Chapter 4: How Neurons Use Electric Signals to Transmit Information Flashcards
who speculated that electricity might be the messenger that spreads info thru the nervous system?
Stephen Gray
who discovered electrical stimulation?
Luigi Galvani
passage of an electrical current from the uninsulated tip of an electrode thru tissue, resulting in changes in the electrical activity of the tissue (muscle contraction)
electrical stimulation
who demonstrated that electrical stimulation of the neocortex causes movement?
Guastav Theodor Fritsch + Eduard Hitzig
who first (unethically) demonstrated that the brain of a conscious person could be stimulated electrically to produce movement of the body
Roberts Bartholow
who was the first to measure the brain’s electrical currents w/ a voltmeter
Richard Caton
graph of electrical activity from the brain, which is mainly composed of graded potentials from many neurons
electroencephalogram (EEG)
who proved that electrical messages in nerves is not the same as real electricity on a wire?
Hermann von Helmholtz
nerves conduct info at ___, whereas electricity flows along a wire about ___
30-40m/s; 1 million times faster
who’s idea was it that waves of chemical change travel along an axon to deliver a neuron’s message?
Julius Bernstein
the neurons of most animals are tiny, around ___ in diameter
1-20 micrometres
device that measures the strength of electrical voltage by recording the difference in electrical potential between 2 points
voltmeter
who first noticed that the North Atlantic squid Loligo vulgaris had giant axons?
J.Z. Young
how big are the North Atlantic squid Loligo vulgaris’ axons?
can be as large as 1mm in diameter
how does the North Atlantic squid propel itself?
- with fins
- by contracting its mantle to force water out (via stellate ganglion)
squid diagram
a. giant axon
b. mantle axons
c. stellate ganglion
who used the North Atlantic squid’s axons to determine the neuron’s ionically based electrical activity (Nobel Prize)?
Alan Hodgkin + Andrew Huxley
specialized device that serves as a sensitive voltmeter, registering changes in voltage over time
oscilloscope
the units used when recording the electrical charge from a nerve/neuron
millivolts + milliseconds
a microscopic insulated wire or a saltwater-filled glass tube whose uninsulated tip is used to stimulate or record from neurons
microelectrode
Hodgkin and Huxley learned that the ___ is a change in the concentration of specific ions across the cell membrane
nerve impulse
3 factors that influence the movement of anion/cations into or out of cells
- diffusion
- concentration gradient
- voltage gradient
in a semipermeable membrane, one half will be positively charged and the other negative, and the voltage difference will be greatest ____
close to the membrane
at equilibrium, the differential concentration of the chloride ions on the 2 sides of the membrane produces ___
a difference in charge (voltage)
most biological membranes are ___ because ___
semipermeable; they have ion channels embedded
the inside of the membrane at rest has a charge of ___ relative to the extracellular side
-70mV
a store of potential energy is called the membrane’s ___
resting potential
4 charged particles that take part in producing the resting potential
ions of:
1. sodium (Na+)
2. potassium (K+)
3. chloride (Cl-)
4. large protein molecules (A-)
__ and __ ions are more concentrated in the intracellular fluid
protein (A-) and potassium (K+)
__ and __ ions are more concentrated in the extracellular fluid
sodium (Na+) and chloride (Cl-)
3 features that contribute to the cell membrane’s resting charge
- because the membrane is relatively impermeable to large molecules, the negatively charged proteins (A-) remain inside the cell
- ungated potassium + chloride channels allow potassium (K+) and chloride (Cl-) ions to pass more freely, but gates on sodium channels keep out positively charged sodium ions (Na+)
- Na+ – K+ pumps extrude Na+ from the intracellular fluid and inject K+
what creates the resting potential?
protein anions (A-) are manufactured inside the cell and have no channels to cross the membrane and leave the cell
why do potassium (K+) cations not balance out the charge of the protein anions inside the cell?
