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Neuroscience > Module B-04 > Flashcards

Module B-04 Flashcards

1
Q

2 types of synapses

A

1) electrical

2) chemical

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2
Q

How to electrical synapses conduct?

A

ions move through membrane spanning gap junctions to the next cell

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3
Q

Describe structure of gap junction channel

A
  • Formed by two hemichannels called Connexons
  • Each connexon has 6 subunits called Connexins
  • Each connexin has 4 membrane spanning regions
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4
Q

Cells of CNS where electrical synapses occur

A

1) Hormone-secreting cells of the hypothalamo-pituitary axis
2) Some spinal motor neurons
3) Hippocampal pyramidal cells
4) Mesencephalic nuclear cells
5) Retinal cells
6) connect Astrocytes (K+ buffering and Ca2+ signalling)

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5
Q

Cells of PNS where electrical synapses occur

A

Schwann cells

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6
Q

Speed and direction of electrical synapses

A

Fast (0.1 ms) and can be uni or bidirectional

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7
Q

Where does transmitter vesicle release occur in chemical synapses

A

from presynaptic cells at the ACTIVE ZONE of the synaptic Bouton

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8
Q

3 locations on the neuron where neuronal chemical synapses occur

A

1) Axodendritic (on dendrites)
2) Axosomatic (on cell bodies)
3) Axoaxonic ( on axon hillock and near synaptic terminal)

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9
Q

________ and __________ synapses are mainly inhibitory

A

Axoaxonic and Axosomatic

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10
Q

__________ synapses are mainly excitatory

A

Axodendritic

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11
Q

How do Axosomatic and Axoaxonic inhibition differ?

A

Axosomatic inhibit Action potential

Axoaxonic inhibit transmitter release (AP do occur)

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12
Q

What are Tripartite synapses

A

occur btw astrocyte , postsynaptic and presynaptic neuron

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13
Q

What is role of Astrocyte in Tripartite synapses?

A

uptake of transmitter released and release others fr uotake by neurons (eg glutamate to glutamine)

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14
Q

5 traditional criteria for substance to be classified as neurotransmitter:

A
  1. synthesis in presynaptic neurons
  2. storage in preparation for release
  3. release by presynaptic neurons, typically in a calcium-dependent fashion
  4. binding to specific postsynaptic receptors
  5. removal from synapses by specific mechanisms
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15
Q

5 groups of LOW molecular weight neurotransmitters:

A

1) Acetylcholine
2) Monoamines
3) Amino Acids
4) Purines
5) Gases

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16
Q

3 Groups of Monoamines and examples

A

1) Catecholamines- Dopamine, Norepi and Epi
2) Indoleamines - Serotonin and Tryptamine
3) Others - Histamine and taurine

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17
Q

5 amino acid neurotransmitter

A

1) Glycine
2) Glutamate
3) Aspartate
4) Homocysteine
5) GABA

18
Q

4 Purine neurotransmitters

A

1) Adenosine
2) ATP
3) ADP
4) AMP

19
Q

2 Gases neurotransmitters

A

1) NO

2) CO

20
Q

Describe synthesis of Low Molecular weight Neurotransmitters

A
  • synthesized in cytosol
  • loaded into clear vesicles (some in dense core vesicles)
  • tethered to cytoskeleton near active zone
21
Q

Describe synthesis of High Molecular weight Neurotransmitters

A
  • synthesized in soma as propeptides
  • transported by anterograde axonal transport in Large dense core vesicles
  • converted along the way into multiple transmitter molecules
  • the vesicles are stored further away from active zones
  • eg : opioid peptides of pain regualtion
22
Q

Describe synthesis of Nitric Oxide (NO) Neurotransmitter

A
  • Ca2+ enters cell through NDMA receptor

- Ca2+-Calmodulin complex forms => activates NO synthase => converts L-arginine to L-citrulline and NO

23
Q

Isoform of NO synthase in neurons

A

nNOS

24
Q

Is NO stored?

A

no , it is synthesized on demand by Ca release which can come from presynaptic neuron

25
Q

How is Dopamine loaded into vesicles

A

by a H+- Dopamine antiport on vesicular membrane

26
Q

What tethers vesicles to cytoskeleton?

A

Synapsin

27
Q

How are vesicles released from cytoskeleton

A

Phosphorylation of synapsin by calcium calmodulin-dependent protein kinase

28
Q

How are vesicles moved towards active zone for exocytosis?

A

by Rab proteins

29
Q

How do vesicles dock on nerve terminal membranes?

A

a. Vesicular membranes have v-SNARE proteins and the nerve membrane has t-SNARE proteins
b. v-SNARE protein synaptobrevin binds to t-SNARE protein
syntaxin
c. v-SNARE protein synaptotagmin binds to t-snare protein neurexin

30
Q

How is neurotransmitter released after vesicle docks?

A

vesicular membrane protein Synaptophysin forms the fusion pore in the nerve terminal membrane

31
Q

What is the role of Ca2+ in neurotransmitter release?

A
  • release of vesicle ( indirect phosphorylation of Synapsin)

- opening of inserted fusion protein

32
Q

How is return of Ca2+ to normal levels (the slower falling phase)?

A
  • Ca2+ ATPase and a Ca2+/Na+ exchange system

- Sequestration of Ca2+ ions within the smooth endoplasmic reticulum and mitochondria of the nerve terminal

33
Q

When are low and High mol weight transmitters co released

A
  • low nerve stimulation rates (100 Hz), the rise in [Ca2+]i

spreads further, thereby promoting exocytosis of the large dense core vesicles

34
Q

Describe recycling of small clear vesicles

A
  • Endocytosis mediated by the protein clathrin,which coats the vesicle.
  • Once internalized, the vesicles lose their coats and fuse
    with the endosome, which forms new vesicles for refilling
35
Q

Describe recycling of dense core vesicles

A
  • endocytosis.

- The empty vesicles are transported retrogradely to the soma for refilling

36
Q

2 categories of receptors

A

1) Ionotropic

2) Metabotropic

37
Q

What happens to an ionotropic receptor upon binding of a neurotransmitter?

A
  • causes conformational change
  • either opens or closes central ion passing pore
  • changes ionic conductance which affects membrane potential
38
Q

examples of ionotropic receptors

A

Nicotinic AChR;
GABAA receptor;
NMDA receptor for glutamate

39
Q

What happens to an metabotropic receptor upon binding of a neurotransmitter?

A
  • binding of neurotransmitter causes dissociation of G protein subunits => interact with second messenger
  • signaling cascades activate kinases, liberate calcium and promote phosphorylation of channels for K+, Ca2+ or Cl-
40
Q

examples of metabotropic receptors

A

muscarinic AChR

norepinephrine receptors

41
Q

____________ receptors have short lived and faster action

A

Ionotropic

42
Q

____________ receptors affect metabolism and gene expression

A

Metabotropic

Neuroscience (32 decks)

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