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Flashcards in Synaptic Transmission Deck (37)
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0
Q

Inhibitory Post Synaptic Potential

A

Change in membrane potential that lowers the likelihood that threshold will be reached in post synaptic cell. Stabilizes the resting potential.
Occurs at inhibitory synapse.
Ex: The opening of potassium channels cause IPSP.
The opening of Cl- channels are inhibitory because they stabilize the resting potential, entering the cell as it becomes more positive due to Na+ influx

1
Q

Excitatory Post-Synaptic Potential

A

Change in membrane potential that raises the likelihood that threshold will be reached in post synaptic cell.
Occurs at excitatory synapse.
Ex: The opening of sodium channels cause an EPSP.

2
Q

Convergence

A

Multitude of synapses from many different presynaptic cells affect a single post synaptic cell

3
Q

Divergence

A

A single post synaptic cell can send branches to affect many other post synaptic cells

4
Q

Electrical synapses

A

The plasma membrane of the presynaptic and post synaptic cells are joined via gap junctions.
Allows the local currents resulting from arriving action potentials to flow directly across the junction through the connecting channels from one neuron to the other.
Communication btwn cells = extremely rapid

5
Q

Chemical synapse structure

A

Axon of the presynaptic neuron ends in an axon terminal which holds the synaptic vesicles that contain neurotransmitter molecules.
Post synaptic density: specialized area adjacent to the axon terminal with a high density of membrane proteins.
Synaptic cleft: EC space which separates the presynaptic and post synaptic neurons and prevents direct propagation of the current from the presynaptic neuron to the post synaptic cell.

6
Q

Events in the presynaptic cell

A
  1. AP reaches terminal
  2. Voltage gated Ca2+ channels open
  3. Calcium enters axon terminal
  4. Neurotransmitter is released and diffuses into the cleft
  5. Neurotransmitter binds to post synaptic receptors
  6. Neurotransmitter removed from synaptic cleft
7
Q

Events in a post synaptic cell

A

Neurotransmitter binds to receptor (reversible, noncovalent event), specific ion channels open/close in post synaptic membrane which eventually leads to changes in the membrane potential.

8
Q

Temporal Summation

A

When the second synaptic potential adds to the previous one and creates a greater depolarization than from one input alone.
Input signals arrive from the same presynaptic cell at different times.
Potentials summate because there are a greater number of open ion channels and therefore a greater flow of positive ions.

9
Q

Spatial summation

A

Two inputs occur at different locations on the same cell.
Interaction of multiple EPSPs through spatial and temporal summation can increase the inward flow of positive ions and bring the post synaptic membrane to threshold so that APs are initiated.

10
Q

What and why do different parts of the neuron have different thresholds?

A

Initial segment has a more negative threshold than the membrane of the cell body and dendrites. Easier to bring to threshold.
Due to a higher density of voltage gated Na+ channels in this area of the membrane.

11
Q

Ionotropic receptors

A

Ion channels which are activated by Neurotransmitters

Fast

12
Q

Metabotropic receptors

A

Receptors which act indirectly on separate ion channels through a G protein and/or a second messengers
Slow

13
Q

Unbound Neurotransmitters are removed from the synaptic cleft when they are…

A
  1. Actively transported back into the presynaptic axon terminal (reuptake) or into nearby glial cells
  2. Diffuse away from the receptor site
  3. Are enzymatically transformed into inactive substances, some of which are transported back into the axon terminal for reuse
19
Q

Pre-synaptic inhibition

A

When the presynaptic effect decreases the amount of neurotransmitter being released for a neuron.

20
Q

Pre-synaptic facilitation

A

When the presynaptic effect increases the amount of neurotransmitter being released for a neuron.

22
Q

Axo-axonic synapse

A

An axon terminal of one neuron that ends on an axon terminal of another.
Can alter the calcium concentration in the second axon terminal or affect neurotransmitter synthesis there.

23
Q

Autoreceptors

A

Activated by Neurotransmitters or other chemical messengers released by the axon terminal itself.
Provide an important feedback mechanism that the neuron can use to regulate its own neurotransmitter output.

25
Q

Presynaptic factors that determine synaptic strength

A

A. Availability of neurotransmitter
1. Precursor molecules
2. Amount/activity of the rate limiting enzyme in the pathway for neurotransmitter synthesis.
B. Axon terminal membrane potential
C. Axon terminal Ca2+
D. Activation of membrane receptors on presynaptic terminal
1. Axo-axonic synapses
2. Autoreceptors
3. Other receptors
E. Certain drugs and diseases, which act via the above mechanisms A-D.

