Pyramidal Tract Flashcards
The motor system is made up two divisions:
1. Responsible for 1’ control of voluntary movement carried out by 2 main tracts (1b)
- Supporting role in production of well-coordinated movements. Composed of?
- Pyramidal system
- Responsible for 1’ control of voluntary movement carried out by 2 main tracts:
(1b) Corticospinal and Corticobulbar - Extrapyramidal system
- Supporting role in production of well-coordinated movements
- Basal ganglia + Cerebellum
Longest and largest descending fiber tract in the human CNS? What is it concerned with?
Pyramidal tract
-concerned with voluntary discrete, skilled movements; control of muscles involved in speech and vocalization
Pyramidal tract are called as such because?
Fibers pass through the medullary pyramids
The pyramidal system is made up of two main tracts which are?
- Corticospinal tract (Lateral and Anterior/Ventral)
2. Corticobulbar tract
The pyramidal tract fibers arise from 3 areas which are?
Sensorimotor cortex: 1. >Gyrus: Precentral gyrus (1/3 of axons) >BA: BA 4 >Functional cortex: Primary Motor cortex
2.
>Gyrus: Postcentral gyrus
>BA 3, 1, 2
>Fxnal cortex: Primary Sensory Cortex
- Premotor/Secondary Motor Cortex (BA 6) and some frontal eye fields (BA 8)
10% of axons from the precentral gyrus (3% of entire CST) arise from?
What’s unique about it?
Pyramidal Cells of Betz found at the 5h layer of the cerebral cortex
-Unique because they send their axons directly to the anterior horn cells in the spinal cord. Thus, said to be responsible for highly skilled movements.
What are much represented on the motor homunculus?
Tongue, Lips, Face, Fingers, Hands
-Because these parts are concerned with highly skilled movements thus, more neurons are needed to control these movements
Where are the lower limbs represented in the cerebral cortex?
Paracentral lobule (surrounding the central sulcus)
If a px comes in with weakness more on the lower ex rather than the upper, then the vessel most probably occluded is?
ACA because it supplies the medial portion of the brain.
If a px comes in with a weakness more on the face/upper extremities than the lower, then the artery most probably occluded is the?
MCA because it supplies the dorsal and lateral portions of the cerebral hemispheres.
Most medial portion of BA 6 just anterior to the paracentral lobule? Fxn?
Supplementary motor area
-Plays a special role in integrating movements that are performed simultaneously on both sides of the body
Neurons in the Descending Pathway and their location?
1st order neuron
-cell body in cerebral cortex
2nd order neuron
- internuncial neuron in the anterior gray column of the SC
- has a short axon
3rd order neuron (LMN or Final Common Pathway)
- anterior gray column of the spinal cord
- axon innervates skeletal muscles through the anterior root of the spinal nerve
T or F. The descending pathway 1st order neurons terminate on the 2nd order neurons.
Not all. Some directly terminate on 3rd order neurons (as in reflex arcs).
Reflex has 4 components which are?
- Receptor organ
- Afferent neuron
- Efferent neuron
- Effector organ
Corticospinal Tract path?
Cerebral cortex -> Corona radiata -> posterior limb of the Internal capsule -> Cerebral Peduncles (middle 3/5) -> Pons -> Pyramids in upper medulla -> Pyramidal decussation (caudal medulla)
In the posterior limb of the internal capsule, fibers controlling the upper limbs are located where?
More anteriorly
Occlusion in the fibers supplying the internal capsule will present?
Very dense manifestations because the fibers are closely packed together so px may present with paralysis or weakness of all three (arms, trunk, lower limbs)
What is Lacunar syndrome?
Small infarcts in subcortical areas of the brain due to occlusion of a single small perforating artery
In the middle 3/5 of the cerebral peduncle, the fibers that influence the upper limbs would be located where? Lower limbs?
Upper limbs - medially
Lower limbs - laterally
In the caudal medulla, 75-90% of the fibers are (crossed, uncrossed) which are part of which CST which will terminate where?
75-90% are crossed and these are part of the lateral CST which will terminate at the anterior gray column of ALL SC segments
10-15% are uncrossed and part of anterior/ventral CST which will eventually cross before terminating on the anterior horn cells in the cervical and upper thoracic region
Lesion anywhere from the cerebral cortex up to the upper medulla just before the pyramidal decussation would produce paralysis on which side of the body? Beyond that which side of the body is affected?
> CONTRALATERAL HALF. Beyond the pyramidal decussation, the weakness is in the IPSILATERAL HALF
Localization of the tracts in the SC:
- Anterior CST
- Lateral CST
- In the anterior funiculus close to the anterior median fissure
- In the lateral funiculus of the SC
Spinal cord lesion produces a weakness on which side of the body?
IPSILATERAL
Why is there better motor control of the upper versus the lower extremities?
Because most of the pyramidal tract fibers terminate at the cervical spinal cord level
