descending tracts

Question 1

what are the descending tracts for?

Answer 1

motor signals sent from brain to lower motor neurones

lower motor neurones that directly innervate muscles to produce movement

Question 2

what can the motor tracts be functionally divided into?

Answer 2

• pyramidal tracts

- extrapyramidal tracts

Question 3

describe the general passage of the pyramidal tracts and what is it responsible for?

Answer 3

• originate in cerebral cortex
• carry motor fibres to spinal cord and brain stem
• responsible for voluntary control of musculature of body/face

Question 4

describe the general passage of the extrapyramidal tracts and what is it responsible for?

Answer 4

• originate in brain stem
• carry motor fibres to spinal cord
• responsible for involuntary and automatic control of all musculature e.g. muscle tone, balance, posture, locomotion

Question 5

what can be said about all neurones in descending motor system?

Answer 5

• no synapses within descending pathway
• at termination of desc tracts, neurones synase with lower motor neurone
• so all neurones in dec motor system = upper motor neurones

Question 6

what can the pyramidal tracts be subdivided into?

Answer 6

• corticospinal tracts (supplies musculature of body)

- corticobulbar (supplies musculature of head and neck)

Question 7

where does the corticospinal tract begin? what do they receive input from?

Answer 7

• begin in cerebral cortex

- receive a range of inputs from: primary motor cortex, premotor cortex, supplementary motor cortex, somatosensory area

Question 8

when happens to the neurones after originating from the cortex?

Answer 8

• neurones converge
• descend through internal capsule
• neurones pass through crus cerebri of midbrain
• pons
• medulla

Question 9

why is the internal capsule clinically important?

Answer 9

internal capsule particular susceptible to compression from hemorrhagic bleeds
“capsular stroke”
can cause lesion of descending tract

Question 10

what happens in the most inferior part of the medulla?

Answer 10

tract divides into 2:

• lateral corticospinal tract decussate, descend into spinal cord, terminate at ventral horn, from here lower motor neurones go onto supply muscles of body
• anterior corticospinal tract remains ipsilateral, decussate and terminate in ventral horn of cervical and upper thoracic segmental levels

Question 11

where do the corticobulbar tracts arise from? what inputs?

Answer 11

• lateral aspect of primary motor cortex

- receive same inputs as corticopsinal tracts

Question 12

describe the passage of this tract

Answer 12

• fibres converge and pass through internal capsule to brainstem

Question 13

where do the neurones terminate?

Answer 13

on motor nuclei of cranial nerves

here they synapse with lower motor neurones –> carry motor signals to muscles of face and neck

Question 14

what is important to remember about the organisation of the corticobulbar fibres?

Answer 14

many of these fibres innervate motor neurones bilaterally

Question 15

where does the extrapyramidal tract originate and what does it do?

Answer 15

• brainstem and carry motor fibres to spinal cord

- involuntary and automatic control of all musculature

Question 16

what are the 4 tracts?

Answer 16

• vestibulospinal
• reticulospinal
• rubrospinal
• tectospinal

Question 17

which ones decussate?

Answer 17

rubrospinal and tectospinal

so provide contralateral innervation

Question 18

where do the vestibulospinal pathways arise? where does it convey info to?

Answer 18

• vestibular nuceli which receive input from organs of balance
• convey balance info to spinal cord (remains ipsilateral)

Question 19

what do fibres in this pathway control?

Answer 19

control balance and posture by innervating anti-gravity muscles (flexors of arm, extensors of leg)

Question 20

what are the 2 reticulospinal tracts and where do they arise?

Answer 20

• medial reticulospinal tract arises from pons

- lateral reticulospinal tract arises from medulla

Question 21

what does the medial reticulospinal tract facilitate?

Answer 21

voluntary movements, inc. muscle tone

Question 22

what does the lateral reticulospinal tract facilitate?

Answer 22

inhibits voluntary movements, dec. muscle tone

Question 23

where does the rubrospinal tract originate? what kind of innervation does it have?

Answer 23

• originates from red nucleus
• as fibres emerge, they decussate and descend into spinal cord
• contralateral

Question 24

what is the function of the rubrospinal tract?

Answer 24

exact function unclear

thought to play role in fine control of hand movements

Question 25

where does the tectospinal tract begin?

Answer 25

• superior colliculus of midbrain

- superior colliculus receives input from optic nerves

Question 26

what happens to the tectospinal tract then do?

Answer 26

neurones quickly decussate and enter spinal cord

terminate at cervical levels of spinal cord

Question 27

what is the function of the tectospinal tract?

Answer 27

coordinates movements of head in relation to vision stimuli

Question 28

what are the cardinal signs of an upper motor neurone lesion?

Answer 28

• hypertonia - inc. muscle tone
• hyperreflexia - inc. muscle reflexes
• clonus - involuntary, rhythmic muscle contractions
• Babinski sign - extension of hallux in response to blunt stimulation of sole of foot
• muscle weakness