Senile plaques and neurofibrillary tangles are the hallmark pathological features that are observed in the brain of an alzheimer’s patient. Senile plaques are deposits of a distinct protein fragment called beta-amyloid, which induces neuronal cytotoxicity, and neurofibrillary tangles are abnormal structures that are formed by changes in the tau protein inside nerve cell bodies. The nerve cells in the brains of alzheimer’s patients progressively  shrink and die. Such neuronal death occurs first in the brain regions that are responsible for memory and language, but it ultimately spreads to the entire brain. the neural  networks of alzheimers patients are impaired by the decreased brain concentrations of acetylcholine, which is a neurotransmitter that is involved in intercellular signaling, and deficiencies in the production of other neurotransmiters , such as somatostatin, serotonin, and norepinephrine.