Skip to main content
UploadLanguage (EN)Support
BusinessMobileSocial MediaMarketingTechnologyArt & PhotosCareerDesignEducationPresentations & Public SpeakingGovernment & NonprofitHealthcareInternetLawLeadership & ManagementAutomotiveEngineeringSoftwareRecruiting & HRRetailSalesServicesScienceSmall Business & EntrepreneurshipFoodEnvironmentEconomy & FinanceData & AnalyticsInvestor RelationsSportsSpiritualNews & PoliticsTravelSelf ImprovementReal EstateEntertainment & HumorHealth & MedicineDevices & HardwareLifestyle
Uploaded byAmberRao1
PPTX, PDF3,332 views

Resting membrane potential and action potential

The document discusses the resting membrane potential and action potential in neurons. It explains that: 1) The resting membrane potential is around -70mV, created by different ion concentrations inside and outside the neuron. 2) Graded potentials are local, short-lived changes in membrane potential caused by ion channels opening briefly in response to stimuli. 3) Action potentials are brief, large changes in potential from -70mV to +30mV caused by voltage-gated sodium and potassium channels. The influx of sodium ions depolarizes the membrane before potassium channels repolarize it. 4) Action potentials propagate along the axon as one area repolarizes and depolarizes the next, allowing nerve

Health & Medicine◦
Downloaded 88 times
Ambreen Umar RESTING MEMBRANE POTENTIAL AND ACTION POTENTIAL
Electrical Current and the Body  Potential energy generated by separated charges is called voltage.  Reflects the flow of ions rather than electrons  There is a potential on either side of membranes when the number of ions is different across the membrane
Role of Ion Channels  Types of plasma membrane ion channels:  Passive, or leakage, channels – always open  Chemically gated channels – open with binding of a specific neurotransmitter  Voltage-gated channels – open and close in response to membrane potential (change in charge)  Mechanically gated channels – open and close in response to physical deformation of receptors
Operation of chemical Gated Channel
Operation of a Voltage-Gated Channel
Gated Channels  When gated channels are open:  Ions move along chemical gradients, diffusion from high concentration to low concentration.  Ions move along electrical gradients, towards the opposite charge.  Together they are called the Electrochemical Gradient  An electrical current and Voltage changes are created across the membrane
Electrochemical Gradient  The EG is the foundation of all electrical phenomena in neurons.  It is also what starts the Action Potential.
Resting Membrane Potential (Vr)  The potential difference (–70 mV) across the membrane of a resting neuron  It is generated by different concentrations of Na+, K+, Cl , and protein anions (A )  The cytoplam inside a cell is negative and the outside of the cell is positive. (Polarized)
Membrane Potentials: Signals  Used to integrate, send, and receive information  Membrane potential changes are produced by:  Changes in membrane permeability to ions  Alterations of ion concentrations across the membrane  Types of signals – graded potentials and action potentials
Changes in Membrane Potential  Changes are caused by three events  Depolarization – the inside of the membrane becomes less negative  Repolarization – the membrane returns to its resting membrane potential  Hyperpolarization – the inside of the membrane becomes more negative than the resting potential
Changes in Membrane Potential
Graded Potentials  Short-lived, local changes in membrane potential  Decrease in intensity with distance  Their magnitude varies directly with the strength of the stimulus  Sufficiently strong graded potentials can initiate action potentials
Graded Potentials  A stimuli from sensory input causes the gated ion channels to open for a short period of time.  Positive Cations flow into the cell and move towards negative locations around the stimuli.  Alternately the now negative area on the outside of the cell will flow towards the positive areas.  However, this spread of depolarization is short lived because the lipid membrane is not a good conductor and is very leaky, so charges quickly balance out.
Graded Potentials
Graded Potentials
Action Potentials (APs)  A brief change in membrane potential from - 70mV(resting) to +30mV (hyperpolarization)  Action potentials are only generated by muscle cells and neurons  They do not decrease in strength over distance  An action potential in the axon of a neuron is a nerve impulse
Action Potential: Step 1 Resting State  Na+ and K+ channels are closed  Leakage accounts for small movements of Na+ and K+  Each Na+ channel has two voltage-regulated gates  Activation gates – closed in the resting state  Inactivation gates – open in the resting state
Action Potential: Step 2 Depolarization Phase  The local depolarization current flips open the sodium gate and Na+ rushes in.  Threshold: when enough Na+ is inside to reach a critical level of depolarization (-55 to - 50 mV) threshold, depolarization becomes self-generating
Action Potential: Step 2 Cont.  Na + will continue to rush in making the inside less and less negative and actually overshoots the 0mV (balanced) mark to about +30mV
Action Potential: Step 3 Repolarization Phase  After 1 ms enough Na+ has entered that positive charges resist entering the cell.  Sodium inactivation gates close and membrane permeability to Na+ declines to resting levels  As sodium gates close, voltage-sensitive K+ gates open  K+ exits the cell and internal negativity of the resting neuron is restored
Action Potential: Step 3 Repolarization Phase  After 1 ms enough Na+ has entered that positive charges resist entering the cell.  Sodium inactivation gates close and membrane permeability to Na+ declines to resting levels  As sodium gates close, voltage-sensitive K+ gates open  K+ exits the cell and internal negativity of the resting neuron is restored
Action Potential: Step 4 Hyperpolarization  Potassium gates are slow and remain open, causing an excessive efflux of K+  This efflux causes hyperpolarization of the membrane (undershoot).  The neuron is insensitive to stimulus and depolarization during this time
Action Potential: Role of the Sodium-Potassium Pump  Repolarization  Restores the resting electrical conditions of the neuron  Does not restore the resting ionic conditions  Ionic redistribution back to resting conditions is restored by the sodium-potassium pump
Phases of the Action Potential  1 – resting state  2 – depolarization phase  3 – repolarization phase  4 – hyperpolarization
Propagation of an Action Potential  When one area of the cell membrane has begun to return to resting the positivity has opened the Na+ gates of the next area of the neuron and the whole process starts over.  A current is created that depolarizes the adjacent membrane in a forward direction  The impulse propagates away from its point of origin
Propagation of an Action Potential (Time = 0ms)
Propagation of an Action Potential (Time = 1ms)
Propagation of an Action Potential (Time = 2ms)
Coding for Stimulus Intensity  All action potentials are alike and are independent of stimulus intensity  Strong stimuli can generate an action potential more often than weaker stimuli  The CNS determines stimulus intensity by the frequency of impulse transmission
THANK YOU