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- Glossary
agonist
Due to the lock-and-key principle, transmitters (messenger substances) can only bind to specific receptors. However, an agonist is chemically so similar to this transmitter that it can also bind to this receptor and thus trigger an identical response. Partial agonists, on the other hand, only trigger a weaker response, while inverse agonists bind to the receptor and inhibit its response.
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Accommodation
Change in the thickness of the lens of the eye by the ciliary muscles. This adjustment process increases the refractive power of the lens, allowing objects at different distances to be seen clearly.
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Action potential
In excitable cells (e.g., neurons or muscle cells), very rapid changes in electrical potential occur across the cell membrane. This event is the basis for signal conduction along the axon of the nerve cell. The action potential continues along the cell membrane and, according to the all-or-nothing principle, only occurs when the cell has been sufficiently excited.
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- Glossary
All-or-nothing principle
According to this principle, an electrical potential is only triggered in the cell when a certain threshold value of stimulus intensity has been exceeded. The response either occurs completely or not at all.
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Allocortex
A phylogenetically ancient region of the cortex (cerebral cortex) which, unlike the isocortex (also called neocortex), has fewer than six cell layers – in the hippocampus, for example, only three. The allocortex is divided into the paleocortex and archicortex, as well as the periallocortex, which is a transitional form between the allocortex and isocortex.
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Alpha waves
Neuroscientists distinguish between different types of brain waves based on their frequency. Alpha waves oscillate in the mid-frequency range between approximately 8 and 12 hertz. They occur, for example, in a relaxed waking state, such as when test subjects are tired or have their eyes closed, i.e., when there is no mental activity. In the brain, they originate primarily in the parietal lobe. They are also called "Berger's waves" Hans Berger, who first described them.
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Amacrine cells
Amacrine cells are interneurons of the retina. They are located between photoreceptors and bipolar cells on the one hand and ganglion cells on the other. The name was coined by Ramón y Cajal and means "without axon."
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Anvil
The middle of the three ossicles in the middle ear transmits the vibration from the malleus to the stapes.
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- Glossary
Amnesia
A form of memory disorder that affects the memory for facts and events. The unconscious memory for, for example, sensorimotor skills such as driving a car or riding a bike remains intact.
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- Glossary
Ampakine
A group of active substances that belong to the "neuroenhancers" and can improve cognitive performance. Among other things, they increase attention span, promote memory, and facilitate learning processes. Their effect is based on binding to AMPA receptors in the brain, which facilitates synaptic transmission at glutamatergic synapses and enhances overall neuronal signal transmission.
