Local Functions of the Spinal Cord Segmental Spinal Reflexes Flashcards
what is an alpha efferent neuron
with its cell body in the ventral grey horn of the spinal cord, innervates the extrafusal muscle fibre
what is the gamma efferent neuron
its cell body in the ventral grey horn of the spinal cord, innervates the polar region of the intrafusal muscle fibre
what is a lower motor neuron
neurons associated with motor function that have their cell body in the CNS and their axon leaves the CNS in a cranial or spinal nerve to synapse via a neuromuscular junction with striated, smooth or cardiac muscle
could be considered to be peripheral motor neurons
what is the reflex arc
involves both the peripheral nervous system and the CNS
sensory/afferent nerve brings information into the CNS where the input is linked to a motor/efferent nerve that connects back to a muscle
hard-wired into nervous system
what is a response/reaction
cortically mediated
sensory/afferent info is integrated and interpreted in the cerebral cortex and a motor/efferent response is initiated as consequence
what is the upper motor neuron
neurons confined to CNS that are associated with motor function
could be considered to be central motor neurons
what is the anatomical pattern of UMN and LMN in the spinal cord
what are the common structures of a reflex arc
- receptor system
- afferent (sensory) nerve
- efferent (motor) nerve
- effector system - muscle
what is a muscle spindle and stretch reflex
fight gravity
muscle spindle –> when muscle stretches –> 1a afferent neurons carry information all the way up to the dorsal nerve root –> dorsal horn of spinal cord –> synapse on ventral gray column in gray matter –> alpha efferent neuron to extrafusal muscle fibres
what is the function of interneurons in the stretch reflex
inhibit efferent neurons that innervate antagonist muscle
inhibited alpha motor neuron to muscle fibres –> so they don’t counteract stregnth of muscle contracting
what happens when arc is interrupted
interruption with any of components –> decreased function
diminished/absent reflex
how can afferent/efferent sides of reflex arc be differentiated
- resting muscle tone –> decreased = efferent side
–> normal = afferent side
- resistance to forced extension/flexion –> decreased = either side
- sensation –> decreased = afferent side
- muscle bulk –> decreased, rapid, severe = efferent side
what reflexes are affected by spinal cord dysfunction
- thoracic limb
- pelvic limb
- sphincter
- cutaneous trunci
what nerves do the flexor (withdrawal) reflex test
sciatic nerve
what nerves do the patellar reflex test
femoral
what nerves do the perineal reflex test
pudendal
how is the patellar reflex performed
hold limb such that stifle is semi-flexed
percussion of patellar tendon (muscle stretch receptors)
reflex –> brisk, controlled extension of stifle
what nerve is responsible for patellar reflex and what spinal cord segment
femoral nerve
spinal cord segments L4-6 (cranial aspect lumbar intumescence)
what ist he patellar reflex pathway
- 1a afferent fibre in muscle (annulospiral receptor)
- efferent ventral gray column to quadriceps muscle
- extension of stifle
how is the pelvic limb withdrawal performed
lateral recumbency
pinch digit with fingers (sensory)
varying degree of stimulus
reflex –> flexion of hip, stifle, tarsus
what nerve is involved in the pelvic limb withdrawal and what segments of the cord
sciatic nerve
L6, 7, S1
how is the perineal reflex done
pinch perineum on both sides
sensory receptors perineum
reflex –> contracting of the anus and clamping of tail (pudendal nerve –> anus, caudal nerves –> tail)
what is the nerve of the perineal reflex and the spinal cord segment
pudendal nerve
S1-Cd5 spinal cord segments
