Synapses

• Utilise neurotransmitters, such as acetylcholine
• When an action potential reaches the axon terminal it stimulates voltage-gated Ca2+ channels to open
• Ca2+ floods the cytoplasm of the cell and binds to vesicles containing neurotransmitter
• These vesicles are then stimulated to exocytose their contents into the synaptic cleft
• Acetylcholine diffuses across the synaptic cleft to bind to receptors on the post-synaptic neuron and stimulating a new action potential

Comparison:

Has a time delay of 1ms

Unidirectional 

Has the potential for signal modulation

• Include gap junctions
• Gap junctions are a physical pore-like connection between cells
• Formed of proteins called connexins, which form connexons which join together
• Molecules of <1kDa can pass through

Comparison

Faster, no time delay

Bidirectional

Potential for signal relay

• Are connections between neurons and muscles
• Utilise acetylcholine
• Acetylcholine stimulates the depolarisation of the sarcolemma
• The action potential propogates down the t-tubules, which sit in between the sarcoplasmic reticulum
• The action potential stimulates the sarcoplasmic reticulum to release its stores of Ca2+ to stimulate the muscle contraction cycle

• Summation = the combining of multiple action potentials to allow the threshold value of -50mV to be reached 
• Spatial summation = the combining of action potentials from several different neurons
• Temporal summation = the combining of action potentials from the same neuron
• Cancellation = action potentials may be excitatory or inhibitory, therefore they may cancel each other out