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 Synaptic Vesicles: 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.