A and P Polarization

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  • 1. Action Potential – electrical signalcarried by an axon in a nerveoCaused by ionsoIs an electrochemical responseoResult from the disturbance of thepotential difference across the axonplasma membrane
  • 2. Excitability – the ability tocreate an action potential inresponse to a stimulus2 Types of excitable cellsin body are muscle andnerve cells.
  • 3. Potential differencemeasure of the chargedifference across theplasma membrane.Measured in millivolts(mV)
  • 4. Neuron Resting potential –electrical charge difference of -85to - 70 mV. outside inside
  • 5. A negative sign is used becauseinside is negative compared tooutside of plasma membrane.
  • 6. What creates the potentialdifference:1.Large negative proteins aretrapped inside the cell2.Sodium-potassium pump -Pumps 3 Na + out for every 2 K +it pumps into the cell.
  • 7. What creates the potential difference: 1. Large negative proteins 2. Sodium-potassium pump3.Potassium channels allow K + todiffuse out of the cell 3 2 1
  • 8. Electrical properties of the axon at rest:othere is no action potentialrunning down the axonoOutside + and inside is -comparativelyoWhen potential differencegreatest
  • 9. Characteristics of an action potential:•All or none event•There must be a stimulus
  • 10. Characteristics of an action potential:•Stimuli may include •Moving cell (touch) •Light (sight) •Change in temperature (hot/cold) •Chemicals (taste) •Electrical shock (not normal)
  • 11. Steps of a nerve impulse:1. Polarization•Axon is at its resting potential.• Axon is ready to do work, receivea stimulus. (Has potential energy)
  • 12. Steps of a nerve impulse:1. Polarization2. Depolarizationoccurs in response to astimulus and is when there isno more separation of chargeacross the plasma membrane
  • 13. Steps of a nerve impulse:1. Polarization2. DepolarizationHow is a neuron depolarized? A.Stimulus hits channel proteins called gates located in the plasma membrane B. These gates open allowing Na+ to rush into the cell
  • 14. Steps of a nerve impulse:1. Polarization2. DepolarizationHow is a neuron depolarized? C. The action potential changes from -85mV to +30 mV D. The inside of the plasma membrane is now + and outside – (reversed)
  • 15. Depolarization
  • 16. Steps of a nerve impulse:1. Polarization2. Depolarization3. Repolarization – when thepotential difference acrossthe plasma membrane isrestored to resting potential.
  • 17. Steps of a nerve impulse:1. Polarization2. Depolarization3. RepolarizationHow does repolarization occur?A. Sodium gates close.B. Potassium gates open; K+ rushesout of the cell resting potential isrestored.
  • 18. 3. RepolarizationHow does repolarization occur? NOTE: It takes less than 1 millisecond for depolarization and repolarization to take place.
  • 19. Don’t write this!!!!But wait!!! This is not whatwas originally our restingpotential set up was it???
  • 20. Don’t write this!!!Very good! No it wasn’t. Wehad more Na+ on outside, nowthe sodium is on the inside.Guess what will start to pumpnow?
  • 21. Steps of a nerve impulse: 1. Polarization 2. Depolarization 3. RepolarizationHow does repolarization occur?A. Sodium gates close.B. Potassium gates openWrite now!!!C.Sodium –potassium pump will re- establish original ion concentrations of resting potential. • Takes 1 millisecond • Axon can not receive next stimulus
  • 22. Types of stimuli1. Threshold stimulusIs strong enough to trigger theaction potential.Once it is reached there is nostopping the action potential fromtraveling.
  • 23. Types of stimuli1. Threshold stimulus2. Subthreshold stimulus –Is a stimulus not strongenough to trigger the actionpotential.
  • 24. Types of stimuli1. Threshold stimulus2. Subthreshold stimulus3. Local potential –Caused by a subthresholdpotentialCauses a depolarization in thearea of the stimulus but not strongenough to create an actionpotential to travel the axon
  • 25. How does the action potentialtravel down the axon?The action potential is strongenough to depolarize theadjacent area of membraneopening the sodium gates causinga wave of depolarization.
  • 26. Refractory period – pump isbringing stimulate portion ofmembrane back to original restingpotential ion concentration.During this time this sectioncannot respond to anotherstimulus, keeps action potentialfrom traveling wrong direction.
  • 27. Two types of refractory periods:1.Absolute refractory period – nomatter how strong the stimulusthere is no action potential2. Relative refractory period – if thestimulus is strong enough it willproduce an action potential
  • 28. Don’t writeRemember – actionpotential is all or none –so how do you feeldifferent levels ofintensity?
  • 29. Level of intensity of senation is determined by:1.Frequency of action potentials.The higher the frequency thegreater the intensity.2. Whether or not the axon ismyelinated determines type ofconduction.
  • 30. Level of intensity of senation is determined by:1.Frequency of action potentials2. Whether or not the axon is myelinated.Continuous conduction –unmyelinatedthe wave of depolarization movesdown the complete plasmamembranedull, slow pain
  • 31. Level of intensity of senation is determined by:1.Frequency of action potentials2. Whether or not the axon is myelinated.Continuous conductionSaltatory conduction myelinated impulse jumps from node to node. Sharper pain
  • 32. Nerve impulses travel fromone neuron to the next whenthe nerve impulse travelsacross the synapse.
  • 33. NS Synapse – junction betweentwo neuronsSynaptic cleft – space in thesynapseNeurotransmitter –chemical thatstimulates the dendrite of the nextneuron to depolarize.
  • 34. Pre -synaptic neuron – firstneuron in a seriesPost – synaptic neuron – secondneuron in a series
  • 35. How does action potentialtravel across synapse?1.Action potential reachesthe pre-synaptic terminal.2.Ca +gates open and Ca+rushes in.
  • 36. How does action potential travel across synapse?3.Ca+ trigger release of the neurotransmitter from the synaptic vesicles.4. Neurotransmitter travels across the synaptic cleft and binds to receptors on the post-synaptic neuron.
  • 37. How does action potential travel across synapse?5. This stimulates ion gatesto open.
  • 38. 2 types of synapses1.Excitatory –•Neurotransmitter stimulates Na+gates to open at post-synapse•Enough Na + gates must open forcreation of an action potential inthe post-synaptic membrane
  • 39. 2 types of synapses1.Excitatory –Types of summation:A. Temporal summation – onepre-synaptic axon has a highenough frequency of actionpotentials to send enoughneurotransmitter to open enoughNa+ gates to continue the nerveimpulse.
  • 40. B. Spatial Summation –•have several pre-synapticneurons that excite one post-synaptic neuron.•enough Na+ gates will open foraction potential to travel throughnext neuron.
  • 41. 2 types of synapses:1.Excitatory2.InhibitoryNeurotransmitter opens K+channels on post-synapticmembraneK + will rush out of cellcausing hyperpolarization; anincrease in potentialdifference (-80mV to -90mV)
  • 42. 2 types of synapses:1.Excitatory2.Inhibitory filters out unnecessary info Mostly this type in body
  • 43. Types of Neuron Arrangement:1.Convergent circuit– more thanone pre-synaptic neuron goes toone post-synaptic neuron.
  • 44. Ty pes of Neuron Arrangement:1. Convergent circuit2. Divergent circuit one pre-synaptic neuron sends asignal to several post-synapticneurons.This spreads the message todifferent parts of the body.Ex. To muscles and brain
  • 45. Types of Neuron Arrangement:3. Oscillating circuit – a neuronsends the message back to itself.A single stimulus can result in along lasting signal.Ex. Alarm clock = stimulus, stayawake due to oscillating circuit.Circuit may stop due to fatigue ofneuron or interference.