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Physiology Cells


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Why is myelin so important for motor control? What is its function?
demyelination may result in the action potential arriving at the next Node of Ranvier to have strength to fire an action potential.
If action potentials traveling down a nerve are usually the same size and shape, how is information coded by nerves?
Variation in the frequency of the action potentials can be used as the “code” for information transmission along axons.
What is Myelin’s function?
To act as an insulator around the nerve axon & to increase conduction velocity.
How does size and myelination affect the conduction velocity of an action potential down a nerve?
myelinated axon has a greater conduction velocity than an unmyelinated fiber that is 100x larger in diameter.
Explain primary hyperkalemia
Inherited disorder of painful spontaneous muscle contractions, followed by periods of paralysis
Explain primary hyperkalemia the cellular disfunction.
mutation in the voltage-gated Na channels that result in a decreased rate of voltage inactivation. Longer-lasting action potentials in skeletal muscle cells and increased K efflux. increased extracellular K causes depolarization, results in cell unable to fire action potential
Why do cardiac muscle have action potentials with long durations?
Rapid entry of Na into the cell via Na channels similar to nerve and skeletal muscles, causes rapid depolarization and overshoot. These sodium channels are called Fast Channels. Next enters plateau phase where Slow Channels (Ca) open and close at a slower rate. These Slow channels are called L-type Ca Channels allow Ca to enter the ventricular cell during the plateau phase stimulating the release of more Ca form the SR to initiate the cell contraction. Repolarization happens when L-type Ca Channels close and by a much delayed opening of the K channels.
Why do smooth muscle have action potentials with long durations?
Many lack Na channels. Depolarization is caused primarily by Ca channels (similar to the Ca channels in the plateau phase of cardiac cells), (open and close slowly). Smooth muscles have very little SR, the Ca that enters through these channels are vital for excitation-contraction. Repolarization is caused by the closing of the slow Ca channels and a simultaneous delayed opening of the K channels.
Name two toxins produced by sea organisms that poison Na+ channels. How do these poisons act?
Tetrodotoxin (TTX)
How does saxitoxin work?
Blocks Na channels. It is produced by reddish-colored dinoflagellates that are eaten by shellfish
How does Tetrodotoxin (TTX)work?
Blocks the Na channel. TTX binds to the extracellular side of the sodium channel
It is found in ovaries of puffer fish.
How does Tetraethylammonium (TEA)work?
blocks the K channel on the cytoplasmic side.
What other organs are affected by CF?
Liver and Gallbladder:
Small intestine:
Reproductive Tract:
What is Cystic Fibrosis
genetic disease in which ion channels in epithelial cells are defective. There is a genetic deficit in the CF gene which causes a defect in chloride transport. Faulty chloride channels in the membrane results in an impermeability of epithelial cells to chloride ions.
How is Chloride effected in cystic fibrosis?
nability for chloride to normally cross the cell membrane leads to clogging of the airways with a thick mucus. In fact, infections also develop. These lead to impeded breathing
What process causes H2O to move from one side of a membrane to the other? Is it active or passive?
Refractory Periods - What are two types of refractory periods.
Absolute & Relative
Absolute refractory
time period the membrane is unable to fire a second action potential no matter how strong the stimulus.
Relative refractory
During this time period a stronger than normal stimulus can trigger another action potential.
membrane potential will change from negative to positive inside the cell. This is called the __________
peak of the action potential, Na+ inactivation gates _____ (Na+ conductance goes down). Na+ no longer moves _______ the cell.

As the membrane ______ it will reach a threshold voltage.
2. As the membrane________ it will reach a threshold voltage.
1. In their resting states, most Na+ and K+ channels will be ________.
resting membrane potential to a more negative voltage, i.e., from -60 mV to - 85 mV. Note-. -85 V is also a higher potential difference across the cell membrane.
membrane potential toward zero, i.e., -70 mV to -58 mV. Note: as the membrane potential gets closer to zero, it will reach a threshold at which point the cell will produce an action potential.
rapid change in membrane potential that is propagated with the same size and shape along a nerve or over the entire length of a muscle.
Action Potential
What would be the effect of hyperkalemia on the resting membrane potential of a nerve cell?
Depolarization- the movement of resting potential to less negative
What would be the effects of hypokalemia on the resting membrane potential of a muscle cell?
Hyperpolarize cells (increase in magnitude) of the resting membrane potential. This may be a result of long-term use of diuretics. (hyperpolarization- the movement of resting potential to more negative.)
What is the importance of the use of drugs such as digitalis that inhibit Na+/K+ ATPase in the heart?
Cardiac glycosides (digitalis) increase the force of contraction by inhibiting Na+, K+ -ATPase in the myocardial cell membrane. As a result of this inhibition, the intracellular [Na+] increases, diminishing the Na+ gradient across the cell membrane. Na+ - Ca++ exchange
depends on the size of the Na+ gradient and thus is diminished, producing an increase in intracellular [Ca++].
plasma and cytoplasmic concentrations of K+, Na+ and Cl-.
Plasma Concentration: K= 4, Na= 135-145 Cl= 115

