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Nervous System Notes Ch. 19.1 Functions of the Nervous System • The nervous system receives information about what is happening both inside and outside you body. • It also tells your body to respond to information. • It also helps maintain HOMEOSTASIS! Receiving Information • Your nervous system tells you that something is happening around you: – Like a fly buzzing around your head. – Or the wind is blowing – Or a friend is telling a funny joke. – It also checks your body for glucose levels or when you feel sick. Responding to Information • Any change or signal in the environment that makes you react is called a stimulus. • The fly buzzing is a stimulus. • When your body REACTS, it is called a response! • Swatting the fly is a response. Responding to Information • There are 2 kinds of responses: • Voluntary = things you think about doing: – Swatting the fly • Involuntary = things your body does without thinking: – Heart beats, breathing in your sleep Maintaining Homeostasis • The nervous system helps maintain Homeostasis by directing the body to respond appropriately to the information is receives. – If you are hungry, your nervous system tells you to eat! = homeostasis! – Homeostasis = the things your body does to keep you alive in that “just right” kind of way. The Neuron • Neuron is the name for Nerve Cells! • They carry messages around your body! • These messages are called Nerve Impulses! Neuron Structure • The neuron is made of 3 major sections: – The cell body – Axon – Axon tips Structure Cont. • The Cell body contains – The nucleus (brain of the cell) – Dendrites (thread like extensions that catch nerve impulses) • There can be MANY dendrites forming a large “net”. Axon • The Axon carries the impulses toward the next Neuron’s cell body. • It’s like the highway the impulse takes from point A to point B. • THERE IS ONLY 1 AXON PER NEURON Axon Tips • The Axon tips shoot out charged chemicals that act like electricity in the body. • These chemicals are the messages that are sent through your body. Kinds of Neurons • 3 major kinds of neurons –Sensory Neurons • These neurons “sense” your surroundings and send the message to your SPINAL CORD or BRAIN! They sense pressure or heat and cold. Cont. –Interneurons • These neurons carry messages from one neuron to the next neuron. “Middle Men” –Motor Neurons • These connect to muscles or glands to cause a response. (move leg muscle, sweat!) How a Nerve Impulse Travels • Nerve impulses can travels as fast as 120 meters per second! THAT’S FAST! • Messages travel from the Cell Body, down the axon, and to the axon tips! The Synapse • After the nerve impulse reaches the axon tip, there is a space between neurons! • This space is the synapse! How an Impulse is Transferred • For a nerve impulse to be carried along at a synapse, it must cross the gap between the axon and the next structure. • The axon tips release chemicals that carry the impulse across the gap. • It’s like a car trying to get from one side of the river to the next on a ferry boat!