Dorsal root ganglia are clusters of nerve bodies of sensory neurons located alongside the spinal cord. Sympathetic ganglia form long chains on either side of the spinal cord. They deliver information about stress, impending danger, and the fight-or-flight response. Parasympathetic nerves have their nerve cell bodies in small ganglia located within the organ they innervate. Peripheral nerves contain the axons of both motor neurons and sensory neurons that connect with the spinal cord.
They are surrounded by multiple layers of connective tissue. The nervous system has a variety of specialized receptors. Chapter 6 - Nervous Tissue Nervous system is specialized for the rapid communication of information from one region of the body to another.
Nervous system is divided anatomically into two major components: Central nervous system CNS — consists of the brain and spinal cord Peripheral nervous system PNS — peripheral nerves and ganglia Nervous system is divided functionally into two major components: Somatic nervous system — conscious voluntary movements Autonomic nervous system — regulates the functions of internal organs - further divided into two subdivisions: Sympathetic nervous system — involved in functions requiring quick responses i.
Fig Motor Neuron. Granules called Nissl bodies are found in the cytoplasm of the cell body. Within the cell body, extremely fine neurofibrils extend from the dendrites into the axon. The axon is surrounded by the myelin sheath , which forms a whitish, non-cellular, fatty layer around the axon.
Outside the myelin sheath is a cellular layer called the neurilemma or sheath of Schwann cells. The myelin sheath together with the neurilemma is also known as the medullary sheath. This medullary sheath is interrupted at intervals by the nodes of Ranvier.
Nerve cells are functionally connected to each other at a junction known as a synapse , where the terminal branches of an axon and the dendrites of another neuron lie in close proximity to each other but normally without direct contact. Information is transmitted across the gap by chemical secretions called neurotransmitters. It causes activation in the post-synaptic cell.
Template:WikiDoc Sources. Category : Tissues. The relationship of these glial cells to the structure of the CNS is seen in Figure One of the two types of glial cells found in the PNS is the satellite cell. Satellite cells are found in sensory and autonomic ganglia, where they surround the cell bodies of neurons. This accounts for the name, based on their appearance under the microscope.
They provide support, performing similar functions in the periphery as astrocytes do in the CNS—except, of course, for establishing the BBB.
The second type of glial cell is the Schwann cell , which insulate axons with myelin in the periphery. Schwann cells are different than oligodendrocytes, in that a Schwann cell wraps around a portion of only one axon segment and no others. Oligodendrocytes have processes that reach out to multiple axon segments, whereas the entire Schwann cell surrounds just one axon segment.
The nucleus and cytoplasm of the Schwann cell are on the edge of the myelin sheath. The relationship of these two types of glial cells to ganglia and nerves in the PNS is seen in Figure Whereas the manner in which either cell is associated with the axon segment, or segments, that it insulates is different, the means of myelinating an axon segment is mostly the same in the two situations.
Myelin is a lipid-rich sheath that surrounds the axon and by doing so creates a myelin sheath that facilitates the transmission of electrical signals along the axon. The lipids are essentially the phospholipids of the glial cell membrane. Myelin, however, is more than just the membrane of the glial cell. It also includes important proteins that are integral to that membrane.
Some of the proteins help to hold the layers of the glial cell membrane closely together. The glial cell is wrapped around the axon several times with little to no cytoplasm between the glial cell layers. For oligodendrocytes, the rest of the cell is separate from the myelin sheath as a cell process extends back toward the cell body.
A few other processes provide the same insulation for other axon segments in the area. For Schwann cells, the outermost layer of the cell membrane contains cytoplasm and the nucleus of the cell as a bulge on one side of the myelin sheath. During development, the glial cell is loosely or incompletely wrapped around the axon Figure The edges of this loose enclosure extend toward each other, and one end tucks under the other.
The inner edge wraps around the axon, creating several layers, and the other edge closes around the outside so that the axon is completely enclosed. Myelin sheaths can extend for one or two millimeters, depending on the diameter of the axon.
Axon diameters can be as small as 1 to 20 micrometers. If the myelin sheath were drawn to scale, the neuron would have to be immense—possibly covering an entire wall of the room in which you are sitting. Several diseases can result from the demyelination of axons. The causes of these diseases are not the same; some have genetic causes, some are caused by pathogens, and others are the result of autoimmune disorders. Though the causes are varied, the results are largely similar.
The myelin insulation of axons is compromised, making electrical signaling slower. Multiple sclerosis MS is one such disease. It is an example of an autoimmune disease. The antibodies produced by lymphocytes a type of white blood cell mark myelin as something that should not be in the body. This causes inflammation and the destruction of the myelin in the central nervous system. As the insulation around the axons is destroyed by the disease, scarring becomes obvious.
This is where the name of the disease comes from; sclerosis means hardening of tissue, which is what a scar is. Multiple scars are found in the white matter of the brain and spinal cord. The symptoms of MS include both somatic and autonomic deficits.
Control of the musculature is compromised, as is control of organs such as the bladder. It is also the result of an autoimmune reaction, but the inflammation is in peripheral nerves. Sensory symptoms or motor deficits are common, and autonomic failures can lead to changes in the heart rhythm or a drop in blood pressure, especially when standing, which causes dizziness.
As an Amazon Associate we earn from qualifying purchases. Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4. Skip to Content Go to accessibility page. Anatomy and Physiology My highlights. Table of contents. Levels of Organization. Support and Movement.
Regulation, Integration, and Control. Fluids and Transport. Energy, Maintenance, and Environmental Exchange. Human Development and the Continuity of Life. By the end of this section, you will be able to: Describe the basic structure of a neuron Identify the different types of neurons on the basis of polarity List the glial cells of the CNS and describe their function List the glial cells of the PNS and describe their function.
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