Week 3 Review

Question 1

define excitability as it relates to cells

Answer 1

-having ability to go from RMP (-70mV), have a sudden change, then back to RMP

Question 2

how does excitability relate to nervous tissue

Answer 2

• excitability = cell’s ability to generate a signal -pain, retinas, sense of smell/taste
• losing your sense of smell/taste is an example of a loss of excitability

Question 3

Explain the difference between the resting membrane potential and the equilibrium potential of K+ in a nerve cell

Answer 3

-Equilibrium potential of K is established b/w conc gradient (inward) and electrical gradient (outward) and with it an electrical potential -maintain equilibrium inside and outside cell -K channels leaking so inside stays more negative than outside (-90 mV) -RMP = membrane potential of a cell that is stable; no net flux of movement (-70 mV)

Question 4

Explain how the electrochemical gradient defines the equilibrium potential of K+

Answer 4

-K equilibrium potential is established when inward K movement = outward K movement, so net flux = 0. -This potential represents balance b/w the effects of conc gradients and electrical gradients, resulting in an electrochemical gradient

Question 5

If the concentration of a positive ion is 10 fold greater inside than outside a cell, and the membrane is slightly permeable to that ion, will the resulting RMP become more positive or more negative over time?

Answer 5

-more negative -the positive ion will want to move down its conc gradient, so it will go outside the cell, resulting in a more negatively charged intracellular space at RMP

Question 6

If the concentration of a negative ion is 10 fold greater inside than outside a cell, and the membrane is slightly permeable to that negative ion, is the resulting RMP more positive or negative?

Answer 6

-more positive -the negative ion will want to move down its conc gradient, so it will go outside the cell, resulting in a more positively charged intracellular space at RMP

Question 7

Briefly explain what the Nernst equation allows us to calculate

Answer 7

-electrochemical equilibrium in the cell -helps us determine RMP

Question 8

define resting membrane potential (RMP)

Answer 8

the membrane potential of a cell that is stable (not producing an impulse)

Question 9

factors that influence RMP

Answer 9

-ratio of the conc of ions on either side of the membrane -specific permeability of the membrane to each ion -resulting electrical properties inside and outside of the cell

Question 10

define threshold potential

Answer 10

-baseline needed in order to initiate an action potential -“all or nothing” -has to become less negative/more positive

Question 11

define depolarization

Answer 11

-occurs when Na channels open up and Na starts entering cell -peak value is when Na equilibrium potential is reached -no further change in amount of Na entering cell

Question 12

define repolarization

Answer 12

-occurs when Na channels close and K channels open -inside of cell becomes more negative -K moves out of cell, down chemical gradient -goal = return cell to its RMP

Question 13

define hyperpolarization

Answer 13

-overshoot RMP then rising back to RMP -due to some K+ channels remaining open while the rest of the channels are closing (leakiness) -hyperpolarized cell is more negative and has greater difficulty reaching threshold potential again

Question 14

Explain the sequence of events that occur over the course of a complete action potential. Explain the sequence in terms of ion movement and open/closed channels.

Answer 14

Question 15

Explain why nerve depolarization is a positive feedback loop and repolarization of the same cell is a negative feedback loop.

Answer 15

• depolarization = sodium channels open, Na enters cell, more channels open
• repolarization = sodium channels close, potassium channels open

Question 16

Explain the All-or-None phenomenon as it relates to an action potential occurring in nerves.

Answer 16

• A cell has to reach its threshold potential in order for it to initiate depolarization
  
  • If it does not reach this threshold, it will not activate an action potential

Question 17

Why does a sushi chef serving you the liver of a pufferfish hold your life in his very hands? Why is lidocaine an effective local anesthetic?

Answer 17

• puffer fish has a toxin that blocks sodium channels that causes your heart to stop
• lidocaine blocks sodium channels as well (locally)
  
  • can be injected in heart to control defective AP
  • limits Na channels from opening by blocking the transmission of their signals, so limits pain signals

Question 18

Why do action potentials not decrease in magnitude with transmission? What would happen if they did?

Answer 18

• the propagation of an AP is an all or none effect
  
  • If there was a decrease in magnitude it would no longer travel down the axon
• AP strength can potentially decline, however, if traveling over a long distance
• myelin sheath is critical in preserving AP integrity
  
  • demyelination results in abnormalities in AP delivery
    
    • ex: patients with MS

Question 19

What would happen if the RMP continuously equaled the threshold potential?

Answer 19

• at threshold potential it would make a signal continuously firing
  
  • there would be no refractory period
  • could cause the skeletal muscle to continuously contract
• that’s why there is a refractory period

Question 20

The magnitude of the peak positive component of an AP approximates the ___________ of Na+ (explain)

Answer 20

• equilibrium potential
• this is when the intracellular conc of Na+ is at its highest
• at this point, no more sodium will flow into the cell

Question 21

What is the sequence of opening and closings of membrane pores/channels during an AP?

Answer 21

• sodium channels open for Na+, inside of cell
• at end of depolarization, Na+ channels will close
• K channels will be open so that they will go outside of the cell
• K channels slow to close, causing hyperpolarization, making the inside of the cell more negative
• repeats the process going down the axon

Question 22

Explain afterpolarization or hyperpolarization including an explanation of how it happens.

