MODULE 2- Electrical Signals of Nerve Cells Flashcards
what do nerve cells do
generate electrical signals to encode information
**resting membrane potential
the constant voltage across the membrane when the cell is at rest (40-90 mV)
**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 neurotransmitters
**action potential
a nerve impulse or spike that travels along an axon
**passive electrical response
occurs without any unique neuronal property in response to a stimulus
**hyperpolarization
a stimulus that causes the membrane to become more negative than that of the resting membrane potential
**active electrical response
occurs when a stimulus causes the membrane potential to increase past threshold (threshold potential), thereby generating a depolarizing AP
**once threshold is reached, APs are ____
all or none
**where is stimulus intensity encoded
AP frequency
subthreshold responses of receptor potentials
responses are graded in proportion to stimulus strength or intensity
neuronal electrical signals can be transmitted over ____
long distances
poor spread of passive electrical signals is experimentally demonstrated with what
injection of a subthreshold current
passive current flow/conduction
decays with distance along an axon
long distance propagation via APs is experimentally demonstrated with what
injection of a suprathreshold current
active current flow/conduction
shows a constant amplitude of the AP (doesn’t decay) along an axon
what do anesthetic drugs interfere with
neuronal electrical signaling
3 types of anesthetic drugs
-local
-regional
-general
local anesthesia
-blocks pain receptor electrical signaling at the site
-blocks Na+ channels involved in AP generation
regional anesthesia
reduces pain sensation over a larger body area, such as during child delivery
general anesthesia
-causes unconsciousness or lack of sensation + muscle relaxation
-main effect is to hyperpolarize neurons, making them more difficult to excite
what do ion movements produce
electrical signals
**2 requirements for generating cellular electrical signals
-concentration gradient (difference) of specific ions across the membrane
-membrane is selectively permeable to some ions, made possible by ion channel proteins
what are active transporters + ion channels responsible for
ion movements across neuronal membranes
active transport
move something against its concentration gradient
active transporters
-actively move selected ions against concentration gradient
-create ion concentration gradients
ion channels
-allow ions to diffuse down concentration gradient
-are selectively permeable to certain ions
simple lab experiment demonstrating electrochemical equilibrium
-membrane permeable to only K+
-K+ first moves down its concentration gradient
-then, it moves down its electrical gradient
-chemical + electrical forces continue to balance until dynamic equilibrium + no net movement is reached
when is electrochemical equilibrium reached
when there is no further net movement of K+
what relationship does Nernst equation predict
linear relationship between the transmembrane concentration gradient + the membrane potential
what do electrical + chemical forces create
membrane potentials
what is predicted by the Nernst equation + electrochemical equilibrium
the electrical potential generated across the membrane at electrochemical equilibrium (equilibrium potential) for a SINGLE PERMEANT ION
2 roles of permeant ion gradients + electrical potentials in electrochemical equilibrium
-perform an experiment to confirm electrochemical equilibrium
-it is possible to change the ion flux by changing either the potential imposed in the membrane or the transmembrane concentration gradient for an ion
what ions generate the resting membrane potential
potassium ions
concentration gradients across neural membranes are…
comparable for all species investigated
the concentration of which 4 ions gradients enable the calculateion of the Nernst equilibrium potential
K+, Na+, Ca2+, Cl-
resting membrane potential of squid neuron membrane
-65 mV
equilibrium potential for K+
-75 mV
what is indicated by resting membrane potential of squid neuron membrane (-65 mV) is closest to equilibrium potential for K+ (-75 mV)
indicates the resting membrane is more permeable to K+ than any other ion
how large is giant nerve cells of squid compared to mammalian neurons
100-1,000x larger
-their large size is what makes them easy to work with
why did giant nerve cells evolve in squid
to evade predators
what does the large-diameter of the squid neuron’s axon mean
faster than normal propagation of APs
role of K+ in neuronal resting membrane potentials
-living squid neuron bathed in solution
-raise the [initial K+] until it equates [final K+] -> resting membrane potential ~ 0
-resting membrane potential varied with log [final K+] with a slope that approaches 58 mV per 10-fold change in [final K+]
-Hodgkin + Katz showed that:
-permeability to K+ is higher than for any other ion
-[final K+] > [initial K+]
-the resting membrane potential of a squid giant axon is determined by the K+ concentration gradient across the membrane
what 2 things did Hodgkin + Katz show
-permeability to K+ is higher than for any other ion
-[final K+] > [initial K+]
Goldman equation for multiple permeant ions
an extension of the Nernst equation, taking the [ions] gradients + their respective permeabilities into account
during depolarization, what happens to membrane potential
membrane potential becomes more positive as it tries to reach the E of Na+
during repolarization, what happens to membrane potential
membrane potential becomes more negative as it tries to reach the E of K
compare permeability of K to Na for the steps of AP graph
-resting potential: P of K > P of Na
-depolarization: P of Na is increasing
-at top/peak of AP: P of Na > P of K
-repolarization: P of Na is decreasing
-back to resting potential: P of K > P of Na
what do APs arise from
sequential changes in sodium + potassium permeability
at rest, how permeable is neuronal membrane to Na+
only slightly permeable
during depolarization + overshoot phases, how permeable is neuronal membrane to Na+
extremely permeable to Na+
-due to opening of Na+ sensitive channels that are closed when at rest
what do membrane pumps ensure + why
ensures that [initial Na+] > [final Na+]
-so that during depolarization, Na+ rushes in toward the E of Na
resting state is due to what
the high permeability of K
depolarization is due to what
due to the transient increase in permeability of Na+
all APs have what 3 things
-overshoot
-falling phase
-undershoot
how do APs differ
differ widely in amplitude + duration of these various phases, depending on the neuron part (dendrite, axon, soma) + type (Purkinje neuron, motor neuron, etc.) from which they are recorded
AP steps
AP steps (5)
- neuron at rest
- rising phase
- overshoot
- falling phase
- undershoot
AP steps
- neuron at rest
(due to active transport of Na/K pump)
K+ inside > K+ outside
Na+ inside < Na+ outside
P of K > P of Na
AP steps
- rising phase
initial depolarization due to receptor potential or synaptic potential
-increase in P of Na; Na channels open
AP steps
- overshoot
P of K < P of Na
-Na channels open
-K channels open
AP steps
- falling phase
P of Na decreases
-Na channels close
-K channels open
AP steps
- undershoot
P of K > P of Na
-K channels open
**what is permeability determined by
the number of ion channels that are open
