Spinal Reflexes SDL Flashcards
what are the components of the reflex arc
what are touch/nocioception
- free nerve endings: mainly in hairy skin (not specific to a particular stimulus)
- terminal encapsulations: hairy skin –> pacinian (local pressure), ruffini (tension in collagen fibres), merkels (deformation of skin), meissners (sideways shearing)
what are the components of muscle spindle receptors
what is the muscle spindle and stretch reflex (8)
- spindle organs are located within skeletal muscle belly
- composed of intrafusal fibres (gamma efferent neuron and alpha efferent neuron)
- stimulation of Ia afferent fibre occurs when tension occurs in nuclear region of the intrafusal muscle fibre
- impuse created by tension travels in the la afferent fibre, with its cell body in spinal ganglion
- the axon synapses on the alpha efferent neuron within the ventral grey horn of the spinal cord
- results in contraction of the extrafusal muscle fibre
- concurrently collaterals from the Ia afferent stimulate interneurons in the ventral grey horn that are inhibitory to the alpha neurons innervating antagonistic muscles
- results in constant, low level of contraction within muscles –> results in muscle tone, as well as ability to maintain posture in gravitational forces
what are the structures shown
what are the structures shown
what are the structures shown
what are the structures shown
what occurs when the reflex arc is interrupted
receptor - diminished/absent
afferent nerve - diminished/absent
efferent nerve - diminished/absent
effector - diminished/absent
how are afferent/efferent sides of the reflex arc differentiated
what is the afferent pathway of the withdrawal reflex touch/nocioception
- afferent pathway: pinching digit –> stimulation of sensory receptors in skin and deep subcutaneous tissues
dorsal aspect of paw: sensory input travels up radial nerve
palmar aspect: sensory input travels up ulnar/median nerves
- travels to nerve cell body (in spinal ganglion) and axon passes into spinal cord through dorsal roots
- spinal cord segments: radial nerve (C7, C8, T1 (T2)), ulnar nerve (C8, T1 (T2)), median nerve (C8, T1 (T2))
- axons extend cranial/caudal in dorsolateral funiculus with collaterals synapsing on interneurons within grey matter of spinal cord
what is the efferent pathway of the withdrawal reflex touch/nocioception
- interneurons synapse on motor neurons in ventral grey matter
2. shoulder flexion: axillary (C6-8) and radial (C7-T2) nerves
3. elbow flexion: musculocutaneous (C6-8) nerves
4. carpal/digital flexion: median (C8-T2) and ulnar (C8-T2) nerves
what is the afferent pathway of the patellar reflex
- as tendon is stretched –> stimulation of nuclear bag region of annulospiral organ of the intrafusal muscle fiber
- receptor’s impulse travels in the 1A afferent nerve fibers
- sensory fibers travel in the femoral nerve to the cell body in the spinal root ganglion
- axon enters the spinal cord via the dorsal nerve root L4-5(6)
what is the efferent pathway of the patellar reflex
- axon travels into ventral grey matter and stimulates alpha motor neuron
- axons of these neurons travel in the femoral nerve and cause contraction of quadriceps and extension of stifle
what are upper motor neurons
never leaves CNS
cell body in brainstem or forebrain
axons synapse on LMN in spinal cord
what are the functions of upper motor neuron
- initiate voluntary movement (organizes & directs activity of the LMN)
- maintaining muscle tone to retain balance and control posture (modulates LMN activity on antigravity muscles)
what are lower motor neurons
connects CNS with muscle
cell body in spinal cord
axons project into peripheral nervous system (PNS) via spinal nerves to connect with striated or smooth muscles at neuromuscular junction
what are the functions of the LMN
induce muscle contraction when stimualted
how is LMN activity modulated
predominatly inhibitory action of the UMN