Answer 22

Afterpolarization/Hyperpolarization: Voltage gated K channels remain open after the potential reaches resting level and are slowly closing causing leakiness of K

Question 23

Describe a graded potential. What are some characteristics of graded potentials?

Answer 23

• Graded potential = changes in a membrane potential that vary in amplitude, depending on the strength of the stimulus
• Typically found in Dendrites (slide 67)
• Do not have to be all or none
• They are local acting
• An example is smell: when you can maybe smell a little or have a strong smell
  
  • a single graded potential is not strong enough to bring about an actional potential
  • if enough receptors are stimulated, enough GP will be generated to meet the threshold potential in order to create a depolarization

Question 24

While APs are usually unidirectional, describe a situation where that is not the case.

Answer 24

• APs that are not unidirectional; can be bidirectional
• An example of this is hitting your funny bone (Ulnar Nerve) because it can travel up or down your arm

Question 25

The speed of propagation of an AP in larger diameter nerve fibers is _____ (faster/slower) than the propagation of an AP in smaller diameter nerves

Answer 25

faster

Question 26

What is the myelin sheath? What is the physiological function of a myelin sheath?

Answer 26

• An insulator for the axon and allows for nerve conduction velocities to increase
• Restarts the AP process
  
  • the AP occurs at the node of Ranvier
• People with MS have a myelin sheath that is deteriorating

Question 27

What is the effect of a hyperpolarizing receptor potential on the receptor?

Answer 27

prevents backflow down the axon, another action potential is harder to achieve

Question 28

Describe the actions of a pacemaker potential.

Answer 28

• Gradually increases the voltage of a cell’s membrane
  
  • this increase in voltage occurs between action potentials
• Example: Heart beats a certain amount a minute in the SA Node
• In patients with heart transplants, the pacemaker drives the heart rate
• Basically the pacemaker lets the cell’s membrane potential reach the threshold

Question 29

If the extracellular K+ concentration in a person is increased with no accompanying change in intracellular K+ concentration, what happens to the resting potential and the action potential?

Answer 29

RMP would become more positive, bringing it closer to the threshold, making it easier to produce an AP

Question 30

Why is an action potential like “igniting a trail of gunpowder”?

Answer 30

Once the AP starts, it keeps traveling down the axon and cannot be stopped

Question 31

Describe the anatomy and physiology of a synapse and its components.

Answer 31

• anatomy: pre/post synaptic neuron, synaptic cleft (space between presynaptic membrane and post synaptic membrane), receptors on both sides, neurotransmitters all throughout, channels
• physiology: permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cells
  
  • action potential reaches terminal
  • voltage-gated Ca2+ channels open
  • calcium enters axon terminal
  • neurotransmitter is released and diffuses into the synaptic cleft
  • neurotransmitter binds to postsynaptic receptors

Question 32

Describe how an action potential reaching a synapse can “live to fight another day” as opposed to dying on the spot.

Answer 32

• Graded potentials will help action potential to fire
• EPSP = the summation of graded potential needed to bring about depolarization
• presynaptic firing down line and gets to one and does not have enough to fire AP
• excitatory or inhibitory

Question 33

Propose the usefulness of inhibitory postsynaptic potentials (IPSP)

Answer 33

• They stop letting potassium out of the cell
• Example of inhibitory: touch hot burner and eventually stop sending signals

Question 34

Why might excitatory postsynaptic potentials be useful?

Answer 34

• Making it easier to reach an AP
• Could possibly make drugs more effective

Question 35

Hypothesize a mechanism of action for BOTOX® (onabotulinumtoxinA)

Answer 35

blocks ACh; prevents AP

Question 36

Suggest the functional impact of antibodies generated in a person that are specific for a postsynaptic excitatory receptor

Answer 36

• Most Typical: block ACh
• Could affect the block cleft enzymes that metabolize NT, bind to receptor on postsynaptic membrane to block (antagonist) or mimic (agonist) transmitter actions, or inhibit or stimulate 2nd-messenger activity within postsynaptic cell

Question 37

Suggest a functional impact if a person has large numbers of antibodies specific for acetylcholinesterase

Answer 37

A lot more Acetylcholine in the synaptic cleft; hangs around longer to stimulate post-synaptic membrane

Question 38

This man lives in the Amazon river basin and is using this blow gun to hunt monkeys and other game. The dart he propels toward his unsuspecting prey is coated with curare. Death is rapid. Suggest a way that his poison might cause death. Suggest a way curare might be used in a modern day surgery or intensive care unit.

Answer 38

• Like “Tetrodotoxin” example
• beneficial effects: used as blocker
• used clinically to bring about muscle relaxation
• negative effect: death

Question 39

The venom Phoneutriatoxin produced by banana spiders slows sodium channel inactivation. Physiologically, what occurs if one is bitten by a banana spider?

Answer 39

Neurotransmitters blocked; nothing would be transmitted; paralysis

Question 40

Organophosphates such as round up and malathion, binds acetylcholinesterase. How does it kill that cockroach you saw running across the kitchen last week?

Answer 40

• At home Raid or insecticides have active ingredient organophosphate
  
  • inhibits acetylcholinesterase
    
    • enzyme unavailable to breakdown ACh
    • ACh will be around longer
      
      • creates multiple muscle contractions until cockroach eventually dies