Mechanism of brain cell death When a reduction in blood flow lasting seconds occurs, the brain tissue suffers ischemia, or inadequate blood supply. If the interruption of blood flow is not restored in minutes, the tissue suffers infarction followed by tissue death. When the low cerebral blood flow persists for a longer duration, this may develop into an infarction in the border zones (areas of poor blood flow between the major cerebral artery distributions). In more severe instances, global hypoxia-ischemia causes widespread brain injury leading to a severe cognitive sequelae called hypoxic-ischemic encephalopathy. An ischemic cascade occurs where an energetic molecular problem arises due to lack of oxygen and nutrients. The cascade results in decreased production of adenosine triphosphate (ATP), which is a high-energy molecule needed for cells in the brain to function. Consumption of ATP continues in spite of insufficient production, this causes total levels of ATP to decrease and lactate acidosis to become established (ionic homeostasis in neurons is lost). The downstream mechanisms of the ischemic cascade thus begins. Ion pumps no longer transport Ca2+ out of cell, this triggers release of glutamate, which in turn allows calcium into cell walls. In the end the apoptosis pathway is initiated and cell death occurs. There are several arteries that supply oxygen to different areas of the brain, and damage or occlusion of any of them can result in<unk> . The carotid arteries cover the majority of the cerebrum. The common carotid artery divides into the internal and the external carotid arteries. The internal carotid artery becomes the anterior cerebral artery and the middle central artery. The ACA transmits blood to the frontal parietal. From the basilar artery are two posterior cerebral arteries. Branches of the basilar and PCA supply the occipital lobe, brain stem, and the cerebellum. Ischemia is the loss of blood flow to the focal region of the brain. This produces heterogeneous areas of ischemia at the affected vascular region, furthermore, blood flow is limited to a residual flow. Regions with blood flow of less than 10 mL/100 g of tissue/min are core regions (cells here die within minutes of a<unk> . The ischemic penumbra with a blood flow of <25 ml/100g tissue/min, remain usable for more time (hours). Types of<unk>  There are two main divisions of<unk> s: ischemic and hemorrhagic. Ischemic<unk>  involves decreased blood supply to regions of the brain, while hemorrhagic<unk>  is bleeding into or around the brain. Ischemic * Ischemic<unk> , the most common is caused by a blockage of a blood vessel in the brain, usually caused by thrombosis or emboli from a proximal arterial source or the heart, that leads to the brain being starved of oxygen. The neurologic signs and symptoms must last longer than 24 hours or the brain infarction is demonstrated, mainly by imaging techniques. * Transient ischemic attack (TIA) also called a mini-stroke. This is a condition in which the blood flow to a region of the brain is blocked, but blood flow is quickly restored and the brain tissue can fully recover. The symptoms are only transient, leaving no sequelae, or long-term deficits. In order to diagnose this entity, all neurologic signs and symptoms must have been resolved within 24 hrs without evidence of brain infarction on brain imaging. Hemorrhagic * Subarachnoid haemorrhage occurs when blood leaks out of damaged vessels into the cerebrospinal fluid in the subarachnoid space around the brain. The most common cause of a subarachnoid hemorrhage is an aneurysm rupture due to the weakened blood vessel walls and increased wall stress. The neurologic symptoms are produced by the blood mass effect on neural structures, from the toxic effects of blood on the brain tissue, or by the increasing of intracranial pressure. * Intracerebral haemorrhage is bleeding directly into the brain rather than around the brain. Causes and risk factors include hypertension, blood thinning medications, trauma, and arteriovenous malformations. Brain infarct
Cerebrovascular disease
Anti-Hu associated encephalitis
Cardiovascular disease
Disease
Stroke
Cancer
Urologic disease
Central nervous system disease