2: Resting Potential & Action Potential

Question 1

How Does a Receptor Potential Cause an AP?

Answer 1

• Occurs @ sensory receptors in a graded manner
• -Depends on stimulus strength
• Ie. Camera example

Question 2

How Does a Synaptic Potential Cause and AP?

Answer 2

• From 1+ neuron(s) to another
• Occurs @ synaptic contact
• B/w axon of pre-syn neur & dendrite of post-syn neur
• Two excitatory pulses
• -E1 = depol but no AP (not strong enough)
• -E2 = fires after & depol = strong, causing an AP
• AP is all-or-none here
• -Occurs only @ or ^ threshold

Question 3

Explain an Action Potential

Answer 3

• Memb is depolarized past threshold, by a receptor or synaptic potential
• VGNa channels open from depolarization
• -Activation gate is repelled from depol inside
• -More depol activates more channels
• Eventually, inside is so depolarized that it will repel the gating charge of the inactive gate & cause VGNa chans to go into their inactive state
• VGK channels open now (w a delay)
• -K flows out, causing the falling phase & undershoot
• Na chans close, ending the refractory period
• K chans close, ending the undershoot & restoring the membrane to its resting potential

Question 4

How Does Novocain Work?

Answer 4

Local Anesthetics

• VGNa channels open and are blocked by novocain
• -Prevents Na from coming in
• No AP sent to travel to brain
• Can’t feel any tissue damage b/c the signal can’t be sent

Question 5

How Does Tetrodotoxin Work?

Answer 5

• Is a neurotoxin that blocks VGNa channels & is difficult to unbind
• Causes death by paralysis of respiratory muscles
• Found in puffer fish ovaries & liver
• Produced by bacteria that live w/in the fish
• 1200X deadlier than cyanide
• -Single puffer fish could kill 30 humans

Question 6

How Does Saxitoxin Work?

Answer 6

• Neurotoxin found in butter clams, or any shellfish
• Not as potent as TTX but is still harmful
• Shellfish come in contact w toxal algael bloom & can store this for after a year of initial contact
• -Causes paralytic shellfish poisoning
• -Most recover from it
• Develop paresthesia: pins & needles

Question 7

What is the Importance of the Refractory Period?

Answer 7

Uniderectional AP Conduction

• APs move in one direction along the axon
• -Can only happen where it hasn’t yet been
• Na chans are inactivated in the opposite direction & can’t function

Upper Limit on the Firing Rate of a Neuron

• Places an upper limit of firing rate
• Max = 500AP/ sec