The nervous system is divided into two:
- The central nervous system (CNS), which consists of the brain and spinal cord
- The peripheral nervous system (PNS), composed of the nerves of the body
Each of these two broad divisions in turn has 2 parts. One part called the somatic component is responsible for controlling the muscles responsible for movement (skeletal muscles) and for transmitting sensory information.
Another part called the autonomic component is concerned with the control of the heart muscle, the smooth muscles (such as those found in the digestive tract), and the glands (tissues responsible for production of substances like sweat, saliva, tears and various hormones).
The brain is the highest centre of control of body functions such as sight, smell, hearing, speech, breathing, urination, movement and behaviour. The brain substance is jelly-like and is enveloped by 3 layers of tissue called the meninges. All these are contained in a bony cavity called the skull which protects it from external sources of injury.
The brain tissue produces a fluid called cerebrospinal fluid (CSF). This fluid provides protection for nervous tissues and a water-bath in which the brain can float, thus effectively reducing the 1500g weight of the brain to just 50g. It is also an important pathway for removing the waste products produced by the brain.
The brain continues down through an opening at the base of the skull as the spinal cord. The spinal cord is a lower level of control, and is more spontaneous than the brain in coordinating the activities of the body. The meninges also continue down with it to wrap around it. CSF also flows around the spinal cord.
Symptoms of Neurological Disease
Problems with the nervous system can present with any of the following symptoms depending on the affected part. However, when some of them like headache or dizziness occur alone, it may not necessarily mean something is wrong with your nervous system. But you might just want to check with your doctor for proper evaluation.
- Loss of awareness
- Loss of consciousness
- Memory impairment
- Alteration of perception, including déjà vu
- Dizziness, vertigo
- Loss of balance
- Loss of sense of smell
- Loss of taste
- Loss of vision
- Double vision
- More than double vision
- A visual sensation of stationary objects swaying back and forth
- Tinnitus (ringing or whistling sensation in the ears)
- Difficulty with speech
- Difficulty swallowing
- Abnormal movements of muscles (including cramps)
- Abnormal movements of parts of the body
- Impairment of control of limbs
- Altered sensation
- Loss of sensation
- Impairment of sexual function
- Impairment of bladder control
- Impairment of bowel control
Headache is a common symptom, but when it occurs alone, it is seldom associated with significant neurological disease.
After a proper consultation with a doctor, the likely underlying cause of headache or facial pain can usually be identified. If nothing is found after examining the nervous system, then it is not likely that something is really wrong with your nerves. In this case, all you may need is reassurance and some painkillers to take the ache away.
Possible causes of headache
• Tension-type headache (persistent daily headache)
This is the most common type of headache. The cause is incompletely understood, however emotional strain or anxiety is a common precipitant.
It comes as a ‘dull’, ‘tight’ or ‘pressure-like’ pain, usually constant and generalised but often radiates forward from the back of the head. It may continue for weeks or months without stopping, although the severity may vary. A person with tension-type headache can usually go about their normal activities. It is characteristically less severe in the morning and becomes more troublesome as the day goes on.
Typically, the headache does not respond well to treatment with painkillers, and excessive use of the pain killers, especially those containing codeine, may actually worsen it. Physiotherapy is usually beneficial and the doctor may prescribe some other type of drug to help.
Migraine occurs in about 3 times more females than males, usually before the age of 40. The cause is incompletely understood but genetic and hormonal factors have been implicated. Most females have attacks at certain point in their menstrual cycle, and contraceptive pills seems to worsen it. Foods such as cheese, chocolate and red wine have also been identified to trigger migraine. Attacks also often occur after periods of stress such as at weekends or at the beginning of a holiday.
The classical migraine attack starts with a general feeling of being ill and irritability, then an ‘aura’ (which may be in the form of visual disturbances or a sensation of tingling followed by numbness which moves from one part of the body to another), then a severe throbbing headache in one half of the head with an aversion to light and vomiting.
• Cluster headache
Cluster headaches are 10-50 times less common than migraine and occurs 5 times more in males. The cause is unclear. There are no provoking diets and there is little evidence for genetic influences. It however usually occurs in heavy smokers with a higher than average alcohol consumption.
