Nervous tissue where is it located

The axons are responsible for transmitting impulses over long distances from cell body. The cell body is like a factory for the neuron. It produces all the proteins and contains specialized organelles such as nucleus, granules and Nissl bodies. Neuron : This image illustrates the parts of a neuron. The dendrites receive incoming signals while axons propagate signals away from the neuron cell body.

The myelin sheath surrounds and insulates the axon. The axon is surrounded by a whitish, fatty layer called the myelin sheath. Outside the myelin sheath there is a cellular layer called the neurilemma. In the peripheral nervous system, Schwann cells are neuroglia cells that support neuronal function by increasing the speed of impulse propagation.

The Schwann cells are underlain by the medullary sheath. The medullary sheath is interrupted at intervals by the nodes of Ranvier. Illustration of the Schwann Cells and the Myelin Sheath : Transmission electron micrograph of a myelinated axon. The myelin layer concentric surrounds the axon of a neuron, showing Schwann cells.

The nervous system consists of nervous tissue, which is composed of two principal types of cells called neuron and neuroglia. Nervous tissue, one of the four main tissue types, is composed of neurons and supporting cells called neuroglia. There are six types of neuroglia—four in the central nervous system and two in the PNS.

These glial cells are involved in many specialized functions apart from support of the neurons. Neuroglia in the CNS include astrocytes, microglial cells, ependymal cells and oligodendrocytes. In the PNS, satellite cells and Schwann cells are the two kinds of neuroglia. Astrocytes are shaped like a star and are the most abundant glial cell in the CNS.

They have many radiating processes which help in clinging to the neurons and capillaries. They support and brace the neurons and anchor them to the nutrient supply lines. They also help in the guiding the migration of young neurons. Astrocytes control the chemical environment around the neurons. Microglial cells are small and ovoid un shape with thorny processes.

Different types of neurons control or perform different activities. For instance, motor neurons transmit messages from the brain to the muscles to generate movement. Sensory neurons detect light, sound, odor, taste, pressure, and heat and send messages about those things to the brain.

Other parts of the nervous system control involuntary processes. These include keeping a regular heartbeat, releasing hormones like adrenaline, opening the pupil in response to light, and regulating the digestive system. When a neuron sends a message to another neuron, it sends an electrical signal down the length of its axon. At the end of the axon, the electrical signal changes to a chemical signal. The axon then releases the chemical signal with chemical messengers called neurotransmitters pronounced noor-oh-TRANS-mit-erz into the synapse pronounced SIN-aps —the space between the end of an axon and the tip of a dendrite from another neuron.

One is the axon and one the dendrite. Bipolar cells are not very common. They are found mainly in the olfactory epithelium where smell stimuli are sensed , and as part of the retina. Multipolar neurons are all of the neurons that are not unipolar or bipolar. They have one axon and two or more dendrites usually many more.

With the exception of the unipolar sensory ganglion cells, and the two specific bipolar cells mentioned above, all other neurons are multipolar. Some sources describe a fourth type of neuron, called an anaxonic neuron. Anaxonic neurons are very small, and if you look through a microscope at the standard resolution used in histology approximately X to X total magnification , you will not be able to distinguish any process specifically as an axon or a dendrite. Any of those processes can function as an axon depending on the conditions at any given time.

Nevertheless, even if they cannot be easily seen, and one specific process is definitively the axon, these neurons have multiple processes and are therefore multipolar. Neurons can also be classified on the basis of where they are found, who found them, what they do, or even what chemicals they use to communicate with each other. Some neurons referred to in this section on the nervous system are named on the basis of those sorts of classifications Figure For example, a multipolar neuron that has a very important role to play in a part of the brain called the cerebellum is known as a Purkinje commonly pronounced per-KIN-gee cell.

It is named after the anatomist who discovered it Jan Evangelista Purkinje, — Glial cells, or neuroglia or simply glia, are the other type of cell found in nervous tissue. They are considered to be supporting cells, and many functions are directed at helping neurons complete their function for communication.

And research may find much more about them in the future. There are six types of glial cells. Table Astrocytes have many processes extending from their main cell body not axons or dendrites like neurons, just cell extensions. Those processes extend to interact with neurons, blood vessels, or the connective tissue covering the CNS that is called the pia mater Figure Generally, they are supporting cells for the neurons in the central nervous system.

Some ways in which they support neurons in the central nervous system are by maintaining the concentration of chemicals in the extracellular space, removing excess signaling molecules, reacting to tissue damage, and contributing to the blood-brain barrier BBB.

The blood-brain barrier is a physiological barrier that keeps many substances that circulate in the rest of the body from getting into the central nervous system, restricting what can cross from circulating blood into the CNS. Nutrient molecules, such as glucose or amino acids, can pass through the BBB, but other molecules cannot. This actually causes problems with drug delivery to the CNS. Pharmaceutical companies are challenged to design drugs that can cross the BBB as well as have an effect on the nervous system.

Like a few other parts of the body, the brain has a privileged blood supply. Very little can pass through by diffusion. Most substances that cross the wall of a blood vessel into the CNS must do so through an active transport process. Because of this, only specific types of molecules can enter the CNS.

Glucose—the primary energy source—is allowed, as are amino acids. Water and some other small particles, like gases and ions, can enter. While this barrier protects the CNS from exposure to toxic or pathogenic substances, it also keeps out the cells that could protect the brain and spinal cord from disease and damage. The BBB also makes it harder for pharmaceuticals to be developed that can affect the nervous system.

Aside from finding efficacious substances, the means of delivery is also crucial. There are a few processes that extend from the cell body. Each one reaches out and surrounds an axon to insulate it in myelin. One oligodendrocyte will provide the myelin for multiple axon segments, either for the same axon or for separate axons.

The function of myelin will be discussed below. Microglia are, as the name implies, smaller than most of the other glial cells. Ongoing research into these cells, although not entirely conclusive, suggests that they may originate as white blood cells, called macrophages, that become part of the CNS during early development. While their origin is not conclusively determined, their function is related to what macrophages do in the rest of the body. When macrophages encounter diseased or damaged cells in the rest of the body, they ingest and digest those cells or the pathogens that cause disease.

Microglia are the cells in the CNS that can do this in normal, healthy tissue, and they are therefore also referred to as CNS-resident macrophages. The ependymal cell is a glial cell that filters blood to make cerebrospinal fluid CSF , the fluid that circulates through the CNS. Because of the privileged blood supply inherent in the BBB, the extracellular space in nervous tissue does not easily exchange components with the blood.

Ependymal cells line each ventricle , one of four central cavities that are remnants of the hollow center of the neural tube formed during the embryonic development of the brain.

The choroid plexus is a specialized structure in the ventricles where ependymal cells come in contact with blood vessels and filter and absorb components of the blood to produce cerebrospinal fluid. These glial cells appear similar to epithelial cells, making a single layer of cells with little intracellular space and tight connections between adjacent cells. They also have cilia on their apical surface to help move the CSF through the ventricular space. The relationship of these glial cells to the structure of the CNS is seen in Figure One of the two types of glial cells found in the PNS is the satellite cell.

Satellite cells are found in sensory and autonomic ganglia, where they surround the cell bodies of neurons. This accounts for the name, based on their appearance under the microscope.