The next part of Lesson 3 had to do with the nervous system. The nervous system can be broken down as into the Central and Peripheral nervous systems. The central nervous system consists of the brain and spinal cord while the peripheral accounts for all the other nerves. The peripheral system can be broken into the somatic and autonomic systems, the autonomic system controls functions like heart beat, breathing, digestion etc... the somatic is responsible for voluntary functions. Both of these systems have motor and sensory nerves. The autonomic nervous system has both a sympathetic and parasympathetic nervous system. The sympathetic nervous system is responsible for the fight or flight response, when activated it does things like dilate the pupils, increase heart rate, inhibit digestion and relax the bronchi to make taking in more oxygen possible. When the parasympathetic nervous system is activated it has the opposite effect, the pupils and bronchi are restricted, heart rate is slowed and digestion is stimulated.
There are two types of cells that make up the nervous system, Glial cells and Neurons. Glial cells provide structural support and remove debris while Neurons process and transmit information. There are three different types of neurons; sensory, motor and interneurons, the interneurons connect neurons to one another. Below is a very rough drawing of a neuron. The Soma is the center of the cell and contains the nucleus. Branching off of the soma are the Dendrites, dendrites connect to other neurons and are the receivers for the cell. The axon transmits the electrical charge (when a neuron fires) to the terminal buttons, the mylin sheath (not present on all neurons) helps to speed up this process. The terminal buttons release neurotransmitters to neighboring neurons and the process repeats. Neurotransmitters can be either inhibitory or excitatory, excitatory neurotransmitters increase the chance that a neuron will fire while inhibitory ones decrease that chance. So to put it all together lets say an excitatory neurotransmitter is received by the dendrites of a neuron, if enough are received the neuron will fire off an electrical signal that runs down the axon and tells the terminal buttons to release more neurotransmitters once they do the cycle repeats with the next neuron.