Brain and Behaviour: Resting Membrane Potential PDF

Brain and Behaviour Resting membrane potential UTS Graduate School of Health UTS Graduate School of Health Membrane potentials Picture attribution link UTS Graduate School of Health Membrane potentials At...

Brain and Behaviour Resting membrane potential UTS Graduate School of Health UTS Graduate School of Health Membrane potentials Picture attribution link UTS Graduate School of Health Membrane potentials At rest, while axons are not propagating action potentials there are a number of processes that are occurring. There are different Concentration (concentration gradient) Ionic charges (electrical gradient) of molecules in the intracellular and extracellular space These are working simultaneously and form the resting membrane potential UTS Graduate School of Health Membrane potentials Diffusion force drives molecules from high to low concentration Electrical force drives molecules from high (+ve) to low (-ve) ionic charge Picture attribution link UTS Graduate School of Health Membrane potentials Picture attribution link  UTS Graduate School of Health Membrane potentials Electrical and concentration gradients create difference forces There are many molecules that have different concentration gradients Given this, there will be a point where the forces from the electrical and concentration gradients have equalised This is called the equilibrium Picture attribution link potential - where electrical and concentration forces are equal In the neuron this occurs at -70mV UTS Graduate School of Health Membrane potentials Concentration gradient Na+ K+ Ca2+ OA- Cl- Extracellular space Intracellular space UTS Graduate School of Health Membrane potentials Electrical gradient Na+ Positive K+ Negative +ve Ca2+ -ve OA- Cl- Extracellular space Intracellular space UTS Graduate School of Health Membrane potentials Electrical and chemical gradient Na+ Positive K+ Negative +ve Ca2+ -ve OA- Cl- Extracellular space Intracellular space UTS Graduate School of Health Membrane potentials Electrical and chemical gradient OA- × OA- -ve voltage Extracellular space Intracellular space UTS Graduate School of Health Membrane potentials Electrical and chemical gradient Na leak channel K leak channel Ca leak channel Cl leak channel Extracellular space Intracellular space UTS Graduate School of Health Membrane potentials Electrical and chemical gradient ATP more K+ × 2 -ve voltage Na+ × 3 Extracellular space Intracellular space  UTS Graduate School of Health Membrane potentials Electrical and chemical gradient Na has an electrical + concentration gradient forcing it into the neuron BUT Na+ the leak channels are less permeable to Na (than K) For K, -70 mV is when the forces from the K+ concentration gradient equal forces from the electrical gradient Extracellular space Intracellular space  UTS Graduate School of Health Membrane potentials Na+ / K+ pump 2 K+ ions → into the cell and 3 Na+ → out of the cell Ions moved by active transport Moved against their concentration gradient using energy (ATP) Leak channels K+ leak channels are in greater abundance than Na+ leak channels Greater permeability to K+ than Na+ at rest Equilibrium potential (-70mV) The concentration gradient and electrical gradient, create forces on the potassium ion. The point at where the concentration gradient (forcing K outside the cell) and the electrical gradient (forcing K inside the cell) is -70mV. UTS Graduate School of Health Membrane potentials Electrical and chemical gradient Energy from K+ flowing with its gradient K+ Cl- Energy from Na+ flowing with its gradient Na+ × 3 Ca2+ Extracellular space Intracellular space UTS Graduate School of Health Membrane potentials Cl- and K+ symporter K+ travels Cl- out of the cell together K+ (travelling with its concentration gradient) creates energy for Cl- to travel against its concentration gradient Na+ and Ca2+ exchanger Anitiport (1 Ca2+ ion travels out of the cell and 3 Na+ travel into the cell) Uses the energy from the Na+ travelling with its concentration gradient to allow Ca2+ to travel out of the cell UTS Graduate School of Health Membrane potentials Na+ K+ Ca2+ -60 to -80mV OA- Cl- Extracellular space Intracellular space Brain and Behaviour Graded potentials UTS Graduate School of Health UTS Graduate School of Health Graded potentials Picture attribution link Picture attribution link UTS Graduate School of Health Graded potentials A neuron has a ‘resting potential’ of approx. -70mV This potential can change as a result of a stimulus Less negative (i.e. -60mV | Depolarisation | EPSP) More negative (i.e. -75mV | Hyperpolarisation | IPSP) Called a graded membrane potential The neuron EPSP IPSP temporality changes the voltage around the membrane Picture attribution link UTS Graduate School of Health Graded potentials Based on what we know from resting membrane potentials, Na+ what would make a neuron depolarise K+ ↓ in membrane permeability Ca2+ to K+ OA- ↑ in membrane permeability to Na+ and Ca2+ Cl- -70mV to -60mV UTS Graduate School of Health Graded potentials Based on what we know from resting membrane potentials, Na+ what would make a neuron hyperpolarise K+ ↑ in membrane permeability Ca2+ to K+ and Cl- OA- ↓ in membrane permeability to Na+ and Ca2+ Cl- -70mV to -80mV UTS Graduate School of Health Graded potentials Picture attribution link UTS Graduate School of Health Graded potentials Picture attribution link UTS Graduate School of Health Graded potentials Temporal summation: summation of stimuli from a single neuronal synapse over a short period of time (i.e. The target neuron receives stimuli from the same neuronal synapse in quick succession). Spatial summation: Summation that involves the stimulation of several spatially separated neurons at the same time (The target neuron receives different stimuli from different neuronal synapses at the same time) Picture attribution link UTS Graduate School of Health Graded potentials Picture attribution link Brain and Behaviour Action potentials UTS Graduate School of Health UTS Graduate School of Health Action potentials The axon hillock/trigger zone receives many stimuli that cause EPSPs (green) and IPSPs (pink) There is an voltage threshold (-55mV), that once surpassed, causes a rapid and large depolarisation of the neuron down the axon. Action potential Picture attribution link  UTS Graduate School of Health Action potentials Na+ Voltage gated ion channels - These channels ‘sense’ voltage, which will cause them to open or close - There are separate channels for Na and K - These channels also have an K+ ‘activated’ and ‘inactivated’ state - Na and K voltage gated channels and K leak channels are important for action potentials  UTS Graduate School of Health Action potentials All or nothing electrical potential Are of the same magnitude (approx. +40mV), no matter how much the threshold is surpassed Occurs in 3 phases 1. Depolarisation phase 2. Repolarisation phase 3. Refractory period (hyperpolarisation) Picture attribution link  UTS Graduate School of Health Action potentials Voltage gated Na channels open Increased membrane permeability to Na and movement of Na into Na+ the neuron. +40 K+ -55mV Picture attribution link to +40mV  UTS Graduate School of Health Action potentials Na channels close and become inactive +40 K+ -55mV Picture attribution link to +40mV  UTS Graduate School of Health Action potentials Voltage gated K channels open Increased membrane permeability to K and movement of K out of the neuron. K leak channels (which are always open) also contribute to K movement +40 K+ +40mV Picture attribution link to -80mV  UTS Graduate School of Health Action potentials Voltage gated K channels close Reduced membrane permeability to K. Normal leak channels and Na / K pump restore the resting membrane potential ATP K+ × 2 +40 Na+ × 3 -80mV Picture attribution link to -70mV UTS Graduate School of Health Action potentials Absolute refractory period Time during an action potential when a second stimulus (no matter how strong) cannot initiate another action potential. Relative refractory period Time during which a stronger- than-threshold stimulus can evoke another action potential Picture attribution link