Pons (Ventral Metencephalon)
Located superior to the medulla and ventral to the cerebellum. The pons is a bridge that connects different parts of the brain with the cerebellum, these structures are called peduncles . The pons consists of white & gray matter & CN V. White Matter: contains sensory and motor tracts. Many of these tracts are passing through the pons between the forebrain and cerebellum. Gray Matter: The Pontine Nuclei signals for voluntary movements from motor areas of the cerebral cortex. Vestibular Nuclei also contained in the medulla, are components of the equilibrium pathway from the inner ear to the brain. Pneumotaxic Area and Apneustic Area of the Respiratory Centre together with the medullary rhythmicity centre, they help to regulate breathing.
Midbrain (Mesencephalon)
Extends from the pons to the diencephalon. The aqueduct of the midbrain (cerebral aqueduct) passes through the midbrain connecting the 3 rd with the 4 th ventricles. Like the medulla and pons, the midbrain contains white & gray matter as well as fibres for CN III & IV. White Matter: contains sensory & motor tracts including the crus cerebri which carries motor information to the brainstem. Gray Matter: Nuclei include the red nucleus, tegmental nucleus and the substantia nigra. The substantia Nigra contains the dark pigment melanin which secretes dopamine.
Reticular Formation
Much of the brainstem & midbrain consists of clusters of gray matter interspersed among bundles of white matter. This netlike arrangement is called the Reticular Formation . This area extends from the upper spinal cord, throughout the brain stem, and into the lower diencephalon. There are both ascending sensory neurons and descending motor neurons. Part of the reticular formation called the Reticular Activating System (RAS) consists of sensory axons that project to the cerebral cortex and help maintain consciousness and is active during awakening from sleep. The reticular formation’s descending functions include regulating posture and muscle tone.
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