1. Transmission & Impulses Across a Synapse

2. First, let’s label a few key parts on this diagram:
Terminal knob
Pre-synaptic membrane
Post-synaptic membrane
Synapse
Secretory vesicle
Receptors
Contractile proteins (add these on to the diagram!)
Dendrite

3. Step 1- Arrival of the Impulse
Electrical movement of signal ends at axon bulb
Depolarization/repolarization events (Na+/K+ ions) carry signal

4. Step 2- Movement of Ca2+ Ions
Presynaptic membrane become permeable to Ca2+
Ca2+ floods into axon bulb
Causes contractile filaments to shorten  vesicles drawn to membrane

5. Step 3- Release of Neurotransmitter
Neurotransmitters released through EXOCYTOSIS into synapse
An active process (ATP needed)
So… Mitochondria are often in this region!

6. Step 4- Movement Across Synapse
Neurotransmitter DIFFUSES across the synaptic gap
Moves from high to low concentration
2 important neurotransmitters:
- Acetylcholine (Ach)… most common
- Noradrenalin (NA)

7. Step 5- Binding with Receptors
Ach received in post synaptic membrane by receptors
“All or none” response
Remaining Ach in synapse cleared by enzyme Acetylcholine esterase

8. Step 6- Next neuron fires!
Ach binding to receptors cause Na+ gates to open
Impulse continues along dendrite (electrically)