Hippocampus

Hippocampus Hippocampus

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The hippocampal Network: The hippocampus forms a principally uni-directional network, with input from the Entorhinal Cortex (EC) tht forsms connections with the Dentate Gyrus (DG) and CA3 pyramidal neurons via the Perforant Path (PP - split into lateral and medial). CA3 neurons also receive input from the DG via the Mossy Fibres (MF). They send axons to CA1 pyramidal cells via the Schaffer Collateral Pathway (SC), as well as to CA1 cells in the contralateral hippocampus via the Associational Commisural (AC) Pathway. CA1 neurons also receive inputs direct from the Perforant Path and send axons to the Subiculum (Sb). These neurons in turn send the main hippocampal output back to the EC, forming a loop.

Perirhinal-LEC-hippocampus The perirhinal cortex sends projections to the lateral entorhinal cortex (LEC). This innervation runs from and to the superficial layers (layers II and III). These in turn project to the CA1-subiculum junction as part of the LEC projection to the hippocampus, part of the perforant path. Reciprocal projections return to the LEC, but to deeper layers (layer V), with intra-LEC connections closing the loops. Postrhinal-MEC-hippocampus: Similar to the perirhinal cortex, the postrhinal cortex sends also projections to the entorhinal cortex, but in this case to the medial entorhinal cortex (MEC). This innervation again runs from and to the superficial layers (layers II and III). These in turn project to the proximal CA1 (nearer to CA3) and the distal subiculum as part of the perforant path. Reciprocal projections return to layer V of the MEC, with intra-MEC connections closing the loops

Hippocampus

Functions

• action selection
• motor control
• procedural learning
• habit formation (bruxism)
• eye movements
• emotional functions

Currently popular theories implicate the basal ganglia primarily in action selection, that is, the decision of which of several possible behaviors to execute at a given time.

Structures

• striatal

• • internal capsule (white matter)
  • caudate
  • putamen

• pallidal

• • external (globus pallidus)
  • internal (entopeduncular nucleus)

• nigral
• subthalamic

The basal ganglia form a major brain system in all species of vertebrates, but the basal ganglia of primates (including humans) have special features that justify a separate consideration. As in other vertebrates, the primate basal ganglia can be divided into striatal, pallidal, nigral, and subthalamic components. In primates, however, the two pallidal subdivisions are called the external and internal (or sometimes lateral and medial) segments of the globus pallidus, whereas in other species they are called the globus pallidus and entopeduncular nucleus. Also in primates, the striatum is divided by a large tract of white matter called the internal capsule into two masses of gray matter that early anatomists named the caudate nucleus and putamen -- in most other species no such division exists, and only the striatum as a whole is recognized. Beyond this, the complex topography of connections between the striatum and cortex means that functions are segregated within the primate striatum in ways that do not apply to other species.

Basal Ganglia Images

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