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Psych 211 (neuro) > Synaptic communication > Flashcards

Synaptic communication Flashcards

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1
Q

What do we know about ion channels?

A
  • the DNA letters (exact sequence of nucleic acids) that encode these proteins in numerous species
  • the exact string of amino acids that form these proteins
  • their precise 3 dimensional shape
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2
Q

How can we test if an amino acid is important for selectivity of an ion channel?

A
  • alter the DNA sequence and change the protein
  • synthesizing this strand of DNA in the lab and then injecting it into a cell; get cell to make our modified version of this protein
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3
Q

How can cells read foreign DNA and make the corresponding protein?

A
  • if we attached a gene promoter region to the start of the DNA to tell the cell this gene should be read
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4
Q

What are gene promoters?

A
  • regions of DNA that initiate gene transcription
  • indicate which cells should read the gene and when (instructions)
  • different gene promoters are found just before every protein-encoding gene in the genome
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5
Q

What are hydrated ions?

A
  • When dissolved in water, ions get surrounded by water molecules
  • encased by a hydration shell
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6
Q

How is it that an ion channel can be permeable to K+ but not Na+? How do potassium ion channels only let in the bigger element?

A
  • Ion channel selectivity filters are precisely designed to replace the hydration shell of a particular ion
  • K+ ions are equally happy when inside the pore of a potassium ion channel or when surrounded by water
  • Na+ ions are too small to comfortably fit (unhydrated) in the pore of a potassium ion channel, so they prefer to stay outside of those ion channels with their hydration shell intact
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7
Q

How many voltage gated potassium channels are there?

A
  • 40
  • no perfect voltage- gated potassium channel
  • each cell can choose to express one or any combination of them to optimize cell function
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8
Q

What are the 2 types of cells in the central nervous system?

A
  • neurons
  • glia
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9
Q

What are neurons responsible for?

A
  • the electrical signals (action potentials) that communicate information about sensations and movements
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10
Q

What are glial cells?

A
  • serve a variety of support functions for neurons
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11
Q

How many neurons and glia are in the human brain?

A
  • estimated 85 billion of each
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12
Q

What are the 4 types of glial cells in the CNS?

A
  • astrocytes
  • ependymal cells
  • microglia
  • oligodendrocytes
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13
Q

What are astrocytes?

A
  • provide a structural matrix
  • physically surround synapses and blood vessels
  • regulate the ionic composition of the extracellular solution
  • help with neurotransmitter clearance
  • regulate blood flow and nutrient distribution in response to changes in neural activity
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14
Q

What are ependymal cells?

A
  • line the fluid filled ventricles at the center of the brain and spinal cord
  • circulate cerebrospinal fluid
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15
Q

What are microglia?

A
  • the smallest glial cells
  • the brain’s clean-up crew; removing dead cells and other debris
  • serve an immune function and protect the brain from invading microorganisms
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16
Q

What are oligodendrocytes?

A
  • produce the myelin sheath
  • extend branches of their cell membrane
  • each branch wraps many times around a nearby axon
  • create many
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17
Q

What is myelin sheath?

A
  • a wrapping of fat (glial cell membrane)
  • electrically insulates the axon
  • speeds up conduction of the action potential
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18
Q

What are the nodes of Ranvier?

A
  • 1 micron gap
  • exposed segments of myelinated axons
  • only places where myelinated axons feel a charge difference between inside and out
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19
Q

How are ions distributed within a cell?

A
  • equal except right by cell membrane
  • inside, negative charges hug cell membrane
  • outside, positive charges hug cell membrane
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20
Q

How is the charge distributed within an axon?

A
  • charge distributed across axon, weakening over time
  • no one ion making the distance, all step over at same time
  • right before action potential dies off, it hits the next node which launches the next action potential
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21
Q

What is the impact of myelination?

