Neuron Membrane Potentials

Neuron Membrane Potentials Neuron Action Potential: The Creation of a Brain Signal: At resting membrane potential (~ -70 mV), there is higher [Na+] outside of the cell and higher [K+] inside of the cell The neuron cell membrane is very permeable to potassium ions and slightly to sodium Absolute Refractory Periods: a time where there is no further depolarization allowed and is what pushes an AP down the axon (so that it won’t go backwards) Relative Refractory Period: typically in the hyperpolarized state meaning you would need a larger than average stimulus in order to generate an AP Action Potential Velocity: Proprioception: perception/awareness of your body in 3 dimensional space Large diameters (less resistance to ion flow) and myelin sheath (decreases the capacitance) increase AP’s speed immensely Guillain-Barre Syndrome is the destruction of Schwann Cells (myelin sheath in the PNS) and Multiple Sclerosis is the destruction of oligodendrocytes (myelin sheath in the CNS - brain & spinal cord) Neuron Graded Potential Description: Graded Potentials: occur in the dendrites/soma of a neuron and are typically slight fluctuations in membrane potential (can be excitatory or inhibitory) → graded potentials can depolarize a cell enough to trigger an action potential (AP) Neuron Resting Potential Description: [Ca2+] is higher outside of the neuron than inside (didn’t know that!!) Remember, each ion has concentration gradient and electrical gradient that it wants to abide by, and sometimes they get confused (such as in K+’s case) Neuronal Resting Potential Mechanism: The neuron naturally makes organic anion molecules (negatively charged proteins and such), decreasing the membrane potential Also, the Sodium-Potassium Pump establishes membrane potential by moving 3 Na+ molecules out of the cell and 2 K+ molecules into the cell Concentration only really ever changes inside the cell because there is so much extracellular fluid that changes in ion concentrations are essentially negligible The membrane is much more permeable to potassium than it is to sodium and that’s why equilibrium potential is closer to that of potassium than sodium Neuron Graded Potential Mechanism: Depolarization will occur with ligand gated Na+ or Ca2+ channels while hyperpolarization will occur with ligand gated K+ and Cl- ion channels Neuron Action Potential Description: Threshold for an AP is typically around -60 mV The size of an AP is typically the same with the same type of neuron (all or nothing) APs do not degrade with distance like graded potentials do Neuron Action Potential Mechanism: Voltage gated Na+ channels are what starts the AP at the trigger zone, making the membrane potential go up to near +40 mV, and then close stopping sodium from entering the cell Potassium then leaks out through leak channels and also through voltage gated potassium channels, repolarizing/hyperpolarizing the cell Effects of Axon Diameter & Myelination: Basically, the larger diameter allows more possible pathways for the ions to travel down the axon without colliding with something Basically, the myelin sheath makes the membrane much thicker, increasing the distance between the packing of the opposite charges (decreasing the capacitance) Nodes of Ranvier: have a much higher capacitance than the myelinated sections of the axon but are necessary in order to regenerate the full size of the action potential