The brain is a master organ for control and communication within the body and also with the surroundings. Amongst all, the human brain is the most complex and highly developed of all the brains. Larger and more complicated animals have a greater need for an organ to control activities of the body. Hence, more highly developed animals have more highly evolved brains.
Basic features of a brain
In spite of their great differences, all brains have some common features:
- All brains are composed of neurons or nerve cells
- All brains possess at least three major sections: a sensory section, an integrating section and a motor section
The overall function of the brain, which is deemed as behaviour, is determined by two factors – the precise way in which these three divisions are connected and the presence of other special brain centres.
What is Medulla Oblongata? – Definition
The brain majorly can be classified into the forebrain, midbrain and the hindbrain. This lower part of the brain, hindbrain, further can be distinguished into the Cerebellum, Medulla Oblongata and Pons Varolii.
The word Medulla Oblongata has its origins from Latin, where “medis” corresponds to middle and “oblongata” corresponds to long. Hence, the medulla is a long-stem like structure, piriform, conic resembling. It is found in the lowest region of the brain chiefly regulating the autonomic functions such as breathing, heartbeat and digestion. It is critically important as it connects the spinal cord, pons and the cerebral cortex. Additionally, it assists to maintain body posture and governs our reflexes.
In view of importance in controlling head and facial musculature, the medulla oblongata is regarded as the “spinal cord of the head”.
Medulla Oblongata – Highlights
- The medulla oblongata develops from the myelencephalon
- It is the most caudal brainstem structure situated in the posterior-most part of the brainstem merging with the spinal cord
- Dimensions – at its largest, the medulla is 3 cm long and 2 cm wide with a thickness of 1.25 cm
- It is home to all descending and ascending tracts carrying signals between the spinal cord and the brain
- Its broad portions unite the overlying pons hence the narrow section continues with the spinal cord
- The intersection between the spinal cord and medulla concurs with the upper border of the first cervical vertebra (Atlas)
- In addition to the other sections of the hindbrain, the medulla spaces out in the infratentorial space
- The medulla regulates a number of autonomic functions
- Commissural fibres define the base of the medulla. It crosses over from the ipsilateral side in the spinal cord to the contralateral side in the brainstem, underlying which is the spinal cord
- It can be segregated into –
- An upper posterior section connected to the lower part of the 4th ventricle – it is the “open part of the medulla”
- Lower section with the central canal – it is the “closed part of the medulla”
Also see: Body fluids and circulation
Medulla Oblongata – Location
It is located anterior to the cerebellum in the brain stem, inferior to the pons. It is the lowest section of the hindbrain. It is situated in the anterior section of the posterior cranial fossa, stretching down to the foramen magnum
Posteriorly – vallecula of the cerebellum
Anteriorly – meninges and clivus
The topmost part of the medulla goes on to form the fourth cerebral ventricle. This ventricle is a cavity holding the cerebrospinal fluid and continues with the cerebral aqueduct.
Medulla Oblongata Anatomy – Structure
The medulla oblongata is a portion of the brainstem linking the spinal cord and the pons. It extends through the foramen magnum to the levels of the atlas. It is embraced dorsally above the foramen magnum by the cerebral hemispheres.
Medulla extends from the pronto-medullary junction until the plane below the foramen magnum for close to 0.5 cm. The medulla spinalis has a central canal that extends into its lower half to open in the four ventricles at its upper half. The cerebrospinal fluid surrounds the medulla from the inside (central canal) and outside (subarachnoid space). The medulla is situated between the two lobes of the cerebellum (anterior cerebellar notch).
Key components of the medulla oblongata
Medulla is divided into two major parts –
- Ventral medulla – the front portion
- Dorsal medulla – rear portion. It is also known as the tegmentum
1. Median fissures
Along the posterior and anterior portions of the medulla, shallow grooves are found, these are the median fissures.
The upper part of the medulla ventrally, is deeply grooved in the midline along with a bold complexity on either side, these are the pyramids. It is as a result of the contained cortico-spinal fibres. Some of the fibres overlap each other hence obliterating the anterior median fissure, which is known as the decussation of the pyramids. The external arcuate fibers originate from the anterior medial fissures above the decussation of the pyramids, running lateral across the surface of the pons
They are the two round masses of white matter situated on the facing sides of the anterior median fissure.
3. Olivary bodies
In the upper part of the medulla, the area between the posterolateral and anterolateral sulcus is distinguished by a swelling, a pair of oval structures known as the olivary bodies or olives. It contains nerve fibres linking the cerebellum and pons with the medulla. The swelling is as a result of the large mass of gray matter, the inferior olivary nucleus.
4. Fasciculus gracilis
The rear end of the medulla between the posterolateral sulcus and posterior median comprises tracts entering from the posterior funiculus of the spinal cord. These structures are the Fasciculus gracilis situated intermediate to the midline and laterally to the fasciculus cuneatus. These structures typically are the continuation of the bundle of nerve fiber tracts extending from the spinal cord to the medulla.
The terminal end of the fasciculi possesses round elevations referred to as the gracile and cuneate tubercles. These are as a result of the nucleus cuneatus and nucleus gracilis. Overlying the tubercles, a triangular fossa occupies the posterior aspect of the medulla forming the floor of the 4th ventricle. This fossa, on either side, is enclosed by the inferior cerebellar peduncle.
Right laterally immediate to this fasciculus cuneatus is the tuberculum cinereum, which is yet another longitudinal elevation caused as a result of the spinal nucleus of the trigeminal nerve.
Medulla Oblongata Function
The medulla is critical in performing some important body functions pertaining to the regulation of the mental, motor and sensory processing. It is responsible to regulate the autonomic functions of the body while it connects the higher levels of the brain to that of the spinal cord.
- It relays nerve impulses between the spinal cord and the brain
- Controls autonomic functions
- Regulates mood
- Coordinates movements of the body
- It is the reflex centre for coughing, vomiting, sneezing, swallowing
- It is the vasomotor center: baroreceptors
- It is the cardiac centres: parasympathetic and sympathetic system
Primarily, the medulla is the control centre for respiratory and cardiovascular activities. It is responsible to regulate the blood pressure, heart rate, respiratory rate and other such life-sustaining activities. Additionally, it also regulates involuntary reflexes such as gagging, sneezing and swallowing. It coordinates the voluntary actions namely movement of the eye too.
Medulla houses many cranial nerve nuclei crucial for the head, speech, digestion of food and movement of the shoulder. It transmits sensory impulses between the peripheral and central nervous systems. The medulla also relays sensory information to the thalamus which finally reaches the cerebral cortex.
This was a brief on medulla oblongata, its anatomical features, meaning and functions. Visit us at BYJU’S for more content important for NEET preparation.