This section serves as an introduction to the basic anatomy of the brain, head, neck, and spine. Brain anatomy is complex, and a complete discussion is beyond the scope of this text.
The human brain can be roughly divided into the cerebrum, thalamus, brain stem, and cerebellum. The cerebrum is comprised of the cerebral cortex, basal ganglia, and limbic system. The brain stem includes the midbrain, pons, and medulla. The cerebellum is composed of the cerebellar hemispheres and vermis.
Figures 3.1 to 3.10 illustrate the structures and blood vessels of the brain, head, neck, and spine.
Surface anatomy of the brain. The cerebral cortex is composed of gyri (ridges) and sulci (intervening depressions) divided into 4 lobes: frontal, parietal, temporal, and occipital. The frontal lobe is separated from the parietal lobe by the central sulcus. The sylvian fissure separates the temporal lobe from the more superiorly located frontal and parietal lobes. The occipital lobe is separated from the parietal lobe by the parieto-occipital sulcus.
Vascular distribution of the brain parenchyma. An understanding of the territories of the major intracranial vessels is important in the diagnosis of stroke and other vascular lesions. The anterior cerebral arteries (blue) supply the anterior parasagittal regions. The middle cerebral arteries (pink) supply most of the lateral cortex of the frontal and superior temporal lobes. The posterior cerebral arteries (green) supply the inferior temporal and occipital lobes.
Circle of Willis. The circle of Willis describes a loop of arteries that supply most of the brain. The posterior circulation consists of the 2 vertebral arteries that join to form the midline basilar artery. The basilar artery terminates into paired posterior cerebral arteries. The anterior circulation is predominantly supplied by the internal carotid arteries that terminate into the anterior and middle cerebral arteries. The anterior communicating artery connects both the anterior cerebral arteries, while the posterior communicating arteries connect the anterior and posterior circulation. The circle of Willis plays an important role in providing collateral supply in the setting of arterial occlusions and strokes.
Supraventricular level (top): At the supraventricular level, the frontal and parietal lobes are seen in cross section. The falx cerebri is a dural reflection that separates the 2 hemispheres. The superior sagittal sinus is seen posteriorly. Lateral ventricular level (bottom): The lateral ventricles are seen on this level as paired frontal horns anteriorly and the atria more posteriorly. The basal ganglia are seen, as are the thalami.