Peripheral Nerves Flashcards
What are the layers of a peripheral nerve (3)
- Endoneurium
- Perineurium
- Epineurium
What is the endoneurium
CT that surrounds axons schwann cells and other endoneurial components
What is the perineurium
Dense CT that forms the fascicles
How many layers thick is the perineurium
Up to 15 layers
What is the perineurium made of
Type I and II collagen
What is the epineurium
CT that surrounds nerve fascicles
What are the 2 parts of the epineurium
- Epifasicular
2. Interfascicular
What is the epifasicular
Surrounds the entire nerve (outer layer)
What is the interfascicular
Separates the nerve fascicles
How is the perineurium attached to the epineurium
Loosely attached
What does the perineurium being loosely attached to the epineurium allow for
Sliding to occur between fascicles
True or False:
There are arteries in nerves
True
What happens to the nerve at places where it spilts
The nerve becomes stiff and may not slide well
What does movement of the nervous system do (3)
- Prompts the flow of blood throughout the nerve
- Prompts removal of waste
- Stimulates axoplasmic flow in the axon
What are the 2 types of axoplasmic flow in an axon
- Anterograde
2. Retrograde
Do the capillaries in the nerves have smooth muscle
No
What does the capillaries not having smooth muscle require
The nerve needs to be moved to pump blood throughout the nerves
Are there lymphatics in nerves
No
What does not having lymphatics in nerves make it hard to do
Get rid of swelling
What is the direction and magnitude of nerve excursion dependent upon
The relationship between the nerve and the axis of rotation in the moving joint
Where does nerve excursion first occur
The site immediately adjacent to the moving joint
What is convergence
Nerve tissue is moving toward the joint causing motion
What is divergence
Nerve tissue moving away from the joint causing motion
When does convergence occur
When the nerve is tensioned at the joint moving
When does divergence occur
When the nerve is slackened at the joint moving
Going from wrist flexion to wrist extension what occurs to the median and ulnar nerves
They are both tensioned so convergence occurs
Going from elbow flexion to elbow extension what occurs to the median and ulnar nerves
Median nerve is tensioned so convergence occurs
Ulnar nerve is slackened so diverengce occurs
True or False:
Nerves try to move back to the resting position of the nerve
True
Are myelin and CT able to stretch and fold
Yes’m
True or False:
Nerves are a lot of CT with small amounts of fascicles within them
True
Where is it apparent that nerves are full of CT and small amounts of fascicles
The cubital tunnel
What does tensile stress lead to in nerves
Elongation of the nerve (strain)
What occurs to the nerve in addition to the elongation
Transverse contraction in the center of the nerve occurs
What does the transverse contraction result in
Increased intraneural pressure
What does the amount of strain placed on the nerve depend on
Its relationship to the axis of rotation in the moving joint
Where does the most movement and strain occur during movement
At the joint moving
True or False:
Sliders put limited to no strain on the nerve
True
True or False:
Tensioners put more strain on the nerve
True
What does a steep slope on the stress strain curve indicate
That the tissue isn’t very compliant
What amount of repetitive strain can nerves tolerate
6-8%
When do you start to see damage in a nerve due to the strain
11%
What can peripheral nerve injuries be classified as (2)
- Mononeuropathy
2. Polyneuropathy
What is mononeuropathy
Single nerve issue
What is polyneuropathy
Multiple nerve problem
What are the 3 types of damage that occur to nerve
- Traumatic myelinopathy
- Traumatic axonopathy
- Severance
What is the pathology of a traumatic myelinopathy
Demyelination
What is the pathology of a traumatic axonopathy
Axonal damage
What is the pathology of severance
Axonal damage and demyelination
What is the typical recovery of a traumatic myelinopathy
Complete and rapid recovery
What is the typical recovery of a traumatic axonopathy
Slow by regrowth of axons but good prognosis because Schwann cells are usually intact
What is the typical recovery of severance
Typically slow with incomplete recovery
True or False:
Myelin is able to regenerate as long as the nucleus is still intact in the Schwann cell
True
What causes a traumatic axonopathy
Nerve on tension for a long period of time
In animal models what amount of prolonged lengthening lead to ischemia in the sciatic nerve
8%
In the animal model why was the reperfusion of the nerve potentially more damaging secondary to hyperemic blood flow
Because the amount of blood in the nerve is increased more than normal leading to increased pressure
