Central And Peripheral Nervous System Definition

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Central And Peripheral Nervous System Definition – The peripheral nervous system is functionally divided into sensory and motor divisions, and each is further divided into somatic and visceral divisions.

The sensory (afferent) section carries signals from various receptors (sensory organs and simple sensory nerve endings) to the central nervous system (CNS). This pathway informs the central nervous system (CNS) about stimuli in and around the body.

Central And Peripheral Nervous System Definition

Central And Peripheral Nervous System Definition

The motor (efferent) division transmits signals from the central nervous system (brain and spinal cord) mainly to the glands and muscle cells that carry out body reactions. Cells and organs that respond to these signals are called effectors.

The Nervous System: Facts, Function & Diseases

The communication role of the nervous system is performed by nerve cells or neurons. These cells have three basic physical properties that allow them to communicate with other cells:

There are three general classes of neurons that correspond to the three major aspects of nervous system function listed above (eg, excitation, conduction, and secretion):

There are many types of neurons, but a good starting point for the discussion is the motor neuron of the spinal cord. The control center of a neuron is the neurosome, also called the soma or cell body. It has a centrally located nucleus with a large nucleolus. Cytoplasm contains mitochondria, lysosomes, Golgi complex, numerous inclusions and branched rough endoplasmic reticulum and cytoskeleton. The cytoskeleton consists of a dense network of microtubules and neurofibrils (bundles of actin filaments) that divide the rough endoplasmic reticulum into darkly stained areas called the chromatophilic substance. This is unique to neurons and helps identify them in tissue sections with mixed cell types. Mature neurons do not have centrioles and cannot undergo further mitosis after adolescence. Thus, dying neurons are usually irreversible; Surviving neurons cannot regenerate to replace lost neurons. However, neurons are unusually long-lived cells, able to function for over a hundred years. But even in adulthood, some parts of the central nervous system (CNS) contain unspecialized stem cells that can divide and regenerate nervous tissue to a limited extent.

The main inclusions in the neuron are glycogen granules, lipid droplets, melanin, and a golden-brown pigment called lipofuscin, which is produced when lysosomes break down worn-out organelles and other products. Lipofuscin accumulates with age and pushes the nucleus to one side of the cell. Lipofuscin granules are also called “worn-out granules” because they are most abundant in older neurons. They appear to be detrimental to neuronal function.

Introduction To The Central And Peripheral Nervous Systems

The soma of most neurons give rise to many thick processes that divide into a large number of dendrites—named for their striking resemblance to the bare branches of a tree in winter. Dendrites are the main site for receiving signals from other neurons. Some neurons have only one dendrite, and some have thousands. The more dendrites a neuron has, the more information it can receive and incorporate into decision making. As confusing as dendrites are, they provide highly precise pathways for receiving and processing neural information.

On one side of the neurosome is a tubercle called the axon tubercle, from which the axon (nerve fiber) arises. The axon is cylindrical and relatively unbranched for most of its length, although it may give rise to several branches known as axon collaterals near the soma, and most axons branch extensively at their distal end. Axons specialize in rapid transmission of nerve signals to points distant from the soma. Its cytoplasm is called axoplasm, and its membrane is called axolemma. A neuron never has more than one axon, and some neurons have none.

Soma range from 5 to 135 µm in diameter, and axons range from 1 to 20 µm in diameter and from a few millimeters to over a meter in length. Such dimensions are more impressive if you expand them into the dimensions of familiar objects. If the soma of a spinal motor neuron were the size of a tennis ball, its dendrites would form a dense, dense mass that could fill a 30-seat classroom from floor to ceiling. Its axon would be up to a mile long, but slightly narrower than a garden hose. A neuron must collect molecules and organelles in its “tennis ball” soma and transport them through its “mile-long garden hose” to the end of the axon.

Central And Peripheral Nervous System Definition

At the distal end, the axon usually has a terminal arborization—an extensive complex of slender branches. Each branch ends with a bulbous terminal of an axon (terminal button), which forms a connection (synapse) with the next cell. It contains synaptic vesicles filled with neurotransmitters. In autonomic neurons, however, axons have many bumps called varicosities along their length. Each varix contains synaptic vesicles and releases neurotransmitters.

