Spinal Reflexes II

Question 1

Reflex arc

Answer 1

-receptors in periphery
-sensory neuron along dorsal root towards the spinal cord
-synapse onto interneuron
-motor neuron from spinal cord to the muscle

Question 2

Criteria for reflex

Answer 2

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

Question 3

Damage to reflex arc

Answer 3

-damage to any component in this reflex arc results in the loss of the reflex

Question 4

Reflex fatigue

Answer 4

-muscle reflexes will fatigue when eliciting them in a non-physiological manner

Question 5

Muscle tone

Answer 5

-the ability of muscles to resist an imposed stretch
>the stretch reflex is a physiological mechanism to maintain muscle tone
>increased muscle tone during complex movements (will always have some tone when at rest)

*not the same as muscle tension (strength of extrafusal fiber contraction)

Question 6

Muscle tone clinically

Answer 6

-allows for the ability to detect abnormal changes in muscle tone (inappropriate changes in muscle tone)

-allows for ability to assess muscle tone when animal is recumbent
>reflex will elicit flexion/extension of joints
>understand what is normal muscle tone/resistance

Question 7

Muscle tone increase vs. decreases

Answer 7

-increases muscle tone= increased resistance
-decreased muscle tone=flaccid limbs

Question 8

Decreased muscle tone

Answer 8

-denervation of muscles will result in decreased (or loss) of muscle tone
>gamma neurons are no longer connected, therefore not in control of muscle spindles =results in inability to respond/resist muscle stretch

Question 9

What is decreased muscle tone a sign of?

Answer 9

-decreased muscle tone is a sign of peripheral damage (lower motor neurons or sensory neuron) OR damage to the spinal cord AT the level of the reflex arc = reflex arc damage
**decreased tone=sluggish or absent reflex

Question 10

Brains impact on increased muscle tone

Answer 10

-Cerebrum (brain) has influences on the reflex arc (Net inhibitory input under normal conditions)
>upper motor neurons come from brain (if damaged then will have loss of inhibitory imput so reflexes will be exaggerated)
>lower motor neurons from spine to muscle

Question 11

Increased muscle tone

Answer 11

-when there is a lesion in the CNS (brain/spinal cord) results in decreased descending input (inhibition) on reflex arcs and causes increase in muscle tone
increased muscle tone is a sign of central damage (upper motor neurons)

Question 12

Withdrawal Reflex

Answer 12

-an unpleasant (noxious) stimulus (ex. touching feet in cats and dogs) applied to the distal limb, resulting in flexion of the limb as it moves away from the stimulus
-results in variability of response related to the strength of the stimulus

Question 13

Muscle activation of withdrawal reflex

Answer 13

A coordinated response from the entire limb (>1 muscle)
- activation of flexor muscles
- inhibition of the extensor muscles

Question 14

Cross extensor reflex

Answer 14

-extension of contralateral limb in response to noxious stimulus (ex.animal stepping on thorn, other leg will catch itself)
should not occur when laying down, but if it does occur then there is upper motor neuron damage

Question 15

Panniculus reflex

Answer 15

-twitch of the cutaneous trunci muscle in response to cutaneous stimulation
> usually bilateral response (muscles contract on both sides, together)
>L4 and up cranially will synapse with interneuron and pass signal to lateral thoracic nerve (motor)= C8-T1, and trigger cutaneous trunci muscle/reflex

Question 16

Perineal reflex

Answer 16

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