1-Synaptic Transmission

Question 1

info flow within a neuron

Answer 1

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

Question 2

info flow between neurons

Answer 2

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

Question 3

structure of electical synapse

Answer 3

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

Question 4

significance of electrical synapses

Answer 4

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

mediate chemical coupling in a network

synchronize electric activty with pop of neurons

Question 5

intercellular chemical signaling

Answer 5

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

Question 6

morphology of synapses

Answer 6

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

Question 7

neuron-neuron pathway

Answer 7

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

Question 8

SNARE complex

Answer 8

synaptic release machinery

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

Question 9

recovery of presynaptic terminal

Answer 9

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

Question 10

Ca sequestration

Answer 10

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

Question 11

vesicle endocytosis

recyling

Answer 11

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

Question 12

types of neurotransmitters

small molecule

Answer 12

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

Question 13

classes of postsynaptic receptors

Answer 13

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

Question 14

EPSP

excitatory postsynaptic potential

Answer 14

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

Question 15

IPSP

inhibitory postsynaptic potential

Answer 15

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

Question 16

slow postsynaptic response

Answer 16

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

Question 17

synaptic delay

Answer 17

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

Question 18

dopamine clearance

Answer 18

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

Question 19

summation of synaptic responses

Answer 19

@ 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

Question 20

unconventional transmitter

Answer 20

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

Question 21

neurotransmitter criteria

Answer 21

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

Question 22

neuropeptide synthesis

Answer 22

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

released with high frequency stimulation along with small molecule

Question 23

neuromuscular junction

Answer 23

motor axon terminals embedded in grooves in muscle fiber surface

has junctional folds for postsyn membrane and multiple active zones

Question 24

NMJ transmission

Answer 24

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

Question 25

nicotinic acetylcholine receptors

Answer 25

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

Question 26

unique features neuromuscular transmission

Answer 26

-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

Question 27

toxins targetting NMJ

Answer 27

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

Question 28

eaton lamber syndrome

Answer 28

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

Question 29

myasthenia gravis

Answer 29

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

Question 30

acetylcholine receptor blockers

Answer 30

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

Question 31

cholinesterase inhibitors

Answer 31

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