A
  • speeds up conduction of the action potential 20x
  • The amplitude of the action potential (+40 mV) is regenerated at each node of Ranvier because this is the only place where myelinated axons can access extracellular fluid
  • speed of the action potential also depends on the thickness of the axon
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22
Q

Where are all the voltage-gated ion channels in a myelinated axon concentrated?

A
  • at the nodes of Ranvier
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23
Q

What is saltatory conduction?

A
  • Action potentials in myelinated axons appear to jump from one node of Ranvier to the next
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24
Q

Which axons have the fastest action potentials?

A
  • thick, myelinated
  • 100 meters/second
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25
Q

Which axons have the slowest action potentials?

A
  • thin, unmyelinated
  • 1 meter/second
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26
Q

What is a synapse?

A
  • junction between the axon terminal of the sending neuron and the cell membrane of the receiving neuron
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27
Q

What can happen when a neurotransmitter activates a receptor on the receiving neuron?

A
  • consequence can be excitatory, inhibitory, or modulatory
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27
Q

What are synaptic vesicles?

A
  • contain molecules of neurotransmitter
  • dock at presynaptic membrane and release neurotransmitter into the synaptic cleft
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28
Q

What is the synaptic cleft?

A
  • space between the pre- and postsynaptic membrane
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29
Q

What is the presynaptic membrane?

A
  • axon terminal of the sending neuron
  • where neurotransmitter is released from
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30
Q

What is the postsynaptic membrane?

A
  • membrane of the receiving cell that is opposite the axon terminal
  • neurotransmitters released from presynaptic membrane flow across the synapse to postsynaptic membrane, where they bind and activate receptors
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31
Q

What is electron microscopy?

A
  • allows us to see small anatomical structures such as synaptic vesicles
32
Q

The diameter of things

A

0.001 mm - 1 micron (um) = 1000 nanometers (nm)
- small synaptic vesicle: 30 nm
- typical protein: 3 nm
- mitochondria: 1 um

33
Q

small synaptic vesicle

A
  • job to breakdown neurotransmitter
  • can hold 5000 molecules
34
Q

What is a ligand?

A
  • a signalling molecule that binds to a receptor
35
Q

What are ligand receptor interactions?

A
  • signalling within and between cells
36
Q

What are the 2 categories of neurotransmitter receptors?

A
  • ionotropic receptors
  • metabotropic receptors
37
Q

What is a binding site?

A
  • place on a receptor where a ligand binds
38
Q

What is an ionotropic receptor?

A
  • a ligand gated ion channel and a receptor
  • ion channel that opens in response to ligand binding
  • Its effects on the membrane potential are very brief and peak within a few milliseconds (instant and fast)
39
Q

What is a metabotropic receptor?

A
  • receptor that is NOT an ion channel
  • g protein coupled receptor
  • ligand binding typically triggers an intracellular g protein signalling cascade, which can have diverse effects on cell function
  • signalling cascades take time, and effects are usually not evident for at least 100ms if not much longer
40
Q

What are intracellular receptors?

A
  • receptors located inside the cell
41
Q

What are surface receptors?

A
  • receptors located on the cell membrane
42
Q

What are the 2 types of surface receptors?

A
  • postsynaptic receptors
  • presynaptic receptors
  • extrasynaptic receptors
43
Q

What is a postsynaptic receptor?

A
  • receptor located on postsynaptic membrane
  • Can be ionotropic or metabotropic (most synapses contain both)
44
Q

What is a presynaptic receptor?

A
  • receptor located on presynaptic membrane
45
Q

What is a extrasynaptic receptor?

A
  • receptor located near but outside a synapse
46
Q

How is neurotransmitter signalling in the synapse kept brief?

A
  • diffusion
  • enzymatic deactivation
  • reuptake
    They stop neurotransmitters from reaching the end of the synapse or clear them away they do
47
Q

What is diffusion?

