Nervous System: Synaptic Transmission

Question 1

How does synaptic transmission between neurons work?

Answer 1

It uses chemical synapses between a target and presynaptic neuron. This is also known as an axodendritic synapse

Question 2

How does synaptic transmission between a neuron (motorneuron) and a muscle fibre work?

Answer 2

It uses a neuromuscular junction (“end plate”). Axons outside the CNS connect to muscle fibres at neuromuscular junctions/end plates

Question 3

What types of synapse is a neuromuscular junction/endplate

Answer 3

it is excitatory synaptic transmission

Question 4

The neurotransmitter in neuromuscular junctions/endplate

Answer 4

Acetylcholine (Ach)

Question 5

What is the ionic mechanism of End-plate potentials (EPPs)

Answer 5

The transient opening of ion channels selective to BOTH Na+ and K+ (also known as non-selective cationic channels). Membrane potential will go between each of their equilibrium potentials

Question 6

What is EPP always?

Answer 6

Suprathreshold i.e. always triggers an AP as it’s depolarisation is sufficiently larger to reach threshold

Question 7

What is the process of synaptic transmission at a neuromuscular jucntion/endplate?

Answer 7

1. An action potential arrives from the cell body of a motor neuron which is transmitted to the PREsynaptic terminal. Once AP has invaded terminal it causes the opening of voltage gated Ca channel.
2. There is a lot more Ca outside the cell membrane than inside so when channel is open there is an influx of Ca through the presynaptic terminal/button
3. Entry of Ca into the PREsynpatic terminal causes fusion of synaptic vesicles (small structures storing neurotransmitters , Acetylcholine) with the synaptic membrane
4. Content of vesicles diffuses to synaptic cleft, neurotransmitters bind to receptors in POSTsynaptic membrane (ligand/chemically gated channels)
5. Ligand gated-ion channels open and ions move into cell
6. Leading to depolarization in POSTsynaptic mem (EPP - form of synaptic potential, local depolarization of the mem, current spreads passively in both directions in loops)

Question 8

Types of channels involved in synaptic transmission at a neuromuscular junction/endplate

Answer 8

voltage gated Ca channels

ligand gated ion channels

Question 9

Length of synaptic delay

Answer 9

0.5ms (short)

Question 10

The two types of chemical synapses in the CNS

Answer 10

Excitatory and inhibitory synapses

Question 11

What is a excitatory postsynaptic potential (EPSP)

Answer 11

the depolarisation of the post synaptic membrane

Question 12

What is the inhibitory postsynaptic potential (IPSP)

Answer 12

the hyperpolarization of the postsynaptic membrane

Question 13

The neurotransmitter in excitatory postsynaptic potentials (EPSP)

Answer 13

Mainly Glutamic acid (glutamate) and also ACh

Question 14

Ionic mechanism of EPSPs

Answer 14

The transient opening of non selective channels that are permeable to Na+, K+ and sometimes Ca2+ which causes a depolarisation of the membrane somewhere in-between the ions equilibrium potentials

Question 15

The neurotransmitter in inhibitory postsynaptic potentials (IPSP)

Answer 15

Mainly GABA or glycine

Question 16

Ionic mechanism of IPSPs

Answer 16

the transient opening of ligand gated K+ channels (has to be ligand gated because it is receptor changes in permeability). it causes a hyperpolarisarion that doesn’t last for long

Question 17

The two types of neurotransmitters

Answer 17

Small molecule neurotransmitter/classical neurotransmitters AND neuropeptides/neuromodulators

Question 18

Properties of Small molecule neurotransmitter/classical neurotransmitters

Answer 18

fast action (within milliseconds) and act directly on postsynaptic receptors

Question 19

Examples of small molecule neurotransmitter/classical neurotransmitters

Answer 19

Amino acids (glutamate, GABA, glycine), Acetylcholine (ACh), Amines: serotonin (5-HT), noradrenaline, dopamine

Question 20

Examples of neuropeptides/neuromodulators

Answer 20

Neuropeptide Y (NPY), Substance P, Kisspeptin, Enkephalin

Question 21

Properties of neuropeptides/neuromodulators

Answer 21

they are larger molecules that act indirectly (metabotropic) that act on postsynaptic receptors and modulates the action of other neurotransmitters. It is slow (seconds to minutes)

Question 22

The three factors determining synaptic action

Answer 22

1. Type of neurotransmitter / neuromodulator
2. Type of neurotransmitter receptor/ channel complex expressed in the postsynaptic membrane
3. Amount of neurotransmitter receptor present in the postsynaptic membrane

Question 23

What is Synaptic plasticity

Answer 23

Amount of neurotransmitter receptor present in the postsynaptic membrane. There are two types of receptors
LTP or LTD (receptors are not static in membrane/dynamic)

Question 24

What is LTP

Answer 24

Long-term potentiation

Question 25

What is LTD

Answer 25

Long-term depression

Question 26

What are the three main subtypes of glutamate receptors

Answer 26

1. AMPA Receptor 2. NMDA Receptor 3. Kainate Receptor

Question 27

Properties of the glutamate AMPA receptor

Answer 27

when activated by glutamate, it opens and is non-selective for Na and K = depolarises

Question 28

Properties of the glutamate NMDA receptor

Answer 28

permeable to Na, K and Ca, is very important if permeable to Ca, too much in nerve cells = Excitotoxicity

Question 29

Stages of neurotransmitter inactivation and recovery

Answer 29

1. Diffusion away from the synapse 2. Enzymatic degradation in synaptic cleft 3. Re-uptake (most aa and amines) + recycling 4. Transporters in presynaptic membrane

Question 30

Why is the re-uptake of neurotransmitters important

Answer 30

Nerve cells don’t have to make neurotransmitters from scratch

Question 31

Enzyme that degrades ACh

Answer 31

Achase

Question 32

Examples of specific neurotransmitter transporters in the presynaptic membrane (in nerve and glia cells)

Answer 32

glutamate transporter, dopamine transporter or serotonin transporter

Question 33

How do neurotransmitter transporters in the presynaptic membrane take in neurotransmitters

Answer 33

Chemical connects to transporter, change in shape of transporter, shift of molecule across membrane and released on other side (usually against conc gradient) - taking in chemicals like dopamine and serotonin

Question 34

Voltage of an individual synapse received by neurons in their axon initial segment in the postsynaptic membrane

Answer 34

0.1mV (very small)

Question 35

What needs to happen to EPSPs in order to depolarise the initial segment to threshold to generate an AP

Answer 35

They need to be enhanced or they will be ignored as they do not reach the threshold

Question 36

Temporal Summation of postsynaptic potential at axon initial segment

Answer 36

influx of Ca (not enough time to remove) so greater release of neurotransmitter. A single presynaptic neuron stimulates the creation of action potentials in a postsynaptic neuron when it fires at a fast-enough rate that the sum of EPSPs in the postsynaptic neuron moves above threshold.

Question 37

Spatial Summation of postsynaptic potential at axon initial segment

Answer 37

E 1 and 2 coming through two synapses are activated at same time/almost same time, postsynaptic will summate and reach threshold