Synaptic Transmission Flashcards
What is sic transmission?
The term ‘synaptic transmission’ refers to the process by which neighbouring neurons communicate with each other by sending chemical messages across the gap (synapse) that separates them. In other words a nerve impulse passes across the synaptic cleft from one neuron (the presynaptic neuron) to another (the postsynaptic neuron)
Explain the process of synaptic transmission
When a neuron is in resting state the inside of the cell is negatively charged compared to the outside. Neurons must transmit information both within the neuron and from one neuron to the next. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur – this creates an electrical impulse that travels down the axon towards the end of the neuron (this process is known as electric transmission).
Once an action potential has arrived at the axon terminal it needs to be transferred to another neuron. To achieve this it must cross the gap between the pre-synaptic neuron (the neuron transferring the action potential) and the post-synaptic neuron (the neuron receiving the action potential). This area is called the synapse and includes the end of the pre-synaptic neuron, the membrane of the post-synaptic neuron and the gap in between. The physical gap between the pre-synaptic neuron and postsynaptic neuron is called the synaptic cleft. On the axon terminal are a number of sacs known as synaptic vesicles. These vesicles contain chemical messengers, known as neurotransmitters, which assist in the transfer of the action potential. As the action potential reaches the vesicles, it causes them to release their contents through a process called exocytocis.
The released neurotransmitter diffuses across the synaptic gap where it binds to specialised receptors on the surface of the dendrites of the post-synaptic neuron that recognise it and are activated by that particular neurotransmitter. The whole process of synaptic transmission takes only a fraction of a second, with the effects terminated at most synapses by a process called re-uptake. The neurotransmitter is taken up again by the pre- synaptic neuron where it is stored for later release. The quicker the neurotransmitter is taken back the shorter the effects.
What are neurotransmitters?
Neurotransmitters are chemical messengers that carry signals from the pre-synaptic neuron across the synaptic cleft to the receptor site on the post-synaptic neuron.
What are the different types of treat neurotransmitters?
Neurotransmitters can be classed as either excitatory or inhibitory in their action. Inhibitory neurotransmitters are generally responsible for calming the mind and body, inducing sleep and filtering out unnecessary excitatory signals. Excitatory neurotransmitters are likely to increase your chances to activate or carry out a behaviour (e.g to be aggressive)
Examples of X excitatory neurons
Adrenaline and dopamine
Please note that all neurotransmitters can be inhibitory or excitatory apart from GABA which is inhibitory)
Examples of inhibitory neurons
Serotonin and gaba
What does an excitatory neurotransmitter do?
An excitatory neurotransmitter binding to a post-synaptic receptor causes an electrical charge in the membrane of the post-synaptic neuron resulting in an excitatory post-synaptic potential (EPSP), meaning that the post-synaptic cell is more likely to fire. An inhibitory neurotransmitter binding to a post-synaptic receptor results in an inhibitory post-synaptic potential (IPSP), making it less likely that the neuron will fire.
What is the summation?
A nerve cell can receive both EPSP’s and IPSP’s at the same time. The likelihood that the cell will fire is determined by adding up the excitatory and the inhibitory synaptic input. The net result of this calculation, known as summation, determines whether or not the cell will fire.
How can you increase the strength of an EPSP?
The strength of an EPSP can be increased in two ways. In spatial summation a large number of EPSPs are generated at many different synapses on the same post-synaptic neuron at the same time. In temporal summation a large number of EPSPs are generated at the same synapse by a series of high-frequency action potentials by a pre-synaptic neuron. The rate at which a particular cell fires is determined by what goes on in the synapse. If excitatory synapses are more active the cell fires at a high rate. If inhibitory synapses are more active the cell fires at a much lower rate, if it fires at all.
