The
medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply
the medulla. The medulla contains the cardiac,
respiratoryRespiratory center is located in the medulla oblongata which is the lowermost part of the brain stem. RC receives controlling signals of neural, chemical and hormonal natures and controls the rate and depth of respiratory movements of the diaphragm and other respiratory muscles...
,
vomitingThe area postrema is a part of the brain that controls vomiting. It was discovered in 1953 by Utah Pharmacologists Herbert L. Borison and S. C. Wang .-Location:It is located in the lateral reticular formation of the medulla oblongata...
and vasomotor centers and deals with
autonomicThe autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
functions, such as breathing, heart rate and blood pressure.
Two parts: open and closed
The medulla is often thought of as being in two parts:
- an open part or superior part where the dorsal surface of the medulla is formed by the fourth ventricle
The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle...
.
- a closed part or inferior part where the central canal
For the engineering project, see Indiana Central Canal.The central canal is the cerebrospinal fluid-filled space that runs longitudinally through the length of the entire spinal cord. The central canal is contiguous with the ventricular system of the brain...
lies within the medulla.
Between the anterior median sulcus and the anterolateral sulcus
The region between the anterior median sulcus and the anterolateral sulcus is occupied by an elevation on either side known as the
pyramid of medulla oblongataThe anterior or ventral portion of the medulla oblongata is named the pyramid and lies between the anterior median fissure and the antero-lateral sulcus....
. This elevation is caused by the
corticospinal tractThe corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....
.
In the lower part of the medulla some of these fibers cross each other thus obliterating the anterior median fissure. This is known as the
decussation of the pyramidsThe two pyramids contain the motor fibers that pass from the brain to the medulla oblongata and medulla spinalis, corticobulbar and corticospinal fibers....
.
Some other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as the external arcuate fibers.
Between the anterolateral and posterolateral sulci
The region between the anterolateral and posterolateral sulci in the upper part of the medulla is marked by a swelling known as the
Olivary bodyIn anatomy, the olivary bodies or simply olives are a pair of prominent oval structures in the medulla oblongata, the lower portion of the brainstem...
.
It is caused by a large mass of gray matter known as the
inferior olivary nucleusThe inferior olivary nucleus is the largest nucleus situated in the olivary body, part of the medulla oblongata.-Function:It is closely associated with the cerebellum, meaning that it is involved in control and coordination of movements, and likely also sensory processing and cognitive tasks.There...
.
Between the posterior median sulcus and the posterolateral sulcus
The posterior part of the medulla between the posterior median sulcus and the posterolateral sulcus contains tracts that enter it from the posterior funiculus of the spinal cord. These are the
fasciculus gracilisThe fasciculus gracilis is a bundle of axon fibres in the dorsomedial spinal cord that carries information about fine touch, vibrations, and conscious proprioception from the lower part of the body to the brain stem...
, lying medially next to the midline, and the
fasciculus cuneatusThe fasciculus cuneatus is a bundle of nerves in the spinal cord which primarily transmits information from the arms...
, lying laterally.
These fasciculi end in rounded elevations known as the gracile and the cuneate tubercles. They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus.
Just 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 ventricleThe fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle...
. The fossa is bounded on either side by the
inferior cerebellar peduncleThe upper part of the posterior district of the medulla oblongata is occupied by the inferior peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves....
, which connects the medulla to the
cerebellumThe cerebellum is a region of the brain that plays an important role in the integration of sensory perception, coordination and motor control...
.
Lower part
The lower part of the medulla, immediately lateral to the fasciculus cuneatus, is marked by another longitudinal elevation known as the
tuberculum cinereumIt is a raised area between the rootlets of the accessory nerve and posterolateral sulcus. It overlies the spinal tract of trigeminal nerve....
.
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 nerveThe trigeminal nerve is responsible for sensation in the face. Sensory information from the face and body is processed by parallel pathways in the central nervous system....
.
Base
The base of the medulla is defined by the
commissural fibersThe commissural fibers or transverse fibers connect the two hemispheres of the brain. They include:* the transverse fibers of the corpus callosum* the anterior commissure* the posterior commissure* the lyra or hippocampal commissure....
, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.
Functions
The medulla oblongata controls
autonomicThe autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
functions, and relays nerve signals between the
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
and
spinal cordThe spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain. The brain and spinal cord together make up the central nervous system. It is around 45 cm long in men and around 43 cm long in women. The length of the spinal cord is much shorter than...
. It is also responsible for controlling several major points and
autonomicAutonomic can refer to several things, including:*Autonomic nervous system*Autonomic Computing*Autonomic system *Autonomic Networking...
functions of the body:
- respiration
In animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
(via dorsal respiratory groupThe dorsal respiratory group is located in the dorsomedial region of the medulla, and is composed of cells in the solitary tract nucleus. The DRG is found in many types of fish and mammals.-Respiratory effects:...
and ventral respiratory groupThe ventral respiratory group is a column of neurons located in the ventrolateral region of the medulla, extending from the caudal facial nucleus to -400μm obex...
)
- blood pressure
Blood pressure is the pressure exerted by circulating blood on the walls of blood vessels, and is one of the principal vital signs. During each heartbeat, BP varies between a maximum and a minimum pressure...
- swallowing
Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth, to the pharynx, into the esophagus, with the shutting of the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration...
- vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Undesired vomiting may result from many causes, ranging from gastritis or poisoning to brain tumors, or elevated intracranial pressure...
- defecation
Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Humans usually defecate from three times a week, up to three times a day...
- urination
Urination, also known as micturition, voiding, peeing, and more rarely, emiction, is the process of disposing of urine from the urinary bladder through the urethra to the outside of the body. In healthy humans, the process of urination is under voluntary control; in infants and individuals with...
- reflexes
Blood supply
Blood to the medulla is supplied by a number of arteries.
- Anterior spinal artery
In human anatomy, the anterior spinal artery is the blood vessel that supplies the anterior portion of the spinal cord. It arises from branches of the vertebral arteries and is supplied by the anterior segmental medullary arteries, including the artery of Adamkiewicz, and courses along the anterior...
: The anterior spinal artery supplies the whole medial part of the medulla oblongata. A blockage (such as in a stroke) will injure the pyramidal tract, medial lemniscusThe medial lemniscus, also known as Reil's band or Reil's ribbon, is a pathway in the brainstem that carries sensory information from the gracile and cuneate nuclei to the thalamus.-Path:...
, and the hypoglossal nucleusThe hypoglossal nucleus is a cranial nerve nucleus, and it extends the length of the medulla, and being a motor nucleus, is close to the midline...
. This causes a syndrome called medial medullary syndromeMedial medullary syndrome, also known as inferior alternating syndrome, hyploglossal alternating hemiplegia, or lower alternating hemiplegia, is a set of clinical features resulting from occlusion of vertebral artery or of branch of vertebral or lower basilar artery...
.
- Posterior inferior cerebellar artery
The posterior inferior cerebellar artery , the largest branch of the vertebral, is one of the three main arterial blood supplies for the cerebellum.-Course:...
(PICA): The posterior inferior cerebellar artery, a major branch of the vertebral artery, supplies the posterolateral part of the medulla, where the main sensory tracts run and synapse. (As the name implies, it also supplies some of the cerebellumThe cerebellum is a region of the brain that plays an important role in the integration of sensory perception, coordination and motor control...
.)
- Direct branches of the vertebral artery
The vertebral arteries are branches of the subclavian arteries.The two vertebral arteries and the basilar artery are sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with blood supplied to the anterior part of the...
: The vertebral artery supplies an area between the other two main arteries, including the nucleus solitarius and other sensory nuclei and fibers. Lateral medullary syndromeLateral medullary syndrome is a disease in which the patient has difficulty with swallowing or speaking or both owing to one or more patches of dead tissue caused by interrupted blood supply to parts of the brain.-Signs and symptoms:This syndrome is...
can be caused by occlusion of either the PICA or the vertebral arteries.
Death by hanging
When someone is hanged with a rope tied around his/her neck, the axis vertebra (containing sharp projections) may pierce the medulla oblongata due to the pressure of the rope. This stops involuntary actions controlled by the medulla oblongata, like breathing, the beating of one's heart, etc.