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About neuron
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Overview-neuron
The complexity and diversity in nervous systems is dependent on the interconnections between neurons, which rely on a limited number of different signals transmitted within the neurons to other neurons or to muscles and glands. The signals are produced and propagated by chemical ions that produce an electrical charge that moves along the neuron.
Neurons exist in a number of different shapes and sizes and can be classified by their morphology and function. The anatomist Camillo Golgi grouped neurons into two types; type I with long axons used to move signals over long distances and type II without axons. type I cells can be further divided by where the cell body or soma is located. The basic morphology of type I neurons, represented by spinal motor neurons, consists of a cell body called the soma and a long thin axon which is covered by the myelin sheath. Around the cell body is a branching dendritic tree that receives signals from other neurons. The end of the axon has branching terminals (axon terminal) that release transmitter substances into a gap called the synaptic cleft between the terminals and the dendrites of the next neuron.
The anatomy and the properties of the surface membrane determine the behavior of a neuron. The surface membrane is not uniform over the entire length of a neuron, but is modified in specific areas: some regions secrete transmitter substances while other areas respond to the transmitter. Other areas of the neuron membrane have passive electrical properties that affect capacitance and resistance. Within the neuron membrane there are gated ion channels that vary in type, including fast response sodium channels that are voltage-gated and are used to send rapid signals.
Publicat de health victorro la 07:22 0 comentarii
Etichete: neuron, Overview
History
The neuron's place as the primary functional unit of the nervous system was first recognized in the early 20th century through the work of the Spanish anatomist Santiago Ramón y Cajal.Cajal proposed that neurons were discrete cells that communicated with each other via specialized junctions, or spaces, between cells This became known as the neuron doctrine, one of the central tenets of modern neuroscience. To observe the structure of individual neurons, Cajal used a silver staining method developed by his rival, Camillo Golgi The Golgi stain is an extremely useful method for neuroanatomical investigations because, for reasons unknown, it stains a very small percentage of cells in a tissue, so one is able to see the complete micro structure of individual neurons without much overlap from other cells in the densely packed brain.
Publicat de health victorro la 07:21 0 comentarii
Etichete: History, neuron
Anatomy and histology
Neurons are highly specialized for the processing and transmission of cellular signals. Given the diversity of functions performed by neurons in different parts of the nervous system, there is, as expected, a wide variety in the shape, size, and electrochemical properties of neurons. For instance, the soma of a neuron can vary from 4 to 100 micrometers in diameter.
* The soma is the central part of the neuron. It contains the nucleus of the cell, and therefore is where most protein synthesis occurs. The nucleus ranges from 3 to 18 micrometers in diameter.
* The dendrites of a neuron are cellular extensions with many branches, and metaphorically this overall shape and structure is referred to as a dendritic tree. This is where the majority of input to the neuron occurs. Information outflow (i.e. from dendrites to other neurons) can also occur, but not across chemical synapses; there, the backflow of a nerve impulse is inhibited by the fact that an axon does not possess chemoreceptors and dendrites cannot secrete neurotransmitter chemicals. This unidirectionality of a chemical synapse explains why nerve impulses are conducted only in one direction.
* The axon is a finer, cable-like projection which can extend tens, hundreds, or even tens of thousands of times the diameter of the soma in length. The axon carries nerve signals away from the soma (and also carry some types of information back to it). Many neurons have only one axon, but this axon may - and usually will - undergo extensive branching, enabling communication with many target cells. The part of the axon where it emerges from the soma is called the axon hillock. Besides being an anatomical structure, the axon hillock is also the part of the neuron that has the greatest density of voltage-dependent sodium channels. This makes it the most easily-excited part of the neuron and the spike initiation zone for the axon: in neurological terms it has the most negative action potential threshold. While the axon and axon hillock are generally involved in information outflow, this region can also receive input from other neurons.
Publicat de health victorro la 07:20 0 comentarii
Etichete: Anatomy, histology
Action on other neurons
A neuron affects other neurons by releasing a neurotransmitter that binds to chemical receptors. The effect upon the target neuron is determined not by the source or the neurotransmitter, but by the type of receptor that is activated. A neurotransmitter can be thought of as a key, and a receptor as a lock: the same type of key can in principle be used to open many different types of locks. Receptors can be classified broadly as excitatory (causing an increase in firing rate), inhibitory (causing a decrease in firing rate), or modulatory (causing long-lasting effects not directly related to firing rate). In principle, a single neuron, releasing a single neurotransmitter, can have excitatory effects on some targets, inhibitory effects on others, and modulatory effects on other still. As an example, neurons in the substantia nigra whose axons release the neurotransmitter dopamine in the striatum have excitatory effects on some target cells, mediated by D1 receptors, and inhibitory effects on other target cells, mediated by D2 receptors.
In fact, however, the two most common neurotransmitters in the brain, glutamate and GABA, have actions that are largely consistent. Glutamate acts on several different types of receptors, but all of them have effects that are either excitatory or modulatory. Similarly GABA acts on several different types of receptors, but all of them have effects (in adult animals, at least) that are inhbitory. Because of this consistency, it is common for neuroscientists to abuse the terminology by referring to cells that release glutamate as "excitatory neurons", and cells that release GABA as "inhibitory neurons". Since well over 90% of the neurons in the brain release either glutamate or GABA, these labels encompass the great majority of neurons. There are also other types of neurons that have consistent effects on all of their targets, for example "excitatory" motor neurons in the spinal cord that release acetylcholine, and "inhibitory" spinal neurons that release glycine.
Publicat de health victorro la 07:19 0 comentarii
Etichete: Action, neurons, on
Classification by neurotransmitter production
Neurons differ in the type of neurotransmitter they manufacture. Some examples are
* cholinergic neurons - acetylcholine
* GABAergic neurons - gamma aminobutyric acid
* glutamatergic neurons - glutamate
* dopaminergic neurons - dopamine
* serotonin neurons - serotonin
Recent Posts
Overview-neuron
The complexity and diversity in nervous systems is dependent on the interconnections between neurons, which rely on a limited number of different signals transmitted within the neurons to other neurons or to muscles and glands. The signals are produc...
History
The neuron's place as the primary functional unit of the nervous system was first recognized in the early 20th century through the work of the Spanish anatomist Santiago Ramón y Cajal.Cajal proposed that neurons were discrete cells that communicated...
Anatomy and histology
Neurons are highly specialized for the processing and transmission of cellular signals. Given the diversity of functions performed by neurons in different parts of the nervous system, there is, as expected, a wide variety in the shape, size, and elec...
Action on other neurons
A neuron affects other neurons by releasing a neurotransmitter that binds to chemical receptors. The effect upon the target neuron is determined not by the source or the neurotransmitter, but by the type of receptor that is activated. A neurotransmit...
Classification by neurotransmitter production
Neurons differ in the type of neurotransmitter they manufacture. Some examples are * cholinergic neurons - acetylcholine * GABAergic neurons - gamma aminobutyric acid * glutamatergic neurons - glutamate * dopaminergic neurons - dopamine ...
