Brain Development and Injuries As far as brain development is concerned only study these notes In humans the CNS starts to form when one is 2 weeks after gestation By birth it weighs about a quarter of a pound After a year it s a little over 2 pounds Once adulthood it s about 3 pounds You do see development after birth through adolescence and even into adulthood The brain goes through 5 different stages of development First stage is proliferation This is simply the production of new cells During very very early development there are stem cells that line the ventricles these divide and become primitive neurons or primitive glial cells Second stage is migration After cells become either neurons or glial cells they go to where they need to be This is what happens during migration They have help on their destination Immunoglobins and chemokines help cells migrate If there s a problem with these cells one will see a problem with migration mental retardation is the least problem Third stage is differentiation This stage neurons start to form their unique shape It s not uncommon for the axon to grow first sometimes one will see neurons migrate with the axon dragged behind them Fourth stage is myelination Glial cells produce myelin This starts in the back of the CNS spinal cord hind brain midbrain and then forebrain Synaptogenesis is where the formation of synapses takes place This continues throughout life it doesn t stop For the most part the neurons one is born with is it There are 2 places in the brain that we know of where the formation of new neurons takes place throughout life The olfactory bulb and the hippocampus important for learning and memory During development of the CNS we start out with a lot more neurons than we need There are a couple of reasons why this is the case Some refer to it as neural Darwinism only those that are strong and fit will survive The other hypothesis relates to different head sizes because bigger heads require more neurons Part of what determines where the neurons need to go is determined by what they need to get to These targets also send out chemicals called neurotrophins They promote survival of incoming axons these axons are exposed to more trophins possibly making them fitter The neurons that aren t used are supposed to die and do so via the process of apoptosis This is programmed cell death These trophic factors are released throughout life Trophic factors help with synaptogenesis A lot of these experimental operations one hears about like using stem cells are also supplemented with trophic factors because they promote survival Possible exposure to a class of chemicals called teratogens is a problem people have to be concerned with Teratogen is anything that can cause permanent damage to the developing fetus There are several aspects of a teratogen one needs to be worried about threshold dose at what level does it become harmful stage sensitivity period of development at which a teratogen can have negative effects Most prominent teratogen in U S and probably the world is alcohol Different effects of alcohol based on trimester By third trimester all CNS development is already set Alcohol is known to cause a disorder called fetal alcohol syndrome which causes mental retardation and some physical characteristics facial and growth abnormalities cardiovascular problems distractibility impulsivity Alcohol stunts dendritic growth in unborn kids as well Once it s formed the brain is not set in stone It fine tunes and changes through the life Enriched environments are helpful in enriching the brains resulting in the growth of more dendrites More education is correlated with more dendritic branches Blind people are more sensitive to sound and smell other senses This is the result of the unused occipital cortex taking on other uses in order to help out In an MRI one can see activation in the occipital cortex along with the auditory when listening to something If one practices a lot there might be some sensory reorganization as a result of that practice like playing musical instruments for years With musicians the parietal and temporal areas will have developed a little differently because of all the practice they ve put in This can lead to problems One problem has been studied extensively because for many musicians it s a career ender It s called focal hand dystonia Focal hand dystonia is a problem for anyone who plays an instrument with their hands Over time the sensory representation for certain fingers will bleed over or encroach upon the somatosensory areas in the parietal area responsible for other fingers this eventually means one cannot differentiate between the two fingers There are no treatments to treat focal hand dystonia Phantom limb pain is also involved with sensory reorganization This involves a limb that is no longer physically present really hurting Previously the amputation had continued further and further in an attempt to get rid of the phantom limb pain This does nothing The brain is used to getting a lot of sensory information from limbs but suddenly nothing is coming That means it rewires itself so the brain are that used to get information from the missing limb gets information from another place No one knows why one gets pain A way of getting rid of pain is tricking the mind that the amputated arm is in fact intact by using mirrors and then unclenching a fist The pain goes away BRAIN INJURIES There are many different causes of brain injuries Some viruses some tumors some diseases cause brain damage Two causes we will focus on will be strokes and closed head injuries means skull isn t pierced An edema is a swelling of the brain that results from too much fluid entering the brain This is a common cause of brain injury It can cause inter cranial pressure leading to the brain pressing up against the skull and blood vessels rupturing If one is taken to an ER one of the first things they will do is give anti inflammatories to get that swelling down Things to do if you suspect someone is having a stroke Smile Lift both arms Say a simple sentence and ask the possibly affected person to repeat it If that person can t do any one of those three things call 911 Time is critical in treating a stroke It is possible to have a mini stroke that you don t even notice It s usually a harbinger of worse things so one should go in and check things out Ischemia is one kind of stroke it s more common It occurs when a blood clot or some other kind of