Lecture 3 Flashcards
Depolarization due to action potentials decay rapidly as a distance from stimulus…
Increases
Are single action potentials usually sufficient to carry information along a neuron?
Nah
Why is it important that action potentials are propagation?
- initial AP starts a new AP in adjacent membrane
- each new AP is full strength and follows the same step
- allows for full strength APs to travel the full length of the neuron
What is conduction velocity?
Speed at which APs are conducted away from initiation site
What does conduction velocity depend on?
The time and length constants
What is the time constant?
How fast membrane can depolarize to 63% of max AP voltage.
What is the length constant?
How far depolarization travels before falling below 63% of max
What does the time constant depend on?
- Depends on the number of channels
- depends on how well the membrane holds a charge
What happens to the membrane resistance when there are more open channels?
-lower resistance, more ion flow, faster depolarization
What happens to the membrane capacitance when there is less charge in the membrane?
-more transferred ions inside, faster depolarization
For a smaller time constant, what would you want?
- more open channels
- less charge in the membrane
How a longer length constant, what do you want?
- high resistance, less open channels, fewer ions leaking out
- more cytoplasm than membrane
What is the length constant dependent on
?
- open channels
- internal resistance
Can thick or thin nerves conduct impulses quicker>
THICK
Increasing the diameter lowers the internal resistance which results in what?
Faster conduction
-higher length constant means faster conduction
What combination of time and length constants would result in most rapid conduction?
Low time constant and high length constant
What is it called when action potentials jump between the nodes of ranvier?
Saltatory conduction
Why is saltatory conduction a thing?
- myelin doesn’t allow any ion flux at that part which increases membrane resistance and increases the length constant
- the ions then focus on the nodes which decreases the nodes membrane resistance and decreases the time constant
- basically shortens the nerve
What kind of nerve is likely to be the most heavily myelinated?
Motor
MS is a demyelination disease that attacks which nervous system?
The central nervous system!!!!
What does a loss of myelin do to the length constant?
It decreases the length constant, so APs might not be propagated
Electrical synapses are what kind of junctions?
Gap junctionssss
What is an electrical synapse?
Direct connections between cells which allows ions to flow between
Where would you find electrical synapses?
Heart, smooth muscle, bladder, places where you need coordinated contraction
What are the advantages and disadvantages of electrical synapses?
They are fast, but they do not allow for any integrations from other sources.
-it can travel in both directions
What is a chemical synapse?
Information is transported via chemicals across the synaptic cleft
What are the advantages and disadvantages of chemical synapses?
-slow, but allow for integration
What are the four steps of synaptic transmission?
- propagation of AP
- release of neurotransmitter
- binding of neurotransmitter to receptors
- effect on post-synaptic cell
What signals the release of neurotransmitters?
-when AP reaches the terminal, voltage gated calcium channels open. Calcium entering causes the release of NT
If the neurotransmitters depolarize the post synaptic cell, what kind of response is it? What ions are responsible for this?
-excitatory! Sodium and calcium!
If the neurotransmitters hyperpolarize the post synaptic cell, what kind of response is that? What things do this?
Inhibitory! Open potassium channel. Close chloride channel
Describe the neuromuscular junction
- AP opens voltage gated calcium channel
- calcium causes release of acetylcholine
- acetylcholine binds to post-synaptic cell
- the nicotine can receptors are essentially sodium channels which depolarize the cell and cause muscle constriction
What enzyme breaks down acetylcholine? And what does it break it down into?
Acetylcholine esterase
-breaks it down into choline and acetate
What does botulinum toxin do?
Blocks the release of acetylcholine
What does curare do?
- arrow poisons
- blocks acetylcholine receptors
What does Neostigmine do?
Acetylcholine esterase inhibitor
-increases contractions
What does hemicholinium so?
Blocks choline reabsorption
-so no acetylcholine
What are the uses of hemicholinium?
- irreversible disruption of NMJ
- chemical warfare
- nerve gas
- pesticide
