lecture 3 electricity in neurons Flashcards
how does information flow in the nervous system?
electricity
what field of study studies the flow of information in the nervous system
electrophysiology
who was the first electrophysiologist
luigi galvani
what did luigi galvani discover
used electricity attached to frog legs and noticed the legs twitched, showing how important electricity is for motor movements (inspired frankenstein)
what are ions
ions are atoms that are electrically charged (neutral atoms have an equal amount of protons and electrons, ions dont)
difference between cation and anion
anions are negatively charged (extra electrons) and cations are positively charged (more protons than electrons)
do electrons or ions move in neurons
ions
what is membrane potential
differences in net charge between inside and outside of neuron
what makes up the cell membrane
phospholipid bilayer (phosphate hydrophilic head and hydrocarbon hydrophobic tail), cholesterol, integral and peripheral proteins
what cation is mostly in the extracellular space
sodium (na+)
what cation is mostly in the intracellular space
potassium (k+)
can ions pass through the phospholipid membrane
no, it is impermeable to charged atoms due to the hydrocarbon tail being nonpolar
what causes membrane potential
ion selective channels
what are ion selective channels made of
different polypeptide units
how do ions pass through protein channels
they have “pores”
how does water pass through the bilayer
aquaporin
what kind of transport is ion flux
passive diffusion (or brownian motion), no added energy required
what is the channel pore for cations lined with
negatively charged amino acid groups that repel anions (and vice versa)
what is ion selectivity for one cation over another related to
hydration shell of water molecules
how does passive flux across membranes happen
via permeable channels (no channels, no ions)
*also water cant cross without aquaporins
when is eqilibrium reached
when concentrations no longer change (equal flux in both directions)
what is membrane potential/electrical gradient
measure of difference in net charge between inside and outside of membrane = 0 mV
why are there leak channels?
leak channels bring the membrane potential back to normal after the na/k pump brings increases the concentration gradient to create energy
why is the membrane potential more permeable to potassium than sodium
potassium is more permeable and there are more potassium channels open (which is why the cell’s membrane potential is close to potassium’s equilibrium potential of -80 mv)
when is equilibrium of a cell reached
when the concentration and chemical gradient are equal and opposite
what is the concentration/chemical gradient
measures the amount of each ion
what is the electrical gradient
measures the amount of charge (net positivity or negativity) on either side of the membrane
Electrical Potential Difference
a difference in potential energy that exists when there
is a separation of charges (an electrical gradient, see below). Measured in volts (V) and
typical potentials in neurons are measured in millivolts (mV)
Resting Potential
the electric potential difference
across a cell’s membrane at rest (i.e. not during an action potential or a synaptic potential).
A typical neuronal resting potential is about -65 mV, meaning that the inside is more
negative than the extracellular fluid
Capacitor
an insulator (i.e. cell membrane),
separating two conducting materials, that can store
charge. In neurons, capacitance determines how
quickly the membrane potential can respond to
changes in current
Contrast ways electricity in the nervous system differs from electricity in wires
What is a lipid bilayer composed of and how are these molecules arranged? Why, in the
absence of channels, is it so impermeable to ions
What are ion selective channels, and briefly describe what they do and what causes their
selectivity
If a membrane of a cell is permeable to all ions, is there a point when net ion flow across
the membrane finally stops
Diagram how a cell membrane is like a capacitor
