Medulla: The English word ‘Medulla’ derives from the Latin word ‘medius’ meaning ‘middle’ or ‘core’ or ‘marrow’. Medulla often implies a deep region within a structure, such as the renal medulla or the medulla of the adrenal gland.
Medulla was the word Vesalius used for the spinal cord, inspired perhaps by the name the Greeks favored: myelos rachites, “marrow of the spine”. Indeed, the soft neural tissue of the spinal cord within the vertebral canal of the spinal column does remind one of marrow present in the hollow shaft of a long bone (in the space appropriately called the medullary cavity). Conus medullaris (conus terminalis or medullary cone) is the cone-shaped lower part of the spinal cord.
“Marrow” or medulla still appears in many English dictionaries as an alternative name for the spinal cord, though this definition has been long since discarded by anatomists.
In spite of being connected to the brain, it is the spinal cord that’s referred to as medulla oblongata. The term was first used by the German anatomist Lorenz Heister in 1740 and it’s not clear why: its meaning does not make a lot of sense (“oblong-shaped spinal cord” or as some translate it, “rather long spinal cord”) and there had been a reasonable term in use earlier, the medulla prolongata, which does make sense (“spinal cord extension”). Nonetheless, medulla oblongata became established while medulla prolongata disappeared.
Heister’s original use of the term was for the entire brain stem. In 1750, the Swiss anatomist Albrecht von Haller restricted the use to its present meaning: the thumb-size segment of brain stem continuous with the spinal cord.
Blood supply of the Medulla
Medulla is supplied by a number of arteries.
Posterior inferior cerebellar artery: This is a main branch of the vertebral artery, and provides the posterolateral part of the medulla, where the main sensory tracts run and synapse. It additionally supplies part of the cerebellum.
Anterior spinal artery: This supplies the entire medial part of the medulla oblongata.
Direct branches of the vertebral artery: The vertebral artery supplies an area between the other two main arteries, including the solitary nucleus and other sensory nuclei and fibers.
Function of the Medulla
The medulla oblongata joins the higher levels of the brain to the spinal cord and is responsible for several functions of the autonomous nervous system that include:
- The key to ventilation via signals from the carotid and aortic bodies. Respiration is regulated by groups of chemoreceptors. These sensors detect changes in the acidity of the blood, thus if the blood is considered too acidic by the medulla oblongata electrical signals are transmitted to intercostal and phrenical muscle tissue rising their contraction rate in order to reoxygenate the blood. The ventral respiratory group and the dorsal respiratory group are neurons included in this regulation. The pre-Bötzinger complex is a cluster of interneurons involved in the respiratory function of the medulla.
- Vasomotor center – baroreceptors
- Cardiovascular Center – sympathetic, parasympathetic nervous system
- Reflex centers of vomiting, coughing, sneezing, and swallowing. These reflexes which include the pharyngeal reflex, the swallowing reflex (also known as the palatal reflex), and the masseter reflex can be termed, bulbar reflexes.
- Reflex centers of vomiting, coughing, sneezing, and swallowing. These reflexes that include the pharyngeal reflex, the swallowing reflex, and the masseter reflex can be termed, bulbar reflexes.