Health Assessment E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Serie: Vital Notes for Nurses
- Sprache: Englisch
Health assessment is central to effective planning, implementation and evaluation of nursing care. All nurses are accountable for the care they provide and need to be able to accurately determine patient needs in order to plan and deliver evidence-based care. Vital notes for nurses: Health assessment provides students with the knowledge required to consider the many different factors which can influence patient’s health, comfort, well-being and recovery and to confidently assess patient needs.
Vital notes for nurses: Health assessment explores concepts of holism, health and illness, factors to consider when assessing patients, communication skills needed for assessment, and all aspects of holistic assessment including physical, psychological, social, cultural and spiritual factors and nutritional needs.
* Provides a concise, accessible introduction to health assessment
* Includes physical, psychological, social, cultural and spiritual health assessment
* Explores essential concepts in assessment and care planning
* Within the Vital Notes for Nurses series
* Adopts a holistic approach
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Seitenzahl: 566
Veröffentlichungsjahr: 2015
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Table of contents
Cover
Title
Copyright
Preface
Acknowledgements
Dedication
List of contributors
1: The human body
Section 1: Introduction
Anatomical terms
Levels of organisation of the body
Hierarchy of functions
The basic structure of cells
Homeostasis
Organ systems
Section 2: The integumentary system
Structure of the skin
Thermoregulation and the skin
Section 3: The musculoskeletal system
The human skeleton
Bone
Joints
Muscular tissue
Section 4: The nervous system
Structure and function of the nervous system
The central nervous system (CNS)
The autonomic nervous system (ANS)
Sensations
Somatic senses
Pain
Section 5: The special senses
The eye
The ear
Section 6: The endocrine system
Hormones
Negative and positive feedback mechanisms
Section 7: The respiratory system
The mechanism of breathing
The transport of oxygen
The transport of carbon dioxide
Section 8: The cardiovascular system
The blood
The heart
Blood vessels: arteries, capillaries and veins
Section 9: The lymphatic and immune system
Components
Functions
Section 10: The digestive system
Functions
Organs of the digestive system and their location
Section 11: The urinary system
The kidney and its functions
Section 12: The reproductive system
Female reproductive system
The male reproductive organs
2: Nursing assessment and care planning
Introduction
Nursing assessment and the nursing process
Advantages of using a conceptual model in assessment
Key issues and developments
3: Concepts of health, illness and holism
Introduction
Being ‘healthy’
Health beliefs and health behaviour
Illness, sickness and disease
Seeing the person as a whole
Assessment
4: Factors to consider when assessing patients
Section 1: Introduction
Ethical aspects of assessment
Respect for persons - definition
Privacy
Confidentiality
Respect for dignity
Truthfulness
Section 2: The environment, health status, age and cognitive ability of the patient, learning disability and health assessment
Environment
Health status of the patient
The patient’s age
Cognitive development and ability
The assessment of children
Section 3: Gender and health assessment
Trends and patterns of health and disease among men and women
Health issues and dilemmas for men and women
A health assessment approach: some practical aspects to consider
5: Communication skills for holistic health assessment
Introduction
Definition and classification
Factors that facilitate effective communication
Skills needed during holistic health assessment
Barriers to communication during holistic assessment
Record keeping
6: Physical assessment
Section 1: Introduction
The purpose of physical assessment
Approach to physical assessment
Preparation for physical assessment
Techniques of physical assessment
The general survey and vital signs
Section 2: Physical assessment of the integumentary system
The skin
Assessment of nails
Assessment of hair (see Table 6.6)
Section 3: Physical assessment of the respiratory system
Taking a health history
Physical examination
Section 4: Physical assessment of the cardiovascular system
Relevant health history
Risk factors for coronary heart disease
Physical examination
Section 5: Physical assessment of the nervous system
Relevant health history
Examination
Section 6: Physical assessment of the eyes, ears, nose and throat
The eyes
The ears
The mouth, nose, sinuses and throat
Section 7: Physical assessment of the digestive system
Relevant health history
Risk factors
Physical assessment
Section 8: Physical assessment of the urinary tract system
Assessment of the urinary system
Assessment of the prostate gland
Section 9: Physical assessment of the musculoskeletal system
The musculoskeletal system (also see Chapter 1)
Assessment
Section 10: Physical assessment of the female and male reproductive systems
Examination of the breast
Examination of the female genitalia
Assessment of the male reproductive system
Record keeping
7: Assessment of nutritional status
Introduction
Purpose of nutritional assessment
Components of food
Nutritional requirements
Dietary guidelines
Assessing nutritional status
Dietary assessment
Nutritional interventions
8: Social assessment in healthcare
Introduction
The purpose of social assessment
Health policy: assessing social needs
Nursing models, social influences and assessment
Nursing and interprofessional approaches to social assessment
The social assessment/analysis framework
The levels of social assessment
9: Psychological assessment
Introduction
What is psychological health?
Why conduct a psychological assessment?
What to assess
How to conduct the psychological assessment
Nurses’ role in assessment
The assessment process
Accurate reporting and documentation
10: Cultural and spiritual health assessment
Cultural health assessment
Spirituality and spiritual needs
Glossary
Index
End User License Agreement
List of Tables
1: The human body
Table 1.1 Directional terms.
Table 1.2 Organelles and their functions.
Table 1.3 Major organ systems.
Table 1.4 Movements at synovial joints.
Table 1.5 The three main parts of the ear and their functions.
Table 1.6 Endocrine glands, their hormones and their functions.
Table 1.7 Components of lymphatic and immune system.
Table 1.8a Organs of the digestive system and their functions.
Table 1.8b Accessory organs of digestion.
Table 1.9 Processes in urine formation.
Table 1.10 Organs and functions of the female reproductive system.
Table 1.11 Male reproductive organs.
2: Nursing assessment and care planning
Table 2.1 Identification of problems and the range of actions to be taken.
Table 2.2 Use of nursing models of care for organising assessment data.
Table 2.3 Scoring of self-care activities (Eshun–Smith model of care, 1999).
Table 2.4 Example of a care plan.
3: Concepts of health, illness and holism
Table 3.1 Review of systems (see also Chapter 6).
4: Factors to consider when assessing patients
Table 4.1 Vital signs: normal range for different age groups.
Table 4.2 Overview of psychosocial and cognitive development stages (Mooney, 2000; Phillips, 1998; Whalley
et al.,
2002).
6: Physical assessment
Table 6.1 Types of structures assessed by different parts of the hands.
Table 6.2 Percussion sounds.
