1. (D): The resting membrane potential of neuron and muscle fibers is approximately −70 mV. This potential is defined as the electric potential inside the cell minus that outside the cell. This potential is maintained as a result of ionic concentration gradient across the semipermeable cell membrane. (Daube 2002, p. 53)

2. (B): The value of the resting membrane potential depends on the concentration of ions across the semipermeable cell membrane. The ion with the highest intracellular concentration is potassium (68 mmol/L) and the ions with the highest extracellular concentrations are sodium (142 mmol/L) followed by chloride (105 mmol/L). (Daube 2002, p. 54)

3. (C): The Hodgkin-Huxley model is a scientific model that describes how action potentials in neurons are initiated and propagated. This mathematical model was based on experimental measurements of the time and voltage dependence of sodium and potassium conductances in giant squid axons. Drs. Hodgkin and Huxley received the 1963 Nobel Prize in Physiology for this work. (Daube 2002, p. 56)

4. (A): The Nernst potential or electromotive force of every ion is determined by its ionic concentration, its conductance per unit area and the capacitance of the membrane. In the steady state, sodium has a Nernst potential of +60 mV and has the highest extracellular concentration. Potassium has a Nernst potential of −66 mV and has the highest intracellular concentration. (Daube 2002, pp. 53-54)

5. (D): Slow calcium spikes are depolarizing potentials mediated by slow calcium channels that are activated by membrane depolarization and inactivated by repolarization and increased intracellular calcium concentrations. They are involved in the intrinsic bursting behavior of pyramidal cells and the formation of the paroxysmal depolarization shift (PDS). They are also involved in early afterdepolarization. (Ebersole and Pedley 2003, pp. 4-5; Daube 2002, pp. 58-59)

6. (B): Postsynaptic potentials are nonpropagating nerve or muscle potentials caused by neurotransmitter-induced opening or closing of channels. These excitatory or inhibitory potentials constitute normal synaptic transmission. EPSPs are mostly mediated by opening of sodium channels allowing entry of sodium inside the cell causing cell depolarization. IPSPs are mostly mediated by opening of chloride channels allowing entry of chloride inside the cell and potassium channels allowing exit of potassium outside the cell, causing cell hyperpolarization. (Fisch 1999, pp. 6-7; Daube 2002, p. 57)

7. (C): Action potentials are referred to as all-or-none phenomenon. They occur when the neuronal membrane is depolarized beyond a critical threshold. This threshold is lowest at the axon hillock located at the junction of the axon to the cell body. Action potentials have an amplitude of approximately 110 mV and lasts about 1 ms. (Fisch 1999, p. 8)

8. (A): Action potentials velocity is faster in myelinated fibers, compared to unmyelinated ones. The myelin sheath alters the cable properties of axons. The myelin sheath decreases membrane capacitance and conductance, decreases the time constant and increases the space constant along the nodes of Ranvier. (Daube 2002, p. 55)