BilZ0r
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What is a neuron?
What is a neuron?
The most important properties of a neuron is its ability to fire an action potential and to release neurotransmitters. Anatomically, a neuron is analogous to a tree: it has roots in the form of a huge number of of branching dendrites (the receiving end of a neuron), it has a trunk, in the form of an axon (the transmitting section of a neuron) and a branches, in the form of axonal arborizations or terminals (Fig 1 and 2). Generally, a neuron can be seen as an integrator and disseminator of information. Figure 2 shows a real image of a single neuron filled so it can be visualize independently of the hundreds of neurons surrounding it. This image shows the dendritic spines of a dendrite (the small dots along the length of many of the dendrites). Each of those these spines will make at least one connection (or synapses) with a neighboring neuron, there will also be many synapses which we can not see, this means that this neuron makes thousands of connections with other neurons. Although we can not see it’s axonal terminals, it is safe to assume that this cell then makes thousands of connections with other neurons. Hence a neuron both receives inputs from a huge number of neurons, as well as giving inputs to a large number of neurons.
Functionally, a neuron is similar to a piece of wire, with a few changes. For one, information is generally only sent in one direction. Neurotransmitters are chemicals that are released by neurons in order to send signals to other neurons. Neurotransmitters are released by the axonal terminals of one cell, and diffuse across the synapse to the dendrites of another cell. Here neurotransmitters can bind to “receptors” and effect the neuron in many ways, but importantly they can alter the probability of it firing an “action potential”, the electrical signal which neurons send over long distances. These principles are discussed further in the “electrical properties of the neuron” and the “chemical properties of the neuron” chapters.
Another difference between a neuron and a piece of wire, is that a neuron can alter the nature of the information it is going to transmit depending on previous signals it has received, that is to say, it is not a passive conductor but a small processor, capable of making decisions. There are some 100 billion neurons in the brains of humans. Each one making and receiving thousands of connections. This results in an unfathomable number of connections and pathways, signals can move through the brain in. Integrative processing allows the overwhelming depth of information received by the sensory organs to be processed into discrete, meaningful perceptions. Conversely, the dissemination of information allows for associative processes to occur. These principles are discussed further in the “signaling properties of neurons”
What is a neuron?
The most important properties of a neuron is its ability to fire an action potential and to release neurotransmitters. Anatomically, a neuron is analogous to a tree: it has roots in the form of a huge number of of branching dendrites (the receiving end of a neuron), it has a trunk, in the form of an axon (the transmitting section of a neuron) and a branches, in the form of axonal arborizations or terminals (Fig 1 and 2). Generally, a neuron can be seen as an integrator and disseminator of information. Figure 2 shows a real image of a single neuron filled so it can be visualize independently of the hundreds of neurons surrounding it. This image shows the dendritic spines of a dendrite (the small dots along the length of many of the dendrites). Each of those these spines will make at least one connection (or synapses) with a neighboring neuron, there will also be many synapses which we can not see, this means that this neuron makes thousands of connections with other neurons. Although we can not see it’s axonal terminals, it is safe to assume that this cell then makes thousands of connections with other neurons. Hence a neuron both receives inputs from a huge number of neurons, as well as giving inputs to a large number of neurons.
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Figure 1. Schematic of a neuron
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Figure 2. Micrograph of a filled neuron, probably a hipocampal pyramidal cell. Neuron image thanks to www.lebenswissen.de/pix/ Dendritic spine image thanks to tonto.stanford.edu/~viktor/
Functionally, a neuron is similar to a piece of wire, with a few changes. For one, information is generally only sent in one direction. Neurotransmitters are chemicals that are released by neurons in order to send signals to other neurons. Neurotransmitters are released by the axonal terminals of one cell, and diffuse across the synapse to the dendrites of another cell. Here neurotransmitters can bind to “receptors” and effect the neuron in many ways, but importantly they can alter the probability of it firing an “action potential”, the electrical signal which neurons send over long distances. These principles are discussed further in the “electrical properties of the neuron” and the “chemical properties of the neuron” chapters.
Another difference between a neuron and a piece of wire, is that a neuron can alter the nature of the information it is going to transmit depending on previous signals it has received, that is to say, it is not a passive conductor but a small processor, capable of making decisions. There are some 100 billion neurons in the brains of humans. Each one making and receiving thousands of connections. This results in an unfathomable number of connections and pathways, signals can move through the brain in. Integrative processing allows the overwhelming depth of information received by the sensory organs to be processed into discrete, meaningful perceptions. Conversely, the dissemination of information allows for associative processes to occur. These principles are discussed further in the “signaling properties of neurons”
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