CEREBRAL PEDUNCLES

CEREBRAL PEDUNCLES

Cerebral peduncles include:

1. Basis pedunculi

2. Substantia nigra

3. Tegmentum, which includes red nucleus.

1. Basis Pedunculus

Basis pedunculus consists of pyramidal tract fibers in the middle, temporopontine fibers laterally and frontopontine fibers medially.

2. Substantia Nigra

Substantia nigra is situated below the red nucleus. Substantia nigra is considered as one of the components of basal ganglia.

3. Tegmentum

Tegmentum lies dorsal to substantia nigra and is actually the upward continuation of the reticular formation in pons. Tegmentum comprises three decussations and red nucleus.

Decussations in tegmentum

i. Superior cerebellar peduncle, which is formed by fibers between cerebellum and other parts of

CNS. These fibers are predominantly efferent fibers from dentate nucleus of cerebellum; few

fibers are from other cerebellar nuclei such as nucleus globosus and nucleus emboliformis.

ii. Forel decussation, which is due to the crossing of rubrospinal tracts from either side

iii. Meynert decussation, which is due to the crossing of medial longitudinal bundle that is

formed by efferent fibers of 3rd, 4th and 6th cranial nerves.

Red Nucleus

Red nucleus is a large oval or round mass of gray matter, extending between the superior colliculus and

hypothalamus.

Parts of red nucleus

Red nucleus has two parts:

1. Nucleus magnocellularis, which is formed by large cells. Fibers from this form the rubrospinal and

rubrobulbar tracts. Nucleus parvocellularis, which is formed by smaller cells. Fibers from this form mainly the rubroreticular tract.

Connections of red nucleus

Afferent connections: Red nucleus receives fibers from:

1. Nucleus parvocellularis, which receives fibers from motor cortex (area 6) – corticorubral fibers

2. Nucleus magnocellularis, which receives fibers from motor cortex (area 6) – pallidorubral fibers

3. Nucleus magnocellularis, which receives fibers from dentate nucleus (of opposite side) – cerebellorubral or dentatorubral tract.

Efferent connections: Red nucleus sends efferent fibers to various parts of brain and spinal cord:

1. Rubrospinal tract to spinal cord

2. Rubrobulbar tract to medulla

3. Rubroreticular fibers to reticular formation

4. Rubrothalamic tract to lateral ventral nucleus of thalamus

5. Rubroolivary tract to inferior olivary nucleus

6. Fibers to nuclei of 3rd, 4th and 6th cranial nerves.

Functions of red nucleus

1. Control of muscle tone: Because of its connections with cerebellum, vestibular apparatus and skeletal

muscle, the red nucleus plays an important role in facilitating the muscle tone.

2. Control of complex muscular movements: Red nucleus controls the complex muscular

movements. It plays an important role in the integration of various impulses received from many

important areas of brain.

3. Control of righting reflexes: Red nucleus is the center for all righting reflexes except optical righting

reflexes.

4. Control of movements of eyeball: Through its efferent connections with nuclei of 3rd, 4th and 6th

cranial nerves, red nucleus plays an important role in the control of ocular movements (Chapter 165).

5. Control of skilled movements: Red nucleus plays an important role in controlling the skilled muscular

movements by its connections with spinal cord and cerebral cortex

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