Hippocampus
definition
The name hippocampus comes from Latin and translates as seahorse.
The hippocampus as one of the most important structures of the human brain bears this name based on its seahorse-like shape. It is part of the telencephalon and is found once in each half of the brain.
anatomy
The name hippocampus comes from Latin and translates as seahorse. The hippocampus as one of the most important structures of the human brain bears this name based on its seahorse-like shape. It is part of the telencephalon and is found once in each half of the brain.
The telencephalon, also called the endbrain, is the largest of the five brain segments. As part of the central nervous system, the human brain is usually divided into the following sections: endbrain, diencephalon / diencephalon, midbrain / mesencephalon, hindbrain / metencephalon and posterior brain / myeloncephalon.
The endbrain is in turn divided into around five different lobes. In the temporal lobes of both hemispheres, the hippocampi are located at the bottom of the fluid-filled lateral ventricles. If you make an imaginary horizontal cut at eye level, they appear as a rolled structure on the lower cut surface.
The hippocampus is also further subdivided: gyrus dentatus, cornu ammonis / ammonium horn and subiculum together form the formatio hippocampi, a functional unit. Similar to the cerebral cortex, the hippocampus also consists of a layer of nerve cells. Information from the sensory organs arrives at the dentate gyrus, is selected in the Ammon's horn, passed on via the subiculum and subdivided. In addition, the hippocampus receives and transmits signals from and to other brain regions.
Brain lobe
Frontal lobe = red (frontal lobe, frontal lobe)
Parietal lobe = blue (parietal lobe, parietal lobe)
Occipital lobe = green (occiptital lobe, occipital lobe)
Temporal lobe = yellow (temporal lobe, temple lobe).
Cerebrum (1st - 6th) = endbrain -
Telencephalon (Cerembrum)
- Frontal lobe - Frontal lobe
- Parietal lobe - Parietal lobe
- Occipital lobe -
Occipital lobe - Temporal lobe -
Temporal lobe - Bar - Corpus callosum
- Lateral ventricle -
Lateral ventricle - Midbrain - Mesencephalon
Diencephalon (8th and 9th) -
Diencephalon - Pituitary gland - Hypophysis
- Third ventricle -
Ventriculus tertius - Bridge - Pons
- Cerebellum - Cerebellum
- Midbrain aquifer -
Aqueductus mesencephali - Fourth ventricle - Ventriculus quartus
- Cerebellar hemisphere - Hemispherium cerebelli
- Elongated Mark -
Myelencephalon (Medulla oblongata) - Big cistern -
Cisterna cerebellomedullaris posterior - Central canal (of the spinal cord) -
Central canal - Spinal cord - Medulla spinalis
- External cerebral water space -
Subarachnoid space
(leptomeningeum) - Optic nerve - Optic nerve
Forebrain (Prosencephalon)
= Cerebrum + diencephalon
(1.-6. + 8.-9.)
Hindbrain (Metencephalon)
= Bridge + cerebellum (10th + 11th)
Hindbrain (Rhombencephalon)
= Bridge + cerebellum + elongated medulla
(10. + 11. + 15)
Brain stem (Truncus encephali)
= Midbrain + bridge + elongated medulla
(7. + 10. + 15.)
You can find an overview of all Dr-Gumpert images at: medical illustrations
Function of the hippocampus
The hippocampus represents the functional interface between human short-term and long-term memory.
With the help of the sensory organs, consciousness perceives an enormous amount of information from the environment without interruption. These are passed on to the central nervous system, where they reach the hippocampus from the cerebral cortex via the entorhinal cortex.
After processing the content, they get to the other hippocampus and to other structures of the limbic system, which is mainly attributed to emotional and drive-controlled behavior.
The impressions and information collected are not stored in the hippocampus, but are first selected and compared with impressions that have already been experienced. In this way, the hippocampus acts as a coordinating “middleman” between new information and what is already known.
It shapes human memory by transferring content from short-term to long-term memory. Existing information is compared and modified if there is a variance.
If it is a question of repeatedly perceived or similar impressions, these are increasingly solidified in the memory. Their relevance is increasing. Not only factual information is processed in the hippocampus, but also emotional information. The feeling sensation is intensified together with other structures of the limbic system.
The structure of the hippocampus is subject to plastic changes. New connections between the individual nerve cells can ensure a faster transfer of information into long-term memory.
Read more on the subject here: Long-term memory
Diseases of the hippocampus
What role does the hippocampus play in depression?
In some of the people suffering from depression, a decrease in size (atrophy) of the hippocampus can be observed in studies. In particular, people with chronic (lasting for many years) Depression or people with a very early onset of the disease (already in early adulthood) affected.
