Ch 10 Brain Damage & Neuroplasticity (pt2)

March 20, 2013

Causes of Brain Damage

Brain Tumors Cerebrovascular Disorders (Strokes)

Cerebral Hemorrhage & Ischemia Closed-Head Injuries Infections

Bacterial & Viral NeurotoxinsGenetic FactorsProgrammed Cell Death

Genetic Factors

Normal human cells have 23 pairs of chromosomes

An extra chromosome 21 results in Down syndrome Occurs in 0.15% of births▪ Likelihood increases with maternal age

Flattened skull & nose, inner eye folds of skin, short fingers, intellectual impairment & medical complications

Programmed Cell Death

Apoptosis: genetic self-destruct program for neurons (cell suicide)

Functions in early development by eliminating extra, unnecessary neurons

Also involved in brain damage Passive cell death (necrosis) occurs only

when neurons are damaged severely The majority is due to apoptosis

Neurons slowly shrivel, die & break down without inflammation or causing damage to nearby cells

Neuropsychological Diseases

Epilepsy Parkinson’s Disease Huntington’s Disease Multiple Sclerosis Alzheimer’s Disease

Epilepsy

Main symptom is repeated seizures, caused by chronic brain dysfunction

Different types of seizures Convulsions▪ Motor seizures; involve tremors (clonus), rigidity (tonus)

& loss of balance and consciousness Others happen with seemingly no change in

behavior All of the previously discussed causes of brain

damage can cause epilepsy Often associated with problems at inhibitory

synapses

Epilepsy

Diagnosed with scalp electroencephalography (EEG)

People often experience a weird psychological change before a convulsion (epileptic aura) Ex: bad smell, déjà vu,

hallucination Can give a hint of brain area

causing seizures

Epilepsy

2 types1. Partial

Partial seizure does not involve the whole brain

Caused by synchronous burst of neuron firing

2. Generalized Entire brain is involved Grand mal (“classic” seizure) Petit mal (no convulsions)

Parkinson’s Disease

Symptoms of a resting tremor, muscular rigidity, difficulty initiating movement, slow movement, masklike face

Associated with degeneration of the substantia nigra in the midbrain Primarily of dopaminergic neurons So symptoms can be alleviated by L-

Dopa injections (but not permanently) Other treatments include dopamine

agonists

Huntington’s Disease

Another progressive motor disorder Late stages involve severe cognitive

decline Onset around age 40

No cure & usually death within 15 years Rare Has a strong genetic basis

If a parent has it, 50/50 chance child will have it

Multiple Sclerosis

MS is a progressive disease that attacks the myelin of axons in the CNS

Eventually causes dysfunction in the axons & scar tissue develops (sclerosis)

An autoimmune disorder Symptoms include visual

disturbances, muscular weakness, numbness, tremor & ataxia (loss of motor coordination)

Genetic & environmental influences

Alzheimer’s Disease

The most common cause of dementia Likelihood of having it increases with age

10% of age 65+; 35% of age 85+ Progressive disease

Early stage: memory decline, attention problems & personality changes

Mid stage: confusion, irritability, anxiety, problems with speech, swallowing & bladder control

Ultimately terminal Can only be certain of diagnosis

during autopsy Presence of neurofibrillary tangles &

amyloid plaques

Neuroplastic Responses

Neuroplastic responses to brain damage

1. Degeneration2. Regeneration3. Reorganization4. Recovery of function

Neural Degeneration

aka neural deterioration 2 types1. Anterograde degeneration

Degeneration of distal segment▪ (Section of axon between the cut & the synaptic

terminal)▪ Segment no longer gets energy from the cell body

2. Retrograde degeneration Degeneration of proximal segment▪ (Section of axon between the cut & the soma)▪ If the axon cannot reestablish contact with a target,

the neuron eventually dies

Neural Regeneration

Regrowth of damaged neurons Not as successful in mammals as in

lower vertebrates & inverts Almost nonexistant in CNS of adult

mammals Regrowth from proximal stump 2-3

days after axonal damage Does not necessarily mean that

function will be returned

Neural Reorganization

The brain can effectively reorganize itself in response to damage Other areas can compensate for the damaged

area’s function Ex: blind individuals have little use for

visual cotex, so the auditory & somatosensory cortex expands into this region, giving them heightened sensitivity to hearing & touch

Works by strengthening existing connections & making new ones

Neuroplasticity & the Treatment of Nervous System Damage

May be possible to reduce brain damage by blocking neural degeneration Apoptosis inhibitor proteins Nerve growth factor Estrogren ▪ Potentially explains why several brain

disorders are less common in women Molecules that limit degeneration

also promote regeneration

Neuroplasticity & the Treatment of Nervous System Damage

Regeneration in mammalian CNS doesn’t normally happen, but in the lab it can be induced

Potential treatment with transplantation of fetal tissue into the brain or injection of embryonic stem cells

Rehabilitation training can help by encouraging brain reorganization Ex: treadmill for spinal cord injuries

Physically & mentally active individuals are less likely to contract neurological disorders & if they do, their symptoms are more mild & they have fuller recovery