Synaptic Transmission


Introduction

The human brain consists of billions of billions of neurons that are constantly communicating with each other. Communication between neurons is the reason we sense, perceive, think, feel and act, but how exactly do these neurons convey information? Neurons aren't physically connected to each other; tiny gaps called synapses, separate each and every one of them. Thus neurons must transmit information across synapses using chemicals in order for information to travel through the vast network of connections in our brains. The process by which neurons communicate across synapses is called 'synaptic transmission'.



Below is a diagram of a group of neurons. Neurons don't touch each other directly. Instead the axons of one neuron and the dendrites of another are separated by tiny synapses. Information travelling from one neuron to another always starts at a dendrite and continues along the cell body to the axon. It is at the end of the axon, called the axon terminal, where synaptic transmission begins.



The neuron sending the signal is called the pre synaptic neuron, the neuron receiving the signal is called the post synaptic neuron. When an action potential reaches an axon terminal of the pre synaptic neuron it causes vesicles contained within the axon terminal to move towards the synapse and release chemicals called neurotransmitters into the synapse. These neurotransmitters bind with the receptors on the dendrites of the post synaptic neuron which can trigger an action potential in the post synaptic neuron. Receptors are sensitive to the shape of the neurotransmitter so that a receptor can only bond with a specific neurotransmitter. Once the message has been conveyed the neurotransmitters are released from the receptors in the synaptic space. Some of them are broken down by enzymes and some are reabsorbed by the pre synaptic neuron.


Review Questions

Question: Below is an unlabelled diagram of two neurons that share a connection. Drag and drop the labels onto the correct location.


Question: 2. Below is a close up picture of the location where synaptic transmission occurs. Drag and drop the labels to the correct locations.