In the context of depression, there is a change in the concentration of the neurotransmitters norepinephrine and serotonin. As a result, the signal transmission between the nerve cells is weakened and nerve cells regress and shrink.
At the same time there are no other nerve cells in the Dentate gyrus (Part of the hippocampus) educated. These processes can be further intensified by the stress-related release of the stress hormone cortisone in the development of depression.
For these reasons, the hippocampus shrinks in patients with chronic depression. The processes in the hippocampus are initially reversible with adequate drug therapy.
This topic could also be of interest to you: Drugs for depression
What role does the hippocampus play in Alzheimer's disease
The hippocampus is the center for learning and memory processes in the brain. It transfers information from short-term to long-term memory. For this reason, the hippocampus is one of the first structures in the brain to be affected in Alzheimer's disease.
While the exact causes for the development of Alzheimer's disease are still unclear, it is considered certain that it is due to the deposition of protein breakdown products (-Amyloid plaques, tau fibrils) the signal transmission between nerve cells is disrupted. The lack of signal transmission between the nerve cells leads to regression (atrophy) of the brain tissue.
These deposits of the above-mentioned protein degradation products can be detected in the hippocampus at an early stage of the disease. This disrupts important learning and memory processes. In particular, the short-term memory is often affected at the beginning of the disease. In the further course, hippocampal atrophy (decreased growth of cells in the hippocampus with shrinkage of brain tissue) occur.
Read about other possible causes of this disease below: Causes of Alzheimer's
What role does the hippocampus play in sclerosis?
Sclerosis of the hippocampus, also known as hippocampal sclerosis, is associated with a large loss of nerve cells and is often associated with temporal lobe epilepsy. Sclerosis is a degenerative process that is accompanied by hardening. Certain tissues or organs transform into functionless, sclerosed tissue.
Temporal lobe epilepsy represents the largest variant in terms of percentage of the clearly anatomically localizable forms of epilepsy. Typical symptoms are a preceding unpleasant feeling in the digestive tract, followed by repeated, brief loss of consciousness with rhythmic, smacking movements of the mouth and spreading body movements.
In the majority of cases, the cause of epilepsy is so-called mesial temporal sclerosis with varying degrees of failure of nerve cells. One possible therapy option for sclerosis is surgical removal, in which the declining memory function is a side effect that has to be calculated.
Increasing sclerotherapy of the hippocampus region can also be observed in dementia.
Read more about this topic in our article: dementia
What role does the hippocampus play in epilepsy?
In epilepsy, neurons in the brain are overexcited, which manifests itself in numerous symptoms. A common source of overexcitation in temporal lobe epilepsy is the hippocampus.
The long-term overexcitation of the nerve cells leads to the death of the nerve cells and a remodeling of the tissue with increasing scarring in the area of the hippocampus (so-called Ammon's horn sclerosis).
At the same time, the hippocampus also represents a target structure in the treatment of temporal lobe epilepsy with the help of deep brain stimulation. This therapy option is indicated when drug therapy fails. Targeted stimulation of brain structures in the hippocampus with a low current strength leads to a decrease in the over-excitability of the nerve cells.
If you have further interest in this topic, then read our next article below: Epileptical attack
Hippocampal Atrophy - What Is The Cause?
Hippocampus atrophy is the term used to describe tissue atrophy caused by a decrease in the number of cells in the area of the hippocampus. This tissue shrinkage can have many causes and with the help of imaging (Computed tomography, magnetic resonance imaging) be detected.
Alzheimer's disease is a common cause of atrophy of the hippocampus. In this disease, relevant atrophy of the brain tissue can be detected in the early stages. The detection by means of imaging is an important component in the diagnosis of Alzheimer's disease.
Another cause of hippocampal atrophy is chronic depression. However, there is often only visible atrophy of the tissue at an advanced stage of the depression.
In particular, the frequent influence of stress and psychological childhood trauma can significantly inhibit the growth of the hippocampus.
In addition, a (mute) Stroke lead to tissue atrophy in the area of the hippocampus. The lack of blood supply to the nerve cells during a stroke leads to the death of these cells and subsequent scarring of the tissue.
MRI of the hippocampus
Magnetic resonance imaging, also known as MRI, is the imaging diagnosis of choice when assessing possible pathological changes in the brain, including the hippocampus region in the temporal lobe. As part of an epilepsy diagnosis, even small lesions or abnormalities can be identified and treated at an early stage. In the MRI of the brain, the hippocampus is shown as a multi-layered, spiral-shaped structure. Pathological changes appear as an increase or enrichment of signals. The destruction of nerve cells and the sclerotherapy of the brain tissue can be detected in this way.
Read more information on this topic at: MRI of the brain
