ZOO 600 : NEUROPHYSIOLOGY
M. Sc. ZOOLOGY: 3 Credits
Lecture 3-4
➢ Review of classification of neurons and their functions.
➢ Blood brain barrier and its physiological importance, CSF composition, formation and drainage.
➢ Physiological characteristics of neuronal cell membrane components for impulse conduction.
➢ Electrophysiology of neuron.
➢ Comparison of action potentials of Giant axon of Squid and mammalian neuron,
➢ Voltage and Cell-Patch Clamp Techniques.
➢ Myelin ultrastructure and Nodes of Ranvier,
➢ Nerve impulse conduction in Myelinated and Unmyelinated neurons.
https://qbi.uq.edu.au/brain/brain-anatomy/what-blood-brain-barrier
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
The Cell Membrane
➢ The membrane that separates the neuron from other cells and from the extracellular fluid is of extreme
importance in understanding neuronal function.
➢ The neuronal membrane is a complex molecular machine with a number of important adaptations that
perform specific information-processing function for the cell.
➢ The neural membrane is a very old invention in evolution, one that was so successful that it has
remained unchanged in both invertebrate and vertebrate nervous systems.
The neuronal membrane, like other cell membranes, consists of a lipid bilayer in which proteins, including
ion channels, are embedded.
Although three major types of lipids such as phospholipids, cholesterol, and glycolipids are present in the
neuronal membrane, phospholipids are the most abundant type.
Physiological characteristics of neuronal cell membrane components for impulse conduction
Neurons are highly polarised cells and are functionally divided into two domains and based on these two
domains, the plasma membrane is functionally separated into membrane compartments,
1. The somatodendritic membrane: Responsible for receiving signals and
2. Several distinct segments of the axon: responsible for transmitting signals
In addition, neurons develop a diversity of functional and morphologic subdomains
• dendritic spines,
• synaptic buttons,
• Ranvier nodes, etc.,
which implies that, throughout their lifetime, neurons need to precisely control their local molecular composition.
These membrane compartments/domains are essential for the directional propagation of action potential from the soma
to the axon tip and for formation of neural circuits among neurons; however, the mechanisms underlining this
compartmentalization are unclear.
These compartments maintain distinct distributions of membrane proteins without obvious structural barriers at their
boundaries.
In addition, although the movement of membrane proteins between different compartments across the boundary is
slower than that within a compartment.
Biochemically, the main constituents of biological membrane are the glycerophospholipids.
Physiological characteristics of neuronal cell membrane components for impulse conduction
Three characteristics of the neuron
1. Semi permeability of the membrane,
2. Osmotic balance, and
3. Electroneutrality on each side
create an equilibrium electrical potential at which the inside of the membrane is more negative than
the outside.
In most neurons this potential, called the membrane potential, is between −60 and −75 millivolts.
When the inside of the plasma membrane has a negative charge compared to the outside, the
neuron is said to be polarized.
Any change in membrane potential tending to make the inside even more negative is
called hyperpolarization, while any change tending to make it less negative is called depolarization.
Physiological characteristics of neuronal cell membrane components for impulse conduction
The neuronal membrane
The principles outlined above can be applied to the neuron and its ionic contents.
The plasma membrane of the neuron is semipermeable, being highly permeable to K+ and slightly
permeable to Cl− and Na+.
In the extracellular fluid, electroneutrality is preserved by a balance between a high concentration of Na+ on
the one hand and a high concentration of Cl−, as well as small quantities of impermeant anions such as
bicarbonate, phosphate, and sulphate, on the other.
In the cytoplasm, where K+ concentration is high, the concentration of Cl− is much below that necessary to
balance the sum of the positive charges. Electroneutrality is maintained there by negatively charged
impermeant proteins and phosphates.
Osmotic balance is maintained between the extracellular fluid and the cytoplasm by movement of water
through the plasma membrane when the total concentration of particles on one side is not equal to that on
the other.
Physiological characteristics of neuronal cell membrane components for impulse conduction
Membrane Transport-Proteins
Essential nutrients (e.g., sugars, amino acids, and nucleotides) need to enter the neuron, whereas
metabolic waste products must be removed from the neuron.
In addition, the concentration of various ions has to be maintained within the neuron. Therefore, this
necessitates influx of some ions and efflux of others.
These functions are carried out by different membrane transport-proteins.
Two types of proteins are implicated in the transport of solutes across the neuronal membrane:
(1) carrier proteins and
(2) channel proteins.
The main difference between channel and carrier proteins is that channel proteins have a
fixed conformation in the cell membrane whereas carrier proteins flip between two
conformations while transporting molecules.
Membrane transport proteins
Channel proteins and carrier proteins are the two types of membrane transport proteins
found in the cell membrane.
Both types of proteins are involved in passive transport through facilitated diffusion and
active transport through cotransporters like uniporters, antiporters, and symporters.
Transport proteins are specific to the molecules which are transported through them.
Channel proteins are capable of transporting molecules at a very high rate compared to
carrier proteins.
The main difference between channel proteins and carrier proteins is their mechanisms of
transporting molecules across the membrane.
Membrane transport proteins
Ion channel and ion pump are two types of proteins
that transport ions across the cell membrane.
Ion channels transport ions passively without the
use of energy while the ion pumps transport ions
actively with the use of energy.
So, this is the key difference between ion channel
and ion pump.
Moreover, ion channel needs only a single gate
while the ion pump needs at least two gates.
Membrane transport proteins
Membrane transport proteins
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction
Physiological characteristics of neuronal cell membrane components for impulse conduction