17 Gated ion channels Flashcards
Which direction does neural signal flow in neurons?
dendrites -> axon -> synapse -> dendrites
What is membrane potential measured by?
voltage (V) across cell membrane
the diff between inside and outside
What does a -70mV mean for membrane potential?
voltage inside is -70mV lower than outside
What is the Na+ and K+ conc in ECF and ICF?
ECF
* Na+ is high
* K+ is low
ICF
* Na+ is low
* K+ is high
Can ions freely diffuse across membrane?
No only small and non-polar or lipid soluble
Why do ions hardly pass through membrane lipid?
cuz its repelled or trapped by membrane hydrophilic head
ions are hydrophilic
Why is the hydrophilic head negatively charged?
cuz they have phosphate group
What is the exchange in Na-K ATPase? What does it lead to?
3Na+ out and 2K+ in = -1
generates negative membrane potential
What do you leaky K channels contribute to?
A negative membrane potential
* work better than sodium channel
* facilitated diffusion
What is resting potential?
Membrane potential at resting state
* at about -70mV = polarised state
What is the -70mV of resting potential mainly due to?
Na+/K+ ATPase
How do we activate neuron?
reach threshold -50mV
How do we reach the threshold of neuron, presynaptic -> post synpatic?
Neurotransmitter from presynaptic flow to ligand gated ion channels on post-synaptic through synaptic clef.
once bound to specific neurotransmitter, ligand gated Na+ channels open, then increase membrane potential
How can membrane potential be decreased?
ligand-gated Cl-
* inhibitory neurotransmitters can bind to ligand gated Cl- channels and when there is an increase in Cl- in the neuron, the membrane potential decreases
what does excitatory and inhibitory graded potentials contribute to?
excitatory -> depolarization
inhibitory -> hyperpolarization
What happens during depolarization?
Na+ influx
what happens during hyperpolarization?
K+ efflux or Cl- influx
why are graded potentials integrated?
a single weak excitatory graded potential (EP) cannot generate AP but integration of multiple excitatory potentials can generate AP
but EPs cant be too seperated
What is AP generated by spatial and temporal summation?
temporal: generated by temporal summation by burst of excitatory postsynaptic/graded potentials
spatial: simultaneous excitatory potentials
What happens if excitatory and inhibitory potentials co-exist?
cancel each other = no AP
What are the features of graded potential/postsynaptic potential?
- induced at post-synaptic region
- short lived, transient
- various in strength depending on amount of neurotransmitter
what happens at resting stage?
-70mV
* both voltage gated Na+ and K+ channel are closed
What happens at depolarization?
- a stimulus (increased membrane potential) opens some Na+ channel
- if threshold is reached (-50mV), more Na+ channels open = spike/peak of AP
- if not, no AP, all or none rule
- Na+ channel is inactivated after a brief opening
What happens at early and late repolarization?
early (+30mV)
* Na+ channels are inactivated while K+ channels open = membran potential begin to decrease
Late (-70mV)
* some Na+ channels become closed state (from being inactivated)
* more are closed when membrane potential decreases
What happens during hyperpolarization?
- more negative than resting potential
- voltage gated K+ channel still opens for further decrease (as K+ channels close more slowly than Na+ channel)
- all Na+ channel in closed state (at the end of hyperpolarization)
What are the 2 refractory periods?
- only closed Na+ channels can be opened
- absolute refractory period - Na+ channels inactivated
- relative refractory period - some but not all Na+ channels are closed, need stronger stimulus to produce AP
What happens during the process of propogation?
- Na+ influx generated by AP establish intracellular electric current
- electric current travels to adjacent region to generate AP
- electric current continue to travel for propagation of AP
What happens at the axon terminus?
Ca2+ channel open, they enter the cell, signal to vesicles to move to the membrane, docked vesicles release nerotransmitter by exocytosis, neurotransmitter diffuses across the synaptic clef and bind to receptors
AP vs graded potential: travelling distance, amplitude/strength, stimulus, summation/integration, function, gated ion channels
What are 4 examples of neurotoxins?
- tetrodotoxin - Na+ channel inhibitor
- chlorotoxin - Cl- channel inhibitor
- Conotoxin - Ca2+ channel inhibitor
- Botulinum toxin (botox) - inhibitor of synaptic vesicles release (paralyze faical muscles = reduce wrinkles)
