action potential
The quickest electrical signal that can be generated and propagated
in neuronal cells with a maximal speed of around
120 meters/second. The action potential possesses several peculiar
features: it requires a primer to be generated (for instance through
activation of excitatory synapses), it maintains the same maximal value
once the stimulation threshold has been reached and it propagates along
the membrane of the nerve or muscular cell without undergoing decay.
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amyloid protein
Main component, in the form of a modified insoluble protein, of the
amorphous material present in neuritic plaques. The
presence in the brain tissue of these plaques filled with altered amyloid
protein are a peculiar aspect of Alzheimer’s disease.
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axon
Main process originating
from the neuron cell body and making contacts with
neighboring neurons or neurons and other cells (for instance muscle
cells) that may even be very far away (in large animals it may
reach the length of some meters from the head to the trunk). In the
terminal part of the axons and of their collaterals, the
synaptic terminals form
functional connections with other neurons.
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cerebral ventricles
System of enlarged spaces connected by small ducts inside cerebral
structures. They are filled with a fluid whose hydrostatic pressure
contributes to maintain shape of the brain. They also constitute an accessory
system for the humoral connection among different nervous regions.
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dendrites
Branches of various size,
up to several millimeters long, originating from the cell body that
constitute the main receiving system of the
neuron. On the dendrites of neurons with the more
complex branching, several thousands (and in some cases some tens of
thousands) of
synaptic terminals may from contacts that transmit signals
from other neurons.
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hippocampus
Brain region located below the surface of the brain's temporal lobe,
essential for some memory processes, in particular for the consolidation
of short term memory into long term memory.
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hypothalamus
Deep region of the brain important for the control of several vital functions,
such as body temperature, food intake and reproductive activity.
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MRI (Magnetic Resonance Imaging), PET (Positron Emission Tomography)
Non-invasive techniques (i.e. they do not require surgery) to study
cerebral activity. They are increasingly used for diagnostic purposes,
but they promise to become very important for basic science too, as they
allow us to study the state of activity of different brain areas in relation
to different functional activities.
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neural networks
Computational systems used in the field of artificial intelligence,
constructed in such a way as to incorporate main characteristics of brain's neural
circuits, in particular the presence of neural elements linked by
connections whose "weight" can be modified by training. The training of a
neural network may be compared to the natural property of synaptic
plasticity, i.e. the ability of neural circuits to modify functionally
and structurally their signaling and connectivity as a consequence of
learning and memory.
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neuritic plaques
Accumulation of altered proteic materials and of degenerating
axonal and
dendritic terminals in the extracellular spaces
comprised among neurons in areas affected by
neurodegenerative processes tipically found in the brain tissue of
Alzheimer's disease patients.
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neurodegenerative pathologies
These diseases cover several forms of both acute and chronic injuries,
from cerebral ischemia to dementia, which are characterized by
degeneration occurring in various regions of the brain with the consequent death of
a large number of
neurons.
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neurofibrillary
tangles
Packed fibrils made by
altered filamentous proteins found inside degenerating neurons. Typical
neurofibrillary tangles are found in degenerating neurons of the
cerebral cortex and the hippocampus of patients of Alzheimer's disease.
Similar fibrillary aggregates are also found in other
neurodegenerative pathologies such as prion diseases and motor neuron pathologies that
lead to progressive paralysis.
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neuron
Main cell type of the nervous system: about 100 billion neurons are
present in the human brain. Each neuron is integrated in neural circuits
in which nervous signals travel as electrical signals along the neuron
and are converted in chemical signals at the synaptic contacts between
two neurons. The chemical message is then converted again in an
electrical signal and so on.
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neurotransmitters
Molecules that mediate signal transmission at the level of the synapse.
Many neurotransmitters are small molecules such as the amine
acetylcholine, the first neurotransmitter discovered, or amino acids
like glutamate, the most abundant brain neurotransmitter. Some
neurotransmitters have a more complex structure, being formed by small
peptides made up of short amino acid sequences. Multiple post-synaptic
receptors exist for each neurotransmitter, mediating action that can
result excitatory or inhibitory in nature.
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Parkinson's disease
Neurodegenerative pathology initially
characterized by hand tremor and subsequently by rigid and uncontrolled
movements, finally ending in dementia symptoms. The cause of the
disease is the degeneration of a particular population of brain
neurons which use dopamine as a
neurotransmitter and which connects a
deep posterior brain region (the substantia nigra) to a more anterior
region (the corpus striatum). At later stages of the disease, the
neurodegenerative process extends to other regions of the brain.
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schizophrenia
Major neuropsychiatric disease that results in profound alterations of
the personality, hallucinations, violent behavior and suicide tendency.
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synapse
Connections between neurons (or between neurons
and other cells such as muscle) where transmission of neural signals
takes place. A typical chemical synapse (a limited number of electrical
synapses also exists) is made by an axon terminal (pre-synaptic element)
which, following the arrival of an electrical impulse in its membrane,
releases a chemical mediator (neurotransmitter) into the inter-synaptic
cleft which separates it from the receiving area of a post-synaptic
neuron. The neurotransmitter, through its binding to receptor proteins
present in the post-synaptic membrane, activates different biochemical
reactions that modify the flux of ions (small electrically charged molecules). As a consequence, a new electrical signal (the synaptic
potential), excitatory or inhibitory in nature, is generated in the
receiving neuron.
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