Membrane Transport and The Neuron - QA
Which of the following statements correctly describes the plasma membrane?
a) it is a dynamic fluid structure that is in constant flux
b) it is a solid structure formed by phospholipids and cholesterol designed to be stable against pressure
c) it is a flexible protein barrier supported by cholesterol rods
d) it is a unique, solid barrier custom designed for each type of cell
Which of the following would not be a constituent of a plasma membrane?
b) messenger RNA
*Components of The Plasma Membrane:
Which of the following is a principle of the fluid mosaic model of cell membrane structure?
a) phospholipids consist of a polar head and a nonpolar tail made of three fatty acid chains
b) the lipid bilayer is a solid at body temperature, thus protecting the cell
c) phospholipids form a bilayer that is largely impermeable to water-soluble molecules
d) all proteins associated with the cell membrane are contained in a fluid layer on the outside of the cell
*Fluid Mosaic Model:
Solutions with a higher concentration of solutes than the concentration inside the cell are ___.
*interstitial fluid can be either hypotonic [lower concentration than intracellular fluid causing the cell to swell], isotonic [equivalant concentration to intracellular fluid causing no change to occur], or hypertonic [higher concentration than intracellular fluid causing the cell to shrivel]
What is a difference between primary and secondary active transport?
In primary active transport, the transport protein gets phosphorylated; in secondary active transport, the transport protein is not phosphorylated.
*energy is still needed for both methods, but secondary active transport is driven by the energy use of energy in primary active transport
Which of the following processes allows cells to concentrate material that is present only in very small amounts in the extracellular fluid?
b) receptor-mediated endocytosis
*endocytosis can transport substances out of the cell through phagocytosis [pseudopodium 'grabs' large particles], pinocytosis [indent in plasma membrane pinches off - forming a vacuole - for fluids and solutes], or receptor-mediated endocytosis [use of receptors to attract particles and vacuoles to bring substances into the cell]
What does "isotonic fluid loss" mean?
Water and electrolytes are lost in equal proportions.
If cells are placed in a hypertonic solution containing a solute to which the membrane is impermeable, what could happen?
The cells will lose water and shrink.
*impermeable means not allowing something to pass through, in this case, the solute
A red blood cell would swell if its surrounding solution were ___.
Which of the following types of glial cells produce the myelin sheaths that insulate the neural fibers in the CNS?
d) ependymal cells
*oligodendrocytes [provide support and insulation to axons through the form of the myelin sheath], astrocytes [biochemically support the endothelial cells that form the blood-brain barrier, provide nutrients to nervous tissue, maintain extracellular ion balance, and are involved in the repair and scarring process of the brain and spinal cord], microglia [main form of active immune defense in the central nervous system], ependymal cells [lines the ventricles in the brain and the central canal of the spinal cord to produce cerebrospinal fluid and as a reservoir for neuroregeneration]
Collections of nerve cell bodies outside the central nervous system are called ___.
What does the difference in the K+ and Na+ concentration on either side of the plasma membrane (and permeability of the membrane to those ions) generate?
Resting membrane potential
*as potassium ions and sodium ions slowly diffuse through the membrane, Na+/K+ ATPase maintains the concentration gradients
*at rest, there are relatively more sodium ions outside the cell than potassium and vice versa for inside the cell
Immediately after an action potential has peaked, which cellular gates open?
*Steps of An Action Potential:
1. -70 mV when a pulse is sent through reaching about -50mV to reach the threshold
2. DEPOLARIZATION: sodium gates open to allow sodium ions to follow both chemical and electrical gradients bringing the intracellular charge to +30mV
3. REPOLARIZATION: action potential had peaked and therefore sodium gates close and potassium gates open to bring the electrical gradient back to rest through following its chemical gradient
4. AFTER-HYPERPOLARIZATION: Na+/K+ ATPase works to rebalance the chemical gradients and bring the electrical gradient back up to -70mV
When a sensory neuron is excited by some form of energy, the resulting graded potential is called a:
a) postsynaptic potential
b) generator potential
c) excitatory potential
d) action potential
Which of the following is not true of graded potentials?
a) they increase amplitude as they move away from the stimulus point
b) they are short-lived
c) they can be called postsynaptic potentials
d) they can form on receptor endings.
During depolarization, the inside of the neuron's membrane becomes less negative.
*depolarization is the second step of an action potential where sodium channels open and positive ions flow into the membrane
Strong stimuli cause the amplitude of action potentials generated to increase.
*once they reach the threshold, action potentials have a set value where they peak and become at rest - this does not vary
When one or more presynaptic neurons fire in rapid order it produces a much greater depolarization of the postsynaptic membrane than would result from a single EPSP; this event is called ___ summation.
An inhibitory postsynaptic potential (IPSP) is associated with ___.