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Block 3 Found Sci > 1-Synaptic Transmission > Flashcards

1-Synaptic Transmission Flashcards

1
Q

info flow within a neuron

A
  1. dendrites- collect signals
  2. cell body- integrates incoming signals + gen outgoing
  3. axon- passes signal to dendrites
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2
Q

info flow between neurons

A
  1. electrical (minority) or chemical (neuron-neuron, neuron-muscle) synapse
  2. presynaptic neuron
  3. synaptic cleft
  4. postsynaptic
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3
Q

structure of electical synapse

A

1+ gap junction channels b/t pre and postsynaptic membranes permeable to ions and small moles

6 connexin > connexon > gap junction

bidirectional, fastest, low selectivity

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4
Q

significance of electrical synapses

A

@ most tissues - nervous system, myocardial, intestinal smooth muscle, cochlea

mediate chemical coupling in a network

synchronize electric activty with pop of neurons

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5
Q

intercellular chemical signaling

A
  1. hormones- neurohormone if substance released into the bloodstream by neuron
  2. neurotransmitters- local distribution by diffusion, released at synapse by neuron, synaptic mechanism when post synaptic cell very close, paracrine mechanism when several near by cells
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6
Q

morphology of synapses

A
  1. presynaptic terminal with active zone where vesicular release happens
  2. synaptic cleft
  3. postsynaptic site
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7
Q

neuron-neuron pathway

A
  1. transmitter syn and stored in vesicles
  2. action potential invades presynaptic terminal
  3. depolarization = opening of voltage gate Ca channels
  4. influx of Ca thru channels
  5. vesicles fuse with presynaptic membrane
  6. transmitter released via exocytosis, vesicle recycles via endocytosis
  7. transmitter binds receptor in postsynaptic membrane
  8. open or closing post syn channels, ligand gated ion
  9. postsyn current excitatory or inhibitory potential
  10. removal of transmitter via glial uptake or enzymes
  11. retrieval of vesicular membrane from plasma membrane
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8
Q

SNARE complex

A

synaptic release machinery

transmembrane proteins in vesicles and presyn plasma membrane for helix complex to dock and fuse vesicle

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9
Q

recovery of presynaptic terminal

A
  1. repolarize as K leaves thru voltage gated K channels
  2. voltage gated Ca channels close so Ca stop flowing into synaptic terminal
  3. free Ca removed from cytoplasm via sequestration
  4. vesicle recycled
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10
Q

Ca sequestration

A

three ways
1. diffusion
2. Ca binding proteins
3. transported to internal Ca stores
4. pumped or transported outside cell via secondary active antiporter

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11
Q

vesicle endocytosis

recyling

A
  1. clathrin recruited to vesicular membrane
  2. clathrin triskelia assemble into coat that curves membrane
  3. dynamin ring forms to pinch off membrane
  4. coated vesicle translocated by actin fila
  5. Hsc-70 and auxilin uncoat vesicle

fusion is rapid but recylcing takes more time so if prolonged firing activity then exhause the vesicle pool

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12
Q

types of neurotransmitters

small molecule

A
  1. amino acids - glutamate (excitatory), GABA (inhibit), glycine, serine, aspartate
  2. acetylcholine
  3. amines- histamine, monoamines (serotonin), catecholamines (dopamine, norepinephrine, epinephrine

syn and packed into small clear core vesicles at nerve terminals

low frequency stimulation

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13
Q

classes of postsynaptic receptors

A
  1. ionotropic- ligand gated ion channel, rapid changes in mem potential, local
  2. metabotropic- G protein coupled, slow change in mem potential since multi steps, diffusive, signal amp
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14
Q

