Electrical Properties of Nerve Cells Part 1 Flashcards
What causes receptor potential?
Due to the activation of
sensory neurons by external stimuli
How do neurons respond to external stimuli (receptor potential)?
These neurons respond to the external stimuli (ex: touch) with a receptor
potential that changes the resting potential for a fraction of a second
What is synpatic potenital reocrded throuhg?
Synpatic contacts
When does an action potential occur?
Occurs when a neuron sends information down an axon, away from the cell body
Action Potential Function
Responsible for long range transmission of information within the nervous system and allow the nervous system to transmit information
to its target organs, such as muscle
Effects of current on membrane potential?
injection of small amounts of current result in small shifts of membrane potential
Effects of stopping current injection on membrane potential
When current injection stops, the membrane potential recovers to the resting potential
Hyperpolarized
A change in a cell’s membrane potential that makes it more negative
Depolarization
Change in cell’s membrane potential that makes it more positive
Graded Potential
A change in the electrical potential on the membrane of an nerve cell in response to a stimulus, and where the magnitude of change is proportional to the strength of the stimulus
Electrochemical Equilbrium
when the movement of ions down their electrical gradient is equal and opposite in direction to the movement of ions down their concentration (chemical) gradient.
Equilibrium Potential
Refers to the membrane potential at which there is no net movement of an ion across the plasma membrane into or out of the cell
Three types of neuronal signals
1)Receptor potential
2) synaptic potential
3) Action potential
Steps of Action Potential
1) Rest: Leaky K+ channel and Na+/K+ pump are in action.
2) Rising Phase: Initial depolarization brings to threshold. Once reached, voltage gated Na+ channels open.
3) Falling Phase: K+ voltage gated channels open and Na+ channels inactivate.
4) Undershoot (Refractory): K+ voltage channels remain open, Na+ still inactivated.
5) “Return to rest”: Both voltage gated channels begin to close.
Synaptic Potential
The electrical signal associated with communication between neurons at synaptic contacts.
Action Potential
Responsible for long-range transmission of information within the nervous system or to target organs
Passive electrical responses:
Does not require a unique property of the neuron
Active electrical response:
Action potentials and requiring a fundamental change in how proteins will respond
What is the difference in electric potential between the interior and the exterior of a biological cell?
Membrane potential, measured in mv
The amplitude of the action potential is INDEPENDENT of the magnitude of the current used to evoke it. What is this principle?
all-or-none response,
What property is DEPENDENT on the magnitude of the current?
frequency of action potentials
If a current-passing electrode produces a current that yields a(n) ______ change in membrane potential as shown in Fig. C, then the magnitude of the resulting potential change will ______ with increasing distance from the site of current injection (B). This is known as ______ conduction.
subthreshold, decay, passive
If a current-passing electrode produces a current that yields a(n) ______ change in membrane potential as shown in Fig. C, then the magnitude of the resulting potential change will remain ______ with increasing distance from the site of current injection (B). This is known as ______ conduction.
suprathreshold, constant, active
Why does passive conduction decay over time? How can this be prevented?
ion dissipation, myelin which helps to speed up action potential conduction by acting as an electrical insulator
Active Transporters
Membrane proteins are responsible for actively moving selected ions against their concentration gradient and creating ion concentration gradients?
Ion channels
Membrane proteins are selectively permeable to certain ions and allow these ions to move passively down their concentration gradients
Both hyperpolarizing and depolarizing electrical stimulation result
Graded Potential
Some _______ channels types (non-gated) in the plasma membrane are “leaky” allowing a _______ diffusion of K+ out of the cell
potassium, slow facilitated
Why do all cells in the body have a negative-inside resting potential compared to the outside?
1)The membrane of the
resting neuron is more permeable to K+ than any other ion so the resting potential is closer to the equilibrium potential
2)more K+ inside than outside due to transporter activity so more cations are leaving than entering the cell
Why are squid axons larger than the standard mamallian axon?
Giant neurons evidently evolved in squid because they enhanced the animal’s survival. These neurons helped produce a jet propulsion effect that
allows the squid to move away from
predators at a remarkably fast speed.
Increasing the external K⁺ concentration makes the resting membrane potential more (POSITIVE / NEGATIVE).
POSITIVE since increasing the external K+ concentration causes depolarization
What did Hodkin and Katz find about Na+ concentration and rate or rise of action potential?
External Na+ concentration reduces both the rate of rise of the action potential and its peak amplitude
Hodgkin and Katz found that lowering the Na⁺ concentration had very little effect on what variable
Resting membrane potential
Capacitive Current
The redistribution of charge that occurs across the membrane when the membrane potential is set to a given command voltage
The action potential arises from the coordinated activation of two conductance
1) A sodium conductance (transient inward current) that activates rapidly and drives the rising phase of the action potential
2) A a potassium conductance (delayed outward current) that activates more slowly and contributes to the falling phase of the action potential and the undershoot.
What happens as the membrane becomes more depolarized?
The inward current decreases and outward current increases
Relationship between current and sodium
Removal of external Na⁺ causes this initial inward current to become outward, an effect that is reversed by restoration of external Na⁺. (sodium moved out of the cell)
What is the relationship between both peak Na+and K+ conductance and membrane potential?
Both peak Na⁺ conductance and steady-state K⁺ conductance increase as the membrane potential becomes more positive.