Peripheral Nervous System

Not all neurons fit the previous description. Neurons are classified structurally according to the number of processes extending from the soma:

All the proteins needed by the neuron must be made in the soma, where protein-synthesizing organelles such as the nucleus, ribosomes, and rough endoplasmic reticulum are located. However, many of these proteins are essential in the axon, for example to repair and maintain the axolemma, to serve as ion channels in the membrane, or to function in the axon terminal as enzymes and signaling molecules. Other substances are transported from the axon terminals back to the soma for disposal or recycling. The two-way movement of proteins, organelles, and other materials along the axon is called axonal transport. Movement from the soma down the axon is called anterograde transport, and movement from the axon to the soma is called retrograde transport.

Materials move along axonal microtubules, which act as monorails, guiding them to their destination. But what is the “engine” that moves them along the rails? Anterograde transport uses a motor protein called kinesin, while retrograde transport uses dynein (the same protein responsible for motility of cilia and flagella). These proteins carry material “on their backs” when they are stretched like muscle myosin heads to attach to and move along microtubules.

) neurons of the nervous system. Because they are so extensively branched, they make up about 50% of the mass of nerve tissue. However, they outnumber cells called neuroglia or glia cells by at least 10 to 1. Glial cells protect neurons and help them function.

Autonomic Nervous System: Anatomy, Divisions, Function

The word glia, which means “glue”, refers to one of their roles – to connect neurons and provide a support structure for nervous tissue. In the embryo, they form a framework that guides young migrating neurons to their destination. Wherever a mature neuron is not in synaptic contact with another cell, it is covered by glial cells. This prevents neurons from contacting each other except at specific points for signal transmission, ensuring the integrity of their conduction pathways.

There are six types of neuroglia, each with a unique function. The first four types are found only in the central nervous system (brain and spinal cord):

The myelin sheath is a spiral layer of insulation around nerve fibers formed by oligodendrocytes in Schwann cells in the central nervous system (brain and spinal cord) and peripheral nervous system. Since it is composed of the plasma membrane of glial cells, its structure is generally similar to that of the plasma membrane. It consists of about 20% protein and 80% lipids, the latter consisting of phospholipids, glycolipids and cholesterol.

Central And Peripheral Nervous System Definition

The production of myelin sheath is called myelination. It begins in the fourteenth week of fetal development, but at birth there is almost no myelin in the brain. Myelination occurs rapidly in childhood and is not complete until late adolescence. Because myelin has a high lipid content, dietary fat is important for the early development of the nervous system. Children under 2 should not be given low-fat foods (skimmed milk, etc.) that may be beneficial for adults.

Organization Of The Nervous System

Note: (a) Schwann cell of the peripheral nervous system that repeatedly wraps around the axon to form a multilayered myelin sheath.

(b) The oligodendrocyte of the central nervous system (brain and spinal cord) synthesizes the axons of some neurons. Here, the myelin is bent inward along the axon as it is laid down.

In the peripheral nervous system, the Schwann cell wraps around a single nerve fiber multiple times, covering 100 compact layers of its own membrane, with almost no cytoplasm between the membranes. These layers form the myelin sheath. The Schwann cell spirals outward, envelops the nerve fiber and ends in a thick outer spiral called the neurilemma. Here, the convex body of the Schwann cell contains its nucleus and most of the cytoplasm. On the outside of the neurilemma is the basal lamina, followed by a thin sleeve of fibrous connective tissue called the endoneurium. To visualize this myelination process, imagine that you are tightly wrapping a nearly empty tube of toothpaste around a pencil. A pencil is an axon, and the spiral layers of a tube of toothpaste are myelin. The toothpaste, like the cytoplasm of the cell, will be pushed out of one end of the tube and form a bead on the outer surface of the envelope like a Schwann cell body.

In the central nervous system

Autonomic Nervous System Basics

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