8/9 – Spinal Reflexes

Question 1

Reflexes:

Answer 1

-rapid, involuntary, stereotypical response to a sensory stimulus
>no conscious thought!

Question 2

What is the criteria for a reflex?

Answer 2

1. Elicit the reflex consistently with a simple sensory stimulus
2. Know neural connections

Question 3

What are the anatomical components of a reflex?

Answer 3

-reflex arch
>sensory component
>reflex center (may or may not have an interneuron)
>motor component
*damage to any part will cause there to be NO reflex

Question 4

What is the clinical significance of reflexes?

Answer 4

-use it to local the lesion
>use neurological deficits and correlate them with a region with the NS

Question 5

What questions do you ask to localize a lesion?

Answer 5

-which peripheral nerve?
-which region of SC integrates signal?
-which regions of CNS contains motor output?

Question 6

What is the purpose of the stretch (myotatic) reflex?

Answer 6

-allows for IMMEDIATE response to unexpected changes in tendon tension/length

Question 7

What is a stretch reflex?

Answer 7

-a rapid or large stretch in a tendon will BRIEFLY result in a rapid (immediate) contraction of the muscle fibers

Question 8

Muscle spindles:

Answer 8

-located inside muscle belly (inside a capsule)
-modified muscle fibers (SENSORY)
-multiple per muscle
-very small
-arranged in PARALLEL with skeletal muscle
-innervation with sensory nerve

Question 9

How does a stretch reflex work?

Answer 9

1. Sensory nerve travels back to dorsal horn of SP
   -wrapped around intrafusal fibers within capsule of the spindle
   -detects change in spindle length
2. Synapse with motor neuron that innervates the same muscle
   -AP and muscle contraction
   -shortens muscle in response to stretch

Question 10

What is the innervation to the quadriceps?

Answer 10

-MOTOR=femoral nerve
-SENSORY=femoral nerve (no sensation to the skin)

Question 11

What are the spinal nerves and spinal segments of a patellar reflex?

Answer 11

-L4, L5, L6

Question 12

What is the function of the patellar reflex?

Answer 12

-stifle extension

Question 13

What are some other reflexes?

Answer 13

-cranial tibial -> hock flexion
-gastrocnemius -> hock extension
-extensor carpi radialis
-triceps brachii
-biceps brachii
-sciatic ->stifle flexion
-thoracic withdrawal -> limb flexion
-pelvic withdrawal -> limb flexion

Question 14

Skeletal muscle and muscle spindles innervation:

Answer 14

-innervated separately allow for constant reflex sensing
>a (alpha) – Y (gamma) co-activation
Ex. running and trip (reflex will still be activated)

Question 15

What is the innervation of skeletal fibers?

Answer 15

-extrafusal fibers
*a-motor neurons

Question 16

What is the innervation of spindle fibers?

Answer 16

-intrafusal fibers
*Y-motor neurons

Question 17

What is muscle tone?

Answer 17

-ability of muscles to resist an imposed stretch
>not the same as muscle tension
*muscles can have tone WITHOUT tension (ex. at rest)

Question 18

What is the physiological purpose of a muscle reflex?

Answer 18

-to maintain muscle tone

Question 19

When might an animal have higher muscle tone?

Answer 19

-in the clinic
>why need to be in lateral recumbency to reduce tone when testing reflexes
-walking on ice

Question 20

Neurological exam:

Answer 20

-reflexes need to be assessed in a NON-weight bearing animals
Ex. damage in brain stem: would still have thoracic and pelvic limb reflexes (likely exaggerated)