Brainstem

The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. It is made up of three main parts: the midbrain, the pons, and the medulla oblongata. Though very small, making up only about 2.6 percent of the brain's total weight, the brainstem plays many important jobs in the body.

It helps control basic life functions such as the heart and respiratory systems. The brainstem regulates heart rate and breathing rate, keeping these processes steady. It also sends out important nerves called cranial nerves that control muscles and feelings in the face and neck. There are ten pairs of these nerves that start in the brainstem.

Besides these jobs, the brainstem helps manage the central nervous system and the body's sleep cycle. It is also a key pathway for messages traveling between the brain and the rest of the body. This includes paths for movement, touch, feeling temperature, and more.

Structure

The parts of the brainstem are the midbrain, the pons, and the medulla oblongata; the diencephalon is sometimes considered part of the brainstem.

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

Midbrain

Main article: Midbrain

The midbrain is divided into three parts: tectum, tegmentum, and the ventral tegmental area. The tectum forms the ceiling and contains structures like the superior and inferior colliculi. The tegmentum forms the floor and contains several important areas. The ventral tegmental area includes the cerebral peduncles.

Midbrain nuclei

The midbrain consists of several important areas, including 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 lies between the midbrain and the medulla oblongata. It contains tracts that carry signals to and from the cerebrum, cerebellum, and thalamus. The pons also houses centers that help control breathing and coordinates activities of the cerebellar hemispheres.

Medulla oblongata

Main article: Medulla oblongata

The medulla oblongata, often called the medulla, is the lower part of the brainstem and connects to the spinal cord. It contains centers that control heart rate, breathing, and blood pressure. It also includes the area postrema, which helps control vomiting.

Pontomedullary junction

The pons meets the medulla at the pontomedullary junction. This area receives 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 contain fibers heading to the spinal cord. Lateral to these are the olives, and further out are the roots of several cranial nerves.

From behind

The back of the medulla shows structures like the posterior median sulcus, gracile fasciculus, and cuneate fasciculus. These are part of the pathways that carry sensory information.

Blood supply

The main blood supply to the brainstem comes from the basilar arteries and the vertebral arteries.

Development

The brainstem develops from two of the three early brain parts formed from the neural tube. The midbrain comes from the mesencephalon. The rhombencephalon (hindbrain) develops into 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

When the brainstem gets sick, it can cause problems with things like seeing, feeling, moving muscles, hearing, balance, swallowing, speaking, and coordination. Doctors can often tell exactly where in the brainstem the problem is by testing these functions.

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

In some places, there are special ways to determine when a person's brainstem has stopped working completely. This means the person cannot wake up or breathe on their own, and all tests show there is no chance of getting better. Doctors check for certain reflexes and responses to make 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