Refractory Period
Refers to the period of time immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation
Feedback cycles
responsible for membrane potential changes during an action potential.
Membrane depolarization activates a (POSITIVE / NEGATIVE) feedback cycle fueled by the voltage-dependent activation of Na+ conductance. This phenomenon is followed by the slower activation of a (POSITIVE / NEGATIVE) feedback loop as depolarization activates a K+ conductance, which helps to (DEPOLARIZE / REPOLARIZE) the membrane potential and terminate the action potential.
positive, negative, repolarize
Action potential propagation requires the coordinated action of two forms of current flow:
Passive and active currents flowing through voltage dependent ion channels
Where are voltage gated sodium and potassium channels located?
Nodes of Ranvier
Function of Myelin
Acts as an insulator to close leaky membranes and speed up propagation of relatively slow action potentials.
saltatory conduction
Describes the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials
Myelin
Insulating layer, or sheath that forms around nerve
myelin sheath
allows electrical impulses to transmit quickly and efficiently along the nerve cells
What type of cells form myelin sheth and where is myelin formed?
PNS, Schwan cells
In the CNS what is myelin formed by?
myelin is formed by oligodendrocytes
Difference between schwan and oliogendrocytes
1) Location
2) scwhann cells in the PNS form a 1:1 relationship with an axon and oligodenfrocytes in the CNS can wrap around myelin, making contact with many axons
What happens if you lose the ability to form compact myelin?
The nerve/neuron doesn’t send the signal and action potential to the muscle at the right speed, causing muscle degeneration
Voltage Clamp
Allows for the macroscopic current of the cell, meaning it measures the current flowing through thousands of voltage gated channels
Patch Clamp
Specialized type of voltage clamp method and allows for the microscopic current of the cell, meaning it measures the current flowing through an individual channel.
Cell-attached recording
Patch clamp configuration involves applying suction to a membrane, creating a seal between the fine-tipped glass electrode and a single membrane channel?
Whole -Cell Recording
Patch clamp configuration involves applying strong suction such that the interior of the pipette becomes continuous with the cell cytoplasm?
Outside-out recording?
Patch clamp configuration involves breaking the membrane such that the membrane will come back together with the extracellular domain exposed
Inside-out Recording?
Patch clamp configuration involves breaking the membrane such that the cytoplasmic domain is accessible?
At a positive membrane potential, the Na⁺ current is (POSITIVE / NEGATIVE) and (INWARD / OUTWARD).
positive, outward (neg potential current is negative nad inward)
Does depolarization active/inactive Na and K+
While depolarization activates and then inactivates Na⁺, it does not inactivate K⁺, allowing it to flow outward for the entire depolarization phase.
Describe the functional state of voltage-gated Na⁺ and K⁺ channels when the membrane potential is hyperpolarized.
The gates of both channels are closed when the membrane potential is hyperpolarized.
Describe the functional state of voltage-gated Na⁺ and K⁺ channels when the membrane potential is depolarized.
When the potential is depolarized, voltage sensors (indicated by +) allow the channel gates to open—first the Na+ channels and then the K+ channels. Na+ channels also inactivate during prolonged depolarization, whereas many types of K+ channels do not
Voltage Gated Channels
are selectively permeable to each of the major physiological ions: Na⁺, K⁺, Ca²⁺, and Cl⁻.
Ligand gated channels
less selective and allow permeation of two or more types of ions through the channel pore
Pore Loop -Voltage gated sodium channels
a filter for certain ions, providing ion selectivity for sodium ions
Selectivity Filter
made of negatively charged amino acid residues, which attract the positive Na+ ion and keep out negatively charged ions such as chloride
Voltage Sensors
enable movement within the membrane in response to changes in membrane potential.
Structure mammalian voltage-gated K⁺ channel when it is hyperpolarized
Closed because the inside of the cell is more negatively charged. These negative charges attract the positively charged voltage sensors, such that the pore is closed
Structure mammalian voltage-gated K⁺ channel when it is depolarized
Open (When the membrane is depolarized, the inside of the cell is more positively charged. These positive charges repel the positively charged voltage sensors, such that the pore is open.)
Co-transpoters
Type of active transporters do not use ATP directly but instead carry multiple ions in the same direction?
Three types of active transporters
1) ATPase pumps
2) Ion Exchangers
3)Co-transporters
Ion exchangers
Do not use ATP directly but instead carry one or more ions up its electrochemical gradient while simultaneously taking another ion down its gradient?
ATPase Pump
Acquired energy directly from the hydrolysis of ATP (examples depicted in figure)?
What two factors does the efflux of radioactive Na⁺ from a squid giant axon depend on?
1) If extracellular K+ is removed, Na+ efflux is reduced
2) If ATP is blocked, the function of this channel is blocked
Correctly order the sequence of events for the movement of ions by the Na⁺/K⁺ pump.
1) Na⁺ binding.
2) Phosphorylation.
b.) Dephosphorylation-induced conformation changes leads to K⁺ release.
d.) Phosphorylation-induced conformation changes leads to Na⁺ release and K⁺
Correctly order the sequence of events for the movement of ions by the Ca²⁺ pump starting with Ca²⁺ binding.
1) ATP binding
2)Phosphorylation
c.) Ca2+ binding
d) Conformational change causes Ca²⁺ release