the potassium concentration is much higher inside the cell to try to balance this, but not all of them enter because of the potassium concentration gradient - they are drawn back out of the cell due to lower numbers outside
the sodium-potassium pump continually exchange __ intercellular sodium ions for ___ potassium ions
3; 2
___ ions are free to leave the cell thru their open channels, but ___ ions are slow to re-enter due to their closed channels
potassium; sodium
__ sodium ions reside on the outside of the axon membrane vs. the inside
10x as many
at equilibrium, there are about __ chloride ions outside the cell vs. inside
12x as many
small voltage fluctuation across the cell membrane
graded potentials
hyperpolarization is due to an efflux of ___, making the extracellular side more ___
K+; positive
depolarization is due to an influx of ___
Na+
graded potentials usually only last ___
a few milliseconds
hyperpolarization + depolarization typically take place on the ___
soma membrane + dendrites
3 channels that underlie graded potentials
- potassium channels: efflux of K+ = hyperpolarization
- chloride channels: influx of Cl- = hyperpolarization
- sodium channels: influx of Na+ = depolarization
what indicates that potassium channels have a role in hyperpolarization?
the chemical tertaethylammonium (TEA), which blocks potassium channels, also blocks hyperpolarization
what indicates the involvement of sodium channels in depolarization?
the chemical tetrodotoxin (TTX), which blocks sodium channels, also blocks depolarization
large, brief reversal in an axon membrane’s polarity that lasts 1ms
action potential
when is the action potential triggered?
when the cell membrane is depolarized to -50mV = threshold potential
the action potential can trigger a total voltage change of ___, reaching as great as ___
100mV; +30mV
gated protein channel that opens/closes only at specific membrane voltages
voltage-activated channels
sequence of action for voltage-activated channels during an action potential
- cell membrane potential reaches -50mV, both sodium & potassium voltage-activated channels open
- voltage-activated sodium channels respond faster vs. potassium, so Na+ influx happens just before K+ efflux
- sodium channels have 2 gates, at +30mV one of them close - Na+ influx happens quickly
- potassium channels open slower and remain longer = reverses Na+ depolarization & even hyperpolarizes the membrane
the state of an axon in the repolarizing period, during which a new action potential cannot be elicited because gate 2 of sodium channels (not voltage-activated) are closed
absolutely refractory
the state of an axon in the later phase of an action potential, during which higher-intensity electrical current is required to produce another action potential & potassium channels are still open
relatively refractory
voltage-activated sodium channels have _ gate(s) and voltage-activated potassium channels have _ gate(s)
2; 1
propagation of an action potential on the membrane of an axon
nerve impulse
the passing along of an action potential is similar to ___ because ___
the domino effect; there is no decrement in the magnitude
refractory periods limit the frequency of action potentials to about one every ____
5 ms
the max rate at which action potentials can occur is about ___
200 per second
___ prevent the action potential from reversing direction and returning to its point of origin
refractory periods
our largest axons are about ___ wide
30 micrometres
the part of the axon that is not covered by myelin
nodes of Ranvier
fast propagation of an action potential at successive nodes of Ranvier
saltatory conduction (leaping)
2 important consequences myelin has for propagating action potentials
- propagation becomes energetically cheaper since action potentials regenerate only at the nodes of Ranvier, not along the axon’s entire length
- myelin improves the action potential’s conduction speed
jumping from node to node ___ the rate at which an action potential can travel along an axon because ___
speeds; the current flowing within the axon beneath the myelin sheath travels very fast
on larger, myelinated mammalian axons, nerve impulses can travel at a rate as high as ___
120 m/s
on smaller, uninsulated axons, nerve impulses can travel only about ___
30 m/s
in multiple sclerosis, the ___ is damaged, which ___
myelin formed by oligodendroglia; disrupts the affected neurons’ ability to propagate action potentials via saltatory conduction
what is at the site of the loss of myelin in patches (MS)?
scarring and/or plaque
who performed experiments on large motor neurons in the vertebrate spinal cord to answer how the neuron integrates such an enormous array of inputs into a nerve impulse?
