Synaptic Transmission, EPSP, IPSP😊

Synaptic Transmission

Types

  • Electrical mode:
    • Mediated by gap junctions
    • Made of connexin protein
    • Fast transmission
  • Slow mode:
    • Mediated by chemicals
    • Post synaptic potential (muscle endplate)
  • Synaptic cleft is space between neurons.
  • Postsynaptic neuron has receptors.
  • Process:
    • Release of NT from presynaptic neuron.
    • NT binding to postsynaptic receptor.
    • Postsynaptic potential/end plate potential (local potential).
    • Undergoes summation.
    • Crosses threshold.
    • Action potential generated.

Types of Synapse

  • Axon - Axon
  • Axon - Somatic
  • Axon - Dendritic

Examples of synaptic inhibitions

  1. Presynaptic Inhibition/Lateral Inhibition (in retina):
      • Interneuron acts on presynaptic terminal.
      • ↓↓ NT release.
  1. Feedback Inhibition
      • α motor neuron excites Renshaw cell inhibition
        • (inhibitory interneuron)
        • Feedback inhibition from
          • Renshaw cell to α motor neuron 
          • through glycine
      • Mnemonic: Riksha → Auto riksha → Glide cheyth poi → muscle idich (motor neuron) → inhibit ayi (feedback inhibition)

Presynaptic neurons:

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  • Action potential reaches nerve terminal → Na enters terminal (via voltage-gated Na+ channel) → Depolarization → Opens voltage-gated Ca2+ channels → Calcium enters → Synaptic facilitation
    • Calcium causes:
      • Vesicle movement to presynaptic membrane.
      • Fusion of vesicle with membrane.
      • Neurotransmitter release.

Toxins affecting neurotransmitter release:

Toxins
Inhibit channels
Effect on NT release
Dendrotoxin
â›” K+ channels
↑↑↑
Saxitoxins & 
Tetrodotoxin
â›” Voltage-gated Na+ channels
↓↓↓
Omega conotoxin
â›” Voltage-gated Ca2+ channels
↓↓↓
  • Mnemonic: Neuron → Nude →→ 4 (Tetradoxin) Sexy (Saxi) Nude (Na) girl → bought Condom (Conoxin → Calcium) too → but Dumb (Dendrotoxin) Pottan (Potassium → Goes out â›” Dendrotoxin) guy went out

Postsynaptic Membrane: EPSP & IPSP

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EPSP
IPSP
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Electrical change on postsynaptic membrane
Electrical change on postsynaptic membrane
NT
Glutamate
Aspartate
GABA (brain), 
Glycine (spinal cord)
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Local Potential
Local hyperpolarization
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↓↓ Negative charge inside
e.g., -70 mV → -65 mV
↑↑ Negative charge inside
Properties
Local potential
Local potential
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Graded, non-propagated
Graded, non-propagated
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Does not follow all-or-none law
Does not follow all-or-none law
Ionic basis
Ca2+ entry
Cl- entry
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K+ channel closure 
K+ exit
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Na+ entry
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notion image
notion image
Glutamate receptors
Stimulation
Metabotropic glutamate receptors
Ca2+ entry & K+ channel closure
AMPA & Kainate receptors
Na+ entry
NMDA receptors
Ca2+ and Na+ entry
GABA receptors
Stimulation
GABA A receptor
Chloride (Cl-) entry
GABA B receptor
Potassium (K+) exit
  • Main mnemonic
    • Nammade (NMDA) NaC (Na, Ca) nnu Ambayth (AMBA) Sodium ()
    • Methayil (Metabotroic) condom (Calcium) and pottane (Potassium) Glue (Glutamate) cheyth
  • Sub Mnemonic:
    • Nude Girl (sodium) kandapo → Ambo (AMBA) → Kayyinn (Kainate) poi → avale entry aakki
    • Nammakk (nmda)→ Condom (calcium) and Nude Girl (sodium) kitti
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