Nervous system (electrophysiology) Flashcards
What are the ways a membrane potential can change due to ion movement?
Depolarize
Repolarize
Hyperpolarize
What happens to the membrane potential when it depolarizes?
Membrane potential becomes more + than the resting membrane potetial and creates an electrical signal
What happens to the membrane potential when it repolarizes?
The depolarized membrane returns to resting potential
What happens to the membrane potetntial when is hyperpolarizes?
The membrane potential becomes less negative than the resting potential
What is the function of ion channels?
Allow the cell to change its ion permeability by opening or closing existing channels on the membrane
What are some examples of ion channels in the membrane?
K+ channels, Na+ channels, Ca2+ channels, Cl- channels
What is the definition of conductance?
The ease in which ions flow through a channel
How is a mechanical gate controlled (opened/closed)?
-deforms due to pressure
How are chemically gated ion channels controlled?
-controlled by intracellular messenger molecules or extracellular ligands that bind to the channel protein
How are voltage gated ion channels controlled?
-respond to changes in the cell’s membrane potential
-open and close when the electrical state of the cell changes
>opens at threshold voltage
Voltage charges across the membrane can be classified into what 2 types of electrical signals?
Graded potentials and action potentials
What are the characteristics of a graded potential?
- variable strength signals
- travel short distances and lose strength as they travel through the cell
- occurs through dendrites and cell body
- mechanically, chemically, o voltage gated channels involved
- what ions are involved; Na+, K+, Ca+
Where do graded potentials occur?
-occurs through the dendrites and cell body
What kind of gated channels are grade potentials involved in?
- mechanical
- chemical
- voltage
What kind of signals do graded potentials produce? How far do they travel?
- variable strength signals
- travels over short distance and lose strength as they travel through the cell
What are the characteristics of an Action potential?
- Very brief, large depolarizations
- travel long distances through a neuron, without losing strength
- occurs at axon hillock (trigger zone)
- All or Nothing
What kind of signals does an action potential produce? How far does it travel?
- very brief, large depolarizations
- travel large distances without losing strength
Where do action potentials occur?
-occur at the axon hillock (trigger zone)
Why is an action potential considered an “ All -or-Nothing” response?
-Action potential occurs if a stimulus reaches threshold or does not occur at all (below threshold)
What does not influence the amplitude of an action potential?
-the strength of a graded potential
How is a action potential initiated?
-when a depolarizing graded potential is strong enough when it reaches an integrating center within a neuron
Conduction of the action potential along the axon requires what types of ion channels to open/close to alter the membrane permeability (2)
- Voltage gated Na+ channels
- voltage gated K+ channels
During the conduction of an Action potential, what channels help regulate the movement of ions?
Activation and inactivation gates
9 steps to create an action potential
1) resting membrane potential
2) depolarizing stimulus
3) As the cell starts depolarizing, Voltage gated Na+ and K+ channels begin to open
4) Rapid entry of Na+ depolarizes the cell
5) As the membrane potential reaches threshold, Na+ channels close and slower K+ channels open
6) K+ moves from cell to extracellular
7) K+ channels remain open and additional K+ leaves cell, hyper polarizing it
8) Voltage- Gated K+ channels then close, less K+ leaks out of the cell
9) cell returns to resting ion permeability and resting membrane potential.
Describe the ion movement during the depolarization phase of an action potential
- rapid entry of Na+
What happens to the Na+ and K+ ion channels when the action potential reaches the threshold?
-Na+ channels close and slower K+ channels open
Describe the ion movement during the repolarization phase of the action potential?
-K+ moves from the cell to the extracellular fluid
What causes the cell to hyperpolarize?
- K+ channels remain open and additional K+ leaves the cell
- Voltage gate K+ channels eventually close and less K+ leaks out of the cell
What happens during the refractory period?
-once an Action potential has begun, a 2nd action potential cannot be triggered during this time (1-2 mill sec), no matter how large the stimulus
What is a subthreshold graded potential?
- starts above the threshold at its initiation point but decreases in strength as it travels through they cell body
- at trigger zone, its below threshold= does not initiate an action potential
What is a Suprathreshold graded potential?
-A stronger stimulus that creates a graded potential that is still above threshold by the time it reaches the trigger zone=initiates action potential
The refractory period is divided into what 2 periods
- Absolute refractory period
- Relative refractory period
Describe the absolute refractory period?
- represents the time required for Na+ channel gates to reset to their resting positions
- ensures one way travel
- 2nd AP cannot occur before the first has finished
Describe the relative refractory period?
- follows the absolute refractory period
- some but not all Na+ channel gates have reset to their original positions
- K+ channels are still open
- a STRONG stimulus may induce a 2nd action potential at this time
Describe saltatory conduction
- the action potential transmits from node to node with myelinated axons
- can only perform an AP at a node of ranvier
What factors can influence a faster action potential?
- large diameter of an axon
- myelinated axons (leak resistant); prevents ion flow of of the cytoplasm
What determines the number of action potentials produced at the axon hillock?
- stimulus intensity
- weak stimulus releases little neurotransmitters
- strong stimulus causes more action potentials and releases more neurotransmitters
What 3 chemical factors alter electrical activity?
1) Normokelemia
2) hyperkalemia
3) hypokelemia
Describe Normokalemia
- blood K+ is in the normal range
Describe hyperkalemia
- increase in blood K+ concentration
- depolarizes cell
- a stimulus that would normally be subthreshold can trigger an action potential
Describe Hypokalemia
- decrease in blood K+ concentration
- hyperpolarizes cell
- a stimulus that would normally be above threshold would less likely be able to fire an action potential
