Lecture 4 Flashcards
List the three characteristics of an action potential.
a. It is all or none
b. Self-propagating: each region of depolarization serves to generate action potentials on either side.
c. Non-decremental: is does not decrease in strength.
List types of ion channels with regard to what they respond to.
a. Ion channels: are channels that allow the passage of ions from one side of the membrane to the other. They are typically very selective, allowing only one kind of ion to pass through.
i. They may always be open (slow-leak channels)
ii. They may be gated only opening when certain conditions are met
1. Ligand gated channels: require the attachment of a chemical messenger such as a neurotransmitter or hormone to a receptor.
2. Voltage gated channels” require a change in the membrane potential.
What do the ligand gated channels require?
require the attachment of a chemical messenger such as a neurotransmitter or hormone to a receptor.
Voltage gated channels require what?
change in the membrane potential
Voltage gated sodium channels have two gates what are they?
Activation gate and inactivation gate
What is the structure of the voltage gated sodium channels?
Channel consists of four domains which consist of 6 hydrophobic transmembrane segments. Has high positive charge
Near the entrance to the channel there are loops from the pore helix that are bound to carbonyl oxygens which form what?
Selectivity filter
The selectivity filter with channels does what?
Smaller hydrated ions such as sodium are not affected by the selectivity filter but are too large to pass through the potassium channels, larger hydrated ions such as potassium will be dehydrated by selectivity filter allowing smaller naked potassium ions to pass through channel
When a sodium channel inactivated it cannot go back to the open state until when?
It transitions to the closed state
Kinetics are much slower in which channel?
Voltage gated potassium channels kinetics are much slower than fast sodium ion channels
What is the primary mechanism for repolarization?
voltage gated potassium channels
What is responsible for the rapid depolarization (upstroke) phase of the action potential?
Voltage sodium channels
What does increasing the diameter of the axon do?
Transmit current and signals faster
In myelinated axons current can only flow across the axon membrane at the points of what?
Least resistance
What do Schwann cells do?
They are the myelin free junctions that form the myelin sheath, this causes the potential flow to jump from one node to the next greatly increasing the speed of conduction.
