Transcript The Nervous System

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.