Hindbrain: Medulla Oblongata and its features

Hindbrain - Medulla Oblongata:

The hindbrain, also referred to as rhombencephalon is one of the parts or divisions of the brain; the others being the forebrain and midbrain respectively.

Please read the introduction to the human brain here.

The immediate processes of survival (for instance, respiration, blood circulation and digestive functions) are coordinated by the hindbrain, specifically through the medulla oblongata, a part of the hindbrain.

Meanwhile, other involuntary (or autonomic processes ongoing in our body are also controlled by the medulla oblongata. Some of these include swallowing, digestion, vasodilation, vomiting, coughing and sneezing.

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The medulla oblongata (simply called the medulla) is seen at the lowermost portion of the brain (or brainstem) where it continues as the spinal cord inferiorly. For this reason, it becomes the primary point of connection between the Central Nervous System (CNS) and Peripheral Nervous System (PNS).

Below is an image showing the Medulla Oblongata:

The medulla merges with the spinal cord at the foramen magnum. The foramen magnum is an opening located at the base of the skull, marking the beginning of the spinal cord. It is shown below:

Superiorly, the medulla oblongata is connected to the midbrain via the pons. To this end, it plays a critical role in the transmission of nervous signals through the cerebrum (superiorly) and the spinal cord (inferiorly).

Please read on the forebrain and cerebrum here.

The medulla comprises of both myelinated white matter and unmyelinated gray matter intermingled together, thus giving rise to a network of interconnected neuronal clusters within the brainstem.

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The following anatomical features are keys to help us identity the medulla oblongata:

• Olive (Olivary body): The olivary body is a pair of oval structures present on the surface of the medulla oblongata. It contains numerous nerve fibers that connect the medulla to the pons and cerebellum respectively.

• Median fissures (Midline Fissures): The median fissures are shallow grooves found on the anterior and posterior parts of the medulla. The posterior median fissure is referred to as the posterior median sulcus and it commences from the end of the fourth ventricle, continuing down into the sulcus of the spinal cord. The fissure (shallow grove) present on the anterior side is simply referred to as the median fissure. It is continuous with the median sulcus of the spinal cord.

• Pyramids: These are two round masses of nerve fibers located on either side of the median fissure. They connect the medulla to the cerebrum, pons and spinal cord respectively. The pyramid are comprised of about one million nerves which crosses themselves in a process termed decussation of the pyramids.

You can read on the midbrain and its division here.

The medulla oblongata is divided into 2 main portions. These are:

The frontal portion (called the ventral medulla). It contains a pair of structures called pyramids (as explained above).

The backward portion is termed the dorsal medulla. It is this dorsal medulla that forms the dorsal region of the fourth ventricle.

Note: In anatomical terms, ventral means (in front or anterior) and dorsal means (rear or back or posterior).

Think of the fourth ventricle as a fluid filled space surrounded by white matter on the outside and gray matter on the inside.

The image below shows the fourth ventricle:

Recall that we have 12 cranial nerves exiting the brain, connecting to different parts of the body. It is noteworthy that the dorsal medulla gives origin to the last 7 seven cranial nerves. Below is a list of all the cranial nerves:

1. Olfactory nerve

2. Optic nerve

3. Oculomotor nerve

4. Trochlear nerve

5. Trigeminal nerve

6. Abducens nerve

7. Facial nerve

8. Vestibulocochlear nerve

9. Glossopharyngeal nerve

10. Vagus nerve

11. Accessory nerve

12. Hypoglossal nerve

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The medulla oblongata is vital for human survival. Injuries related to it may lead to the following:

• Respiratory difficulties.

• Partial paralysis of the opposite side of the body.

• Partial paralysis to the tongue.

• Inability to feel the stimulus of touch, temperature and pain.

• Difficulty in vomiting and swallowing.

• Difficulty in coughing and sneezing.

Worthy of note is the cerebellum which is another part of the hindbrain. It plays a major role in the body's voluntary movement (especially posture). It accounts for about 10% of the brain's size and comprises of two cerebellar hemispheres separated by a structure called the vermis.

Please read more on the cerebellum here.

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