Table 6.3 General physical appearance assessment.
Table 6.4 Skin colour changes and their significance.
Table 6.5 Stages of pressure ulcer development (Potter & Perry, 2001).
Table 6.6 Examination of the hair.
Table 6.7 Examination of posterior and anterior thorax (Figure 6.3).
Table 6.8 Assessment of risk factors.
Table 6.9 Cardiovascular assessment.
Table 6.10 components of assessment of mental status
Table 6.11 The Glasgow Coma Scale.
Table 6.12 The type, function and assessment of the cranial nerves.
Table 6.13 The assessment of motor function.
Table 6.14 Assessment of sensory function.
Table 6.15 Common eye complaints.
Table 6.16 Examination of extraocular structures.
Table 6.17 Ear complaints and their assessment.
Table 6.18 Physical examination of the ear.
Table 6.19 Subjective assessment of the mouth, nose, sinuses and throat.
Table 6.20 Inspection of vomit and faeces.
Table 6.21 Possible finding on auscultation of the abdomen.
Table 6.22 Possible findings on assessment of the perianal region.
Table 6.23 Normal and abnormal characteristics of urine.
Table 6.24 Palpation of the prostate gland.
Table 6.25 Inspection of the breast and nipple.
Table 6.26 Palpation of the breast and nipple.
Table 6.27 Possible findings on assessment of the external genitalia.
Table 6.28 Assessment of internal genitalia.
Table 6.29 Functions of the male reproductive system.
Table 6.30 Assessment of the male reproductive system.
7: Assessment of nutritional status
Table 7.1 Examples of proteins in humans.
Table 7.2 Serving sizes for the food groups in the Food Guide Pyramid.
8: A Social assessment in healthcare
Table 8.1 Checklist of social diversity categories (adapted from World Bank, 2002).
List of Illustrations
1: The human body
Figure 1.1 Abdomino-pelvic regions
Figure 1.2 Hierarchy of phenomena in organisation of the human body
Figure 1.3 (a) A typical cell. (b) The plasma membrane (reproduced with permission from Bray
et al.
, 1999)
Figure 1.4 The feedback system
Figure 1.5 (a) The bony components of the elbow joint. (b) A joint capsule (reproduced with permission from Ellis, 2002)
Figure 1.6 A typical neuron (reproduced with permission from Bray
et al.
, 1999)
Figure 1.7 The brain (reproduced with permission from Bray
et al.
, 1999)
Figure 1.8 The spinal cord – transverse section through thoracic segment (reproduced with permission from Ellis, 2002)
Figure 1.9 Eye in horizontal section (reproduced with permission from Bray
et al.
, 1999)
Figure 1.10 The visual pathway (reproduced with permission from Bray
et al.,
1999)
Figure 1.11 Structure of the ear (reproduced with permission from Bray
et al
., 1999)
Figure 1.12 The upper and lower respiratory system (reproduced with permission from Bray
et al
., 1999)
Figure 1.13 The heart (reproduced with permission from Bray
et al
., 1999)
Figure 1.14 (a) Conduction system and ECG. (b) Standard ECG (reproduced with permission from Bray
et al
., 1999)
Figure 1.15 (a) The digestive tract (reproduced with permission from Bray
et al
.
,
1999). (b) The abdominal quadrants
Figure 1.16(a) The urinary tract system
Figure 1.16(b) A nephron (reproduced with permission from Bray
et al
., 1999)
Figure 1.17 The female reproductive system (reproduced with permission from Bray
et al
., 1999)
Figure 1.18 The male reproductive system (reproduced with permission from Bray
et al
., 1999)
2: Nursing assessment and care planning
Figure 2.1 Stages of the nursing process
Figure 2.2 The Eshun—Smith model
Figure 2.3 The care objectives of the Eshun–Smith model
3: Concepts of health, illness and holism
Figure 3.1 Factors that influence health behaviour, based on the health belief model
Figure 3.2 The health–illness continuum
5: Communication skills for holistic health assessment
Figure 5.1 The process of communication
Figure 5.2 Examples of possible barriers to communication
6: Physical assessment
Figure 6.1 Sites of peripheral pulses
Figure 6.2 Taking the blood pressure and types of equipment that can be used
Figure 6.3 (a) Percussion sequence. (b) Auscultation sequence
Figure 6.4 Sites for auscultation of the heart
Figure 6.5 Measurement of jugular venous pressure
Figure 6.6 The Glasgow Coma Scale – a neurological observation chart
Figure 6.7 (a-d) Normal and abnormal responses on testing reflexes
Figure 6.8 Abnormalities in the retina
Figure 6.9 (a) Otoscopic examination. (b) Examination of a child’s ear
Figure 6.10 Examination of lymph nodes
Figure 6.11 The neutral position
Figure 6.12 Abnormal curvatures of the spine
Figure 6.13 Quadrants of the breast
Figure 6.14 Examination of the breast. Arrows show direction and areas for palpation (adapted with permission from Cox, 2004)
Figure 6.15 External female genitalia (please label)
Figure 6.16 Internal female genitalia (please label)
Figure 6.17 Tanner staging. Pubic hair distribution stages 2–5 which assists in rating sexual maturity (Tanner, 1966)
Figure 6.18 Cervical smear. (a) Cytobrush in cervical canal. (b) Cervical smear with spatula
Figure 6.19 Height of uterine fundus during pregnancy
Figure 6.20 Self-examination of the testes. Each testis should be gently grasped between the thumb and fingers and rolled to ensure all surfaces are palpated, as shown by the arrows
7: Assessment of nutritional status
Figure 7.1 Triacylglycerol
Figure 7.2 The US Department of Agriculture food guide pyramid (www.usda.gov)
8: A Social assessment in healthcare
Figure 8.1 Overview of the social assessment/analysis framework. Entry points and dimensions of enquiry and the level at which assessment may be carried out at each entry point. Developed from the work of the World Bank (2002) and Stimson
et al.
(2003)
Figure 8.2 Basic sociogram
Figure 8.3 Social circles of support
9: Psychological assessment
Figure 9.1 The public and private self (based on Burnard, 1990) (reproduced with permission from Heinemann Professional Publishing)
Guide
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Health Assessment
Anna T Crouch
RGN, RMN, SCM, TCPC, ADM, CertEd,BA (Midwifery Studies),Ed Couns Skills Cert, MA (Ed) Open, ILM CertSenior LecturerThe University Of Northampton
Clency Meurier
RGN, RMN, DipN, CertEd, FETC Cert, BEd (Hons), MSc, PhD,Research Degree Supervision CertSenior LecturerThe University Of Northampton
© 2005 by Blackwell Publishing Ltd
Editorial offices:
Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK
Tel: +44 (0)1865 776868 Blackwell Publishing Inc., 350 Main Street, Malden, MA 02148-5020, USA
Tel: +1 781 388 8250 Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia
Tel: +61 (0)3 8359 1011
The right of the Author to be identified as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.
