Medulla oblongata


Contains vital centers for autonomic reflex control of the circulation, heart and lungs.

Damage to vital centers in the medulla oblongata is usually fatal.

Afferent fibers to the vital centers arise in specialized visceral receptors.

Specialized receptors include carotid, aortic and the medulla itself.

The medulla oblongata is located in the brainstem, anterior and partially inferior to the cerebellum.

It is a cone-shaped neuronal mass responsible for autonomic, involuntary, functions ranging from vomiting to sneezing.

The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and therefore deals with the autonomic functions of breathing, heart rate and blood pressure.

The medulla oblongata of the brain stem contains the cardiovascular center that monitors the levels of dissolved carbon dioxide and oxygen in the blood, along with blood pressure.

The medulla rhythmicity center monitors oxygen and carbon dioxide levels in the blood and adjusts the rate of breathing to keep these levels in balance.

The cardiovascular center adjusts the heart rate and blood vessel dilation to maintain healthy levels of dissolved gases in the blood and to maintain a healthy blood pressure.

During embryonic development the medulla oblongata develops from the myelencephalon.

The mylencephalon is a secondary vesicle which forms during the maturation of the rhombencephalon, also ref2242ed to as the hindbrain.

The word bulbar is retained for terms that relate to the medulla oblongata, particularly in reference to medical conditions.

The word bulbar can refer to the nerves and tracts connected to the medulla, and also by association to those muscles innervated, such as those of the tongue, pharynx and larynx.

Medulla protrudes from the foramen magnum of the skull-base, after which it gives rise to the spinal cord.

The medulla can be thought of as being in two parts:

an upper open part or superior part where the dorsal surface of the medulla is formed by the fourth ventricle.

a lower closed part or inferior part where the fourth ventricle has narrowed at the obex in the caudal medulla, and surrounds part of the central canal.

The anterior median fissure contains a fold of pia mater, and extends along the length of the medulla oblongata.

The anterior median fissure ends at the lower border of the pons in a triangular area, termed the foramen cecum.

On either side of the anterior median fissure are raised areas termed the medullary pyramids.

The medullary pyramids house the pyramidal tract, which are the corticospinal and the corticobulbar tracts of the nervous system.

At the caudal part of the medulla these tracts cross over in the decussation of the pyramids.

Anterior external arcuate fibers originate from the anterior median fissure above the decussation of the pyramids and laterally cross the pons surface.

The region between the anterolateral and posterolateral sulcus

In the upper part of the medulla are a pair of swellings known as olivary bodies.

The olivary bodies are caused by the largest nuclei of the olivary bodies, the inferior olivary nuclei.

The posterior part of the medulla contains tracts that enter it from the posterior funiculus of the spinal cord; gracile fasciculus, lying medially next to the midline, and the cuneate fasciculus, lying laterally.

These fasciculi end in rounded elevations caused by masses of gray matter,known as the gracile and the cuneate tubercles.

Cell bodies of the gracile and the cuneate nuclei are the second-order neuron of the posterior column-medial lemniscus pathway.

The axons of the gracile and the cuneate tubercles, the internal arcuate fibers or fasciculi, decussate from one side of the medulla to the other to form the medial lemniscus.

Above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the fourth ventricle.

The triangular fossa is bounded by the inferior cerebellar peduncles, which connects the medulla to the cerebellum.

The lower part of the medulla, has a longitudinal elevation, the tuberculum cinereum caused by an underlying collection of gray matter known as the spinal trigeminal nucleus.

The base of the medulla is defined by the commissural fibers, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.

Blood to the medulla is supplied by:

Anterior spinal artery which supplies the whole medial part of the medulla oblongata.

Posterior inferior cerebellar artery, a major branch of the vertebral artery, and supplies the posterolateral part of the medulla, where the main sensory tracts run and synapse.

Direct branches of the vertebral artery supplies an area between the other two main arteries, including the solitary nucleus and other sensory nuclei and fibers.

Forms in fetal development from the myelencephalon.

Its final differentiation of the medulla is seen at week 20 gestation.

It connects the higher levels of the brain to the spinal cord.

It is responsible for several functions of the autonomous nervous system which include:

The control of ventilation via signals from the carotid and aortic bodies.

Respiration is regulated by groups of chemoreceptors, which detect changes in the acidity of the blood.

If the blood becomes too acidic, the medulla oblongata sends electrical signals to intercostal and phrenic muscle tissue to increase their contraction rate and increase oxygenation of the blood.

Cardiovascular center part of sympathetic, parasympathetic nervous system

Vasomotor center with baroreceptors.

Reflex centers of vomiting, coughing, sneezing, and swallowing.

These reflexes: the pharyngeal reflex, the swallowing reflex and the masseter reflex are termed, bulbar reflexes.

A stroke can injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus, causing a medial medullary syndrome.

A Lateral medullary syndrome can be caused by the blockage of either the posterior inferior cerebellar artery or of the vertebral arteries.

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