High density voltage gated ion channels: triggering action potential through rest of axon

Highly extended + developed plasma membrane surrounding + insulating axon

Low capacitance limits depolarisation to impulses at successive Nodes of Ranvier. Saltatory propagation

• Lipid bilayer
• Ions
• Ion channels
  
  • Passive potassium channel
  • Sodium (Na+)/ Potassium (K+) Exchange Pump
  • Rapid Voltage Dependent Sodium (Na+) Channel
  • Slow Voltage Dependent Potassium (K+) Channel
• Membrane potetnial

• Voltage dependent calcium channel
• Metabotropic ion Channels
• Neurotransmitters

• Stimulus target cell depolarise threshold potential
• Voltage gated Na+ channels open + membrane depolarises: Na+ influx diffusion
• Peak action potential: Voltage gated K+ channels opens and K+ leave cell diffusion. Na+ channels close and membrane potential becomes increasingly negative
• Membrane phyperpolarised K+ ions. Hyperpolarised membrane refractory period
• Membrane potential restored: K+ channel close. Na+/K+ transporter restores

• Presynaptic vesicles contain neurotransmitter (Ach) at neuromuscular junction (NMJ)

• Vesicles contain ATP + specific membrane-associated proteins, allow them to be drawn to presynpatic active zone - presynaptic membrane + recycled

• Presysnaptic active zone: specialized areas vesicle release found opposite postsynaptic secondary folds + contain high density voltage dependent Ca2+ channel.

• Mitochondria + vesicles cluster near darkly stained patches in terminal membrane:

• Cleft substance found only at cholinergic NMJ + contains enzyme AChE, inactivates acetylcholine by hydrolysis

• Synaptic cleft separates presynaptic terminal from post synaptic membrane

• Acetylcholine receptors translate released neurotransmitter into postsynpatic electrical event: preferentially found between functional fold. Associated with non-selective cation channel

• Binding ACh to receptor induces conformational change in receptor, leading to opening of this channel. Influx Na+ and efflux of K+. Leads to membrane depolarization, activates voltage dependent ion channels. NMJ, release of contents of single vesicle produces small postsynaptc depolarisation (minature end plate potetinal). more viescles released, mepps simmate to give larger resposne end-plate potential**: generate action potential