It characteristically comes as a brief, periodic, severe, one-sided pain around the eye, accompanied by production of tears on the eye affected, as well as nasal congestion. These symptoms typically occur at a particular time of the day (usually in the early hours of the morning).
• Trigeminal neuralgia
This is characterised by a sharp pain in the area from the lower eyelid to the jaw, usually in people over the age of 50 years.
The pain is severe and very brief but repetitive. It may be triggered by touching certain parts of the face, by cold wind blowing against the face, or by eating.
• Post-coital and exercise-induced headache
This usually affects men in their thirties and forties. They develop a sudden, severe headache at the climax of sexual intercourse. It does not persist for more than 15 minutes, though a less severe, dull headache may persist for some hours.
A very similar headache may occur during exercise, especially if this is attempted with unaccustomed vigour in an unfit person.
• Bleeding into the brain
This is a medical emergency, which can occur as a result of a stroke, trauma, some blood-thinning drugs, exercise, straining and sexual excitement. It may also just occur on its own. Elderly people or those who misuse alcohol are at increased risk. The headache may be sudden and very severe, and consciousness may be lost. Vomiting may also be present.
• Brain tumour
Brain tumours are an uncommon cause of headache, and headaches don’t always come with them. Headaches caused by brain tumours are usually accompanied by other symptoms of brain dysfunction depending on the part of the brain affected. The symptoms come on slowly and may get worse with time. The site of the ache may vary, but not necessarily with the location of the tumour.
• Infection like meningitis or encephalitis
Meningitis is an infection of the coverings of the brain (meninges). Encephalitis is an infection of the brain tissue itself. Both are serious conditions which usually cause headache accompanied with fever. It is important to consult your doctor as soon as possible if you have a high fever with headache.
• Pus (abscess) in the brain
Abscess may form within the brain tissue from an infection by bacteria which may enter through penetrating injury, or spread from ear infections, or from already infected blood. It may present with headache, fever, neck stiffness and drowsiness.
• Inflammation of the blood vessels in the brain
The blood vessels in the brain tissue may become inflamed and swollen and cause headache. The headache is often localised to the area supplied by the blood vessel involved, and the skin above the area may be painful to touch.
• Post-herpetic neuralgia
This is headache and facial pain that may occur several years after chickenpox. It is common in the elderly and people with low immunity.
• Referred pain from other structures (eye socket, jaw, neck)
Due to nerve interconnections, pain from any part of the head can be felt as a headache. The pain usually starts from the part originally affected and then spreads.
Loss of consciousness
Loss of consciousness, other than in sleep, suggests a global dysfunction in the brain. This most commonly occurs because of a recoverable loss of supply to the whole brain (fainting). It can also occur due to a seizure. There are other less common causes of loss of consciousness.
A fainting attack is usually preceded by a brief feeling of light-headedness. Then there follows a darkening of vision and there may be a ringing in the ears. During a syncopal attack, incontinence of urine can occur and there is often stiffening and brief twitching of the limbs, but tongue-biting never occurs.
Some seizures may cause loss of consciousness, falling to the ground and convulsion. But some may only cause alteration of consciousness without falling to the ground.
This is an abnormal perception of movement of the environment and occurs because of an abnormality in sensory information from the eyes, joint position sense and the system involved with body balance. Vertigo commonly arises because of inappropriate input from the part of the inner ear that maintains balance, and this type is usually short-lived. It may also arise from disorders in the brain substance itself, and this type is often persistent. A careful analysis of the entire picture will help your doctor find out the cause of your vertigo.
Loss of memory may last for a short while before resolving (transient), or may become persistent. The former predominantly affects middle-aged people and lasts only a few hours at most. It tends not to recur. Persistent memory loss can be caused by conditions like dementia. If your memory loss persists, the doctor needs to assess you to exclude serious neurological disease.
Alteration of perception
Abnormal perception can occur in any of the sensory modalities: hearing, vision, smell, taste and touch. When perception is distorted, the perceived object is correctly recognized but altered in some way, such as alteration of the intensity of sound, quality, colour or distortions of form. These occur in psychiatric disorders but also many organic conditions such as epileptic seizures.
