spinal reflexes Flashcards
what is a reflex ?
automatic response to change in the environment
coordinated, involuntary , initiated by stimulus applied to peripheral receptors
how does the stretch reflex relate to spinal reflexes ? (4)
sensorimotor loop
evoked by tendon tap
abolished by cutting dorsal roots of spinal cord
relies on sensory afferent feedback - not just mechanical response
what occurs during a stretch reflex ?
MS detect changing in muscle length during contraction
this evokes increase in spindle firing rate
sent to spinal dorsal horn by 1a afferent neurons
how does alpha motor neurons link to the stretch reflex ?
alpha MN are activated in spinal ventral horn
muscle contraction of agonist and synergists
what is meant by reciprocal inhibition ?
agonist muscles are inhibited due to contraction of agonist
what are the 2 types of intrafusal fibres ?
nuclear bag fibres
nuclear chain fibres
both respond to stretch
what are nuclear bag fibres ?
innervated by 1a afferents
larger due to nuclei being bunched together
what is a nuclear chain fibre ?
innervated by both 1a and 2 afferents
nuclei is in series
what is co-contraction ?
activating both agonists and antagonist muscles
what is the mono synaptic loop ? (3)
its possible to infer how many neurones are involved in a reflex by its latency
faster the response, fewer the neurones
antagonist muscles are inhibited at linger latencies
what are the supraspinal components ?
EMG response to stretch has 2 components
M1 latency - monosynaptic reflex
M2- transcortical loop
what is Klippel-feil syndrome ?
premotor neurons from cortex divide to innervate both sides of body
moving one hand means mirrored movement on the other hand - contralateral
which supra spinal component is found in klippel-feil syndrome ?
M2 is observed on the contralateral side
what is hyperrflexia/spasticity ? (3)
descending input from Brian act to regulate reflex gain in spinal cord
spinal injuries abolish the input
this increase reflex gain output - hyperrflexia
what is intrathecal baclofen ?
GABA-B agonist which elicits presynaptic inhibition of afferent fibres
decreases Ca+, hyperpolarisation reduces neurotransmitter release
what does intrathecal baclofen involve ? (4)
catheter put in cerebrospinal fluid
baclofen is inserted causing spinal dorsal inhibition
decreases muscle tone + spasms
used for spinal cord injuries
what is the main purpose of the stretch reflex feedback loop ?
negative feedback loop prevent major disturbances to regulation of controlled variables
what is servo-assistance in terms of the purpose of the stretch reflex ?
reflex helps maintain accuracy of movement in small deviations
voluntary commands form motor cortex drive movement which the reflex corrects small deviations
what is the Hoffman reflex ?
elicited by activation of 1a sensory nerves
evokes muscle contraction via monosynaptic spinal reflex
what are the differences in stimulation between 1a afferent fibres and motor fibres - Hoffman reflex??
1a activated at lower intensities - larger axon diameter
motor fibres have smaller diameters so need higher intensity
- abolished H-reflex due antidromic signals
how does associative learning link to the Hoffman reflex ?
reflex behaviour can be modified by reinforcement - operant conditioning
due to plasticity in the corticospinal tract
what is the flexion withdrawal reflex ?
painful sensory stimulus causes flexor muscles to activate and extensors to inhibit to flex limb away from stimulus
what is reflex adaptability ? (3)
at rest, goggle tendon organ inhibits ongoing muscle activity - negative feedback
when walking GTO increases extensor activity for positive feedback
helps produce enough force during stance phase
simplify the gait phase-dependent golgi feedback
GTO reflex contributes to transition between stance and swing
positive feedback - stance
neg feedback - swing
