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
T or F. The CSTs are the sole pathway for serving voluntary muscles.
NO! They just form the pathway that confers SPEED and AGILITY to voluntary movements.
Upper motor neuron vs lower motor neuron lesion location
Upper motor neuron is from neuron 1 (cerebral cortex) to neuron 2 (internuncial neuron); LMN: neuron 3 so anywhere from the anterior horn of the SC up to the point where it innervates the muscle
Activation of CST generally evokes what response to the ff:
- interneurons and motor neurons of flexor muscles
- Extensor muscles
- Excitatory postsynaptic potential
2. Inhibitory postsynaptic potential
Effect of pyramidal and extrapyramidal~ tracts on muscle tone?
Pyramidal - increase ms tone
Extrapyramidal - inhibit ms tone
The corticobulbar tract arise from?
Face region of the 1’ motor cortex (BA 4), premotor (BA 6), and frontal eye fields (BA 8)
Fibers of CST pass through which portion of the internal capsule?
Genu
Fibers of ___ will project parts of reticular formation as corticoreticular fibers in the pons and medulla
Corticobulbar tract
For CBT, the projections are bilateral (come from both contralateral and ipsilateral cortex) except 2 CN:
CN VII (Facial motor nucleus)
CN XII (Hypoglossal nucleus)
Tectospinal and tectobulbar
- Origin
- Fibers tract
- Termination
- Function
- Origin: Superior colliculus
- The fibers cross immediately in the dorsal tegmental decussation and incorporated at the Medial Longitudinal Fasciculus
- Terminate in:
A. LMN in the brainstem (for tectobulbar)
B. In the anterior gray column in upper cervical segments of the SC in Rexed laminae VI, VII, VIII - Function
- To mediate reflex postural movements of head and neck in response to visual and perhaps auditory stimuli
Rubrospinal tract
- Origin
- Tract
- Termination
- Function
- Red nucleus (level of superior colliculus)
- Fibers cross immediately in the ventral tegmental decussation —> then descend down the brainstem —> to enter the lateral funiculus of SC
- Terminate in the internuncial neurons (in the anterior gray column of the SC in all levels (laminae V, VI, VII)
- Function
- Influence tone control or facilitate the activity of flexor muscle groups
Interstitiospinal tract
- Origin
- Tract
- Termination
- Function
- Main difference from other two
- Origin: Interstitial nucleus of Cajal
- Forms part of Medial Longitudinal Fasciculus
- Terminate at the anterior horn of all upper cervical levels of SC in laminae VII and VIII
- Function: modulates reflex postural movements in response to visual and vestibular stimuli (similar to tectospinal and tectobulbar)
- UNCROSSED
Lateral Vestibulospinal Tract
- Origin
- Tract
- Receives afferents coming from (2)?
- Function
- Crossed or uncrossed?
- Origin: Lateral vestibular nucleus
- It descends in the anterolateral funiculus —> terminates in Rexed laminae VII & VIII on alpha and gamma motor neurons from the cervical and lumbosacral levels
- Vestibular nerve and cerebellum
- Function:
- For the maintenance of upright posture and balance (so tract excites the extensor motor neurons) - UNCROSSED
Medial Vestibulospinal Tract
- Origin
- Tract
- Termination
- Receives afferent from?
- Function
- Crossed or uncrossed?
- Origin: Medial Vestibular Nucleus
- Descends in MLF —> then located in the anterior funiculus of SC (as far as midthoracic)
- Terminates in the same laminae as LVST (Rexed laminae VII & VIII)
- Primary vestibular and cerebellum
- Function
- To maintain upright posture but excites neck up to the back motor neurons (midthoracic level) ONLY - BOTH
Reticulospinal Tracts consist of?
- Pontine (Medial) RST
2. Medullary (Lateral) RST
Pontine (Medial) Reticulospinal Tract
- Origin
- Contra- or ipsilateral?
- Tract
- Function
- Origin: Pons
- IPSILATERAL
- Tract: Descends chiefly in anterior funiculus of the SC (in all cord levels) and ends in laminae VII & VIII
- Function: Facilitatory to extensor motor neurons
Medullary (Lateral) Reticulospinal Tract
- Origin
- Contra/ipsilateral?
- Tract
- Function
- Origin: Medulla
- Has both crossed and uncrossed fibers
- Tract: Fibers will project bilaterally to spinal levels then descends both ipsi- and contralaterally in the lateral funiculus of the spinal crod in all cord levels. Then it will synapse in laminae VII & IX
- Function: Inhibitory to extensor motor neurons
