1. UNIT 3 – BIOLOGICAL BASES OF BEHAVIOR
MODULE 9 – BIOLOGICAL PSYCHOLOGY AND NEUROTRANSMISSION

2. MODULE 9 – BIOLOGICAL PSYCHOLOGY AND NEUROTRANSMISSION
How is Flushing a Toilet Like a Neuron Firing? 1 - All-or-Nothing Principle 2 - Direction of Impulse 3 - Refractory Period 4 - Threshold 5 - Resting Potential 6 - Action Potential 7 - Depolarization

3. All-or-Nothing Principle
- Once the threshold is reached, the neuron will fire at full strength. If the threshold is not reached, the neuron will not fire.
– the toilet either flushes completely or not at all; it doesn’t flush a little or a lot

4. Direction of Impulse
- The nerve impulse flows in one direction. The dendrites receive incoming nerve impulses from other neurons, and the axon transmits the impulse to another neuron or receptor. 
– the toilet only flushes one way, the impulse can’t come the other direction (you hope!)

5. Refractory Period
-The period after a neuron fires, at which time it is less susceptible to stimulation from other neurons. The neuron must recharge itself electrically until it reaches polarization. Once this occur, the neuron is ready to fire again. – after you flush the toilet, it won’t flush again for a certain period of time, even if you push the handle repeatedly

6. Threshold
- A point of excitation on the neuron that must be reached for an action potential to occur.
– you can push the handle a little bit, but it won’t flush until you push the handle past a certain point (this corresponds to the level of excitatory neurotransmitters that a neuron must absorb before it will fire)

7. Resting Potential
- Negatively charged ions wait for stimulation within the axon. The neuron is said to be inactive and is waiting for another action potential.
–the toilet is waiting to fire, and the water in the tank represents the overall negative charge inside the neuron waiting for depolarization

8. Action Potential
-A change in the balance of the overall charge of the neuron causes the electrochemical signal to travel (it is fired) along the axon.
– opening the flap in the tank and the water rushing through the pipes

9. Depolarization
- When stimulated, the channels along the axon allow positively charged sodium (NA+) and potassium (K+) ions to ender. This causes subsequent sodium (NA+) and potassium (K+) channels to open, thus propelling the electrochemical process down the axon.
– represented by the toilet flushing