Biological electricity Flashcards
Excitable tissue
Allows animals to respond more rapidly to changing environmental conditions and maintain homeostasis
How do nerve cells generate electricity?
They generate a PD across the membrane which is stored by the electrochemical gradient where it is released when ions flow across the membrane causing a change in charge (depolarisation).
Cable properties
Biological materials are bad conductors and so have bad cable properties therefore electrical potentials produced can only spread a few mm before dissipating
What is resistance factor?
Resistivity in comparison to copper where the higher the number the worse they are at conducting.
Do action potentials have a high or low frequency?
Low frequency (100Hz)
Resting potentials
Energy difference across the cell membrane
Generates action potentials
Derives from: electrolytes in physiological fluids, negative proteins, selective-permeability of the cell membrane, and the work of the Na+ and K+ pump
Why is there PD across the cell membrane?
Due to an imbalance of K ions on either side of the membrane (70mV or -70mV). This can be changed by ions travelling across the membrane via osmosis.
Why is the cell negative?
Because of large negative protein ions which can’t move across the membrane
What is the only ion able to cross the membrane in resting state?
Potassium ions (K)
How can the resting PD be calculated?
By measuring the concentration of K+ ions using the Nernst equation (Vm = 58 log K+o/K+i)
Na+/K+ pump
Na+ moves in as K+ leaks out which results in the PD falling and the cell becoming deexcited
What is an action potential?
An active biological process that regenerates an initial signal along the length of a nerve
Voltage-gated channels
Channels which only allow Na+ through when the membrane is depolarized
Why do action potentials occur?
Due to sodium ions rapidly entering and changing the polarity of the local electric field
What are the 3 phases of polarization?
Depolarization, repolarization and undershooting
