Ch 11 Chemical Synapses

Synaptic vesicles

filled with chemical messengers (neurotransmitters); transmit signals from presynaptic to postsynaptic neurons at chemical synapses

Synaptic cleft

small ECF-filled space; separates presynaptic and postsynaptic neurons in chemical synapses (gap junctions connect neurons in electrical synapses)

Postsynaptic neuron has neurotransmitter receptors

bind neurotransmitter secreted from presynaptic neuron

synaptic delay

time gap between arrival of action potential at axon terminal and effect on postsynaptic membrane

Chemical synapses are

unidirectional (unlike electrical synapses); allows for variable signal intensities; more neurotransmitter released from presynaptic neuron leads to stronger response at postsynaptic neuron

What happens first at a chemical synapse

Action potential in presynaptic neuron triggers opening of voltage-gated calcium ion channels in axon terminal

After the voltage-gated calcium ion channels open what happens

Influx of calcium ions causes synaptic vesicles to release neurotransmitter into synaptic cleft

After the neurotransmitters are released into the synaptic cleft,

Neurotransmitters bind to receptors on postsynaptic neurons

After the neurotransmitters bind to receptors on postsynaptic neurons

Ion channels open, leading to local potential and possibly action potential if threshold reached