![]() ![]() A key difference between myelin and the insulation on a wire is that there are gaps in the myelin covering of an axon. Myelin acts as insulation much like the plastic or rubber that is used to insulate electrical wires. Many axons are wrapped by an insulating substance called myelin, which is actually made from glial cells. Because the axon hillock represents the beginning of the axon, it is also referred to as the initial segment. Within the axon hillock, the cytoplasm changes to a solution of limited components called axoplasm. This is a tapering of the cell body toward the axon fiber. Where the axon emerges from the cell body, there is a special region referred to as the axon hillock. The major parts of the neuron are labeled on a multipolar neuron from the CNS. Figure 1 shows the relationship of these parts to one another. This gives the neuron a polarity-meaning that information flows in this one direction. Information flows through a neuron from the dendrites, across the cell body, and down the axon. The dendrites are usually highly branched processes, providing locations for other neurons to communicate with the cell body. The other processes of the neuron are dendrites, which receive information from other neurons at specialized areas of contact called synapses. It is the axon that propagates the nerve impulse, which is communicated to one or more cells. That single axon can branch repeatedly to communicate with many target cells. Neurons are usually described as having one, and only one, axon-a fiber that emerges from the cell body and projects to target cells. But what makes neurons special is that they have many extensions of their cell membranes, which are generally referred to as processes. The cell body contains the nucleus and most of the major organelles. Parts of a NeuronĪs you learned in the first section, the main part of a neuron is the cell body, which is also known as the soma (soma = “body”). The three-dimensional shape of these cells makes the immense numbers of connections within the nervous system possible. An important part of the function of neurons is in their structure, or shape. ![]() They are responsible for the electrical signals that communicate information about sensations, and that produce movements in response to those stimuli, along with inducing thought processes within the brain. Neurons are the cells considered to be the basis of nervous tissue. Neurons are important, but without glial support they would not be able to perform their function. Ongoing research pursues an expanded role that glial cells might play in signaling, but neurons are still considered the basis of this function. Glial cells, or glia, are known to play a supporting role for nervous tissue. They are electrically active and release chemical signals to target cells. They are responsible for the computation and communication that the nervous system provides. Neurons are the primary type of cell that most anyone associates with the nervous system. ![]() Nervous tissue is composed of two types of cells, neurons and glial cells. Describe the structure of each of the following:.Sensory neurons with cell bodies in the dorsal root ganglia of the vertebrate spinal cord are pseudo-unipolar: one branch projects to the periphery (to sensory receptors in the skin, joints, and muscle), the other to the spinal cord.By the end of this section, you will be able to: Pseudo-unipolar neurons initially develop as bipolar cells, but at some point the two processes that extend from the cell body fuse to form a single neurite. Some vertebrate sensory neurons are classified as pseudo-unipolar. Examples of bipolar neurons include most invertebrate sensory neurons and bipolar cells of the vertebrate retina. Some neurons in the vertebrate brain have a unipolar morphology: a notable example is the unipolar brush cell, found in the cerebellum and granule region of the dorsal cochlear nucleus.Ī third morphological class, bipolar neurons, extend just one axon and dendritic process from the cell body. In multipolar neurons, multiple processes extend from the cell body including dendrites and axons. ![]() Most neurons in the central nervous systems of vertebrates, including mammals, are multipolar. The cell bodies of invertebrate unipolar neurons are often located around the edges of the neuropil, in the so-called cell-body rind. Most neurons in the central nervous systems of invertebrates, including insects, are unipolar. The neurite then branches to form dendritic and axonal processes. A unipolar neuron is a neuron in which only one process, called a neurite, extends from the cell body. ![]()
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