Transmission Across a Synapse

1. Transmission Across a Synapse

2. An electron micrograph

3. Step 1 • After an action potential arrives at an axon bulb, Ca2+ enters the bulb. • Ca2+ allow the synaptic vesicles to fuse with the pre-synaptic membrane. • This is an example of exocytosis and requires ATP from cellular respiration in the mitochondria.

4. Step 1

5. Step 2 • Neurotransmitters are released into the synaptic cleft. • neurotransmitters diffuse across the gap and bind to the receptor proteins on the postsynaptic membrane of dendrite.

6. Step 2

7. Step 3 • If enough neurotransmitters bind to the receptor membrane proteins in the postsynaptic membrane of the dendrite.... • the Na+ channels open and Na+ diffuse into the dendrite producing an action potential in the neuron. • There are specific receptor proteins for specific neurotransmitters.

8. Step 3

9. What happens to the neurotransmitters? • Enzymes can rapidly inactivate the neurotranmitter once it has performed its function. • Acetylcholinesterase breaks down acetylcholine. OR • The pre-synaptic membrane rapidly reabsorbs the neurotransmitters, re-packaging them into synaptic vesicles (endocytosis) or for molecular breakdown.

10. Some exciting neurotransmitters – and some not-so exciting ones! • At least 25 neurotransmitters have been identified. • Excitatory Acetylcholine – controls muscles and help regulate memory, (sometimes inhibitory) Norepinephrine – fight or flight Glutamate – most common excitatory neurotransmitter. Involved in learning and memory. • Inhibitory Dopamine – feelings of pleasure. GABA – regulates muscle tone. Seratonin – controls mood, appetitie & sensory perception Melatonin – helps regulate circadian rthythms, sleep-wake cycle.

11. Recall QuizCan you identify the numbers?

12. The Numbers • Postsynaptic membrane • Pre-synaptic membrane • Synaptic vesicle • Mitochondrion • Synaptic cleft • neurotransmitter • Receptor membrane protein • Ion channel • Postsynaptic dendrite • Axon bulb

13. Place the events in order. • Neurotransmitters diffuse across the synaptic cleft. • Na+ diffuse through the opened channels on the postsynaptic membrane. • The action potential arrives at an axon bulb. • Neurotransmitters bind to receptor proteins. • Ca2+ enter the axon bulb and cause synaptic vesicles to fuse with the pre-synaptic membrane. • An action potential begins at the next neuron.