N14- Descending motor pathways Flashcards
Where is the primary motor cortex found?
anterior to central sulcus
what is caused by the crossing of motor fibres across the midline?
the right cortex controls muscles on the left side of the body and vice versa (in almost all cases)
How can you tell the difference between a motor and sensory homunculus?
A sensory homunculus has genitalia and a motor one does not
How many descending tracts are there?
1 large main one and several small ones
What is the main descending tract?
Corticospinal tract
What does the corticospinal tract control?
Control of precision and speed of skilled movements, particularly of distal limb muscles (e.g. digits)
What do tracts of the corticospinal tract form?
visible ridges referred to as the ‘pyramids’ on the anterior surface of the medulla
What are the pyramids on the anterior surface of the medulla called?
pyramidal tract
Where do 85% of fibres cross in the corticospinal tract?
in the caudal medulla at the decussation of the pyramids
Where does the corticospinal tract project from?
Primary cortex and areas around it to the spinal cord
What do the crossed fibres form?
Lateral corticospinal tract
what do the uncrossed fibres form?
Ventral corticospinal tract
Where do the uncrossed fibres cross?
Segmentally at whatever segment they are terminating in
What does the pre central gyrus project?
internal capsule
What motor systems are collectively referred to as the extrapyramidal system?
- Tectospinal tract
- Vestibulospinal tract
- Reticulospinal tract
What does the tectospinal tract input mostly to?
cervical segments
Where do fibres originate in the tectospinal tract?
In the superior colliculus which is in a region of midbrain called the tectum
What does the tectospinal tract mediate?
The superior colliculus receives visual information and so this tract is thought to mediate reflex movement due to visual stimuli
Where is the crossed tract limited to in the tectospinal tract?
Upper portion of spinal cord
Where does the fibres originate in the vestibulospinal tract?
ipsilateral vestibular nuclei of pons and medulla (these in turn receive input from vestibular apparatus and cerebellum
Where do fibres from the vestibule nuclei in the vestibulospinal tract project to?
projects ipsilaterally in spinall cord and to antigravity muscles of lower limbs
what does the reticular formation form?
central core of the brainstem
Where does the reticulospinal tract receives input from?
all parts of the CNS
Name one of the functions of the reticulospinal tract.
influencing of voluntary movement
where do fibres originate in the reticulospinal tract?
areas of the reticular formation in pons and medulla
what do fibres in the reticulospinal tract originating in the pons do?
facilitate extensor movements and inhibit flexor movements
what do fibres in the reticulospinal tract originating in the medulla do?
the opposite of the fibres originating in the pons
What does it mean that some fibres extend to many spinal levels?
help coordinate movement involving upper and lower limbs
