PH1124 - conduction & synapse transmission Flashcards
what are the types of ion channels? (2)
- voltage gated ion channels
- ligand gated ion channels
where are voltage gated ion channels found?
- axons and nodes of ranvier
where are ligand gated ion channels found?
- in the synapse
What happens at resting state?
The environment is more negative on the outside of the neuron then on the inside at -70mv there is more potassium on the inside than outside and more sodium outside than in the axon this is maintained by the sodium potassium pump.
What is the ratio of sodium to potassium in the pump?
3 sodium’s are pumped out and 2 potassium’s are pumped in.
what is the difference between relative and absolute when talking about action potentials?
Absolute means there can not be another action potential after a signal has been fired however relative means that sometimes another signal can be sent but it is hard.
What is the threshold value?
-50mV/-60mV
What are the 2 steps to depolarise a membrane?
1 local current depolarise membrane to its threshold.
2 Sodium channels open allowing rapid influx of soduim
What is the depolarization potential?
+40mV
What are the 2 steps to repolarize the membrane?
voltage gates close despite membrane being depolarized.
K channels opens releasing K which causes hyperpolarisation.
What is the refractory period?
a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.
How is an action potential propagated along an axon?
An action potential causes more channels to open due to the local change in membrane potential, the membrane channels behind become inactive therefore the action potential can only move in one direction.
How does myelin speed up the rate of transmission?
A process called saltatory conduction insulates the sheath meaning a local current can flow passively along a greater distance of the axon getting to the other end quicker.
What are synapses?
gaps between neurons where connections between the axon and dendrites take place a chemical neurotransmitter takes information from the presynaptic neuron to the postsynaptic cell.
How do the sodium ligand gates work?
Neurotransmitter bind to the ion gate opening the channel for the soduim to flow through and depolarize.
What is a neurotransmitter?
A substances that transmits nerve impulses across a synapse which is synthesises within the presynaptic knob.
How does an action potential cross a synapse?
An action potential arrives at the pre synaptic neurone which causes depolarisation this causes voltage gated calcium channels to opening allowing an influx of calcium in. This triggers vesicles containing neurotransmitter to move and fuse wit the membrane. Neurotransmitter is diffuses across the synapse and binds to receptors on the post synaptic membrane opening them and causing sodium to flow in causing depolarisation of the next axon.
How is acetylcholine (ACh) removed from the synaptic cleft?
Acetylcholine is broken down by the enzyme acetylcholinesterase which breaks it down into acetate and choline, choline is taken back up to the receptor to be resynthesized and terminates the signal.
What are the 3 main types of neurotransmitters?
Esters such as acetylcholine.
Monoamines such as dopamine.
Amino acids such as glutamate.
Where is acetylcholine used and is it inhibitory or excitatory?
Found in the synapses from neeves to nerves in PNS, CNS and ANS but also in the neuromuscular junction and it is both inhibitory and excitatory depending on the receptor either ion channel or G protein coupled
Where is noradrenaline, dopamine and serotonin found and are they excitatory or inhibitory.
In the brain stem and in the cortex as well as other brain regions also in the spinal cord. They are both excitatory and inhibitory mainly activating on g coupled receptors.
are monoamines excitatory or inhibitory?
- both excitatory and inhibitory mainly activating on g coupled receptors
how are monoamines reuptaken?
- energy dependent mechanism where ATPase creates a concentration gradient which drives the opening of a channel and the ions then equilibrate as the channel opens
How to drugs interfere with the reuptake of neurotransmitter?
They block the re-uptake transporter protein e.g reboxetine blocks the noradrenaline re-uptake transporter.
What are the examples of amino acid neurotransmitters?
Glutamate and GABA
Where are amino acid neurotransmitters found and are they excitatory or inhibitory?
Found in the brain GABA is only inhibitory and Glutamate is only excitatory.
How are glutamate and GABA made?
Glutamine to Glutamate via glutamine synthetase. Glutamate to GABA via glutamate decarboxylase.
BY what cell is both glutamate and GABA predominantly recycled by?
Astrocytes.
How is GABA recycled back to glutamine?
GABA is converted to succinate semialdehyde which can enter the citric acid cycle via a dehydrogenase enzyme. After the cycle glutamate synthase converts to metabolite to glutamate which can then be converted to glutamine by glutamine synthetase.
What is the difference between excitatory and inhibitory neurotransmission?
Inhibitory transmission will cause the increase of chloride ions into the post synaptic neuron which will not cause an action potential.
How is the activity of the neurotransmitter stopped?
Rapid enzymatic destruction.
Uptake into nerve terminals or neighbouring cells.
Diffusion away from the synapse followed by one of the above.
What will a agonist do to the activity at the synapse?
Increase activity as activates the receptors.
What will antagonists do to the activity at the synapse?
Decrease the activity as blocks the receptors.
What will inhibition of the reuptake do to the activity at the synapse?
Increase the activity because it will block the reuptake so there will be more neurotransmitter in the synapse.
If synthesise enzymes of the neurotransmitter are inhibited what will that do at the activity of the synapse?
Decrease activity as less neurotransmitter is released.
If degradation enzymes are inhibited what will that do to the activity of the synapse?
Increase activity as more neurotransmitter remains in the synaptic cleft.
