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Summary A* Nervous Coordination notes
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A* Nervous Coordination notes
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Nervous coordinationWhy is it important for cells to communicate and be coordinated?
Species evolved to have cells which perform specialised functions so therefore cells depend on other
cells to carry out functions they no longer specialise in e.g., provide O2/ glucose for respiration or
remove waste etc
Compare the 2 principle coordination systems (NS left and HS right)
-transmission by neurones whereas transmission is in the blood stream
-short lived response vs long lasting response
-communication is by nerve impulses whereas communication is by chemical hormones
-rapid transmission vs slow transmission (usually)
-localised response (specific body parts) vs widespread response which only effects target cells
-temporary and reversible effect vs permanent and irreversible effect
-both interact in order to maintain constancy in the internal environment
-both use chemical messengers
Sensory neurones
Transmit nerve impulses from receptor
Motor neurone
Transmits nerve impulses to an effector
Intermediate/ relay neurones
Transmit nerve impulses between neurones
(Structure of a motor neurone)
What is an axon?
A single, long fibre which carries impulses away from the cell body
Describe the cell body
Contains all usual organelles with large amounts of RER associated with neurotransmitters
Describe dendrites
Extensions which carry nerve impulses towards cell body
Dendrons
Extensions of the cell body which divide into dendrites
Schwann cells
Cells which surround the axon, protecting and insulating it
, Insulation
Does not allow charged ions to pass through
Schwann cells
Wrap themselves around the axon many times building layers of membranes called the myelin
sheath in the lipid myelin= a myelinated neurone
Nodes of Ranvier
Constructions between adjacent Schwann cells where there is not myelin sheath, 2-3 micrometres
long and occur every 1-3mm in humans
Describe the ‘nerve impulse’
Self-propagating wave of electrical activity that travels along the axon membrane, temporary
reversal of the electrical potential difference across the axon membrane
What are the 2 states?
Resting and action potential
Resting potential
-when a neurone is not conducting an impulse
-there is a difference in the electrical charge inside and outside the neurone
-this difference= resting potential
-axon is said to be polarised
-ions involved = Na+ and K+
-there is an unequal distribution of positive ions
The Axon Membrane
Na+ and K+ ions pass across the phospholipid bilayer using specific channel proteins that allow
facilitated diffusion
What are the 2 types of channel proteins?
Gated- open/ close can be controlled
Open- allow FD of ions at all times = unhindered
Describe the Na+-K+ pump
Active transport of 3 x Na+ ions out and 2 x K+ ions in
How is resting potential created?
-active transport of Na+ ions out the axon
-gated Na+ channels closed
-only little diffusion of Na+ ions back into axon through open channel proteins
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