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Med Neuro Block 1 > Synapse Structure > Flashcards

Synapse Structure Flashcards

1
Q

What is a synapse?

A

A specialized functional contact zone
(junction) for communication between nerve cells (neuro-neuronal), or between a nerve cell and its effector organ (neuromuscular, neuroepithelial, etc.)

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2
Q

Synaptic transmisssion

A
  • Bridged junction or gap junction

* Unbridged junction: presence of synaptic cleft

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3
Q

Bridged/Gap Junction:

A
  • Bidrectional

* Can be unidirectional

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4
Q

Unbridged junction:

A

• Unidirectional

presynaptic&raquo_space; postsynaptic

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5
Q

Electrical Transmission

A
  • Gap: only 3.5 nm wide
  • Apposing cells each contributes a hemi-channel = connexon
  • 2 connexons form an ion channel: pore size of 1.5 nm in diam.
  • Each connexon: 6 connexins
  • Each connexin: 4 membrane-spanning regions
  • Connexins undergo conformational changes to open or close the pore
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6
Q

Electrical transmission is mediated by ______________.

A

gap junctions

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7
Q

Gap junctions:

A
  • Low-resistance, high-conductance channels bridging the 2 cells
  • Current flows through the junction and depolarizes the postsynaptic cell
  • Most rapid form of synapse between neurons: virtually no synaptic delay
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8
Q

Properties of electrical synapse:

A
  • Speed of transmission: no synaptic delay
  • Synchronization of transmission: 2 or more electrically-coupled neurons
  • Contributes to stereotypic, all-or-none behavior
  • Transmission of developmental and regulatory signals between cells
  • No mechanisms for inhibitory actions
  • No mechanisms for long-lasting changes in effectiveness (modulation) of synapses
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9
Q

____________ is the neurotransmitter of the vagus n. to the heart

A

Ach

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10
Q

___________ is the neurotransmitter of the neuromuscular junction

A

Ach

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11
Q

Chemical Transmission is mediated by:

A

release and diffusion of neurotransmitters into the synaptic cleft

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12
Q

Presynaptic (prejunctional):

A

• Synaptic vesicles
• Active zones:
(presynaptic dense projections)
• Autoreceptors/receptors

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13
Q

Synaptic cleft:

A

• Typically wider than the extracellular

space; 30-50 nm or more

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14
Q

Postsynaptic (end-plate;

postjunctional):

A
  • Receptors

* Postsynaptic density (PSD-95)

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15
Q

Morphological Types of CNS Chemical Synapses:

A

Gray’s type I (Asymmetric)

Gray’s type II (Symmetric)

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16
Q

Gray’s Type I (asymmetric):

A
  • Round synaptic vesicles
  • Wide synaptic cleft
  • Prominent PSDs
  • Often associated with excitatory synapses
17
Q

Gray’s Type II (symmetric):

A
  • Flat or pleomorphic vesicles
  • Narrow cleft
  • Less prominent PSDs
  • Often associated with inhibitory synapses
18
Q

Monoaminergic synapses:

A
  • Dense-core vesicles
  • Axonal varicosities
  • Wide synaptic cleft
  • No prominent pre- & post-synaptic densities
19
Q

Peptidergic synapses:

A
  • contain large dense-core vesicles

* Vesicles are of different sizes & shapes

20
Q

Neuromuscular Junction:

A
  • Presynaptic dense bars
  • Ca++ channels
  • Primary & secondary synaptic clefts
  • AChE and basal lamina in clefts
  • Postsynaptic junctional folds
  • Ach receptors face active zones
  • Voltage-gated Na+ channels along sides and depths of folds
21
Q

Myasthenia Gravis:

A

Disease of chemical transmission at the neuro-muscular synapse
• Severe weakness of muscles
Autoimmune: most common Antibodies against one’s own nicotinic acetylcholine receptors (AChR) in muscles. Congenital and heritable: rare
• Treatment: Inhibitors of acetylcholinesterase

22
Q

What are symptoms of myasthenia gravis?

A

• Severe weakness of muscles
Autoimmune: most common; antibodies against one’s own nicotinic acetylcholine receptors (AChR) in muscles
Congenital and heritable: rare

23
Q

How is myasthenia gravis treated?

A

Inhibitors of acetylcholinesterase

24
Q

Tetanus toxin:

A

cleaves VMAP

25
Q

Botulinum toxins:

A

cleave VAMP or t-SNARE

26
Q

α-Latrotoxin:

A

binds to neurexin

27
Q

Synapsin I:

A
  • binds vesicles to cytoskeleton
  • phosphorylated by Ca2+/calmodulin-dependent protein kinase
  • when intracellular Ca2+ is increased&raquo_space; releases vesicles from the cytoskeleton
28
Q

Rab3A:

A
  • a neuron-specific GTPase

* binds to vesicles essential for propelling vesicles to the active zone

29
Q

Synaptotagmin:

A
  • has 5 Ca2+-binding sites

* major Ca2+-sensing protein that triggers vesicular exocytosis

30
Q

NSF:

A

N-ethylmaleimide-sensitive factor (an ATPase):
• cytosolic
• hydrolyzes ATP to release the complex

31
Q

v-SNARE (vesicular SNAP Receptor proteins) = VAMP (vesicle-associated membrane protein):

A

Synaptobrevin: binds t-SNARE

32
Q

t-SNARE (target membrane SNAP Receptor):

A

Syntaxin: a plasma membrane protein

SNAP-25: a plasma membrane protein of 25 kDa

33
Q

What is the process for v-SNARE & t-SNARE associate proteins?

A

v-SNARE & t-SNARE associate&raquo_space; docking & fusion&raquo_space; NSF & SNAP bind to complex & dissociate it

34
Q

Neurexin:

A

plasma membrane protein

may also interact with vesicle proteins

35
Q

SNAP:

A
  • soluble NSF attachment protein
  • unrelated to SNAP-25
  • cytosolic
  • binds to NSF
36
Q

Postsynaptic Receptors:

A

determine postsynaptic response

37
Q

Common biochemical features:

A

Common biochemical features:
Membrane-spanning proteins with external recognition sites for specific transmitter molecules.

Effector function triggered in target cell:
• Directly activates gating of ion channel -or-
• Indirectly activates gating through second messenger cascade

• A given transmitter binds to conserved families of receptors and is associated with specific physiological functions

Med Neuro Block 1 (11 decks)

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