wiki笔记--Hippocampus proper--2021/10/1

Hippocampus proper

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Hippocampus proper

 

Hippocampus location and regions in a human, coronal plane

 

Basic circuit of the hippocampus, shown using a modified drawing by Ramon y Cajal. DG: dentate gyrus. Sub: subiculum. EC: entorhinal cortex

Details

Identifiers

Latin

hippocampus proprius, cornu Ammonis

NeuroNames

182

TA98

A14.1.09.327

TA2

5520

FMA

62493

Anatomical terms of neuroanatomy

[edit on Wikidata]

The hippocampus proper refers to the actual structure of the hippocampus which is made up of four regions or subfields. The subfields CA1, CA2, CA3, and CA4 use the initials of cornu Ammonis, an earlier name of the hippocampus.

Contents

· 1Structure

· 1.1CA1

· 1.2CA2

· 1.3CA3

· 1.4CA4

· 2Additional images

· 3References

Structure[edit]

There are four regions in the hippocampus proper which form a neural circuit called the trisynaptic circuit.

CA1[edit]

CA1 is the first region in the hippocampal circuit, from which a major output pathway goes to layer V of the entorhinal cortex.

(这CA1岂不是扮演了thalamus的角色，与entorhinal cortex形成了类似thalamus-cortex的互射模式。entorhinal cortex与CA1之间形成的互射模式带来的是时间长短的自我意识，即感受某个情绪持续的时间。) 

Another significant output is to the subiculum.

CA2[edit]

CA2 is a small region located between CA1 and CA3. It receives some input from layer II of the entorhinal cortex via the perforant path. Its pyramidal cells are more like those in CA3 than those in CA1. It is often ignored due to its small size.

CA3[edit]

CA3 receives input from the mossy fibers of the granule cells in the dentate gyrus,

（由于dentate gyrus中的可再生神经细胞就是其granular layer中的stellate cell，显然mossy fibers中的axons是常被更新的。常更新，也意味着被彻底遗忘，我们往往都不记得一个月以前自己的状态，所谓的人总是在变的，也所谓的15天可以建立一个新的习惯，这个新的习惯就是新的mossy fibers替换了原有的，产生了新的状态。） 

and also from cells in the entorhinal cortex via the perforant path. The mossy fiber pathway ends in the stratum lucidum. The perforant path passes through the stratum lacunosum and ends in the stratum moleculare. There are also inputs from the medial septum and from the diagonal band of Broca which terminate in the stratum radiatum, along with commisural connections from the other side of the hippocampus.

The pyramidal cells in CA3 send some axons back to the dentate gyrus hilus, but they mostly project to regions CA2 and CA1 via the Schaffer collaterals. There are also a significant number of recurrent connections that terminate in CA3. 

（我觉的人的内向安静和外向活泼性格应该被CA1和CA3决定，因为只有CA3能兴奋VTA和与另一侧的CA3联系，而内向安静性格是CA1主动投射CA1的结果，外向活泼性格是CA3主动投射VTA的结果，附带着投射到CA1。而内向安静性格或者处于威胁状态下的人，他们的VTA都被抑制住了，所以CA3没办法唤醒被抑制的VTA（比如被basolateral complex of amygdala通过nucleus accumbens抑制VTA），那么也就变成内向安静状态，比如处于淘气的孩子，被爸爸大声呵斥，被震到的孩子能够安静下来做出服从行为。而带有抑郁气质的人是通过interpeduncular nucleus来抑制VTA，从而自动地处于内向安静状态。）

Both the recurrent connections and the Schaffer collaterals terminate preferentially in the septal area in a dorsal direction from the originating cells. CA3 also sends a small set of output fibers to the lateral septum.

The region is conventionally divided into three divisions. CA3a is the part of the cell band that is most distant from the dentate (and closest to CA1). CA3b is the middle part of the band nearest to the fimbria and fornix connection. CA3c is nearest to the dentate, inserting into the hilus. CA3 overall, has been considered to be the “pacemaker” of the hippocampus. Much of the synchronous bursting activity associated with interictal epileptiform activity appears to be generated in CA3. Its excitatory collateral connectivity seems to be mostly responsible for this.

（其实不然，只有CA3投射到lateral septum，进而投射至VTA；另一个前提是the medial septum and the diagonal band of Broca的放电受到median raphe nucleus的调控，出现抽搐症状时，locus coeruleus强烈兴奋，通过自身的自我抑制反馈来抑制自身的兴奋，但是重要的点是这里的弥散性神经细胞高同步性放电带来全脑脑电波的一致性现象。结果是：缺少median raphe nucleus的抑制效果，the medial septum and the diagonal band of Broca中弥散性神经细胞高同步放电，导致CA3高同步放电，从而导致lateral septum高同步放电，从而导致VTA高同步放电，VTA的一个重要分支到达amygdala，因此导致amygdala高同步放电，amygdala的一个重要分支到达locus coeruleus，从而导致locus coeruleus高同步放电，通过反身抑制的机制，locus coeruleus高同步停止放电，从而出现全脑的脑电波出现振荡频率一致性现象，波峰、谷代表高norepinephrine浓度，低振幅时代表停止放电，直到弥散性调节神经细胞耗净递质，但是具体是哪一环节-dopamine、acetylcholine、norepinephrine，暂时还没有确定，经过几分钟的抽搐，甚至是几秒钟的抽搐，median raphe nucleus终于可以放电，从而抑制the medial septum and the diagonal band of Broca，打破了高同步放电的状态。由于大脑皮层的高度同步化，在抽搐期间不会留下任何记忆，但是会记得带来的内环境感受，比如疲劳，意识（即记忆能力）丧失。）

 CA3 uniquely, has pyramidal cell axon collaterals that ramify extensively with local regions and make excitatory contacts with them. CA3 has been implicated in a number of working theories on memory and hippocampal learning processes. Slow oscillatory rhythms (theta-band; 3–8 Hz) are cholinergically driven patterns that depend on coupling of interneurons and pyramidal cell axons via gap junctions, as well as glutaminergic (excitatory) and GABAergic (inhibitory) synapses. Sharp EEG waves seen here are also implicated in memory consolidation.[1]

CA4[edit]

CA4 is often called the hilus or hilar region if considered as a part of the dentate gyrus. Unlike the pyramidal neurons in CA1 and CA3, the neurons here include mossy cells that primarily receive inputs from the granule cells in the dentate gyrus in the form of mossy fibers.[2][3] They also receive a small number of connections from pyramidal cells in CA3. They, in turn, project back into the dentate gyrus at distant septotemporal levels.