Physiology Unit 2 Action Potentials and Myelination

How does depolarization occur in terms of location?

it is highly localized

What diffuses down the axon during depolarization?

Na+ and positive charges

What does highly localized depolarization allow for?

propagation of depolarization

What is the all or nothing response?

once the threshold potential (-55mV) is released an action potential is triggered

What is the amplitude of all action potentials?

100mV

What does a stronger stimulus increase?

frequency of action potentials and number of axons stimulated

What is the absolute refractory period?

the time following an action potential when the membrane cannot respond to another stimulus

What conformation are Na+ channels in during the absolute refractory period?

inactive conformation

What does the absolute refractory period prevent?

retrograde propagation of action potential

How long is the absolute refractory period in large axons?

0.4 msec

How many impulses can a large axon go conduct per second?

1000

How long is the absolute refractory period in small axons?

about 4 msec

How many impulses can small axons conduct per second?

250

What is the time period of transition to resting state following the absolute refractory period called?

relative refractory period

What are the conformations of Na and K ion channels during the relative refractory period?

K+ channels are still open and some Na+ channels are open while some are still inactivated

During the relative refractory period how can a new action potential be conducted?

it must overcome only some Na+ channels being open while K+ channels are still open and reach the depolarization threshold

Is ion diffusion alone sufficient to conduct a signal?

no

What is the progressive loss of signal amplitude called?

decrement

What allows diffusion 1-2mm and where is it located and not located?

cable properties and located in dendrites but not axons

What allows axons to conduct an impulse?

propagation

What kind of feedback loop is axon to axon propagation?

positive feedback loop

What will increase the speed of signal during propagation?

a thicker and warmer axon

What covers every PNS axon?

neurilemma

What is the neurilemma formed of?

nucleus and cytoplasm of schwann cells

Is the neurilemma myelination?

no

Increased myelination contributes to increased what?

fine motor control

One schwann cell wraps around how much of an axon?

1mm

Is there neurilemma in the CNS?

no

Nodes of Ranvier are highly concentrated what channels?

Na+

How far apart are the nodes of Ranvier?

1-2mm

What percent of energy do action potentials use in the CNS?

47%

Are A and B fibers myelinated or unmyelinated?

myelinated

What are the characteristics of A fibers?

5-20 micrometer diameter, 12-130m/sec conduction speed, sensory neurons, skeletal motor neurons

What are B fiber characteristics?

2-3 micrometer diameter, up to 15m/sec conduction speed, longer absolute refractory period than A fibers, afferent sensory neurons, autonomic preganglionic motor neurons

What are C fiber characteristics?

0.5-1.5 micrometer diameter, 0.5-2m/sec conduction speed, longest absolute refractory period, sensory neurons, autonomic postganglionic motor neurons

Does nerve regeneration occur more in the PNS or CNS?

PNS

What promotes nerve regeneration in PNS?

neurilemma

What can happen if nerves regenerate in the CNS?

misalignment