what does damage of UMN cause
release of LMN from inhibition = increased extensory tone, increased reflexes and spasticity
what criteria is needed for differentiation between LMN and UMN signs
- posture
- motor function
- spinal reflexes
- resting muscle tone
- muscle atrophy
how does posture allow differentiation between LMN and UMN
LMN: difficulty in supporting weight
UMN: normal
how does motor function allow differentiation between LMN and UMN
LMN: flaccid paresis/paralysis
UMN: spastic paresis/paralysis
how does resting muscle tone allow differentiation between LMN and UMN
LMN: decreased to absent
UMN: normal to increased
how does spinal reflexes allow differentiation between LMN and UMN
LMN: decreased to absent
UMN: normal to increased
how does muscle atrophy allow differentiation between LMN and UMN
LMN: early & severe (neurogenic atrophy)
UMN: late & mild (disuse atrophy)
what are the neurolocalizations based on the presence of UMN or LMN signs
what lesions will induce LMN signs to all limbs
affecting spinal nerve roots or peripheral nerves (polyradiculopathies or polyneuropathies)
what is the peripheral nerve organization
cranial intumescence: brachial plexus and thoracic limb
caudal intumescence: lumbosacral plexus and pelvic limb, sphincters and tail
what are the reflexes associated with cervical intumescence
- flexor (withdrawal) reflex: sensory –> varies with area stimulated
motor–> musculocutaneous, axillary, median, ulnar, radial
- cutaneous trunci reflex: sensory –> skin dorsal trunk (T2-L4)
motor –> lateral thoracic nerve
how is the thoracic limb withdrawal reflex tested
lateral recumbency
pinch digit with fingers to stimulate nociceptors
varying degree of stimulus
what is the reflex of thoracic limb withdrawal
flexion of carpus, elbow and shoulder
what is the anatomy in the thoracic limb withdrawal
- afferent: radial, median, ulnar nerves (C7, C8, T1 & T2 segments)
- efferent: axiallary, musculocutaneous, median, ulnar, radial nerves (C6, C7, C8, T1, T2 segments)
how is the cutaneous trunci reflex performed
pinch skin over dorsum
1 inch off midline from level of iliac wing to T2 vertebra (shoulder) on both sides
what is the reflex of the cutaneous trunci
bilateral contraction of the cutaneous trunci muscle, whichever side stimulated
what is the anatomy of the cutaneous trunci pathways
- afferent: spinal nerves T2-L2 segments
- efferent: C8-T1 spinal cord segments, lateral thoracic nerve
how is cutaneous trunci reflex localized
what are the test reflexes associated with lumbosacral intumescence
- flexor (withdrawal) reflex: sensory and motor –> sciatic nerve
- patellar reflex: sensory and motor –> femoral
- perineal reflex –> sensory and motor –> pudendal
how is the spinal patellar reflex performed
hold patients limb such that the stifle is semi-flexed
percussion of patellar tendon (muscle stretch receptors)
what is the patellar reflex
brisk, controlled extension of stifle
what is the anatomy of the patellar reflex
afferent and efferent pathways:
femoral nerve
spinal cord segments L4-L6 (cranial aspect lumbar intumescence)
how is the pelvic limb withdrawal test done
lateral recumbency
pinch digit with fingers (stimulate nociceptors)
varying degree of stimulus
what is the pelvic limb withdrawal reflex
flexion of hip, stifle and tarsus
what is the anatomy of the pelvic limb withdrawal
afferent and efferent pathways:
sciatic nerve
L6, L7 and S1 spinal cord segments
how is the perineal reflex done
pinch perineum (hemostat)
both sides
nociceptors/touch receptors perineum
what is the perineal reflex
contraction of the anus and clamping of tail
pudendal nerves (anus)
caudal nerves (tail)
what is the pathway of the perineal reflex
pudendal nerve
S1 and Cd5 spinal cord segments
how can spinal reflexes be graded
absent (0)
decreased (1)
normal (2)
increased (3)
clonus (4): repetitive/oscillating reflex following one single stimulation
