HEADACHE

Pain that occurs over various parts of the head is called headache. It is one of humankind’ s most common afflictions. In the united State alone, up to 50 million person seek medical help for this problem every year, and about half a billion dollars is spent on headache remedies annually.

Most headache are caused not by organic disease but by fatigue, emotional disorder, or allergies. Intermittent tension headaches are caused by worry, anxiety, overwork, or inadequate ventilation. The most common type – a chronic tension headache- is often caused by depression. Only about 2 % of all headache result from organic disorder, including diseases of the eye, ear, nose, throat, and sinuses; brain tumors, hypertension, and aneurism (the ballooning of artery, brought about by a weakness in the arterial wall)

Brain tissue itself is sensitive to pain, as is the bony covering of the brain (the cranium) Headache pain result from the stimulation of such-pain sensitive structures as the membranous lining of the brain (the meninges) and the nerves of the cranium and upper neck.

This stimulation can be produce by inflammation, by the dilation of blood vessels of the head, or by muscle spasms in the neck and head. Headache brought on by muscle spasms are classified as tension headache; those caused by the dilation of blood vessels are called vascular headache. These are the major grouping of headache, besides those brought on by organic disorder.

Brain Micro Structure

The brain is composed of nerve cells (or neurons), glial cells, and nutrient blood vessels. Neurons transmit nerve impulses, and glial cells, which account for half of the brain’s weight, form the supporting structure of the brain.

Each multipolar neuron has a soma, or cell body, from which extends a single large process, or axon, along which impulses are transmitted to other neurons when the soma is sufficiently excited by incoming impulses. Axons of functionally similar neurons are frequently grouped as more or less discrete fiber tracts. The somas from which they arise are grouped as nuclei, or ganglia. The soma also has shorter processes, called dendrites, whose principal function is to receive incoming nerve impulses. The area at the dendrites where the terminal branch of an axon comes into contact with another neuron to another across synapses. When the combined interplay of many incoming impulses reaches a certain threshold, the soma depolarizes and sends a nerve action potential down its axon to other nerve cells and their processes.

The term afferent and efferent describe nerve tracts as going toward or away from the cerebral cortex or other higher brain structures. The corticospinal nerve tract from cortex to spinal cord is efferent, with somas of the cells of origin in the cortex, their axons traveling downward to the cord, away from the highest center. The terms sensory and afferent are used synonymously, as are motor and efferent.

The exposed living brain in a soft mass of glistening grayish white tissue which numerous small, bright red arteries and bluish veins are visible. The brain is protected by the skull and three membranes, called meninges. When the brain is “fixed” with chemicals. It becomes firm and can be sliced. Apparently to nerve endings sensitive to pain exist within the brain. Large blood vessels supplying the brain and certain sensory nerve attached to the brain stem are pain sensitive.

Brain Evolution

During the first few weeks of embryonic life, the bodies and central nervous systems of different vertebrates are remarkably similar. It is difficult to differentiate between the human embryo at the gestational age of one month and the embryo of an amphibian, fish, reptile, or rodent at a comparable stage. All have tails, primordial (primitive) gill clefts, and similar nervous systems, including primordial brains in the form of small bulges in the neural tube. The early embryos of these vertebrates most closely resemble, on a miniature scale, the adult fish, which is the oldest true vertebrate on the phylogenetic, or evolutionary, ladder. The developing human embryo, including the brain, passes through stages that, on a small scale, resemble the evolution of its ancestors. The embryological development of the human brain thus parallels the evolution of the brain. The small bulges in the primitive neutral tube gradually enlarge and form the anatomical divisions of the future adult brain, or encephalon. These division are the hindbrain, midbrain, and forebrain.

In Primitive animals, the forebrain lags in development, but certain parts of the brain that are essential to survival of the species develop much more than others. In fish and amphibians, the olfactory (smell) system, including the ofloctory cortex, the cortex being the outer layer of the brain, is particularly well developed.

In Reptile and birds, both evolutionary descendants of the amphibians, the corpus striatum (a mass of gray matter close to the thalamus) is well developed and serve as a coordination center for reflexes involving the eye and birds is extremely large compared to the rest of the brain, because it controls the motor coordination and balance necessary for flight. The visual systems of reptiles and birds are also well developed.

In the mammals, the olfactory cortex is part of a large neuronal system, the limbic system. The ancient olfactory system has been modified to serve not only smell but also the behavioral responses known as emotion and sexual behavior. Embryologically and according to evolutionary development, the mammalian brain gradually enlarges because of the expansion of the neocortex (composed of the frontal, parietal, occipital, and temporal lobes). The neocortex reaches its fullest development in the primates specifically in humans.

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