exam 3- nervous system 2 Flashcards
what is a nerve called when it has varying diameters
nerve made of many nerve cells of varying axon diameters- so the nerve is called a mixed nerve or a compound nerve (b/c mixed size)
each individual axon is wrapped with connective tissue called ___
groups of axons bundled and held together by another
set of internal connective tissue called ___
entire nerve held by…
endoneurium
perineurium
outer connective tissue called epineurium
describe the 2 AP properties that depend on axon diamater
1- threshold voltage directly proportional to axon diameter- small diameter gives AP, large diameter gives passive local response at certain voltage
2- AP velocity/propagation directly proportional to axon diameter- larger diameter –> easier it is to depolarize membrane b/c longitudinal distance
describe graphs of relationship b/w AP velocity and axon diameter
of vertebrate myelinated neuron: linear- larger diameter = faster AP
myelinated vs. unmyelinated:
unmyelinated- axon diameter range is much larger (goes up to 1000 micrometers) –> even with largest diameter, AP velocity is relatively slow (25 m/s)
myelinated- unmyelianted axon diameter is 50 times larger than the myelinated axon in vertebrates, however much slower (shows great advantage of myelin- speeds AP velocity, allows individual neurons to be smaller, and allows more neurons to be packed in NS
describe initial experiment done to classify neurons in certain groups
axons of diff diameters- put stimulator on one end and put recording and reference electrodes on surface of nerve –> give max stimulus so all neurons are firing and recording/reference electrodes record the sum of all the AP’s given by all the individual neurons
giving stimulus creates large depolarization (sum of all individual neuron APs)- large polarity across membrane surface- wave of depolarization moves down the nerve
- wave of neg charge first hits the recording electrode and causes voltmeter to swing negative (when voltmeter swings neg, causes upward change in polarity/membrane potential)
- AP/wave of neg charge is now in middle b/w recording and reference electrodes (area of membrane behind AP where recording electrode is is now back at rest)
- AP now reaches the reference elctrode (area around reference electrode is neg, area at recording is at rest, positive)- change in membrane potential swings back down to positive direction
–> compound, diphasic compound AP
what is a compound AP? in the first experiment
compound AP- reading the sum of all the APs generated by neurons, but doing this by reading the change in potential at the surface of the nerve
2 phases: initial upward neg phase and then downward pos phase (first hitting recording electrode and then reference electrode) –> b/c of this, called diphasic compound AP (dcAP)
to eliminate the second downward curve, crush the nerve in b/w recording and reference electrodes- prevents AP from being propagated past that point
–> eliminated second phase, so created a monophasic compound AP (MCAP)
what ppl studied to classify groups of neurons
area under MCAP is proportional to…
explain
this is the basis for…
the number of individual neurons firing
- first low curve shows a very low stimulus intensity that only activates the smallest diameter neurons, lowest threshold voltage
- increase stimulus intensity –> pass threshold of larger diameter neurons –> area under the curve gets bigger
- reach max stimulus intensity –> pass threshold of all neurons –> peak AP reaches max (area under curve represents all neurons firing)
this is the basis for motor unit summation
describe experiment where max stimulus is given and AP’s that result over distance
max stimulus and record 15 mm away from stimulator –> one large AP
max stimulus and record 30 mm away –> get AP that has a shoulder on it (looks like 1 AP starting to separate into 2)
record 100 mm away –> almost 3 APs (separating into 3 peaks)
record 150 mm away –> first initial AP now has separated into 5 separate APs
in the graph that shows the 5 AP peaks from a max stimulus over 150 mm of distance, describe what the 5 APs each represent
the 5 APs represent the 5 classes of neurons based off diameter and conduction velocity
(largest diameter neurons conduct APs at fastest velocity)
1st AP represents largest diameter neurons (at fastest velocity, so reach recording electrode first)
2nd peak comes off the first, represents class of neurons w/ second largest diameter (2nd fastest)
3rd peak represents 3rd largest
4th peak = 4th largest and fastest
5th…
why don’t you see the separation of 5 AP peaks at 15 mm away?
the classes of neurons haven’t had time to separate yet
name the 5 classes of neurons and the name of the classification system
Erlanger and Gasser classification
A-alpha
A-beta
A-gamma
B
C
over time, the classification of neurons have also come to be classified by…
some of the neurons (especially sensory neurons) have also come to be classified by numbers (class I, II, III, IV)
type A and B (A-alpha, beta, gamma & B) are ___ fibers
myelinated
type C neurons, even among ___, are ___ fibers
vertebrates
unmyelinated (naked axons)
which class of neurons has the largest diameter
A-alpha
