The nervous system is your body s way of sending instantaneous messages to nerves throughout the body Reflexes are a very simple type of these signals The cells of the nervous system are called neurons and they are what sends and receives these signals Dendrites are the branches at the end of neurons that almost but not quite touch the next neuron in front of it Axons are yet another part of neurons and they are more like the central body of the neuron with lots of information going through it The glia forms the myelin sheath which provides insulation to neural signals going through the axons Glia is about 1 10th the size of the neurons but about 10 times as numerous If dendrites are at one end of the axon then the terminal buttons are at the other end Synapse a specialized junction where chemical messages cross from one neuron to a second It separates the terminal button of one neuron from the dendrite of the closest neuron Neurotransmitters are released from the terminal buttons and they are received by the dendrites of the next neuron If received enough they will fire and the neuron is activated Chemical messages are either excitatory or inhibitory The cerebral cortex has 12 15 billion neurons The cerebellum has 70 billion The spinal cord has 1 billion The nervous system is divided into the Central Nervous System spine and brain Peripheral Nervous System all the individual neurons 1 Sensory Division sensory neurons 2 Motor Division motion and motor neurons I II Somatic Nervous System controls muscles Autonomic Nervous System helps agitate and then calm you down Sympathetic nervous system is a fight or flight system that makes us more aggressive and ready to act Parasympathetic nervous system is a system that calms us down We also divide the brain into a few different lobes 1 Occipital vision 2 Frontal planning ahead complex thinking 3 Temporal hearing 4 Parietal integrates information from all senses A lot of the slowest nerves are related to pain temperature and itch We can use EEG CT PET and mRI to study the brain If someone were to electrically stimulate the top part of someone s brain you d swear they touched your leg consult September 22 lecture Neurons and the brain form during the embryonic stage when parts of the ectoderm roll up and form the neural tube which produces hundreds of thousands of neurons per minute The most important change in development is long term potentiation aka the strengthening of synaptic bonds In adolescence neural pruning results in a drop in neuron production and synaptic connections While this is meant to eliminate unnecessary neurons and strengthen existing ones a lot of scientists think mental illnesses form here due to necessary neurons accidentally being eliminated Hebb s rule neurons that fire together wire together Left side of the brain controls right side of body and vice versa contralateral control