Unit 5 Lecture 36 Flashcards
Define propagation
The process by which an action potential spreads throughout the length of an axon to the axon terminal
What is the 1st step of action potential propagation?
Na+ enters the membrane -> local (+) current inside cell
How do currents spread during propagation?
ELECTRIC currents spread LATERALLY to depolarize adjacent membranes
What effect does an increase of Na+ into the cell have on the membrane potential difference?
Depolarizes the membrane
Explain continuous conduction
Na+ makes a (+) current -> depolarizes nearby membrane -> that new membrane reaches threshold and starts an AP -> Na+ makes a current in this new region -> depolarizes 3rd membrane -> AP -> Keeps going
How does Na+ get through the membrane?
There was an initial local depolarization that opened voltage gated Na+ channels
What is important about continuous conduction?
Axons do NOT have myelin sheaths
What two factors effect the SPEED of propagation?
- Size of axon
2. Myelination
What is true about the size of an axon during propagation?
The BIGGER the axon diameter, the FASTER the current flow
Why are bigger axons faster in propagating currents?
Resistance of current flow decreases as the size of the axon increases
What is true about myelination during propagation?
Having myelin sheaths makes current flow FASTER bc Na+ channels open at each node
What is myelin sheaths?
An insulating layer (sheath) around axons in the CNS and PNS
What makes myelin sheaths?
Olgiodendrocytes in CNS
Schwann Cells in PNS
Explain saltatory conduction
Na+ channels open at node of ranvier -> depolarizes adjacent node -> opens that node -> depolarizes 3rd node -> keeps going
What are the differences between continuous conduction and saltatory conduction?
Continuous = NO myelin sheaths -> slower propagation
Saltatory = myelin sheaths -> faster propagation
What are demyelination diseases?
Diseases which damages the myelin sheath of an axon in the central NS or peripheral NS
Name two examples of demyelination diseases
Multiple sclerosis in CNS
Guillan-Barre in PNS
How is an electrical signal (AP) transmitted from one excitable cell to another?
Synaptic Transmission
Describe the basis of synaptic transmission
Same basic events that occur during neuromuscular transmission w/ a synapse
Describe the events of synaptic transmission
- Nerve impulse opens voltage gated Ca2+ channels and Ca2+ comes in
- Ca2+ causes synaptic vesicles to bond w/ presynaptic terminal and releases neurotransmitter into the synapse
- Neurotransmitters bind to proteins (receptors) on postsynaptic terminal which open Ligand-gated channels
- EPSPs or IPSPs
What are the two post-synaptic graded potentials?
- Excitatory Post-Synaptic Potential (EPSP)
2. Inhibitory Post-Synaptic Potential (IPSP)
Define excitatory post-synaptic potential
Depolarizes (if Na+ enters)
*Increase the likelihood of post-synaptic AP occurring
Define inhibitory post-synaptic potential
Hyperpolarizes (if K+ leaves or Cl- enters)
*Decreases the likelihood of post-synaptic AP occurring
What happens at the trigger zone of an axon?
Generates AP depending on the net summation of EPSPs and IPSPs
Define spatial summation
- Many pre-synaptic neurons connect to one post-synaptic neuron
- Signals from many pre-synaptic neurons add up at the trigger zone
Define temporal summation
- 1 pre-synaptic neuron connects to 1 post-synaptic neuron
- There is an increased repetition of AP from 1 pre-synaptic neuron
