B

Figure 1 Histology of the six layers of the cerebral cortex illustrating the types and arrangements of neurons (A) and myelinated nerve fibers (B) Numbers 1-6 in A indicate the layers of the cerebral cortex. Numbers 1 and 2 in B indicate the bands of Baillarger (reproduced with permission from J. A. Kiernan, Barr's, the Human Nervous System. Lippincott-Raven, Philadelphia, 1998).

surface of the brain. The third layer of cells is quite thick, containing many pyramidal neurons, and its name, the external pyramidal layer, is derived from these cells. These pyramidal neurons are of medium size and the size increases toward the deepest part of layer 3. The apices of these pyramidal neurons also extend toward the surface of the brain. The pyramidal neurons in this layer form connections with other regions of the cerebral cortex, including the opposite (contralateral) side of the brain. The internal granular layer, or layer 4, contains numerous small cells that are densely packed together. Some of these small cells are stellate (star-shaped), whereas others are small pyramidal cells. As will be discussed later, this layer is particularly prominent in regions of the cortex dedicated to receiving sensory information. The fifth layer of the cerebral cortex, the internal pyramidal (or ganglionic) layer, contains both medium-sized and large pyramidal neurons that, like other pyramidal cells, have their dendritic apices extending toward the exterior surface ofthe brain. In the region ofthe motor cortex some of these cells are very large and are known as the pyramidal cells of Betz. Neurons of layer 5 give rise to the bulk of the axons, corticofugal fibers, projecting to subcortical regions. Sometimes, layers 4 and 5 have a condensation of horizontal fibers that are called the bands of Baillarger. These horizontal fibers are seen in myelin-stained tissue (Fig. 1B). The deepest and final layer 6, the multiform (orpolymorph) layer, is composed of small neurons that can be stellate, pyramidal, or another type of cell with elongated cell bodies called fusiform neurons. This layer also gives rise to corticofugal fibers terminating primarily in the thalamus. Beginning in layer 3 and through layer 6, the pyramidal neurons send axons internally that form bundles of myelinated fibers. As each layer containing pyramidal neurons contributes to these bundles they become progressively thicker.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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