What are the major tissues of the nervous system?
Written by Sheariah R. Torrillo
What are the major tissues of the nervous system? These cells are your neurons and glial cells. Your neurons are responsible for communicating through electrical signals. While your glial cells, also supporting cells, maintains the environment around your neurons.
The nervous system has a vast array of functions. Being complex in nature, it can control your body’s internal environment to promote homeostasis and regulation. Even being complex, it only has two major types of cells in its nerve tissue for signiﬁcant tissues.
Your neurons, also known as your nerve cells, are cells under polarization. These cells propagate the functions of your nervous system. They do this by conducting certain nerve impulses. These cells are the basis of the nervous tissue and are responsible for many things. It includes the communication and computation of the nervous system. They can release chemical signals that target cells and are electrically active.
Neurons are also accountable for such electrical signals. It allows the communication of information about sensations. Not only that, but it will enable the production of movement. It responds to certain stimuli and induces thought processes within your brain.
A signiﬁcant factor in your neurons’ function is their shape and structure. Together with their three-dimensional shape, these cells can make diverse connections. Such connections are within the nervous system, which makes them possible. These specialized cells are in high amounts and are amitotic too. It can no longer be replaced if one neuron is in destruction since neurons do not undergo mitosis.
The structure of a typical neuron contains three essential parts. It includes your cell body or soma, a single axon, and one or two dendrites. The cell body has a nucleus and at least one nucleolus. It has typical cytoplasmic organelles but lacks centrioles. Dendrites also referred to as ﬁbers, are cytoplasmic extensions and axons. It projects from your cell body and is sometimes branching and short.
This structure increases their surface area to receive signiﬁcant signals from other neurons. When it comes to its number within a neuron, it varies. Known as afferent processes, it transmits impulses towards the neuron cell body. Only one axon is present when projecting from each cell body. Known as the efferent process, it elongates in shape. It also carries impulses away from your cell body.
Meanwhile, your glial cells play a supporting role in your nervous tissue. It is also known as glial or neuroglial cells. It also has a structural function within your central nervous system. It regulates immune response, nerve ﬁring rates, and brain plasticity. Glial cells exist in both your peripheral nervous system and central nervous system. Scientists have shown that glial cells are your brain’s other half in functionality.
Its size has two types, macroglia, and microglia. Your macroglia, also known as more giant glial cells, can help neurons develop. It also migrates, insulates, and protects them. Your microglia is also known as your small type of glia. It has phagocytic properties when digesting foreign particles.
Types of glial cells are also present. It includes astrocytes, Oligodendrocytes, Schwann cells, Ependymal cells, Radial glia, and microglia. They all have signiﬁcant functions for your central nervous system and glial cells.
How are neurons classiﬁed?
Neurons classify themselves in the functionality of signals along with their structure. It includes how speciﬁc signals travel about your central nervous system. It results in your neurons divided into three different types. These types are your sensory neurons, interneurons, and motor neurons.
Sensory neurons, also known as your afferent neurons, are unipolar. It transmits information from the sensory receptors of your skin. It also scoped your internal organs towards your central nervous system for processing. Interneurons are extensively involved in the integration of signals. This type of neuron is present between your sensory and motor pathways. The majority of this type of cell is in conﬁnement within your central nervous system.
Motor neurons, also known as your efferent neurons, are multipolar. It transmits information away from your central nervous system towards a particular type of effector.
Neurons are classiﬁed in their structure. Its basis is on the number of processes extending out from your cell body. Neurons are then classiﬁed into three major groups. It includes neurons that are multipolar, bipolar, and unipolar.
Multipolar neurons are the signiﬁcant type of neurons in your central nervous system. It is also the efferent division of your peripheral nervous system. This type of neuron has three or more processes that extend out from your cell body. IN humans, they comprise more than 99% of their neurons.
Bipolar neurons are rare and are present in your olfactory system and the retina of your eye. This type of neuron only has two processes that extend in opposite directions from your cell body. One process is your dendrite, and the other process is your axon.
Unipolar neurons are present in the afferent division of your peripheral nervous system. This type of neuron has a single and short process. It extends from your cell body and branches into two or more processes. These processes then extend in opposite directions. The peripheral process is also known as the process that extends peripherally. It associates with your sensory reception. The process that extends toward your central nervous system is signiﬁcant.
What is the difference between an axon and a dendrite?
Axons carry nerve impulses away from your cell body. At the same time, dendrites carry nerve impulses from synapses to your cell body. Both your axon and dendrites are two components of your nerve cells. It functions to maintain nerve impulses to your spinal cord, brain, and body. This is so to coordinate certain functions.
For its structure, axons are long and thread-like. In contrast, dendrites are short branched extensions of your nerve cells. A nerve cell has only one axon but many dendrites. Axons arise from an axon hillock. It is also knowns as a conical projection, and dendrites arise direct from your nerve cell. Axons are very long and branched at their ends, while dendrites are very short and branched all along. Axons can either be myelinated or non-myelinated, while dendrites are non-myelinated.
Axons are from the efferent component of your nerve impulse. In comparison, dendrites are from the afferent part of your nerve impulse. For axons, the tips of the terminal branches are extensive in the form to form synaptic knobs. At the same time, no synaptic knobs are present at the ends of the components of your dendrites. Synaptic knobs for your axon contain vesicles. These vesicles have neurotransmitters, while dendrites do not have vesicles that contain neurotransmitters.