A
  • Passive movement from areas of high concentration to areas of low concentration
  • always happening
  • some neurotransmitters leave synapse and float away
48
Q

What is enzymatic deactivation?

A
  • Destruction of a neurotransmitter by an enzyme
  • put protein in synapse to break down neurotransmitters
49
Q

What is reuptake?

A
  • Reuptake transporters recycle neurotransmitters by pulling them back into the cell that just released them
50
Q

What is postsynaptic potential?

A
  • when a neurotransmitter binds to a postsynaptic receptor and changes the membrane potential of the postsynaptic cell
  • can be fast or slow
  • can be excitatory or inhibitory
51
Q

What is a fast postsynaptic potential?

A
  • Ionotropic receptors produce rapid postsynaptic potentials (1 to 5 ms)
52
Q

What is a slow postsynaptic potential?

A
  • Metabotropic receptors do not always produce postsynaptic potentials, but when they do, they are relatively slow/delayed (~100ms to 10s)
53
Q

What is an excitatory postsynaptic potential?

A
  • EPSP
  • the result of positive sodium ions entering the postsynaptic cell, causing membrane depolarization and perhaps an action potential
54
Q

What is an inhibitory postsynaptic potential?

A
  • IPSP
  • the result of negative chloride ions entering the cell, causing membrane hyperpolarization and fewer action potentials
55
Q

What is depolarization?

A
  • membrane potential of cell becomes less negative than at rest
  • the opening of Na+ ion channels will depolarize a neuron, making it more likely to spike
56
Q

What is hyperpolarization?

A
  • When the membrane potential of a cell becomes more negative than it normally is at rest
  • The opening of Cl- ion channels can hyperpolarize a neuron, making it less likely to spike
57
Q

Are ionotropic receptors excitatory or inhibitory?

A
  • classified as excitatory or inhibitory based on whether they let in Na+ or Cl- ions and thus cause EPSPs or IPSPs
58
Q

Are metabotropic receptors excitatory or inhibitory?

A
  • classified as excitatory or inhibitory, based on whether they cause the opening of Na+ or Cl- (g protein-gated) ion channels
  • some open potassium ion channels (make cell closer to -90mV so inhibitory?)
59
Q

How does a membrane depolarize?

A
  • Sodium ions must enter the cell at a faster rate than potassium ions leave
60
Q

What is neural integration?

A
  • The interaction of the excitatory and inhibitory synapses on a particular neuron
  • When EPSPs and IPSPs occur at the same time, the influx of negatively charged chloride ions diminish the impact of the positively charged sodium ions
  • cancel each other out, no action potential
61
Q

What determines if a neurotransmitter is excitatory or inhibitory?

A
  • some cells express excitatory nt receptors, while other cells express inhibitory nt receptors
  • it is the receptor that is expressed by the postsynaptic cell that determines whether a neurotransmitter will be excitatory or inhibitory, not the neurotransmitter itself
  • we often describe neurons as being excitatory or inhibitory because we know they reliably cause EPSPs or IPSPs in the downstream cells they connect to
62
Q

How does the neural circuit work?

A
  • sensory neuron spikes, sends electrical message down to axon terminal in spinal cord
  • release of neurotransmitter from sensory neuron will depolarize and cause action potential in excitatory interneuron, activates motor neuron and cause reflex
    BUT
  • neuron in cerebral cortex can send action potential to spinal cord to excite an inhibitory interneuron
  • release of nt from inhibitory interneuron will hyperpolarize motor neuron and counteract reflex
  • contest between two competing drives
63
Q

What’s the difference between neural and behavioural excitation?

A
  • inhibitory neuron is a neuron that reliably causes IPSCs in downstream neurons
  • firing of an inhibitory neuron does not always inhibit behaviour
  • Inhibition of inhibitory neurons can generate motor behaviour
  • For every neuron trying to change behaviour in one way, there are other neurons trying to do the opposite
  • hard to determine which ones are trying to cause or prevent a behaviour
  • The firing of excitatory neurons deep in the brain does not necessarily cause movement, and the firing of inhibitory neurons does not necessarily inhibit movement
64
Q

What is a receptor protein?