First published 2005 by Blackwell Publishing Ltd
ISBN-10: 1-4051-1458-4 ISBN-13: 978-1-4051-1458-5
Library of Congress Catalogining-in-Publication Data
Vital notes for nurses : health assessment / edited by Anna T. Crouch, Clency Meurier. p. ; cm.
Includes bibliographical references and index.
ISBN-13: 978-1-4051-1458-5 (alk. paper)
ISBN-10: 1-4051-1458-4 (alk. paper)
1. Nursing assessment. 2. Holistic nursing.
[DNLM: 1. Nursing Assessment. 2. Holistic Nursing. WY 100.4 V836 2005] I. Title: Health assessment. II. Crouch, Anna T. III. Meurier, Clency.
RT48.V58 2005 616.07¢5–dc22
2005013099
A catalogue record for this title is available from the British Library
The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards.
For further information on Blackwell Publishing, visit our website: www.blackwellnursing.com
Preface
The healthcare climate has been undergoing rapid changes, with renewed emphasis on holistic assessment and evidence-based care of clients and patients. There is also the broadening of the scope of practice for nurses, professional academic awards and professional standing for nurses. Nurses are also accountable for their practice and must be able to apply theory to practise safely and effectively. Hence, the knowledge and skills underpinning holistic health assessment to practise effectively to ensure protection of the public are of vital importance. Crucial to this will be the nurse’s ability to assess patients and clients holistically in a variety of settings, to identify their needs, plan and deliver evidence-based and holistic healthcare. Programmes for the education and preparation of nurses should therefore foster an enquiring approach to care. They should also encourage progressive development and the use of appropriate analytical, critical and problem-solving skills. It is important to provide opportunities for nursing students to gain the theoretical knowledge which informs the assessment of patients and clients, enabling them to become competent nurses, able to work safely, confidently and flexibly within a multidisciplinary team setting.
Most current books on health assessment in nursing tend to focus on detailed physical assessment of the client with little or no emphasis on a holistic approach. They are also based on American rather than on generic models of assessment. Moreover, there is little focus on the fundamental knowledge informing health assessment. The intention of this book is to fill such gaps.
This book will therefore be of particular relevance for undergraduate nursing students in foundation programmes both nationally and internationally. It will also be useful to return-to-nursing students and already qualified staff would find it a helpful teaching tool.
Anna Crouch and Clency Meurier
Acknowledgments
Special thanks to Blackwell Publishing for permission to use figures from Bray et al. (1999), Mallet and Dougherty (2000), Ellis (2002) and Cox (2004), as acknowledged within the text. Thanks also to Heinemann Professional Publishing for permission to use Figure 9.1 from Burnard (1990). Thanks to RCN Publishing Company Ltd and the World Health Organisation for giving us permission to adapt and use some of their material and information. Special thanks also to Beth Knight, Lisa Whittington and Amy Brown for their guidance and support.
We also wish to express thanks to Doreen Addicott HND Computing, Cert Ed, BTEC, for all the advice and help she gave in relation to the management of large documents to Gehric Barreau (IT Services), and to Ann Turner T.Dip COT, NA, FCOT (Principal Lecturer OT) for her advice and encouragement.
Special thanks to Sue Allen (Dean, School of Health) for her encouragement and support and to the following students, working colleagues and clinical staff for their comments and suggestions: Claire Barton (Student Nurse), Celina Mfukuo (Student Nurse), Evelyn Osei-Twum (Student Nurse, London South Bank University), Roberta Blankson (BSc Hons Nursing, Postregistration Student Nurse), A Salat (Student Nurse), Angela Hicks (RN, Dip HE, Clinician), Gloria Price (SRN SCM, Clinician), Julie Quilter (SRN, RM, ADM, CertEd, BSc, MA, Senior Lecturer), C Ager (SRN, SCM, DN, MTD, BSc Hons, MA, Principal Lecturer), David Bird (RGN, Adv Cert (HE), Burns & Plastic Nursing (ENB), BSc Hons (Human Biology), MSc, Senior Lecturer), Linda Lilley (RGN, RNT, DMS, FETC, BEd, Senior Lecturer), Penny Paradine (support staff).
Thanks also to A Crouch for the following line drawings: Figures 1.1, 1.3a, 1.4, 1.15b, 1.16a, 2.1, 3.1, 3.2, 5.1, 5.2, 6.13, 6.14, 6.15, 6.16, 6.17, 6.18, 6.19, 6.20, 8.1, 8.2. Thanks also to J Aldridge for Figure 8.3.
Last but not least, thanks to Ian and Peter for their patience and support when needed, and to our Lord Jesus who made the writing of this book possible.
Anna Crouch and Clency Meurier
Dedication
I would like to dedicate this book to the Lord Jesus.
Anna Crouch
I would like to dedicate the book to Marnie, Christopher and Annabel
Clency Meurier
List of contributors
John Aldridge RMN, RMNH, CertEd, MA Senior Lecturer, The University Of Northampton
Sue Allen SRN, SCM, DipNurs, DipNursEd, RNT, MSc Dean, School of Health, The University Of Northampton
Janis Brown RGN, Clin Teaching Cert, CertEd, BSc (Hons) Open, MSc (Science) Open Senior Lecturer, The University Of Northampton
Anna T Crouch RGN, RMN, SCM, TCPC, ADM, CertEd, BA (Midwifery Studies), Ed Couns Skills Cert, MA (Ed) Open, ILM Cert Senior Lecturer, The University Of Northampton
Adelaide Eshun RGN, Cert HSM, BSc (Hons) (Health Sc) Lecturer, The University Of Northampton
Moira Ingham RGN, RNT, MA (Hons) (English & History), MSc (Nursing) Associate Dean, The University Of Northampton
Clency Meurier RGN, RMN, DipNurs, CertEd, FETC Cert, BEd (Hons), MSc, PhD, Research Degree Supervision Cert Senior Lecturer, The University Of Northampton
Stephen O’Brien RGN, RMN, RCNT, BEd (Hons), MSc Principal Lecturer, The University Of Northampton
James O’Reilly BSc, MSc, PhD Senior Lecturer in Human Nutrition, University College of Chester
Jackie H Parkes RMN, BA (Hons), MMedSci, PGDip Principal Lecturer, The University Of Northampton
Graham Rumbold RGN, RNT, CHNT, NDN, BA, MSc Senior Lecturer, The University Of Northampton
Michelle Thompson SRN, RNT, CertEd, FETC, BSc, MSc Principal Lecturer, The University Of Northampton
Wendy Turner RN (LD), RNDip HE Child, ENB 998, PG CertEd, BA (Hons) Evidence Based Practice Senior Lecturer, The University Of Northampton
1The human body
C Meurier
Learning objectives
Use appropriate anatomical terminologies to describe the location of the different organs of the body.
