synaptic transmission

Question 1

explain what chemical transmission is

Answer 1

• neurons communicate with each other within groups known as neural networks
• each neuron is separated from the next by a tiny gap called the synapse
• signals within neurons are transmitted electrically.
• signals between neurons are are transmitted chemically across the synapse
• when the electrical impulse reaches the end of the neurone (known as the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles.

Question 2

explain the role of neurotransmitters

Answer 2

• they are chemicals that diffuse across the synapse to the next neuron in the chain
• once a neurotransmitter crosses the gap, it is taken up by a postsynaptic receptor site on the dendrites of the next neuron (axons TO/dendrites AWAY from the synapse)
• here the chemical message is converted back into electrical impulse and the process of transmission begins again in this other neuron
• the direction of travel can only go one way because neurotransmitters are released from the presynaptic neuron terminal and received by the postsynaptic neuron (receptor site)
• they have specific functions and fit perfectly into the postsynaptic receptor site.

Question 3

explain excitation

Answer 3

• neurotransmitters can have an excitatory effect on the neighbouring neuron. E.g. adrenaline (an element of the stress response which is both a hormone and a neurotransmitter) causes excitation of the postsynaptic neuron by increasing its positive charge and making it more likely to fire.

Question 4

explain what inhibition is

Answer 4

• the neurotransmitter serotonin causes inhibition in the receiving neuron. resulting in the neuron becoming more negatively charged and less likely to fire.

Question 5

explain what summation is

Answer 5

• whether a postsynaptic neuron fires is decided by the process or summation. The excitatory and inhibitory influences are summed
• if the net effect on the postsynaptic neuron is inhibitory then the postsynaptic neuron is less likely to fire.
• if the net is excitatory it is more likely to fire- the inside of the postsynaptic neuron momentarily becomes positively charged. Once the electrical impulse is created it travels down the neuron.
• therefore the action potential of the postsynaptic neuron is only triggered is the sum of the excitatory and inhibitory signals at any one time reaches the threshold.

Question 6

what is synaptic transmission?

Answer 6

the process by which neighbouring neurons communicate with each other by sending chemical messages across the synapse that separates them

Question 7

what us a neurotransmitter

Answer 7

• are brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another.
• can be broadly divided into those that perform an inhibitory and excitatory function.