Spinal Reflexes I Flashcards
Reflex
-a rapid, involuntary, stereotypical response to a sensory stimulus
-protective mechanism
Criteria for reflex
1.elicit the reflex consistently with a simple sensory stimulus
2.known neural connections
Components of a reflex arc
- Sensory component
- Motor component
- Reflex center (might include an interneuron)
Lesion localization
-identify neurological deficits and correlate them to a region within the nervous system
-Need to determine which peripheral nerve, region of the spinal cord integrating signal, and which region of CNS contains motor output
Purpose of stretch reflex
-allows for immediate response to unexpected changes in tendon tension/length
-a rapid or large stretch in a tendon will briefly result in a rapid (immediate) contraction of the muscle fiber
**considered ths simplest of the reflex
Units of stretch reflex/myotatic reflex
-muscle spindles are located inside the muscle belly (inside a capsule)
-modified muscle fibers
-there are multiple
spindles per muscle
-very small (4-10mm)
-arranged in parallel
with skeletal muscle
-innervation with
sensory nerve
Steps of stretch reflex/myotatic reflex
-sensory nerve travels back to dorsal horn of spinal cord
>wrapped around capsule of the spindle
>detects change in spindle length
-synapse with motor neuron that innervates the same muscle
>action potential and muscle contraction
>shortens muscles in response to stretch
**input from peripheral, with synapses onto multiple neurons that will signal to muscle to respond
Patella Reflex
-Motor=femoral nerve
-Sensory= femoral nerve (no sensation to skin)
-Femoral nerve comes from spinal nerves (L4, L5, L6)
-Spinal cord segments (L4, L5, L6)
**FUNCTION: stifle extension
Main Reflex locations
-cranial tibial
-gastrocnemius
-extensor carpi radialis
-triceps brachii
-biceps brachii
-sciatic
Cranial tibial reflex
-peroneal branch of sciatic nerve (L5-S1)
-FUNCTION: hock flexion
Gastrocnemius Reflex
-Tibial branch of sciatic nerve: L5-S1
-FUNCTION: hock extension
Extensor carpi radialis reflex
- radial nerve: C7-T2
-FUNCTION: extension of carpus
Triceps brachii reflex
-radial nerve: C7-T2
-FUNCTION: extension of elbow
Biceps brachii reflex
-Musculocutaneous nerve C7, C6-T2
-FUNCTION: flexion of elbow
Sciatic reflex
-L5-S2
Thoracic withdrawal reflex
-C6-T2
-FUNCTION: limb flexion
Pelvic withdrawal reflex
-L6-S1
-FUNCTION: limb flexion
Muscle spindles
-skeletal muscle and muscle spindles are innervated separately
>skeletal (extrafusal) fibers innervated by alpha-motor neurons
>spindle (intrafusal) fibers innervated by gamma-motor neurons
**Allows for constant reflex sensing= alpha-gamma co-activation, therefore when animal is in motion the reflex can also occur because fiber innervation is different (ex.animal trips when running, reflex can also kick in
Muscle tone
-the ability of muscles to resist an imposed stretch
>not the same as muscle tension… muscles can have tone without tension
>animals in clinic will often have muscle tone making it more difficult to see reflexes
-the physiological purpose of muscle reflex is to maintain muscle tone
Lesions and occurrence of Reflexes
-if you have a lesion in T3-L3 region, then the reflex occurring in L4-L6 will still occur as normal or exaggerated (because the damaged area neurons will sometimes play a role in tone)
-if damage in L4-L6 then reflex either lost or diminished depending on severity
