10 – Spinal Reflexes II

Question 1

Muscle reflexes will fatigue when:

Answer 1

-eliciting them in a NON-physiological manner
Ex. reflex hammer

Question 2

Muscle tone:

Answer 2

-ability of muscles to resist an imposed stretch
-increased during complex movements
*not the same as muscle tension
*muscles can have tone without tension (ex. muscles at rest)

Question 3

Physiological purpose of muscle reflex is:

Answer 3

-to maintain muscle tone

Question 4

Muscle tension:

Answer 4

-strength of extrafusal fibers contraction

Question 5

Clinically we are concerned with muscle tone, ability to:

Answer 5

-detect abnormal changes in muscle tone (inappropriate for the situation)
-assess muscle tone when animal is recumbent

Question 6

Assess muscle tone when animal is recumbent:

Answer 6

-reflex will elicit flexion/extension of joints
-understand what NORMAL muscle tone/resistance is

Question 7

Increased vs. decreased muscle tone:

Answer 7

-increased: INCREASED resistance
-decreased=flaccid limbs

Question 8

What happens if descending tracts from higher level centers are lost?

Answer 8

-get a bigger kick (*more excitation)
>won’t be providing the inhibitory signals that reduces the reflex

Question 9

What do the descending tracts do when the animal is sleeping?

Answer 9

-have even bigger inhibitory signals=even more decreased reflex

Question 10

Decreased tone:

Answer 10

-sluggish or absent reflex

Question 11

What will result in decreased muscle tone?

Answer 11

-denervation of muscles
>gamma-neurons are no longer connected=not in control of muscle spindles
>unable to respond/resist to muscle stretch

Question 12

Decreased muscle tone is a sign of:

Answer 12

-peripheral damage (lower motor neurons or sensory neuron)
-OR damage to SC AT the level of the reflex arc
*REFLEX ARC DAMAGED

Question 13

Cerebrum has influences on:

Answer 13

-the reflex arc
-overall, has a net INHIBITORY input under normal circumstances
>prevents over-activation of reflexes
*upper motor neurons

Question 14

Lower motor neurons include:

Answer 14

-somatic motor neurons
-special visceral motor neurons

Question 15

Increased muscle tone:

Answer 15

-exaggerated reflexes

Question 16

What might result in increased muscle tone?

Answer 16

-when there is a lesion in the CNS (upper motor neurons)
>decreased descending input (inhibition) on reflex arcs

Question 17

Withdrawal reflex:

Answer 17

-an unpleasant stimulus applied to the distal limb
*results in flexion of limb as it moves away from stimulus
-coordinated response from the entire limb (>1 muscle)
>activation of flexor muscles
>inhibition of extensor muscles
-variability in the response (related to strength of stimulus)

Question 18

Cross extensor reflex:

Answer 18

-extension of contralateral limb in response to noxious stimulus
Ex. left leg flexes, right leg has increased tone so it doesn’t collapse
*should NOT have it when they are laying down
>if have it=upper motor neuron damage

Question 19

Panniculus reflex:

Answer 19

-twitch of cutaneous trunci muscle in response to cutaneous stimulation
>usually bilateral response (muscles contract on both sides, together)
-lateral thoracic nerve (motor) -> C8-T1
*start caudal and make your way cranial (T3-L3 region)

Question 20

Perianal reflex:

Answer 20

-examines sensory and motor responses in the perineum (perianal region)
-pudendal nerve (motor and sensory) - spinal segments S1-S3
-touch or pinch to the skin surrounding the anus to activate external anal sphincter muscle