When an action potential reaches the presynaptic terminal, it causes neurotransmitter to be released from the neuron into the synaptic cleft, a 20–40nm gap between the presynaptic axon terminal and the postsynaptic dendrite (often a spine).Īfter travelling across the synaptic cleft, the transmitter will attach to neurotransmitter receptors on the postsynaptic side, and depending on the neurotransmitter released (which is dependent on the type of neuron releasing it), particular positive (e.g. Neurons talk to each other across synapses. On the right is an example from an actual neuron in the mouse's cortex. (Image: Alan Woodruff / QBI) Synapses: how neurons communicate with each other The term is a reference to the shape of an action potential as recorded using sensitive electrical equipment.Ī neuron spikes when a combination of all the excitation and inhibition it receives makes it reach threshold. Neuroscientists often refer to action potentials as ‘spikes’, or say a neuron has ‘fired a spike’ or ‘spiked’. These are respectively termed excitatory and inhibitory inputs, as they promote or inhibit the generation of action potentials (the reason some inputs are excitatory and others inhibitory is that different types of neuron release different neurotransmitters the neurotransmitter used by a neuron determines its effect).Īction potentials are the fundamental units of communication between neurons and occur when the sum total of all of the excitatory and inhibitory inputs makes the neuron’s membrane potential reach around -50 mV (see diagram), a value called the action potential threshold. from -70 mV to -65 mV), and others do the opposite. Some inputs make the neuron’s membrane potential become more positive (or less negative, e.g. It’s constantly going up and down, depending mostly on the inputs coming from the axons of other neurons. Normally, the inside of the cell is more negative than the outside neuroscientists say that the inside is around -70 mV with respect to the outside, or that the cell’s resting membrane potential is -70 mV. There are many channels sitting in the cell membrane (the boundary between a cell’s inside and outside) that allow positive or negative ions to flow into and out of the cell. Neurons are essentially electrical devices. In an intact brain, the balance of hundreds of excitatory and inhibitory inputs to a neuron determines whether an action potential will result.The neurotransmitter can either help (excite) or hinder (inhibit) neuron B from firing its own action potential.At the junction between two neurons ( synapse), an action potential causes neuron A to release a chemical neurotransmitter.Neurons communicate with each other via electrical events called ‘action potentials’ and chemical neurotransmitters.
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