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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