Synaptic Transmission

Question 1

What is a neuromuscular junction?

Answer 1

The connection point of a motor neurons axon onto the muscle fibre

Question 2

What is the vesicle structure inside the synapse? What is its function?

Answer 2

A ball like structure which is where the neurotransmitter is stored before release

Question 3

Where is the synapse located?

Answer 3

At the end of an axon

Question 4

What does the action potential do to the vesicle structure inside the synapse?

Answer 4

It causes it to release its neurotransmitters stored inside the vesicle

Question 5

Where do the neurotransmitters stored in the vesicles get released to?

Answer 5

To the synaptic cleft

Question 6

What is the synaptic cleft?

Answer 6

space between the pre and post synaptic membranes

Question 7

What about the action potential in the synaptic vesicle causes the neurotransmitter to be released?

Answer 7

It opens up Ca2+ voltage gated ion channels

Question 8

What does the Ca2+ do to assist in neurotransmitter release? Where does the Ca2+ go?

Answer 8

Causes the vesicle membranes to merge with the pre-synaptic membrane which leads to exocytosis of the neurotransmitter <> Goes into the synapse

Question 9

What does the neurotransmitters do once in the synaptic cleft?

Answer 9

Interacts with the post-synaptic membrane activating ligand gated receptor channel complexes on their surface

Question 10

What does the ligand gated receptor channel complex open up when activated? What flows through it?

Answer 10

Opens non-selective cationic channels <> All cations (e.g. Na+, K+, Ca2+)

Question 11

What happens to the post-synaptic membrane when the neurotransmitter activates the ligated gated receptor channel complex on it? What movement of particles causes the membrane to depolarise?

Answer 11

It causes the post-synaptic membrane to depolarise <> Na+ goes in, K+ goes out

Question 12

What is the depolarisation of the post-synaptic membrane called?

Answer 12

End plate potential (EPP)

Question 13

What can the end plate potential then do on the muscle tissue?

Answer 13

If it reaches the threshold potential then it will activate Na+ gated ion channels resulting in an action potential being generated that propagates away (in both directions) from the synapse

Question 14

What can the end plate potential then do on the muscle tissue?

Answer 14

If it reaches the threshold potential then it will activate Na+ gated ion channels resulting in an action potential being generated that propagates away (in both directions) from the synapse

Question 15

What is the time delay from an action potential arriving at the synapse to the generation of an action potential in the muscle tissue?

Answer 15

0.5ms

Question 16

What is the neurotransmitter inside the vesicles of the synapse?

Answer 16

Acetylcholine (ACh)

Question 17

Under what circumstances would an action potential in the synapse cause a supra-threshold potential in the post-synaptic membrane?

Answer 17

It will always generate a supra-threshold potential resulting in an action potential

Question 18

What happens after an action potential is generated by the post-synaptic membrane?

Answer 18

It propagates through the muscle tissue

Question 19

What are the two types of chemical synapses isn’t eh CNS?

Answer 19

Excitatory synapse and inhibitory synapses

Question 20

What does depolarisation of the excitatory synapse cause?

Answer 20

Depolarisation of the post synaptic membrane result in the Excitatory postsynaptic potential (EPSP)

Question 21

What does depolarisation of the inhibitory synapse cause?

Answer 21

Hyper-polarisation of the postsynaptic membrane called the inhibitory postsynaptic potential (IPSP)

Question 22

Label the diagram of the process of synaptic activation

Answer 22

Question 23

What are the neurotransmitters that mediate excitatory synapses?

Answer 23

Mainly glutamic acid/glutamate or ACh

Question 24

What is glutamate?

Answer 24

An amino acid

Question 25

What is the ionic mechanic of excitatory postsynaptic potentials (EPSPs)?

Answer 25

Transient opening of ligand gated Na+, K+ and sometimes Ca2+ channels

Question 26

What are the neurotransmitters that mediate inhibitory synapses?

Answer 26

Mainly GABA (gamma-aminobutyric acid) or glycine

Question 27

What is the ionic mechanic of inhibitory postsynaptic potentials (EPSPs)?

