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Nervous System Biology > NSB 3. Synaptic Transmission > Flashcards

NSB 3. Synaptic Transmission Flashcards

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1
Q

What is the definition of synaptic transmission (neurotransmission)?

A
  • process by which neurotransmitters are released by pre-synaptic neuron, bind to and activate the receptors of the post-synaptic neuron
  • neurotransmission is essential for communication betwen 2 neurons
  • it is either excitatory or inhibitory (the neurotransmitters)
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2
Q

What is there a lot of in the neuron? (very vague question)

A

mitochondria!

- because the process requires a lot of energy

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3
Q

What type of gradient is neurotransmission dependent on?

A

electrochemical gradients

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4
Q

What ions are involved in creating the electrochemical gradients required for neurotransmission? (just list them)

A

[1] Na+
[2] K+
[3] Cl-
[4] Ca2+

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5
Q

What is the concentration of Na+ ions extracellularly and intracellularly?

A

Extracellular: 145 mM

Intracellular: 15mM

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6
Q

What is the concentration of K+ ions extracellularly and intracellularly?

A

Extracellular: 4.5 mM

Intracellular: 120mM

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7
Q

What is the concentration of Cl- ions extracellularly and intracellularly?

A

Extracellular: 116mM

Intracellular: 20mM

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8
Q

What is the concentration of Ca2+ ions extracellularly and intracellularly?

A

Extracellular: 2mM

Intracellular: 20 to 100 nM

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9
Q

What are the major ions in the extracellular space? [3]

A

[1] Na+
[2] Cl-
[3] Ca2+

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10
Q

What are the major ions in the intracellular space? [1]

A

[1] K+

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11
Q

Why is Ca2+ important in neurotransmission?

A

it is important to allow for the release of neurotransmitters

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12
Q

In a typical neuron, what is the resting membrane potential?

A

-70 mV

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13
Q

What are 2 examples when the membrane potential will be equal to zero?

A

[1] when the membrane separating 2 fluids is NOT permeable and so, does not allow for the movement of ions

[2] when the membrane separating 2 fluids is permeable to both ions and so there will be the same # of ions in each compartment - reaches an equilibrium

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14
Q

What type of membrane helps to create a membrane potential?

A 
selectively permeable (semi-permeable) membrane
- e.g. only allowing K+ to move through -- allows K+ to leave the cell and create a neg. charge inside the cell (from the residual Cl-)
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15
Q

What pump creates the electrochemical gradient in a cell?

A

Na+/K+ pump

  • it pumps 3 Na+ out and 2K+ in
  • the K+ can then diffuse outwards anyways
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16
Q

What is the difference between voltage-gated and ligand-gated ion channels? Give examples of some.

A

Voltage-Gated Channels:
- they open in response to a voltage (like when the cell gets depolarized)

Ligand-Gated Channels:
- they open in response to ligand binding to them (some chemical signal)

Examples:

  • K+ Channel
  • Na+ Channel
  • Ca2+ Channel
  • Cl- Channel
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17
Q

What is equilibrium?

A

the electrical force balances the chemical force, leading to NO net transport

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18
Q

Explain what the chemical driving force and electrical driving force are in relation to K+.

A

Chemical Driving Force:
- chemical gradient acts as a driving force for diffusion out of the cell

Electrical Driving Force:
- residual neg. charge draws the K+ back into the cell

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19
Q

What is the Nernst Equation?

A

E = 61 x log (Co/Ci)

Co = concentration of ion outside
Ci = concentration of ion inside 
61 = Faraday constant, gas constant, absolute temp., valence ions
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20
Q

What is the equilibrium potential for K+? What does this mean?

A

-87mV/-90mV

    • this means that there is less K+ outisde the cell
    • there are more K+ ions inside the cell
    • this drives the K+ out of the cell
21
Q

What is the equilibrium potential for Na+? What does this mean?

A

+60mV

    • this means that there is less Na+ inside the cell
    • there are more Na+ ions outside the cell
    • this drives Na+ into the cell
22
Q

What is an EPSP?

A

excitatory post-synaptic potential

23
Q

In an axon, what is the direction of the impulse?

A

they go from the dendrites to the axon and the terminal branches - onto the next neuron

24
Q

What are post-synaptic densities?

A
  • is a network of proteins within and adjacent to the postsynaptic membrane
  • they consist of anchoring and scaffolding molecules, signaling enzymes and cytoskeletal components
  • they spatially and functionally organize the neurotransmitter receptors at the synapse
25
Q

List and describe the process of neurotransmitter release once an action potential reaches the axon.

A

[1] action potential reaches + depolarizes the axon terminal

[2] depolarization activates voltage-gated, pre-synaptic Ca2+ channels (N-type + P-type)

[3] localized Ca2+ entry triggers the release of nearby vesicles containing NTs through the activation of Ca2+-sensitive fusion proteins

[4] NTs diffuse into synaptic cleft and activate NT receptors on post-synaptic membrane

[5] NT may also activate pre-synaptic NT receptors (positive/negative feedback)!!

