BIO 336 EXAM 1 QUESTIONS AND ANSWERS
A+ GRADED
3 reasons the voltage inside a cell is -80mV - ANSWER 1. Na+/K+ pump is electrogenic
(pumps send 2K+ in but 3Na+ out)
2. intracellular proteins (anions) are too large to get out
3. cell membrane is permeable to K+, so it diffuses out to lower concentration (chemical
driving force), but is drawn in by an attraction to the negative charge of the cell
(electrical driving force)
Electrochemical equilibrium established - ANSWER K+ being forced out of cell due to
diffusion
Negative resting potential brings K+ into cell
Voltage of cell at: Resting and at Threshold - ANSWER Resting: -80mV
Threshold: -50mV
Voltage of cell@ depolaraztion? What is entering the cell? - ANSWER -50mV to +30mV
Na+
Voltage of cell @ overshoot
And repolarization...what is leaving the cell? - ANSWER Overshoot: +30mV
Repolarization: +30mV to -90mV...K+
Voltage of cell @ hyperpolarization - ANSWER -90mV (K+ channels stay open for 3-4ms)
VGNa+C - ANSWER "Voltage Gated Na+ Channel"
• channel closed @ rest
, • at threshold voltage changes to -50mV, which opens the VGNa+C
• Na+ rushes into the cell (depolarization)
• Voltage of the cell changes from -50 to +30mV
• Action Potential is generated
VGK+C - ANSWER "Voltage Gated K+ Channel"
• Channel closed until cell voltage changes to +30mV
• K+ rushes out (repolarization)
• Cell becomes more negative b/c the K+ channel stays open longer than Na+ channel
Why can't an AP travel backwards? - ANSWER Refractory period (b/c of
hyperpolarization, the cell is more negative then when it was @ rest, so it is too far from
threshold to regenerate another AP)
Conduction velocity
How is this affected by myelin? - ANSWER w/o Myelin (a fatty substance that surrounds
axons) AP's are sent @ only 1m/s. Myelin allows AP's to send @ 100m/s.
AP's occur at... - ANSWER The Nodes of Ranvier, which increases the speed of the
signal
2 medical conditions that result in demyelination of neurons - ANSWER 1. Multiple
Sclerosis
2. Heavy metal poisoning
Fugu - ANSWER AKA: puffer-fish
• Contain TTX (tetradotoxin)
• TTX blocks VGNa+C (can't generate AP)
• Causes death due to respiratory failure
A+ GRADED
3 reasons the voltage inside a cell is -80mV - ANSWER 1. Na+/K+ pump is electrogenic
(pumps send 2K+ in but 3Na+ out)
2. intracellular proteins (anions) are too large to get out
3. cell membrane is permeable to K+, so it diffuses out to lower concentration (chemical
driving force), but is drawn in by an attraction to the negative charge of the cell
(electrical driving force)
Electrochemical equilibrium established - ANSWER K+ being forced out of cell due to
diffusion
Negative resting potential brings K+ into cell
Voltage of cell at: Resting and at Threshold - ANSWER Resting: -80mV
Threshold: -50mV
Voltage of cell@ depolaraztion? What is entering the cell? - ANSWER -50mV to +30mV
Na+
Voltage of cell @ overshoot
And repolarization...what is leaving the cell? - ANSWER Overshoot: +30mV
Repolarization: +30mV to -90mV...K+
Voltage of cell @ hyperpolarization - ANSWER -90mV (K+ channels stay open for 3-4ms)
VGNa+C - ANSWER "Voltage Gated Na+ Channel"
• channel closed @ rest
, • at threshold voltage changes to -50mV, which opens the VGNa+C
• Na+ rushes into the cell (depolarization)
• Voltage of the cell changes from -50 to +30mV
• Action Potential is generated
VGK+C - ANSWER "Voltage Gated K+ Channel"
• Channel closed until cell voltage changes to +30mV
• K+ rushes out (repolarization)
• Cell becomes more negative b/c the K+ channel stays open longer than Na+ channel
Why can't an AP travel backwards? - ANSWER Refractory period (b/c of
hyperpolarization, the cell is more negative then when it was @ rest, so it is too far from
threshold to regenerate another AP)
Conduction velocity
How is this affected by myelin? - ANSWER w/o Myelin (a fatty substance that surrounds
axons) AP's are sent @ only 1m/s. Myelin allows AP's to send @ 100m/s.
AP's occur at... - ANSWER The Nodes of Ranvier, which increases the speed of the
signal
2 medical conditions that result in demyelination of neurons - ANSWER 1. Multiple
Sclerosis
2. Heavy metal poisoning
Fugu - ANSWER AKA: puffer-fish
• Contain TTX (tetradotoxin)
• TTX blocks VGNa+C (can't generate AP)
• Causes death due to respiratory failure
