Alzheimer's disease is otherwise called Chronic brain syndrome. It is characterized by progressive loss of memory followed by general loss of cognitive functions and death. This disease becomes more and more prevalent among aged persons. Occasionally people develop the disease before 50 or even before the age of 40. It affects less than 5 per cent of the population between 65 - 74. In the aged people beyond 80 almost 50 per cent are affected invariably.
Alzheimer's disease is associated with the atrophy of cerebral cortex. Neurons undergo degeneration. In the damaged regions, plaques formed by the degeneration of axons and dendrites, appear.
Alzheimer's disease is commonly attributed to genetic mutation . People with Down syndrome are invariably affected with this disease. It is presumed that atleast two or three genes in chromosome 21 are linked to this disease. However genetics is not the onlyetiological factor, for this disease.
The term Meningitis refers to the inflammatory condition of the brain membranes and the sub-arachnoid space. Meningitis may be caused by bacterial infection, or viral infection or fungal infection. The clinical symptoms of meningitis include headache, photophobia, irritability, stiffness of the neck, fever and other neurological symptoms.
The Russian Physiologist Ivan Pavlov first demonstrated 'the conditioned reflex' phenomenon. The cerebral cortex controls the conditioned reflexes. It is also called the classical conditioning, in which a stimulus comes to elicit a response similar to the response produced by some other stimulus.
In his experiment, Pavlov presented a dog with a sound of a bell (Neutral stimulus) followed by meat (Unconditioned stimulus). This combined stimuli stimulated the dog to salivate (unconditioned response). After many such conditioned pairings the sound alone (Conditioned stimulus) would stimulate the dog to salivate (Conditioned response - CR).
The bell sound initially called the neutral stimulus which after a number of trials pairing with the unconditioned stimulus viz., the meat piece, becomes the conditioned stimulus. Similarly the salivation of the dog during the initial trials of pairing (NS + UCS) is called Unconditioned Response (UR). This unconditioned response later on becomes designated into a conditioned response (CR). It will be elicited just by bell sound (CS).
The conditioned reflexes are developed in animal's life in association with previously established reflexes. This is the basis of learning and memory.