The medial longitudinal fasciculus lies anterior to the periaqueductal grey and plays a role in coordinating eye movements. The red nucleus is involved with movement and contains many connections with the cerebellum. The periaqueductal grey is thought to play a role in pain suppression.
The raphe nuclei contain serotonergic neurons and project widely throughout the brain. The ventral tegmental area also contains dopaminergic neurons and plays a role in reward pathways.
The substantia nigra contains dopaminergic neurons that help to regulate movement associated with the basal ganglia. The largest of the raphe nuclei are in the anterior midline of the periaqueductal grey, and the location of the ventral tegmental area is near the midline medial to the red nucleus. The midbrain also includes many other important nuclei, including but not limited to the substantia nigra at the base of the midbrain, the red nucleus anterior medially at the level of the superior colliculus, and the dorsal raphe nucleus. The oculomotor nerve arises from the midbrain in the oculomotor sulcus on the medial surface of the crus cerebri, within the interpeduncular cistern. The other cranial nerve that arises from the midbrain is cranial nerve III, the oculomotor nerve. The trochlear nerve is unique among cranial nerves as it is the only one to emerge from the posterior surface of the brainstem.
Just inferior to the inferior colliculi at the posterior midline of the brainstem cranial nerve IV, the trochlear nerve emerges. The inferior colliculi are involved in auditory processing and connect to their corresponding medial geniculate nuclei through the inferior brachium. Each superior colliculus sends fibers to the corresponding lateral geniculate body and optic tract through the superior brachium. The superior colliculi are involved in visual reflexes such as saccadic eye movements. The posterior surface of the midbrain contains the corpora quadrigemina, which are composed of bilateral superior colliculi and bilateral inferior colliculi. The midbrain is separated relative to the cerebral aqueduct, with the posterior portion being the tectum (floor) and anterior to the aqueduct serving as the tegmentum (roof). The periaqueductal grey surrounds the cerebral aqueduct. The midbrain contains the cerebral aqueduct centrally, which connects the third ventricle superiorly with the fourth ventricle inferiorly. The crus cerebri carry motor cortical spinal fibers, corticonuclear fibers, and pontine fiber tracts. The anterior part of the midbrain contains the crus cerebri with the interpeduncular fossa located between them. It also connects posteriorly to the cerebellum via the superior cerebellar peduncles. The midbrain serves as the connection between the pons and the diencephalon. This section overviews the major structures located in each area of the brainstem, followed by a summary of the course of the major pathways through the brainstem. The brainstem contains many different nuclei and tracts. The following activity addresses the nuclei, tracts, and functions of the brainstem. Clinicians can localize lesions of the brainstem with a thorough knowledge of brainstem anatomy and functions. Ten of the twelve cranial nerves arise from their cranial nerve nuclei in the brainstem. These tracts travel both to the brain (afferent) and from the brain (efferent), such as the somatosensory pathways and the corticospinal tracts, respectively. Some of the white matter tract cell bodies are located within the brainstem as well. The white matter tracts of the brainstem include axons of nerves traversing their course to different structures the axons originate from cell bodies located elsewhere within the central nervous system (CNS). The grey matter within the brainstem consists of nerve cell bodies and forms many important brainstem nuclei. The brainstem contains many critical collections of white and grey matter. It is responsible for many vital functions of life, such as breathing, consciousness, blood pressure, heart rate, and sleep. It is composed of three sections in descending order: the midbrain, pons, and medulla oblongata. The brainstem is the structure that connects the cerebrum of the brain to the spinal cord and cerebellum.
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