PHYSIOLOGY 1

Question 1

what is physiology

Answer 1

The study of the functions of the body and their integration

Question 2

membrane potential

Answer 2

The greater the separation of charges across the membrane, the larger the potential.

• separation of ‘charges’ across a membrane
• difference in relative number of cations (+) and anions (-) between intracellular fluid (ICF) and extracellular fluid (ECF)
• separated charges are attracted to one another, therefore the force of attraction can be used to perform work – ‘potential’ measured in volts (but we use mV)

Question 3

Permeability concentration

Answer 3

ICF is more negative than ECF
Typically, RMP in neurons is -70mV

ECF = Na: 150 P:5 Anions: 0
ICF = Na: 15 P:150 Anions: 65
Relative permeability= Na: 1 K=25-30

Question 4

Key ingredients for a membrane potential

Answer 4

An ion concentration gradient (Na+/K+ pump is good!)

A selectively permeable membrane - cell membranes are good! Lots of K+ ‘leak’ channels (ungated ion channels)

• Look at Nernst Equation

Question 5

The Nernst Equation

Answer 5

Resting cells are mainly permeable to K+ ions,
so resting membrane potential close to the
Nernst potential for K+
E (k) = -90mV
E (Na) = +60 mV
a long way from the RMP (-70mV), because at rest, membrane permeability to Na+ is much lower than to K+

Question 6

Resting membrane potential (RMP)

Answer 6

Resting membrane potential is a balance between concentration gradient, electrical gradient and permeability for each ion

Question 7

RMP

Answer 7

RMP is always closest to the equilibrium potential of the ion to which the cell is most permeable

Question 8

Summary: Resting membrane potential

Answer 8

• Difference in relative number of cations and anions between ICF and ECF means ‘potential’ exists, with ICF being more negative than ECF
• RMP depends on balance between concentration gradient, electrical gradient and membrane permeability for each ion
• Resting cells are most permeable to K+ so it exerts the greatest influence on RMP ie. At rest Vm closest to EK

Question 9

Membrane Potential vs Action Potential

Answer 9

All living cells have a membrane potential
Specialised cells - of ‘excitable’ tissues (eg
nerve and muscle cells) - can transiently
change their membrane potential by changing ion permeability
These changes act as electrical signals:
‘Action Potentials