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The Nervous System Peripheral Nervous System Sympathetic system: prepares body for stress or action & triggers fight or flight reactions Parasympathetic system: returns body systems to normal, lowers heart & breathing rates, promotes digestion The Neuron: A Powerful Computer • • • • • Neurons Sensory neurons Motor neurons Interneurons Glial cells Reflexes The Neuron Major Parts of a Neuron The Neuron: A Powerful Computer • Neural impulses: The brain in action – Ions – Action potential – All-or-none law – Myelin Ion Flow that Produces an Action Potential Neural Firing • A resting neuron is negatively charged • If a portion is stimulated beyond its threshold, it briefly reverses polarity • This polarity reversal travels down the neuron • Neurotransmitters are released at the axon terminals Synapse • Tiny gap between an axon terminal & another neuron (or specialized cell). • Firing neurons release neurotransmitters that cross the synapse. • Synaptic Vesicles: – Hold the neurotransmitter. – Neural firing drives them to the synapse, where they release their chemicals. Synapse • The neurotransmitter binds to the receptor site on the target cell • Ion gates open • Excess neurotransmitter is reuptaken Neurotransmitters • After crossing the synapse, the neurotransmitter is reuptaken or degraded • There are more than 40 known types • Different neurotransmitters have different effects • Drugs, neural diseases often affect neurotransmitters Neurotransmitters • Acetylcholine: important for learning, memory, muscle movement • Serotonin: influences mood and regulates food intake • Dopamine: important to movement and to frontal lobe activity • GABA: important in inhibiting neural activity • Norepinephrine: maintains alertness & wakefulness • Endorphins: regulate firing of pain neurons Drugs • Many drugs influence synaptic transmission • Drugs can be agonistic or antagonistic Agonistic Drugs • Increase synthesis of neurotransmitter, or • Increase release of neurotransmitter, or • Activate receptors, imitate neurotransmitter, or • Inhibit reuptake of neurotransmitter Antagonistic Drugs • Interfere with release of neurotransmitter, or • Occupy and block neurotransmitter sites, or • Cause neurotransmitter loss from vesicles. Psychology and Neurons Tying human behavior to neurons is difficult. There may be 100 billion neurons in your body. Each neuron has many connections.