Essential Clinically Applied Anatomy of the Peripheral Nervous System in the Limbs

Paul Rea

• Publisher: Academic Press
• Year: 2015
• Print ISBN: 9780128030622
• eBook ISBN: 9780128030639
• Topic: Medicine
• Subtopic: Neurology

Essential Clinically Applied Anatomy of the Peripheral Nervous System in the Limbs is designed to combine the salient points of the anatomy of the PNS with typical pathologies affecting the nerves of the upper and lower limbs. The book is a quick reference guide for those studying and treating neuromuscular disease such as neurologists, neurosurgeons, neuroradiologists, and clinical neurophysiologists. Readers will find easy-to-access facts about the anatomy of the nerves in the limbs, coupled with clinically applied scenarios relevant to that area being discussed, as well as clinical findings on examination. The book's purpose is to provide the reader with a succinct presentation of the relevant anatomy of the PNS in the limbs and how it is directly applicable to day-to-day clinical scenarios. It presents the reader with an easily accessible format to clinically applied PNS anatomy that is perfect for quick reference. Chapters review the nerves of the upper and lower limbs, and the origins, course, distribution and relevant pathologies affecting each. These pathologies present typical injuries to the nerves of the PNS, as well as clinical findings on examination and treatments. - Provides a resource on the anatomy of the PNS nerves in the limbs, including key facts and summary tables that are essential to clinical practice - Reports on typical injuries to the nerves of the PNS, as well as clinical findings on examination and treatments - Presents a succinct, yet comprehensive, format with quick and easy access facts for quick reference - Includes comprehensive chapters on nerves of the upper and lower limbs, discussing origin, course, distribution, and relevant pathologies

Chapter 1

Overview of the Nervous System

Abstract

Broadly speaking, the nervous system can be divided into two major areas – central and peripheral. The central nervous system comprises the brain and the spinal cord. The peripheral nervous system comprises all of the nerves – cranial, spinal, and peripheral, including the sensory and motor nerve endings of these nerves.

Keywords

central nervous system

spinal nerves

cranial nerves

forebrain

midbrain

hindbrain

hypothalamus

thalamus

peripheral nervous system

spinal cord

1.1. Divisions of the nervous system

1.1.1. Central Nervous System

The CNS is comprised of the brain and the spinal cord. The role of the CNS is to integrate all the body functions, from the information it receives. Within the peripheral nervous system (PNS), there are abundant nerves (group of many nerve fibers together), however, the CNS does not contain nerves. Within the CNS, a group of nerve fibers traveling together is called a pathway or tract. If it links the left- and right-hand sides, it is referred to as a commissure.

1.1.1.1. Neurons

Within the CNS, there are many, many millions of nerve cells called neurons. Neurons are cells that are electrically excitable and can transmit information from one neuron to another by chemical and electrical signals. There are three very broad classifications of neurons – sensory (which process information on light, touch, and sound to name some sensory modalities), motor (supplying muscles), and interneurons (which interconnect neurons via a network).

Typically, a neuron comprises a few simple features, though there are a variety of specializations that some have depending on the location they are found within the nervous system. In general, a neuron has a cell body. Here, the nucleus, or the powerhouse of the neuron, lies within its cytoplasm. At this point, numerous fine fibers enter called dendrites. These processes receive information from adjacent neurons keeping it up-to-date with the surrounding environment. Through these dendrites, the amount of information that a single neuron receives is significantly increased. From a neuron, there is a long single process of variable length called an axon. This conducts information away from the neuron, or the cell body. Some neurons however have no axons and the dendrites will conduct information to and from the neuron. In addition to this, a lipoprotein layer called the myelin sheath can surround the axon of a principal cell. This is not a continuous layer along the full length of the axon. Rather, there are interruptions called nodes of Ranvier. It is at this point where the voltage-gated channels occur, and it is here that conduction occurs. Therefore, the purpose of the myelin sheath is to enable almost immediate conduction between one node of Ranvier and the next, thus ensuring quick communication between neurons, and keeping those nerves up to date with body processes around them.

The size of neurons however varies considerably. The smallest of our neurons can be as small as 5 μm, and the largest, for example, motor neurons, can be as large as 135 μm. In addition, axonal length can vary considerably too. The shortest of these can be 100 μm, whereas a motor axon supplying the lower limb, for example, the toes, can be as long as 1 m.

In the PNS, neurons are found in ganglia, or in laminae (layers) or nuclei in the central nervous system (CNS).

Neurons communicate with each other at a point called a synapse. Most of these junctional points are chemical synapses where there is the release of a neurotransmitter that diffuses across the space between the two neurons. The other type of synapse is called an electrical synapse. This form is generally more common in the invertebrates, where there is close apposition of one cell membrane and the next, that is, at the pre- and postsynaptic membranes. Linking these two cells is a collection of tubules called connexons. The transmission of impulses occurs in both directions and rapidly. This is because there is no delay in the neurotransmitter having to be activated and released across the synapse. Instead, the flow of communication depends on the membrane potentials of the adjacent cells.

1.1.1.2. Neuroglia

Neuroglia, or glia, are the supportive cells for neurons. Their main purpose is not in relation to the transmission of nerve impulses. Rather, they are involved in provision of nutrients, maintenance of a stable homeostatic environment, and the production of the myelin sheath. There are two broad classifications of neuroglia – microglia and macroglia.

Microglia have a defensive role and...

Table of contents

• Cover
• Title page
• Table of Contents
• Copyright
• Preface
• Acknowledgments
• Chapter 1: Overview of the Nervous System
• Chapter 2: Upper Limb Nerve Supply
• Chapter 3: Lower Limb Nerve Supply
• Subject Index