Perforant path input from EC layer II enters the dentate gyrus and is relayed to region CA3 (and to mossy cells, located in the hilus of the dentate gyrus, which then send information to distant portions of the dentate gyrus where the cycle is repeated). The lamellar concept is still sometimes considered to be a useful organizing principle, but more recent data, showing extensive longitudinal connections within the hippocampal system, have required it to be substantially modified.
HIPPOCAMPUS ANATOMY CA SERIES
This observation was the basis of his lamellar hypothesis, which proposed that the hippocampus can be thought of as a series of parallel strips, operating in a functionally independent way. The perforant path-to-dentate gyrus-to-CA3-to-CA1 was called the trisynaptic circuit by Per Andersen, who noted that thin slices could be cut out of the hippocampus perpendicular to its long axis, in a way that preserves all of these connections. Subicular neurons send their axons mainly to the EC. Pyramidal cells of CA1 send their axons to the subiculum and deep layers of the EC. Pyramidal cells of CA3 send their axons to CA1. Granule cells of the DG send their axons (called "mossy fibers") to CA3. There is also a distinct pathway from layer 3 of the EC directly to CA1. These axons arise from layer 2 of the EC, and terminate in the dentate gyrus and CA3. Most external input comes from the adjoining entorhinal cortex, via the axons of the so-called perforant path. The major pathways of signal flow through the hippocampus combine to form a loop.
HIPPOCAMPUS ANATOMY CA PLUS
To refer to the hippocampus proper plus dentate gyrus and subiculum. Use the term "hippocampus proper" to refer to the four CA fields, and "hippocampal formation" Transition to the cortex proper (mostly the entorhinal area of the cortex). After this come a pair of ill-defined areas called the presubiculum and parasubiculum, then a After CA1 comes an area called the subiculum. The CA areas are all filled with densely packed pyramidal cells resembling those of the cortex. NextĬome a series of Cornu Ammonis areas: first CA4 (which underlies the dentate gyrus), then CA3, thenĪ very small zone called CA2, then CA1. Proper, forming a pointed wedge in some cross-sections, a semicircle in others. Structure, a tightly packed layer of small granule cells wrapped around the end of the hippocampus The first of these, the dentate gyrus (DG), is actually a separate Starting at the dentate gyrus and working inward along the S-curve of the hippocampus means traversing a Schematic diagram showing location of the hippocampus.īasic Hippocampal Circuit File:CajalHippocampus (modified).pngīasic circuit of the hippocampus, shown using a modified drawing by Ramon y Cajal. While most neuroscientists no longer believe in the concept of a unified "limbic system", these regions are highly interconnected and do interact with one another. Paul MacLean once suggested, as part of his triune brain theory, that the limbic structures comprise the neural basis of emotion. These limbic include the hippocampus, cingulate cortex, olfactory cortex, and amygdala. The structures that line the edge of the hole collectively make up the so-called limbic system (Latin limbus =īorder), with the hippocampus lining the posterior edge of this hole. Topologically, one can think of the surface of a cerebral hemisphere as a sphere with an indentation where it attaches to the midbrain. Shape of human hippocampus and associated structures. Due to the three-dimensional curvature of this structure, two-dimensional sections such as are commonly seen in preserved specimens or neuroimaging pictures can show a number of different shapes, depending on the angle and location of the cut. In primate brains, including humans, the portion of the hippocampus near the base of the temporal lobe is much broader than the part at the top. For example, in the rat, the two hippocampi look similar to pair of bananas, joined at the stems.
HIPPOCAMPUS ANATOMY CA FULL
This general layout holds across the full range of mammalian species, from hedgehog to human, although the details vary. It has a distinctive, curved, shape that has been likened to the sea horse monster of Greek mythology and the ram's horns of Amun in Egyptian mythology. The hippocampus is a neural structure in the medial temporal lobe. Nissl-stained coronal section of the brain of a macaque monkey, showing hippocampus (circled).