CBNS 120 MIDTERM 2 QUESTIONS WITH VERIFIED
ANSWERS
Equation relating voltage, current and rin. - answers - rin = v/i
Define the membrane time constant (τ). - answers - τ is the time required for a first order
exponential process to decay to 1/e of its original value, or to increase to 1-1/e of its
maximum value.
How is membrane time constant (τ) related to membrane resistance and capacitance? -
answers - τ = rc
Equation describing an exponential time course of decreasing membrane voltage
following current injection and how it is related to τ. - answers - v(t) = v(t=0)e-t/τ
What happens to rin and cin as cell size increases? - answers - rin decreases, because
membrane surface area increases, providing more ion channels through which current
flows. Cin increases with membrane surface area, since more membrane is available to
store charge.
Define the length (space) constant (λ). - answers - λ is the distance over which voltage
decreases to 1/e of its original value.
How is λ related to rm and ri? - answers - λ = (rm/ri)1/2. Λ increases with the square
root of rm and with the reciprocal of the square root of ri. As rm increases, less current
flows across the membrane, thus allowing proportionally more current to flow through ri.
, leading to an increase in λ. As ri decreases, λ increases, since more current travels
axially.
8. As axon diameter increases, how are rm and ri affected? - answers - axon diameter
(radius) is inversely proportional to rm. Axon diameter is inversely proportional to the
square of the radius.
Rm - answers - rm/2pi*a
Ri - answers - ri/pi * a2
9. Write the equation relating λ to rm, ri, and axon radius (a). As a increases, what
happens to λ? Please explain. - answers - λ = (arm/2ri)1/2.
Epp - answers - end plate potential. In the neuromuscular junction of the pns, caused by
depolarization and if regulated by ach in the post synaptic terminals
ANSWERS
Equation relating voltage, current and rin. - answers - rin = v/i
Define the membrane time constant (τ). - answers - τ is the time required for a first order
exponential process to decay to 1/e of its original value, or to increase to 1-1/e of its
maximum value.
How is membrane time constant (τ) related to membrane resistance and capacitance? -
answers - τ = rc
Equation describing an exponential time course of decreasing membrane voltage
following current injection and how it is related to τ. - answers - v(t) = v(t=0)e-t/τ
What happens to rin and cin as cell size increases? - answers - rin decreases, because
membrane surface area increases, providing more ion channels through which current
flows. Cin increases with membrane surface area, since more membrane is available to
store charge.
Define the length (space) constant (λ). - answers - λ is the distance over which voltage
decreases to 1/e of its original value.
How is λ related to rm and ri? - answers - λ = (rm/ri)1/2. Λ increases with the square
root of rm and with the reciprocal of the square root of ri. As rm increases, less current
flows across the membrane, thus allowing proportionally more current to flow through ri.
, leading to an increase in λ. As ri decreases, λ increases, since more current travels
axially.
8. As axon diameter increases, how are rm and ri affected? - answers - axon diameter
(radius) is inversely proportional to rm. Axon diameter is inversely proportional to the
square of the radius.
Rm - answers - rm/2pi*a
Ri - answers - ri/pi * a2
9. Write the equation relating λ to rm, ri, and axon radius (a). As a increases, what
happens to λ? Please explain. - answers - λ = (arm/2ri)1/2.
Epp - answers - end plate potential. In the neuromuscular junction of the pns, caused by
depolarization and if regulated by ach in the post synaptic terminals