Discuss the relationship between cells, tissues, organs and systems in relation to the whole organism.
List the components of each body system and explain how they contribute to the function of the system.
Discuss how the different parts and systems of the body work together to maintain homeostasis.
Section 1: Introduction
Whether a health assessment is being performed to identify a health problem or to evaluate risk factors for health education purposes, a good understanding of biological knowledge is important (Carroll, 2004). Familiarisation with the common terminologies used for the different structures of the body, for example, enables effective communication of assessment findings to colleagues and other health professionals. Disease states and their impact can only be fully appreciated against the background of normal body structure and functions. In this chapter, the body will be looked at in a systematic way, starting from an examination of its basic organisation and the maintenance of internal stability to looking at individual organ systems.
Anatomical terms
To begin with, it is useful to provide an orientation of the body – looking at body regions, directional terms to describe one body part relative to another, and spaces and cavities that contain the different internal organs. This will facilitate precise and concise reporting of the assessment of the body. By using the exact anatomical term to describe the area of complaint of a particular symptom, attention can be focused more quickly to that specific area (Thibodeau & Patton, 2004).
Body regions
The body is conventionally divided into two major regions:
Axial.
This consists of the head, face, neck and trunk or torso.
Appendicular.
This consists of the shoulder girdles, the upper limbs, pelvic girdles and lower limbs.
Directional terms
Directional terms are used to locate body structures. They are usually grouped in opposite pairs, e.g. superior/inferior, anterior/ posterior. Directional terms only make sense when they are used to describe one structure relative to another. We refer, for example, to the elbow being superior to the wrist although they are both located in the superior aspect of the body. Directional terms are shown in Table 1.1.
Body cavities
The internal organs are located within spaces in the body called cavities. There are two main cavities: dorsal and ventral. The dorsal cavity, situated near the dorsal surface of the body, contains the brain in the cranial cavity and the spinal cord in the vertebral canal. The ventral cavity, located near the anterior part of the body, can be further divided into three cavities, namely thoracic, abdominal and pelvic. The diaphragm separates the thoracic cavity from the abdominal cavity. The largest organs in the thoracic cavity are the lungs. The heart is embedded in the mediastinum, i.e. the space between the two lungs. There is no physical separation between the abdominal and pelvic cavities and they are often referred to as the abdominopelvic cavity. The cavities contain internal organs that are collectively called viscera. To enable the precise location of organs, the abdominopelvic cavity is divided into nine smaller compartments as shown in Figure 1.1.
Table 1.1Directional terms.
Directional term
Definition
Examples
Superior
Towards the top. Upper part of a structure. Towards the head (cephalic or cranial)
The head is superior to the lower limbs and the knee is superior to the ankle
Inferior
Towards the bottom. The lower part of a structure. Away from the head
The diaphragm lies inferiorly to the lungs
Anterior or ventral
Towards the front
The sterrnum is anterior to the heart
Posterior or dorsal
Towards the back
The thoracic vertebrae are posterior to the heart
Medial
Towards the midline
The heart is medial to the lungs
Lateral
Further away from the midline. Towards the sides
The lungs are lateral to the heart
Proximal
Refers to a structure that is closer to any point of reference
The proximal part of the nerve running along the arm is the part closest to the spinal cord
Distal
Further away from a point of reference
In the hand, the phalanges are distal to the carpals
Superficial
Towards or on the surface of the skin
The skin is superficial to the muscles
Deep
Away from the surface of the body
The intestines are deep to the surface of the skin of the abdomen
Figure 1.1 Abdomino-pelvic regions
Levels of organisation of the body
The human body and its many parts are categorised into six levels of organisation, which influence body structure and functions. Ranging from the smallest to largest, these differing levels are as follows.
Chemical level
The body is made up of atoms and molecules. Atoms (e.g. carbon, oxygen, hydrogen) are the smallest units of matter. When two or more atoms joined together, they become molecules (e.g. water). Molecules in turn combine with other atoms and molecules to form macromolecules in the cytoplasm of the cells, which enables normal cellular functions. If this is not maintained, disease or death may result.
Cellular level
Cells are the basic structural and functional units of an organism. They consist of atoms and molecules. Each human organism begins life as a single cell, when the sperm fertilises the ovum. The fertilised ovum, now called a zygote, then divides into two cells, four cells, eight cells and so on. During development, these cells undergo differentiation, i.e. the transformation of unspecialised cells into specialised cells.
Tissue level
Tissues are aggregates of cells that work together to perform a particular function. The cells of the body are organised into four primary tissues: epithelial, connective, muscle and nervous. Epithelial tissue covers body surfaces and, lines cavities, hollow organs and ducts. Connective tissue is mainly a support tissue, connecting, anchoring and supporting the structures of the body. Connective tissue is characterised by large amount of extracellular material, called matrix, in the spaces between the connective tissue cells. Muscle tissue is responsible for movement. Nervous tissue consists of neurons and neuroglia. Neurons generate and transmit messages whereas neuroglia provide neurons with anatomical and functional support.
Organ level
Two or more different types of tissues join together to form an organ. For example, the heart is an organ and is composed of three different types of tissues: epithelial (endothelial), muscle and connective. Organs have specific functions. The specific function of the heart is to pump blood.
System level
A system is a group of organs that work together to perform a common function. The heart and blood vessels work together to transport blood around the body and is referred to as the cardiovascular system. The other systems of the body are integumentary, skeletal, muscular, nervous, respiratory, lymphatic and immune, gastrointestinal, urinary, endocrine and reproductive.
Organism level
All structures and systems in the body combine to make the human organism.
Hierarchy of functions
The levels of organisation show something of a hierarchy but each level in the hierarchy is as important as the other. Disturbance at one level may affect the activity of the other levels. This can go up or down the hierarchy as shown in Figure 1.2. For example, the chemicals within the cells influence their function, which in turn affects the activity at the next level and so on. Events at the level of the organism (and ultimately in the environment) can also affect activities of the lower levels. For instance, the availability or choice of diet can affect the functions of the cells.
