Electrical Signals within the Nervous System (lec 2)

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Presentation transcript:

Electrical Signals within the Nervous System (lec 2)

Electrical Signals within the NS 1-Action potential 2-Electrotonic(graded) potential

Fig. 12.13

Myelination increase membrane resistance & decrease membrane capacitance.

Classification for Peripheral Fibers Fiber size: I, II, III, IV Conduction velocity: A, B, C Major afferent Major efferent Nolte 9-21

Susceptibility of Different Types of Fibers to Conduction Block by Various Agents Most susceptible Effect Least susceptible Block by hypoxia B A C Block by pressure Block by local anesthetics

Absolute & Relative Refractory Period

Refractory period

Action potential Regenerative, Threshold Move along axon Voltage gated channels Propagates All or None Amplitude above 100 mv Short duration Depolarizing then repolarizing Refractory period No summation. Function: carries information faithfully unchanged from one end of neuron to other, without decrement.

Convulsion/Fit/Seizure

Effect of ionic composition on nerve fiber excitability: Hypercalcaemia & Hypokalemia Decrease n.f. excitability. Hypocalcaemia increase n.f. excitability