Exam 2: Myelin & Synapses Flashcards
What is the name of the “insulation” that is found on neurons?
Myelin sheath
What is myelin derived from?
Sphingomyelin in the cell wall
What type of cells create myelin?
Glial cells = supporting cells in the nervous system
Specific Examples:
CNS: Oligodendrocytes
PNS: Schwann Cells
T/F Myelin slows down action potentials
False
Explain how Schwann cells work
Schwann cells grow and wrap themselves in a spiral around a neuron. Each layer that is wrapped around becomes increasingly compact with water being squeezed out more and more. Water becomes fully pushed out of the cell and it becomes a good insulator. You are left with a lipid compound that provides protection, speed, and efficiency.
How do signals move when there is a myelin sheath present?
Signals “jump” in steps underneath the myelin sheath
What are the openings between myelination called?
Nodes
What do nodes contain?
Fast Na+ channels
If you want to block myelinated neurons in anesthesia, what do you need to do?
Give more anesthetic to block all of the dense sodium channels found within the nodes
T/F Having more sodium channels at the nodes means that the cell has an overall higher amount of sodium channels than cells without nodes.
False; Just because you have a dense amount of sodium channels at the nodes does not mean you have more sodium channels overall
What is saltatory conduction?
Movement of the action potential from one node to the next
What does the myelin coating make the nerve more resistant to?
Crush injuries
T/F When we lose myelination within our CNS it is difficult to replace
True
What happens when we lose myelin in our optic nerve?
Our vision becomes cloudy, delayed, and we might lose peripheral vision
What are 3 examples of demyelinating diseases?
- MS
- Optic Neuritits
- Guillain-Barre Syndrome
What causes demyelinating diseases?
Genetics
Infection
Autoimmune hyperreactivity
Polyneuropathies
What is something easy to repopulate in cell walls?
Na/K pumps
What happens if there are fast sodium channels further down the line with only a long stretch of sodium-potassium pumps?
Sodium will be pumped out of the cell and there won’t be any to continue to the next node and continue signaling correctly
What is it called when one cell wants to talk to another?
Synapse
Where do direct electrical synapses occur?
Gap junctions
What is a connexon and what is it comprised of?
A connexon is a conduit that allows for ionic current to pass from one cell to another; A connexion is comprised of 6 connexin proteins and bound to the connexon in an adjacent pair
What can move through gap junctions?
Small ions via simple diffusion (Na; Ca can also move but it is larger and clunky so it doesn’t fit as well as Na)
Are electrical synapses fast or slow overall? In the heart?
Overall they can be very fast; the heart purposefully has a lower number of gap junctions in very specific places to purposefully slow down
What are chemical synapses?
Electrical signals that are related cell to cell via a chemical intermediary
