Lecture 1 - The Action Of Drugs On Nerve Cell Function 1 & 2 Flashcards
Why is the Na-K ATP-are pump referred to as an electrogenic pump?
Creates a charge disparity (between the outside and inside of the membrane)
Why do ions need specific ion channel?
(Charged) ions cannot pass through the phospholipid bilayer, due to the hydrophobic (fatty acid) tails
Specific ion channels (proteins) create hydrophilic pathways for ions to pass through
Why are Na+ ions used in the generation of APs?
Because at membrane potential (-70mV), Na+ is out of equilibrium (ENa = +30mV)
Therefore Na+ ions will want to flow into the cell down the conc / electrical gradient
Where does the Na+K+ ATP-are pump get its energy from?
ATP hydrolysis
Where does depolarisation occur in myelinated neurones?
Nodes of Ranvier
What should be the target of drugs for MS (multiple sclerosis) and why?
Blocking K+ channels
In MS, you want to PROLONG the duration of the AP (i.e. depolarisation) to give more chance of the AP jumping across the plaque
Do this by blocking K+ channels that cause repolarisation
What provides connectivity in the NS?
Neural networks
What structures protect the CNS?
Brain - skull
Spinal cord - vertebral column
What is used to record electrical activity of the brain?
Electroencephalograms (EEG)
What is the purpose of keeping Na+ ions out of equilibrium across the cell membrane?
Resting membrane potential = -70mV
(Inside of the cell is more negative than the outside)
Maintained by selective permeability of cell membrane to different ions and the Na+/K+ pump
The Na+ ion concentration is much higher outside the cell than inside, and this concentration gradient tends to drive Na+ ions into the cell. However, the cell membrane is relatively impermeable to Na+ ions, which are prevented from freely entering the cell by ion channels that are mostly closed at rest.
By keeping the concentration of Na+ ions out of equilibrium across the membrane, the neuron is primed to generate an action potential when the appropriate stimulus is received. When the neuron is stimulated, ion channels open, allowing Na+ ions to rapidly flow into the cell, depolarizing the membrane and generating an action potential.
Thus, by maintaining an unequal distribution of Na+ ions across the membrane, the neuron is able to generate and propagate action potentials in response to appropriate stimuli, allowing for proper communication between neurons and other cells in the body.
What is the normal direction of an impulse in a neurone?
From the… to the …
From the SOMA to the AXON TERMINALS
What is the net gradient (and movement) of K+ ions?
K+ ions move out of the cell down the CONC GRAD - bc there’s greater [K+] inside the cell than outside
K+ ions move into the cell down ELECTRICAL GRAD - bc +ve charged ions are attracted to net -ve charge inside the cell
The conc grad > electrical grad = net movement of K+ ions OUT of the cell
What is the net gradient for Na+ ions?
Na+ ions move INTO cell down conc & electrical gradients
Net gradient INTO cell
What is the Nernst / Equilibrium potential for Na+?
ENa = (RT/zF).ln([Na]o/[Na]i)
ENa ~ +30mV
What is the intracellular concentration of organic anions (A-)?
130mM
(These don’t have ion channels)
What is the function of the NS?
Acts as a communications network
Receives sensory info
Initiates actions - i.e. hormone release / muscle contraction
What is the function of neurones?
Communication / memory
What is the function of glia?
Support / communication
What is the equation for the Nernst / Equilibrium potential of K+?
Ek = (RT/zF).ln ([K]o/[K]i)
Ek~ -70mV
(Approximately equal to [resting] membrane potential)
Explain the variables in the Nernst / Equilibrium potential
Ex = (RT/zF).ln ([X]o/[X]i)
R = gas constant
T = temp (K)
z = valency of ion (Na+ / K+)
F = faraday constant
[X]o = conc X+ outside the cell
[X]i = conc X+ inside the cell
Explain the Nernst / Equilibrium equation
The Nernst equation is a mathematical formula used to calculate the equilibrium potential for an ion across a membrane.
It tells us the electrical potential required to balance the conc gradient of an ion across a membrane. At equilibrium, the electrical potential generated by the conc gradient is equal and opposite to the membrane potential, resulting in no net movement of the ion across the membrane.
If the membrane potential of a neurone is more + than the equilibrium potential, then ions will tend to move INTO the cell. If the membrane potential of a neurone is less + than the equilibrium potential, ions will tend to move OUT of the cell.