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The nervous system is made up of neurons , specialized cells that can receive and transmit chemical or electrical signals, and glia    , cells that provide support functions for the neurons by playing an information processing role that is complementary to neurons. A neuron can be compared to an electrical wire—it transmits a signal from one place to another. Glia can be compared to the workers at the electric company who make sure wires go to the right places, maintain the wires, and take down wires that are broken. Although glia have been compared to workers, recent evidence suggests that also usurp some of the signaling functions of neurons.

There is great diversity in the types of neurons and glia that are present in different parts of the nervous system. There are four major types of neurons, and they share several important cellular components.

Neurons

The nervous system of the common laboratory fly, Drosophila melanogaster , contains around 100,000 neurons, the same number as a lobster. This number compares to 75 million in the mouse and 300 million in the octopus. A human brain contains around 86 billion neurons. Despite these very different numbers, the nervous systems of these animals control many of the same behaviors—from basic reflexes to more complicated behaviors like finding food and courting mates. The ability of neurons to communicate with each other as well as with other types of cells underlies all of these behaviors.

Most neurons share the same cellular components. But neurons are also highly specialized—different types of neurons have different sizes and shapes that relate to their functional roles.

Parts of a neuron

Like other cells, each neuron has a cell body (or soma) that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components. Neurons also contain unique structures, illustrated in [link] for receiving and sending the electrical signals that make neuronal communication possible. Dendrites are tree-like structures that extend away from the cell body to receive messages from other neurons at specialized junctions called synapses . Although some neurons do not have any dendrites, some types of neurons have multiple dendrites. Dendrites can have small protrusions called dendritic spines, which further increase surface area for possible synaptic connections.

Once a signal is received by the dendrite, it then travels passively to the cell body. The cell body contains a specialized structure, the axon hillock    that integrates signals from multiple synapses and serves as a junction between the cell body and an axon    . An axon is a tube-like structure that propagates the integrated signal to specialized endings called axon terminals . These terminals in turn synapse on other neurons, muscle, or target organs. Chemicals released at axon terminals allow signals to be communicated to these other cells. Neurons usually have one or two axons, but some neurons, like amacrine cells in the retina, do not contain any axons. Some axons are covered with myelin    , which acts as an insulator to minimize dissipation of the electrical signal as it travels down the axon, greatly increasing the speed on conduction. This insulation is important as the axon from a human motor neuron can be as long as a meter—from the base of the spine to the toes. The myelin sheath is not actually part of the neuron. Myelin is produced by glial cells. Along the axon there are periodic gaps in the myelin sheath. These gaps are called nodes of Ranvier    and are sites where the signal is “recharged” as it travels along the axon.

Questions & Answers

what is anatomy
Mohamed Reply
no idea
Benard
Anatomy is the branch of science that deals with the study of internal and external structures of an organism
Bigenis
Anatomy is the branch of science that deals with the study of the internal structure of an organism
Nana
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Julius Reply
What's the function of epiglottis
Ugo Reply
What Is The Other Name For Intestinal Juice?
Justin Reply
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rick Reply
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prokaryotic and eukaryotic
Yazi
prokaryotic cell and eukaryotic cell
Grace
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globin
Joelia
Globin
globulins
EZRA
globulins
SASMITA
globulins
Grace
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Emmanuel Reply
Parasitic movement is a problem for all of us. So is its companion, parasitic tension. Parasitic movement is the excess contraction of muscles that you don't actually need to complete an action.
freya
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Nyandera
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Ocen
absorption may simply mean utilization of food in the body
Bigenis
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Thiza Reply
eukaryotic cells which posses a true nucleus that is the DNA is enclosed and covered by a nuclear membrane
Grace
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hi
Lagos
23 haploid and 23diploid
Patson
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Joelia
morning
Kazula
hi
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Angela
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Angela
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Julius
what is the important of sex
Aremu Reply
why did human being need sex?
Aremu
because he/she have feelings
Chripine
reproduction...to make more
Yazi
due to active harmon
Manish
One important of sex is to reproduce
Emma
to ensure the countinuty of life
Yusuf
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for sexual satisfaction and birth
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Asiya Reply
The strength or force that allows something to continue or grow stronger or faster as time pass
Emma
What is Centripetal Force?
Justin
centrepital force is the inward force required to keep a body moving with constant speed in a circular path
Yusuf
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Takii Reply
List four condition necessary for seed germination
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water,air(oxygen),light,temperature
Hassan
water, light, oxygen and temperature
lilchris
water, oxygen, light temperature
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water oxygen light and temperature
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sun light, temperature, water, oxygen
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water, oxygen, light, tell.
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what is anatomy
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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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