What does the prolonged pressure from the increased fluid lead to
Damage to myelin because there are no lymphatics
What does acute compression of 20-30 mmHg interfere with in a nerve
Venous blood flow
What does acute compression of 35-50 mmHg cause
Reduced capillary flow
What does acute compression of 70 mmHg cause
Complete ischemia
What does chronic compression lead to in a nerve (4)
- Epineural fibrosis
- Demyelination
- Axonal degradation
- Perineural thickening
What does injury to peripheral nerves lead to
Wallerian degeneration
What is Wallerian degeneration
Everything distal to the injury dies and is broken down and taken up by the body
What happens to the proximal end of the damaged peripheral nerve
Upregulation of proteins from the cell body trying to recapture the lost end
When a nerve is severed what happens to the nerve endings
They retract away from the site of injury
When does Wallerian degeneration occur
When axons are injured
What does blockage of axonal transport do
Limits the flow of neurotrophic factors
What occurs due to the increased disruption of axonal transport
Axonal spheroids grow
What is an axonal spheroid
Build up of substances in an axon
What occurs once the axonal spheroid is formed
Wallerian degeneration leaving an end bulb on the proximal axon
Is the end bulb myelinated or not
Not myelinated
True or False:
There is a large deposition of Na+ channels at the end bulb of damaged nerves
True
What does the large deposition of Na+ channels lead to
Spontaneous firing seen in people with chronic pain
Does the nerve need to be severed to have nerve death
Nope the terminal end could not get the appropriate nutrients due to a blockage which leads to a build up of fluid causing an end bulb
True or False:
Damage of a nerve can be due to constant use
True (carpal tunnel)
True or False:
Na+ channels accumulate at end bulbs and areas of demyelination
True
What does the accumulation of Na+ channels in the regions of demyelination and end bulbs likely to occur due to
Abnormal trafficing
What does the accumulation of Na+ channels cause
Potential for ectopic discharge and pacemaker capability in neuropathic pain
What is ectopic discharge
When nerve stimulation occurs at a sight other than the normal site of stimulation
When does spontaneous ectopic firing in an injured nerve begin in myelinated axons
As early as 16 hours
When does spontaneous activity in unmyelinated axons that are damaged appear
Weeks following the initial injury
What fibers have spontaneous firing (2)
- A-beta
2. A-delta
What is nociceptive pain
Pain due to stimulation of nociceptors largely dominated by C-fibers
What is neuropathic pain
Pain due to A-beta and A-delta fibers
When do C-fibers kick in during neuropathic pain
Much much later
True or False:
Damage to axons leads to ectopic firing
True
What happens when we activate 2nd messengers for a long time
Adaption over time
True or False:
Substance P is upregulated in large diameter dorsal root ganglion neurons following an axotomy
True
True or False:
Phenotypic switching is likely the reason A-beta fibers contribute to neuropathic pain
True
Know chart about sequence of severed nerves
OKIE DOKIE
What are the negative signs and symptoms of peripheral nerve injury
Decreased nerve conduction velocity
Why is there decreased nerve conduction velocity
Demyelination occurs leading to no saltatory conduction
Get EMG slide cleared up by Dr. Brown
OK
What types of nerves have the ability to regenerate
Peripheral nerves
How long can a peripheral nerve take to heal
Several months
What needs to occur for axonal regeneration
Wallerian degeneration
Even though peripheral nerves can regenerate there is no guarantee the nerve will grow back completely
True
What does injury to the peripheral nerve do
Stimulate a number of signaling cascades that stimulate the upregulation of regeneration related genes
How much does a peripheral nerve grow a day
1 mm/day
True or False:
Peripheral nerve injuries stimulate second messengers
True
What does the stimulation of second messengers stimulate
Transcription of proteins and other substances that influence nerve growth
True or False:
Myelin growth is rapid
True
When does Wallerian degeneration occur in a completely severed nerve
3-5 days
What happens if a neuroma forms after injury
You will not get reconnection of the nerve
What do sliders increase
Axonal flow
What causes faster regrowth of nerves
Endurance training
True or False:
Resistance training leads to slower regrowth of nerves
True
What do tensioners do
Allows us to elongate tissue potentially leading to realignment of tissues
True or False:
The outcomes of resistance and endurance training eventually came out to be the same
True
Motivation
Good luck dude you are almost done for the summer!! Keep pushing and you will make it through!