Cytoplasmic Concentration: K= 140, Na= 9.2, Cl= 3-4
At rest, the cell membrane is much more permeable to ______.
concentration is much higher In the cytoplasm, ____ will tend to diffuse out of the cell, making the inside of the cell more negative.
All cells (excitable, i.e., nerve or muscle) or (non-excitable, i.e., fat) have a ____(+ or -) resting membrane potential.
-binds adenelate cyclase to C-amp and turns on, increase production, increase fluid in GI tract
Mg+ ____ intracellular than in the cyctoplasm,
The energy for active transport may be primary come from ?
secondary uses energy from the ___ gradient.
occurs when an impermeable solute creates an osmotic pressure difference across a membrane, which drives water flow.
repolarization is caused by the opening and closing of channels.
How are Ca++ concentrations maintained inside the cell?
Calcium is controlled by the Na/Ca+ pump to the outside of the cell and to intracellular vesicular organelles
Name two other ion pumps. SR./Ca pump & ion transport pump.
Na/Ca+ pump and Na/H+ ion pump in the stomach and kidneys.
The most common ion pump moves Na+ and K+ (Na+/K+ pump) Why is this pump so important to the cell?
Maintain Na/K conc Na out, K in, nerve funct, and transmission.
Name four ions that are transported by Primary Action Transport.
Requires energy directly derived from the break down of ATP or some other high energy phosphate.
Primary Active Transport
derives it's energy from stored forms of ionic concentration differences
Secondary Active Transport
solution has fewer osmotically active particles in the solution than a typical cell.
hypotonic solution
solution has more osmoticity active particles in the solution.
hypertonic solution
solution has approximately the same number on both sides of the cell membrane.
Which way will water move in each case?
hypotonic, hypertonic, isotonic
Isotonic = conc is same on both sides (cells and plasma = 154), hypertonic water to move out of the cell conc >154 cause cells to shrink, hypotonic water to move into the cell causes cells to cell conc <154.
is the concentration of osmotically action particles per unit volume. Note: These particles will not easily move across a cell membrane. They determine the cell tonicity or tonicity of extracellular fluid.
What are Osmoticity Active Particles?
The particles or solutes become diluted due to osmotic flow of water across memb
The movement of water across a cell membrane is called _______? (water movement occurs from area of lower solute conc to one of high solute conc.)
what are factors that will affect H2O movement?
Concentration of water, size of solute water, perm of memb. Temp
amount of pressure to stop osmosis from one side to other. Controlled by solute amount.
osmotic pressure
   What are ion channels?
Channels that allow ion diffusion. Ions are charged molecules and therefore insoluble in lipid solvents. Ion ch are controlled be either voltage difference, neurotransmitters or regulatory molecules.
How does H20 cross cell membranes?
Lipids are more readily transported. Through aquaporins or Osmosis from low conc to greater across memb
What does saturating a system mean?
Saturating the system means there is more substance to be carried than carriers available.
passive movement of a substance down its concentration gradient-using carrier mediated transport. (goes from more conc to less conc w/o energy.
Facilitated Diffusion
Factors affecting diffusion across a membrane:
Distance the substance must move (increased time).Area of the membrane (larger = more particles in)
Concentration (increased conc more diffusion)
Permeability of substance (lipids in easier than water).
permit K+ to leak out of cells increasing K+ outside the cell permits K+ to come out of the cell
Leak Channels
How does cholesterol get across the cell membrane?
Mainly are dissolved in the bilayer of the membrane, get into cell into receptor mediated endocytosis via clathrin on cytoplasmic surface of plasma memb covered with bristles, regions are coated pits, give rise to coated vesicles which are involved in recepetor mediated endocytosis.

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