Ross & Wilson Anatomy and Physiology in Health and Illness (63 page)

Enlargement of the gland is associated with some autoimmune diseases, such as thyrotoxicosis and Addison’s disease.

Tumours are rare, although pressure caused by enlargement of the gland may damage or interfere with the functions of adjacent structures, e.g. the trachea, oesophagus or veins in the neck.

In myasthenia gravis (
p. 376
), most patients have either thymic hyperplasia (the majority) or thymoma (a minority), although the role of thymic function in this disorder is not understood.

For a range of self-assessment exercises on the topics in this chapter, visit
www.rossandwilson.com
.

CHAPTER 7

The nervous system

Cells and tissues of the nervous system
139

Neurones
139

Nerves
142

Neuroglia
142

Response of nervous tissue to injury
144

Central nervous system
145

The meninges and cerebrospinal fluid (CSF)
145

The meninges
145

Ventricles of the brain and the cerebrospinal fluid
146

Brain
148

Blood supply to the brain
148

Cerebrum
148

Diencephalon
152

Brain stem
153

Cerebellum
154

Spinal cord
154

Grey matter
155

White matter
156

Peripheral nervous system
158

Spinal nerves
159

Thoracic nerves
164

Cranial nerves
164

Autonomic nervous system
167

Disorders of the brain
172

Increased intracranial pressure
172

Head injuries
173

Cerebral hypoxia
174

Stroke (cerebrovascular disease)
175

Dementia
176

Parkinson’s disease
176

Effects of poisons on the brain
176

Infections of the central nervous system
177

Bacterial infections
177

Viral infections
177

Demyelinating diseases
178

Multiple sclerosis (MS)
178

Acute disseminated encephalomyelitis
179

Diseases of the spinal cord
179

Motor neurones
179

Sensory neurones
180

Mixed motor and sensory conditions
180

Diseases of peripheral nerves
181

Peripheral neuropathy
181

Guillain–Barré syndrome
181

Bell’s palsy
181

Developmental abnormalities of the nervous system
182

Spina bifida
182

Hydrocephalus
182

Tumours of the nervous system
182

ANIMATIONS

7.1
Divisions of the nervous system
138

7.2
The neurone
139

7.3
The nerve impulse
140

7.4
The synapse
141

7.5
Brain ventricles
146

7.6
Main parts of the brain
148

7.7
Areas of the brain that control body functions
148

7.8
Vertebral column and spinal nerves showing nerve roots
155

7.9
Reflex arc of patellar impulse
158

7.10
Cranial nerves
164

7.11
Impulse conduction in the autonomic nervous system
167

7.12
Comparison of autonomic and somatic conduction system pathways
167

7.13
Autonomic neurotransmitters
167

7.14
Functions of the sympathetic nervous system
170

7.15
Functions of the parasympathetic nervous system
170

7.16
Haematomas
174

7.17
Thromboembolic stroke
175

7.18
Parkinson’s disease
176

The nervous system detects and responds to changes inside and outside the body. Together with the endocrine system, it controls many vital aspects of body function and maintains homeostasis. To this end the nervous system provides an immediate response while endocrine activity is, in the main, slower and more prolonged (
Ch. 9
).

The nervous system consists of the brain, the spinal cord and peripheral nerves. The structure and organisation of the tissues that form these components enables rapid communication between different parts of the body.

Response to changes in the internal environment regulates essential involuntary functions, such as respiration and blood pressure. Response to changes in the external environment maintains posture and other voluntary activities.

For descriptive purposes the parts of the nervous system are grouped as follows:

•
the
central nervous system
(CNS), consisting of the brain and the spinal cord

•
the
peripheral nervous system
(PNS) consisting of all the nerves outside the brain and spinal cord.

The PNS comprises paired cranial and sacral nerves – some of these are sensory (afferent), some are motor (efferent) and some mixed. It is useful to consider two functional parts within the PNS:

•
the sensory division

•
the motor division (
Fig. 7.1
).