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BIOSCI 107 Part Two > Nervous System: Synaptic Transmission > Flashcards

Nervous System: Synaptic Transmission Flashcards

1
Q

How does synaptic transmission between neurons work?

A

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

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2
Q

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

A

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

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3
Q

What types of synapse is a neuromuscular junction/endplate

A

it is excitatory synaptic transmission

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4
Q

The neurotransmitter in neuromuscular junctions/endplate

A

Acetylcholine (Ach)

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5
Q

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

A

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

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6
Q

What is EPP always?

A

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

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7
Q

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

A
  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)
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8
Q

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

A

voltage gated Ca channels

ligand gated ion channels

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9
Q

Length of synaptic delay

A

0.5ms (short)

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10
Q

The two types of chemical synapses in the CNS

A

Excitatory and inhibitory synapses

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11
Q

What is a excitatory postsynaptic potential (EPSP)

A

the depolarisation of the post synaptic membrane

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12
Q

What is the inhibitory postsynaptic potential (IPSP)

A

the hyperpolarization of the postsynaptic membrane

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13
Q

The neurotransmitter in excitatory postsynaptic potentials (EPSP)

A

Mainly Glutamic acid (glutamate) and also ACh

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14
Q

Ionic mechanism of EPSPs

A

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

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15
Q

The neurotransmitter in inhibitory postsynaptic potentials (IPSP)

A

Mainly GABA or glycine

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16
Q

Ionic mechanism of IPSPs

A

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

17
Q

The two types of neurotransmitters

A

Small molecule neurotransmitter/classical neurotransmitters AND neuropeptides/neuromodulators

18
Q

Properties of Small molecule neurotransmitter/classical neurotransmitters

A

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

19
Q

Examples of small molecule neurotransmitter/classical neurotransmitters

A

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

20
Q

Examples of neuropeptides/neuromodulators

A

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

21
Q

Properties of neuropeptides/neuromodulators

A

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)

22
Q

The three factors determining synaptic action

A
  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
23
Q

What is Synaptic plasticity

A

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)

24
Q

What is LTP

A

Long-term potentiation

25
Q

What is LTD

A

Long-term depression

26
Q

What are the three main subtypes of glutamate receptors

A
  1. AMPA Receptor
  2. NMDA Receptor
  3. Kainate Receptor
27
Q

Properties of the glutamate AMPA receptor

A

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

28
Q

Properties of the glutamate NMDA receptor

A

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

29
Q

Stages of neurotransmitter inactivation and recovery

A
  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
30
Q

Why is the re-uptake of neurotransmitters important

A

Nerve cells don’t have to make neurotransmitters from scratch

31
Q

Enzyme that degrades ACh

A

Achase

32
Q

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

A

glutamate transporter, dopamine transporter or serotonin transporter

33
Q

How do neurotransmitter transporters in the presynaptic membrane take in neurotransmitters

A

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

34
Q

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

A

0.1mV (very small)

35
Q

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

A

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

36
Q

Temporal Summation of postsynaptic potential at axon initial segment

A

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.

37
Q

Spatial Summation of postsynaptic potential at axon initial segment

A

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

BIOSCI 107 Part Two (17 decks)

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