Motor Systems 5 Tone and Posture - Ebner

Question 1

Definition of postural tone:

Answer 1

Definition of postural tone: Tonic muscle activity in those muscles that oppose gravity

Question 2

What are the two ways that you can increase postural tone?

Answer 2

1 - Directly increase alpha-motorneuron activity

2 - Reflex route to increase motorneuron activity
Increase gamma motorneurons will increase alpha-motorneurons

Question 3

How does the vestibulospinal tract affect postural tone?

Answer 3

It controls postural tone through increasing and decreasing alpha-motorneuron activity directly

• The medial tract projects to axial muscles
• The lateral tract projects to limb muscles

Question 4

What are the inputs to the vestibulospinal tract?

Answer 4

Vestibular organs (duh!)
And cerebellum

Question 5

What is the main way that the reticulospinal tract controls postural tone?

Answer 5

It can affect alpha-motorneurons BUT the MAIN way is through gamma-motorneurons.

It activates gamma-mn’s and gamma mn’s activate alpha-mn’s!

Question 6

So which part of the reticulospinal tract is excitatory and which is inhibitory?

What controls these two tracts

Answer 6

Pontine reticular formation - Excitatory to gamma

Medullary reticular formation - Inhibitory to gamma

PRF - normally inhibited by cortex
MRF - normally activated by cortex

(This explains the tone and reflex changes associated with upper motor neuron syndrome)

Question 7

What spinal tract medaites reflexes associated with changes in muscle tone and posture?

Answer 7

Vestibulospinal tract

Question 8

IF you are on all fours on a peice of wood and all the sudden it tips forward, what are your reflexes going to do to your muscles?

Answer 8

Extension of neck
extension of arms
flexion of legs

Question 9

Lets say your hamster is on all fours in his hamster ball. If the ball is titled to rotate is spinal axis to the right (right side of head down), what are his muscles going to do?

Answer 9

produces extension of limbs on the right and flexion of limbs on the left

Question 10

A friend of yours is in a knife fight (bad idea). His spinal cord gets transected, cutting all the descending systems.

Where are his intital symptoms, and then symptoms after 1-2 months?

Answer 10

INITIAL
a. Flaccidity- no postural tone
b. Absence of reflexes
c. Persists for 1-2 months
d. (Shows descending systems produce tone)

1-2 Months

a. reflexes return and are HYPERactive
b. muscle tone returns - hyper

Question 11

Your friend wonders why after a couple months his reflexes and tone is coming back hyperactive. What can you tell him?

Answer 11

Its because of:
Denervation hypersensitivity
(degradation of NT’s is not occurring because enzymes have been lost in damaged synapse?)

Gliosis - astrocytes come in and fill up the damage, try to restore order in void

Question 12

What is decerebration?

Answer 12

Decerebration:

• Due to lesion below the red nucleus
• Tonic cortical input to 2 reticulospinal tracts interrupted
• Normally the cortex would inhibit the pontine reticulospinal tract and excite the medullary reticulospinal tract
• With cerebrum gone gamma increases a LOT
• Increased tone in extensors of arms and legs

Question 13

With severe cerebral spasticity, hwo can you treat it? (like for severe cerebral palsy)

Answer 13

Baclofen
or
Cut the dorsal roots to relieve the extensor tone

Question 14

What is decortication?

Answer 14

Decortication:

• involves more rostral lesions above red nucleus
• extension of legs, but flexion of upper extremities -The mechanism for forelimb flexion is thought to be disinhibition of red nucleus, which leads to increased activity in flexor motor neurons in the cervical cord