The basic structure of cells
The human body is composed of billions of cells and the functions of these cells ultimately determine the function of the human organism.
Figure 1.2 Hierarchy of phenomena in organisation of the human body
Cells are the basic unit of structure and function of the body. Cells become specialised for different tasks but their basic structure remains essentially the same. A cell has three parts (Figure 1.3):
an outer membrane or plasma membrane
cytoplasm
nucleus (some cells, e.g. erythrocytes do not have a nucleus).
The plasma membrane
The plasma membrane is a phospholipid bilayer, into which a variety of proteins are immersed, that forms the boundary between the intracellular and extracellular environments of the cell. It controls the selective passage of substances into and out of the cell. The proteins within the cell membrane have a variety of functions. Some proteins form channels for substances to pass through. Others act as receptors, cell recognition molecules, adhesion molecules and enzymes.
The cytoplasm
The cytoplasm consists of all the contents, including the intracellular fluid (cytosol) and organelles, between the nucleus and the cell membrane. The organelles (listed in Table 1.2) are necessary for the biological processes of cellular life.
The nucleus
The nucleus is the most prominent intracellular structure and is found in most cells. Cells like the skeletal cells have multiple nuclei, while erythrocytes or red blood cells have none (Widmaier et al., 2004). The nucleus contains the genetic material, deoxyribonucleic acid (DNA). The DNA molecules are organised into genes, which carry the information that passes from one generation to the next and also contain the code for protein synthesis. Genes are arranged into single files of DNA called chromosomes. Chromosomes also contain a special class of proteins called histone proteins or histones. In humans, there are 46 chromosomes.
Although the DNA contains the code for specifying the amino acid sequences in proteins, it does not itself participate directly in the synthesis of proteins in the ribosomes (Widmaier et al., 2004). Information is transferred to the ribosomes for the assembly of proteins by the ribonucleic acid (RNA). The process of making a copy of the code, whereby information is transferred from the DNA to RNA, is called transcription. The RNA, also known as messenger RNA, then leaves the nucleus to travel to the ribosomes where the coded information in the RNA is used to assemble the protein – a process known as translation. An alteration in the sequence of the DNA is known as a mutation. The resulting faulty code can lead to the synthesis of an abnormal protein, e.g. faulty haemoglobin in sickle cell disease.
Figure 1.3(a) A typical cell. (b) The plasma membrane
(reproduced with permission from Bray et al., 1999)
Table 1.2Organelles and their functions.
Organelles
Functions
Mitochondria
Scattered throughout the cells, they are the sites of energy (ATP) production
Ribosomes
Sites of protein synthesis
Rough endoplasmic reticulum (rough ER)
A network of folded membranes. Rough ER is studded with ribosomes
Smooth endoplasmic reticulum (smooth ER)
Smooth ER has no ribosomes attached to its surface. Fatty acids, steroids and cholesterol are synthesised in smooth ER
Golgi complex
Flat membrane-like sacs. Newly synthesised proteins are modified in the Golgi complex and packed into vesicles that are then transported to where they are needed in the cell or exported out of the cell by a process called exocytosis
Lysosomes
Vesicles which contain digestive enzymes for the breakdown of molecules
Centrosome
Consists of two centrioles and is important in cell division
Cytoskeleton
A network of microfilaments in the cytoplasm contributing to the cell’s strength and shape. Also helps to generate movements
The environment of the cells
Cells have a fluid environment. There is fluid within the cells, around the cells and in the blood vessels. The fluid inside the cells is called intracellular fluid and that outside the cells extracellular or interstitial fluid. The fluid contains various salts or electrolytes as well as many dissolved substances, such as nutrients and oxygen. The composition of the intracellular fluid differs from that of extracellular fluid. Body fluids are located within two main compartments:
intracellular fluid (28 L in a 70 kg person) and
extracellular fluid (14 L in a 70 kg person, of which 11L is interstitial fluid and 3L plasma).
Homeostasis
For the body to function normally, the internal environment of the cells has to stay relatively constant. Variables such as the chemical composition of the fluid that surrounds the cells, its temperature, acid level (pH) and glucose level have to remain stable for the cells to function optimally. Homeostasis is defined as a state of relative constancy of the internal environment (Fox, 2004). This is achieved by the balancing of inputs and outputs (Widmaier et al., 2004). All organ systems contribute to homeostasis but the nervous and endocrine systems in particular play a vital role.
Feedback systems
The stability of the internal environment is maintained by feedback systems or feedback loops (Figure 1.4), which is a concept derived from engineering. A feedback system is a cycle of events whereby the status of a controlled condition is continually monitored and adjusted as required. It has three basic components:
Receptor.
The receptor monitors changes in the controlled condition and sends the input to the control centre.
Control or integrating centre.
The control centre evaluates the input and sends an output to the effector.
Effector.
The effector receives the output from the control centre and produces a response to the changes in the controlled condition.
Figure 1.4 The feedback system
Table 1.3Major organ systems.
System
Organs and tissues
Functions
Integumentary
Skin, appendages
Protection against injury and dehydration. Defence against micro-organisms. Temperature regulation
Musculoskeletal
Bones, cartilage, ligaments, tendons, joints, skeletal muscle
Support. Protection. Movement. Red bone marrow produces blood cells
Nervous
Brain, spinal cord, peripheral nerves, cranial nerves, special sense organs
States of consciousness. Regulation and co-ordination of many body functions. Detection of changes in internal and external environment
Endocrine
Glands producing hormones – pituitary, thyroid, parathyroid, adrenal, pancreas, testes, ovaries
Regulation and co-ordination of activities such as growth, metabolism, reproduction, blood pressure, water and electrolytes balance
Respiratory
Nose, pharynx, larynx, trachea, bronchi, lungs
Exchange of carbon dioxide and oxygen. Regulation of blood pH
Cardiovascular
Heart, blood vessels (arteries, veins, capillaries), blood, lymphatic vessels and lymph
Transport of blood and other materials
Lymphatic and immune
Lymph vessels and nodes, spleen, thymus, white blood cells
Return of lymph to the blood. Defence against foreign invaders
Digestive
Mouth, pharynx, oesophagus, stomach, intestines and accessory organs such as salivary glands, pancreas, liver and gall bladder
Digestion and absorption of nutrients, water and salts
Urinary
Kidneys, ureters, bladder, urethra
Regulation and composition of body fluids through control secretions of salts, water and wastes
Reproductive
Male: testes, penis and associated ducts and glands
Production of sperm, transfer of sperm to females
Female: ovaries, fallopian tubes, vagina, mammary glands
Production of eggs, provision of a conducive environment for the developing embryo and foetus, nutrition of the infant
Negative and positive feedback systems
There are two types of feedback system: negative and positive. The negative feedback system reverses or opposes changes in a controlled condition. For example, if the blood glucose is rising or falling, it returns it to normal through a series of actions. A negative system is important for the maintenance of health. A positive feedback system reinforces changes in a controlled condition and is on the whole detrimental to health, e.g. if the body temperature starts to rise, the positive feedback system will amplify the rise.