28
Q

Postsynaptic factors that determine synaptic strength

A

A. Immediate past history of electrical state of post synaptic membrane
B. Effects of other Neurotransmitters or neuromodulators acting on post synaptic neuron
C. Up or down regulation & desensitization of receptors
D. Certain drugs/diseases

29
Q

General factors that determine synaptic strength

A

A. Area of synaptic contact
B. Enzymatic destruction of neurotransmitter
C. Geometry of diffusion path
D. Neurotransmitter reuptake

30
Q

How might a drug/toxin act on signal transmission in neurons?

A

A. Increase leakage of neurotransmitter from vesicle to cytoplasm, exposing it to enzyme breakdown
B. Increase neurotransmitter release into cleft
C. Block transmitter release
D. Inhibit transmitter synthesis
E. Block transmitter reuptake
F. Block cleft enzymes that metabolize transmitter
G. Bind to receptor on post synaptic membrane to block (antagonist) or mimic (agonist) transmitter action
H. Inhibit or stimulate second messenger activity within post synaptic cell

31
Q

Agonists

A

Drugs that bind to a receptor and produce a response similar to the normal activation of that receptor

32
Q

Antagonists

A

Drugs that bind to the receptor but are unable to activate it

33
Q

Neuromodulators

A

Often modify the post synaptic cell’s response to specific Neurotransmitters, amplifying/dampening the effectiveness of ongoing synaptic activity.
Associated with slower events like learning, development, motivational states, and some types of sensory or motor activities.

34
Q

Acetylcholine

A

Released by cholinergic neurons.
Synthesized in cytoplasm of synaptic terminals and stored in synaptic vesicles.
After release/activation of receptors, concentration of ACh is decreased by acetylcholinesterase (on pre/post-synaptic membranes).
Choline -> reused
ACH conc. -> reduced by simple diffusion away from synapse and eventual breakdown via an enzyme in the blood
Binds to: Nicotonic and Muscarinic Receptors

35
Q

Cholinergic neurons

A

Neurons that release ACh

36
Q

Nicotonic receptors

A

An ACh receptor that responds not only to ACh but to nicotine.
In the brain they are important in cognitive functions and behavior.
Receptor contains a ligand gated channel
Channels open = depolarization

37
Q

Muscarinic Receptors

A

ACh receptor stimulated by acetylcholine and muscarine.
Prevalent at some synapses in brain, and at junction where PNS inner gates peripheral glands/organs like salivary glands/heart.
These receptors couple with G proteins, which then alter the activity of a number of different enzymes and ion channels

38
Q

Dopamine, Norepinephrine, Epinephrine

A

Catecholamines formed from Tyrosine.
Play essential roles in states of consciousness, mood, modivation, directed attention, movement, blood pressure regulation, and hormone release.
After activating receptors, catecholamine conc in the synaptic cleft declines: due to a membrane transporter protein transporting it back to the axon terminal, and enzymes in the EC fluid/axon terminal like monoamine oxidase breaking it down.

39
Q

Adrenergic

A

Describes neurons that release norepinephrine or epinephrine.
Also to describe the receptors to which those chemicals bind.
Metabotropic: use 2nd messengers to transfer a signal from the surface of the cell to the cytoplasm

40
Q

Serotonin

A

Produced from tryptophan.
Slow to effect –> works as a neuromodulator
Excitatory effect on muscle control pathways.
Inhibitory effect on pathways that mediate sensations.

41
Q

Glutamate

A

An excitatory amino acid.
Majority of receptors are ionotropic, subtypes = AMPA and NMDA receptors
Cooperative via ->
Long term Potentiation: mechanism which couples frequent activity across a synapse with lasting changes in the strength of signaling -> major process in learning/memory.

42
Q

AMPA receptor

A

Glutamate binds to channel –> channel becomes permeable to both Na+ and K+, but the larger entry of Ca+ creates a depolarizing EPSP of the post synaptic cell.

43
Q

NMDA receptor

A
  1. Glutamate must bind to channel
  2. A magnesium ion blocks NMDA channels when the membrane voltage is near the negative resting potential, and to move it out of the way the membrane must be significantly depolarized by the current through AMPA channels.
    Channel mediates substantial Ca2+ flux.
    Mediates excitotoxicity.
44
Q

GABA

A

The major inhibitory neurotransmitter in the brain.
Modified form of glutamate.
Postsynaptically binds to either ionotropic or metabotropic receptors.
Ionotropic receptor: increases Cl- flux into the cell, resulting in hyperpolarization of the post synaptic membrane.
Ex: Xanax and Valium bind GABA receptors as well. Ethanol targets GABA synapses and inhibits excitatory synapses –> global brain depression

45
Q

Glycine

A

The major neurotransmitter released from inhibitory interneurons in the spinal cord and Brainstem.
Binds ionotropic receptors on postsynaptic cells that allow Cl- to enter, preventing them from approaching threshold.
Helps regulate skeletal muscle contraction.