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Bio 361 > Lecture 12: Synapses > Flashcards

Lecture 12: Synapses Flashcards

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Biology 101 flashcards
1
Q

Synapse overview

A

=junctions between and transmission of info between a neuron and its target cells
-target cells may be other neurons (synapse), muscle cells (neuromuscular junction), or gland cells (neuroglandular junction)

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2
Q

Electrical synapse (rare)

A

-electrotonic current flows from presynaptic neuron to postsynaptic and changes the potential of pot.

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3
Q

Chemical synapse (common)

A

-action potentials of pre- cause release of chemical messengers, who then bind to specific receptors on post- and activate a signal transduction pathway

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4
Q

transmission from neuron to cell, neuromediator

A

-synthed in neurons, released in synaptic cleft by presynaptic neuron following depolarization, and binds to receptor on postsynaptic membrane, which transduces the signal to target cell

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5
Q

example: neuromuscular junction (NMJ)

A
  • somatic motoneurons terminate in an arborization of axon branches, called terminal boutons
  • location of innervation is called NMJ
  • muscle side of NMJ called the motor end plate (MEP), a region of muscle cell membrane that is highly excitable
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6
Q

NMJ: neuromediator=acetylcholine

A
  • neurotransmitter released at the NMJ in skeletal muscle is ACh, and has an excitatory effect
  • ACh is also a neurotransmitter in the CNS and PNS (autonomic), and can be excitatory or inhibitory
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7
Q

Synaptic transmission: two pools of neurotransmitters

A
  1. Readily releasable pool (RRP)
    2.Reserve pool (RP)
    both contained in vesicles in synapse
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8
Q

Readily releasable pool (RRP)

A
  • located at the active zone of the synapse
  • bound to docking proteins at the synaptic membrane
  • ready to be released in the synaptic cleft
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9
Q

Reserve Pool

A
  • bound to the cytoskeleton at some distance from the plasma membrane
  • waiting to be docked
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10
Q

Synaptic transmission 2: role of Ca2+ VG channels at axon terminals

A

Eca2+= 130mv (resting Vm is -70mv)

  • action potentials at axon terminal depolarize membrane, opening VG Ca2+ channels, increasing Pca++
  • large electrochemical gradient for Ca++ drives them inside the cell
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11
Q

Synaptic transmission 3: Ca++ and release of synaptic vesicles

A

RRP: ca++ stimulates vesicles bound on docking proteins to fuse with membrane, undergo exocytosis and release neurotransmitters
RP: ca++ stimulates vesicles waiting to be docked to move and bind to docking proteins, allowing neurotransmitters to be ready for release when NEXT AP reaches axon terminal

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12
Q

Synaptic transmission 4: ca++ translates electrical message into chemical message

A
  • higher the frequency of APs, the more frequently membrane is depolarized, opening ca++ VG channels more frequently, increasing intracellular ca++, so more vesicles of neurotransmitters fuse with cell membrane and are released into synaptic cleft and bound to receptors as post-, creating a larger response
  • therefore ca++ will transduce the electrical info about strength and length of stim into a chemical message
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13
Q

Magnitude of postsynaptic response depends on:

A
  • concentration of neurotransmitter in synaptic cleft
  • number of receptors present in postsynaptic membrane
  • affinity of receptors for neurotransmitter
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14
Q

synaptic transmission 5: stopping release of vesicles/regulation of ca++

A

-APs stop, Ca++ ATPase pumps them out of cytoplasm, and intracellular buffers bind Ca++

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15
Q

synaptic transmission 6: activating transduction pathway of postsynaptic cell

A
  • once released, neurotransmitter binds to receptors in membrane of postsynaptic cell
  • when neurotransmitters bind onto their specific receptors, signal transduction pathway is activated and target cell responds
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16
Q

synaptic transmission 7: removing neurotransmitters from cleft:

A

removed by: passive diffusion, active uptake by presynaptic neuron or astrocytes, or enzymess from cleft degrade them (ie. acetylcholinesterase degrades acetylcholine)

17
Q

Signal Coding: dendrites and cell body

A

Strength: coded by amplitude of GP
duration: coded by duration the GP lasts before repolarising back to resting Em

18
Q

Signal Coding: hillock and axon

A

strength: coded by frequency of AP
duration: coded by duration of train of AP

19
Q

Signal coding: synaptic cleft

A

strength: concentration of neurotransmitter
duration: duration of neurotransmitter release

20
Q

Diversity of Synapses

A
  • wide variety of neurotransmitters released at synapses of different neurons; some excitatory, other inhibitory
  • some neurotrans mod the properties of channels or receptors
  • receptors for these neurotransmitters vary among neurons, such that in some a single neurotrans. may excite, while in other it inhibits
21
Q

inotropic neurotransmitter receptor

A

=receptor is an ion channel, often ligand-gated; create a fast, short term change in potential, and can be excitatory or inhibitory

22
Q

metabotropic receptor

A

NOT an ion channel

  • activation initiates a signal transduction pathway that transmits its ignal via secondary messenger
  • may affect ion channels, modulate properties of channels or receptors, or affect the transcription of proteins (of receptors, enzymes, or ion channels)
  • relatively slow and long term changes
23
Q

inhibitory neurotransmitters

A
  • cause hyperpolarization (IPSPs: inhibitory postsynaptic potentials)
  • make postsynaptic cell less likely to generate an AP
24
Q

excitatory neurotransmitters

A
  • cause depolarization (EPSPs: excitatory postsynaptic potentials)
  • make postsynaptic cell MORE likely to generate an AP
25
Q

Prozac: a SSRI (selective serotonin reuptake inhibitor)

A
  • a monoanime neurotrans. in the CNS and digestive
  • in CNS it is involved in regulation of mood, appetite, and sleep
  • present in all animals (ubiquitous)
  • linked to depression
  • SSRIs used to treat clinical depression, anxiety disorders, and some personality disorders
26
Q

Mechanism of SSRIs

A

10% of serotonin released by presynaptic cell is lost, 90% binds to post

  • then released and taken up by presynapse for further use
  • SSRIs are thought to inhibit the reuptake of serotonin by the presynapse, increasing serotonin concentration in synaptic cleft
  • only effective on people severe depression, less so with mild or moderate
27
Q

cocaine

A
  • dopamine is a catecholamine monoamine neurotransmitter in the CNS
  • 5 known dopamine receptors for human brain, DRD1-DRD5, 5 being a “reward” transmitter and affinity for it is 10x greater
  • DAT is a transmembrane protein that pumps dopamine from cleft back into presynapse
  • cocaine is a serotonin-norepinephrine-dopamine reuptake inhibitor
  • cocaine causes dopamine to accumulate in the synaptic cleft
  • regular use leads to down-regulation of dopamine receptors in postsynapse

Bio 361 (17 decks)

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