What is a Schwann cell?
A Schwann cell, also known as your neurilemma cell, is a glial cell. It is under your peripheral nervous system. It aids in separating and insulating your nerve cells. This type of cell also can produce the myelin sheath around neuronal axons.
This type of cell has its name after Theodor Schwann. He is a German physiologist who discovered Schwann cells during the 19th century. Schwann cells are equal to oligodendrocytes. It is a type of neuroglia in your central nervous system.
Schwann cells stimulate themselves to increase some constituents of the axonal surface. In instances where motor neurons are severed, causing nerve terminals degenerate. Schwann cells act to occupy the original neuronal space. When it comes to degeneration and regeneration, Schwann cells that remain after the generated nerve determines the route.
When it comes to the course and process of degeneration, which follows regeneration, ﬁbers regenerate in a way that they go back to their original target sites.
What is the difference between myelin sheath and Schwann cell?
Schwann cells wrap around the axon of your neuron to form your myelin sheath. Your myelin sheath serves as an electrically insulating layer. Schwann cells and the myelin sheath are two types of structures in the axon of your neuron.
At the same time, Schwann cells produce myelin, while myelin can increase the speed signal of transmission. Schwann cells are also glial cells. It swaddles around the nerve ﬁber of your peripheral nervous system. It forms the myelin sheaths of your peripheral axons. These are cells that wrap around the neuron’s axon and secrete myelin.
On the other hand, your myelin sheath is an insulating covering surrounding the axon. It also has various spiral layers of the myelin. It is discontinuous at the nodes of Ranvier and increases the speed at which a nerve impulse can travel along an axon. It consists of myelinating Schwann cells. It then serves as an electrical insulator. This insulator speeds up the signal transmission through your neurons.
How does myelination differ in the CNS and PNS?
Myelin is present in both your central and peripheral nervous systems. But, only the central nervous system is affected by the myelin sheath. In the central nervous system, myelin is fabricated by oligodendrocytes that are considered to be special cells. In the peripheral nervous system, myelin is generated by Schwann cells.
Two types of myelin, as mentioned, are chemically different, but both perform the same function—both function towards promoting the efﬁcient transmission of a nerve impulse along the axon.
Different glial cell types make myelin differently, depending on their location. Schwann cells make myelin in your peripheral nervous system. At the same time, oligodendrocytes are in your central nervous system. One Schwann cell forms a single myelin sheath in the peripheral nervous system. Your
oligodendrocytes send cell processes towards myelinate multiple segments on many axons in the central nervous system.
There are several morphological and molecular variations between nerve ﬁbers in the central nervous system and the peripheral nervous system for nerve ﬁbers. However, the basic myelin sheath arrangement and the electrophysiological characteristics are the same.
What is a node of Ranvier?
The nodes of Ranvier are a periodic gap in the insulating sheath on the axon of speciﬁc neurons. Myelin-sheath gaps are particular axonal segments that lack myelin. It functions in facilitating the rapid conduction of nerve impulses. Louis-Antoine Ranvier ﬁrst discovered this type of myelin cover. He is a French histologist and pathologist who ﬁrst discovered it in 1878.
When it comes to the composition of the myelin sheath, it has concentric layers of lipids. It includes cholesterol and a possible amount of phospholipids and cerebrosides. Thin layers of protein also separate these. This arrangement gives way to a high-resistance and low-capacitance electrical insulator.
However, your nodes of Ranvier interrupt the insulation at intervals. This discontinuity enables certain impulses to jump from node to node. This process is saltatory conduction.
What forms the nodes of Ranvier?
The nodes of Ranvier are characterized by specialized and short regions in the axonal membrane that is not insulated by myelin. The nodes contain high concentrations of voltage-gated sodium ion channels. It is responsible for raising the membrane voltage during creating an action potential that is all-or-nothing.
The nodes of Ranvier, which also include adjacent regions, have high concentrations of the structural proteins ankyrins. It is responsible for the anchorage of proteins towards the axonal cytoskeleton. In terms of pathological distribution of essential nodal proteins, it can lead to dysfunction in the propagation of nerve impulses. It also includes ion channels and cell adhesion molecules.
The node of Ranvier is highly organized in terms of its structure and molecular composition. It stems from the cell borders of its neighboring Schwann cells. It also forms the insulating myelin sheath around axons of a larger caliber.
The node of Ranvier is a site of excitation. It is full of Nav channels, also known as voltage-gated Na channels. These channels concentrate on the node. But it has little presence under the myelin sheath. From a physiologic point of view, the node of Ranvier is the component of the ﬁber present. It handles the action potential’s generation and propagation.
The nodes of Ranvier are approximately one μm wide. It also exposes the neuron membrane to external environments. These gaps are full of ion channels that mediate the exchange of speciﬁc ions.
It includes chloride and sodium, which requires forming an action potential. An action potential is the reversal of the electrical polarization of the neuron membrane. It initiates and is a part of a wave of excitation that travels along the axon.
When it comes to the action potential, it propagates by one node of Ranvier. It also reestablishes at the next node along the axon. It enables the action potential to travel at a pace along the ﬁber.
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