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. Depolarizationoccurs 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)
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 stimulusIs 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 subthresholdpotentialCauses 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 –unmyelinatedthe wave of depolarization movesdown the complete plasmamembranedull, 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 neuronsSynaptic cleft – space in thesynapseNeurotransmitter –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.InhibitoryNeurotransmitter opens K+channels on post-synapticmembraneK + 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.