Module 3 Lecture 5 - Propagations Flashcards
How are the signals from an action potential transmitted?
From one nerve cell to another
What are the four regions of a nerve cell and explain what each one is used for in terms of generating an action potential
- Input Zone
- Composed of dendrites and cell body where signals from other neurons are being received
- Graded potentials are generated when the dendrites receive information from a neuron - Triggering Zone
- Axon hillock region of the Nerve cell containing the highest density of Na+ voltage channels which initiates an action potential - Conducting Zone
- Action potential is conducted in an undiminishing manner - Output Zone
- Neurotransmitters are released to send signals to other cells
Where along the nerve cell (neuron) is the action potential generated and what are the two methods that keep the action potential running without further stimulation?
Action potential is generated at the axon hillock and without further stimulation it is led by:
1. Contagious Conduction
2. Saltatory Conduction
What is contagious conduction?
Action potential is propagated at every patch of the membrane down the length of the axon
Explain how contagious conduction works in this picture?
At the axon hillock there is a high concentration of Na+
* Local current flow allows for Na+ to disperse themselves along the axon itself going to adjacent inactive areas
* Along the membrane are more sensitive sodium channels which are triggered allowing Na+ to enter the cell
In the graphs there is a continous explosive depolarization along the axon until the very end.
Once an action potential is initiated in one part of the membrane, aself perpetuating cycle is initiated. What does this mean?
The action potential itself does not travel down the entire membrane. It triggers an identical action potential in the adjacent inactive area of the membrane
What is one way propagation?
Current cannot flow backwards due to the area of the membrane that was already activated currently being in its “refractory period”
Seen in contagious conduction
When speaking of saltatory conduction what is it relevant to?
Myelinated fibres
Myelinated fibres are covered by myelin at regular intervals along the axon
* Myelin: 80% phospholipid and 20% Insulator (prevents leakage of charge)
Myelin sheaths are made by different things in the C.N.S. & the P.N.S. What are they?
- Schwann cells in the PNS make myelin sheaths
- Oligodendrocytes make myelin sheaths
Shwann cells make 1 myelin sheath per cell while Oligodendrocytes make multiple myelin sheaths for one cell
What is the name of the location where current flow can generate action potentials in between the axonal membrane?
Nodes of Ranvier
Axonal membrane has a 2 micrometre gap for every 1 mm of the axon which is exposed to the ECF and that is the node of Ranvier
How is the action potential propagated from one node of ranvier to another node?
The distance between two nodes is short enough that the electrical impulses can jump from an active node to an adjacent inactive node
Jumping of a impulse = saltatory conduction
How is the rate of conduction different for a myelinated vs unmyelinated axon?
Myelinated fibres allow for 50 times more faster conduction than if it were unmyelinated
When impulse reaches the inactive area this opens up Na+ voltage channels to allow sodium to be more permeable to the membrane
How is saltatory conduction different from contagious?
Not a continous depolarization & repolarization
Myelin determines how fast the charges move
Relationship between fibre diametre and velocity of action potentials
Larger the fibre diamtere the faster the action potential
Magnitude of charges that are in movement depends on what?
- Difference in potential between two electrically adjacent areas
- Resistance to electrical charge movement between two regions
