7. Control of movement 1/ involuntary motor output

Question 1

How the LMNs in the spinal cord arranged topographically?

Answer 1

Medial pathways projecting to proximal and axial muscles

Lateral pathways projecting to distal muscles

Question 2

How to the ascending and descending tracts vary in contents?

Answer 2

White matter = ascending and descending tracts

Grey matter = cell bodies and dendritic connections

Question 3

What is neural structures is seen as the:
Coordinator/predictor?
Integrator?
Gatekeeper?

Answer 3

Coordinator/predictor: Cerebellum
Integrator: Basal ganglia
Gatekeeper: Thalamus

Question 4

What are the two major systems of descending pathways from brain to motor centres?
How do they differ in the information they carry?

Answer 4

1. Ventromedial pathways
   - Mainly control posture and locomotion
   - Control the axial and proximal muscles
   - Mainly controlled by the brainstem
2. Lateral pathways
   - Control voluntary movements
   - Control distal muscles
   - Mainly controlled by cerebral cortex (via the corticospinal tracts)

Question 5

What drives the involuntary movements to maintain posture in the ventromedial pathway?>

Answer 5

Predictively (postural set)

Reflexively (compensation)

Question 6

Is posture control voluntary or involuntary?

Answer 6

The interplay between voluntary and involuntary movement is vital for seamless movement and adaptation to the environment

Note that voluntary movement (bending over, extending an arm/leg) has important ramifications for involuntary movement such as postural movement

Question 7

When generating a compensatory response for posture, the information is sent from?

Answer 7

1. Muscle proprioceptors
2. Sense of balance derived from movements of the head relative to the earths gravitational field (vestibular apparatus)
3. Visual inputs (detecting movements in visual field representing movement of the body)

These sensory inputs converge on nuclei in the brainstem and so the POSTURAL SET is generated there.
These nuclei all receive information from the voluntary circuit collaterals which provides feed forward information

Question 8

What are the different compensatory reflexes for posture of the following parts of the body:
Body? 
Head/body?
Body?
Head and trunk?

Answer 8

Vestibular - body
Collicula – head/body Reticular - body
Tectal – head and trunk

Question 9

What are the medial and lateral components of the vestibulospinal pathway?

Answer 9

The medial vestibular nucleus projects bilaterally to cervical MNs to provide:
- control over the position of the head

WHEREAS

The lateral vestibular nucleus projects ipsilaterally to spinal MNs to provide:
- extensor control over ipsilateral proximal limb and axial muscles

Question 10

Role of lateral vestibulospinal pathway?

Answer 10

Principle effect is to:

1. facilitate ipsilateral extensor motor neurones
2. inhibit flexor motor neurones

innervating the proximal and axial muscles
i.e. EXTENSION

Overall effect is to increase the tone to the antigravity muscles when the vestibular system signals a loss of postural stability

Question 11

How does the lateral vestibulospinal pathway enhance reflexes?

Answer 11

Some of the neurones facilitated are Gamma motor neurone efferents ( a type of lower MN)

This then enhances muscle spindle mediated stretch reflex’s

Question 12

Role of the vestibulocollic relfexes?

Which pathway?

Answer 12

Act on the neck to keep the head stable

Part of the MEDIAL vestibulospinal pathway

Question 13

In the medial vestibulospinal pathway, during infancy what happens following strong flexion and extension?

Answer 13

Strong flexion/extension of the neck induces limbs reflexes which are lost after infancy. Neck flexion:

• -> extension of lower limbs
• -> flexion of upper limbs (and vice versa)

Name: Symmetrical tonic neck reflex

Question 14

What controls the cervicocolic reflex?
Reinforces what?
Results in?

Answer 14

What controls the cervicocolic reflex?
Cervicocollic reflexes are mediated proprioceptively by muscle spindles in neck muscles as well as receptors in joints of cervical vertebrae.

Reinforces what?
This type of reflex reinforces the Vestibulocollic reflexes

Results in?
Cervicocollic reflexes cause contraction of muscles in stretched muscles to oppose the action and so stabilize the head
In this way they tend to return the head to its normal position in space.

Question 15

What is the cervicospinal asymetic tonic neck reflex?

Answer 15

This reflex mediates limb movement as a function of head on trunk position and augments the vestibular reflexes.
It sends messages via the vestibular nucleus along vestibulospinal tracts

i.e. The position of the neck differentially alters tone in the muscles of the arm

Question 16

What is the purpose of the reticular formation?

Answer 16

The reticular formation co-ordinates movement for maintenance of posture
based on FEED FORWARD information

Question 17

How does the reticular formation maintain posture?

Answer 17

To do this it has an excitatory part (Pontine reticular nucleus) and an inhibitory part (Medullary reticular nucleus).

These receive ascending and descending information from multiple sources, and both project to AXIAL ANTIGRAVITY and LIMB EXTENSOR muscles

Question 18

WHERE DOES THE RETICULOSPINAL PATHWAY RECEIVE IT’S INFORMATION FROM?

Information about how to counter any postural instability is then processed in the reticulum, a course of action is decided upon and corrective output is routed via

Answer 18

Information for integration in the reticulum comes from

1. Principally cortical areas (corticoreticular pathways)
2. Vestibular nuclei
3. Proprioception (ascending spinal), vision
4. Cerebellar output

Output via…

1. Alpha motor neurons innervating trunk and proximal limb effectors (correct for shift in center of gravity etc.)
2. Excitation/inhibition of gamma motor neurons which increase muscle tone (correct for shift in weight bearing etc.)

Question 19

What is the influence of the reticular pathway on emotion expression?

Answer 19

Effects the LIMBIC SYSTEM.

Influence manifests as the physical expression of emotion. Forms the basis of body language

Question 20

Other name for tectospinal pathway?

Answer 20

Colliculospinal pathway

Question 21

What are the ventromedial pathways….

Answer 21

Tectospinal
Reticulospinal
Lateral and medial Ventrospinal

Question 22

What is the tectospinal pathway?

Function?

Answer 22

This contralateral pathway arises in the superior colliculus which receives a direct input from the retina

This pathway only projects as far as the CERVICAL spinal segments.

Function:

1. Coordinate eye movements to head and neck movements
2. Move the head/neck so that points of visual interest can be focussed on the fovea

E.g. Owl movement