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- 1Topic 11: Propagation of the Action potential Excitation of the MembraneAt the excited section of the membrane:
- The internal surface is charges positively
-The external surface is charged Negatively - 2Local CurrentsLocal Currents: currents on the surface of the membrane between the excited and unexcited section.
- 3Direction of the local CurrentsIn the external surface of the membrane
- from unexcited towards the excited
In the internal surface of the membrane
- from the excited towards the unexcited - 4Conduction of the excitationIn the vicinity of the excited section
- the membrane potential decreases
- reaches the threshold value
- an action potential is generated - 5Distrubution of the membrane potential along the fibre-The membrane potential decreases exponentially away from the point of excitation
-The decay rate can be determined by the membrane and cytoplasm resistivity. - 6The length constant-At a distance x=A the membrane potential is smaller than at the point of excitation by a factor of e=2.72
The length constant
grow with increasing the:
-Diameter of the nerve fiber
-Membrane thickness
-Membrane resistivity - 7Model validityThe model describes the conduction of graded potentials in real nerve fibers.
-Weakly dipolarising potentials
-Hyper polarising potentials - 8Conduction of the action potentialThe model is unsuited to the action potential
- nerve impulses do not decay over time or along the fibre
-The local potentials simply dipolarise the membrane to the threshold - 9Conduction speed-Living creatures benefit from high conduction speed of nerve impulses
-Giant axons- large diameter nerve fibers - 10Increasing the conduction speed-Vertebrates speed up the conduction of nerve impulses using myelinated nerve fibers
- increasing the fibrediameter to much is not feasible - 11MyelineMyeline is composed of. Lipids, Cholestrol, Proteins
- The myeline resistivity is much larger than the resistivity of membrane
- Myeline is a good insulator - 12The myeline sheathA layer surrounding the axon, thicker than the membrane
- 13Advantages of saltatory conduction-High conduction speed of the impulses
- up to 100 m/s
-ten times higher relative to the unmyelinated fibers with same diameter - 14Blocking of myelinated fibers (nodes)-If one node is blocked by an aneshtetic
- the excitation jumps over to next node
If two nodes are blocked
- the impulse cant propagate anymore
- the length constant is not large enough - 15Demyelination and DismyelinationDemyelination: Loss of the myeline sheath
Disorder in the imune system
Dismyelination: defective structe and function of the myeline sheath.
Genetic mutation
- Schcizophrenia
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- FlashCards sobre Sem título, criado por engjeeell em 15-06-2015.
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