Lecture 5 Reading Notes:
Electrical Signals In Nuerons:
Again to understand:
When membrane potential is at rest then its voltage is -70mV which is the normal
- Depolarization: When the sodium levels are high and the membrane potential Is
- Hyper polarization: When potassium levels are high and the membrane potential
is highly negative
- Repolarization: The membrane returns to the resting membrane potential
The Goldman Equation describes the resting membrane potential:
There are three factors that help the membrane potential of a cell to work:
1) The distribution of ions around the plasma membrane
2) The permeability of the plasma membrane to the ions so they can pass easily
3) The charge of the ions
Gated ion channels allow neurons to alter their membrane potentials:
- If the membrane potential is not permeable to the ions that pass by, then the ions
wont be efficient to work with the membrane potential and signals wont be sent.
- However, if the membrane potential is permeable, then ions will work with the
membrane potential to send signals which is important.
How do neurons depolarize, repolarize and hyperpolarize? It happens by changing the
permeability of the membrane potential by the addition of sodium and potassium ions.
NOTE: The changing of the permeability of the membrane potential gives electrical
IMPORTANT NOTE: membrane channel ( adding sodium and potassium) will only
happen if the ligand ( stimulus) attaches to the neurotransmitter!!
Fact: when a specific gated ion channel opens, the membrane poterntial becomes more
permeable to that ion to any other ions.
Equilibrium potential: the membrane potential where the electrical and
chemical gradients prefers the movement of a particular ion exactly balance each other, and there is no net movement of that ion across the membrane.
Even though the membrane potential is far from this equilibrium
potentials of an ion, this ion will still move to the membrane potential because
its electrical chemical force is really large.
BUT When membrane potential= equilibrium potential, the ion
movement will stop obviously because there is no force to move that ion or
any reason actually to move that ion.
Studying ion channels:
- Voltage clamp: it is used for studying ion channels in a single cell
The Voltage clamp experience:
Its like the squid experiment:
They hold the voltage across a membrane by injecting this voltage using an electrode and
this makes the membrane changes every time a signal passes by
This experiment is used to explain the electrical properties of the membrane in the cell
- Aside to the voltage clamp, there is the patch clamp: It studied the
properties of single channels
So the different between voltage clamp and patch clamp is that voltage clamp studies
a whole region of the cell and a large region of the membrane while patch clamp just
studied the region of a single channel.
Signal in dendrites and cell body:
-Vertebrate motor neurons (afferent) receive signals in the form of a chemical
-Membrane-bound receptors in the dendrites or cell body transduce (convert) this
incoming chemical signal into an electrical signal in the form of a change in the
membrane potential (Just like the lecture, the chemical signal is changed into a electrical
signal when it enters the dendrites)
binding of neurotransmitter to a ligand causes ion channels in the
membrane to open or close, changing the permeability of the membrane and
altering the movement of ions. (LIGAND HAS TO BIND INORDER TO
Change in permeability changes the membrane potential and causes an
These dendrites and cell body in the membrane potential are called
Graded potential: it is a change in the membrane potential
that varied in magnitude when stimulus occurs and helps in the
opening or closing of ion channels
Graded potentials vary in magnitude
Graded potentials vary in magnitude depending on the
strength of the stimulus a strong stimulus, such as a high concentration of
neurotransmitter will help the increase of the ion channel
Graded potentials are short-distance signals
Graded potentials can travel through the cell but decrease in strength as they get further
away from the open ion channel
This is called conduction with decrement
Example: a neuron with a ligand-gated Na channel on the membrane
When a neurotransmitter (ligand) binds to a ligand-gated Na channel, the channel
opens and Na+ ions move into the cell
Entry of Na+ = depolarization in a small area of the membrane surrounding the opened
The positive charge spreads along inside the membrane, causing depolarization.
This phenomenon is called electrotonic current spread
The graded potential signal gets weaker as it travels
Several features of the neuron influence why this happens, including leakage of charged
ions across the cell membrane, the electrical resistance of the cytoplasm, and the
electrical properties of the membrane.
Because graded potentials cannot be transmitted across long distances without