March 6, 2013

IV. Synapse
     A. Excitatory
          1. When the nerve impulse reaches the synaptic knob, sodium comes rushing in, making the interior positive. (35+)
          2. This knocks Ca2+ off of its binding sites on the inner membrane, and it bonds to the synaptic vessicles.
          3. This releases excitatory neurotransmitters into the synaptic cleft where it bonds to the receptor sites on the post-synaptic membrane of the next neuron.
          4. This opens the sodium gates, making the resting charge closer to the threshold (-50). It it reaches -50mv, it will "fire".
     B. Inhibition - post-synaptic neuron is less likely to fire.
          1. Same
          2. Same
          3. An inhibitory neurotransmitter is released into the cleft and it bonds to receptor sites on the post-synaptic neuron.
          4. This opens chlorine channelse and chlorine diffuses in, making the interior more negative (-90) and less likely to fire.

Note 1: All neurotransmitters must be immediately broken down by enzymes or else their effect will continue long after the impulse stops.

Note 2: These neurotransmitters are constatly battling with one another in the synapses of our body. The Parasympathetic Nervous System is the reason why our neurons are less likely to fire at night.

Note 3: Summation - When the sum total of Excitatory (+) and Inhibitory (-) neurotransmitters "add up" to the Post-synaptic neuron reaching the threshold. 2 types:
     1. Temporal - one or a few neurons are firing enough times within a given unit of time to achieve summation. (quickly putting your finger on a piece of ice)
     2. Spacial - many neurons fire at once and release enough neurotransmitters to achieve summation (putting your whole hand quickly on the table)