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Physio 💗 > 4 Synaptic Physio > Flashcards

4 Synaptic Physio Flashcards

1
Q

Synapse - a junction/specialized contact zone

(1) Who coined the word?
(2) Derived from the Greek word which means to __

A

(1) Charles Scott Sherington

(2) to clasp

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2
Q

Classes of synapse according to morphology/structure?

A

A. Gap Junction

B. Cleft

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3
Q

Gap Junctions
(1) Characteristics
(2) Function
(3) Flow:
A. Unidirectional, Bidirectional, or Multidirectional?
B. Fast or slow transmission? Resistance? Pass filters?
(4) Size of gap between cells
(5) Location?
(6) Electrical pattern produced is SPECIFIC and can be modulated by which electrical patterns?
(7) Effect changes in the coupling between cells? (2)

A

(1) Made up of 12 connexins or 2 connexons
(2) A communicating junction which allows electrical synapses or water-soluble particles such as ions and small molecules to pass from 1 cell to the next
(3) Bidirectional flow, fast transmission, low resistance, low pass filters
(4) 2 nm
(5) Present in cardiac muscle, smooth muscle, glial cells/nervous system
(6) Modulated by: Voltage, Intracellular pH, Ca2+
(7) Single channel conductance, Formation of new gap junctions or removal of existing ones

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4
Q

What is a hemichannel?

A
  • A channel present in only one membrane.
  • There’s influx and efflux of ions in our out of the cell.
  • Connexons made up of connexin
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5
Q

What is a pannexon?
>Composition
>Type of channel
>Similarities and differences from connexon
>Function
>Under normal conditions, open or closed?
>How is it activated?

A
  • Formed by pannexins
  • Hemichannel unlike connexons which can either be a hemi- or channel
  • vs. Connexons
    (1) Hemichannel
    (2) Similar structure except for addition of glycogen in pannexin
  • Function: Mediators of apoptotic processes, communicate the intracellular and extracellular compartments
  • Under normal/resting conditions, it is closed
  • Activation by various pathological stimuli: O2-glucose deprivation, Metabolic inhibitors, or S nitrosylation
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6
Q

History
(1) What is synaptic transmission? Who coined the word synapse?

(2) Types of Synapse based on function? Who discovered them?
(3) Who was able to show that the membrane is polarized?

A

(1) Process by which neurons transfer information at a synapse; Charles Sherrington
(2) Otto Loewi: Chemical synapse; Edwin Furshpan and David Potter: Electrical synapse
(3) John Eccles through the glass microelectrode

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7
Q

Two conflicting theories about neurons? Which is correct?

A

(1) Neural Doctrine by Spaniard Santiago Ramon Y Cajal
“Each neuron is its own entity, isolated from its neighboring neurons by small spaces”

(2) Reticular Theory by Camille Golgi
“Neurons are not distinct units, but are fused together acting as a whole.”

Both have a point.

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8
Q

Mutations in gap junctions?
*NTK

Point: Important for tissue homeostasis

A

(1) Congenital deafness
(2) Congenital cataracts
(3) Bullous pemphigoid
(4) Demyelinating disease (Charcot-Marie Tooth)
(5) Oculodentodigital dysplasia/ODD syndrome

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9
Q

Junctional complexes?

A
  1. Tight Junction
    - Zonula occludens
    - Made up of only 1 protein
    - Tight; will not allow passage of substances and seals neighboring cells together in an epithelial sheet to prevent leakage of molecules between them
  2. Gap
    - 2 connexons adhering together forming a tunnel-like structure for the passage of small molecules

Others:

  1. Desmosomes
    - for exchange/transfer of tension between cells; bidirectional
    - has MECHANICAL function (no electrical)
    - joins the IFs in 1 cell to those in the neighbor’s
  2. Hemidesmosomes
    - 1 side only
    - anchors IFs in a cell to the basal lamina
  3. Adherens junction
    - joins actin bundle in 1 cell to a similar bundle in neighboring cell
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10
Q

Classes of synapse based on function?

A
  1. Electrical
    - use of small ions flowing through GJ
    - around 2 nm
  2. Chemical
    - presence of a synaptic cleft or space bigger than GJ
    - around 20 nm space between
    - presence of vesicles containing NTs which has to diffuse in a synaptic cleft then bind to receptor found in the postsynaptic membrane.
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11
Q

Three parts of a chemical synapse?

A

(1) Knob (Axon; presynaptic)
(2) Synaptic cleft
(3) Receptive sites (Receiving cell axon or dendrite; postsynaptic)

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12
Q

Three types of synapses?

A
  1. Synapse with another neuron
  2. NMJ
  3. Neuroglandular synapses
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13
Q

Synaptic connections between neurons?

A

(1) Axo-dendritic
(2) Axo-somatic
(3) Axo-axonic
(4) Dendro-dendritic

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14
Q

Divergent vs. convergent neuronal circuitry or pathway? Effect?

What is a reverberating circuit?

A

Divergent - stimulating 1 neuron will have many widespread/diffused effects

Convergent - several neurons converge and have 1/local/discrete effect

Reverberating circuit - chain of neurons containing collateral synapses with previous neurons in the chain; effect: prolonged effect than stimulation

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15
Q

Occlusion vs. subliminal fringe?

A

Occlusion
-effect of two synapsed neurons could be less than summation of effects because of overlap/convergent connection in the effects

Subliminal fringe
-Neuron A and B have parallel pathway. Thus, stimulating 1 would also somehow subliminally stimulate parallel branches of neuron B.

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16
Q

What are possible causes of synaptic delay?

A

(1) Release of NT from vesicles
(2) Diffusion through cleft
(3) Binding with postsynaptic receptors & opening ion channels

17
Q

How does exocytosis occur?

