Chapter 5 Flashcards
The proteins that are almost always present in the plasma membrane and permit water to pass freely through the membrane are called what?
Aquaporins
Define Osmosis.
Net diffusion of water across a semipermeable membrane.
In order for (net) osmosis to occur what conditions must be met?
- Concentration of water must be different
2. Membrane permeable to water AND impermeable to a solute.
What is the osmotic concentration blood plasma (ECF)?
~ (about) 300mOsM (million Osmolar)
What would happen to the osmotic concentration of the blood if you ate many potato chips without drinking fluids?
Concentrations would increase
Define isotonic.
no change in cell volume
Define hypotonic.
cell volume increases; water enters the cell
“hippo-hypo”
Define hypertonic.
sucks water from a cell; cell volume decreases
Define simple diffusion. Make a list of the important molecules that move by simple diffusion.
Diffusion directly across the phospholipid bilayer of a membrane. (O2, CO2, lipid steroid testosterone)
What about simple diffusion could be considered an advantage to a cell? Disadvantage?
Advantage - Molecules pass through quickly - fast
Disadvantage - Not good control
Make a list of important molecules that cross cell membrane by diffusion through channel proteins.
Na+, K+, Cl-
Explain how protein-carriers are different from channel proteins.
Channel proteins require a protein to open the channel whereas protein-carriers change the shape of the channel (protein) in order for it to open.
What about facilitated diffusion (as a process) could be considered advantageous to a cell?
- Uses no ATP
2. Provides cell with control
Define active transport.
Requires cellular ATP to move molecules across the cell membrane against the concentration gradient.
Where are somatic motor neurons located in the spinal cord?
in the ventral horn
What is the name of the protein that generates and maintains the gradients for Na+ and K+ in a living cell?
Na+/K+ Pump
Which structural type(s) of neurons may be sensory?
Bipolar, unipolar
Which structural type(s) of neurons may be motor?
Multipolar
Define (net) diffusion
Movement of molecules from high to low concentration.
Provide a mechanistic explanation as to why diffusion occurs.
It occurs in order to make an even concentration throughout.
Define passive transport.
Does not require ATP to move molecules across membrane - uses potential energy stored in concentration (Facilitated diffusion)
List the factors that influence the rate at which molecules diffuse. Explain how changes in each will affect the rate of diffusion.
- The higher the gradient, the faster the diffusion rate
- Diffusion is faster over short distances
- The higher the temperature, the faster the rate of diffusion
- Smaller molecules diffuse more quickly
What is the gradient?
the difference between concentrations.
Briefly explain what protein-mediated transport is.
a protein “mediates” or makes it happen.
What about channel proteins can be considered advantageous? disadvantage?
Advantages: 1. Does not need ATP, 2. Gives cell control
Disadvantages:
Define facilitated diffusion. List the important molecules that are moved by facilitated diffusion.
Transport that is passive and moves molecules down their concentration gradient stopping when concentrations are equal on both sides of the membrane.
Glucose, sodium, chloride (GLUT4)
Describe in detail the activity of calcium pumps found in the sarcoplasmic reticulum of skeletal muscle cells.
ATP is used to power the pump which moves Ca+ out of the cell.
Describe in detail the activity of the Sodium/Potassium pump. In which body cells are these proteins found?
Found in all body cells.
The Na+/K+ pump maintains the gradients for sodium and potassium in a living cell by pumping in K+ and pumping out Na+. The ECF is almost all Na+ and the ICF is almost all K+. 30-60% of BMR goes to powering this pump. It cost 1 ATP to move 3 Na+ ions out and 2 K+ in.
Where is most of the sodium found in the body?
ECF
Where is most of the potassium found in the body?
ICF
Define the term “Resting Membrane Potential” (RMP)
difference in charge across the cell membrane when the cell is at rest (measured in mV)
Which ion is the most important in determining the resting membrane potential (RMP)?
K+ (potassium)
what is osmolarity?
the expression of concentration for biological solutions; the number of osmotically active particles per liter of solution. Expressed in osmoles per liter (OsM)
What is the equation for converting between molarity and osmolarity?
molarity (mol/L) x particles/molecule (osmol/mol) = osmolarity (OsM)
Define isosmotic
two solutions containing the same number of solute particles per unit volume.
Define hyperosmotic
If solution with higher osmolarity than another solution
Define hyposmotic
A solution that has fewer osmoles per unit volume than another solution.
Define tonicity
a measure of the effective osmotic pressure gradient (as defined by the water potential of the two solutions) of two solutions separated by a semipermeable membrane
Which structural type(s) of neurons may be sensory?
Unipolar, sometimes bipolar
Which structural type(s) of neurons may be motor?
multipolar
Which structural type(s) of neurons may be association?
multipolar
The cell bodies of somatic motor neurons in the spinal cord are typically found in the what?
gray matter of the ventral horn of the spinal cord
The cell bodies of somatic sensory neurons are typically found where in the body?
in the ganglia throughout the spine
What happens to the RMP as the extracellular K+ is increased? Use on of the following pairs of terms to describe this: (more/less, negative/positive)
More negative (repolarization)
What generates the gradients for Na+ and K+ in a living cell.
Sodium Potassium pump
What could happen to the membrane potential of a person’s cells if his ECF concentration of K+ was elevated?
becomes more negative - possible Hyperpolarization?
If Na+ channels were suddenly opened in a resting neuron what would happen to the MP?
it would become more positive (depolarization)
What was the threshold voltage to generate an action potential (AP)?
-55mV
State the law that describes the action potential threshold property.
All or none
Explain the mechanism of the action of lidocaine. Explain how it is a useful compound in medicine.
Lidocaine is a voltage-gated Na+ channel blocker. Without Na+ flowing in, the AP stops and won’t send the pain sensation to your brain. It is useful in surgeries and other invasive procedures.
What is the effect of increasing stimulus intensity on AP frequency?
There would be no effect to the AP as it will always be the same - The intensity would be encoded in the signal.
What 2 factors influence conduction velocity?
- the presence of schwann cells with knodes of Ranvier
2. Neuron size - the larger the neuron, the more energy can flow
What is the resting membrane potential of a typical neuron?
-70mV
What is the threshold of a typical neuron?
-55mV
What is the action potential of a typical neuron?
+30mV
What is the depolarization phase of an action potential? What is happening during this phase?
The phase in which membrane potential becomes more positive (-70mV - +30mV) Na+ is entering the cell
What is the repolarization phase of an action potential? What is happening during this phase?
The phase in which membrane potential become more negative; membrane potential moves back toward the resting membrane potential (+30mV - -70mV)
What is hyperpolarization? What is happening during this phase?
The membrane potential becomes lower than resting potential (more negative than -70mV). It is due to the slow closing of the K+ channel.
When drawing an Action Potential what is the y axis labeled? What is the x axis labeled?
Y-axis - Membrane Potential (mV) (bottom -90mV up to +30mV)
X-axis - Time (msec) (left 0 to right, about 4
What is the absolute refractory period?
the delay that happens after the first action potential has begun, before the second can be triggered (the period of time which no new AP can be formed - the time required for the Na+ channel gates to reset to their resting positions - about 1-2msec)
What is the relative refractory period?
follows the absolute refractory period. During this time some, but not all, Na+ channel gates have reset to their original positions and some K+ channels are still open.
