Neural Control & Coordination

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A

Na

B

Na

3. PRØPÅGÅTÏØÑ ØF ÅÇTÏØÑ PØTËÑTÏÅL

At sites ahead (site B),

outer surface is positive

and inner surface is

negative. As a result,

a current flows on the

inner surface from site A

to site B.

The

sequence

is

repeated

along

the

axon and the impulse is

conducted.

On the outer surface,

current flows from site

B to site A to complete

the circuit. Hence, the

polarity

is

reversed

and action potential is

generated at site B, i.e.,

action potential at site

A arrives at site B.

The rise in permeability

to Na⁺ is extremely

short lived. It is quickly

followed by a rise in

permeability to K⁺.

Immediately, K⁺ diffuses

outside the membrane

and

restores

the

resting potential of the

membrane at the site

of excitation. Thus, the

fibre becomes ready for

further stimulation.

+ + ++ + ++ + + + + + + +

+++

+++

Na⁺

Stimulus

applied

Excited axon

K⁺

High Na⁺ + + +

+ + +

+ + + +

+ + + +

+ + + + +

+ + +

+ + + + +

++ +

++ +

+ +

Na⁺

Na⁺

Na⁺

Na⁺- K⁺ Pump

Resting axon

Polarised

membrane

K⁺

K⁺

K⁺

K⁺

K⁺