Biology Times (^19)
July
In both a neuron and an electrical circuit,
this voltage rises to the steady state level
asymptotically in the response to an external
current. Once the external current is shut off,
the voltage drops in a similar asymptotic
way.
- The following diagram depicts extracellular
fluid (ECF) and axoplasm (AP) separated
by axolemma. Which of the following
expression best describes the distribution of
ions between the two chambers?
(a) [Na+]AP = 10 [Na+]ECF
(b) [K+]ECF = 30 [K+]AP
(c) [Na+]ECF = 10 [Na+]AP
(d) [K+]AP = [K+]ECF
- Which of the following correctly represents
the permeability of the resting axonal
membrane to Na+, K+ and proteins?
(a) Proteins < Na+< K+
(b) Proteins < K+< Na+
(c) Proteins < Na+ = K+
(d) K+< Na+< Proteins
3. Sodium-potassium pump expels
(a) Three K+ outward for two Na+ into the
cell.
(b) Three Na+ outward for two K+ into the
cell.
(c) Two Na+ outward for three K+ into the
cell.
(d) Two K+ outward for three Na+ into the
cell.
4. The most abundant extracellular cation is:
(a) Na+ (b) K+ (c) Ca+ (d) H+
5. Pick the correct option regarding the
ionic gradients across the resting neuronal
membrane.
(a) Axoplasm has high concentration of Na+
(b) ECF has high concentration of proteins
(c) Axoplasm has low concentration of K+
(d) ECF has low concentration of K+
6. Sodium-potassium pump
(a) Is a passive transport mechanism
(b) Expels two Na+ for every 3 K+ imported
into the cell
(c) Maintains ionic gradients across the
resting membrane
(d) Triggers action potential
7. The electrical potential difference across the
plasma membrane in the absence of stimuli is
called
(a) Action potential
(b) Resting membrane potential
(c) Threshold potential
(d) Spike potential
8. Traces A, B and C in the given diagram
depict the changes in the membrane potential
(Vm) as well as changes in the membrane’s
permeability to Na+ (PNa) and K+ (PK). Select
the option that correctly identifies A, B and
C.