Descending tracts Flashcards
What are the two main groups of descending tracts?
Pyramidal - originate in cerebral cortex, pass through medullary pryamids of the medulla oblongata
Extra-Pyramidal - Originate in the brainstem
What is the function of the pyramidal descending tracts?
Voluntary control of musculature of the face and body
What is the function of the extra-pyramidal descending tracts?
Involuntary and autonomic control of musculature eg muscle tone, balance and posture
What is an upper motor neurone?
A neurone that has both its cell body and axon within the CNS
What are the two pyramidal tracts?
Corticospinal
Corticobulbar
What is the function of the Corticospinal tract?
Supplies musculature of the body
What is the function of the Corticobulbar tract?
Supplies musculature of the face
What are the three main inputs for the Corticospinal tract?
Primary motor cortex
Premotor cortex
Supplementary motor area
Also somatosensory which regulates the ascending tracts
What happens to the neurones of the Corticospinal tract immediately after leaving the cortex?
They converge and pass through the internal capsule Important as the internal capsule is particularly susceptible to compression from heamorrhagic bleeds
Briefly, what is the path of the Corticospinal tract?
Leaves cortex, passes trough internal capsule, pass through crus cerebri, pons and then into medulla then split into anterior and lateral tracts
What is the route of the anterior Corticospinal tract?
Descending ipsilaterally in the spinal cord
Decussate and terminate in the ventral horn of lower cervical/upper thoracic levels
What is the route of the lateral Corticospinal tract?
Decussate and descend in the contralateral side of the spinal cord
Terminate in the ventral horn
Briefly, what is the route of the Corticobulbar tract?
Arise in primary motor cortex (With inputs from Primary motor cortex, Premotor cortex and Supplementary motor area)
Fibres converge and pass through internal capsule
Terminate on the motor nuclei of the cranial nerves
Most Corticobulbar tract fibres innervate bilaterally, which cranial nerves do not receive bilateral innervation?
Facial nerve has contralateral innervation
Hypoglossal nerve has contralateral innervation
What are the four extra-pyramidal tracts?
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal
Which of the extra-pyramidal tracts decussate?
Rubrospinal
Tectospinal
Therefore innervate contralateral side
Which of the extra-pyramidal tracts do not decussate?
Vestibulospinal
Reticulospinal
Therefore innervate ipsilateral side
What is the function of the Vestibulospinal tracts?
Balance
Posture by innervating antigravity muscles
Briefly, what is the route of the Vestibulospinal tract?
Arises in vestibular nucleus (Receives input from organs of balance)
Conveys balance information to ipsilateral spinal cord
What are the two branches of the Reticulospinal tract?
Medial
Lateral
What is the function of the Medial Reticulospinal tract?
Voluntary movement
Increases muscle tone
Where does the Medial Reticulospinal tract originate?
In the Pons
What is the function of the Lateral Reticulospinal tract?
Inhibits voluntary movement
Decreases muscle tone
Where does the Lateral Reticulospinal tract originate?
In the Medulla
Briefly, what is the route of the Rubrospinal tract?
Originates in the Red nucleus (Midbrain structure)
Decussate as emerge from nucleus
Travel down contralateral side of the spinal cord so contralateral innervation
What is the function of the Rubrospinal tract?
Unsure, but thought to be fine hand movements
Briefly, what is the route of the Tectospinal tract?
Begins in superior colliculus of the midbrain (Receives input from the optic nerves)
Decussate immediately and enter the spinal cord on the contalateral side
Terminate at cervical levels
What is the function of the Tectospinal tract?
Co ordinates movements of the head in relation to visual stimuli
Why are the pyramidal tracts vulnerable to damage?
They extend the whole length of the spinal tract without synapsing
They pass through the internal capsule which is a high risk area for haemorrhage
What are the signs of damage to the Corticospinal tract?
Hypertonia Hyperreflexia Clonus Babinski's sign Muscle weakness (On the contralateral side)
What are the signs of damage to the Corticobulbar tract?
Mostly muscle weakness as there is bilateral innervation, However Facial nerve will have spastic paralysis of contralateral lower quadrant of the face
Hypoglossal nerve will have spastic paralysis on the contralateral side so tongue will point to contralateral side
How are the extra pyramidal tracts most likely to be damaged?
Degenerative diseases
Tumours
Encephalitis (Inflammation of brain tissue)
What are the signs of extra pyramidal tract damage?
Disorders of involuntary movement
Diskinesias
