Nerve cells II Flashcards
Define current
Movement of electrical charges (of K+/Na+)
What are the SI units for current?
Amps (I)
Define resistance
Hindrance to movement of ions - Plasma membranes give resistant flow of ions
What are the SI units for resistance?
Ohms (R)
Define conductance
Allow charges to move through (opp of resistance)
What are the SI units for conductance?
Seimens (g)
Define voltage
Electrical potential energy made by separating opp charged ions
What are the SI units for voltage?
Volts (V)
What is the equation of Ohms Law?
V = IxR V = Voltage I = Current R = Resistance
Describe the properties of action potentials
Have short duration (1msec)
Elicited in all-or-nothing
Nerve cells code intensity of info by freq of AP
Describe the link between stimuli intensity and frequency
When intensity of stimuli increases, size of AP doesn’t change but freq increases
What is an undershoot?
Hyperpolarisation
What is the resting membrane potential of neurons?
-70mV (approximately)
What are the 5 stages of generating an action potential?
Resting potential Depolarisation Repolarisation Hyperpolarisation Threshold
Describe a nerve cell at rest
Inside nerve cell is slightly more negative
What are resting potentials dependent on?
Chemical/Physical properties of ion flow
Natural adaptations of neurons ( ion channels/pumps)
What is the importance of resting potentials?
The basis of all electrical signalling
Describe the Nernst equation
Used to calculate equilibrium potential for ions based on conc inside/outside a cell
Note: Always measuring inside compared to outside
Describe equilibrium potential for K+
Only permeable to K+
Inc conc of K+ inside cell than outside
As K+ leaves cell, leaves neg ions causing inside to become more negative so pulls K+ ions back in (by force exerted)
Describe the difference between resting and equilibrium potential
As membrane is ~40x more permeable to K+ at rest, more K+ leak channels than Na+ leak channels
Describe Goldman Hodgkin Katz equation
Shows membrane isn’t permeable to one ion
Used to calculate Vm when many ions cause resting potential
Summarise nerve cells II
All potentials- From ions moving across membranes
2 forces act on ions - Diffusion (high>low conc)/ Electrical (towards opp charge+away from like charge)
Each ion that flows through channels reaches equilibrium btw 2 forces
Equilibrium potential for each ion determined by Nernst Equation
K+ make negative potentials/Na+ make positive potentials
