What organ coordinates most of the activities of the nervous system? Through what part of the body do most messages reach or leave the brain? The brain and spinal cord form what part of the nervous system? What connects the central nervous system to muscles and sense organs throughout the body? What carries signals throughout the nervous system? Name some parts of a nerve cell, or neuron. What do we call the tiny space between neurons over which signals must pass from neuron to neuron? What do we call the electrical signals that have reached the end of an axon and have become chemical signals? What special nerve cells allow us to see, hear, feel, taste, and smell the world around us? What special nerve cell allows us to move? Anything that brings about a response Examples * stimulus step on nail * response jerk foot up * stimulus see bright light * response squint Eyes Basic units of the nervous system Axon tips Dendrites reach out and grab sensory information and send it to the cell body Axons carry the message away from the cell body to another neuron sensory neurons receive sensory info from environment and send it to the brain or spinal cord interneurons in the brain and spinal cord, they decide what to do with the message from the sensory neuron motor neurons carry reaction message away from the brain toward muscles Neurons do not touch. Messages are transferred by chemicals jumping across the gap between two neurons, called a synapse. Sensory neurons in the ear hear breaking glass. The brain takes the message from the sensory neurons and decides if a response is necessary. The brain decides the response should be to cover eyes with hands. This message leaves the brain via a motor neuron. The motor neuron dead- ends in a muscle, telling the muscle to contract and jerk up the arms. Example taken from an issue of National Geographic, p. 528 Central is brain and spinal cord, only Peripheral is all nerves outside the brain and spinal cord. It connects the body to the brain and spinal cord. Sensory neurons travel toward the brain or spinal cord for message interpretation. Motor neurons travel away from the brain or spinal cord for responses. Spinal cords diameter gets larger and larger as you go up the back toward the brain. Spinal nerves have both sensory and motor neurons, so messages travel in two directions somatic nerves that go to the skeletal muscles, so voluntary autonomic involuntary (sympathetic and parasympathetic) Involuntary, automatic responses to stimuli Controlled by spinal cord, not brain Leaving out the brain enables the body to react faster