ANATOMY
OF THE MEDIAL (MIDSAGITTAL) SURFACE OF THE BRAIN IN SITU
The entire extent of
the neuraxis, from the spinomedullary junction through the brain stem,
diencephalon, and telencephalon, is visible in a midsagittal section. The
corpus callosum, a major commissural fiber bundle interconnecting the two
hemispheres, is a landmark separating the cerebral cortex above from the
thalamus, fornix, and subcortical forebrain below.
The ventricular system,
including the interventricular foramen (of Munro); the third ventricle
(diencephalon); the cerebral aqueduct (midbrain); and the fourth ventricle
(pons and medulla), is visible in a midsagittal view. This subarachnoid fluid
system provides internal (the ventricular system) and external (cerebrospinal
fluid in the subarachnoid space) protection to the brain and also may serve as
a fluid transport system for important regulatory molecules. The thalamus
serves as a gateway to the cortex. The hypothalamic proximity to the median
eminence (tuber cinereum) and the pituitary
gland reflects the
important role of the hypothalamus in regulating neuroendocrine function. A
midsagittal view also reveals the midbrain colliculi, sometimes called the
visual (superior) and auditory (inferior) tecta. See Video 3-1.
CLINICAL POINT
The right and left
hemispheres are interconnected by commissural fiber bundles. The largest is the
corpus callosum, which interconnects all lobes with their counterparts. The
anterior commissure interconnects regions of the temporal lobes. When these
commissural fiber bundles are disconnected (split brain), the hemispheres do
not know what their counterparts are doing, and inputs to one hemisphere cannot
produce an appropriate response from the opposite hemi- sphere. With a split
brain, only a more generalized recognition of mood states occurs between the
two hemispheres, presumably communicated through interconnections between lower
structures, such as the diencephalon and brain stem.
