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The Anatomy of the Facial Nerve. Symptoms of Neuromyelitis Optica Spectrum Disorder. 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. During development, the medulla oblongata forms from the myelencephalon.
The final neuroblasts from the alar plate of the neural tube produce the sensory nuclei of the medulla. The basal plate neuroblasts give rise to the motor nuclei. It is also responsible for regulating several basic functions of the autonomic nervous system, including:. Learning Objectives Describe the location and function of the medulla oblongata region of the brain stem. Key Points The medulla oblongata is the lower half of the brainstem. It controls autonomic functions and connects the higher levels of the brain to the spinal cord.
The medulla oblongata is responsible for regulating several basic functions of the autonomic nervous system, including respiration, cardiac function, vasodilation, and reflexes like vomiting, coughing, sneezing, and swallowing. Key Terms tuberculum cinereum : A raised area between the rootlets of the accessory nerve and posterolateral sulcus that overlies the spinal tract of trigeminal nerve. These structures are involved in cerebellar motor learning and the perception of sound.
The medulla is often divided into two parts: An open or superior part where the dorsal surface of the medulla is formed by the fourth ventricle. A closed or inferior part where the metacoel caudal part of fourth ventricle lies within the medulla oblongata.
While these cardiovascular and respiratory centers are clearly what led 19th century neuroscientists to consider the medulla the center of vital functions, the full range of activities of the medulla is considerably more diverse. In addition to the reflexive cardiovascular and respiratory actions mentioned above, neuronal groups in the medulla are also responsible for other reflexive actions like swallowing, coughing, sneezing, and vomiting.
Vomiting is controlled by an area of the medulla called the area postrema , which is not protected by the blood-brain barrier. This lack of blood-brain barrier protection allows neurons in the area postrema to come into contact with the blood. By doing so, area postrema neurons can detect potentially toxic substances in the blood and trigger vomiting if present.
There are a number of other important nuclei in the medulla. Several cranial nerve nuclei are found there, as well as the inferior olivary nuclei , which are densely interconnected with the cerebellum and thought to play a role in motor control. The nucleus gracilis and nucleus cuneatus are both found in the medulla; they are important nuclei along a pathway called the dorsal columns-medial lemniscus , which carries sensory information to the brain.
The medulla's position as the lowest part of the brainstem also causes it to also be a conduit for a number of tracts that pass from the spinal cord into the brainstem and from the brainstem into the spinal cord. For example, the corticospinal tract a major descending tract for voluntary movementpasses from the medulla into the spinal cord.
The corticospinal tract and another tract called the corticobulbar tract , which is involved with movement of the head and neck, form triangular bundles of fibers in the medulla that create ridges on the outside of the brainstem. The bundles and associated ridges have been termed the medullary pyramids , and the corticospinal and corticobulbar tracts are often referred to as the pyramidal tracts because of their association with the pyramids. At the junction of the medulla and spinal cord, the corticospinal tract decussates , or crosses over to the other side of the body, before continuing down into the spinal cord.
The location of this decussation is referred to as the pyramidal decussation. Thus, the medulla oblongata's functions are extraordinarily diverse and include those that are essential to life as well as to other important activities like movement.
Due to its role in regulating vital functions, however, you could make the argument that the medulla is perhaps the most important area of the brain.
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