The Membrane Potential and Cell Signalling Flashcards
Explain how the membrane potential forms
The sodium pump creates a high intracellular conc. of K+ ions and low Na+ conc.. Due to presence of potassium channels, the cell membrane is slightly permeable to K+ ions, which diffuse out down conc. grad.. But cell membrane is far less permeable to Na+, so these ions can’t diffuse in to replace lost +ve charge inside the cell. This buildup of -ve charge inside the cell creates the membrane potential.
Define resting membrane potential
Refers to the membrane potential of cells not engaged in a major physiological response involving the plasma membrane, such as contraction or secretion
Define depolarisation
describes a fall (in magnitude) of the membrane potential i.e. intracellular environment becomes more positive
Define hyperpolarisation
describes an increase in magnitude of the membrane potential i.e. intracellular environment becomes more -ve
What is the potassium equilibrium potential (Ek)?
This describes the membrane potential at which the electrostatic attraction drawing K+ ions into the -ve charged cell balances with the tendency of the ions to diffuse out of the cell down their concentration gradients. Calculated using the Nernst equation. It’s usually very close to the measured resting membrane potential.
Typical resting membrane potential of a skeletal and smooth muscle cell?
-90mV (same as astroglia), -60mV respectively
Typical resting membrane potential of a neuron?
-60 to -70mV
How to calculate the electrochemical gradient
difference between equilibrium potential for the ion in question and the membrane potential
Simplification of the Nernst equation for equilibrium potential?
Ek = -61z*log(Ci/Co)
Why does equilibrium potential rarely equal measured resting membrane potential?
equilibrium potential only accounts for the concentration gradient of K+ ions. The exact membrane potential depends on all the ion gradients across the membrane, as well as it’s permeability to these ions
What is the Goldman equation?
A modification of the Nernst equation taking into account multiple ions and the permeability of the membrane to those ions. Remember Ci/Co flips for -ve ions.
Difference between ligand and voltage gated ion channels
The former open in response to specific chemical signals, while the latter open in response to a change in membrane potential.
Disadvantages of hormones
Relatively slow signalling speed, and can’t have an impact on one particular cell
Why type of signalling do nerve cells perform?
Synaptic signalling. Very fast and specific, e.g. locomotion requires contraction of very specific muscles at specific moments in a movement
Roughly how far do neurotransmitters need to diffuse from the nerve terminal to the target cell?
about 20nm
How are signalling molecules stored?
Many stored in membrane bound vesicles prior to exocytosis. Some are too lipid soluble to be stored in vesicles alone, so they are stored bound to specific storage proteins in vesicles (steroid hormones and prostaglandins). These hormones are carried in the blood to their targets bound to plasma proteins due to their water insolubility.
Hormones that are secreted in vesicles, i.e. water soluble, polar.
Acetylcholine, glycine, glutamate, epinephrine, histamine, 5-hydroxytryptamine, somatostatin, vasopressin, growth hormone, insulin
Hormones able to diffuse through the plasma membrane, i.e. lipid soluble
Estradiol-17, tri-iodothyronine, prostaglandin, nitric oxide
Can you name ten chemical classes of signalling molecule?
Esters, Amino acids, Amines, Peptides, Proteins, Steroids, Iodinated amino acids, Eicosanoids, Inorganic gas, Nucleosides and nucleotides
Define transduction in terms of cell signalling
the link between detection of a signal (i.e. binding of receptor and signalling molecule) and the response
Define agonist
substances that bind to and activate a particular receptor
Define antagonist
substances that block the effect of an agonist
Where are receptors found?
All are proteins. Many are present in the plasma membrane where they can bind to water-soluble signalling molecules in the extracellular fluid. Hydrophobic signalling molecules bind to cytoplasmic and nuclear receptors. Some intracellular organelles possess receptors for signalling molecules generated within the cell (second messengers) e.g. endoplasmic receptors for inositol trisphosphate.
How does acetylcholine have different affects on different cell types?
It binds to different receptors, causing skeletal muscle to contract (nicotinic) but slowing the heartbeat when released from the ends of the vagus nerve (muscarinic)
