Transmission & Impulses Across a Synapse

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

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

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

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

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)

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

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