The brain and nervous system

All our thinking processes physical activities and sensations, are initiated, controlled, and co-ordinated by the brain and nervous system. If you accidentally put your hand into some hot water, you will pull it away immediately. This response (called a reflex) is brought about by messages that are sent at high speed through the nervous system. The brain is like an extremely complicated computer, with thousands of electrical messages traveling from place to place. But it is much more than a computer because it makes us conscious persons with feelings and emotions.

The skull encloses the brain. The spinal cord comes down from it and goes down the spine (vertebral column). The human brain is of a soft consistency. It has a soft material on the outside called the grey matter which contains the basic cell units of the brain. These cells are called neurons; there are about 100 billion neurons in the brain. In the deeper parts of the brain there is a whitish firm material, called the while matter, which contains the connecting tracts, which carry the messages from the neurons. The brain is divided into the - cerebrum, cerebellum, and brain stem. Surrounding the soft brain tissue on the outside are two membranes (the meninges) with a thin layer of fluid (cerebro-spinal fluid, CSF) between them. The CSF nourishes the brain and also serves as a shock absorber, so that the brain is cushioned from damage when a person jumps around or bangs the head. There is a cavity in the inside of the brain, which is filled with CSF. This cavity continues as a canal inside me spinal cord. Doctors put in a needle at the back of the spine and get a small amount of CSF (Present between the two coverings of the meninges) for examination, to diagnose diseases such as meningitis and encephalitis.

The functions of the brain and nervous system may be broadly divided into; Higher functions such as thinking, speaking; remembering things (memory), emotions, appreciation of music; motor functions such as movements of the different parts of the body, sensory functions like appreciation of sensations such as pain, touch, seeing, hearing, taste, and smell, balance and coordination of movement in the different parts of the body and involuntary (unintentional) functions. Involuntary functions are two types, regular functions such as breathing and the beating of the heart and certain involuntary reactions with are referred to as reflexes which are usually take place at the level of the spinal cord.

The cerebrum controls the higher functions as well as motor and sensory functions. It is divided into 2 halves (left and right) which are called cerebral hemispheres. The left hemisphere controls the right side of the body, and the right hemisphere the left side of the body. The left hemisphere is said to be dominant in right handed people, and the right hemisphere in left handed people. The cerebellum is situated at the back of the brain. Its main function is to co-ordinate movements of the skeletal muscles and help maintain balance, a function which it shares with the inner ear. The cerebrum and cerebellum lead to the brain stem, which continues downwards as the spinal cord. The Spinal cord is a cylindrical structure that comes down through the vertebral column (spine) to the lower part of the back of the body. Nerves proceed from the brain stem and spinal cord to all parts of the body. In this way every part of the body is connected to the brain which ultimately controls all its activities.

Non limb girdle pattern muscular dystrophies with involvement of cranial musculature -1

Facioscapulohumeral muscular dystrophy is an autosomal dominant disease, though a family history may not be evident because expression of the disease can be mild. Phenocopies resulting from spinal muscular atrophy, mitochondrial myopathy and inclusion body myositis have been reported, but diagnosis by DNA analysis has greatly reduced diagnostic uncertainty in recent years. Weakness typically begins in the face (though the face may be unaffected in some individuals) or shoulder muscles, with sparing of the extraocular, pharyngeal and lingual muscles. Inability to whistle is characteristic. In later stages, dramatic scapular winging develops, and weakness of the scapular fixators allows ‘over-riding’ of the scapulae above the shoulders, like a pair of wings. Lower limb weakness may not be conspicuous, but foot drop and later proximal weakness can occur. Creatinine kinase levels, EMG and muscle biopsy may show only minimal abnormalities. Diagnostic confirmation depends on the demonstration of abnormally small 4q35-specific DNA fragments following digestion with restriction site enzymes. Recent evidence suggests an inverse correlation between the size of these fragments and disease severity. The genes responsible have not yet been identified. No treatment is available, but scapulothoracic arthrodesis can improve upper limb function in patients with severe limitation of arm elevation.

Oculopharyngeal muscular dystrophy presents with ptosis and weakness of the extraocular muscles, muscles of the pharynx and larynx (causing progressive dysphagia and dysphonia), and the facial, limb-girdle and even distal muscles. It is an autosomal dominant disorder, but gene penetrance varies considerably. Cases may be mild to severe and can present at almost any age, though typically in the sixth decade and beyond. Creatinine kinase may be only minimally increased and biopsy can show a range of changes which may include rimmed vacuoles and ragged red fibers typical of a mitochondrial myopathy. Ultrastructural studies may reveal pathognomonic accumulations of 8.5 nm filaments in a proportion of myonuclei. Recently, diagnosis by DNA analysis has become available. The disease is associated with a GCG triplet expansion at the poly-A binding protein 2 (PABP2) gene at 14q11. It is suggested that this expansion might cause mutated PABP2 monomers to aggregate in nuclei, resulting in filament accumulations.

Distal myopathies
Several neuromuscular diseases present with distal weakness and wasting of the limbs. This pattern commonly results from peripheral neuropathies, including Charcot–Marie–Tooth disease, and from anterior horn cell diseases such as spinal muscular atrophy. It can also be encountered in primary muscle diseases, notably myotonic dystrophy, congenital myopathies and inclusion body myositis. In addition, several rare forms of genetically determined distal myopathy have been described. These can be distinguished to some degree by mode of inheritance and  whether  the  anterior  or  posterior  compartment  of  the lower legs is principally affected. A common form is Miyoshi myopathy, which particularly affects the gastrocnemius and soleus muscles. Like LGMD2B, it is a dysferlinopathy. Several of these diseases are rimmed vacuolar myopathies, a feature shared with the hereditary inclusion body myopathies.

Congenital  myopathies
Congenital myopathies are classified on the basis of specific histological features. Patients can present at any time from childhood to adult life, usually with distal weakness. A long, thin facies and high arched palate are common. This group of disorders includes centronuclear and myotubular myopathies, nemaline myopathy and central core disease.

Myotonic  disorders
Myotonia is prolonged contraction of muscle, with subsequent slowed relaxation, following activation. It results from genetic or acquired changes in excitability of muscle surface membranes and is found in several primary muscle diseases. Neuromyotonia is a clinically similar phenomenon of neurogenic origin.