Cells And tissues Of The Nervous system
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The human body is made up of hundreds of trillions of cells. Cells of the nervous system, called neurons, are used to send information to the brain using electrochemical processes. In the brain alone, there is about one hundred billion neurons. Neurons can come in many different shapes and sizes. Some are only four microns wide, but some can be as wide as 100 microns, and as long as three feet! (Note- 1 micron = .001mm)
Neurons are similar to most other cells in the body. They are surrounded by a cell membrane, contain nuclei, have organelles like mitochondria, contain cytoplasm, and go through most cell processes like protein synthesis and energy production, however they do not perform mitosis. Neurons are the oldest and longest cells in your body, and you have the same neurons for your whole life. Although other cells die and are replaced, many neurons are never replaced when they die. In fact, you have much fewer neurons when you are older compared to now. The only place where neurons can grow back is in a part of your brain called the hippocampus.
They also have their own unique parts, called dendrites* and axons. They are used to send information from cell to cell. Dendrites receive information, and axons send information out to other cells.
Cells communicate with each other through electrochemical processes. To do this, they have dendrites and axons, but also synapses and special chemicals (neurotransmitters).
Neurons are similar to most other cells in the body. They are surrounded by a cell membrane, contain nuclei, have organelles like mitochondria, contain cytoplasm, and go through most cell processes like protein synthesis and energy production, however they do not perform mitosis. Neurons are the oldest and longest cells in your body, and you have the same neurons for your whole life. Although other cells die and are replaced, many neurons are never replaced when they die. In fact, you have much fewer neurons when you are older compared to now. The only place where neurons can grow back is in a part of your brain called the hippocampus.
They also have their own unique parts, called dendrites* and axons. They are used to send information from cell to cell. Dendrites receive information, and axons send information out to other cells.
Cells communicate with each other through electrochemical processes. To do this, they have dendrites and axons, but also synapses and special chemicals (neurotransmitters).
Classifying Nervous system cells
There are two classes of cells in the nervous system: neurons, which process information, and glia, which make sure the neurons are working and provide nourishment and repair to the cell. One way to classify neurons is by the number of extensions that extend from the neuron's cell body (soma). Here are a few examples:
Bipolar neurons have two extensions from the cell body. Neurons like retinal cells (cells that assist in vision) and olfactory epithelium cells (cells responsible for the sense of smell) are bipolar cells.
Bipolar neurons have two extensions from the cell body. Neurons like retinal cells (cells that assist in vision) and olfactory epithelium cells (cells responsible for the sense of smell) are bipolar cells.
Multipolar neurons have many extensions, but have only one axon. Spinal motor neurons (neurons that send information to your muscles, telling them to move), pyramidal neurons, and Purkinje cells are multipolar.
Pseudounipolar Cells
Pseudounipolar cells are a special class of neuron. Instead of having one axon and one dendrite, they have two axons and no dendrites at all. An example of a pseudounipolar cell is a dorsal root ganglion (left).
Another way to classify cells is by the direction they send information. Sensory, or Afferent neurons send encodesensory information from your sensory organs (your skin, eyes, nose, tongue, and ears) to the central nervous system, while Motor, or Efferent neurons send information from your central nervous system. There are also interneurons, which send information between the two.
Dendrites and Axons- What's the difference?
Actually, there are quite a few differences:
Dendrites:
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Axons:
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more on Dendrites
Dendrites are continuations of the cell membrane, extending the sensitive surface into the surrounding nervous tissue. The pattern of the cells branches have a wide range among neurons, and they reflect the function that particular cell performs. Sometimes, the function of a neuron can be identified just by looking at the pattern of dendritic branches. The dendrites' thin, branching shapes, increase the synaptic connections in brain tissue. The patterns of the dendritic branches change through the dendrite. Near At greater distances, the spines become larger and more elaborate.
Many neurons have dendrites with a special kind of connection, called dendritic spines. Dendritic spines are one micron long 'thorns' that stretch out from the dendrite. They are small and relatively simple near the base of the cell, but as the branches spread, they become longer and more elaborate, sometimes developing branches of their own. Dendritic spines modify themselves over time, and change with 'learning'. They can have many purposes, and -though small- are an important feature of cells in the nervous system.
Many neurons have dendrites with a special kind of connection, called dendritic spines. Dendritic spines are one micron long 'thorns' that stretch out from the dendrite. They are small and relatively simple near the base of the cell, but as the branches spread, they become longer and more elaborate, sometimes developing branches of their own. Dendritic spines modify themselves over time, and change with 'learning'. They can have many purposes, and -though small- are an important feature of cells in the nervous system.
Gila
Glial cells compose Gila tissue, the massive support system needed in order for the nervous system to function properly. Gila are NOT neurons. Glial cells can't conduct nerve impulses like neurons can, but they still do a plethora of important jobs to keep the nervous system running.
Providing support to the brain, helping to repair and maintain the system, and providing metabolic functions to the nervous system are just a few of a Gila cell's functions.
In humans, there are four kinds of Gila cells. They are:
Interestingly enough, the white matter in the brain gets its color from a large number of myelinated nerve cells.
Providing support to the brain, helping to repair and maintain the system, and providing metabolic functions to the nervous system are just a few of a Gila cell's functions.
In humans, there are four kinds of Gila cells. They are:
- Astrocytes - These are found in capillaries of the brain and create the blood-brain barrier, which prevents dangerous substances from entering the brain.
- Microglia - These are the glial cells that remove waste from neurons and protect against microorganisms like bacteria. They are very small.
- Oligodendrocytes and Schwann Cells- Cells in the central nervous system that wrap around axons to form the myelin sheath, a white matter which coats and insulates the cell. 'White matter' found in the brain is covered in these Gila, giving white matter it's name. Oligodendrocytes and Schwann cells also help in the conduction of impulses. Nerves with a myelin sheath can conduct impulses much faster than nerves that don't.
Interestingly enough, the white matter in the brain gets its color from a large number of myelinated nerve cells.
While the nervous system is essential to the proper functioning of the body, it could not work properly without other systems. The digestive system provides it with energy, the circulatory provides it with blood and nutrients, and the respiratory system provides it with oxygen. Without these other body systems, the brain could not function, and without the nervous system, the body could not survive.