[6] recycling/uptake of NTs are done through Glutamine Synthetase [GLUL]

26
Q

What are the types of pre-synaptic Ca2+ channels that are activated when an action potential depolarized the axon terminal?

A

N-type or P-type

27
Q

What aids in the recycling/uptake of NTs?

A

Glutamine Synthetase - GLUL

28
Q

What is a tripartite synapse?

A
  • refers to the functional integration and physical proximity of the presynaptic membrane, postsynaptic membrane, and their intimate association with surrounding glia
  • astrocyte processes are in close contact with the synapses
29
Q

What are the functions of astrocytes in tripartite synapses?

A
  • they recycle NTs (through glutamine synthetase)
  • they secrete neurotransmitters and gliotransmitters (glutamate, D-serine, TNF-alpha etc.)
  • they buffer extracellular K+
30
Q

What are the 2 types of neurotransmitter receptors? (just list them)

A

[1] Receptor with Intrinsic Ion Channel
- Ionotropic Receptors

[2] G-Protein Coupled Receptors
- Metabotropic Receptors

31
Q

Explain how ionotropic receptors and g-protein coupled receptors work.

A

Ionotropic Receptors:

  • fast synaptic transmission
  • NTs bind to ligand-gated channels which increase permeability to ions
  • – e.g. nicotinic receptor for Na+

G-Protein Coupled Receptors:

  • slower synaptic transmission
  • activated receptor triggers activation of G protein that either: __ inside cell that modifes ion channels
  • —- (a) directly modifies function of ion channels or
  • —- (b) triggers production of chemical second messenger (e.g. cAMP)
  • mediates short term + long term effects (e.g. gene expression)
32
Q

Which NT receptor allows for fast synaptic transmission?

A

iontropic receptors

33
Q

Which NT receptor leads to slower synaptic transmission?

A

g-protein coupled receptors

34
Q

What are the main excitatory neurotransmitters in the CNS?

A

[1] glutamate

[2] acetylcholine

35
Q

What are the main inhibitory neurotransmitters in the CNS?

A

[1] GABA

[2] Glycine

36
Q

Which receptors does the neurotransmitter, glutamate, act on? [3]

A

[1] AMPA
[2] NMDA
[3] Kainate receptors

37
Q

What are some other classical NTs (other than the excitatory and inhibitory ones)? [3]

A

[1] Serotonin
[2] Dopamine
[3] Noradrenaline

38
Q

What can the excitation of inhibitory neurons lead to?

A

an inhibitory response

39
Q

What is co-transmission?

A

It is when classical, small molecule NTs are co-released with larger, peptide neurotransmitters
– small NT + large, peptide NT

40
Q

What is the difference in function between the small NT and the large, peptide NT?

A

small NT:
- fast response is mediated by this

peptide NT:
- a neuromodulatory, slow response is mediated by this

41
Q

What is an IPSP?

A

inhibitory post synaptic potential

42
Q

How does an inhibitory synapse work?

A

the NT binding increases the permeability to either K+ or Cl- causing the “holding” of resting membrane potential or small hyperpolarisation
– membrane potential moves farther away from the action potential threshold

    • if Cl- enters the cell, membrane potential becomes more negative
    • if K+ leaves the cell, membrane potential becomes more negative
43
Q

What is summation? What are the 2 different types?

A

Summation is the addition of EPSPs together that allows for an action potential threshold to be reached and teh action potential to be fired.

2 Types:
[1] Temporal Summation
[2] Spatial Summation

44
Q

What is temporal summation?

A
  • the EPSPs last for about 15msec
  • therefore, high frequency activation of a single pre-synaptic terminal can cause summation if the interval between intervals is less than 15msec
45
Q

What is spatial summation?

A

EASY DEFINITION: the effect of triggering an action potential in a neuron from one or more presynaptic neurons

  • most synapses terminate on dendrites (there is a loss of current due to membrane leakage + EPSP declines with distance)
  • some synapses end on soma (very low resistance [due to large diameter] and local EPSP or IPSP can spread through soma
  • SYNAPSES NEAR SOMA HAVE MORE EFFECT THAN SYNAPSES ON DENDRITES on the potential of the soma
  • activation of multiple pre-synaptic terminals on dendrites can cause summation
46
Q

What happens when the axon reached a threshold of -50mV?

A
  • this is the threshold potential

- when depolarization reaches the threshold it leads to the activation of voltage-gated Na+ channels in the axon hillock

47
Q

What is the refractory period? How long does the refractory period normally last for? What happens during repolarization?

A

refractory period: period of time in which the membrane is depolarized and another action potential cannot be sent through

  • – usually lasts for about 0.001 to 0.002 seconds
  • – this means that around 500 to 1000 impulses can be sent per second

repolarisation occurs through:
[1] opening of K+ channels and facilitated diffusion of K+ out of cell
– I guess they are brought back in through the Na+/K+ pump
[2] Na+ actively transported out of cell

48
Q

Why is the glutamate receptor important in neurotransmission and sodium channel gating?

A
  • glutamate is an excitatory NT

- it allows for the excitation of the axon and the opening of the Na+ channels

Nervous System Biology (4 decks)

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