Descending spinal tracts - Extrapyramidal tracts

Question 1

What are the extrapyramidal tracts responsible for?

Answer 1

Involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion

Question 2

What are the 4 extrapyramidal tracts?

Answer 2

1. vestibulospinal tracts
2. reticulospinal tracts
3. rubrospinal tracts
4. tectospinal tracts

Question 3

Do the vestibulospinal and reticulospinal tracts provide ipsilateral or contralateral innervation?

Answer 3

These tracts do not decussate so they provide ipsilateral innervation

Question 4

Do the rubrospinal and tectospinal tracts provide ipsilateral or contralateral innervation?

Answer 4

These tracts do decussate so provide contralateral innervation

Question 5

Where does the rubrospinal tract originate?

Answer 5

Red nucleus of the midbrain tegmentum

Question 6

What does the rubrospinal tract exert control over?

Answer 6

Exerts control over the tone of limb flexor muscles, being excitatory to the motor neurones of these muscles

Question 7

Outline the rubrospinal tract

Answer 7

Axons leaving the red nucleus cross in the ventral tegmental decussation, after which they descend into the spinal cord = contralateral innervation

Question 8

Outline the tectospinal tract

Answer 8

The tectospinal tract originates at the superior colliculus of the midbrain. These neurones cross in the ventral tegmental decussation and enter the spinal cord, terminating at the cervical levels.
Coordinates movements of the head in relation to vision stimuli

Question 9

Where does the vestibulospinal tract originate?

Answer 9

Originates at the vestibular nuclei situated in the pons and medulla

Question 10

Outline the vestibulospinal tract

Answer 10

1. Axons from cells of the lateral vestibular nucleus (Deiter’s nucleus) descend ipsilaterally as the lateral vestibulospinal tract, which is located in the ventral funiculus
2. The medial vestibular nucleus contributes descending fibres to the ipsilateral medial longitudinal fasciculus, also known as the medial vestibulospinal tract - terminates in the cervical cord

Question 11

What is the role of the vestibulospinal tract?

Answer 11

1. Both the medial and lateral vestibulospinal tract are involved in the upright maintenance of posture by innervating anti-gravity muscles
2. Medial vestibulospinal tract - performs the synchronization of the movement of the eyes with the movement of the head so that eyes do not lag behind when the head moves to one side - important for maintaining the balance of the body

Question 12

What are the two reticulospinal tracts

Answer 12

1. medial reticulospinal tract
2. lateral reticulospinal tract

Question 13

Outline the medial (pontine) reticulospinal tract

Answer 13

Arises from the pons, descends ipsilaterally through the anterior funiculus of the spinal cord. It synapses at all levels of the spinal cord with interneurons that inhibit the flexor and gamma motor neurones that stimulate the extensors of the axial and proximal limb musculature

Question 14

Outline the lateral (medullary) reticulospinal tract

Answer 14

Arises from the medulla, descends ipsilaterally through the anterior funiculus of the spinal cord. Effect is the opposite to that of the medial reticulospinal tract - inhibitory effect on extensors and excitatory effect on flexors of the axial and proximal limb musculature

Question 15

What is the role of the reticulospinal tracts?

Answer 15

Reticulospinal fibres influence voluntary movement, reflex activity and muscle tone by controlling the activity of both alpha and gamma motor neurones. They also mediate pressor and depressor effects on the circulatory system and are involved in the control of breathing