keskiaivojen

Keskiaivojen (the midbrain, lat. mesencephalon) on the upper portion of the brainstem, located between the diencephalon and the pons. It functions as a conduit for signals between the forebrain and hindbrain and contains several structures that contribute to sensory processing, motor control, and arousal.

Anatomy and key structures: The midbrain is traditionally described as having a tectum (roof) and a tegmentum (floor), with ventral cerebral peduncles forming the front. The tectum contains the superior and inferior colliculi, which mediate visual and auditory reflexes, respectively. The tegmentum houses important nuclei and tracts, including the red nucleus, the substantia nigra, and the periaqueductal gray matter, as well as the nuclei of cranial nerves III (oculomotor) and IV (trochlear). The cerebral peduncles carry major motor pathways from the cortex to the brainstem and spinal cord.

Blood supply and connections: The midbrain receives arterial blood primarily from branches of the posterior cerebral artery and the superior cerebellar artery. It forms essential connections with the thalamus, basal ganglia, cerebellum, and spinal cord through ascending and descending pathways, integrating sensory inputs with motor commands and contributing to motor coordination and posture.

Clinical relevance: Lesions in the midbrain can produce oculomotor dysfunction, facial sensory or motor symptoms, and movement disorders depending on the affected nuclei and tracts. Degeneration of the substantia nigra is a hallmark of Parkinson’s disease, and midbrain strokes can cause a range of motor, sensory, and eye movement deficits.