Spinal bulb: Function, Structure, Development, Key Terms and Examples

It controls autonomous functions and connects the higher levels of the brain with the spinal cord.

Key points

The medulla oblongata is the lower half of the brainstem. It controls autonomous functions and connects the highest levels of the brain with the spinal cord.

The spinal bulb is responsible for regulating several basic functions of the autonomic nervous system , including breathing, cardiac function, vasodilation and reflexes, such as vomiting, coughing, sneezing and swallowing.

Key terms

Tuberculum cinereum: elevated area between the accessory nerve roots and the posterolateral sulcus covering the spinal tract of the trigeminal nerve.

Cerebellar peduncle: the structure that connects the medulla with the cerebellum.

Sympathetic system: the division of the autonomic nervous system responsible for stimulating the fight or flight response of the body.

Olive grove: any of a pair of prominent oval structures in the medulla oblongata that contains the olivary nuclei. These structures are involved in cerebellar motor learning and sound perception.

Parasympathetic system: the division of the autonomic nervous system responsible for the relaxation or inhibition of various bodily functions.

Examples

A stroke can damage the pyramidal tract, the medial lemniscus and the hypoglossal nucleus. This causes a syndrome called medullary medullary syndrome, a type of alternating hemiplegia characterized by recurrent episodes of paralysis on one side of the body.

The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts in which ambiguity will not be generated, it is often referred to simply as marrow.

The cord contains the cardiac, respiratory, vomiting and vasomotor centers and regulates autonomic and involuntary functions, such as respiration, heart rate and blood pressure.

Division of the medulla

An open or superior part where the dorsal surface of the cord is formed by the fourth ventricle.

A closed or lower part where the metacoel (caudal part of the fourth ventricle) is inside the medulla oblongata.

Structure

The region between the anterior median and the anterolateral grooves is occupied by an elevation on both sides known as the pyramid of the medulla oblongata. This elevation is caused by the corticospinal tract. In the lower part of the medulla, some of these fibers cross each other, thus erasing the anterior medial fissure.

This is known as the decussation of the pyramids. Other fibers that originate in the anterior medial fissure above the decussation of the pyramids and extend laterally through the surface of the protuberance are known as external arcuate fibers.

The region between the anterolateral and posterolateral groove in the upper part of the medulla is marked by a swelling known as the olivary body, caused by a large mass of gray matter known as the lower olivary nucleus.

The posterior part of the medulla between the posterior median and the posterolateral grooves contains tracts that enter from the posterior funiculus of the spinal cord . These are the fasciculus gracilis, which is located medially next to the midline, and the fasciculus cuneatus, which extends laterally.

The fascicles end in rounded elevations known as funny and cuneate tubers. They are caused by masses of gray matter known as the gracilis nucleus and the cuneatus nucleus.

Just above the tubers, the posterior part of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the fourth ventricle. The fossa is bounded on both sides by the inferior cerebellar peduncle, which connects the medulla with the cerebellum.

The lower part of the marrow, immediately lateral to the fasciculus cuneatus, is marked by another longitudinal elevation known as the tuberculum cinereum. It is caused by an underlying collection of gray matter known as the spinal nucleus of the trigeminal nerve.

The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the trigeminal nerve.

The base of the cord is defined by the commissural fibers, which cross from the ipsilateral side in the spinal cord to the contralateral side in the brainstem; below this is the spinal cord.

Embryonic development

During development, the medulla oblongata is formed from the myelocephalus. The final neuroblasts of the alar plate of the neural tube produce the sensory nuclei of the cord. The neuroblasts of the basal plate give rise to the motor nuclei.

Function of the medulla oblongata

The spinal bulb controls the autonomic functions and connects the upper levels of the brain with the spinal cord. It is also responsible for regulating several basic functions of the autonomic nervous system, which include:

  • Breathing: chemoreceptors.
  • Heart center: sympathetic system, parasympathetic system.
  • Vasomotor center: baroreceptors.
  • Reflex centers of vomiting, coughing, sneezing and swallowing.