Hippocampus proper

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Hippocampus proper

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Hippocampus location and regions in a human,?coronal plane

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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.

(這CA1豈不是扮演了thalamus的角色，與entorhinal cortex形成了類似thalamus-cortex的互射模式。entorhinal cortex與CA1之間形成的互射模式帶來的是時(shí)間長短的自我意識(shí)，即感受某個(gè)情緒持續(xù)的時(shí)間。)?

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中的可再生神經(jīng)細(xì)胞就是其granular layer中的stellate cell，顯然mossy fibers中的axons是常被更新的。常更新，也意味著被徹底遺忘，我們往往都不記得一個(gè)月以前自己的狀態(tài)，所謂的人總是在變的，也所謂的15天可以建立一個(gè)新的習(xí)慣，這個(gè)新的習(xí)慣就是新的mossy fibers替換了原有的，產(chǎn)生了新的狀態(tài)。）?

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.?

（我覺的人的內(nèi)向安靜和外向活潑性格應(yīng)該被CA1和CA3決定，因?yàn)橹挥?span id="5tt3ttt3t" class="color-pink-03">CA3能興奮VTA和與另一側(cè)的CA3聯(lián)系，而內(nèi)向安靜性格是CA1主動(dòng)投射CA1的結(jié)果，外向活潑性格是CA3主動(dòng)投射VTA的結(jié)果，附帶著投射到CA1。而內(nèi)向安靜性格或者處于威脅狀態(tài)下的人，他們的VTA都被抑制住了，所以CA3沒辦法喚醒被抑制的VTA（比如被basolateral complex of amygdala通過nucleus accumbens抑制VTA），那么也就變成內(nèi)向安靜狀態(tài)，比如處于淘氣的孩子，被爸爸大聲呵斥，被震到的孩子能夠安靜下來做出服從行為。而帶有抑郁氣質(zhì)的人是通過interpeduncular nucleus來抑制VTA，從而自動(dòng)地處于內(nèi)向安靜狀態(tài)。）

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.

（其實(shí)不然，只有CA3投射到lateral septum，進(jìn)而投射至VTA；另一個(gè)前提是the?medial septum?and the?diagonal band of Broca的放電受到median raphe nucleus的調(diào)控，出現(xiàn)抽搐癥狀時(shí)，locus coeruleus強(qiáng)烈興奮，通過自身的自我抑制反饋來抑制自身的興奮，但是重要的點(diǎn)是這里的彌散性神經(jīng)細(xì)胞高同步性放電帶來全腦腦電波的一致性現(xiàn)象。結(jié)果是：缺少median raphe nucleus的抑制效果，the?medial septum?and the?diagonal band of Broca中彌散性神經(jīng)細(xì)胞高同步放電，導(dǎo)致CA3高同步放電，從而導(dǎo)致lateral septum高同步放電，從而導(dǎo)致VTA高同步放電，VTA的一個(gè)重要分支到達(dá)amygdala，因此導(dǎo)致amygdala高同步放電，amygdala的一個(gè)重要分支到達(dá)locus coeruleus，從而導(dǎo)致locus coeruleus高同步放電，通過反身抑制的機(jī)制，locus coeruleus高同步停止放電，從而出現(xiàn)全腦的腦電波出現(xiàn)振蕩頻率一致性現(xiàn)象，波峰、谷代表高norepinephrine濃度，低振幅時(shí)代表停止放電，直到彌散性調(diào)節(jié)神經(jīng)細(xì)胞耗凈遞質(zhì)，但是具體是哪一環(huán)節(jié)-dopamine、acetylcholine、norepinephrine，暫時(shí)還沒有確定，經(jīng)過幾分鐘的抽搐，甚至是幾秒鐘的抽搐，median raphe nucleus終于可以放電，從而抑制the?medial septum?and the?diagonal band of Broca，打破了高同步放電的狀態(tài)。由于大腦皮層的高度同步化，在抽搐期間不會(huì)留下任何記憶，但是會(huì)記得帶來的內(nèi)環(huán)境感受，比如疲勞，意識(shí)（即記憶能力）喪失。）

?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.