Spinal Reflexes I

Question 1

Reflex

Answer 1

-a rapid, involuntary, stereotypical response to a sensory stimulus
-protective mechanism

Question 2

Criteria for reflex

Answer 2

1.elicit the reflex consistently with a simple sensory stimulus
2.known neural connections

Question 3

Components of a reflex arc

Answer 3

• Sensory component
• Motor component
• Reflex center (might include an interneuron)

Question 4

Lesion localization

Answer 4

-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

Question 5

Purpose of stretch reflex

Answer 5

-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

Question 6

Units of stretch reflex/myotatic reflex

Answer 6

-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

Question 7

Steps of stretch reflex/myotatic reflex

Answer 7

-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

Question 8

Patella Reflex

Answer 8

-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

Question 9

Main Reflex locations

Answer 9

-cranial tibial
-gastrocnemius
-extensor carpi radialis
-triceps brachii
-biceps brachii
-sciatic

Question 10

Cranial tibial reflex

Answer 10

-peroneal branch of sciatic nerve (L5-S1)
-FUNCTION: hock flexion

Question 11

Gastrocnemius Reflex

Answer 11

-Tibial branch of sciatic nerve: L5-S1
-FUNCTION: hock extension

Question 12

Extensor carpi radialis reflex

Answer 12

• radial nerve: C7-T2
  -FUNCTION: extension of carpus

Question 13

Triceps brachii reflex

Answer 13

-radial nerve: C7-T2
-FUNCTION: extension of elbow

Question 14

Biceps brachii reflex

Answer 14

-Musculocutaneous nerve C7, C6-T2
-FUNCTION: flexion of elbow

Question 15

Sciatic reflex

Answer 15

-L5-S2

Question 16

Thoracic withdrawal reflex

Answer 16

-C6-T2
-FUNCTION: limb flexion

Question 17

Pelvic withdrawal reflex

Answer 17

-L6-S1
-FUNCTION: limb flexion

Question 18

Muscle spindles

Answer 18

-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

Question 19

Muscle tone

Answer 19

-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

Question 20

Lesions and occurrence of Reflexes

Answer 20

-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