Homeostasis and disease
Homeostasis promotes normal cellular activity (Tortora & Grabowski, 2004). Homeostatic functions operate with maximum efficiency and effectiveness during childhood and young adulthood but become less and less efficient in late adulthood and old age (Thibodeau & Patton, 2004). A disorder or disease may occur if the normal balance of the body’s processes is disturbed. If the homeostatic imbalance is severe, death may result. Tortora & Grabowski (2004) define a disorder as any disturbance of structure and/or function, and a disease as an illness characterised by a recognisable set of symptoms (subjective changes of body functions) and signs (observable changes).
Organ systems
Most of the cells of the body are isolated from the external environment. Consequently, they rely on the organ systems for their ‘servicing’, i.e. obtaining materials that are needed for their functions and removing the waste products of metabolism. As discussed, through the homeostatic regulatory mechanisms, the organ systems also ensure that the internal environment of the cells stays relatively stable. Widmaier et al. (2004) identify ten major organ systems. These are listed in Table 1.3.
Section 2: The integumentary system
The integumentary system includes the skin and its appendages, i.e. hair, nails and specialised sweat- and oil-producing glands. The skin covers the external surface and is the largest organ of the body, accounting for about 16% of the total body weight. Knowledge of anatomy and physiology of the skin and its major roles in thermoregulation, protection, sensation and vitamin D metabolism can assist nurses in assessment of skin conditions and general physiological disturbances (Casey, 2002). In fact, the skin acts as a window for many systemic disorders. For example, signs of cardiovascular, respiratory, renal, hepatic and digestive disorders may be observed in the skin. Because of its exposed location, the skin is also vulnerable to damage from trauma and pressure, burns, ultraviolet light, micro-organisms, parasites, fungi, pollutants and allergens. Inspection of skin is a fundamental part of health assessment.
Structure of the skin
The skin consists of two main parts:
epidermis
dermis.
Subcutaneous (adipose) tissue connects the skin to underlying structures but is not part of the skin. It stores fat and also contains large blood vessels and pressure receptors.
Epidermis
The epidermis is the outer epithelial layer of the skin. It is composed of four or five distinct layers or strata. The deepest layer is the stratum basale, which continually undergoes mitotic activity or cell division to produce new skin cells. These are slowly pushed to the surface. The stratum basale also contains melanocytes, which produce melanin. Melanin provides protection from ultraviolet radiation. Ultraviolet radiation, as well as systemic hormones such as adrenocorticotrophic hormone (ACTH), stimulates production of melanin. Excess ACTH production by the pituitary gland, as in adrenal insufficiency or Addison’s disease, results in the skin becoming very tanned (Porth, 1998). If the stratum basale is destroyed, the skin cannot regenerate itself and scar tissue is formed. The outermost layer of the skin consists of dead keratinised cells that act as a strong protective barrier. Protection against mechanical abrasion is linked to the ability of the skin to desquamate (Tortora & Grabowski, 2004).
Dermis
The dermis is the inner layer of the skin and is connected to the epidermis by papillae. It is made of connective tissue containing collagen and elastic fibres, which give the skin its strength and elasticity. The dermis contains blood vessels and various sensory receptors as well as hair follicles and sweat glands. The deep veins in the dermis act as a reservoir for approximately 1.5 litres of blood (Bray et al., 1999). This blood is pushed back into the general circulation during haemorrhage or shock through the action of the sympathetic nervous system. This diversion of blood makes the skin look pale, cool and mottled in appearance (Porth, 2005).
The hypodermis or subcutaneous tissue
This is not strictly speaking part of the skin. The hypodermis contains a layer of subcutaneous fat cells (or adipose tissue), which forms the link between the skin and the rest of the body. The hypodermis provides a cushioning layer and some thermal insulation (Tortora & Grabowski, 2004).
The appendages or accessory structures of the skin
The hair
The human skin is covered with millions of hairs, most visible in the scalp, eyelids and eyebrows while the lips, palms of the hands and soles of the feet are hairless (Thibodeau & Patton, 2004). In response to hormone secretion at puberty, coarse hair develops in the pubic area and axilla.
Hair consists of a shaft and root. The root penetrates deep into the dermis and surrounding it is the hair follicle. Hair growth begins from a cluster of cells called the hair papilla located at the base of the hair follicle. The papilla is nourished by a dermal blood vessel. Sebaceous glands and arrector pili muscles are associated with the hair follicle.
The nails
The nails are plates of hard keratinised cells, consisting of a nail body, free edge and nail root. Under the nail is a layer of epithelium called the nail bed. The nail bed has a pink tinge as a result of the rich blood supply underneath and low oxygen levels in the blood cause the nail bed to turn blue or cyanosed (Thibodeau & Patton, 2004).
Skin glands
These are of two types: sudoriferous or sweat glands and sebaceous glands. The sweat glands are grouped into eccrine and apocrine glands. The eccrine glands are numerous and they produce a watery substance called perspiration or sweat, the main function of which is to assist in the reduction of body temperature. Indeed, evaporation of sweat from the skin surface is responsible for about 15% of heat loss at room temperature (Bray et al., 1999). The apocrine glands are found primarily in the skin of the armpit and around the genitals and produce a thick fluid. The odour associated with this secretion is due to contamination and decomposition of skin bacteria (Thibodeau & Patton, 2004).
The sebaceous glands secrete an oily substance known as sebum in the hair and skin. This lubricates the skin and hair. The increase in dryness and cracking of the skin in late adulthood and old age is due to a reduction of sebum secretion (Thibodeau & Patton, 2004).
