Brainstem

The brainstem (or brain stem) is the back part of the brain that links the cerebrum to the spinal cord. It has three main parts: the midbrain, the pons, and the medulla oblongata. Even though it is small, it is very important for our bodies.

The brainstem helps control basic body functions like the heart and respiratory systems. It manages heart rate and breathing rate to keep them steady. It also sends out special nerves called cranial nerves that control muscles and feelings in the face and neck. There are ten pairs of these nerves that begin in the brainstem.

In addition, the brainstem helps manage the central nervous system and our sleep cycle. It is also a major path for messages moving between the brain and the rest of the body. This includes paths for movement, touch, feeling temperature, and more.

Structure

The brainstem has three parts: the midbrain, the pons, and the medulla oblongata. The diencephalon is sometimes included in the brainstem, too.

The brainstem stretches from just above the tentorial notch down to the first cervical vertebra below the foramen magnum.

Midbrain

Main article: Midbrain

The midbrain has three sections: tectum, tegmentum, and the ventral tegmental area. The tectum makes up the top part and includes areas like the superior and inferior colliculi. The tegmentum forms the bottom part and holds several key regions. The ventral tegmental area contains the cerebral peduncles.

Midbrain nuclei

The midbrain includes many important spots, such as the periaqueductal gray, oculomotor nerve nucleus, trochlear nerve nucleus, red nucleus, substantia nigra pars compacta, reticular formation, central tegmental tract, ventral tegmental area, and rostromedial tegmental nucleus.

Pons

Main article: Pons

The pons sits between the midbrain and the medulla oblongata. It has pathways that send and receive messages to and from the cerebrum, cerebellum, and thalamus. The pons also helps control breathing and works with the cerebellar hemispheres.

Medulla oblongata

Main article: Medulla oblongata

The medulla oblongata, often just called the medulla, is the lower part of the brainstem and links to the spinal cord. It has centers that manage heart rate, breathing, and blood pressure. It also has the area postrema, which helps with vomiting.

Pontomedullary junction

The pons and medulla meet at the pontomedullary junction. This spot gets blood from the vertebral arteries and the posterior inferior cerebellar artery.

Appearance

From the front

In the middle of the medulla is the anterior median fissure. On each side are the medullary pyramids, which have fibers going to the spinal cord. Next to them are the olives, and farther out are the roots of some cranial nerves.

From behind

The back of the medulla shows parts like the posterior median sulcus, gracile fasciculus, and cuneate fasciculus. These help carry sensory information.

Blood supply

The brainstem mainly gets its blood from the basilar arteries and the vertebral arteries.

Development

The brainstem grows from two of the three early brain parts formed from the neural tube. The midbrain comes from the mesencephalon. The rhombencephalon (hindbrain) becomes the pons, cerebellum, and medulla.

Function

The brainstem helps control important things like breathing, heart rate, staying awake, and focusing your attention.

It has three main jobs:

1. The brainstem helps send messages between the body and the brain. It carries feelings like pain and temperature, as well as touch and pressure. It also sends messages from the brain to muscles.
2. Many important nerves, called cranial nerves, start or end in the brainstem. These nerves help control the face, head, and other parts of the body.
3. The brainstem helps control the heart, breathing, how sensitive we are to pain, and how alert we are.

Main article: Cranial nerves

Ten of the twelve pairs of cranial nerves are connected to the brainstem. Some nerves start in the midbrain, some in the pons, and others in the medulla. These nerves leave the brainstem and help control different parts of the body.

Clinical significance

If the brainstem gets sick, it can cause problems with seeing, feeling, moving, hearing, balance, swallowing, speaking, and coordination. Doctors can often find out where in the brainstem the problem is by testing these actions.

Sometimes, strokes can affect the brainstem and cause serious issues. There are also conditions where fluid-filled spaces, called syrinxes, can develop here. These can happen from birth, after an injury, or because of a tumor.

In some places, there are special ways to tell when a person's brainstem has stopped working completely. This means the person cannot wake up or breathe on their own. Doctors check for certain reflexes and responses to be sure before making this decision.

Additional images

The midbrain, pons, and medulla oblongata are shown in this picture of a human brain.

3D visualization of the brainstem in an average human brain