BIOL 2020U Lecture Notes - Cumulate Rock, Myelin, Schwann Cell

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29 Jan 2013
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Neurones
Soma: nerve cell body / contains nucleus, cell organelles / synthesise of neurotransmitter
Dendrites: branching extensions from nerve cell soma
o Stimulated by other neurones \ transmit impulses towards soma
Axon: single extension that extends from the soma to the target cell
o Myelinated axon is surrounded by Schwann cells (myelin sheath)
o Have nodes of Ranvier and are rich in myelin (lipid)
Table 16-7-1
NEURONE
STIMULATED
BY
TRANSMITS IMPULSES
TO
STRUCTURE
Sensory
Receptor
Relay neurone
Cell body in root cell
ganglion
Relay
Sensory neurone
Motor neurone
No axon
Motor/effector
Relay neurone
Gland, muscle
(effector organ)
Schwann cells
Change In Membrane Permeability Leading To The
Generation Of An Action Potential
Stimulus reaches threshold
Voltage-regulated sodium channels open / influx of Na+ / down electrochemical gradient
/ +ve feedback
Depolarisation / inside becomes +ve / membrane potential reverses
o //Depolarisation opens sodium channels in adjacent membrane
Potassium channels open (slower than Na+ gates) / diffusion of K+ ions out of neurone
Repolarisation
Sodium channels close
Hyperpolarisation due to overshoot in movement of K+out of the cell
o //Membrane potential is lower than resting potential
o //Interior of the cell becomes -ve \ membrane is more permeable to K+ ions than
to Na+ ions
Sodium-potassium pump restores RESTING POTENTIAL
[GRAPH] Highest positive membrane potential is the action potential
The Role Of The Neurone Membrane In The Establishment
Of A Resting Potential
MEMBRANE IS POLARISED: inside of axon is more -ve than outside
A resting potential of -70mV is maintained by [EXAM BYA7 JUN2002]
o Negatively charged proteins/large anions inside axon
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