Thermoregulation and the skin
By regulating sweat secretion and the flow of blood close to the surface of the body, the skin plays a key role in the regulation of body temperature (Thibodeau & Patton, 2004). This is achieved by a negative feedback system in which an ‘increase or decrease in the variable being regulated brings about responses that tend to move the variable in the direction opposite the direction of the original change’ (Widmaier et al., 2004: p9). Any changes in body temperature are detected by thermoreceptors in the skin and deeper organs. The information is fed back to the control centre (i.e. hypothalamus), which in turn will send impulses to the effector organs to adjust the body temperature. If the body temperature is high, there is vasodilation of the blood vessels in the skin, allowing warm blood to flow close to the skin surface, hence causing heat loss to the environment. Conversely, when the body temperature drops, vasoconstriction of the skin blood vessels takes blood away from the surface to effect a reduction in heat loss.
Section 3: The musculoskeletal system
The musculoskeletal system consists of the bones, skeletal muscles and joints. The overall function of the musculoskeletal system is to provide a rigid framework and support structure for the body as well as allowing movement in conjunction with the nervous system. Familiarity with the names, shapes and positions of individual bones enables one to locate other organs, e.g. the radial artery, where the pulse is usually taken, is named for its closeness to the radius (Tortora & Grabowski, 2004).
The human skeleton
The skeleton has two principal divisions: axial and appendicular. The axial skeleton includes the bones of the skull, face, ossicles, hyoid bone, ribs, sternum and vertebrae. The appendicular skeleton consists of the bones of the upper and lower limbs as well as the girdles (shoulder and pelvic), which connect the limbs to the axial skeleton. There are 206 bones in the adult (although there may be some biological variations): 80 in the axial skeleton and 126 in the appendicular skeleton (Tortora & Grabowski, 2004).
Bone
Bone is a connective tissue, consisting of a hard matrix that surrounds widely separated cells. The matrix also contains collagen fibres and calcium phosphate, providing flexibility and hardness. There are two types of bone: compact and cancellous. Compact bone is hard and dense and forms the external layer of all bones and the bulk of the diaphyses or shafts of long bones. Cancellous or spongy bone tissue makes up the ends (epiphyses) and centres of the bones.
Functions of skeleton and bone tissue
Bones perform the following functions:
support for the body and soft tissues
protection of internal organs
movement, in conjunction with the skeletal muscles and motor neurons
production of blood cells in the red bone marrow
storage of calcium and phosphate.
Joints
The joint is the point of contact between bones, between cartilage or between teeth and bones (Tortora, 2005). There are three types of joints: synovial, cartilaginous and fibrous:
Synovial joints
have space between the articulating bones, allowing them to be freely movable.
Figure 1.5
shows the special characteristics of synovial joints.
Cartilaginous joints
are held together by cartilage and only allow slight movement. There is no cavity between the bones.
Fibrous joints
are joined together by fibrous connective tissue. They permit no movement, e.g. cranial joints.
Types of movements at synovial joints
The shapes of the articulating surfaces in synovial joints dictate the types of movements that are possible. The principal movements are shown in Table 1.4.
Table 1.4 Movements at synovial joints.
Movements
Description
Flexion
Bending
Extension
Stretching out
Abduction
Movement away from the midline
Adduction
Movement toward the midline
Circumduction
Movement of the distal part of the body in a circle. The ball and socket joints (e.g. shoulder and hip joints) permit circumduction
Figure 1.5(a) The bony components of the elbow joint. (b) A joint capsule
(reproduced with permission from Ellis, 2002)
Muscular tissue
There are three types of muscular tissue: skeletal, smooth and cardiac. Skeletal muscles are attached to bones by tendons and move the skeleton. A few skeletal muscles (e.g. facial muscles) are attached to structures other than bone. When skeletal muscle tissues are examined under the microscope, alternating light and dark bands are visible; hence they are called striated muscles. As skeletal muscles can be consciously controlled, they are also referred to as voluntary muscles (Tortora, 2005) and are supplied by the voluntary nervous system. Skeletal muscles also assist with posture and produce body heat when contracting.
Smooth muscles are located in the walls of hollow organs (e.g. blood vessels, digestive tract, bronchi). They appear non-striated under the microscope, hence the term smooth. Smooth muscles control internal processes such as peristalsis and blood pressure. They are termed involuntary muscle because they are not under our conscious control but are regulated by the autonomic division of the nervous system.
Cardiac muscle is the middle layer (myocardium) of the heart. Contraction of the heart muscle enables blood to be pumped round the body. The action is involuntary, i.e. cannot be consciously controlled. The heart muscle has the property of autorhythmicity, i.e. it has a builtin rhythm whereby each cardiac contraction is initiated by its own pacemaker or sinoatrial node, although its rate is adjusted by the autonomic nervous system (Tortora, 2005).
Section 4: The nervous system
Along with the endocrine system (see page 28), the nervous system is responsible for co-ordinating and regulating body functions, thus playing a crucial part in the maintenance of homeostasis. The nervous system has a rapid mode of action whereas the endocrine system acts more slowly.
Structure and function of the nervous system
The functional units of the nervous system are the neurons. Neurons are specialised to respond to physical and chemical stimuli and conduction of nerve impulses (Fox, 2004). They are supported by neuroglia. Unlike mature neurons, neuroglia are able to multiply and divide. In fact, brain tumours are derived from neuroglia and not neurons (Fox, 2004).
A neuron (Figure 1.6) is divided into three parts: a cell body, dendrites and an axon. The cell body and dendrites receive the input or stimulus to the cell; the outputs are sent down by the axon in the form of impulses (action potentials). The points of contacts between neurons are called synapses. When an impulse reaches the end of an axon terminal, it triggers the release of neurotransmitters from vesicles, enabling the impulse to cross the synapse and depolarise the next neuron. Figure 1.6 shows the structure of a motor neuron.
Figure 1.6A typical neuron
(reproduced with permission from Bray et al., 1999)
The nervous system consists of two structural divisions: the central nervous system (CNS) and the autonomic nervous system (ANS).
The central nervous system (CNS)
The CNS is composed of the brain and spinal cord. These are very delicate structures and, besides being encased in bones, are protected by three connective tissues layers: the dura mater, arachnoid mater and pia mater. There is a space called the subarachnoid space between the dura and arachnoid mater, into which cerebrospinal fluid (CSF) circulates. The CSF acts as a shock absorber as well as providing nourishment for the nervous tissue. Inflammation of the meninges is called meningitis and is usually caused by bacterial or viral infection.
The brain
The brain is located within the cranial cavity. It can be subdivided into four major divisions: the cerebrum, diencephalon (thalamus and hypothalamus), the brainstem (midbrain, pons and medulla) and cerebellum. Figure 1.7 shows the brain.
