Anoxia can occur in a wide variety of settings including heart attack, drowning, carbon monoxide poisoning, and numerous other causes. The brain consumes a third of the energy in the human body and after six or seven minutes without oxygen the brain begins to die.

Anoxia primarily affects the grey matter of the brain, which is on the outside of the brain, over the white matter. Anoxia will affect areas of the brain such as the basil ganglia, the hippocampus, and the cerebellum. On MRI it may show as a blurring of the division between a grey and white matter or showing laminar necrosis. If anoxia damage is visible on MRI, the outcome is generally considered poor.

Hypoxia on the other hand is a context in which the human body is receiving some oxygen but not enough oxygen. Under these circumstances, by relieving the situation can generally bring the individual back without permanent damage to the brain. However, an extended, hours long hypoxic event could cause permanent brain injury.

Blunt trauma would occur when the head strikes an immoveable object, or a heavy object confronts the head. This will generally involve tissue damage or bruising to the area close to the point of impact and may include damage to the opposite side of the brain (known as coup-contrecoup injury).

Concussion is a word that is thrown around rather loosely. Basically, a concussion would be the equivalent of a mild TBI. Concussions can be rated on a scale from one to three according to their severity. A concussion can be blunt trauma to one area or a more diffuse whole brain type of injury.

This is a bruise or superficial injury to the outside of the brain that occurs when it comes in contact with the inner surface of the skull. This is seen most commonly in a car accident involving the shaking of the frontal lobes against the boney bottom of the brain pan.

The cranial nerves come from the brain through the skull and surround the head and they can be injured during trauma. Out of the eight cranial nerves the most common injuries are as follows:

• First (sense of smell) - this is the most damaged cranial nerve and can often result in anosmia (loss of sense of smell or reduced smelling). Less than half of those with injury to the first cranial nerve recover. This greatly affects and diminishes the sense of taste.

• Second (visual) - injury here can affect the sight but is often a temporary problem.

• Third (eye) Vision Problems

• Fourth (eye) Vision Problems

• Fifth (face) Trigenial-injury can create an ultra painful condition in the face, usually an electrical type burst of pain on contact with the face.

• Sixth (vision) - this can affect the workings of the muscles involved in vision and can result in double vision.

• Seventh (facial) - commonly seen with a fracture of the temporal bone, this injury can result in immediate or delayed facial paralysis or facial pain syndrome.

• Eighth (hearing) - again, if there is a temporal fracture near the ear, bleeding in the middle ear and dizziness can result.

• Nine (throat) Tongue control

• Ten (vagus) taste, swallowing, speech difficulties

• Eleventh (shoulder pain)

• Twelfth (tongue)

More serious "diffuse" injuries can occur in, for example, a high-speed auto collision, where the head is moved at a high rate of speed or stops at a high rate of speed. Obviously, if the speed changes are slowed (someone falling on a mattress instead of a concrete floor) there is less chance of injury. Please note that these types of injuries can occur with or without the head striking anything at all.

The degree of injury has to do with whether or not it is a linear movement of the brain (straight ahead and straight back like a woodpecker) or is rotational. Rotational forces are well known to cause more severe injury than a linear type of force. If, for example, a person's head is turned to the side when they are rear-ended, they will have, on average, a worse outcome than if they were looking straight ahead. Most TBIs involve complex forces that are both rotational, linear and combinations of the above. This can result in widespread diffuse axonal injury, whereby the neurons, the brain's actual brain cells that make up the grey matter of the brain, are injured. The human brain can be seen as a grapefruit with the grey matter being the skin of the grapefruit and the white matter being everything inside the skin. The grey matter consists of neurons which "speak" to other neurons in the brain through electrical impulse. The electrical impulse is sent through feelers which are call synapsis which reach out and connect to hundreds, if not thousands, of other neurons within an incredibly small space. The number of connections of synapsis in the brain goes to the high trillions.

The density of the grey matter is higher than that of the white matter beneath it. The white matter consists of telephone lines of a sort, ultra-thin spaghetti like strands that are insulated like an electric wire by a myelin sheath. The white matter allows communication to exist between the different lobes of the brain. White matter becomes injured because of stretching during trauma. The stretching either snaps or damages the myelin sheath of the white matter resulting in later death or impairment.

The common place for traumatically induced lesions in the brain is at the grey-white junction. This is the place where the grey matter connects to its telephone lines, and because of the differing density of grey and white matter we commonly find signs of damage in this area after trauma.

Sometimes after trauma, blood remnants or other material may block the drainage of CFS out of the brain resulting in increased pressure. This can occur either acutely or chronically. Usually, the first symptom will be gait unsteadiness and if that arises, go to the emergency room. A shunt can be placed in the patient to allow excess fluid to be leaked off before causing irreparable harm.

Patients can suffer increased pressure inside of the brain wall as a result of bleeding, swelling or contusion. Unfortunately, when the pressure increases inside of the skull, it reduces the ability of blood flow to get properly to the brain resulting in reduced brain profusion. If the intracranial pressure rises into abnormal levels, it can shift the entire brain in one direction or the other, a phenomenon known as "midline shift." This is a serious condition that could lead to death. If the midline shift is severe enough, it can herniate the tissues separating the two halves of the brain, resulting in early catastrophic injury. If there is an issue of increased intracranial pressure (ICP), an ICP monitor can be installed in the brain of the patient. Treatment to reduce pressure includes:

• Hyperventilation to reduce blood volume;

• Ingestion of medications to decrease swelling such as Manitol;

• Administration of Dexamethasome;

• Finally, if needed, surgical evacuation of the source of the bleed.

Propofol may also be administered to reduce elevated ICP.

This is bleeding within the brain itself, most commonly in the temporal or frontal lobes.

Small blood vessels in the brain can be torn when a patient sustains a blow to the head. Leakage will form a clump of blood that can interfere with the functioning of the brain. These clots develop between the dura, a leathery case around the brain and the inside of the skull. They are usually associated with younger patients and skull fractures. The bleeding can be rapid and cause death within minutes. Half of the patients will have a "lucid interval" which means after the trauma they are conscious and speaking and thereafter fall back into unconsciousness. This occurred with the actress who died on the ski slopes, for example. If problems with pressure can be avoided, then recovery from this type of event can generally be successful. If too much time passes before reduction of the pressure, one might see the dilation of one pupil or both pupils, a bad sign.

Most skull fractures can be diagnosed by x-ray. In most areas of the skull the fracture is observable and can be dealt with.

A temporal bone fracture on the side of the face near the ear, as well as a basil or basilar fracture can be more difficult to diagnose by x-ray. This type of fracture can cause bleeding within the eardrum, called hemotympanum, and can be seen as red on exam. It can also cause ringing in the ears, dizziness, and nerve damage. Commonly the fluid in the brain system, known as CFS can be seen coming out of the ears or nose after such a fracture, for which bed rest and antibiotics are called for. There is a threat of meningitis and if the leak last more than ten days, surgical exploration is necessary.

This is bleeding inside of the leather casing of the brain, called the dura, and the brain itself. These types of bleeds are more common in persons 40 or older because of the shrinking brain giving more room for movement to stretch some of the bridging veins in the brain. Persons on anti-clotting medication are at risk for this type of injury. This can happen acutely, meaning less than three days after the trauma, sub-acutely within three days to three weeks or it can happen chronically three weeks or more after trauma.