CNS Unit 7 Descending Systems Flashcards
In the spinal cord, what contents are in the ventral horn?
- This contains motor nuclei that sends axons out
- Rexed Laminae XI (9), these are motor nuclei for innervation of skeletal muscle - aka Alpha Motor Neurons (LMNs)
The Descending motor pathways are divided into what?
Into Medial and Lateral Systems based on their location in the Spinal Cord (SC)
Where does the Lateral Motor System travel, and where does it synapse?
What is this for?
(In red)
The Lateral Motor Systems travel in the lateral portion of the spinal cord to synapse on lateral motor nuclei: for Distal limb movements and favoring flexors
Skilled movement
Where does the Medial Motor System travel, and where does it synapse?
What is this for?
(In blue)
The Medial motor systems travel in anteromedial portions of spinal cord to synapse on medial motor nuclei for Proximal limb/trunk movements and favoring extensors
Deal with posture and postural balance
What are the tracts in the Lateral Motor System?
- Lateral Corticospinal Tract
- Rubrospinal Tract
What are the tracts in the Medial Motor System?
- Anterior Corticospinal Tract
- (Medial/Lateral) Vestibulospinal Tract
- (Pontine/Medullary)
Reticulospinal Tract - Tectospinal Tract
6 total
What is the function of the Lateral Corticospinal Tract?
Most clinically important descending motor pathway
- Controls voluntary, fine, skilled movement of extremities (distal movements)
- Unique contribution is to activate muscles independently of other muscles
Has 2 pathways
- 1st order neuron- UMN
- 2nd order neuron- LMN
Describe the Pathway of the Lateral Corticospinal Tract?
- Originates at the Pre-central Gyrus (B.A 4)
- It then descends through the Posterior Limb of the Internal Capsule
- It then travels to the Basis Pedunculi of the Midbrain
- It then travels to the Basis Pontis of the Pons
- It then Decussates at the Pyramidal Decussation of the Caudal Medulla (~85-90% of fibers, others go to Anterior Corticospinal tract)
- It then goes to the Lateral Corticospinal tract, where it then goes to synapse at the Anterior Horn to then go to the muscle
With the Corticospinal Tract, what happens if there is a lesion above the Pyramidal Decussation?
This will cause Contralateral weakness
With the Corticospinal Tract, what happens if there is a lesion below the Pyramidal Decussation?
This will cause Ipsilateral weakness
The Lateral Corticospinal Tract also contains Corticobulbar Fibers, what do these fibers do?
They have direct control of the Cranial Nerves (in “bulb” aka brainstem) to move the face, tongue, jaw, eyelids, and eyes
What is the pathway of the Rubrospinal Tract?
- This originates at Red Nucleus of Midbrain (Mesencephalon)
- It decussates immediately and crosses to opposite side ventral tegmental decussation
- It then descends through pons and medulla, then into lateral spinal cord to enter anterior horn and synapse with lateral LMN
Its thought to be involved in movement of contralateral limbs - This tract ends in Cervical Spine
With the Rubrospinal tract, if there is a lesion to one entire half of the midbrain what would happen?
It would result in bilateral deficits
What is important to know for the Anterior Corticospinal Tract?
remember from the LCST, ~85-90% cross at the pyramidal decussation
- The Remaining 10-15% of the fibers that did not cross form the Anterior Corticospinal Tract
- Controls voluntary movement of Bilateral axial and Girdle Musculature (Proximal muscles, i.e. neck, trunk)
What is the Pathway for the Anterior Corticospinal Tract?
Basically the same was LCST, except it DOES NOT Decussate
- Originates at the Pre-central Gyrus (B.A 4)
- It then descends through the Posterior Limb of the Internal Capsule
- It then travels to the Basis Pedunculi of the Midbrain
- It then travels to the Basis Pontis of the Pons
- It goes to the Pyramid (in the medulla) and continues down to the Ventral horn (Somewhere in C-Spine)
Where does the Lateral Vestibulospinal Tract originate, whats its pathway and what does it do?
Originates at the Lateral Vestibular Nucleus in the Pons; It the descends ipsilaterally
- Goes through entire spinal cord
- In charge of balance for the whole body
Where does the Medial Vestibulospinal Tract originate, what its pathway and what does it do?
Originates at the medial (and inferior) Vestibular Nuclei in the Rostral Medulla
- This then splits (one contralaterally and one ipsilaterally) and descends bilaterally
- Terminates in cervical and thoracic cord
- In charge in maintenance of head/neck tone
Where does the Pontine Reticulospinal Tract originate, whats it pathway and what does it do?
- Originates in the Reticular Formation in the Pons (Metencephalon)
Same as Medullary RST - It descends ipsilateral through entire spinal cord to anterior horn to synapse on Medial LMNs
- Involved with Posture and Gait-related movements
Where does the Medullary Reticulospinal Tract originate, whats it pathway and what does it do?
- Originates in the Reticular Formation in the Medulla (Mylencephalon)
Same as Pontine RST - It descends ipsilateral through entire spinal cord to anterior horn to synapse on Medial LMNs
- Involved with Posture and Gait-related movements
Where does the Tectospinal Tract originate, what is the pathway, whats its function?
- Originates in the Superior Colliculus (tectum of midbrain) and crosses immediately at Dorsal Tegmental Decussation
- It then descends contralateral, then enters the Anterior Horn to end in the Cervical Spine
- Involved in coordination of head and eye movement (e.g. movement in response to visual and auditory stimuli), but function is uncertain