Coronal Sections

This is the first of three chapters showing sections of entire human brains, in this case illustrating approximately coronal planes. Forebrain structures are emphasized, but parts of the brainstem and cerebellum are indicated as well. The organization of various functional systems in the forebrain (e.g., thalamus, hippocampus) and other parts of the central nervous system is presented in Chapter 8 .

Drawings showing typical areas of arterial supply in each section are also provided in this and the next two chapters. We simplified these in two major ways. First, arterial territories are shown as sharply demarcated from each other, when in reality there is significant interdigitation and overlap. Second, perforating arteries arise from all the vessels of the circle of Willis, but we lumped together those from the posterior communicating and posterior cerebral arteries, and those from the anterior communicating and anterior cerebral arteries.

Figure 5.1

The hemisected brain from Fig. 1.7 , used in much of this chapter to indicate planes of section.

Figure 5.2

The planes of section shown in this chapter, indicated on three-dimensional reconstructions.

(Courtesy Dr. John W. Sundsten, Department of Biological Structure, University of Washington School of Medicine.)

Figure 5.3

(A–X) Twenty-four coronal sections of a brain, arranged in an anterior-to-posterior sequence from the anterior edge of the corpus callosum to the beginning of the occipital lobe. (A) Anterior end of the genu of the corpus callosum (1) . Convolutions that compose most of the frontal lobe are the superior (3) , middle (4) , and inferior (5) frontal gyri, orbital gyri (6) , and gyrus rectus (8) . The cingulate gyrus (2) is cut twice, once above and once below the genu of the corpus callosum. The olfactory sulcus (7) , which will be occupied by the olfactory tract at a slightly more posterior level, lies just lateral to gyrus rectus.

(B) The anterior horn of the lateral ventricle (3) appears. A septum pellucidum (2) forms the medial wall of each lateral ventricle. The corpus callosum is now cut in two places, once through its body (1) above the septum pellucidum and once (4) as the genu begins to taper into the rostrum below the septum pellucidum.

(C) The head of the caudate nucleus (1) appears in the lateral wall of the lateral ventricle. The anterior region of the insula (2) is also visible at this level, overlying the caudate nucleus.

(D) The rostral end of the putamen (3) is separated from the head of the caudate nucleus (1) by the anterior limb of the internal capsule (2) . The putamen, the larger of the two parts of the lenticular nucleus, is overlain for its entire extent by the insula (4) . The olfactory tract (7) lies in the olfactory sulcus, just lateral to gyrus rectus (8) . The section passes through the tip of the temporal lobe (6) , separated from the frontal lobe by the lateral sulcus (5) .

Coronal sections. (E) The globus pallidus (5) makes its appearance medial to the putamen (4) ; the two together compose the lenticular nucleus. Nucleus accumbens (6) , the region of continuity between the putamen and the head of the caudate nucleus (2) , is also apparent. The septum pellucidum (1) is continuous with the septal nuclei (7) . (The proximity of nucleus accumbens to the septal nuclei was reflected in its earlier but now outmoded name, nucleus accumbens septi —“the nucleus leaning against the septum.”) The anterior limb of the internal capsule (3) still occupies the cleft between the lenticular nucleus and the head of the caudate nucleus. Shown enlarged in Fig. 5.4 .

(F) The level of the interventricular foramen (1) and anterior commissure (5) is a transition point for many structures—for example, from the head to the body of the caudate nucleus (2) and from the anterior horn to the body of the lateral ventricle (9) . This section shaves off the anterior end of the thalamus (3) , passes through the genu of the internal capsule (4) , and cuts the fornix twice (8) as it curves ventrally toward the hypothalamus. The olfactory tract (6) joins the base of the forebrain, and the optic chiasm (7) appears. Shown enlarged in Fig. 5.5 .

(G) Anterior diencephalon. Characteristic diencephalic features include the third ventricle (12) , hypothalamus (8) with its attached infundibulum (7) , and thalamic nuclei—anterior (1) and ventral anterior (2) . The external (3) and internal (4) segments of the globus pallidus are now apparent, as is the anterior end of the amygdala (9) . Fibers that will cross in the anterior commissure (5) accumulate beneath the lenticular nucleus. The fornix is cut twice, through the body (13) and column (10) . The optic tract (6) and posterior limb of the internal capsule (11) are also present.

(H) The mammillothalamic tract (7) enters the anterior nucleus (8) of the thalamus. The two thalami fuse in the interthalamic adhesion (1) or massa intermedia, which bridges the third ventricle (6) . The ansa lenticularis ( 3 , literally “the handle of the lenticular nucleus”) emerges from the inferior surface of the globus pallidus and hooks around the posterior limb of the internal capsule (2) . The amygdala (4) is larger, and the middle of the three zones of the hypothalamus (the tuberal zone, 5 ) is present. Shown enlarged in Fig. 5.6 .

Coronal sections. (I) Additional efferents from the globus pallidus penetrate the posterior limb of the internal capsule (2) as the lenticular fasciculus and collect on the other side (1) before entering the thalamus. The column of the fornix (4) continues through the hypothalamus, where it will soon end in the mammillary body. The surface of the temporal lobe includes the superior (3) , middle (5) , and inferior (6) temporal gyri and the occipitotemporal gyrus (7) , adjacent to the parahippocampal (8) gyrus. The amygdala (9) has reached nearly maximal size.

(J) Midthalamus. The dorsomedial (2) and ventrolateral (3) nuclei are prominent at this level. The optic tract (6) proceeds posteriorly toward its thalamic termination in the lateral geniculate nucleus. The column of the fornix is ending in the mammillary body (10) , which in turn gives rise to the mammillothalamic tract (9) . The lateral ventricle is another in a series of forebrain structures to be cut twice, here through the body (1) and through the inferior horn (8) , which has appeared adjacent to the amygdala (7) . Both the putamen (4) and the globus pallidus (5) begin to get smaller.

(K) Level of the mammillary bodies (7) of the hypothalamus. Efferents from the globus pallidus and cerebellum collect beneath the thalamus in the thalamic fasciculus (2) before moving dorsally into the ventral lateral (1) and ventral anterior (see Fig. 5.3G ) nuclei. The appropriately named subthalamic nucleus (3) appears beneath the thalamus. The amygdala (4) begins to get smaller, and the hippocampus (6) assumes a position adjacent to the inferior horn of the lateral ventricle (5) . Shown enlarged in Fig. 5.7 .

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Dec 29, 2019 | Posted by in NEUROLOGY | Comments Off on Coronal Sections
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