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
what is the perineal reflex pathway
- afferent sensory receptors of perineum
- efferent ventral gray column to anal sphincter muscle
what is the pelvic limb withdrawal pathway
- afferent sensory from skin pinch
- interneuron 1: dorsal gray column to ventral gray column
- efferent: ventral gray column to flexor muscles
what are the test reflexes associated with the cervical intumescence
- flexor (withdrawal): sensory –> varies with area stimulated. motor –> musculocutaneous, axillary, median, ulnar, radial
- biceps reflex: sensrory & motor: musculocutaneous
- triceps reflex: sensory & motor: radial
- cutaneous trunci reflex: sensory –> skin dorsal trunk (T2-L4), motor –> lateral thoracic nerve
how is the thoracic limb reflex performed
lateral recumbency
pinch digit with fingers (sensory)
reflex –> flexion of carpus, elbow and shoulder
what nerves and what segments are involved in the thoracic limb withdrawal
axillary, musculocutaneous, median, ulnar, radial
C6, 7, 8, T1, 2 segments
what is the thoracic limb reflex pathway
- afferent sensory from skin on dorsal aspect of paw
- interneuron 1: C7-T1 dorsal to ventral horn
- interneuron 2: C6 to T2 dorsolateral funiculus
- efferent motor to flexor muscles of shoulder
how is the cutaneous trunci reflex performed
pinch skin over dorsum
1 inch off midline from level of ileal wing to T2
reflex –> bilateral contraction of the cutaneous trunci muscle
what nerve and what spinal segments are involved in the cutaneous trunci reflex
C8-T1 spinal cord segments
lateral thoracic nerve
what is the cutaneous trunci reflex pathway
- afferent neurons from dermatomes –> neuron 1 from ipsilateral dorsal gray column
- neuron 2 (contralateral) dorsal gray column to contralateral dorsal gray column of T2
- neuron 3 dorsal gray column to ventral gray column of T1
- efferent: neuron 4 ventral gray column to cunatenous trunci muscles
what occurs if segmental spinal limb reflexes are intact
upper motor neurom lesion
what occurs if segmental spinal limb reflexes are affected
lower motor neuron lesion
what is hyper-reflexia
real –> release of inhibition from UMNs
pseudo –> reduction in action of antagonistic pair
what is clonus
oscilation of stifle
UMN lesion affecting pelvic limb
what is exaggerated patellar reflex
unopposed reflex
LMN sciatic dysfunction
disproportionately large and uncontrolled stifle extension
due to failure of antagonistic pair
