A neuron represents a nerve cell which is the basic building block of the nervous system. Neurons are very similar to other cells that are present in the human body in different numbers of ways, but there is only one key difference between neurons and other cells. Neurons possess the ability to transmit information throughout the body.
Sensory neurons help to carry information from the sensory receptor cells throughout the body and also upto the brain. Nerves represent individual nerve cells that are a collection of neurons and part of our nervous system. These are located throughout the body under the skin, through and around the organs, and towards the centre area of the brain.
Nerves
Nerve, is a white cordlike bundle of fibres, that is surrounded via a sheath, that connects the nervous system to other parts of the body. The nerves help in the conduct of impulses towards or away from the central nervous mechanism. About 12 pairs of the cranial nerves in humans are attached to the brain, and about 31 pairs of the spinal nerves are attached to the spinal cord. The fibres comprising the individual nerves are numerous, and save the ones arising in the sympathetic ganglia, extending from the brain or spinal cord upto the peripheral structures which they innervate. In respect of function, nerve fibres are commonly divided into two categories namely, sensory (afferent) and motor (efferent). The fibres of these categories and their subdivisions comprise the functional components of the nerves. A combination of such components vary greatly in the individual cranial nerves; whereas in the spinal nerves they are more uniform.
Types of nerves
There are various ways to classify the nerves. The first and most common classification of the nerves is based on the way they transmit information.
Afferent (sensory) nerves
The nerves that help in conduction of signals from the periphery to the central nervous system are known as the afferent or sensory nerves. These nerves can be further divided into somatic sensory (that helps in carrying information from the skin, skeletal muscle and joints) and visceral sensory (from visceral organs, like those of liver or kidneys). All these sensory impulses are sent to the CNS by the ascending tracts.
Efferent (motor) nerves
The nerves that conduct signals from the central nervous system to the periphery are known to be efferent or motor nerves. Efferent nerves help to convey motor impulses away from the CNS, upto the effector organs like the muscles and glands. They can be classified into two different divisions: somatic motor nerves (that helps to provide innervation to the skeletal muscles) and visceral motor nerves (these are a part of the autonomic nervous system and they help to innervate smooth muscle, cardiac muscle and glands). All motor impulses are sent along the PNS by descending tracts.
An easy way to remember this terminology is that The signals from the efferent nerves leave the central nervous system and from the afferent nerves enters the central nervous system. Finally they get the mixed nerves that comprises both sensory and motor fibers.
Mixed nerve
Nerves that possess both afferent sensory and efferent motor fibers are known as mixed nerves. They transfer messages in both directions at once.
Neuron
Neurons represent the cells that are present within the nervous system and transmit information to other nerve cells, muscle, or gland cells. Majority of the neurons possess a cell body, an axon, and dendrites. The cell body comprises the nucleus and cytoplasm. The axon extends from the cell body and mainly gives rise to many other smaller branches before ending at nerve terminals. Dendrites extend from the neuronal cell body and receive messages from other neurons. Synapses are the major contact points where one neuron can communicate with another. The dendrites are surrounded via synapses that are formed by the ends of axons from other neurons.
Parts of a Neuron
Neurons greatly vary in size, shape, and structure based on their role and location. Thus, all neurons possess three essential parts: a cell body, an axon, and dendrites, these are discussed below:
Cell body
It is also called a soma, the cell body represents the centre section of the neuron. The cell body comprises genetic information, maintains the structure of neurons , and provides energy to carry out different activities. Like other different cell bodies, a neuron’s cell body comprises a nucleus and different specialized organelles. It’s covered by a membrane that helps in both protecting it and allowing it to interact with its immediate surroundings.
Axon
An axon represents a long, tail-like structure. It joins with the cell body at a specialized junction known as the axon hillock. Many axons are insulated by a fatty substance known as myelin. Myelin helps axons to conduct different electrical signals. Neurons mainly possess only one main axon.
Dendrites
Dendrites represent the fibrous roots that emerge from the cell body. Similarly like the antennae, dendrites also receive and process signals from the axons of other neurons. Neurons can possess more than one set of dendrites, that is called dendritic trees.
Types of neurons
Neurons greatly vary in structure, function, and genetic makeup. There are about five major types of neuron forms. Each form combines several elements of the basic neuron shape.
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Multipolar neurons: These neurons possess a single axon and symmetrical dendrites that emerge from it. It is the most common form of neuron present in the central nervous system.
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Unipolar neurons: these are generally found only in invertebrate species, these types of neurons possess only a single axon.
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Bipolar neurons: these possess two extensions usually extending from the cell body. At the end of one side is present the axon, and the dendrites lie on the other side. These forms of neurons can be mostly found in the retina of the eye. But they can also be found in different parts of the nervous system that help the nose and ear to function.
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Pyramidal neurons: these neurons possess only one axon but several dendrites to form a pyramid like shape. These are generally the largest neuron cells and are commonly found in the cortex.
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Purkinje neurons: these neurons possess multiple dendrites that extend out from the cell body. These neurons can be inhibitory neurons, meaning that they release neurotransmitters that keep other neurons from firing.
Conclusion
A neuron is mainly a single specialised cell that is responsible for transmission of information by electrical and chemical impulses. They are generally found in the brain, spinal cord, and peripheral nerves. Whereas a nerve cell represents another name for a neuron. Sensory neurons and motor neurons are the two common types of neurons. A nerve is usually made up of several different types of neurons. In the peripheral nervous system, a nerve represents an enclosed cable-like bundle of axons and nerve fibres in the peripheral nervous system. Autonomic nerves, motor nerves, and sensory nerves are the three common types of nerves. With this we come to an end of this topic. We hope that you were able to clear all your concepts regarding neurons and nerves.