Lecture 2: Electrical Signals of Nerve Cells Flashcards
What is resting membrane potential?
the constant voltage across the membrane when a cell is at rest (~-40 to -90 mV), typically -60mV
What are the 3 types of neural electrical signals?
- Receptor potential – a change in potential when sensory neurons are stimulated.
- Synaptic potential – a change in potential when one neuron stimulates another across a synapse using a neurotransmitter.
- Action potential – a nerve impulse or spike that travels along an axon.
What’s a passive electrical response?
occurs without any unique neuronal property in response to a stimulus
What’s hyperpolarization?
a stimulus that causes the membrane to become more negative than that of the resting membrane potential
What’s an active electrical response
occurs when a stimulus causes the membrane potential to increase past the threshold (threshold potential), thereby generating a depolarizing action potential
Why do nerve cells generate electrical signals?
to encode information
true or false: action potentials aren’t all or none
false
what is stimulus intensity encoded in action potentials?
frequency
What is passive current flow?
conduction along an axon decays with distance
true or false: generally, neurons are poor conductors of electrical signals
true
What is active current flow?
conduction along an axon shows a constant amplitude of the action potential (does not decay with distance)
How is long-distance propagation via action potentials experimentally demonstrated?
with the injection of a suprathreshold current, which causes depolarization above the threshold for an AP
How is the poor spread of passive electrical signals experimentally demonstrated?
with the injection of a subthreshold current
What are the 2 requirements for generating cellular electrical signals?
- Concentration gradient (difference) of specific ions across the membrane.
- Selective permeability of the membrane to some ions, made possible by ion channel proteins.
What do active transporters do?
actively move selected ions against their concentration gradient and create ion concentration gradients
What do ion channels do?
allow ions to diffuse down the concentration gradient and they’re selectively permeable to certain ions
What is the Nernst equation used for?
to predict the electrical potential generated across the membrane at electrochemical equilibrium (equilibrium potential) for a single permeant ion
What do resting and action potentials rely on?
permeabilities to different ions
At rest, what is the membrane more permeable to?
Much more permeable to potassium than sodium
During depolarization, what happens to membrane permeability?
sodium permeability is increasing
What is membrane permeability at the AP peak?
much more permeable to sodium than potassium
During repolarization, what happens to membrane permeability?
sodium permeability decreasing
What happens to membrane permeability when returning to rest?
much more permeable to potassium than sodium
What is the Goldman equation?
an extension of the Nernst equation, taking the [ions] gradients and their respective permeabilities into account
Why were squid used in early neurophysiological experiments?
they have giant axons, therefore easy for electrophysiological experiments to measure concentrations of different ions
true or false: there’s more potassium intracellularly vs. extracellularly
true
true or false: there’s more sodium, chloride and calcium extracellularly
true
what ion generates the resting membrane potential
potassium
What are the 2 findings of the Hodgkin and Katz squid neuron experiment?
- permeability to potassium is higher for any other ion
- 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
describe the Hodgkin and Katz experiment
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)
true or false: action potentials arise from sequential changes in sodium and potassium permeability
true
What is the role of sodium in generating an action potential?
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
What kind of AP will you see with a low extracellular [Na+]?
smaller amplitude
What kind of AP will you see with higher extracellular [Na+]?
larger action potentials
What are the AP phases?
rising, overshoot, falling, undershoot
true or false: APs differ widely in amplitude and duration of their phases, depending on the neuron part and type
true
what do anesthetic drugs interfere with?
neuronal electrical signaling
what are the 3 types of anesthetic drugs?
- Local: block pain receptor electrical signaling at the site.
- Regional: reduce pain sensation over a larger body area, such as during child delivery.
- General: causes unconsciousness or lack of sensation and muscle relaxation.
What are the anesthetic mechanisms?
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
What’s an example of local anesthesia?
Lidocaine inhibits sodium channels and blocks action potentials
What’s an example of regional anesthesia?
Zolpidem activates large inhibitory synaptic potentials as it works as a GABA receptor agonist
Give 2 examples of general anesthesia
- Ketamine is applied intravenously and acts as a glutamate receptor antagonist as it reduces excitatory synaptic potential
- Halothane affects K+ channels, allowing the membrane to become more hyperpolarized, it’s harder to generate an AP and needs a greater stimulus