EPSP

excitatory postsynaptic potential

A

fast response mediated by ionotropic receptors and glutamatergic synapse

brings potential Vm closer to threshold, depolarization

glutamate gated channels permeable to Na and K but Na>K

will decay over time

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15
Q

IPSP

inhibitory postsynaptic potential

A

fast response mediated by ionotropic receptors

GABA receptors/gated ion channels permeable to Cl chemical driving force > Vrest so influx of Cl to hyperpolarize IPSP

away from threshold, also decay

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16
Q

slow postsynaptic response

A

mediated by metabotropic receptors so can either decrease (excite) or inc (inhibit) conduction thru Cl/K channels

G protein or second messangers, may link to ionic channels

17
Q

synaptic delay

A

pause b/t arrival of action potential in presyn and onset of potential change in postsyn
-events leading to fusion in presyn
-diffusion of transmitter across cleft
-activation of postsyn channels

1-2 msec at fast chem synapses (ionotropic) and longer with metabotropic

18
Q

dopamine clearance

A

many abused drugs like cocaine bind bind to dopamine transporters @ presyn terminals = inc of synaptic DA level

19
Q

summation of synaptic responses

A

@ CNS - indiv EPSP too small for action potential threshold in postsyn cell

graded effect of all synapses is summed in time and space at initial axon segment until sufficiently depolarized and voltage gated sodium channels open

20
Q

unconventional transmitter

A
  1. purines- adenosine when ATP degraded, needs purinergic receptor
  2. NO- not packed into vesicle since gas
  3. endocannabinoids- product of enzymatic degradation of membrane lipids
21
Q

neurotransmitter criteria

A
  1. packed into synaptic vesicles
  2. Ca dependent release
  3. bind to specific receptors
22
Q

neuropeptide synthesis

A

precursors made in nucleus then packed into large dense core vesicles for transport to terminal

released with high frequency stimulation along with small molecule

23
Q

neuromuscular junction

A

motor axon terminals embedded in grooves in muscle fiber surface

has junctional folds for postsyn membrane and multiple active zones

24
Q

NMJ transmission

A
  1. action potential
  2. Ca enters voltage gate channels
  3. Ach released
  4. Na enters postsyn folds to create local current b/t depolarized end plate and adjacent muscle plasma membrane
  5. muscle fiber action potential initated then propogated in membrane
  6. Ach degradation
25
Q

nicotinic acetylcholine receptors

A

nAchR aka Ach gated ion channels are ionotropic, permeable to Na and K but Na>K

26
Q

unique features neuromuscular transmission

A

-each indiv muscle fiber innervated by one motor neuron
-only excitatory not inhibition input
-only one type neurotransmitter Ach
-only one type receptor nAch R
-multi active zones at one terminal
-multi terminals on one muscle fiber
-strong transmission to ensure AP

27
Q

toxins targetting NMJ

A
  1. botulism- in soil, water, foodborne, targets motor neurons to paralyze = muscle weak, botox
  2. tetanus- wound contamination, targets interneurons to disinhibit/hyperexcite = tetanic contractions

both cleave SNARE proteins

28
Q

eaton lamber syndrome

A

presynaptic disorder
-freq in pts with small cell carcinoma of lung
-antibodies to voltage gated Ca channels in presynaptic terminal of somatic motor nerves
-less Ca enters presyn terminal so less Ach released = muscle weakness

29
Q

myasthenia gravis

A

postsynaptic disorder
-severe muscle weakness from antibodies vs nAchR in NMJ so dec # of functional postsyn receptors

use neostigmine to indirectly enhance function of existing AchR by inc extracellular Ach levels, reversible Ach inhibitor

30
Q

acetylcholine receptor blockers

A
  1. tubocurarine
  2. curare- poison from bark of south american tree
  3. alpha-bungarotoxin from peptide of venom of banded krait snake, irreversibly blocks nAchR
31
Q

cholinesterase inhibitors

A
  1. edrophonium, short acting inhibitor to dx myasthenia gravis, long acting inhibitors to treat
  2. organophosphorus compounds aka sarin gas and pesticides irreversibly bind

Block 3 Found Sci (60 decks)

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