University:
Binghamton University
Course:
BIOL 313 | Cellular Neurobiology
Academic year:

2024
Views:

109

Pages:

3
Author:

CrystalMintah

Conductance and Resistance So action potential first in one patch of the membrane That area is a positive The sodium ions that enter are repelled by that positive one so they move away If and where enough ions have been collected at the new membrane patch, they will depolarize it to cross the threshold and generate a new action potential in that spot. The old location may be negative at this point but since sodium channels there have a refractory period So action potential moves away down the axon How efficiently these ions move along the axon depends on….. 1. The low resistance inside the cytoplasm, low resistance means they can move easier a. Internal resistance depends on portion diameter A large diameter has a lower resistance potential than a small diameter - The larger diameter = efficient ions moving = quick action potential why do invertebrates have a larger diameter Also, membrane resistance Rm is a way of expressing how leaky the membrane is. If the membrane is less leaky then that means more ions stay inside and will be there to depolarize the next patch of membrane. Resistance To get efficient movement of ions down the axon you want a high membrane resistance and a low internal resistance. If you pass a depolarization into a neuron, the depolarization of the membrane will be larger at the location where you passed the depolarization and will decline as you move away from that location. Vm declines exponentially The length contact (lambda) tells you the distance before Vm declines to the 1/e of its initial value Lamda = square root of membrane resistance divided by internal resistance How long does it take to depolarize the next patch of membrane? There is a time constant! Depends on the membrane capacitance The cell membrane is a capacitor - Chargeable phosphate heads separated by a non-conducting lipid center - Before ions can move, the membrane capacitor must be charged up POSITIVE CHARGED IONS INSIDE LINE UP ALONG THE MEBRANE TO BE MET BY negatively charged ions and can move away from the flow. - Takes a little bit of time to do this Time is taken both when it starts and is ending Time constant = T= Cm-rm (T) tells you how long it takes for the membrane potential to reach (-)/e on about 63% of its final value Myelin and Compatenec Myelin is something that helps an action potential move faster along a membrane When myelin decreases, membrane competence decreases becaus competence is when charged recognize each other across a membrane, however, it is nonconductive, and ions on either side of the membrane cannot detent each other Myelin also increases membrane resistance because there are no ways to cross through the myelin for an ion - no way to leak out So an action potential in a myelinated axon: positive ions move away from the site of the initial action potential, and Dont generate action potential until they reach a spot where there's no myelin and the voltage-gated sodium channels can work to let in ions = node of rainier. Have to be located in a place where Vm can cross the threshold due to ionic movement. At the nodes, sodium channels are dense so they are more likely to generate an action potential