Neurophysiology 4: Motor System (Lecture 78)

Question 1

Is central input/UMN required for all LMN function?

Answer 1

NO

Reflexes!

Question 2

What is the myotatic reflex? What are examples?

Answer 2

Stretch reflex
Monosynpatic (one synapse)
Antigravity

Ex:) Patellar, biceps, triceps reflex

Question 3

Why are myotatic reflexes so important?

Answer 3

Muscle tone and posture

Question 4

If there isn’t enough muscle tone, what happens to the trunk?

Answer 4

Begins to sway (sag)

Stretching of hypaxial muscle

Question 5

What are polysynaptic reflex arcs?

Answer 5

multiple synapses within CNS between sensory input and LMN output

Question 6

What required for polysnaptic reflex arcs? What are examples of polysnaptic reflex arcs?

Answer 6

Interneurons

Tendon reflex, flexor limb withdrawal, perineal reflex, panniculus reflex

Question 7

What is the tendon reflex? How much stimulus is required to make this fire?

Answer 7

Extreme muscle contraction -> causes golgi tendon organ to fire -> inhibits lower motor neuron
Lots of stimulus…has low resting membrane potential

Question 8

What are two protective reflexes?

Answer 8

Tendon and withdrawal/crossed extensor reflex

Question 9

What is the withdrawal reflex?

Answer 9

Sensory nerve transmits stimulus to spinal cord
Spinal cord interneurons PROMOTE activity in ipsilateral flexor LMN
Spinal cord interneurons INHIBIT activity in ispilatereral extensor LMN

Question 10

What is the crossed extensor reflex?

Answer 10

To have a leg to stand on …. LITERALLY

Interneurons promote activity in contralateral extensor LMN
Interneurons inhibit activity in contralateral flexor LMN

Question 11

Explain the crossed extensor reflex (pinching toe of Dalmatian and then it pushes other leg down)

Answer 11

When normal animal is in recumbent the contralateral limb should NOT extend.

This means that there is a loss of inhibitory UMN activity

Question 12

Where does the Panniculus reflex occur? What is an example?

Answer 12

Spinal nerves T1-L7
-bilateral transmission via interneurons in fasciculus proprius
-lateral thoracic nerve (C8-T1) to cutaneous trunci m. Bilaterally

Horse fly landing on horse and horse twitching skin

Question 13

What is another name for fasciculus proprius?

Answer 13

Propriospinal tract
Around the grey matter
Allows for intersegmental coordination

Question 14

Describe Schiff Sherrington reaction

Answer 14

TL spinal injury

Paralysis in hind limbs, but over extension of thoracic limb —this occurs bc fasciculus proprius

Question 15

What is gaining initiated by?

Answer 15

UMN but maintained by LMN and Fsciculus Proprius

Question 16

If a LMN is damaged, what happens to muscle strength?

Answer 16

Decreased paresis/-plegia

Question 17

If a LMN is damaged, what happens to muscle size?

Answer 17

Decreased rapid atrophy

Question 18

If a LMN is damaged, what happens to muscle tone?

Answer 18

Decreased hypotonia/atonia

Question 19

If a LMN is damaged, what happens to muscle reflexes?

Answer 19

Diminished
Hyporeflexia/Areflexia

Question 20

If an UMN is damaged, what happens to muscle strength?

Answer 20

Decreased paresis/-plegia

Question 21

If an UMN is damaged, what happens to muscle size?

Answer 21

Decreased to normal slow atrophy

Question 22

If an UMN is damaged, what happens to muscle tone?

Answer 22

Increased to normal hypertonia

Question 23

If an UMN is damaged, what happens to muscle reflex?

Answer 23

Exaggerated to normal hyperreflexia