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Control and coordination notes
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Monday, 1 February 2021NotesbyALk
CHP 15
CAIE
Nerves & Neurons
1
, 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.
2
fi
, 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 :
3
ff ff ff fl
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