Neuroanatomy L5: Peripheral nerve biomechanics Flashcards
Axonal transport relies on _______.
O2
Neurons have ____ (small/large) body (soma) and axons ha _____ lengths.
large; varying
What is a soma?
contains organelles required for cell to maintain itself
(makes macromolecules, neurotransmitter- need)
What are the glial cells of the PNS called?
schwaan cells
What are the glial cells of the CNS called?
olidendrocytes
What is anterograde transport?
cell body to axonal terminal
What is retrograde transport?
from axonal terminal to cell body
Is anterograde transport fast or slow?
Fast
How does axonal swelling occur?
if there is obstruction
What occurs in axonal swelling?
disconnect proximal from distal.
This means distal stump will degenerate
An axon is _____ (high/low) maintenance- ______ (must/does need to be) supported
high; must
What type of connective tissue is endoneurium?
Loose connective tissue proper
Is endoneurium around every axon?
Yes
What is perineurium?
Lamellated sheath enclosing funiculi
What is the function of perineurium?
Bundle axons together
What type of connective tissue is perineurium?
dense irregular CTP
What are 3 things that perineurium consists of? Why?
- Type I collagen
- Type II collagen
- elastic fibres
circular, oblique and longitudinal
What are 2 types of connective tissue in epineurium?
- interfascicular areolar connective tissue
- outer external sheath (DICTP)
What is the function of epineurium?
between adjacent fascicles or funiculi (same)- “packing”
What is the function of interfascicular areolar connective tissue in epinerium?
fill in space
What is the function of outer external sheath (DICTP) in epinerium?
outer limit of a peripheral nerve- including axon (more formed)
What is the function of the mesoneurium?
between nerve and muscle
What type of tissue is mesoneurium?
loose areolar CTP surrounding nerve
List 2 functions of why some nerve structures made of dense connective tissue proper.
- restricts unwanted movement
- provides restriction of forces or movement
List 2 functions of why some nerve structures made of loose connective tissue proper.
- allow movement between structures
- has spaces for pathway for blood vessels
(small nerve innervate larger nerve)
The structure of a nerve is constantly changing along its ______. This means that they are always _______ with the whole length of the nerve in a ______ fashion (i.e, when you section a nerve you will always find _____ (different/same) number of fascicles)
CHECK
length; interweaved; uniform; different
The size and number of fascicles are _____ (directly proportional/inversely proportional) to each other.
Inversely proportional
Less number of fascicles means that they are _____ (larger/smaller) in size
larger
More number of fascicles means that they are _____ (larger/smaller) in size
smaller
There are ____ (more/less) fascicles which are _____ (large/small) in size where a nerve crosses a joint? Why?
More; smaller
provides more flexibility (similar to collagen) but still have strength (related to CSA)
A nerve ________ (needs/does need) a good blood supply. Why?
needs
relative tortuosity of the blood vessels accommodates strains and gliding of the nerve during motion
What is the function of the vascular plexus in epineurium?
to support (wouldn’t only want one-) want multiple
What is the vascular system in endoneurium like?
longitudinal interconnected vessels
What is the extrinsic vessel in mesoneurium like? What is their function? List 2.
longitudinal vessels that are interconnected
- Acts as as a safety/back up if one of them is occluded
- Supplies nutrients
How can nerves be a source of pain?
They are innervated
What are the 2 purposes of physios knowing nerve loading techniques (i.e nerve flossing)?
- advice patients to avoid specific positions
- give exercise to move/make sure nerve keeps gliding
When do nerve injuries occur?
When the load imparted to the nervous system exceeds its tolerance to mechanical forces, then injury can occur
What are the 4 factors that the type of pathology and extent of injury depends on?
- TYPE of loading (tension, compression, shear)
- AMOUNT of load (or deformation)
- RATE of which the tissue is load (slow or rapid- viscoelastic- strain rate)
- DURATION: acute (severing or rapid stress= rupture) VS repetitive (overload –> ultimate stress limit will decrease) or chronic (pathologically affected by chronic compression to tension)
The capacity of the NS to regenerate depends on ____the injury occurs, the ____ nervous system having greater capacity to heal and regenerate than the _____ nervous system.
where; PNS; CNS
What happens first in a nerve: elongation or tension.
Elongation
The length of a nerve & its axons between 2 points on a limb is ____ (longer/shorter) than a straight line.
longer
What is “undulating” a nerve?
- waving (has some level of slack/toe-in region)
- in-built levels/areas of slack before structures of peripheral nerve undergo tension
What are 3 characteristics of “undulating” a nerve?
