Peripheral nerves

Question 1

Axonal transport

Answer 1

relies on O2

neurons are post - mitotic ! = when lesioned, can’t be replaced therefore need to maintain themselves and renew themselves throughout life

Question 2

nerve structure

Answer 2

Endoneurium = loose CTP
Perineurium = lamellated sheath enclosing funiculi
dense irregular CTP
Type I & II collagen + elastic fibres – circular, oblique & longitudinal Epineurium = i) interfascicular areolar connective tissue
ii) outer external sheath (DICTP)
Mesoneurium = loose areolar CTP surrounding nerve

Question 3

functions of nerve Loose CTP

Answer 3

Loose CTP = allows mvmt btwn structures and has spaces to allow spaces for blood vessels

Question 4

nerve structure 2

Answer 4

The structure of a nerve is constantly changing along its length
more and smaller fascicle where nerve crosses joint

Question 5

Anastomotic network of blood vessels

Answer 5

Vascular plexus in epineurium
Vascular system in endoneurium
Vascular system in perineurium
Extrinsic vessel In mesoneurium

Question 6

Nerve response to loading

Answer 6

Impaired nerve biomechanics is associated with compromised nerve function

“physical therapists who understand the adaptive responses of nerves to specific physical stresses will be better prepared to provide reasoned interventions to modify specific aspects of the stresses.”

Question 7

Nerve injury

Answer 7

When the load imparted to the nervous system exceeds its tolerance to mechanical forces, then injury can occur.

The capacity of the NS to regenerate depends on where the injury occurs, the PNS having greater capacity to heal and regenerate than the CNS.

Question 8

The type of pathology and extent of injury depends on the

Answer 8

The type of pathology and extent of injury depends on the
Type of loading (tension, compression, shear)
Amount of loaf (or deformation)
rate at which the tissue is loaded
duration: acute versus repetitive or chronic

Question 9

First elongation then tension

Answer 9

The length of a nerve & its axons between 2 points on a limb is longer than a straight line
Undulating
• nerve in its bed
• fascicles within nerve 
• axons within fascicles

initial elongation…
the nerve and the fascicles straighten > perineurium 1st to resist load increasing elongation…
nerve fibres straighten
> perineurium, endoneurium, myelin sheath & axon resist lengthening

Question 10

perineurium

Answer 10

main component of peripheral nerve that will resist tension

Question 11

excursion

Answer 11

Displacement or gliding of a nerve relative to the surrounding nerve bed is called excursion

• The direction and magnitude of nerve excursion are dependent upon the anatomical relationship between the nerve and the axis of rotation in the moving joint.
• With elongation of the nerve bed, the nerve glides toward the moving joint.
• Nerve excursion occurs first in the nerve segment immediately adjacent to the moving joint. As limb movement continues, excursion occurs at nerve segments that are progressively more distant from the moving joint.
• Similarly, the magnitude of excursion is greatest in the nerve segments adjacent to the moving joint and is least in the nerve segments distant from the joint.

Question 12

Move from 90˚ elbow flexion to 0˚

Answer 12

Ulnar N glides away from elbow

radial towards

Question 13

Wrist extension from 0° to 60° E

Answer 13

tensioning both, both move towards wrist

Question 14

Typical tensile load-deformation diagram

for excised human peripheral nerve:

Answer 14

Typical stress-strain values:
• Elastic limit 8-20% strain
• Ultimate failure by 30% strain
• Maximum tensile stress (of nerve cross-section) 0.5 – 3.0 MPa
• Maximum tensile stress (of funicular area) 1.7 – 6.2 MPa
• Increase # of funiculi > increased amount of perineurium > increase stress resistance
• Spinal nerve roots (perineurium absent)
• Modulus of elasticity varies along length of nerve
• Physiological failure occurs before elastic limit

Question 15

Stress-relaxation curves

Answer 15

Group A 8.8% strain Group B 16.1% strain

lower relaxation values in group B after 1 hr

Question 16

Peak nerve conduction velocity

Answer 16

Group A 8.8% strain Group B 16.1% strain

B - b - decrease nerve contraction and didn’t recover

Question 17

Nerve blood flow:

Answer 17

Decreasedby ~70%duringtraction

rapid increase in A at release of traction

Question 18

Physical stress on nerves

Answer 18

physical stress placed on peripheral nerve > tensile stress applied longitudinally to peripheral nerve creates an elongation of the nerve (an increase in strain). The transverse contraction that occurs during this elongation is greatest at the muddle of the section undergoing tensile stress.

Question 19

rupture of axons

Answer 19

A nerve retains its elastic properties until the perineurium fails BUT…
The rupture of axons precedes rupture of the perineurium

Question 20

Compression

Answer 20

The relative amounts of fascicular & epineurial tissue varies
• In general, fascicular contribution to cross-sectional area = 30-70%
• Sciatic nerve in gluteal region = 20-30%

Question 21

Chronic loading of neural tissue can also result in neural damage:

Answer 21

• often due to compression of the neural tissue.
• e.g. compression of spinal nerve roots in degenerative spinal disorders,
• e.g. compression loading of the median nerve in the wrist in carpal tunnel syndrome.
• likely that the injury mechanism is a mixture of mechanical
compression and ischemia due to a compromised blood supply to the tissue.