W3: Neurones, Transmitters, Synapses And Receptors

Question 1

What do dendrites do?

Answer 1

Input from other neurones

Question 2

What does the axon hillock do?

Answer 2

Axon potential generation

Question 3

What does the axon do?

Answer 3

Impulse conduction/action potential propagation

Question 4

What does the axon terminal/synaptic bouton do?

Answer 4

Release neurotransmitter

Question 5

Roles of glial cells

Answer 5

Physical and metabolic support
Electrical insulation
Signalling

Question 6

What are the properties of a gap junction (electrical synapse)?

Answer 6

• fastest channel
• direct transfer of ionic current
• bi-directional transfer of ions
• allows synchronous activity between cells
• glia-neurone, glia-glia communication
• found in cardiac myocytes

Question 7

Properties of a chemical synapse

Answer 7

• unidirectional transfer of information - presynaptic to postsynaptic
• presynaptic terminal releases neurotransmitter to interact with postsynaptic membrane receptors

Question 8

What is the process of neurotransmission dependent on?

Answer 8

Action potential dependent

Calcium dependent

Question 9

Process of neurotransmission

Answer 9

1. Action potential invades the nerve terminal
2. Depolarisation of the presynaptic membrane triggers voltage gated calcium channels to open, leading to an influx of calcium ions.
3. Synaptic vesicles fuse with the presynaptic membrane and neurotransmitter is released by exocytosis
4. Diffusion across the synapse and neurotransmitter binds to the receptors on the post-synaptic membrane, depolarising it
5. Rapid termination of the signal occurs

Question 10

How is the signal at the synapse terminated?

Answer 10

Re uptake of neurotransmitter or enzymatic breakdown

Question 11

What is a neurotransmitter?

Answer 11

Chemical messengers at the synapse

Question 12

Amino acid neurotransmitters

Answer 12

Glutamate (major excitatory transmitter in the CNS)

GABBA (major inhibitory transmitter in the CNS)

Question 13

Monoamine neutransmitters

Answer 13

Noradrenaline
Dopamine
5-HT

Question 14

Where is ACh neurotransmitter more present in?

Answer 14

The PNS

Question 15

What are receptors?

Answer 15

Recognition sites for neurotransmitters, causing an intracellular signal when bound to. Membrane spanning protein molecules. Specific to a neurotransmitter.

Question 16

What is an ionotropic receptor?

Answer 16

Receptor operates/ligand gated ion channels

Question 17

What happens when a transmitter binds to an ionotropic receptor?

Answer 17

It causes a conformational change in the receptor which opens the channel and creates a pore to allow ions through it.

Question 18

Do ionotropic receptors have fast or slow transmission?

Answer 18

Fast (not as fast as gap junctions though)

Question 19

What happens at an excitatory ionotropic synapse?

Answer 19

• neurotransmitter binds to receptor protein which changes shape and opens a pore
• sodium influxes into the post synaptic membrane causing a membrane depolarisation
• a single synaptic event will cause a small excitatory post synaptic potential, EPSP
• EPSP lasts a short amount of time and quickly decays away

Question 20

Examples of excitatory ionotropic receptors

Answer 20

ACh nicotinic receptor

Question 21

What happens at an inhibitory ionotropic synapse?

Answer 21

• neurotransmitter binds allowing the channel to open
• Cl- ions will influx into the postsynaptic membrane, causing a membrane hyperpolarisation
• causes a small inhibitory postsynaptic potential, IPSP

Question 22

What happens when a neurotransmitter binds to a metabotropic receptor?

Answer 22

When neurotransmitter binds it causes a conformational change which activates a G-protein. This activates ‘effector systems’, which have indirect effects on excitability of the postsynaptic cell.

Question 23

Do metabotropic receptors have slow or fast transmission?

Answer 23

Slow, but longer lasting effects.

Question 24

What can an activated G-protein do in metabotropic receptors?

Answer 24

• open or close ion channels

- stimulate or inhibit enzymes/secondary messenger systems

Question 25

Examples of metabotropic receptors

Answer 25

ACh muscarinic receptors GABA’B Monoamine receptors (except 5-HT)

Question 26

What synaptic inputs are most influential?

Answer 26

Synaptic inputs which are close to the axon hillock are much more influential over the activity/excitability of a neurone than input from distant dendrites.

Question 27

What happens after a single excitatory ionotropic synaptic event?

Answer 27

A small EPSP is produced

Question 28

What is a small EPSP?

Answer 28

It makes the neurone more excitable (more likely to fire an AP) for a brief period of time. Caused by the ionotropic receptor allowing sodium to enter cells, NOT voltage gated channels

Question 29

When is an action potential produced?

Answer 29

When the level of depolarisation is high enough (reaches threshold potential) such that there is more sodium entering the cell than potassium leaving the cell.

Question 30

What happens if there are e.g. 2 synaptic excitatory events at an ionotropic synapse?

Answer 30

A bigger synaptic event will occur | An increased EPSP is produced through spatial summation

Question 31

What is spatial summation?

Answer 31

The summing of post synaptic potentials generated at separate synapses

Question 32

What happens if multiple excitatory inputs occur at an ionotropic receptor?

Answer 32

Summation occurs Threshold is reached by the ionotropic channels causing more sodium to enter the cell than potassium leaving Depolarisation occurs, opening voltage gated channels

Question 33

What happens if there is a single inhibitory ionotropic event?

Answer 33

A small inhibitory post synaptic potential IPSP is produced

Question 34

What happens if an inhibitory and excitatory input occurs at the same time?

Answer 34

Spatial summation occurs No change in the membrane potential because magnitude or the depolarisation and hyperpolarisation are approximately equal, so cancel each other out.

Question 35

What happens if an individual synaptic input occurs at a high frequency?

Answer 35

Instead of one synaptic event, before it can decay away, another synaptic event depolarises the membrane further and adds to the first. Quick succession with little time to decay away. This can depolarised up to threshold. It causes an increased EPSP due to temporal summation.

Question 36

What is temporal summation?

Answer 36

The summimg of post-synaptic potentials generated at the same synapse, if they occur in rapid succession.