Lecture 2: Electrical Signals of Nerve Cells

Question 1

What is resting membrane potential?

Answer 1

the constant voltage across the membrane when a cell is at rest (~-40 to -90 mV), typically -60mV

Question 2

What are the 3 types of neural electrical signals?

Answer 2

1. Receptor potential – a change in potential when sensory neurons are stimulated.
2. Synaptic potential – a change in potential when one neuron stimulates another across a synapse using a neurotransmitter.
3. Action potential – a nerve impulse or spike that travels along an axon.

Question 3

What’s a passive electrical response?

Answer 3

occurs without any unique neuronal property in response to a stimulus

Question 4

What’s hyperpolarization?

Answer 4

a stimulus that causes the membrane to become more negative than that of the resting membrane potential

Question 5

What’s an active electrical response

Answer 5

occurs when a stimulus causes the membrane potential to increase past the threshold (threshold potential), thereby generating a depolarizing action potential

Question 6

Why do nerve cells generate electrical signals?

Answer 6

to encode information

Question 7

true or false: action potentials aren’t all or none

Answer 7

false

Question 8

what is stimulus intensity encoded in action potentials?

Answer 8

frequency

Question 9

What is passive current flow?

Answer 9

conduction along an axon decays with distance

Question 10

true or false: generally, neurons are poor conductors of electrical signals

Answer 10

true

Question 11

What is active current flow?

Answer 11

conduction along an axon shows a constant amplitude of the action potential (does not decay with distance)

Question 12

How is long-distance propagation via action potentials experimentally demonstrated?

Answer 12

with the injection of a suprathreshold current, which causes depolarization above the threshold for an AP

Question 13

How is the poor spread of passive electrical signals experimentally demonstrated?

Answer 13

with the injection of a subthreshold current

Question 14

What are the 2 requirements for generating cellular electrical signals?

Answer 14

1. Concentration gradient (difference) of specific ions across the membrane.
2. Selective permeability of the membrane to some ions, made possible by ion channel proteins.

Question 15

What do active transporters do?

Answer 15

actively move selected ions against their concentration gradient and create ion concentration gradients

Question 16

What do ion channels do?

Answer 16

allow ions to diffuse down the concentration gradient and they’re selectively permeable to certain ions

Question 17

What is the Nernst equation used for?

Answer 17

to predict the electrical potential generated across the membrane at electrochemical equilibrium (equilibrium potential) for a single permeant ion

Question 18

What do resting and action potentials rely on?

Answer 18

permeabilities to different ions

Question 19

At rest, what is the membrane more permeable to?

Answer 19

Much more permeable to potassium than sodium

Question 20

During depolarization, what happens to membrane permeability?

Answer 20

sodium permeability is increasing

Question 21

What is membrane permeability at the AP peak?

Answer 21

much more permeable to sodium than potassium

Question 22

During repolarization, what happens to membrane permeability?

Answer 22

sodium permeability decreasing

Question 23

What happens to membrane permeability when returning to rest?

Answer 23

much more permeable to potassium than sodium

Question 24

What is the Goldman equation?

Answer 24

an extension of the Nernst equation, taking the [ions] gradients and their respective permeabilities into account

Question 25

Why were squid used in early neurophysiological experiments?

Answer 25

they have giant axons, therefore easy for electrophysiological experiments to measure concentrations of different ions

Question 26

true or false: there's more potassium intracellularly vs. extracellularly

Answer 26

true

Question 27

true or false: there's more sodium, chloride and calcium extracellularly

Answer 27

true

Question 28

what ion generates the resting membrane potential

Answer 28

potassium

Question 29

What are the 2 findings of the Hodgkin and Katz squid neuron experiment?

Answer 29

1. permeability to potassium is higher for any other ion 2. potassium concentration inside the neuronal membrane is greater than the potassium concentration outside the neuronal membrane, therefore resting membrane potential of squid is determined by potassium concentration

Question 30

describe the Hodgkin and Katz experiment

Answer 30

bathed living squid neuron in a solution where they can alter the ion concentration. they raised the outside [K+] until it equated to the inside [K+] (until resting membrane potential increased to 0 mV)

Question 31

true or false: action potentials arise from sequential changes in sodium and potassium permeability

Answer 31

true

Question 32

What is the role of sodium in generating an action potential?

Answer 32

at rest, the neuronal membrane is only slightly permeable to sodium (higher permeability to potassium), during depolarization and overshoot phases there's a transient increase in membrane permeability to sodium as sodium-sensitive channels open (closed at rest), membrane pumps make sure that outside [Na+] is greater than inside [Na+] so during depolarization, sodium rushes in towards the sodium equilibrium potential and the resting state is due to high potassium membrane permeability

Question 33

What kind of AP will you see with a low extracellular [Na+]?

Answer 33

smaller amplitude

Question 34

What kind of AP will you see with higher extracellular [Na+]?

Answer 34

larger action potentials

Question 35

What are the AP phases?

Answer 35

rising, overshoot, falling, undershoot

Question 36

true or false: APs differ widely in amplitude and duration of their phases, depending on the neuron part and type

Answer 36

true

Question 37

what do anesthetic drugs interfere with?

Answer 37

neuronal electrical signaling

Question 38

what are the 3 types of anesthetic drugs?

Answer 38

1. Local: block pain receptor electrical signaling at the site. 2. Regional: reduce pain sensation over a larger body area, such as during child delivery. 3. General: causes unconsciousness or lack of sensation and muscle relaxation.

Question 39

What are the anesthetic mechanisms?

Answer 39

Anesthetics are GABA receptor agonists; GABA is the major inhibitory neurotransmitter in the CNS. Some (e.g., ketamine) are glutamate receptor antagonists (blockers) or attenuators; glutamate is a major excitatory neurotransmitter in the CNS. Inhalation anesthetics (e.g., halothane) are volatile. The main effect is to hyperpolarize neurons, making them more difficult to excite

Question 40

What's an example of local anesthesia?

Answer 40

Lidocaine inhibits sodium channels and blocks action potentials

Question 41

What's an example of regional anesthesia?

Answer 41

Zolpidem activates large inhibitory synaptic potentials as it works as a GABA receptor agonist

Question 42

Give 2 examples of general anesthesia

Answer 42

1. Ketamine is applied intravenously and acts as a glutamate receptor antagonist as it reduces excitatory synaptic potential 2. Halothane affects K+ channels, allowing the membrane to become more hyperpolarized, it's harder to generate an AP and needs a greater stimulus