Nerve Impulses Flashcards
An electrical difference across the membrane of the cell called
Resting potential
2 types electrical signal neurons
Graded potential - short distance communication
Action potential- long distance communication
What in the cell membrane can open and close due to stimuli, changing the potential and creating an electrical current.
Specific ion channels
What are ion channels
Transport channels for ions created by trans-membrane proteins within the neuronal membranes
What happens when ion channels open
Allow specific ions to move through the membrane across an electrochemical concentration gradient.
Eg Na channels allow Na through
K channels allow k through
4 categories of stimulus causing ion channels to open
Voltage
Chemicals
Mechanical pressure
Light
What do neurons at rest possess across the cell membrane
Electrical difference/gradient
How is neuron electrical difference across cell membrane created
Build up of intercellular negative ions and extra cellular positive ions
Separation of charges creates potential energy
Voltage of resting potential
Approx -70mV
Cells exhibiting membrane potential are said to be
Polarised
Meaning charged
Na+ is
Sodium
Cl- is
Chlorine
K+ is
Potassium
Describe extracellular fluid during resting potential
Rich in Na and Cl ions
Carries a POSITIVE charge
Describe intracellular fluid in resting potential
Rich in K and large negative ions which cannot leave cell
Negative charge
What do Na and Cl try to do during resting potential
Move back inside to equalise the charge
How is resting potential polarity maintained by sodium potassium pump
Polarity maintained by
Pumping out 3 Na for every K it pumps back in
What is an action potential
Formation of nerve impulse/signal/excitation
Series of events > decreases/reverses membrane potential then restores it to resting state
2 phases action potential
Depolarisation
Repolarisation
Define depolarisation
The negative membrane potential (-70mV) becomes less negative, reaches zero, then becomes positive.
Describe depolarisation
After being positive the membrane is restored to its negative resting potential of -70mV
Describe process of depolarisation
Triggered by stimulation of nerve ending
Na channels open allowing Na to flood into the cell
Positive charge builds up inside cell
Describe process repolarisation
K channels open much more slowly than Na channels so just as Na channels are closing the K ones open.
Allows K to flood out of cell, restoring membrane potential to -70mV
What is the refractory period
Period of time after repolarisation in which a nerve cannot generate another action potential because N and K are on wrong sides of the membrane
What does Na-K pump do during refractory period
Pumps Na out and some K back into cell
Restores resting potential
Difference absolute and relative refractory period
Absolute - even strong impulse can’t make action potential
Relative - larger than normal stimulus needed to generate action potential
