Spinal Reflexes, Upper Motor Neurones and Control of Movement

Question 1

What do spinal interneurones receive input from?

Answer 1

• Primary sensory axons.
• Descending axons from the brain.
• Collaterals (branches) of LMN’s.
• Other interneurons.

Question 2

What can input to spinal neurones be either?

Answer 2

Excitatory
OR
Inhibitory

Question 3

What generate incoming info to generate an output?

Answer 3

Interneurones

Question 4

Interneurones are either excitatory or inhibitory

Answer 4

TRUE

Question 5

What do inhibitory interneurones mediate?

Answer 5

• The inverse myotatic response.

* RECIPROCAL INHIBITION between extensor and flexor muscles

Question 6

What is reciprocal inhibition important in the initiation of?

Answer 6

Movement by the motor cortex

Question 7

At a joint, what will the voluntary contraction of an extensor stretch?

Answer 7

An antagonistic flexor

Question 8

What does stretching of an antagonistic flexor do?

Answer 8

Initiates the myotatic reflex

Question 9

Once this myotatic reflex is initiated, however, what happens to allow unopposed extension to still occur?

Answer 9

The descending pathways that activate the α-MN controlling the extensor muscles also, via inhibitory interneurons, inhibit the α-MNs supplying the antagonist muscles

Question 10

What do excitatory interneurones mediate?

Answer 10

• The flexor reflex.

* The crossed extensor reflex

Question 11

Describe the flexor reflex.

Answer 11

A noxious stimulus causes limb to flex by:

• contraction of flexor muscles by EXCITATORY INTERNEURONES.
• relaxation of extensor muscles via EXCITATORY + INHIBITORY INTERNEURONES.

Question 12

Describe the crossed extensor reflex.

Answer 12

A noxious stimulus causes limb to extend by:

• contraction of extensor muscles via EXCITATORY interneurons.
• relaxation of flexor muscles via EXCITATORY + INHIBITORY interneurons

Question 13

Why is the crossed extensor reflex important?

Answer 13

It enhances postural support during withdrawal of a foot from a painful stimulus so you don’t fall over

Question 14

What are the controlled movements of the body influenced by?

Answer 14

• Multiple sensory inputs.

* A need to move using internal mechanisms

Question 15

What is found high in the brain? What is its function?

Answer 15

Strategy area
Neocortical areas
Basal ganglia

Question 16

What is found in the middle of the brain? What is its function?

Answer 16

Tactics area
Motor cortex
Cerebellum

Question 17

What is found low in the brain? What is its function?

Answer 17

Execution
Brain stem
Spinal cord

Question 18

Where do the descending spinal tracts originate from?

Answer 18

The cerebral cortex and brain stem

Question 19

What functions are the descending spinal cord tracts concerned with?

Answer 19

1 – Control of movement. 
2 – Muscle tone. 
3 – Spinal reflexes. 
4 – Spinal autonomic functions. 
5 – Modulation of sensory transmission to higher centres

Question 20

Name 2 important descending spinal tracts.

Answer 20

Lateral + Ventromedial

Question 21

What are lateral pathways under the control of?

Answer 21

Cerebral cortex

Question 22

What are lateral pathways important for?

Answer 22

Voluntary control of distal musculature, particularly discrete, skilled, movements (ie. hands and fingers in a ‘fractionated’ manner)

Question 23

What are ventromedial pathways under the control of?

Answer 23

Brain stem

Question 24

What are ventromedial pathways important for?

Answer 24

Posture and locomotion

Question 25

Name a minor lateral pathway.

Answer 25

The rubrospinal tract

Question 26

Where are the cell bodies of the rubrospinal tract located?

Answer 26

In the red nucleus, which receives input from the motor cortex and cerebellum

Question 27

Where do axons of the rubospinal tract decussate?

Answer 27

At the ventral tegmental decussation

Question 28

Once axons of the rubospinal tract have decussated, what do they do?

Answer 28

Descend the spinal cord ventrolateral to the lateral corticospinal tract

Question 29

Where do axons of the rubospinal tract terminate?

Answer 29

Ventral horn

Question 30

What are the effects of lesions of the lateral collumns?

Answer 30

* Loss of ‘fractionated’ movements ie. shoulders, elbow, wrist and fingers can’t be moved independently. * Slowing and impairment of accuracy of voluntary movements. * Little effect on normal posture (ie. standing and sitting).

Question 31

Describe the deficits caused by lesions of the corticospinal tract alone.

Answer 31

Deficits are as profound as those caused by a lesion of the lateral columns, but over time, major recovery can occur

Question 32

Although recovery can occur from deficits caused by lesions of the cortiospinal tract, what can occur?

Answer 32

Weakness of the distal flexors, and an inability to move fingers independently

Question 33

When does recovery of lesions of the corticospinal tract not occur?

Answer 33

If the rubospinal tract is also lesioned

Question 34

Where are the cell bodies of the vestibulospinal tract located?

Answer 34

In the vestibular nuclei (lateral and medial).

Question 35

Where do vestibular nuclei receive input from? What is this via?

Answer 35

From the vestibular labyrinths – via CN VIII. | Cerebellar input is also important

Question 36

Describe how axons from the lateral vestibular nucleus (Deiter’s nucleus) descend.

Answer 36

Descend ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord

Question 37

What do Deiter's nucleus help to do?

Answer 37

Hold upright and balanced posture by facilitating extensor MNs of antigravity muscles (ie. of the leg).

Question 38

What do the axons of the medial vestibular nucleus descend as? Where to?

Answer 38

Descend as the medial vestibulospinal tract, as far as the cervical spinal cord

Question 39

What do medial vestibular nucleus axons activate?

Answer 39

Cervical spinal circuits that control neck and back muscles, guiding head movements

Question 40

Where are the cell bodies of the tectospinal tract located?

Answer 40

In the superior colliculus (aka optic tectum)

Question 41

Where does the superior colliculus receive input from?

Answer 41

* Direct input – from the retina. * From visual cortex. * Afferents conveying somatosensory and auditory information.

Question 42

Where do axons of the tectospinal tract decussate?

Answer 42

In the dorsal tegmental decussation

Question 43

After decussation, describe how axons of the tectospinal tract descend?

Answer 43

Descend close to the midline as the tectospinal tract to the cervical spinal cord, influencing the muscles of the neck, upper trunk and shoulders

Question 44

What does the superior colliculus act as?

Answer 44

A map of the external world, guiding orientation of the head and eyes to an important, new, visual stimulus

Question 45

Where do Pontine (medial) + Medullary (lateral) Reticulospinal Tracts arise from?

Answer 45

Reticular formation

Question 46

What is the reticular formation?

Answer 46

A diffuse mesh of neurones that are located along the length, and at the core of the brainstem

Question 47

How does the pontine tract descend in the spinal cord?

Answer 47

IPSILATERALLY

Question 48

Where does the pontine tract enhance?

Answer 48

Anti-gravity reflexes of the spinal cord

Question 49

What is the function of the pontine tract?

Answer 49

A standing posture. | By facilitating contraction of the extensors of the lower limbs

Question 50

How does the medullary tract descend?

Answer 50

BILATERALLY

Question 51

What does the medullary tract oppose?

Answer 51

The action of the medial tract

Question 52

What does the medullary tract do to anti-gravity muscles?

Answer 52

Releases them from reflex control

Question 53

What is activity in both the pontine and medullary reticulospinal tracts controlled by?

Answer 53

Descending signals from the cortex