The abducens nerves (CN VI) (27) emerge from the pontomedullary sulcus 1 to 2 cm lateral to the midline. The ventral aspect of the pons displays the median pontine sulcus (10), the transversely ridged “belly” of the pons (11), and the ventral aspect of the middle cerebellar peduncle (brachium pontis) (12). The pons is delimited inferiorly by the pontomedullary sulcus (1) and superiorly by the pontomesencephalic sulcus (9). Laterally, the image displays the pyramids of the medulla (3), the preolivary sulcus (2) with the emerging rootlets of the hypoglossal nerve (CN XII), the olive (7), the supraolivary fossette (8), and the retro-olivary sulcus with the emerging rootlets of the glossopharyngeal, vagus and accessory nerves (CN IX, X, and medullary portion of XI). Inferiorly, the anterior median sulcus shows a deflection (5) that indicates the site of the decussation of the pyramids. The anterior median medullary sulcus (4) ascends between the paired medullary pyramids (3) to end superiorly at the foramen cecum (midline portion (6) of pontomedullary sulcus). A, Ventrally, the medulla is separated from the pons by the pontomedullary sulcus (1). B, Dorsal view, C, Lateral view with anterior to the reader’s left. Trapezoid body: the bundle of transverse fibers in the tegmentum of the pons that conveys auditory information bilaterallyįIGURE 15-1 Surface of the brain stem and cranial nerves.
Right cerebral peduncle visible body app full#
Tegmentum: the middle lamina of the full brain stem situated between the basis ventrally and the aqueduct-fourth ventricle dorsally Tectum: the dorsal lamina of the midbrain situated dorsal to the aqueduct Secondary sensory (relay) neurons then receive the sensory data from the primary neuron and convey it onward to tertiary neurons and beyond. Each primary sensory neuron has (1) a peripheral process that extends to peripherally situated sensory endings, (2) a cell body that lies within the dorsal root ganglion or sensory ganglion related to a cranial nerve, and (3) a central process that enters the central nervous system via spinal or cranial nerves to synapse on second order neurons within the CNS. Sensory neurons: primary and secondary (relay). The structures of the lemniscal arc include the paired medial lemnisci medially, the paired lateral lemnisci laterally, and the paired spinothalamic tracts (spinal lemnisci) that angle over from lateral to medial as they ascend through the brain stem.
Lemniscal arc: This term is used to describe the group of ascending axons that, in aggregate, form the paired, transverse arches of white matter in the upper pons and midbrain. It derives from the old term bulb previously used to indicate the entire brain stem.Ĭrus (crura) cerebrorum: the most ventral portion of the midbrain ventral to the anterior border of the substantia nigra and lateral to the interpeduncular fossa Presently, the term cerebral peduncle is most often used to indicate the crus cerebri.Ĭomb system: the bundles of striatal and pallidal fibers passing through the internal capsuleĬorticobulbar: This term refers to fibers that descend from the cerebral cortex to any portion of the brain stem (not just the medulla). As a consequence, the two crura cerebrorum form paired structures situated to each side of the interpeduncular fossa, while the tegmentum of the midbrain forms a single, bilaterally symmetric structure situated dorsal to the crura and ventral to the aqueduct.
On each side, a curved line drawn along the anterior surface of the substantia nigra subdivides the cerebral peduncle into a ventral crus cerebrorum and a dorsal tegmentum. Superior cerebellar peduncle (brachium conjunctivum): the interconnection of the midbrain with the diencephalon and the cerebellumĬerebral peduncles: Classically, the terms left and right cerebral peduncles signify all of the midbrain ventral to the cerebral aqueduct.
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