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Brainstem

Introduction to the Brainstemmade up of;

medulla oblongataponsmidbrain

occupies the posterior cranial fossa of the skull

stalklike in shapeconnects the narrow spinal cord with the

expanded forebrain

Functions of the brainstem serves as a conduit for the ascending

tracts and descending tracts control of respiration and

cardiovascular systems contains the important nuclei of cranial

nerves III through XII.

Medulla Oblongata

Gross Appearance of Medulla Oblongata

medulla oblongata connects;Superiorly ponsinferiorly spinal cord

junction of the medulla and spinal cord is at;origin of C1spinal nervecorresponds approximately to the level of the

foramen magnum


cont…

medulla oblongata is conical in shape

Cavity;upper half expands as the cavity of the 4th

ventriclelower half continuous with central canal of

the spinal cord


anterior surface

Anterior median fissurePyramid

a swelling on each side of the mediancomposed of bundles of nerve fibers, called

corticospinal fibers, which originate in large nerve cells in the precentral gyrus of the cerebral cortex.

pyramids taper inferiorlymajority of the descending fibers cross over to the

opposite side, forming the decussation of the pyramids


anterior surface

Anterior external arcuate fibers• few nerve fibers that emerge from the anterior

median fissure above the decussation• pass laterally over the surface of the medulla

oblongata to enter the cerebellum. Olives

• located posterolateral to the pyramids• oval elevations produced by the underlying inferior olivary nuclei.


anterior surface

In the groove between the pyramid and the olive emerge the rootlets of the hypoglossal nerve (CN XII).

Inferior cerebellar peduncles• located posterior to the olives• connect the medulla to the cerebellum.

In the groove between the olive and the inferior cerebellar peduncle emerge the roots of;• Glossopharyngeal nerve (CN IX)• Vagus nerve (CN X)• Cranial roots of the accessory nerve (CN XI)


posterior surface superior half lower part of the floor of the fourth

ventricle inferior half

• continuous with the posterior aspect of the spinal cord• possesses a posterior median sulcus.

gracile tubercle• an elongated swelling on each side of the median sulcus• produced by the underlying gracile nucleus.

cuneate tubercle• a similar swelling lateral to the gracile tubercle• produced by the underlying cuneate nucleus

Internal Structure of Medulla Oblongata

white matter and gray matter of medulla have been extensively rearranged than the spinal cord.

This rearrangement can be explained embryologically by the expansion of the neural tube to form the hindbrain vesicle, which becomes the fourth ventricle.

extensive lateral spread of fourth ventricle results in an alteration in the position of the derivatives of the alar and basal plates of the embryo.