Answer 27

Usually transient opening of ligand gated K+ channels

Question 28

What are the classification of neurotransmitters?

Answer 28

Small molecule neurotransmitters and Neuropeptides

Question 29

What are the characteristics of small molecule neurotransmitters?

Answer 29

Small molecules that usually fast action and direct on the post synaptic receptors

Question 30

What are some examples of small molecule neurotransmitters?

Answer 30

Amino acids (i.e. glutamate, GABA, glycine etc.), Acetylcholine (ACh) and Amines (serotonin etc.)

Question 31

What are the characteristics of neuropeptides?

Answer 31

Large molecules that have an indirect (i.e. metabotropic) action on postsynaptic receptor or regulatory (i.e. modulatory) action and are slow to react: second to minutes

Question 32

What are some examples of neuropeptides?

Answer 32

Neuropeptide Y, Substance P, Kisspeptin, Enkephaln (remember 2)

Question 33

What are the factors determining synaptic actions?

Answer 33

Type of neurotransmitter/modulator \<\> The type of neurotransmitter receptor in the postsynaptic membrane \<\> The amount of neurotransmitter receptor expressed in the postsynaptic membrane (synaptic plasticity)

Question 34

How can the type of receptor affect the function of the neurotransmitter? Give an example with glutamate

Answer 34

Different types of receptors process the neurotransmitter differently \<\> i.e. Glutamate has four different types of receptors: Kainate, NMDA, AMPA and Metabotropic glutamate receptor (it is indirectly activated by a messenger molecule) \<\> Kainate, AMPA and NMDA are all cationic non-selective ion channel but Kainate and AMPA are permeable to K+ and Na+ only while kainite is also permeable for Ca2+

Question 35

What is calcium important for?

Answer 35

The release of neurotransmitter in the synapse \<\> Contraction of muscles

Question 36

What are the levels of calcium in the brain measured in?

Answer 36

Low µmolL-1

Question 37

What happens if too much glutamate is released?

Answer 37

Causes too much Ca to go through NMDA receptor causing excessive depolarisation and over activation of neurons

Question 38

What happens when there is long-term opening of NDMA receptors?

Answer 38

Causes excessive Ca2+ entry into neurons which damages them by excitotoxicity

Question 39

What are some diseases caused by excitotoxicity?

Answer 39

Parkinsons, alzheimers

Question 40

How is the neurotransmitter inactivated?

Answer 40

It diffuses away form the synapse \<\> Enzymatic degradation \<\> Re-uptake and recycling

Question 41

What enzyme can degrade ACh? Where does this degradation occur?

Answer 41

Acetylcholine esterase in the synaptic cleft

Question 42

What is the re-uptake of neurotransmitters more common for?

Answer 42

Amino acids and amines

Question 43

How are neurotransmitters re-absorbed? What is this called?

Answer 43

Neurotransmitter transports int eh pre-synaptic membrane or the adjacent glia cells \<\> Glutamate transporter

Question 44

What kind of CNS component is particular important in re-uptaking glutamate into the synapse?

Answer 44

Astrocytes

Question 45

What are axon initial segments covered in lots of?

Answer 45

Na+ voltage gated channels

Question 46

What is the function of dendrites?

Answer 46

To increase the surface area of synaptic contacts

Question 47

Up to how many synaptic contacts might there be on a nerve cell?

Answer 47

Tens of thousands

Question 48

How does a nerve cell integrate thousands of synaptic contacts into a signal?

Answer 48

Due to the temporal and spatial summation of postsynaptic potentials at axon initial segment

Question 49

How do the individual synapses contribute to the activation of an action potential?

Answer 49

Some synapses are excitatory and some inhibitory \<\> The excitatory synapses potential produces only a very small potential (0.1mV) and is a passive current so it degrades as it moves through the dendrites to the cell body \<\> The inhibitory synapses produce an opposite charge reducing the effect of EPSPs

Question 50

How can synapses produce an action potential?

Answer 50

Either by producing a series of rapid frequency EPSPs (TEMPORAL) which accumulate and reach supra-threshold potential OR multiple synapses producing an EPSP (SPATIAL) at the same time again accumulating to reach supra-threshold potential