Pyramidal Tract Explained: From Brain To Spinal Cord

Pyramidal Tract Explained: From Brain To Spinal Cord

Describe pyramidal tract with the help of diagram from origin to termination. (or) Draw and label pyramidal pathway.
Answer:

Pyramidal tract:

• These are descending tracts concerned with voluntary activities of the body.
• They are also called corticospinal tracts.
• They are two such tracts.
  • Anterior corticospinal tract.
  • Lateral corticospinal tract.
• The fibres of this tract arises from pyramid like structure in the medulla, thus they are called pyramidal tracts.

Origin:

• Fibers of pyramidal tract arises from following.

Course:

• The fibers of the pyramidal tract descend downwards, in diffused manner and then converge in the form of a fan like structure towards the brain stem as a radiating mass of fibers.
• This radiating mass is called corona radiata.
• Then, these fibers reach thalamus and descends down through.

1. Internal capsule:

• Here, it lie in the genu and anterior two-third of the posterior limb.
• Then, it enters mid-brain.

2. In midbrain:

• Here, it lie ventral to the substantia nigra.

3. In pons:

• Here, the fibers are broken up into a series.
• At the lower border of pons, the fibers are grouped once again.

4. In the medulla:

• The fibers occupies the most ventral part of the medulla.
• Here, the bundle of fibers gives an appearance of the pyramid.
• At the lower border of medulla, the pyramidal tract on each side is divided into 2 bundles of unequal sizes.

80% of fibers:

• Cross over and descend as the lateral corticospinal tract and end on the anterior horn cells.
• While crossing the midline, the fibers form the pyramidal decussation.

20% of fibers:

• Remain uncrossed
• Runs downwards in spinal cord as anterior corticospinal tract.

Termination:

• The fibers from both the tract terminate in the motor neurons of anterior grey horn.
• The axon of the anterior motor neurons leave the spinal cord as spinal nerves and supply the skeletal muscles.