Lecture 5 Flashcards
The axon allows for
Conduction
APs created in axon hillock will travel down the
Axon to reach the muscle cell
How are axons in vertebrate motor neurons?
Long
What are the special structures found in axons that allow for AP conduction over long distances?
- Myelin Sheath
- Saltatory Conduction
What is Myelin?
Fatty substance that wraps in a spiral pattern around axon
Myelin Sheath is secreted by
Schwann cells
Myelin Sheath allows for
Faster conduction compared to non-myelinated axons
What happens during Saltatory Conduction?
New APs are repeatedly created down the length of the axon at the Nodes of Ranvier
Saltatory Conduction prevents the
Continuous movement along myelinated axon
Formation of new APs during Saltatory Conduction is formed due to
The voltage-gated K+ and Na+ channels that open when AP arrives in the nodes of ranvier
End of axon branches into several terminals which are enlarged at each end to form a
Synapse
Where is the electrical signal (or AP) converted into a chemical signal?
At the synapse
What happens once electrical signal is converted?
There is a release of a neurotransmitter
When the AP reaches the synapse, it causes for
Voltage-gated Calcium channels to open
The increase of Ca2+ inside the cell results in
The release of neurotransmitters (or acetylcholine) via exocytosis
When acetylcholine is released, it binds to
Specific receptors on the cell membranes of muscles
Which animals produce myelin?
Vertebrates
What kind of axons do invertebrates have?
Larger diameter axons
APs travel fastest along axons with
Large diameters or axons wrapped in myelin
Conduction speed along an axon (current) is greatest when
- Voltage is high
- Resistance in low
What is the function of the myelin sheath?
It creates regions of high resistance surrounding regions of lower resistance
Large diameter axons also reduce resistance since
Less of the axon’s SA is exposed to the cell membrane (preventing the slow down of AP)
Squids move via jet propulsion, which requires
Large diameter axons
Very large diameter axons function to activate muscles at the
Far end of the squid’s mantle
Smallest diameter axons function to activate muscles in the
Squid’s mantle closest to CNS
