Essential Clinically Applied Anatomy of the Peripheral Nervous System in the Head and Neck

By Paul Rea

Essential Clinically Applied Anatomy of the Nerves in the Head and Neck presents the reader with an easy access format to clinically-applied peripheral nervous system (PNS) anatomy. Perfect for a quick reference to essential details. The chapters review nerves of the head and neck, the origin(s), course, distribution and relevant pathologies affecting each are given, where relevant. The pathologies present typical injuries to the nerves of the PNS, as well as clinical findings on examination and treatments. It details modern clinical approaches to the surgery and other treatments of these nerve pathologies, as applicable to the clinical scenario.

• Surveys the anatomy of the PNS nerves in the head and neck
• Includes key facts and summary tables essential to clinical practice
• Offers a succinct yet comprehensive format with quick and easy access to facts and essential details
• Includes comprehensive chapters on nerves of the head and neck, discussing origin, course, distribution, and relevant pathologies

• Language: English
• Publisher: Academic Press
• Release date: Feb 11, 2016
• ISBN: 9780128036648

Paul Rea

Paul Rea graduated in Medicine from the University of Glasgow and then went into clinical training in a wide range of hospital specialties. He was then appointed as an Associate Lecturer in Anatomy at the University of Glasgow teaching medical, dental and science students. During his time as an Associate Lecturer in Anatomy, he was awarded a scholarship to undertake a part time MSc in craniofacial anatomy alongside his teaching duties. His research won the Scottish Royal Medico-Chirurgical Society of Glasgow prize. He returned to clinical practice in pathology receiving training in all areas of histopathology, including post-mortem analysis. He then returned to the University of Glasgow and was appointed as a University Teacher and subsequently Senior University Teacher. He is also one of the Licensed Teachers of Anatomy, appointed by St. Andrew’s House, Edinburgh. He teaches across the medical, dental and science programmes. He sits on many university committees and is a member of the Dental School Liaison Group. Paul has published in numerous journals and presented his work at many international conferences. He is also involved with public engagement with the Glasgow Science Centre as a Meet the Expert, and was key to the anatomical input to the international exhibition BodyWorks, and was a member of its Advisory Committee. He is also a STEM ambassador. His research involves a successful strategic partnership with the Digital Design Studio, Glasgow School of Art. This has led to multi-million pound investment in creating world leading 3D digital datasets to be used in undergraduate and postgraduate teaching to enhance learning and assessment. This successful collaboration has resulted in the creation of the world’s first taught MSc in Medical Visualisation and Human Anatomy combining anatomy and digital technologies with internationally recognised leading digital experts. Paul is the joint Programme Coordinator for this programme.

Book preview

Shaw-Dunn.

Chapter 1

Overview of the Nervous System

Abstract

This chapter will examine the nervous system providing an overview of the key components from its divisions. There are two main ways to examine the nervous system—from a structural viewpoint and also from a functional perspective. It will highlight the main areas of the brain and spinal cord, as well as the basic constituents of the cells of the nervous system. It introduces the concept of the sympathetic and parasympathetic nervous system and the major roles arts of the nervous system have.

Keywords

Central nervous system; peripheral nervous system; spinal cord; somatic nervous system; autonomic nervous system; functional division

1.1 Overview of the Nervous System

Broadly speaking, the nervous system is divided into two components—central and peripheral. The central nervous system (CNS) comprises the brain as well as the spinal cord. The peripheral nervous system (PNS) comprises all of the nerves—cranial, spinal, and peripheral nerves, including the sensory and motor nerve endings of these nerves.

1.2 Divisions of the Nervous System

1.2.1 Central Nervous System

The CNS is comprised of the brain as well as the spinal cord. The purpose of the CNS is to integrate all the body functions from the information it receives. Within the PNS, there are many, many nerves (group of 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.

1.2.1.1 Neurons

Within the CNS, there are many, many millions of nerve cells called neurons. Neurons are cells which are electrically excitable and 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 of the modalities), motor (supplying muscles), and interneurons (which interconnect neurons via a network).

Typically a neuron comprises some basic features, however there are a variety of specializations that some have dependent on the location within the nervous system. In general, a neuron has a cell body. Here, the nucleus—the powerhouse—of the neuron lies with 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. This way 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. 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 at that point where conduction occurs. Therefore, the purpose of the myelin sheath is to enable almost immediate conduction between one node of Ranvier and the next ensuring quick communication between neurons.

In relation to the size of neurons, this varies considerably. The smallest of neurons can be as small as 5 μm, with the largest for example motor neurons, can be as big 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 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 which 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 very quickly. 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 (Table