2. Introduction:
Ion channels are membrane proteins that allow ions to pass
through the Ion (channel) pore.
Their functions include establishing a
Resting Membrane Potential,
Action Potentials
Other Electrical Signals by regulating the flow of ions across the
cell membrane.
3. Ions transport through channels is extremely rapid.
More than a million ions per second flow through open channels-
a flow rate approximately a thousand times greater than the
rate of transport by carrier proteins.
4. Most ion channels are highly selective in allowing only one
particular type of ion to pass through the pore.
Most of the ion channels that have been identified can exist in
either an open or a closed conformation; such channels are said
to be gated.
5. The Important Gated ion channels are:
Ligand-gated channels
Voltage-gated channels
Ligand-gated channels open in response to the binding of
neurotransmitters or other signaling molecules.
Voltage-gated channels open in response to changes in electric
potential across the plasma membrane.
7. Ligand-gated channels:
Ligand-gated ion channels (Protein pores), also commonly referred
as ionotropic receptors, are a group of transmembrane ion-channel
proteins.
Which open to allow ions such as Na+, K+, Ca2+, and Cl− to pass
through the membrane in response to the binding of a chemical
messenger (i.e. a ligand), such as a neurotransmitter.
The fundamental role of ion channels in the transmission of
electric impulses.
8.
9.
10. Neurotransmitters released from presynaptic cells bind to
receptors on the membranes of postsynaptic cells, where they act
to open ligand-gated ion channels.
Binding of acetylcholine opens a channel that is permeable to
both Na+.
This permits the rapid influx of Na+, which depolarizes the
plasma membrane and triggers an action potential.
11. Due to influx of Na+ ions the fluid become more positive inside
of the cell these leads to depolarization of the plasma membrane.
12. Depolarization of the plasma membrane allows action potentials
to travel down the length of nerve cell axons as electric signals,
Resulting in the rapid transmission of nerve impulses over long
distances.
The arrival of action potentials at the terminus of neurons release
of neurotransmitters, such as acetylcholine, which carry signals
between synapse and cells.
14. Voltage-gated ion channels are a class of transmembrane proteins
that are activated by changes in the electrical membrane potential
near the channel.
The membrane potential alters the conformation changes of the
Ion channels, regulating their opening and closing.
15. Voltage-gated ion-channels found along the length of the axon and
muscles tissues.
Voltage-gated ion-channels are permeable to sodium (Na+),
potassium (K+), calcium (Ca2+), and chloride (Cl–) ions have been
identified.
16. Different types of Voltage gated Channels:
Sodium (Na+) channels
Calcium (Ca2+) channels
Potassium (K+) channels
Chloride (Cl−) channels
19. For example:
Voltage-gated ion-channels actively pumped out Na+ ions from the
cell and pumps K+ ions into cells.
Therefore, in the axon the concentration of Na+ is about 10 times
higher in extracellular fluids than inside the cell.
Whereas the concentration of K+ is approximately 20 times higher
in the cytosol than in the surrounding medium.
20. Their transport results in the establishment of an electric potential
(gradient) across the plasma membrane.
In resting axons there is an electric potential of about - 60 mV
across the plasma membrane, with the inside of the cell negative
with respect to the outside.
The flow of K+ through these channels makes the major
contribution to the resting membrane potential of -60 m V, which is
therefore close to the K+ equilibrium potential.
21. Binding of neurotransmitter results allows Na+ to flow into the
cell.
The sudden entry of Na+ leads to a large change in membrane
potential, which increases to nearly +30 m V.
At this time, the Na+ channels are inactivated and voltage-gated
K+ channels open, substantially increasing the permeability of the
membrane to K+.
22. K+ then flows rapidly out of the cell, driven by both the
membrane potential and the K+ concentration gradient, leading to
a rapid decrease in membrane potential to about - 75 mV.
This change in membrane potential inactivates the voltage-gated
K+ channels and the membrane potential returns to its resting
level of -60 m V.
.
23. Depolarization of adjacent regions of the plasma membrane
allows action potentials to travel down the length of nerve cell
axons as electric signals.
Resulting in the rapid transmission of nerve impulses over long
distances