John C. Eccles
a spinal cord motor neuron has an extensive dendritic tree with as many as __ main branches that subdivide numerous times & are covered w/ ___
20; dendritic spines
brief depolarization of a neuron membrane in response to stimulation, making the neuron more likely to produce an action potential
excitatory postsynaptic potentials (EPSPs)
brief hyperpolarization of a neuron membrane in response to stimulation, making the neuron less likely to produce an action potential
inhibitory postsynaptic potentials (IPSPs)
EPSPs are associated w/ the opening of ___ channels
sodium channels
IPSPs are associated w/ the opening of ___ channels
potassium
why is an action potential not produced on the motor neuron’s cell body membrane even when an EPSP is strong?
the cell body membrane of most neurons do not contain voltage-activated channels - must reach the initial segment
area near where the axon meets the cell body that is rich in voltage-gated channels, which generate the action potential
initial segment
addition of one graded potential to another that occur close in time
temporal summation
addition of one graded potential to another that occur close in space
spatial summation
the ___ always indicates the summed influences of multiple temporal and spatial inputs
cell body membrane
if the threshold level is maintained for a long period, the action potentials will ___
follow one another in rapid succession as quickly as the gates on the voltage-activated channels can reset
inputs that are ___ are usually much more influential than those occurring some distance away
close to the initial segment
some cells in the developing hippocampus can produce additional action potentials called ___ when the cell would normally be refractory
giant depolarizing potentials
giant depolarizing potentials aid in developing the brain’s ___
neural circuitry
reverse movement of an action potential into the soma + dendritic field of a neuron; postulated to play a role in plastic changes that underlie learning
back propogation
in some nonmammalian species, they might lack ___ and have ion channels that respond to ___ rather than voltage
dendritic branches; light
the many differences among neurons suggest that the nervous system capitalizes on ___ to produce ___
structural/functional modifications; adaptive behaviour
transgenic technique that combines genetics + light to excite or inhibit targeted cells in living tissue
optogenetics
the light-activated ion channel channelrhodopsin-2 (ChR2) absorbs ___ light and opens briefly to allow the passage of __, exciting the cell via ___
blue; Na+ and K+; depolarization
the light-activated ion channel halorhodopsin (NpHR) absorbs ___ light and pumps ___ into the cell, inhibiting the cell via ___
green-yellow; Cl-; hyperpolarization
who used optogenetic techniques in mice to silence or activate neurons in the hypothalamus during stress?
Sterley
the base of each hair on your arm is wrapped in ___. when you displace the hair, ___
a dendrite of a touch neuron; the encircling dendrite is stretched
ion channel on a tactile sensory neuron that activates in response to stretching of the membrane, initiating a nerve impulse
stretch-activated channels
an odorous molecule in the air that lands on an ___ and fits itself into a specially shaped compartment opens ___
olfactory receptor; chemical-activated ion channels
amyotrophic lateral sclerosis (ALS) essentially means ___ and ___, primarily due to the death of ___
muscle weakness; hardening of the lateral spinal cord; spinal motor neurons
the axon terminal contacts a specialized area of the muscle membrane called an ___, where the axon terminal releases the chemical transmitter ___
end plate; acetylcholine
on a muscle, the receptor-ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron
end plate
2 steps of muscle contraction
- a motor neuron’s axon collaterals contact a muscle fibre end plane, then acetylcholine attaches to receptor sites on the end plate’s transmitter-activated channels, opening them
- these large membrane channels allow simultaneous influx of Na+ and efflux of K+, generating current sufficient to activate voltage-activated channels, triggering action potentials, causing the muscle to contract
receptor complex that has both a receptor site for a chemical and a pore thru which ions can flow
transmitter-activated channels
how is a transmitter-activated channel on an end plate different from the channels on axons + dendrites?
- a single end plate channel is larger than 2 sodium AND 2 potassium channels combined
- when its transmitter-activated channel opens, they allow both Na+ influx AND k+ efflux through the same pore
in myasthenia gravis, the thymus, which produces antibodies that binds to viruses, makes antibodies that bind to the ___ on muscles, causing ___
acetylcholine receptors; weakness + fatigue
how fast does an action potential travel along a squid’s axon?
25 m/s
myasthenia gravis is an ___, and usually ___ with treatment
autoimmune disease; well controlled
