In which type of nerve fibers is conduction blocked maximally by pressure:
A. C
B. A-alpha
C. A-beta
D. A-gamma
A. C
B. A-alpha
C. A-beta
D. A-gamma
Ans. C. A-beta
A fiber is most susceptible to
pressure; A gamma conducts touch and pressure
Susceptibility of Different
Types of Fibers to Conduction Block by Various Agents
|
Effect
|
Most susceptible
|
Intermediate
|
Least susceptible
|
|
Block by hypoxia
|
B
|
A
|
C
|
|
Block by pressure
|
A
|
B
|
C
|
|
Block by local
anesthetics
|
C
|
B
|
A
|
Two Systems for Classifying
Axons in Peripheral Nerve by Diameter Letter System
|
Type of fiber
|
Diameter, micrometers
|
Conduction velocity,
m/sec
|
General Function
|
|
A-alpha
|
13-22
|
70-120
|
alpha-motoneurons, muscle
spindle primary endings, Golgi tendon organs, touch
|
|
A-beta
|
8-13
|
40-70
|
touch, kinesthesia,
muscle spindle secondary endings
|
|
A-gamma
|
4-8
|
15-40
|
touch, pressure,
gamma-motoneurons
|
|
A-delta
|
1-4
|
5-15
|
pain, crude touch,
pressure, temperature
|
|
B
|
1-3
|
3-14
|
preganglionic autonomic
|
|
C
|
0.1-1
|
0.2-2
|
pain, touch, pressure,
temperature, postganglionic autonomic
|
