Answer
The medulla (medulla oblongata) derives from he myelencephalon which is one of the secondary vesicles of the hindbrain or rhombencephalon. In the adult, the medulla extends from the foramen magnum to a groove adjacent to the pons.
On the anterior surface of the medulla a pair of longitudinal bulges/or ridges--wider rostrally than caudally- constitutes the pyramids which are separated by the anterior median fissure continuous with the same fissure in the spinal cord. The olive a bulge lateral to each pyramid is a prominent feature the medulla. The gracile and cuneate fasciculi of the spinal cord continue rostrally as two pairs of ridges on the posterior aspect of the medulla.
All neural connections-- ascending and descending -- between the brain and the spinal cord pass through the medulla. The ascending fibers bear sensory impulses; they comprise first order neurons of the gracile and cuneate fasciculi which end in the gracile and cuneate nuclei. Here they synapse with second order neurons which cross over (decussate) from the medial lemniscus. The second order ascending neurons terminate in the thalamus where they synapse with third order neurons that rise to the cerebral cortex.
The corticospinal tracts is a pair of descending fibers on the anterior aspect of the medulla. These transmit motor messages from the cerebral cortex to the thalamus, and thence to voluntary (skeletal) muscles. These descending tracts conduct stimuli concerned with most bodily movements below the neck. However, because most of the corticospinal fibers decussate ( pyramidal decussation), most muscles below the neck are controlled contralaterally - by the opposite side of the brain . This excludes muscles in the neck controlled by the tectospinal tract .
Work Step by Step
Neural networks of the medulla are involved in the control of several of the sensory and motor activities of the body/organs:
The sensory functions involve senses of hearing, touch, pressure, taste, equilibrium, pain , and temperature. Some of the motor functions mediated are chewing, salivation, gagging, vomiting, respiration, speech, coughing, sneezing, and sweating, Other such functions are cardiovascular and gastrointestinal activities/functions, and movements of head, neck and shoulders.
Neural signals enter and leave the medulla through the spinal cord ( SC ) as well as through four pairs of spinal nerves. The relevant spinal nerves are the vestibulocochlear (CN VIII), the glossopharyngeal (CN IX), the vagus (X), and the hypoglossal (XII).
Nuclei of the medulla
Additional nuclei and neural centers in the medulla are the inferior olivary nuclei, and some nuclei of the reticular formation RF) that are in the medulla. The inferior olivary nucleus is a relay center for signals on the way to the cerebellum form the lower levels of the brain and the spinal cord. The RF centers in the medulla are the cardiac center, the vasomotor center, and two respiratory centers. The cardiac center controls heart rate (HR) and the force of the heart beat; the vasomotor center regulates blood vessel diameter and thus controls blood pressure. The role of the respiratory centers is to regulate the rhythm and depth of breathing.
