synaptic transmission

Electrical synapse

Electrical synapse - neurones are connected by gap junctions, ions pass directly from one neurone to another, transmissions are extremely fast and there is two-way communication ​

Chemical synapse

Chemical synapse - neurones are separated by synaptic cleft, neurotransmitters are released when action potential reaches the presynaptic terminal, transmission is slower and one-way ​

Otto Leowi

Otto Loewi’s frog heart experiment

stimulated the vagus nerve attached to frog’s first heart

Heart rate slowed down

Collected fluid surrounding first heart

Transferred fluid to the second heart

Findings - second heart also slowed down , despite nerve not being stimulated

Demonstrates that communication between nerves and their target organs could occur through chemical transgression ​

How are neurotransmitters released at the synapse

1. Action potential arrives: An action potential reaches the presynaptic terminal.

2. Calcium channels open: Voltage-gated calcium (Ca²⁺) channels open in the presynaptic membrane.

3. Calcium enters: Ca²⁺ enters the presynaptic terminal down its electrochemical gradient.

4. Vesicle fusion: Calcium triggers synaptic vesicles to fuse with the presynaptic membrane.

5. Exocytosis: Neurotransmitters are released into the synaptic cleft.

6. Receptor binding: Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane.

7. Postsynaptic response: Receptor activation produces a response, which may be excitatory or inhibitory.​

Synaptic potential at neuromuscular junction vs at CNS