CLASSIFICATION OF MOTOR PATHWAYS

CLASSIFICATION OF MOTOR PATHWAYS

There are two methods to classify the motor pathways. In the first method of classification, motor pathways are divided into pyramidal and extrapyramidal tracts. In the second method, motor pathways are classified into lateral and medial systems.

Pyramidal and Extrapyramidal Pathways

Motor pathways are classified into pyramidal and extrapyramidal tracts, depending upon the situation of their fibers in medulla oblongata.

Pyramidal tracts

Pyramidal tracts are those fibers which form the pyramids in upper part of medulla. Pyramidal tracts are

the anterior and lateral corticospinal tracts. These tracts control the voluntary movements of the body.

Extrapyramidal tracts

Motor pathways other than pyramidal tracts are known as extrapyramidal tracts.

Extrapyramidal tracts are:

1. Medial longitudinal fasciculus

2. Anterior and lateral vestibulospinal tracts

3. Reticulospinal tract

4. Tectospinal tract

5. Reticulospinal tract

6. Rubrospinal tract

7. Olivospinal tract.

Extrapyramidal tracts are concerned with the regulation of tone, posture and equilibrium.

Lateral and Medial Motor Systems

Depending upon the location or termination, motor pathways are divided into two categories, namely the

lateral system or pathway and the medial system or pathway. Lateral motor system is phylogenetically new and medial motor system is old.

Lateral motor system

Fibers of this system terminate on motor neurons situated in lateral part of ventral gray horn in spinal

cord (directly or via interneurons) and on equivalent motor neurons of cranial nerve nuclei in brainstem.

Components of lateral system:

1. Lateral corticospinal tract, which arises from different areas of cerebral cortex and terminates

in the alpha motor neurons situated in lateral part of ventral gray horn of spinal cord.

2. Rubrospinal tract, which arises from red nucleus in midbrain

3. Part of corticobulbar tract, which arises from different areas of frontal and parietal lobes of cerebral cortex along with corticospinal tracts. Part of corticobulbar tract belonging to lateral motor system terminates on the nucleus of hypoglossal nerve and motor nucleus of facial nerve. Fibers from hypoglossal nerve innervate the muscles of tongue. Fibers from motor nucleus of facial nerve innervate the muscles of lower part of face.

Functions of lateral motor system:

1. Lateral corticospinal tract activates the muscles of distal portions of limbs and regulates the skilled

voluntary movements

2. Rubrospinal tract facilitates the tone in the muscles, particularly the flexor muscles

3. Corticobulbar fibers of lateral system are concerned with the movements of expression in lower part of

face and movements of tongue.

Medial motor system

Fibers of medial motor system terminate on motor neurons situated in the medial part of ventral gray horn of spinal cord (via interneurons) and on equivalent motor neurons of cranial nerve nuclei, situated in the brainstem.

Components of medial motor system:

1. Anterior corticospinal tract, which arises from different areas of cerebral cortex and terminates in the

alpha motor neurons situated in medial part of ventral gray horn of spinal cord 2. Part of corticobulbar fibers of medial system, which arises from different areas of frontal and parietal lobes of cerebral cortex along with corticospinal tracts. Fibers of corticobulbar tract belonging to medial motor system innervate the muscles of trunk and limbs, muscles of jaw and muscles of upper part of face.

3. Lateral and medial vestibulospinal tracts that arise from lateral vestibular nucleus and medial vestibular

nucleus

4. Reticulospinal tract, which arises from reticular formation in brainstem

5. Tectospinal tract, which takes origin from superior colliculus of midbrain.

Functions of medial motor system:

1. Anterior corticospinal tract is responsible for the maintenance of posture and equilibrium

2. Fibers of corticobulbar tract belonging to medial motor system, innervating muscles of upper part

of trunk are involved in the maintenance of posture and equilibrium. Fibers innervating muscles of jaw

and face are involved in the movements of chewing and movements of eyebrow.

3. Vestibulospinal tract is concerned with the adjustment of position of head and body during angular

and linear acceleration

4. Pontine fibers of reticulospinal tract facilitate the tone of extensor muscles and regulate the postural

reflexes. However, medullary fibers of this tract inhibit the tone of the muscles involved in postural

movements.

5. Tectospinal tract is responsible for the movement of head in response to visual and auditory stimulus.