Brain Damage
Fall 2002

There are many different ways the brain can be damaged. These include:

1) Diseases:

Genetic disorders (e.g., Down's Syndrome).
Infections: bacterial (meningitis; neurosyphilis)
viral (herpes)
prion (Mad cow disease): these are infectious proteins. Degenerative diseases (Parkinson's; Alzheimer's ): related to aging
Cancer: an abnormal growth of neurons or glia in the brain 2) Vascular problems: Stroke: disruption of blood flow to part of brain
Hemorrhage: blood leaks into brain
Ischemia: lack of oxygen to brain 3) Chemical damage: Drugs & Toxins (e.g., lead poisoning; fetal alcohol syndrome; MPTP)
Malnutrition 4) Mechanical damage:
Trauma (e.g., bullets, car accidents, boxing)
Of course, the brain is very well protected to prevent these problems.
 
 

There is a big difference between adult and baby brains in what causes damage.

Baby brains are especially susceptible to chemical damage. This is because: Development requires chemical signals.
Growing neurons can overcome mechanical damage.
  Adult brains are especially susceptible to cell death. This is because: Relatively few new neurons are created in adults
Axon growth is limited.
 
  The three factors that contribute to recovery from brain damage are: 1. Age: Young brains are more likely to recover than old brains.

2. Therapy: The saying "use it or lose it"applies to the brain.

3. Cause of the damage: Gradual loss of neurons allows other areas to compensate.
 

 Recovery occurs because: 1) There are changes in uninjured neurons

2) The patient develops coping strategies (e.g., recognize people by voice, not sight)
 

 Any change in healthy neurons is called Plasticity. Plasticity refers to the brain's flexibility and is known to occur during: development
learning
recovery from damage
  Plasticity can occur in a number of different ways: 1. Synaptic changes Presynaptic change in transmitter release
Postsynaptic change in the number or sensitivity of receptors
  2. Axons sprout collaterals that form new synapses

3. Activate quiet synapses. These are connections that are not usually active.
 

 There is a reorganization of the brain even when damage is in the periphery. For example, neurons in the somatosensory cortex respond to input from a specific region of the body. If this body part happens to disappear (e.g., you cut your arm off), then the cortical neurons that used to respond to your arm will begin responding to neighboring body parts (e.g., the face). The primary mechanism appears to be activation of quiet synapses. The more you use certain parts of your brain the stronger those connections become.
 

Specific disorders:

Epilepsy

Can range from small to complex seizures. There appear to be many types and many causes. The neural mechanism is uncontrolled synchronized neural activity. Loss of GABAergic inhibition will cause epilepsy. Most commonly treated by drugs that facilitate GABA inhibition or inhibit uncontrolled firing of action potentials, although in some cases surgical removal of the focal point or cutting the corpus callosum is used to contain the siezure.


Korsakoff's syndrome

Characterized by anterograde amnesia and partial retrograde amnesia. During the early stages confabulations often accompany these memory problems. Korsakoffís syndrome is caused by the death of neurons in the hypothalamus as a resutl of a thiamine deficiency. This is most likely to occur from poor eating habits in alcoholics.


Alzheimer's Disease

A type of dementia (progressive decline in mental function) that includes anterograde and retrograde amnesia (70% of dementia cases are caused by Alzheimer's disease, 15% are caused by strokes). Eventually all bodily functions are lost. 11% of people in the U.S. between the ages of 65-75 have Alzheimer's disease. The incidence increases approximately 2% with each year after age 75 (20% by 80).

The only way to accurately diagnosis Alzheimer's disease is by examining the brain post-mortum. There are two markers:

Senile plaques are deposits of beta amyloid associated with dead neurons.

Neurofibrillary tangles are intracellular bundles that have broken down.

CAT & MRI scans show a shrunken cortex. Neurons in the cortex and hippocampus, especially those containing ACh, die.

The cause of Alzheimer's disease is unknown. There appears to be a genetic component in some cases. In these cases, Alzheimer's has been linked to chromosome 21.
 

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