Neuroscience -- Chapter 2 – electrical signals of nerve cells
Overview
Neurons are not good conductors of electricity, but they have mechanism that
generate electrical signals based on the flow of ions across plasma membranes.
Rest membrane potential; negative potential on the inside
Action potential; positive potential on the inside
Electrical signals of nerve cells
Resting membrane potential; depends on the type of neuron;
mostly between -40 to -90 mV
Neurons encode information via electrical signals that results
from changes in resting membrane potential.
Types of electrical signals:
1. Receptor potential (slow signal); due to activation of
sensory neurons by external stimuli (light, sound heat,
touch)
Sensory --> nervous system
Larger sensory stimulus = larger amplitude (see the
difference with action potential)
2. Synaptic potential (fast signal); associated with communication between
neurons at synaptic contact. Allows transmission of information from one
neuron to another
Nervous system --> nervous system
Amplitude vary according to the number of synapses activated, strength of
each synapse and amount of synaptic activity.
3. Action potential (very fast signal); type of electrical signal that travels along
their long axons. Responsible for long-range transmission of information.
Nervous system --> motor
Microelectrode to measure membrane potential.
1. Active responses; inject positive current,
depolarization is the result (at a certain
level of threshold potential, action
potential occurs) --> basis of information
transfer in the nervous system
2. Passive responses; inject negative
current, hyperpolarization is the result or
small depolarization --> happens at
synapses because they are small they
give small currents. Inhibitory synapse
gives hyperpolarization. Active synapse
gives small depolarization
Hyperpolarizing responses do not require a unique property of neurons
therefore called passive electrical responses
, Action potentials are considered active responses because they are generated
by selective changes in permeability of the neuronal membrane
Larger currents do not elicit larger action potentials because of the all-or-
nothing rule. Larger current = higher frequency of action potentials (see
picture)
Requirements for electrical signalling between nerve cells:
1. Must be fast
2. Cross long distances
3. Should not loose strength over distance
Long-distance transmission of electrical signals
Axons are long and are not good electrical conductors:
Passive conduction; current pulse is below threshold,
so no action potential and therefore the signal will
decay. Not good for signalling over long distance.
Active conduction; current pulse is higher than
threshold, so action potential and therefore the signal
is constant over distance. Good for signalling over long
distance
How ion movement produce electrical signals
Electrical potentials are generated across membranes:
1. Difference in the concentration of specific ions (active transporters)
2. Membranes are selectivity permeable for some ions (ion channels)
These 2 conditions depend on 2 different kinds of
proteins in the plasma membrane:
1. Active transporters (pumping station); ion
concentration gradient is established by this. They
actively move ions into or out of cell against
concentration gradient
2. Ion channels (lock); selective permeability is due
to ion channels. They allow only certain kinds of
ions to cross the membrane in the direction of
their concentration gradient.
These work together to generate resting membrane potential, action potential,
synaptic potential and receptor potential.
Example:
1. Concentration of K+ on each side of the membrane is
equal --> no electrical potential (no net flux of K+)
2. Concentration of K+ on the inside is higher than on the
outside --> electrical potential of the inside is negative
relative to the outside (net flux of K+ from inside to
outside)
Overview
Neurons are not good conductors of electricity, but they have mechanism that
generate electrical signals based on the flow of ions across plasma membranes.
Rest membrane potential; negative potential on the inside
Action potential; positive potential on the inside
Electrical signals of nerve cells
Resting membrane potential; depends on the type of neuron;
mostly between -40 to -90 mV
Neurons encode information via electrical signals that results
from changes in resting membrane potential.
Types of electrical signals:
1. Receptor potential (slow signal); due to activation of
sensory neurons by external stimuli (light, sound heat,
touch)
Sensory --> nervous system
Larger sensory stimulus = larger amplitude (see the
difference with action potential)
2. Synaptic potential (fast signal); associated with communication between
neurons at synaptic contact. Allows transmission of information from one
neuron to another
Nervous system --> nervous system
Amplitude vary according to the number of synapses activated, strength of
each synapse and amount of synaptic activity.
3. Action potential (very fast signal); type of electrical signal that travels along
their long axons. Responsible for long-range transmission of information.
Nervous system --> motor
Microelectrode to measure membrane potential.
1. Active responses; inject positive current,
depolarization is the result (at a certain
level of threshold potential, action
potential occurs) --> basis of information
transfer in the nervous system
2. Passive responses; inject negative
current, hyperpolarization is the result or
small depolarization --> happens at
synapses because they are small they
give small currents. Inhibitory synapse
gives hyperpolarization. Active synapse
gives small depolarization
Hyperpolarizing responses do not require a unique property of neurons
therefore called passive electrical responses
, Action potentials are considered active responses because they are generated
by selective changes in permeability of the neuronal membrane
Larger currents do not elicit larger action potentials because of the all-or-
nothing rule. Larger current = higher frequency of action potentials (see
picture)
Requirements for electrical signalling between nerve cells:
1. Must be fast
2. Cross long distances
3. Should not loose strength over distance
Long-distance transmission of electrical signals
Axons are long and are not good electrical conductors:
Passive conduction; current pulse is below threshold,
so no action potential and therefore the signal will
decay. Not good for signalling over long distance.
Active conduction; current pulse is higher than
threshold, so action potential and therefore the signal
is constant over distance. Good for signalling over long
distance
How ion movement produce electrical signals
Electrical potentials are generated across membranes:
1. Difference in the concentration of specific ions (active transporters)
2. Membranes are selectivity permeable for some ions (ion channels)
These 2 conditions depend on 2 different kinds of
proteins in the plasma membrane:
1. Active transporters (pumping station); ion
concentration gradient is established by this. They
actively move ions into or out of cell against
concentration gradient
2. Ion channels (lock); selective permeability is due
to ion channels. They allow only certain kinds of
ions to cross the membrane in the direction of
their concentration gradient.
These work together to generate resting membrane potential, action potential,
synaptic potential and receptor potential.
Example:
1. Concentration of K+ on each side of the membrane is
equal --> no electrical potential (no net flux of K+)
2. Concentration of K+ on the inside is higher than on the
outside --> electrical potential of the inside is negative
relative to the outside (net flux of K+ from inside to
outside)
