Brain -the brain is the most powerful organ, yet weighs only about three pounds. It has a texture similar to firm jelly.
It has three main parts:
The cerebrum fills up most of the skull. It is involved in remembering, problem solving, thinking, and feeling. It also controls movement.
The cerebellum sits at the back of the head, under the cerebrum. It controls coordination and balance.
The brain stem sits beneath the cerebrum in front of the cerebellum. It connects the brain to the spinal cord and controls automatic functions such as breathing, digestion, heart rate and blood pressure.
The real work of the brain goes on in individual cells. An adult brain contains about 100 billion nerve cells, or neurons, with branches that connect at more than 100 trillion points. Scientists call this dense, branching network a "neuron forest."
Signals traveling through the neuron forest form the basis of memories, thoughts, and feelings.
Signals that form memories and thoughts move through an individual nerve cell as a tiny electrical charge.
Nerve cells connect to one another at synapses. When a charge reaches a synapse, it may trigger release of tiny bursts of chemicals called neurotransmitters . The neurotransmitters travel across the synapse, carrying signals to other cells.
Other terms: “stroke”, “brain attack”, “acute ischemic cerebrovascular syndrome”
occurs when blood supply to part of the brain is disrupted, causing brain cells to die. When blood flow to the brain is impaired, oxygen and glucose cannot be delivered to the brain. Blood flow can be compromised by a variety of mechanisms.
a "neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours". -WHO
Mechanisms that compromise the blood flow to the brain
In thrombotic stroke, a thrombus (blood clot) usually forms around atherosclerotic plaques. Since blockage of the artery is gradual, onset of symptomatic thrombotic strokes is slower. A thrombus itself (even if non-occluding) can lead to an embolic stroke. if the thrombus breaks off, at which point it is called an "embolus". Thrombotic stroke can be divided into two types depending on the type of vessel the thrombus is formed on:
Large vessel disease
Small vessel disease
Sickle cell anemia, which can cause blood cells to clump up and block blood vessels, can also lead to stroke. Stroke is the second leading killer of people under 20 who suffer from sickle-cell anemia.
Embolic stroke refers to the blockage of an artery by an embolus, a traveling particle or debris in the arterial bloodstream originating from elsewhere. An embolus is most frequently a thrombus, but it can also be a number of other substances including fat (e.g. from bone marrow in a broken bone), air, cancer cells or clumps of bacteria (usually from infectious endocarditis).
Because an embolus arises from elsewhere, local therapy only solves the problem temporarily. Thus, the source of the embolus must be identified. Because the embolic blockage is sudden in onset, symptoms usually are maximal at start. Also, symptoms may be transient as the embolus is partially resorbed and moves to a different location or dissipates altogether.
Emboli most commonly arise from the heart (especially in atrial fibrillation) but may originate from elsewhere in the arterial tree. In paradoxical embolism, a deep vein thrombosis embolises through an atrial or ventricular septal defect in the heart into the brain.
Systemic hypoperfusion is the reduction of blood flow to all parts of the body. It is most commonly due to cardiac pump failure from cardiac arrest or arrhythmias, or from reduced cardiac output as a result of myocardial infarction, pulmonary embolism, pericardial effusion, or bleeding.
Hypoxemia (low blood oxygen content) may precipitate the hypoperfusion. Because the reduction in blood flow is global, all parts of the brain may be affected, especially "watershed" areas - border zone regions supplied by the major cerebral arteries. Blood flow to these areas does not necessarily stop, but instead it may lessen to the point where brain damage can occur. This phenomenon is also referred to as "last meadow" to point to the fact that in irrigation the last meadow receives the least amount of water.
Cerebral venous sinus thrombosis leads to stroke due to locally increased venous pressure, which exceeds the pressure generated by the arteries. Infarcts are more likely to undergo hemorrhagic transformation (leaking of blood into the damaged area) than other types of ischemic stroke.
Intracerebral hemorrhage (ICH) is bleeding directly into the brain tissue, forming a gradually enlarging hematoma (pooling of blood).
It generally occurs in small arteries or arterioles and is commonly due to hypertension, trauma, bleeding disorders, illicit drug use (e.g. amphetamines or cocaine), and vascular malformations.
The hematoma enlarges until pressure from surrounding tissue limits its growth, or until it decompresses by emptying into the ventricular system, CSF or the pial surface. A third of intracerebral bleed is into the brain's ventricles.
ICH has a mortality rate of 44 percent after 30 days, higher than ischemic stroke or even the very deadly subarachnoid hemorrhage.
The symptoms of a stroke are related to the anatomical location of the damage; nature and severity of the symptoms can therefore vary widely.
Ischemic strokes usually only affect regional areas of the brain perfused by the blocked artery. Hemorrhagic strokes can affect local areas, but often can also cause more global symptoms due to bleeding and increased intracranial pressure.
On the basis of the history and neurological examination, as well as the presence of risk factors, a doctor can rapidly diagnose the anatomical nature of the stroke (i.e. which part of the brain is affected), even if the exact cause is not yet known.
If the area of the brain affected contains one of the three prominent Central Nervous System pathways—the spinothalamic tract, corticospinal tract, and dorsal column (medial lemniscus), symptoms may include:
Loss of consciousness, headache , and vomiting usually occurs more often in hemorrhagic stroke than in thrombosis because of the increased intracranial pressure from the leaking blood compressing on the brain.
Sudden numbness or weakness of the face, arm or leg, especially on one side of the body. The loss of voluntary movement and/or sensation may be complete or partial. There may also be an associated tingling sensation in the affected area.
Sudden confusion or trouble speaking or understanding. Sometimes weakness in the muscles of the face can cause drooling.
Sudden trouble seeing in one or both eyes
Sudden trouble walking , dizziness, loss of balance or coordination