Brainstem Anatomy: 6 Functions of the Brainstem

The brainstem is a part of the brain found in the posterior of the skull. Relative to the cerebrum and cerebellum, the brainstem is small, but it controls critical functions related to heart rate, breathing rate, sleep cycles, and hormone regulation.

The brainstem contains three primary parts:

• Midbrain: The midbrain is the upper part of the overall brainstem. It includes the tectum, the tegmentum, and ventral tegmental area. Within the tecum, the rostral (front) midbrain contains the superior colliculus, which helps process vision alongside the diencephalon; the inferior colliculus below it communicates with the body's auditory cortex. This part of the brainstem is also known as the mesencephalon.
• Pons: Beneath the midbrain lies the pons, separated by the superior pontine sulcus. This section of the brainstem transmits signals from the cerebral cortex to the medulla and cerebellum. In this sense, it regulates the activities of both cerebellar hemispheres. It also transmits sensory signals from the spinal cord to the thalamus. During fetal development, the pons arises from the metencephalon, as does the cerebellum.
• Medulla oblongata: The lower half of the brainstem consists of the medulla oblongata, which includes the anterior median fissure, the medullary pyramids (including the corticospinal tract), and the pontine-medulla junction. The medulla regulates cardiovascular functions like blood pressure and heart rate, as well as breathing rates. It also contains the area postrema, which controls certain airflow and muscle contractions, including those involved in vomiting. Beneath the medulla is a decussation of fibers that gives way to the spinal cord. During fetal development, the medulla arises from caudal myelencephalon.

The brainstem is found in the lower posterior of the brain. Within the brainstem itself, midbrain is part of the medial section of the brain, while the pons and medulla oblongata are part of the hindbrain. The brainstem comes into contact with the forebrain at the diencephalon, which contains the thalamus and hypothalamus.

The brainstem receives blood from the basilar arteries and the vertebral arteries which, like all blood vessels in the brain, are tightly packed together to form the blood-brain barrier.

The brainstem plays an important role in many of the body's unconscious functions.

1. 1. Motor function: The brainstem regulates motor control via the corticospinal tract, with midbrain dopamine neurons playing an essential role in enabling voluntary motion.
2. 2. Fine touch: The dorsal column-medial lemniscus pathway governs fine touch sensations.
3. 3. Reaction to pain, itches, and temperatures: The spinothalamic tract helps the body instantly react to external sensations.
4. 4. Facial movements: Cranial nerves connected to the brainstem control eye movements and the tensing of facial muscles.
5. 5. Sleep cycles: Sleep cycles, along with overall alertness, involve the brainstem.
6. 6. Reflexes: The brainstem is the part of the brain that leads directly to the spinal cord, transmitting nerve reflexes almost instantaneously. Neuroscience shows that the spinal cord interacts with all components of the brain, but the most primitive and unconscious of actions originate in the brainstem.

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