Spinal Reflexes Flashcards
The brachial plexus supplies
the thoracic limb
Which nerves arise from the brachial plexus
musculocutaneous, axillary, median, ulnar and radial
Which nerve innervates the most lateral digit (thoracic limb)
Ulnar nerve
What does the radial nerve innervate
All digits and dorsal aspect of paw
What nerves form the brachial plexus
C6 - T2
What nerves form the lumbosacral plexus
L4 - S3
What does the lumbosacral plexus supply
Pelvis limb
What nerve supplies the lateral most digit of the pelvic limb
Sciatic nerve (from L6-S1)
What nerve supplies the medial digit of the pelvic limb
Saphenous branch of the femoral nerve
Arises from L4-L6
What does the peroneal (L6-S1) nerve supply
Dorsal aspect of the paw of pelvic limb
What is the cutaneous trunci muscle responsible for
Twitching of skin, shivering
What type of pathway is occurring in the cutaneous trunci reflex
Sensory (GSA)
What occurs in cutaneous trunci reflex
- Stimulation of cutaneous sensory nerves along back
- Impulse generated by sensory nerve
- Enters spinal cord seg about 1-2 vertical segments cranial to point of stimulation
- Impulse transmitted via spinal pathways of ascending fasiculus proprius
- Goes through thoracolumbar spinal cord to level of C8-T1
- Forms synapse on lower motor neurons of lateral thoracic nerve
What does stimulation of cutaneous trunci result in
Bilateral response
- contraction of cutaneous trunci on both sides, greater response on stimulated side
How do you proceed with cutaneous trunci reflex test
Start from caudal lumbar region and proceed cranially one or two vertebrae at a time
What is the clinical significance of cutaneous trunci reflex
Location of C8 and T1 spinal cord lesion and brachial plexus injuries
- evaluating animals with transverse thoracolumbar spinal cord injury
What does the stretch or myotatic reflex do
Assesses maintenance and control of muscle tone
What muscles have myotatic reflex
All skeletal except extraocular eye muscles
What is the stimulus in myotatic reflex
Stretching of muscle which activated neuromuscular muscle spindle (stretch receptors)
- alpha motor neuron
What is the response of myotatic reflex
Contraction of the same muscle
What pathway is used in myotatic reflex
Sensory (GSA)
Where is the integrating center for the spinal nerves located
In the same spinal cord segment
Where is the integrating center for cranial nerves
In the brain stem
What is an example of a myotatic reflex
Patellar reflex
Is the patellar reflex monosynaptic, disynaptic or multisynaptic
Monosynaptic Reflex Arc
- so there is just one synapse, no interneurons
What is the stimulus in patellar reflex
Dog positioned in lateral recumbency
Evoke by tapping patellar tendon below patella with neural hammer or pleximeter
Stretches quadriceps tendon –> stimulates muscle spindles
This triggers afferent impulse in sensory nerve fiber of femoral nerve that ascends to L4-L6
What is the response to patellar reflex
Sensory nerve synapses with motor neuron
-conducting efferent impulse to quadriceps triggers contraction and causes leg to kick by extending stifle
What is the clinical significance of an absence or decrease in patellar reflex
Lesion/disease of femoral nerve
Lesion/disease of L4, L5 and L6 spinal cord segments
What is the clinical significance of an exaggerated patellar reflex
Upper motor neuron spinal cord lesion
What is the withdrawal/flexion reflex
Involuntary contraction of muscles in response to noxious stimulus
ie. pinching
What is the withdrawal/flexion reflex used to assess
Spinal cord at C6-T2 in thoracic limb
Spinal cord at L6-S2 in pelvic limb
What is the stimulus in withdrawal/flexion reflex
Noxious stimuli on skin of limb –> compression or pinching of toes
Test for nociceptive pathway (mediated by pain receptors)
What is the response to the withdrawal/flexion reflex
Flexion of all joints of limb, protective response
Specific sensory nerves are assessed based on area of skin stimulated
What occurs in the thoracic limb in a normal withdrawal/flexion reflex
Flexion of shoulder, elbow and carpus
What occurs in pelvic limb in normal withdrawal/flexion reflex
Flexion of hip, stifle and hock
Why should you evaluate both lateral and medial digits in a withdrawal/flexion reflex
Because lateral and medial have different innervations
What is the cross extensor reflex
Abnormal reflex found in recumbent animals when doing withdrawal/flexion reflex
What occurs in the cross extensor reflex
Extension of the contralateral limb
Increased tone in extensors of opposite limb to maintain posture in standing animals
Why is the cross extensor reflex a bad prognosis
It indicates reduced input from higher centers (upper motor neuron disease) because integration in producing the proper extension on collateral limb is complex and involves brainstem and cerebral cortex
What nerve is associated with the anal/perineal reflex
Pudendal nerve (S1-S3)
What does the pudendal nerve supply
- external sphincter of anus
- striated muscles of penis, vulva and vestibule
- urethralis muscle
- skin of perineum and caudal thigh
What is the stimulus in an anal/perineal reflex
compression of skin of anus or perineum using forceps
What is the response in an anal/perineal reflex
Evokes an immediate contraction of anal sphincter and flexion of the tail –> so long as caudal spinal cord segment and nerve are intact
What is clonus
Joint moves repeatedly after a single stimulus
