Chemical Messengers

Question 1

What do neurotransmitters do?

Answer 1

The presynaptic nerve ending is separated by a small gap from the post synaptic component, electric current responsible for propagation of action potential along axons cannot bridge the synaptic gap, thus transmission along this gap is accomplished by neurotransmitters

Question 2

Where are postsynaptic component often located?

Answer 2

Dendritic spine

Question 3

Where are neurotransmitters stored?

Answer 3

They are stored in tiny spherical bags called synaptic vesicles in the endings of axons

Question 4

How are neurotransmitters released?

Answer 4

The arrival of an action potential leads to the opening of ion-channels that let in calcium (Ca2+). This activates enzymes that act on a range of presynaptic proteins, snare, tagmin and brevin, these synaptic proteins race around tagging and trapping others, causing releasable synaptic vesicles to fuse with the membrane, burst open and release chemical messenger out of nerve endings

Question 5

What happens to the synaptic vesicles after neurotransmitters are released?

Answer 5

Synaptic vesicles reform when their me,braces are swallowed back up into the nerve ending where they become refilled with neurotransmitter

Question 6

What happens to the neurotransmitter when it is released?

Answer 6

It diffuses across the synaptic cleft and once it gets to the other side, it interacts with receptors in the membrane of the next neuron

Question 7

What do glial cells do around the synaptic cleft?

Answer 7

They have transporters that suck up the transmitter in the cleft which clears the neurotransmitters out of the way before the next action potential comes, these glial cells then process the transmitter and send it back to be stored in the storage vesicles of nerve endings for future use

Question 8

What are some other ways neurotransmitters are cleared from synapse apart from transporters?

Answer 8

• Nerve cells pump the transmitter molecules back directly into their nerve endings
• transmitter is broken down by other chemicals in the synaptic cleft

Question 9

What happens when neurotransmitters interact with receptors?

Answer 9

The neurotransmitter binds with the receptors to cause the opening of ion channel

Question 10

What are ionotropic receptors?

Answer 10

They are receptors that respond to binding by opening an ion channel

Question 11

What happens when ion channel are open?

Answer 11

Ion channel allow positive ions (Na+ or Ca2+) to enter, this inflow of positive current leads to excitation which causes excitatory post-synaptic potential (epsp). If the sum of these epsps reaches the threshold for firing an impulse, a new action potential is set up and signals are passed down the axon of the receiving neuron

Question 12

What is the main excitatory neurotransmitter in the brain?

Answer 12

Glutamate

Question 13

What happens at inhibitory synapses?

Answer 13

Activation of receptors leads to the opening of ion channels that allow the flow of negatively charged ions, causing inhibitory post-synaptic potential (ipsp). This opposes membrane depolarisation and therefore initiation of an action potential at the cell body of receiving neuron

Question 14

What are the two inhibitory neurotransmitters?

Answer 14

GABA and glycine

Question 15

What is the time taken for the arrival of an action potential to the generation of epsp in the next neuron?

Answer 15

1ms

Question 16

What do neurons and inhibition have to do?

Answer 16

Different neurons have to time their delivery of glutamate on to others within a short window of opportunity if the epsps in the receiving neurons are going to add up to trigger a response and the inhibition also has to operate within the same interval to be effective in shutting things down

Question 17

What do metabotropic receptors do?

Answer 17

They adjust or modulate the vast array of chemical processes going on inside neurons

Question 18

What is neuromodulation?

Answer 18

Action of metabotropic receptors

Question 19

Where are metabotropic receptors found?

Answer 19

They are found in complex particles linking the outside of the cell to enzymes inside the cell that affect cell metabolism

Question 20

What happens when neurotransmitter is recognised and bound by a metabotropic receptor?

Answer 20

Bridging molecules called G-proteins and other membrane-bound molecules are collectively triggered. It kickstarts intracellular second messengers into action, engaging a sequence of biochemical events

Question 21

What are the effects of neuromodulation?

Answer 21

Changes in ion channels, receptors, transporters and expression of genes, these changes are slower onset and more long-lasting than those triggered by excitatory and inhibitory transmitters and their effects extend well beyond the synapse

Question 22

What are some examples of messengers acting on G-protein coupled receptors?

Answer 22

Acetylcholine, dopamine, noradrenaline

Question 23

How many noradrenaline neurons are there in human brain?

Answer 23

1600

Question 24

When is noradrenaline released?

Answer 24

It is released in response to various forms of unfamiliarity and stress to organise response of individuals to these challenges

Question 25

What do dopamine do?

Answer 25

Make certain situations rewarding for the animal, by acting on brain centres associated with positive emotional features

Question 26

What do acetylcholine do?

Answer 26

It acts on both ionotropic and metabotropic receptors, it uses ionic mechanism to signal across neuromuscular junction from motor neurons to stretched muscle fibres. It also functions as neuromodulator

Question 27

What is the first neurotransmitter to be discovered?

Answer 27

Acetylcholine