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Intra + Inter neuronal communication (Peripheral neuron (Axon Hillock…
Intra + Inter neuronal communication
Peripheral neuron
Axon Hillock
Tight junction, barrier lateral diffusion
High density voltage gated ion channels: triggering action potential through rest of axon
Between cell body and axon
Centre synaptic summation
Myelin Sheath
Highly extended + developed plasma membrane surrounding + insulating axon
Low capacitance limits depolarisation to impulses at successive
Nodes of Ranvier
.
Saltatory propagation
Nissl Substance
High densities rough Er (ribosomes)
Action potential
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
Synaptic transmission
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
Summation of potentials
Ionotropic metabotropic receptors
Neurotransmitters
Inhibitory
Glycine
GABA
Serotonin
Dopamine
Both
ACh
Norepinephrine
Excitatory
Aspartate
NO
Glutamate