Neurotransmitters & synapses

Question 1

How are neurotransmitters packaged into vesicles?

Answer 1

• enzymes that are needed to make small molecule transmitters are synthesized in the cell body and move to presynaptic terminal
• substrates transported to pre synaptic terminal
• transported into vesicles
• large neuropeptide precursors are synthesised in the cell body packaged into vesicles & transported along microtubule

Question 2

How are neurotransmitters released?

Answer 2

• small vesicles docked near ca2+ channels
• AP invades terminal
• Ca2+ channels open & Ca2+ enters
• vesicles fuse with presynaptic membrane and release contents
• vesicle membrane recycled

Question 3

Describe neurotransmission

Answer 3

• AP arrives at nerve terminal which opens Ca2+ channels
• Ca2+ entry causes vesicle fusion and transmitter release
• receptor channels open, transmitter binds to receptor and causes Na2+ ion channel to open
• Na2+ enters the postsynaptic cell and vesicles recycle

Question 4

what is an axosomatic synapse?

Answer 4

synapse between the axon of one neuron and the body of another

Question 5

what is a axodendritic synapse?

Answer 5

• synapse between dendrite of one cell and a dendrite of another

Question 6

what is a axo-axonic synapse?

Answer 6

• type of synapse, formed by one neuron projecting its axon terminals onto another neuron’s axon

Question 7

What is a mixed cation ion channel?

Answer 7

• channel that for example lets Na+ enter and K+ leave

Question 8

what is an excitatory postsynaptic potential? EPSP

Answer 8

• Postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential
• temporary depolarization of the postsynaptic membrane

Question 9

Compare EPSP vs IPSP

Answer 9

• excitatory (EPSP) = depolarization of postsynaptic cell - sufficient depolarisation could produce AP, eg glutamate in CNS binding to AMPA receptors
• Inhibitory (IPSP) = hyperpolarisation or repolarisation of postsynaptic cell , prevents action potential, eg GABA binding to receptors

Question 10

whats the difference between GABA a and GABA b?

Answer 10

• IPSP, due to Cl- entering the cell (GABA a type) or K+ ions leaving the cell (GABA b type)

Question 11

what happens if EPSP’s summate (adding up together) ?

Answer 11

• EPSP’s can summate to cause the cell to depolarise sufficiently to allow the cell to fire an action potential
• causes the cell to communicate with the next nueron

Question 12

compare and contrast spatial summation vs temporal summation

Answer 12

• Spatial - input to different dendrites
• Temporal - repetitive input onto the same terminal in a dendrite

Question 13

what are the important steps for transmission at a chemical synapse?

Answer 13

1. neurotransmitter synthesis either in presynaptic terminal or in the neuronal cell body
2. concentration and packaging of neurotransmitter molecules in preparation for release
3. release of neurotransmitter into synaptic cleft
4. Binding of neurotransmitter by post synaptic receptor molecules
5. termination of neurotransmitter action preparing the synapse for subsequent (coming after something in time , following ) release of neurotransmitter

Question 14

what is the priming stage of neurotransmitter recycling?

Answer 14

• vesicles in the reserve pool undergo priming to enter readily reversible pool
• involves assembly of SNARE complexes

Question 15

What are snare proteins and what is their function?

Answer 15

• large protein family
• they mediate vesicle fusion - the fusion of vesicles with target membrane or membrane bound compartments
• examples : synaptotagmin & synaptobrevin

Question 16

what is the function of synaptotagmin?

Answer 16

• functions as a calcium sensor
• entering Ca2+ binds to synaptotagmin and Ca2+ bound synaptotagmin catalyses membrane fusion

Question 17

what are the two types of postsynaptic receptors?

Answer 17

1. Ionotropic
2. Metabotropic -

Question 18

What is the difference between ionotropic and metabotropic receptors?

Answer 18

• they are both ligand gated transmembrane proteins
• ionotropic receptors change shape when they are bound to a ligand - channels open and ions flow in eg nAchR
• metabotropic receptors do not have a channel that opens or closes, instead they are linked to a ‘ G protein’, ligand binds to receptor which activates G protein which activates a secondary messenger

Question 19

what is a secondary messenger?

Answer 19

• A secondary messenger is a chemical whose function is to go and activate other particles

Question 20

How is a neurotransmitter removed after release?

Answer 20

• uptake by glial cells
• enzymatic degradation eg acetylcholinesterase
• internalization by postsynaptic process

Question 21

explain the pathway steps of neurotransmitters

Answer 21

Question 22

what is an example of a fast ionotropic receptor?

Answer 22

• Nicotinic Ach receptors
• pentameric receptor - 5 subunits
• Ach binds to the 2 alpha subunits which causes conformational change which ooens ion channel

Question 23

what are the 2 ionotropic glutamate receptors?

Answer 23

• AMPA
• NMDA
• excitatory throughout CNS

Question 24

what is LTP induction?

Answer 24

• long term potentiation
• induction of the NMDA receptor is a chemical synapse in the brain - substantial rise in calcium ion conc in postsynaptic cell

Question 25

what are the main inhibitory neurotransmitters?

Answer 25

• Glycine - mainly spinal chord ( activates Cl- channels)
• GABA released by many inhibitory CNS inter neurons
• GABA a - receptor activation opens Cl- channels ( Cl- enters and causes hyperpolarisation)
• GABA b -metabotropic receptor opens K+ channels - K+ exits cell and causes hyperpolarisation

Question 26

what are neuropeptides?

Answer 26

• chemical messengers made up of small chains of amino acids that are synthesized and released by neurons