Control and coordination notes

Monday, 1 February 2021




NotesbyALk

CHP 15

CAIE




Nerves & Neurons




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, Monday, 1 February 2021



A2 Biology

Control and coordination ( chp15)
In animals, information is transferred

1. Nerves—Nerve bres—rapid and response is short lived

2. Hormones— blood — relatively slow and response is long lasting.



Nervous Communication

1) CNS ( brain and spinal cord)

2) PNS ( Cranial and spinal nerves )



Nerve Impulses

Neurones transmit signals electrical charge( change in distribution of charges
between the plasma membrane)



Resting potential (-65mV)

P.d across the plasma memb where nerve cells is at rest

• Resting neurones doesn’t pass an electrical impulses but it maintain the p.d
across the membrane

• On the outside, Na+ con is higher

• On the inside, K+ con is higher

• The inside of the axon is negatively charged compared to the outside . This is
due to uneven distribution of charged ions brought by the Na-K pump.

• Axon polarized



STEPS!!!!

I. Na+ moves out by Na-K pump.

II. K+ moves in by Na-K pump.

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, Monday, 1 February 2021
III. 3 Na+ moves out while 2K+ enters. So Na+ moves faster ( active transport)

IV. So the outward movement of Na+ is faster than the inward movement of
K+ . So, more K+ in the cytoplasm while there is more Na+ in tissue uid
outside of axon. This creates chemical gradient.

V. Then , Na+ di uses back naturally while K+ ions di use out of axons.

VI. The axon memb is more permeable to K+ ions because there are more leak
channel protein for K+ion. So K+ ions di uses out faster than Na+moving
in .

VII. Electric gradient creates as more and more K+ moves out. So the inside
become more negatively charged than the outside.

VIII.There are large negatively charged protein inside cytoplasm contributes to
(-)ve state overall.

IX. Equilibrium established ( no net movement of ions) . Chemical and electric
gradient is balanced.

X. Axon polarized.



For diagram :




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