It is an individual cell which is the functional unit of the nervous system. It has three major parts soma, dendrites and an axon. It is present in both the central and peripheral nervous system.
There are three types of neurons motor neurons, sensory neurons and interneurons. It is composed of the axon, cell body, and dendrites. Nerve cells are also called neurons. It consists of three parts which are as follows:.
Cell Body - It contains the nucleus and other cell organelles. It is also known as soma the factory of the neuron. It provides and produces all the proteins for the dendrites, axons and synaptic terminals. Dendrites - These are extended from the cell body and receive nerve impulses from other neurons.
Dendrites are the antennae of the neuron and covered by a large number of synapses. Axon - It is a long extension of the cell body that transmits nerve impulses to other cells.
The branches of the axon at the terminal are known as axon terminals. At these terminals, neurons communicate with other cells. In the case of a nerve, the main function of it is to transmit information to various other parts of the body. They form pathways to different parts of the body. Thus, it is with the help of these pathways of nerves that information is transmitted to other parts of the body.
One can see two classifications, when it comes to nerves. According to one classification, nerves are divided into three types: — afferent nerves, efferent nerves and mixed nerves. Afferent nerves carry signals from sensory neurons to the central nervous system. Efferent nerves carry signals from central nervous system to the targeted glands and muscles. Mixed nerves carry both afferent and efferent axons and thus are responsible of the incoming sensory information and the outgoing signals to the muscles and glands.
The second classification is into two types: — spinal nerves and cranial nerves. Spinal nerves distribute signals to most parts of the body, through the vertebral column to the spinal cord. Whereas the cranial nerves distribute signals to different parts of the head brain, brainstem. Nerves are found in the peripheral nervous system. A nerve is considered to be the basic unit of the peripheral nervous system.
A nerve comprises of different types of axons, through which they transmit signals and information to the different body parts. Each nerve is covered with three layers: — the inner endoneurium covering the nerve fibres, perineurium being the middle layer and the outer layer called epineurium. This is the basic structure of a nerve. A nerve is formed by a group of neurons. A neuron, on the other hand, is an individual specialized cell.
The axon bundle of the nerve is wrapped by a connective tissue layer called epineurium. A fascicle is a group of neurons. A cross section of a nerve is shown in figure 1. Figure 1: A Cross-section of a Nerve. Three types of nerves are found based on the direction of transmitting signals within the nervous system.
They are sensory nerves, motor nerves, and mixed nerves. Sensory nerves are also known as afferent nerves, and carry information from the sensory receptors into the central nervous system. Motor nerves carry nerve impulses from the central nervous system to the effector organs. Mixed nerves contain both sensory and motor neurons within the same nerve. Based on the way they are connected to the central nervous system, two types of nerves can be identified as cranial nerves and spinal nerves.
The parts of the head are innervated by cranial nerves , which are connected with the brain. Twelve cranial nerves are found in humans. Most of the body parts are innervated by spinal nerves , which are connected to the spinal cord. Nerve fibers can be divided based on their diameter, velocity of the signal conduction, and the myelinated state of the axons as well. The group A nerves have a large diameter. They are myelinated and have a high signal conduction velocity.
The group B nerves have a small diameter. They are also myelinated, but their conduction velocity is low. The group C nerves are unmyelinated, with a small diameter, and low conduction velocity. The nerves in the left upper limb of humans are shown in figure 2. Figure 2: Nerves in the Left Upper Limb. A neuron is the functional unit of the nervous system which transmits nerve impulses between the central and peripheral nervous systems.
There are three types of neurons based on their function in the nervous system. They are sensory neurons, motor neurons, and interneurons.
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