brainstem

brainstem, area at the base of the brain that acts as the body’s automatic control center, regulating vital functions such as breathing, heart rate, blood pressure, and swallowing. The brainstem also serves as the main communication pathway between the brain and spinal cord.

Anatomy

Anatomically, the brainstem lies between the deep structures of the cerebral hemispheres and the cervical spinal cord. It is divided into three sections in humans: the midbrain (mesencephalon), the pons (metencephalon), and the medulla oblongata (myelencephalon). Nearly all nerve pathways carrying information to and from thecerebrum and cerebellum pass through these regions. Some of these pathways carry sensory information to the brain (afferent pathways), while others carry motor commands from the brain to the body (efferent pathways).

Function

The brainstem contains the origins (nuclei) of almost all the cranial nerves, except those associated with olfaction (smell) and vision. These nerves control movement and sensation in the face, tongue, pharynx (throat), and larynx (voice box), enabling functions such as chewing, swallowing, speaking, facial expression, balance, hearing, and taste. The brainstem also houses groups of nerve cells that help regulate the autonomic nervous system—the system that controls involuntary functions. These centers coordinate both the sympathetic (“fight-or-flight”) and parasympathetic (“rest-and-digest”) responses. The brainstem further helps regulate vasomotor functions that control the diameter of blood vessels and thereby serve an important role in maintaining blood pressure.

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human nervous system: Brainstem

Effects of injury and disease

Because of the important neural structures concentrated in this small portion of the nervous system, even very small lesions of the brainstem may have profound effects. Speech disorders, vestibular disturbance, abnormal consciousness, dysphagia, and respiratory disturbance are a few examples of possible outcomes of brainstem disorders. Damage may also impair eye movements and facial expressions controlled by the cranial nerves that originate in the brainstem. Such disorders can be caused by trauma, tumors, strokes, infections, and demyelination (multiple sclerosis).

The specific symptoms depend on the location and extent of the injury. For example, damage to certain regions of the brainstem can produce locked-in syndrome, a rare condition in which a person remains conscious but is unable to move most voluntary muscles. Severe injury to the brainstem may be life-threatening and can require mechanical support of vital functions. Complete loss of brainstem function is regarded by some experts as equivalent to brain death.