Pyramidal Tract

1. Pyramidal tracts
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

2. Pyramidal tract
 Descending tract
 Cortico-spinal tract
 Formed by the axons of upper motor neurons –Pyramidal cells/ Betz
cells
 Concerned with skillful, voluntary movements, non-postural type,
affecting mainly the flexor muscles of the distal parts of upper and lower
extremeties

3. Pyramidal tract
Pyramidal tract contains one million fibers
About 70% of the fibers are myelinated

4. Origin
One third of the fibers arise from area no 4
One-third of the fibers arise from area no 6
Rest of the fibers from area no 3,1,2

5. Course
Axons of these neurons descend successfully through the
corona radiata,
posterior limb of internal capsule,
middle two-thirds of basis pedunculi of midbrain, pons
and pyramid of the medulla

7. Course
In the lower medulla, 90 percent of the fibers decussate and
enter into the lateral funiculus of the contralateral side
Lateral cortico-spinal tract
Crossed pyramidal tract

8. Course
8% of the fibers pass uncrossed in the anterior funiculus
Anterior coricospinal tract
However terminates in the opposite spinal gray matter after
crossing in the anterior white commissure

9. Course
2% of fibers descend and terminate uncrossed in the lateral
corticospinal tract

11. Lateral corticospinal tract
Located in the lateral funiculus
Cervical segments are superficial
Intermediate fibers for trunk occupy central area
Shorter fibers for upper limb lie in the deeper plane

12. Anterior corticospinal tract
Located in the anterior funiculus
Tract is found only in primates only in man
All the fibers cross midline in the anterior white commissure
and terminate in the contralateral spinal gray matter

13. Termination
Most of the fibers terminate in the lamina IV to lamina VII of
spinal gray matter
And through the interneurons connected to the alpha and
gamma motor neurons
Few fibers terminate directly

15. Functions
They provide stimulating fibers to flexor muscles and
inhibiting fibers to extensor fibers of the trunk
The corticospinal fibers from area 3,1,2 are presumed to
perform inhibition of sensory input
Modulates sensory input

16. Special features
Extends uninterruptedly from cortex to spinal cord
It is named pyramidal tract since it occupies the pyramid of the
medulla
Essential components of UMN and is concerned with skillful-non
postural movements of flexor muscles of trunk and distal parts of
extremeties

17. Special features
It modulates sensory input and helps in smooth performance of
movements
Myelination of corticospinal tracts starts about 3 years after birth
and completed by puberty.
Corticospinal fibers activate alpha and gamma fibers
simultameously ( co-activation)

18. Effect of lesion in the motor cortex
Stroke
Caused by either a ruptured blood vessel that hemorrhages into
brain
Or thrombosis of one of the major arteries supplying blood to the
brain
Loss of blood supply to cortex or CST where it passes through
internal capsule

19. Lesion in the internal capsule
Since the CST passes through the relatively small area in the
internal capsule
Lesion here due to inadequate blood supply
Cause Dramatic loss of function of the opposite side of body
Interruption to the pyramidal tract here leads to hemiplegia or
hemiparesis – paralysis or weakness on entire opposite side

20. Lesion in the internal capsule
This is called upper motor neuron paralysis
In hemiplegia, due to UMN, no atrophy of muscles
But marked stiffness or spasticity is observed

21. THANK YOU