- nerve in its bed
- fascicles within nerve
- axons within fascicles
What happens in “initial elongation” of a nerve?
the nerve and the fascicles straighten –> perineurium 1st to resist load
What happens in “increasing elongation” of a nerve?
nerve fibres straighten –> perineurium (doesn’t fail can continue to stress), endoneurium, myelin sheath &axon resist lengthening
What is something special to note about perineurium?
- first to resist load (dense connective tissue proper)
- main component of nerve that resists tension perineurium can continue to strain (doesn’t fail) but slowly other structures start to undergo stress/strain
What is excursion?
Displacement or gliding of a nerve relative to the surrounding nerve bed
Displacement or gliding of a nerve relative to the surrounding nerve bed is called _______.
excursion
The ______ and ______ (which way and how much it moves) of nerve excursion are dependent upon the anatomical relationship between the ___ and the _______ in the moving joint. Give an example using the median and radial nerve with elbow flexion/extension.
direction; magnitude; nerve; axis of rotation
eg. elbow - flex/ext median (anteriorly to ebow jt)- tensioned in extension radial (posteriorly to elbow jt) - stack in extension
With elongation of the nerve bed, the nerve glides ____ (towards/away from) the moving joint. Give an example of a test for hip flexion.
toward
eg, single leg raise (knee, ankle and lumbar spine in neutral (extension) while lying on bed.
WIll test hip flexion) tibia and common fibula - towards hip lumboscaral - towards hip
Nerve excursion occurs _____ (first/last) in the nerve segment immediately adjacent to the moving joint. As limb movement continues, excursion occurs at nerve segments that are progressively more _____ (proximal/distal) from the moving joint. Give an example using the tibial nerve in the thigh and the leg.
first; distal
Eg. tibial nerve in thigh will move first compared with the one in the leg
The magnitude of excursion is ______(greatest/least) in the nerve segments adjacent to the moving joint and is ______(greatest/least) in the nerve segments distant from the joint.
greatest; least
When moving from 90 degrees elbow flexion to 0 degrees, what happens to the median nerve?
Median nerve in arm and forearm both move towards elbow (converge towards joint medial nerve)
When moving from 90 degrees elbow flexion to 0 degrees, what happens to the ulnar nerve?
Ulnar N glides away from elbow
When moving from wrist extension from 0° to 60° extension, what happens to the median and ulnar nerve?
both medial and ulnar nerve beds lengthen –> both nerves glides towards the wrist (because they are both anterior when in the wrist area)
Where is the most movement of nerve when moving the wrist (movement occurs closest to the joint) when comparing the forearm and arm.
In forearm
What is the elastic limit (%)for a typical tensile load-deformation diagram for a peripheral nerve (slow loading rate) in regards to typical stress/strain values?
8-20% strain
What is the ultimate failure (%) for a typical tensile load-deformation diagram for a peripheral nerve (slow loading rate) in regards to typical stress/strain values?
30% strain
Why is there an increase number in funiculi for a typical tensile load-deformation diagram for excised human peripheral nerve (slow loading rate) compared to typical stress/strain values?
if more funiculi = more perineurium = stronger = can withstand more stress
Why is it important to know the rate of loading?
Different nerve behaviour based on loading rate
Are spinal nerve roots stronger or weaker? Why? What does that mean?
Weaker perineurium absent
Failure at lower stress or strain
Modulus of elasticity varies along length of nerve. Where is it lowest? Why?
closest to the joint- doesn’t resist
What occurs before the elastic limit of a nerve?
Physiological failure occurs before elastic limit
What does the stress-relaxation curves show when nerves are being tensioned?
- If strain a peripheral nerve - still undergoes stress relaxation, especially in in first 20mins and still level off
- Still after 1 hr still (a lot of) 60% of original tension remains in the nerve
What do the peak nerve conduction velocity show when nerves are being tensioned? (group A at 8.9% and group B at 16.1%). Be specific with group A and B.
Group A: can return to function (Function of group A wasn’t decreased due to the strain)
Group B: can’t return to normal function. Function of group B was decrease due to the strain –> impairment of function. Significant deficit in nerve conduction velocity (function of axons). Past the elastic limit, Damage to structures with the nerve. This means the elastic limit (where axonal damage/ axons had impaired function occurs is >8.8% and definitely at 16%
What do the nerve blood flow show when nerves are being tensioned? (group A at 8.9% and group B at 16.1%). Once the traction has been removed, what happens to group A and B.
