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The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. [2] It consists of the cerebral peduncles , tegmentum , and tectum . It is functionally associated with vision, hearing, motor control, sleep and wakefulness, arousal ( alertness ), and temperature regulation.
The cerebral aqueduct (aqueduct of the midbrain, aqueduct of Sylvius, Sylvian aqueduct, mesencephalic duct) is a small, narrow tube connecting the third and fourth ventricles of the brain. [ 1 ] [ 2 ] The cerebral aqueduct is a midline structure that passes through the midbrain .
The pons lies between the midbrain and the medulla oblongata. It is separated from the midbrain by the superior pontine sulcus, and from the medulla by the inferior pontine sulcus. [9] It contains tracts that carry signals from the cerebrum to the medulla and to the cerebellum and also tracts that carry sensory signals to the thalamus.
Cross-section of the midbrain. Tectum. Corpora quadrigemina. Inferior colliculi; Superior colliculi; Pretectum; Tegmentum. Periaqueductal gray; Rostral interstitial nucleus of medial longitudinal fasciculus; Midbrain reticular formation; Dorsal raphe nucleus; Red nucleus; Ventral tegmental area. Parabrachial pigmented nucleus; Paranigral ...
Stimulation of the periaqueductal gray matter of the midbrain activates enkephalin-releasing neurons that project to the raphe nuclei in the brainstem. 5-HT released from the raphe nuclei descends to the dorsal horn of the spinal cord where it forms excitatory connections with the inhibitory interneurons located in Laminae II (aka the substantia gelatinosa).
The brainstem, resembling a stalk, attaches to and leaves the cerebrum at the start of the midbrain area. The brainstem includes the midbrain, the pons, and the medulla oblongata. Behind the brainstem is the cerebellum (Latin: little brain). [7] The cerebrum, brainstem, cerebellum, and spinal cord are covered by three membranes called meninges.
Anatomically, as the name suggests, the MLR is located in the mesencephalon (or midbrain), ventral to the inferior colliculus and near the cuneiform nucleus. [6] Although identifying the exact anatomical substrates of the MLR has been subject to considerable debate, the pedunculopontine nucleus (PPN), cuneiform nucleus, and midbrain ...
The pons in humans measures about 2.5 centimetres (0.98 in) in length. [2] It is the part of the brainstem situated between the midbrain and the medulla oblongata. [ 3 ] [ 4 ] The horizontal medullopontine sulcus demarcates the boundary between the pons and medulla oblongata on the ventral aspect of the brainstem, and the roots of cranial ...