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Biology171 > Cell-Cell Communication > Flashcards

Cell-Cell Communication Flashcards

1
Q

Describe the features of an Electrical Synapse. Where are they especially abundant?

A
  • Electrical signal (current) flows between cells through gap junctions
  • Can be uni- or bi- directional
  • Allows very fast communication between cells
  • Facilitate synchronization of neurons
  • Esp. abundant in retina, cerebral cortex, cardiac & smooth muscle, escape mechanisms (esp. in invertebrates)
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2
Q

Describe the 3 major components of Chemical Synapses

A
  1. Presynaptic cell
    - axon terminals
    - synaptic vesicles (contain NT - usually synthesized in cell body, moves to axon terminals via fast axonal transport)
  2. Synaptic cleft
    - space btwn pre- and post- synaptic cells (~20nm wide)
  3. Postsynaptic cell
    - synapses usually involve dendrites, soma; sometimes axons, axon terminals
    - receptors
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3
Q

Summarize the events of a Chemical Synapse

A
  1. Presynaptic cell
    - AP depolarizes axon terminals
    - voltage-gated Ca++ channels open; Ca++ enters axon terminal
    - Ca++ stimulates exocytosis of synaptic vesicles
    - NT molecules are released into cleft
  2. Synaptic cleft
    - NT molecules diffuse across cleft
  3. Postsynaptic cell
    - NT molecules bind to receptors
    - Response is initiated
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4
Q

Each AP causes the same amount of NT release from a particular axon terminal. So, how can the amount of NT be adjusted?

A

Frequency modulation

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5
Q

Describe Frequency modulation

A
  • Frequency of APs initiated at trigger zone varies w/ intensity/duration of stimulus
    (stronger stimulus -> increase rate of APs)
  • Frequency of APs at axon terminals determines how much NT is released
    (Increase rate of APs -> increase NT release)
    –> Stronger stimulus -> increase NT release
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6
Q

What is GABA? Describe the difference between the 3 types of GABA receptors.

A
  • Major inhibitory NT in CNS; 3 receptor types:
    1. GABAb - metabotropic
  • G protein-coupled receptor; uses 2nd messenger-mediated signal-transduction pathway
    2. GABAa, GABAc - ionotropic
  • ligand-gated Cl- channels
  • At rest [Cl-]out > [Cl-]in (Ecl- = -80mV)
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7
Q

How are the effects of GABA potentiated?

A
  • potentiated by alcohol, benzodiazepines (e.g. valium), barbiturates (e.g. pentobarbital)
  • these substances allosterically modulate GABA ionotropic receptors and increase Cl- influx in response to GABA binding
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8
Q

What happens to GABA receptors in response to alcohol? Chronic alcohol?

A

GABA + EtOH -> Sensitization

Chronic alcohol -> Desensitization

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9
Q

What is Glutamate? Describe the 3 receptor types

A
  • Major excitatory NT in CNS; 3 receptor types:
    1. Metabotropic receptor
  • G protein-coupled receptor; uses 2nd messenger-mediated signal-transduction pathway
    2. Ionotropic: AMPA receptor
  • Ligand-gated Na+/K+ channel
  • Channel opens -> Na+ enters (& K+ exits) -> cell depolarizes
    3. Ionotropic: NMDA receptor
  • Ligand-gated and voltage-dependent Na+/K+/Ca2+ channel
  • At resting potential, Mg2+ blocks ligand-activated gat
  • In order for ions to pass through channel, need: glutamate binding to open gate & depolarize to remove Mg2+
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10
Q

What leads to Long-term Potentiation? What is it?

A
  • Glutamate signaling through AMPA and NMDA receptors can lead to L-TP
  • Enhancement of the postsynaptic cells response to the presynaptic cell as a result of sustained synaptic activity
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11
Q

Describe the positive feedback mechanism involving NMDA receptors and glutamate

A
  • Activation of NMDA receptors activates 2nd messenger pathways leading to:
    1. Increased sensitivity to glutamate (postsynaptic cell)
    2. Increased glutamate release (presynaptic cell)
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12
Q

Where are Acetylcholine (cholinergic receptors) found? Describe 2 receptor types

A
  • CNS, autonomic nervous system, neuromuscular junctions
    1. Muscarinic receptors - Metabotropic
    2. Nicotinic Receptors - Ionotropic
  • Ligand-gated Na+/K+ channel
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13
Q

Name an agonist and 2 antagonists for Acetylcholine cholinergic receptors

A
  • Agonist: Nicotine

- Antagonists: curare, alpha-bungarotoxin

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14
Q

Where are Epinephrin/norepinephrine (adrenergic receptors) found? Describe the 2 major receptor types (G protein-coupled receptors)

A
  • CNS, autonomic nervous system
    1. Alpha receptors
  • a1- receptors: (increase intracellular [Ca++]; increase contraction of smooth muscle)
  • a2-receptors: (decrease intracellular [Ca++]; increase relaxation of smooth muscle; decrease exocrine secretion)
    2. Beta receptors (use G protein coupled to adenylate cyclase -> increase [cAMP] in target cells
  • b1-receptors: (increase contraction of cardiac muscle)
  • b2-receptors: (relaxation of smooth muscle)
  • b3-receptors: (mostly in adipose tissue; increase lipolysis)
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15
Q

What is Divergence?

A

One presynaptic neuron can synapse onto many postsynaptic neurons

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16
Q

What is Convergence?

A

One postsynaptic neuron can receive input from many (thousands) presynaptic neurons

17
Q

Describe Fast Synaptic Potentials

A
  • Rapid onset, short duration (milliseconds)

- NT binds to, opens chemically gated ion channels -> alters ion flow into/out of postsynaptic cell

18
Q

Describe Slow Synaptic Potentials

A
  • Slower onset, long duration (seconds to minutes)
  • NT binds to G protein-coupled receptors ->
  • Activates signal-transduction pathway ->
  • Alters membrane permeability &/or modifies existing proteins &/or alters protein synthesis
19
Q

What is an EPSP?

A

Excitatory PostSynaptic Potential caused by depolarization

20
Q

What is an IPSP?

A

Inhibitory PostSynaptic Potential caused by hyperpolarization

21
Q

What is Spatial Summation?

A

Integration of simultaneous signals (graded potentials) from different synapses

22
Q

What is Temporal Summation?

A

Integration of signals received from a signal synapse at slightly different times

23
Q

What is Presynaptic Inhibition?

A

One neuron releases inhibitory NT onto or near (some of) the axon terminals of a second neuron, causing those axon terminals to release less NT

24
Q

What is Presynaptic Facilitation?

A

One neuron releases excitatory NT onto or near (some of) the axon terminals of a second neuron, causing those axon terminals neuron to release more NT

Biology171 (3 decks)

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