A

(1) Ca2+ enters via VG Ca2+ channel and will bind to synaptotagmin.
(2) Tethering = Synaptobrevin will sort of lasso syntaxin
(3) Once connected, it will pull vesicle towards PM: “docking”
(4) When it’s near the PM = priming
(5) When vesicular membrane meets the PM = “superpriming”
(6) Fusion
(7) Zippering by T-SNAREs
(8) Complete fusion

18
Q

Two structures/configurations of SNARE complexes? Difference?

A

Trans-SNARE complex
-exert inward force

cis-SNARE complex
-no force

19
Q

Complete fusion vs. Kiss-and-Run

Identify if:
Complete fusion or Kiss-and-run
Endocytosis or exocytosis

(1) Dynamin
(2) Clathrin
(3) Calcium

A

Kiss-and-run: Instead of complete fusion, once pore is produced, the NTs leak out briefly —> Dynamin closes pore —> Vesicle recycled.

(1) Dynamin: Endocytosis for kiss-and-run
(2) Clathrin: endocytosis
(3) Calcium: needed for both processes of exocytosis

20
Q

Neurotoxins that block fusion of synaptic vesicles?

A

Toxin -> Target

Tetanus -> Synaptobrevin

Botulinum B, D, F, G -> Synaptobrevin

Botulinum A, E -> SNAP 25

Botulinum C -> SNAP 25, Syntaxin

21
Q

What is a neurotransmitter? Location? Criteria to be considered as a neurotransmitter?

A

A messenger/chemical substance which allows transmission of impulses/signals from one neuron to the next across synapses.

Found in axon endings of both motor and sensory neurons

Criteria
(1) Present in presynaptic nerve terminal

(2) Synthesized by presynaptic neuron
(3) Released on stimulation causing membrane depolarization if released in sufficient amount
(4) Produces rapid-onset and rapidly reversible responses in target cell
(5) Existence of specific receptor
(6) When applied exogenously in reasonable concentrations, it mimics exactly the action of endogenously released transmitter

22
Q

Classes of neurotransmitters?

A
  1. Amino acids
  2. Monoamines
    - Catecholamines
    - Indolamines
  3. Soluble gases
  4. Acetylcholine
  5. Neuropeptides
23
Q

What is the _ neurotransmitter?

  1. Fight or flight
  2. Concentration
  3. Pleasure
  4. Mood
  5. Calming
  6. Learning
  7. Memory
  8. Euphoria
A
  1. Adrenaline
  2. Noradrenaline
  3. Dopamine
  4. Serotonin
  5. GABA
  6. ACh
  7. Glutamate
  8. Endorphins
24
Q

Most NT are both inhibitory and excitatory except for?

A

Aspartate and Glutamate - Excitatory

GABA and Glycine - Inhibitory

25
Q 
Nonpeptide vs peptide transmitters?
>Site of synthesis and packaging?
>Form upon synthesis
>Present in what type of vesicle?
>Mechanism after production
>Latency and duration
A

Nonpeptide

  • Synthesized and packaged in nerve terminal
  • active form already
  • present in small cleat vesicles
  • released at synaptic cleft
  • short latency and short duration

Peptide

  • Synthesized and packaged at soma and transported
  • Not yet active form; needs to be derived from a larger protein
  • present in electron-dense e-
  • long latency and may last a few seconds
26
Q

Acetylcholine derived from?

A

Acetyl-CoA and choline

27
Q

Catecholamines
Derived from?
Reaction?

A

Tyrosine -> Levodopa -> Dopamine -> Norepinephrine -> Epinephrine

28
Q

Tryptophan can produce which NTs? Histidine?

A

Tryptophan: Serotonin and Melatonin

Histidine: Histamine

29
Q

(1) What is a neuromodulator?

(2) Difference from NTs?
A. Receptor
B. Ionic mechanism

A

No direct effect on their own but can modify effects of NTs

A. NT: Ion channel; NM: GPCR
B. NT: Opening of cation or Cl- channels; NM: Opening or closing of voltage gated K+ or Ca2+

30
Q

Synaptic potential types:

A
  1. EPSP (Excitatory Postsynaptic Potential)
    - lead to depolarization
  2. IPSP (Inhibitory Postsynaptic Potential)
    - lead to hyperpolarization
  3. EPP (End Plate Potential)

PSP
-local potential

31
Q

Types of summation

A
  1. Temporal
    - 1 area stimulated repeatedly/increased frequency until threshold reached
  2. Spatial
    - Transmission of an impulse by simulation of 2 or more presynaptic neurons
32
Q

Synaptic Plasticity

A

Modulation of synaptic potential;

Structural and fxnal changes in synapse

33
Q

Presynaptic vs Postsynaptic inhibition

A

Presynaptic

  • specific, aim of a particular input
  • leaves postsynaptic cell out of it
  • Axoaxonic

Poststynaptic
-reduces excitability of entire cell
Mostly effects postysynaptic cell
Axodendritic or axosomatic. I

34
Q

Dynein vs kinesin

A

Dynein - retrograde flow

Kinesin - anterograde flow

35
Q

Why is fatigue of synaptic transmission imp[otant?

A

Avoid overexcitation/xs neuronal activity.

36
Q

Mechanisms of Fatigue

A

(1) Exhaustion/partial exhaustion of stores of transmitter substance
(2) Progressive inactivation of post synaptic membrane receptors
(3) Slow devt of abnormal concs of ions in the postsynaptic neuronal cells

37
Q

Myasthenia gravis

Lambert-Eaton syndrome

A
  • ACh receptor

- VG Ca2+

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