BRAIN STEM-MEDULLA OBLONGATA Lecture by Prof. Ansari, (BDS students only) 13-05-08, Tuesday, 8-30—9-30 am.

Objectives Parts of brain stem. Gross features of medulla oblongata. Cranial nerves attached to medulla. Internal structure of medulla. Nuclei / grey matter of medulla. White matter/ tracts in medulla. Blood supply and applied anatomy.

Parts of brain stem Medulla oblongata Pons Mid-brain

GROSS FEATURES OF MEDULLA OBLONGATA It is a conical shaped part of the brain stem. From the lower border of the pons to the lower border of the foramen magnum is the medulla oblongata. It has ventral surface having pyramids and decussation of pyramidal fibers in the ventral median fissure. It has olive swelling between anterior median sulcus and anteriolateral sulcus.

Dorsal surface of medulla oblongata It has a closed part and an open part, posteriorly. The dorsal median fissure separates the fasciculus gracilis of right side with the left side. The fasciculus cuneatus lies lateral to the fasciculus gracilis. The two fasciculi ends on tubercles of cuneatus and tuberculum gracilis.

The open part of medulla oblongata It forms the floor of IV ventricle, along with the dorsal part of pons. It has ependymal lining, median eminences on either side of median sulcus. It has vagal triangle, hypoglossal triangle and vestibular triangle. It has facial colliculus in the pontine part of IV ventricle.

Cranial nerves attached to the medulla Abducent nerve is attached between upper part of pyramids and the lower border of pons. Hypoglossal rootlets arise between pyramid and olive. Vagal fibers arise from the posteriolateral sulcus and the olive. Auditory nerve and facial nerves are attached between medulla and inferior cerebellar peduncle.

Continuation of brain stem Internal structure of medulla oblongata 27-05-08, Tuesday, 8.30-9.30 am

INTERNAL STRUCTURE OF MEDULLA It is studied by three cross sections, first at the level of motor decussations, second at the mid-olivary nucleus level, and third at the sensory decussations. The white fibers are either descending tracts or ascending tracts. The grey matter of the medulla shows various cranial nerve nuclei.

CROSS SECTION AT MOTOR DECUSSATIONS

CROSS SECTION AT SENSORY DECUSSATION

CROSS SECTION AT MID-OLIVARY NUCLEUS

BLOOD SUPPLY OF MEDULLA

The two vertebral arteries join at the lower border of pons to form basilar artery. Anterior spinal artery is a branch of vertebral artery. Posterior spinal artery is a branch of vertebral artery.

Functions of medulla oblongata The medulla controls vital functions such as breathing, heart rate, and blood pressure. It also contains reflex centres such as vomiting, coughing, sneezing, hiccupping, swallowing, and digestion. Information that passes between the spinal cord and the rest of the brain must pass through the medulla.  In the medulla, sensory and motor axons on the right side cross to the left side and axons on the left side cross to the right side.  As a result, stimuli passing through from the left side of the body are sent to the right side of the brain and signals passing through from the right side of the brain stimulate the left side of the body.

The Nuclei of Cranial Nerves 9 (Glossopharyngeal), 10 (Vagus), 11 (Accessory), and 12 (Hypoglossal) lie in the Medulla.

Trigeminal fibers X fibers Hypoglossal fibers Accessory fibers