking a step due to COM moving outside limits of stability
- all context dependent
what strategy is used on a beam
- hip at a smaller pert magnitude
reactive balance in cerebellar disorders
- problem with scaling response to amplitudes (hypermetria)
- response too big and too long (overshoot and must activate antagonist)
hypermetria
- cerebellar dysfunction
- voluntary movement tend to result in the movement of bodily parts beyond intended goal
locomotion
- a controlled rhythmic act of moving body from one place to another
- involves repeated cycles of movements
- contribution from visual, proprioceptive and vest info
phases of the step cycle (walking)
- stance: 60% cycles (double support first and last 10% of stance phase)
- swing:40% cycle
walking vs running
walking:
- legs move in antiphase
- one foot or the other is in contact with the ground at all times
- includes double support
- plantigrade (placing whole foot on ground)
running:
- legs move in antiphase
- both feet are never on the ground at the same time
- includes flight
- plantigrade (slow jogging), digitigrade (sprinting)
phases of step cycle (running)
- stance: 20%
- swing: 80%
- includes flight period
locomotion of walking (neural gait control) and the muscles involved in each phase
- heel contact
- toe off and initiation of swing
- swing
does the contrex control gait in walking (cat experiment)
- decerebrate cats are still able to generate gait cycle if posture is supported
- rhythmic activity comes from SC
central pattern generator (CPG)
- groups of neurons in the SC organized to alternate rhythmic control of locomotion
- target therapy of SC to recover gait
sensory modulation of locomotion
- controlling phase transition
- correcting for unexpected disturbances
- regulating level of muscle activity
- initiating walking
- stumbling corrective response
stumbling corrective response
- response to same stimulus depends on phase of locomotion
- stimulate top of foot during swing: flexion of limb to clear obstacle
- stimulate top of foot during stance: extension of limb to push over obstacle
