L8-Neurons Flashcards
What does the refractory period prevent?
The backflow of AP.
Ensures UNIDIRECTIONAL propagation of the AP. Limits the frequency of APs.
2 types of refractory periods:
absolute and relative
Why does backward current flow not re-excite previously the active area of a membrane during an action potential?
Because the previously active area is now in its refractory period. No backflow.
During which time is the particular membrane section undergoing and AP in its absolute refractory period?
The absolute refractory period lasts the entire time from opening of the voltage-gated Na+ channel’s activation gates at THRESHOLD, through closure of the inactivation gates at PEAK of AP, until the return to RESTING POTENTIAL when activation gate closes and inactivation gate opens once again.
Why is there a relative refractory period following an action potential? Aka, why is a stronger than normal stimulus required to generate a second action potential?
The relative refractory period occurs due to 2 lingering effects:
1) lingering inactivation of Na+ channels
2) slowness to close of the K+ channels
During this time, fewer than normal Na+ channels are in a position to be jolted open by a triggering event. Simultaneously, K+ is still leaving the cell in a hyperpolarization event.
Does a stronger stimulus generate a larger action potential?
No, but it does generate a greater number of action potentials
Myelination ______ the speed of conduction of action potentials
myelination INCREASES the speed of conduction of action potentials
Myelin consists primarily of ______ molecules
Lipid
Is the myelin coating an insulator or a conductor?
Insulator
Myelin-forming cells in:
a. CNS
b. PNS
a. oligodendrocytes
b. Schwann cells
Tetrodoxin and saxitoxin do what?
Tetrodoxin and saxitoxin are neural toxins which inhibit the function of voltage-gated Na+ channels and thus block APs
Dendrodoxin
Dendrodoxin is a neural toxin which inhibits voltage-gated K+ channels and thus blocks APs
3 basic parts of a neuron
a. cell body
b. dendrites
c. axon
Define “nerve”
a bundle of AXONS outside of the CNS
Define “fiber tract”
a bundle of AXONS inside the CNS
Define “axon hillock”
- Neuron’s trigger zone
- first portion of axon + region of the cell body where axon originates
3 functional classes of neurons:
- efferent neuron
- interneuron
- sensory neuron
3 structural classes of neurons
- multipolar neuron:
- single axon, multiple dendrites.
- integrates lots of information
- majority of neurons in CNS - bipolar neuron:
- 2 extensions.
- specialized sensory neurons (ex: retina nerves, vestibular nerve) - unipolar neuron:
- only has one axon or dendrite.
- common in insects.
2 methods of propagation:
- contiguous conduction
2. saltatory conduction
How does AP spread in contiguous conduction?
- AP spreads along every patch of membrane down the length of the UNMYELINATED axon.
- AP waveform triggers new APs in adjacent areas
Limitations of contiguous conduction?
- AP only affects membrane for short distances (lost through leaky channels)
- Depolarization to threshold takes time
- AP must be regenerated at each point along axon, which takes time
Where are the Na+ and K+ channels located on the axon?
Nodes of Ranvier
Does saltatory conduction occur on unmyelinated or myelinated fibres?
MYELINATED
BEESH
T/F: saltatory conduction is 50X faster than conduction on unmyeinated fibres? Why is this true/false?
True. Because myelin consists of lipids and acts as an insulator, preventing outward movement of electricity.
Which type of conduction carries the most urgent types of info?
Saltatory conduction, because it’s faster.
Why is it important to have fast nerve impulses?
- life-or-death escape from predators
- quick reaction to injury (ex: burn)
- mating dances/intricate animal behaviours
What determines speed of conduction?
- How easily electric charge can move down axon
- how well the axon can hold on to the charge to reduce recharge time
INCREASE CONDUCTION SPEED EITHER BY DECREASING INTERIOR RESISTANCE OR BY DECREASING TRANS-FIBER CAPACITANCE, OR BOTH.
Axonal gigantism effect on conduction
- resistance drops with the square of the diameter
- increases conduction speed in proportion to the squared root of the interior diameter
- easy solution, but takes up space
Myelin effect on conduction
insulation by lipid sheath INCREASES TRANSVERSE RESISTANCE and REDUCES THE TRANSVERSE CAPACITANCE of immediately adjacent internodal membrane.
ie. reduces current flowing through internodal surfaces and speeds internode charging
