PH1124 - conduction & synapse transmission

Question 1

what are the types of ion channels? (2)

Answer 1

• voltage gated ion channels

- ligand gated ion channels

Question 2

where are voltage gated ion channels found?

Answer 2

• axons and nodes of ranvier

Question 3

where are ligand gated ion channels found?

Answer 3

• in the synapse

Question 4

What happens at resting state?

Answer 4

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.

Question 5

What is the ratio of sodium to potassium in the pump?

Answer 5

3 sodium’s are pumped out and 2 potassium’s are pumped in.

Question 6

what is the difference between relative and absolute when talking about action potentials?

Answer 6

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.

Question 7

What is the threshold value?

Answer 7

-50mV/-60mV

Question 8

What are the 2 steps to depolarise a membrane?

Answer 8

1 local current depolarise membrane to its threshold.

2 Sodium channels open allowing rapid influx of soduim

Question 9

What is the depolarization potential?

Answer 9

+40mV

Question 10

What are the 2 steps to repolarize the membrane?

Answer 10

voltage gates close despite membrane being depolarized.

K channels opens releasing K which causes hyperpolarisation.

Question 11

What is the refractory period?

Answer 11

a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.

Question 12

How is an action potential propagated along an axon?

Answer 12

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.

Question 13

How does myelin speed up the rate of transmission?

Answer 13

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.

Question 14

What are synapses?

Answer 14

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.

Question 15

How do the sodium ligand gates work?

Answer 15

Neurotransmitter bind to the ion gate opening the channel for the soduim to flow through and depolarize.

Question 16

What is a neurotransmitter?

Answer 16

A substances that transmits nerve impulses across a synapse which is synthesises within the presynaptic knob.

Question 17

How does an action potential cross a synapse?

Answer 17

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.

Question 18

How is acetylcholine (ACh) removed from the synaptic cleft?

Answer 18

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.

Question 19

What are the 3 main types of neurotransmitters?

Answer 19

Esters such as acetylcholine.
Monoamines such as dopamine.
Amino acids such as glutamate.

Question 20

Where is acetylcholine used and is it inhibitory or excitatory?

Answer 20

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

Question 21

Where is noradrenaline, dopamine and serotonin found and are they excitatory or inhibitory.

Answer 21

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.

Question 22

are monoamines excitatory or inhibitory?

Answer 22

• both excitatory and inhibitory mainly activating on g coupled receptors

Question 23

how are monoamines reuptaken?

Answer 23

• 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

Question 24

How to drugs interfere with the reuptake of neurotransmitter?

Answer 24

They block the re-uptake transporter protein e.g reboxetine blocks the noradrenaline re-uptake transporter.

Question 25

What are the examples of amino acid neurotransmitters?

Answer 25

Glutamate and GABA

Question 26

Where are amino acid neurotransmitters found and are they excitatory or inhibitory?

Answer 26

Found in the brain GABA is only inhibitory and Glutamate is only excitatory.

Question 27

How are glutamate and GABA made?

Answer 27

Glutamine to Glutamate via glutamine synthetase. Glutamate to GABA via glutamate decarboxylase.

Question 28

BY what cell is both glutamate and GABA predominantly recycled by?

Answer 28

Astrocytes.

Question 29

How is GABA recycled back to glutamine?

Answer 29

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.

Question 30

What is the difference between excitatory and inhibitory neurotransmission?

Answer 30

Inhibitory transmission will cause the increase of chloride ions into the post synaptic neuron which will not cause an action potential.

Question 31

How is the activity of the neurotransmitter stopped?

Answer 31

Rapid enzymatic destruction.
Uptake into nerve terminals or neighbouring cells.
Diffusion away from the synapse followed by one of the above.

Question 32

What will a agonist do to the activity at the synapse?

Answer 32

Increase activity as activates the receptors.

Question 33

What will antagonists do to the activity at the synapse?

Answer 33

Decrease the activity as blocks the receptors.

Question 34

What will inhibition of the reuptake do to the activity at the synapse?

Answer 34

Increase the activity because it will block the reuptake so there will be more neurotransmitter in the synapse.

Question 35

If synthesise enzymes of the neurotransmitter are inhibited what will that do at the activity of the synapse?

Answer 35

Decrease activity as less neurotransmitter is released.

Question 36

If degradation enzymes are inhibited what will that do to the activity of the synapse?

Answer 36

Increase activity as more neurotransmitter remains in the synaptic cleft.