spinal reflexes

Question 1

what is a reflex ?

Answer 1

automatic response to change in the environment

coordinated, involuntary , initiated by stimulus applied to peripheral receptors

Question 2

how does the stretch reflex relate to spinal reflexes ? (4)

Answer 2

sensorimotor loop

evoked by tendon tap

abolished by cutting dorsal roots of spinal cord

relies on sensory afferent feedback - not just mechanical response

Question 3

what occurs during a stretch reflex ?

Answer 3

MS detect changing in muscle length during contraction

this evokes increase in spindle firing rate

sent to spinal dorsal horn by 1a afferent neurons

Question 4

how does alpha motor neurons link to the stretch reflex ?

Answer 4

alpha MN are activated in spinal ventral horn

muscle contraction of agonist and synergists

Question 5

what is meant by reciprocal inhibition ?

Answer 5

agonist muscles are inhibited due to contraction of agonist

Question 6

what are the 2 types of intrafusal fibres ?

Answer 6

nuclear bag fibres

nuclear chain fibres

both respond to stretch

Question 7

what are nuclear bag fibres ?

Answer 7

innervated by 1a afferents

larger due to nuclei being bunched together

Question 8

what is a nuclear chain fibre ?

Answer 8

innervated by both 1a and 2 afferents

nuclei is in series

Question 9

what is co-contraction ?

Answer 9

activating both agonists and antagonist muscles

Question 10

what is the mono synaptic loop ? (3)

Answer 10

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

Question 11

what are the supraspinal components ?

Answer 11

EMG response to stretch has 2 components

M1 latency - monosynaptic reflex

M2- transcortical loop

Question 12

what is Klippel-feil syndrome ?

Answer 12

premotor neurons from cortex divide to innervate both sides of body

moving one hand means mirrored movement on the other hand - contralateral

Question 13

which supra spinal component is found in klippel-feil syndrome ?

Answer 13

M2 is observed on the contralateral side

Question 14

what is hyperrflexia/spasticity ? (3)

Answer 14

descending input from Brian act to regulate reflex gain in spinal cord

spinal injuries abolish the input

this increase reflex gain output - hyperrflexia

Question 15

what is intrathecal baclofen ?

Answer 15

GABA-B agonist which elicits presynaptic inhibition of afferent fibres

decreases Ca+, hyperpolarisation reduces neurotransmitter release

Question 16

what does intrathecal baclofen involve ? (4)

Answer 16

catheter put in cerebrospinal fluid

baclofen is inserted causing spinal dorsal inhibition

decreases muscle tone + spasms

used for spinal cord injuries

Question 17

what is the main purpose of the stretch reflex feedback loop ?

Answer 17

negative feedback loop prevent major disturbances to regulation of controlled variables

Question 18

what is servo-assistance in terms of the purpose of the stretch reflex ?

Answer 18

reflex helps maintain accuracy of movement in small deviations

voluntary commands form motor cortex drive movement which the reflex corrects small deviations

Question 19

what is the Hoffman reflex ?

Answer 19

elicited by activation of 1a sensory nerves

evokes muscle contraction via monosynaptic spinal reflex

Question 20

what are the differences in stimulation between 1a afferent fibres and motor fibres - Hoffman reflex??

Answer 20

1a activated at lower intensities - larger axon diameter

motor fibres have smaller diameters so need higher intensity
- abolished H-reflex due antidromic signals

Question 21

how does associative learning link to the Hoffman reflex ?

Answer 21

reflex behaviour can be modified by reinforcement - operant conditioning

due to plasticity in the corticospinal tract

Question 22

what is the flexion withdrawal reflex ?

Answer 22

painful sensory stimulus causes flexor muscles to activate and extensors to inhibit to flex limb away from stimulus

Question 23

what is reflex adaptability ? (3)

Answer 23

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

Question 24

simplify the gait phase-dependent golgi feedback

Answer 24

GTO reflex contributes to transition between stance and swing

positive feedback - stance

neg feedback - swing

Question 25

what are the cough reflex mechanisms ?

Answer 25

inspiratory

compression

expiratory

Question 26

what happens during inspiration in the cough reflex ?

Answer 26

deep inspiration with glottis open

diaphragm and intercoastal muscles used

Question 27

what happens during compression during the cough reflex ?

Answer 27

expiratory muscles contract against a closed glottis

generates large subglottic pressures

trunk muscles used

Question 28

what happens during the expiratory phase of the cough reflex ?

Answer 28

glottis opens causing rapid ejection of airflow