Transmission Impulses Across a Synapse First lets label

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 Ca 2+ Ions • Presynaptic membrane become permeable to Ca 2+ • Ca 2+ 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)