Loss of balance and Falls
Disorders of balance can arise from a number of different abnormalities like loss of vision, disorders with the structures that maintain balance, lack of joint position sense, damage to the cerebellum (the part of the brain responsible for controlling movement), spinal cord damage or leg weakness of any cause.
Loss of senses of smell, taste, hearing and vision
These senses have specific areas in the brain where they have to be processed. Any problem in these areas can manifest as the loss of these senses. The doctor needs to find out if the problem is primarily with the sense organ concerned or with the part of the brain that processes it.
Hallucinations are perceptions that are not based on any real external stimulus. They can occur in any of the senses but the commonest are auditory, for example hearing a voice which no one else hears. Auditory hallucinations occur in many disorders including schizophrenia, organic brain disease, mania and depression.
Visual hallucinations are more suggestive of non-psychiatric conditions, particularly in confused states, illicit drug use or drug withdrawal. However, they do occasionally occur in schizophrenia.
Hallucinations can occur in the absence of mental illness, for example in extreme fatigue or in between sleep and waking, and can occur in bereaved individuals, usually being experiences of either seeing or hearing the lost loved one, and are generally experienced as comforting. They are a normal part of grief in some people.
Disturbances of vision are common and often related to problems with the eye rather than disorders of the nervous system. There may be outright loss of vision, or the movements of both eyes may be disturbed giving rise to
double vision or blurred vision.
Tinnitus is a ringing, rushing or hissing sound in the absence of an appropriate auditory stimulus. It can be caused by almost any problem in the hearing structures. It is strongly associated with hearing loss, although it occasionally occurs with normal hearing.
There are three broad categories of speech disturbance; dysphonia, which is usually caused by a local problem
in the larynx (large airway); dysarthria, which can occur in association with problems affecting the lowest parts of the brain (the brain stem and cerebellum) or muscles with which speech is made; and dysphasia, which is due to lesions of the first or topmost part of the brain (cerebrum).
Dysphonia is the term used to describe hoarse or whispered speech. It is due to a problem with the vocal cords. The most common cause is an inflammation of the larynx.
Dysarthria is characterised by poorly articulated or slurred speech. There is no problem of choice of words but rather a problem with speech delivery.
Dysphasia is a disorder of the language content of speech. There is difficulty in choosing the right words to say, so the person either doesn’t talk or says nonsense words.
Swallowing is a complex activity involving the coordinated action of lips, tongue, soft palate, pharynx and larynx. This mechanism is potentially vulnerable to damage in many different areas of the nervous system, resulting in dysphagia which is usually accompanied by dysarthria (speech articulation problem).
Weakness strictly means reduced muscle power, such as when you find out you are unable to use your limbs like you used to even when you are not tired. It doesn’t mean fatigue or lethargy. It may be caused by a stroke or inherited muscle disorder.
Abnormal movements and clumsiness
These are often caused by a disorder in a part of the brain called the basal ganglia. A common abnormal movement is tremor (shaking or trembling). It can occur at rest or during activity, though more commonly during activity. Tremor can be caused by anxiety in normal people, or caused by disease such as Parkinson’s disease. Some drugs used in treating Parkinson’s disease can also cause other abnormal movements.
Clumsiness on any side of the body is caused by a disorder in the half of the brain controlling that side.
Altered or lost sensation and pain
Although sensory symptoms are often due to neurological disease, this is not always the case; for example, tingling in the fingers of both hands and around the mouth can occur as a result of excessive ventilation or low calcium in the blood. Symptoms such as tingling, numbness and pain may all be caused by damage to the nerves. When there is dysfunction of
the brain mechanisms of body sensation there may be distortion of perception of the wholeness or actual presence of the affected part of the body.
Impairment of sexual function, bladder and bowel control
Impairment of sexual function and bladder control can be caused by a problem with the brain or spinal cord and the nerves that supply the affected part. Bowel incontinence is usually only due to a spinal cord or nerve disease.