Brainstem Anatomy PDF

fig. 18 fig. 23 H fig. 18 fig. 19 ### Hjernestammen On each side of the midline indentation, there are prominences, or elevations, throughout the brainstem. These contain the most important motor pathways, the pyramidal tracts. These contain about 1 million axons that go from the cerebral cortex t...

fig. 18 fig. 23 H fig. 18 fig. 19 ### Hjernestammen On each side of the midline indentation, there are prominences, or elevations, throughout the brainstem. These contain the most important motor pathways, the pyramidal tracts. These contain about 1 million axons that go from the cerebral cortex to the spinal cord and are crucial for initiating voluntary movement. In the medulla oblongata, the prominence is small and called the pyramid (6). In the pons, it is wider and rounded. In the mesencephalon, it is wide and strong. Here it is called *crus cerebri* (plural: *crura*) (7). The superficial location of the most important motor pathways makes them susceptible to damage from lesions of the brainstem. ### Hjernenerverne The surface of the brainstem is marked by the emergence of 10 pairs of cranial nerves (III-XII). Almost all of these emerge from the ventral surface, except the fourth cranial nerve (IV), which emerges from the dorsal surface of the brainstem. The points of emergence are known as the apparent origins. The third cranial nerve (III) and the fourth cranial nerve (IV) emerge from the mesencephalon. The fifth cranial nerve (V), emerges from the pons. The 6th, 7th, and 8th cranial nerves (VI, VII, VIII) emerge from the transition between the pons and medulla oblongata. The last 4 cranial nerves, the ninth, tenth, eleventh, and twelfth cranial nerves (IX, X, XI, XII) emerge from the medulla oblongata. The fourth cranial nerve (IV) emerges from the dorsal surface of the mesencephalon just underneath (8). ### Apparante udspring The apparent origin of a nerve is the point on the central nervous system where it emerges. Here, it leaves the brain or spinal cord. The 1^st and 2^nd cranial nerves do not emerge from the brainstem. They are different in other ways too. In contrast to the spinal nerves, the cranial nerves do not have a clear division between motor and sensory roots. The components are usually mixed together, even at the apparent origin. ### Hjernestammens tre dele The three parts of the brainstem (1), (2), and (3) are easily distinguished from each other on the ventral surface. The transition between the medulla oblongata and the medulla spinalis is smooth. The border is set at the lower edge of the foramen magnum. The topmost part of the brainstem continues without a clear boundary into the diencephalon. The two circles between the *crura cerebri* represent the *corpora mamillaria*, which belong to the diencephalon. ### Bagfladen On the dorsal surface of the brainstem, there is an indistinct border between the pons and medulla oblongata. This is because both are enclosed within the *fossa rhomboidea* (4), and there is no transverse fissure to show the boundary. On the surface of the medulla oblongata, beneath the *fossa rhomboidea*, there are several prominences (arrows) separated by longitudinal furrows. The prominences represent the underlying dorsal columns nuclei, i.e., islands of gray matter that are connected to the tracts in the dorsal columns of the spinal cord. On the dorsal surface of the mesencephalon, there are four rounded prominences, the mounds (8). There are tow upper and two lower mounds.