Cells of the Nervous System The Nerve Impulse Genes can be dominant recessive or intermediate Chromosomes come in pairs 23 in humans They re made of molecules of DNA If genes are dominant show a pretty strong effect either in the homozygote or heterozygote representation If it s recessive only show effect in homozygote situation If the genes are the same it s homozygote if the genes are different it s heterozygote Humans have about 30 000 genes For a long time scientists had thought we have a lot of junk DNA because it didn t seem to be connected to any genes The sex linked chromosomes are the only pair of chromosomes that are not autozonous A sex linked characteristic is almost always X linked X genes have more genes than Y because that s a very small chromosome Sex limited genes can be on any chromosome in either sex but they are activated in only one sex Genetic mutations are very rare If they occur they are recessive and typically only occur on one gene You may actually see changes in genes within one lifetime A whole bunch of our genes can be turned on or off at any time The junk DNA turns on and off the genes they re switches Epigenetics is about changes in genes during the lifetime because of changes being made Scientists want to know the effect of genes compared to environment heritability factor estimate This is an estimate of the variance that is due to genetics correlation coefficient A gene can affect an individual directly or indirectly Indirect effect can be tall kid pushed towards basketball the genes predisposed towards tallness indirectly affect the child CNS is central nervous system brain and spinal cord Consists of two cell types neurons and glial cells 100 billion neurons give or take Neurons have all the same things as the average cell Neurons have a unique shape neurons have a soma where we can find the same things as an average cell Neurons have dendrites which reach out to receive information from other sources like other neurons Dendrites have spines the more dendrites and more spines neurons have the more information a neuron can receive Most neurons also have an axon which stretches out to the presynaptic bulbs axon is usually covered in the myelin sheath a fatty substance All mature neurons have one or no axons The axon sends information to another neuron dendrites receive information Neurons need glucose It s a metabolic process requiring oxygen There are 2 major types of neurons The first are sensory neurons or receptor neurons these are specialized Some are highly sensitive to certain kinds of information like light stimulates the visual sensory neurons which don t respond to sound or smell Motor neuron is the second type Motor neurons in general receive information from other neurons conduct impulses and then send information to appropriate muscle Vast majority of neurons in CNS are inter neurons intrinsic neurons The entirety of the neuron is in a single structure Afferent neuron is one that carries information to another neuron or another structure a for admission Efferent neuron carries information from another neuron or structure e for exit Glial cells don t transmit information across long distances unlike neurons They do exchange chemicals in some cases with neurons Neurons and glial cells occupy about the same amount of space in humans Glial cells are about a tenth as big as neurons meaning we have twice as many glial cells as neurons One type of glial cell is astrocyte A lot of same neurons do the same thing When sending chemicals to carry information astrocytes gather the unneeded chemicals and return them to the neurons They also carry off waste material and dilate blood vessels These cells can also release chemicals that alter the function of neurons Radial glial cell is another type Radial glial are a type of astrocyte They help guide the migration of neurons through the development of the CNS so they end up where they need to be This happens during the development of the fetus Also helps guide the development of the axons Radial glial cells will for the most part convert to astrocytes once the development of the CNS is finished Microglia cell is another type Also important for removing waste material Also very good at finding and removing bacteria microorganisms function like immune cells in the brain Oligodendrocyte are another type If they re in the PNS not CNS they re called Schwann cells Responsible for building the myelin sheath If axons are covered in myelin information is transmitted a lot faster White matter is myelinated axons During cell proliferation cells that are less specialized reproduce much more frequently than the ones that are very specialized Skin cells reproduce very frequently like daily Neurons are the most differentiated specialized cells in the body For the most part once one has all the neurons they don t reproduce for the most part As of today there are two places in the brain where the production of new neurons occurs The olfactory bulb is one place important for sense of smell hippocampus is another place important for memory Glial cells reproduce fairly often The brain CAN change shape and does so primarily by the action of those dendrites More stimulation results in more dendrites Like rats raised in two different environments a cage filled with toys vs a normal cage Blood brain barrier allows some chemicals to get into the brain fairly easily but keeps most chemicals out of the brain Some things are able to cross the barrier faster than others Lipid soluble stuff dissolvable in fats cross the barrier fairly easily Blood brain barrier is composed of endothelial cells These cells bind the blood vessel wall so tightly that not much can get through There is an active transport system that takes needed chemicals into the brain because they can t otherwise get through There s one part of the blood brain barrier that is weaker than the rest of it which is at the back of the head area postremia is responsible for the vomit reflex This allows enough information to get to the brain so you can determine quickly whether or not you need to get rid of something dangerous via vomiting There are many things that can weaken the barrier Radiation some infections some trauma pressure hypotension high blood pressure etc can weaken blood brain barrier If the barrier is damaged it can rebuild itself