When traction a nerve, will decrease blood flow but there was no significant difference between Group A and B.
Decrease blood flow is not the only reasoning for decrease in nerve conduction
Group A: recovered
Group B: did not recover
When a nerve is lengthened, what happens to the diameter? Where does narrowing occur most?
decrease diameter
narrowing occurs in the middle
How does lengthening a nerve (decreasing diameter) affect the nerve? List 2 effects.
- increases intra-axonal pressure and this affects axonal transport mechanism
- Impaired blood flow (increase pressure inside nerve- blood needs pressure gradient- if increase inside higher than venous - no blood flow
What is the the theory of nerve pathology in regards to tension and compression?
if subject a nerve to more tension/compression (chronic or acute) will impede blood flow and axonal transport mechanism
A nerve retains its elastic properties until the ____ fails but usually the rupture of axons _____ rupture of the perineurium
perineurium; precedes
Nerve –> ______ –> axon
fascicle
Axons (can only withstand 4% before fail) - usually fail before the _____. What does that mean for the nerve?
perineurium
Can have a nerve that looks intact but the axons and as a result the function is impaired
The relative amounts of _______ and ______ tissue varies within a nerve,
fascicular; epineurial
What is epineural tissue?
minimize compression on tissue inter-fascicular- bulk packing
In general, fascicular contribution to ______% to ____ %cross-sectional area
30-70%
Forces are imposed on the _____ component of the nerve
main
What is the function of increased epineural tissue?
Increase epineurial tissue acts a s a shock absorber - more epineurial tissue in area that need more shock absorption or protection
Chronic loading of neural tissue can also result in_______. What type of force is this often due to? Give 2 examples of these forces of anatomical structures.
neural damage 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
The likely that the injury mechanism for nerve damage is a mixture of _______ and ______due to a compromised blood supply to the tissue.
mechanical compression; ischemia
What is the function of the axonal transport system?
decrease congestion and pressure inside axon
What is the pathophysiology associated with the development of musculoskeletal peripheral neuropathic pain?
What are the 8 factors that increase pressure in the confines space (in perineurium), which causes impairment of impulse conduction related to amount of intraneural oedema & myelin changes?
- Inflammatory response
- Immune cell activation
- Intraneural oedema
- Further of venous congestion
- Further impairment of axoplasmic flow
- Fibroblast proliferation & fibrosis
- Progressive demyelination
- Axonal degeneration
What is neurodynamics?
Nerve elongation & nerve excursion techniques
What is the purpose of neurodynamics?
a dynamic variation in intraneural pressure when correctly applied may facilitate evacuation of intraneural oedema and reduce symptoms
What is the benefit of nerve gliding exercises?
nerve gliding exercises may also limit fibroblastic activity and minimise scar formation via normal and early use of mesoneurial gliding tissues
What are 2 systemic factors which increase predisposition to a nerve pathology?
- Diabetes
- increase collagen
- increase CSA
- (compromised more easily when goes through tunnel (esp. tarsal tunnel))
- Thyroid disease
What are 5 non-systemic factors which increase predisposition to a nerve pathology?
presence of a nerve disorder is a predisposition for the development of a secondary nerve disorder in the same quadrant “double crush phenomena”
- Axonal transport
- Altered ion channels
- Neuroinflammation
- Central sensitisation
- Altered neural biomechanics
What are the 5 types of Seddon’s and Sunderland’s classification systems of the pathoanatomy of nerve injury?
What is type 1 nerve injury?
Neuropraxia
Temporary conduction block (shock- usually recovers within 1-3 weeks - no physical disruption)
What is type 2 nerve injury?
Axonotmesis
- severing axons fail first (ruptured) but connective tissue tunnels are still intact (
- endoneurial tube, perineurium and epineurium intact
What is type 3 nerve injury?
Axonotmesis + endoneurial tube destroyed
- (perineurium and epineurium intact)
What is type 4 nerve injury?
- Axonotmesis + endoneurial tube & fascicle destroyed
- Fibrosis
- (epineurium intact)
- sensory and motor nerves intermingling- not going to target
What is type 5 nerve injury?
Neurotmesis
- Complete transection of nerve
If connective tissue is still intact during nerve injury, axon can ____ and is guided by _______ to reach correct/target organ
sprout; intact tunnel
While there are 5 types of nerve injuries, clinically, utility- most peripheral nerve injuries are _____.
mixed
Following axonal transection (severed and interrupted axonal transport), whole neuron goes into a different way of functioning- looks different as well. What are 5 changes?