A
  • A protein that is sensitive to a stimulus and passes along the message
  • It can be a neurotransmitter receptor or a receptor for something else
  • either ionotropic or metabotropic
65
Q

What is an ionotropic receptor?

A
  • receptor that is an ion channel
  • Its activation has an immediate consequence on the cell’s membrane potential; causes an EPSP or an IPSP depending on whether the pore of the ion channel is permeable to Na+ or Cl-
66
Q

What is a metabotropic receptor?

A
  • receptor that is not an ion channel
  • typically triggers an intracellular signaling cascade involving g proteins
  • activation can have large or small effects on any cellular process, but the effects won’t be instantaneous, since they depend on intracellular signaling and diffusion
  • All g protein-coupled receptors (GPCRs) are metabotropic receptors
67
Q

What cellular processes can metabotropic receptors affect?

A
  • opening ion channels
  • changing gene expression
  • secretion of substances
  • cell growth
  • cell division (not in neurons)
  • cell death
  • anything the cell wants
68
Q

What is a g protein?

A
  • use GTP molecules, instead of ATP, for the energy they need to catalyze a chemical reaction
  • molecular switches
  • when bound to GTP they are ON
  • while on they can catalyze reactions, lasts between 10 secs and several minutes
  • on is temporary because g proteins convert GTP to GDP, becoming off
  • hard time letting go of GDP
  • need an activated metabotropic receptor to let go of GDP
69
Q

What is the activation cycle of g proteins?

A
  • the cycle starts when a ligand finds a metabotropic receptor
  • ligand binding to metabotropic receptor induces a conformational change that helps the g protein let go of GDP allowing it to bind a molecule of GTP
  • the g proteins diffuse away to trigger chemical reactions
  • At some point the g protein will convert GTP to GDP
  • It will then go back to the metabotropic receptor and wait
70
Q

What are g protein gated ion channels?

A
  • ion channels that are gated by g proteins
71
Q

How is a g protein gated ion channel opened?

A
  • a signaling molecule has to activate a metabotropic receptor
  • allowing a g-protein to become activated
  • activated g protein can bind (directly or indirectly) to a g-protein-gated ion channel
  • ion channel will open, letting ions in
  • metabotropic receptors can cause the opening of many g protein gated ion channels at once
72
Q

Where can synapses form?

A
  • between an axon terminal and smooth dendrite (a dendritic shaft)
  • between an axon terminal and a dendritic spine
  • between an axon terminal and a soma
  • between an axon terminal and another axon terminal (axoaxonic synapse)
73
Q

What are axoaxonic synapses?

A
  • synapse between axon terminal and another axon terminal
  • regulate the amount of neurotransmitter that the second neuron will release when it has an action potential
74
Q

What is presynaptic inhibition?

A
  • axoaxonic synapses can hyperpolarize the axon terminal of the downstream neuron, so its voltage-gated calcium channels will not open as much as they normally do when the there is an action potential
  • The net effect is to reduce neurotransmitter release from the downstream when it has an action potential
75
Q

What is presynaptic facilitation?

A
  • Axoaxonic synapses can depolarize the axon terminal of the downstream neuron, so that its voltage-gated calcium channels are more likely to open when an action potential arrives
  • The net effect is to increase neurotransmitter release from the downstream neuron when it has an action potential
76
Q

What is an autoreceptor?

A
  • a receptor located on presynaptic membrane that makes the cell sensitive to its own neurotransmitter release
  • gated by the release of neurotransmitter from the cell they are in
  • always metabotropic and inhibitory
  • main source of presynaptic inhibition
77
Q

What is a postsynaptic receptor?

A
  • receptor located on the receiving neuron

Psych 211 (neuro) (22 decks)

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