Neurons & Neural Communication Flashcards

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1
Q

2 types of cells in nervous system

A
  • neurons

- glia

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2
Q

3 types of glial cells

A
  • oligodendrocytes
  • astroglia
  • microglia
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3
Q

function of oligodendrocytes

A
  • myelinate/insulate MANY neurons in CNS -> create myelin sheath
  • similar function to Schwann cells (mylinate ONE neuron each in PNS)
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4
Q

function of astroglia

A
  • aka: astrocytes
  • ensheath tripartite synapse and ensure ionic balance within synapse
  • play a role in neuronal communication
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5
Q

function of microglia

A

act as immune cells in CNS

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6
Q

tripartite synapse

A

the proximity of presynaptic membrane, postsynaptic membrane, and surrounding glia and the way these 3 synaptic components produce activity at the synapse

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7
Q

major parts and functions of neurons

A
  • nucleus: contains genetic material
  • cell body: surrounds nucleus and other organelles inside neuron
  • dendrites: receive signals and carry them to cell body
  • axon: carries signals away from cell body (has synaptic bouton/pre-synaptic membrane at end of branch)
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8
Q

types of synapses

A
  • axosecretory: axon terminal secretes directly into bloodstream
  • axioaxonic: axon terminal secretes into another axon
  • axiodendritic: axon terminal ends on dendrite spine
  • axoextracellular: axon with no connection secretes into extracellular fluid
  • axosomatic: axon terminal ends on soma
  • axosynaptic: axon terminal ends on another axon terminal
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9
Q

resting membrane potential

A
  • To measure: put intracellular electrode in neuron and extracellular electrode into extracellular fluid, measure difference
  • Healthy neuron has RMP (or membrane voltage) of between –60 and –80 mV (~70 mV)
  • at rest, more sodium ions outside neuron and more potassium ions inside neuron
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10
Q

generation and conduction of post-synaptic potentials (PSPs)

A
  • occur when a neutrotransmitter molecule binds to a post-synaptic receptor, creating one of two localized effects (EPSP or IPSP)
  • transmission of PSPs graded (varies in size, NOT all-or-none), rapid, and decremental (decreases over time) -> travels like an electrical signal along an uninsulated wire
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11
Q

Excitatory post-synaptic potential (EPSP)

A
  • 1 effect of an NT binding to post-synaptic receptor
  • Depolarizes the membrane (ie. Decrease membrane potential from -70 to -67 -> gets closer to 0)
  • Increases likelihood that postsynaptic neuron will fire an action potential (AP)
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12
Q

Inhibitory post-synaptic potential (IPSP)

A
  • 1 effect of an NT binding to post-synaptic receptor
  • Hyperpolarizes the membrane (ie. Increase the membrane from -70 to -72 -> gets further from 0)
  • Decreases likelihood that postsynaptic neuron will fire an action potential (AP)
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13
Q

summation of PSPs

A
  • both EPSPs and IPSPs sum spatially and temporally
  • spatial summation: when PSPs are released from multiple synapses, combining to produce a greater effect (either greater EPSP or IPSP, or cancel out 1 EPSP and 1 IPSP)
  • temporal summation: when multiple PSPs are released from one synapse in rapid succession, combining to produce a greater effect (either greater EPSP or IPSP)
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14
Q

What is an Action Potential (AP), and how is it generated?

A
  • massive momentary reversal of the membrane potential (e.g., from -70 to +55 mV)
  • not graded (“all or none”: either happens or doesn’t), not decremental, less rapid than PSPs
  • occurs if the sum of the EPSPs and IPSPs is enough to depolarize membrane at axon initial segment above its threshold of excitation (ex. -65mV)
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15
Q

Ionic basis of Action Potentials

A
  • AP generation and conduction are both the result of voltage-activated ion channels
  • when membrane is depolarized (due to PSPs), sodium channels open, driving excitation (lots of sodium outside cell; wants to move in)
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16
Q

3 phases of an Action Potential

A
  • Rising Phase: sodium channels open, causing potassium channels to open too
  • Repolarization: sodium channels inactivate
  • Hyperpolarization: potassium channels close, leading to return to resting potential and a refractory period
17
Q

2 types of refractory periods

A
  • Absolute refractory period: no other AP could happen; causes conduction to only travel 1 way; during rising phase
  • Relative refractory period: another AP could happen, but the buildup to it would be slower; during hyperpolarization
18
Q

3 stages of sodium channels

A
  • closed (before rising phase)
  • open (during rising phase)
  • inactivated (repolarization begins)
19
Q

subthreshold vs. suprathreshold stimulation of an axon

A
  • subthreshold: excitatory potential produced, but not enough to elicit AP
  • suprathreshold: excitatory potential produced that exceeds threshold and produces AP
20
Q

conduction of Action Potentials in myelinated vs. unmyelinated neurons

A
  • myelinated: saltatory conduction -> jumping from one Node of Ranvier to the next -> faster conduction
  • unmyelinated: continuous conduction -> no jumping -> slower
21
Q

Multiple Sclerosis

A
  • Disorder that progressively damages myelin
  • 55-75K in Canada (3 new/day)
  • Canadians have one of the highest rates of multiple sclerosis in the world
22
Q

classic view of neurotransmission

A
  • based on work done at one synapse: the neuromuscular junction (NMJ)
  • What was true for that synapse was once (incorrectly) generalized to all nervous system synapses
23
Q

5 ways in which classic view of neurotransmission was incorrect

A
  • each cell has a single output & releases a single NT
  • NTs deactivated by enzymes
  • NTs produce 1 of either EPSPs or IPSPs
  • each NT has single receptor
24
Q

correction to classic view of neurotransmission: each cell has single output

A
  • true for NMJ, but it’s an exception

- most cells receive input from many cells

25
Q

correction to classic view of neurotransmission: NTs deactivated by enzymes

A
  • true for NMJ -> enzyme deactivates acetylcholine

- rare elsewhere -> reuptake is major mechanism for deactivation of NTs

26
Q

correction to classic view of neurotransmission: NTs produce 1 of either EPSPs or IPSPs

A
  • true at NMJ -> acetylcholine produces EPSPs

- whether NT produces EPSP or IPSP later shown to be function of receptor type, not NT itself

27
Q

correction to classic view of neurotransmission: each NT has single receptor

A
  • Acetylcholine receptors bind nicotine better than muscarine, and vice versa for others
  • but nicotinic and muscarinic receptors are ionotropic (form ion channel pore) and metabotropic (directly linked to ion channel) receptors, respectively
28
Q

correction to classic view of neurotransmission: each cell releases a single NT

A
  • true in NMJ

- “coexistence” of different transmitters found in many cells; neurotransmission a complicated and heterogenous process

29
Q

major types of NTs

A
  • amino acids (ex. glutamate, GABA)
  • monoamines (ex. dopamine, epinephrine, norepinephrine, serotonin)
  • acetylcholine
  • neuropeptides (large molecule NTs… others above are small molecule)