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Ch. 19 Sec. 1 Notes Functions of the Nervous System *The nervous system receives information about what is happening both inside and outside your body *It directs the way in which your body responds to this information *Helps maintain homeostasis *Without your nervous system, you could not move, think, feel pain, or taste Receiving Information *Your body is always aware of what is happening in the environment around you Ex: If it’s too hot, your body will start to sweat *Your body also checks conditions inside your body Ex: Glucose levels Responding to Information *Any change or signal in the environment that can make an organism react is called a stimulus *After your nervous system analyzes the stimulus, it causes a response -What your body does in reaction to a stimulus Maintaining Homeostasis *Nervous system tells your body what you need when you need it Ex: Shivers when cold, grab a blanket Rumbles when hungry, eat food The Neuron *Your nervous system includes the brain *The cells that carry information through your nervous system are called neurons, or nerve cells *The message that a neuron carries is called a nerve impulse The Structure of a Neuron *A neuron has a large cell body that contains the nucleus, threadlike extensions called dendrites, and an axon *The dendrites carry impulses toward the neuron's cell body *The axon carries impulses away from the cell body -Nerve impulses begin in a dendrite, move toward the cell body, and then move down the axon *A neuron can have many dendrites, but only one axon *Axons and dendrites can be called nerve fibers *A bundle of nerve fibers is called a nerve Kinds of Neurons *3 kinds of neurons are found in the body: 1. Sensory neurons -Picks up stimuli from the internal or external environment and coverts each stimulus into a nerve impulse -The impulse travels along the sensory neuron until it reaches an interneuron 2. Interneuron -Carries nerve impulses from one neuron to another 3. Motor neurons -Sends an impulse to a muscle or gland, which react in response How a Nerve Impulse Travels *Every day, billions of nerve impulses travel through your nervous system *They all begin in dendrites; move rapidly toward the neuron's cell body and then down the axon until it reaches the axon tip *A nerve impulse travels along the neuron in the form of electrical and chemical signals -Can travel as fast as 120 m/s The Synapse *When a nerve impulse reaches the axon tip, it can pass to the next structure *Sometimes the structure is the dendrite of another neuron *Other time, the structure is a muscle or a cell in another organ *The junction of passing to the next structure is called 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 tip release chemicals that carry the impulse across the gap