Membrane_potential____+copy+2

Membrane_potential____+copy+2 -...

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Forces and other factors causing electric potential across cell  membranes are 1)  Electrical & 2) Diffusion forces 1) Sodium/potassium pump (active transport protein located  in the membrane requiring ATP, unidirectional & pumps  against concentration gradients)  2) Diffusion forces: depend on concentration differences.  Example potassium andsodium diffuse down their own  concentration gradients 3) Membrane permeability to ions. Membrane is very  permeable to chloride and potassium, but highly  impermeable to sodium. *thus, once sodium is pumped  out, it has a difficult time getting back in the cell.  Only  if sodium channels/pores are open does sodium return to
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inside the cell. Potassium and chloride on the other hand  easily pass through open pores in the membrane.  When sodium is pumped out it creates an electrical  difference across the membrane, positive on the outside &  negative inside. Potassium moves to the negative charge  inside the cell against its own concentration gradient-thus  high potassium inside & high sodium outside. The diffusion  front of potassium toward the outside is opposed by the  electrical forces (negativity) inside cell. What results is a  positive zone (potassium) just outside of the cell membrane  and a negative zone inside (ex. chloride ions) just inside of  the membrane. Adding potassium, but not other ions,  outside of the cell destroys -70mV electric  difference/potential. Why? The diffusion front of potassium  is destroyed.
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Na + /K + pump Passive transporters with open channels Passive transporters with voltage-sensitive gated channels 3Na + 3Na + 2K + 2K + - - - - - - + + + + + + Cytoplasm in cell Outside of cell Active transport=        Battery Capacitor= Membrane Pores= Resistance Ion diffusion thru pores=Current 1) OUABAIN:  blocks Na +  /K pump 2) Tetrodotoxin, saxitoxin, scorpion, poison arrow frog  toxins block voltage gated Na +  channels
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* Cobratoxin and Bungarotoxin (both snakes) block acetylcholine receptors . Black Mamba toxin blocks potassium channels. Widow spider venom contains components known as latrotoxins, which cause the release of the neurotransmitter acetylcholine , stimulating muscle contractions. This can affect the body in several ways, including causing painful abdominal cramps, as well as interfering with respiration, and causing other systemic effects. [2] The venom of Australasian funnel-web spiders and mouse spiders works by opening sodium channels , causing excessive neural activity which interferes with normal bodily function.
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