The cerebrum
The cerebrum is the most prominent part of the human brain, accounting for about 80% of its mass, and is divided into the right and left cerebral hemispheres (Fox, 2004). The corpus callosum, a bundle of nerve fibres, connects the two hemispheres across the midline; it enables transfer of information between the two hemispheres. The outer layer of the cerebrum, called the cerebral cortex, consists of grey matter or cell bodies, which are responsible for higher functions such as motor and sensory functions, speech, memory and other intellectual faculties. The inner layer of the cerebrum, or white matter, consists mostly of myelinated nerve fibres, enabling communication to various regions of the brain as well as the spinal cord.
Each cerebral hemisphere can be anatomically divided into four major lobes: frontal, temporal, parietal and occipital lobes. Each lobe is responsible for a specific function. For instance, the primary motor cortex, located in the frontal lobe, initiates voluntary motor movement to the opposite sides of the body and Broca’s area is responsible for motor speech (Tortora & Grabowski, 2004). The primary somatosensory area is located in the parietal lobe and receives sensory information from the body via the thalamus. The cerebral cortex has projection fibres that connect the cortex to the spinal cord. These projection fibres, also called the pyramidal tract, cross over at the medulla oblongata so that fibres from the left hemisphere supply the right side of the body and vice versa. Afferent or sensory fibres also cross over in the CNS so that sensory information from the right side of the body is taken to the sensory cortex in the left hemisphere and that of the left side of the body to the right hemisphere. Thus, damage to the left hemisphere, as in a stroke, will cause paralysis and loss of sensation to the right side of the body. Wernicke’s area is located in the temporal lobe and parietal lobes and is responsible for interpreting the meaning of speech by recognising the spoken word (Tortora & Grabowski, 2004).
Figure 1.7The brain
(reproduced with permission from Bray et al., 1999)
The basal ganglia or basal nuclei are located deep within the white matter of the cerebrum and are essential for producing automatic movements and postures (Thibodeau & Patton, 2004).
The diencephalon
This is located beneath the cerebral hemispheres and contains the thalamus and hypothalamus. The thalamus is a sensory relay centre and conveys sensory information from the periphery to the sensory cortex and from one brain area to another. It also processes incoming sensory signals, determining whether sensory information will reach the cerebral cortex. The thalamus is part of the system that promotes alertness and causes arousal from sleep (Fox, 2004). The hypothalamus, located below the thalamus, is concerned with maintaining the internal environment of the body. It links the nervous system to the endocrine system through its connection to the pituitary gland.
The brainstem
The brainstem is formed by the midbrain, pons varolii and medulla oblongata. Located between the cerebral cortex and the spinal cord, it is concerned with the basic activities necessary for life. Vital centres such as the cardiac, respiratory and vasomotor centres are located in the medulla. The brainstem also consists of clusters of nuclei known as the reticular formation that modulate the activity of neurons in other brain regions and in the spinal cord (Fox, 2004). The ascending part of the reticular formation, called the reticular activating system (RAS), regulates the sleep–wake cycle. A state of wakefulness or consciousness is maintained when the RAS stimulates the cerebral cortex. Loss of consciousness results from damage to the RAS and/or cerebral cortex.
The cerebellum
The cerebellum lies behind the brainstem and under the cerebrum. It is concerned with co-ordinating body movements, maintaining posture and learning motor skills. Lesions in the cerebellum affect muscle coordination, causing a condition of ataxia.
The spinal cord
The spinal cord is a long, thin cylinder of nervous tissue located in the vertebral canal. It extends from the medulla oblongata to the first lumbar vertebra. The spinal cord consists of two regions: an H-shaped inner region of grey matter and an outer region of white matter. The grey matter consists of two dorsal horns and two ventral horns. Sensory or afferent nerves enter the spinal cord at the dorsal horns and motor or efferent nerves exit at the ventral horns. Each sensory nerve brings sensory information from very specific areas of the skin called dermatomes. Each motor neuron, on the other hand, innervates a small number of muscle fibres, controlling their contraction. The spinal cord has 31 segments (a thoracic segment is shown in Figure 1.8), giving rise to 31 pairs of spinal nerves (also called peripheral nerves) as follows:
Figure 1.8The spinal cord – transverse section through thoracic segment
(reproduced with permission from Ellis, 2002)
Cervical nerves
(C1 to C8): supplying the neck, arms and hands.
Thoracic nerves
(T1 to T12): supplying the chest or thorax, the upper abdomen and back.
Lumbar nerves
(L1 to L5): supplying lower abdomen, the back and front of legs.
Sacral nerves
(C1 to C5): supplying the genitals, regions surrounding the anus and back of the leg.
Coccygeal nerve
(co1).
Besides the 31 pairs of spinal nerves, the peripheral nervous system also consists of 12 pairs of cranial nerves, so called because they evolve from the brain or brainstem. Thus the brainstem controls motor output and receives sensory information from areas above the neck via the cranial nerves.
The autonomic nervous system (ANS)
The ANS regulates the internal organs of the body such as cardiac muscle, smooth muscle and glands. It is responsible for maintaining an optimal environment or homeostasis for the cells to function. It consists of two divisions: sympathetic and parasympathetic. The sympathetic and parasympathetic nervous systems have opposing actions. For instance, mass activation of the sympathetic system helps us to respond to physical activity in emergencies and prepares the body for ‘fight’ or ‘flight’ (Fox, 2004). In sympathetic stimulation, the heart rate increases, blood glucose rises and blood is diverted from visceral organs and skin to the skeletal muscles. The parasympathetic nervous system is responsible for maintaining our body in a resting state. Its activation results in slowing of the heart rate, dilation of visceral blood vessels and increased activity of the digestive tract. Normally the actions of the two divisions must be balanced to maintain homeostasis.
Sensations
The sensory cortex receives and processes sensory information such as hearing, vision, smell, taste, touch, temperature, pain and posture. This enables conscious or subconscious awareness of external or internal conditions of the body. Sensations can be divided into general senses and special senses (Thibodeau & Patton, 2004). General senses include somatic senses (from the skin and joints) and visceral senses (from internal organs). Special senses are smell, taste, vision, hearing and balance.
Somatic senses
There are a number of receptors in the skin, mucous membranes, muscles, tendons and joints that will respond to physical stimuli and produce specific sensations. Mechanoreceptors respond to deformation of the skin and provide information on texture. Thermoreceptors are activated by changes in temperature while nociceptors respond to tissue damage and produce pain sensation. Proprioceptors in joints and muscles give information on the position and movement of body parts.
