Synapse and Neuromuscular Junction

Synapses

• gaps between two neurones end of axon on one neurone and dendrite of another

• action potential is transmitted as neurotransmitters that diffuse across the synapse and bind to the next neurone to trigger an action potential

Function of a synapse

• action potential arrives at synaptic knob (end of neurone) and depolarisation opens Ca+ channels so Ca+ diffuses into knob

• in synaptic knob, vesicles containing neurotransmitters fuse with (pre)synaptic membrane so neurotransmitter is released into synaptic cleft

• neurotransmitter diffuses down concentration gradient to post-synaptic membrane where it binds to complementary receptors on surface

• Na+ channels on post-synaptic membrane open so Na+ diffuses in (if enough neurotransmitter diffuses in then enough Na+ diffuses in above threshold) to depolarise post-synaptic neurone

• neurotransmitter is degraded and released from receptor, so Na+ channels close and post-synaptic neurone re-establishes resting potential

• neurotransmitter is recycled back to presynaptic neurone