- Cell body swells, nucleus moves peripherally = change in metabolic priority from production of neurotransmitters to production of structural materials needed for axon repair and growth
- Degeneration of proximal axon (swelling in distal part of proximal stump)
- Wallerian degeneration (distal stump) starts within 2-4 days of injury
- Schwann cells detach from axons, proliferate & clear cellular & myelin debris (become like macrophages)
- Schwann cells align longitudinally & express stimulating factors to direct nerve regrowth toward target organ. (form new tunnel to guide to target organ)
Following axonal transection (severed and interrupted axonal transport), the cell body ____ (swells/shrinks), nucleus moves ______ (axially/peripherally). This means there is a change in______ priority from production of neurotransmitters to production of structural materials needed for axon ____ and ___.
swells; peripherally; metabolic; repair; growth
Following axonal transection (severed and interrupted axonal transport), there is degeneration of the ________ (proximal/distal) axon (swelling in ___ (proximal/distal) part of proximal stump)
proximal; distal
Following axonal transection (severed and interrupted axonal transport), ______ degeneration (distal stump) starts within 2-4 days of injury
Wallerian
Following axonal transection (severed and interrupted axonal transport), schwann cells detach from ______, proliferate & clear cellular & myelin _____ (become like ______)
axons; debris; macrophages
Following axonal transection (severed and interrupted axonal transport), schwann cells align ____ & express stimulating factors to direct nerve regrowth toward target organ. (form new ___ to guide to target organ)
longitudinally; tunnel
What is the primary repair of nerve transections called?
neurorrhaphy
What are the 2 types of primary repair of nerve transection?
- Epineurial repair
- Fascicular repair
What is Epineurial repair?
bring the outer external sheath together
What is Fascicular repair?
grab perineurium and attach together
When is nerve grafting used?
when primary repair cannot be performed without undue tension.
- if the segments are too far away (distance is too far- and tension)- nerves can’t withstand tension
What is Autografting?
take another sensory cutaneous nerve and interpose it
What are the 4 types of autografts?
- sural N
- medial antebrachial cut
- lateral fem cutaneous
- superficial radial N
What is the rehab process for an autograft? When can full function be returned?
graft repair site & graft itself regain the same tensile strength as the native nerve by 4 wks (limb immobilised during this period to protect the graft)
What is allografting?
from animals
What are synthetic tubes used for?
guide regrowth
What are the 3 types of nerve grafting?
- Autografts
- Allografts
- Synthetic tubes
What are the 3 preoperative goals in a denervated extremity?
- Protection & maintainenance of range of motion
- Bandaging, splinting, ROM exercises to prevent contractures & deformity, support joints, limit oedema, maintain blood and lymphatic flow and prevent tendon adherence.
- Direct muscle stimulation to reduce muscle atrophy / psychological benefit
What are the 3 postoperative goals in a denervated extremity?
- Early-phase sensory re-education decreases mislocalisation and hypersensitivity and reorganises tactile submodalities, such as pressure and vibration.
- Hydrotherapy can be helpful to improve joint contractures and eliminate the effects of gravity during initial motor recovery, thereby enhancing muscular performance.
- Biofeedback may provide sensory input to facilitate motor reeducation.
What is the main pre-operative goals in a denervated extremity?
decrease stress on areas and support joint, muscles, tissues around injury
What is the main post-operative goals in a denervated extremity?
stimulate and re-direct the nerve regrowth towards correct organ (biofeedback electrical stimulation can stimulate nerve growth and sensory and motor repair and maintain muscles with electrical stimulation, hydrotherapy etc)
Electrical stimulation ______ (increases/decreases) sensory & motor neuron regeneration
increases
Based on an experiment, re-innervation of thenar muscles post carpal tunnel release happened in half the time when using ________ compared to the controlled healing
electrical stimulation
What is Tinel’s sign?
A positive tingling sign in response to mechanical stimulation indicates that some regeneration is occurring
How to test for Tinel’s sign?
mechanosensitive- tap
postive sign- tingling
The most important clinical information is ____________ of the sign seen with frequent evaluation of the patient. How is this information found?
progression able to monitor the progression and know where the nerve travels
What does a positive Tinel’s sign that is progressing signify?
Regenerating nerves are able to pass the lesion
What does a positive Tinel’s sign that is static at the site of the injury signify?
site of injury indicates the presence of a neuroma (forming a clump) and the need for exploration
In cases of nerve lesions with large anatomical gaps that had a positive tingling sign, a Tinel sign could not be elicited ______ (proximal/distal) to the site of injury.
distal
