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 nervoussystem 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 nextneuron 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 theaxons. 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 neuronNeurotransmitters are released from the terminal buttons, and they are received by thedendrites of the next neuron. If received enough, they will “fire” and the neuron is activated.Chemical messages are either excitatory or inhibitoryThe cerebral cortex has 12-15 billion neuronsThe cerebellum has 70 billionThe spinal cord has 1 billionThe nervous system is divided into the● Central Nervous System: spine and brain● Peripheral Nervous System: all the individual neurons1. Sensory Division: sensory neurons2. Motor Division: motion and motor neuronsI. Somatic Nervous System: controls musclesII. Autonomic Nervous System: helps agitate and then calm you down➢ Sympathetic nervous system is a “fight-or-flight” system thatmakes us more aggressive and ready to act.➢ Parasympathetic nervous system is a system that calms usdownWe also divide the brain into a few different “lobes”1. Occipital: vision2. Frontal: planning ahead, complex thinking3. Temporal: hearing4. Parietal: integrates information from all sensesA lot of the slowest nerves are related to pain, temperature and itchWe can use EEG, CT, PET and mRI to study the brainIf someone were to electrically stimulate the top part of someone’s brain, you’d swear theytouched your leg (consult September 22 lecture)Neurons and the brain form during the embryonic stage, when parts of the ectoderm roll up andform the neural tube, which produces hundreds of thousands of neurons per minuteThe most important change in development is long term potentiation (aka the strengthening ofsynaptic bonds).In adolescence, neural pruning results in a drop in neuron production and synapticconnections. While this is meant to eliminate unnecessary neurons and strengthen existingones, a lot of scientists think mental illnesses form here due to necessary neurons accidentallybeing eliminatedHebb's rule: neurons that fire together wire togetherLeft side of the brain controls right side of body and vice versa (contralateral