Peripheral Nerves Flashcards
What three types of nerve fibers run inside of a single nerve?
- Motor (ventral, efferent)
- Sensory (dorsal, afferent)
- Autonomic (vasodilation, sweat, etc.)
The amount of nerve fibers depends on the function of the nerve. (Ex: the radial nerve is skinnier than the median nerve but the median nerve has to carry motor, sensory, and autonomic fibers)
What is a motor peripheral nerve?
- Motor nerve fibers originate from the ventral horn of the spinal cord and terminate at the motor end plate located in the muscle
What is a sensory peripheral nerve?
- Sensory nerve fibers originate from the dorsal root ganglia and terminate as free nerve endings
What is the acronym for a motor nerve?
- MOVE (motor, ventral, efferent)
What is the acronym for a sensory nerve?
- SAD (sensory, afferent, dorsal root)
Are axons and nerves the same thing?
No! A peripheral nerve is a “bundle of bundles” of axons
What is the term used for a bundle of axons?
- Fascicles
What is the job of an axon?
- Carries chemical information
- One single axon can measure up to 3 feet (ex: sciatic nerve)
What tissues make up a nerve?
- Epineurium
- Perineurium
- Endoneurium
What is epineurium?
- The outermost layer of a nerve
- Cushions from external pressure and allows for movement
What is perineurium?
- Connective tissue that makes up the walls of the fascicles/bundles
What is endoneurium?
- Surrounds individual nerve fibers, supports, and protects the individual axons
- During surgical intervention, the surgeon has to do microvascular surgery to line up the fascicles so that the endoneurium is reconnected to grow
What is mesoneurium?
- Slick loose connective tissue
- Facilitates gliding
- Peripheral nerves require extraordinary mobility in relation to surrounding tissues. They sometimes slide up to 2 cm when we move! This is because nerves are long and often cross joints some distance from the axes of motion
What are the ideal conditions for a nerve to be healthy?
- Space
- Movement
- Good blood flow
- Lots of oxygen
- Stimulation
- Limited sustained tension
Why is movement essential for nerve health?
- It improves blood flow
- It facilitates gliding of fascicles and nerves
- It facilitates axoplasmic transport (anterograde flow and retrograde flow)
- It also prevents “wrinkling” of the axons within the endoneurium
What covers most peripheral nerve axons?
- Myelin for rapid conduction/transmission
- Schwann cells - produces myelin sheath and wraps around axon
- Nodes of Ranvier aid in fast conduction
T/F: there are two types of axons.
True. Myelinated and unmyelinated axons
What provides nutrition to the nerves?
- Blood supply is provided by large vessels that divide into ascending and descending branches that anastomose to the nerve
What can irritate nerves?
- They do not like to be held in stretch for prolonged periods of time because it decreases the blood flow to the nerve
- Over stretching can cause traction injuries (ex: athletic injuries and MVAs)
- Compression (ex: resting wrists on edge of table or a traumatic compression)
What are the effects of prolonged compression and stretch on nerves?
- Blood flow to the nerve comes to a complete standstill at 50-70 mm Hg of pressure or more than 15.7% of stretch of the nerve
- At 8% elongation the blood flow begins to stop
Are nerves sensitive to vibration?
Yes. A little vibration is good but too much vibration causes damage. Power tools, dental hygienist, city workers using machines like jack hammers, lawn maintenance providers, and motorcyclists need to wear shock absorbing gloves or have handles that absorb shock
- Hickory helps absorb shock
What are signs of peripheral nerve dysfunction?
- Sensory changes: decreased, absent, or abnormal sensation (e.g., allodynia, ectopic foci)
- Autonomic changes: loss of sweating or increase in sweating; loss of “shunting” from superficial capillaries; and other changes (ex: a cast being too tight)
- Loss of sensation occurs before loss of motor function in most cases. Sensory neurons have a better chance of recovery compared to motor neurons because the end plate does not die
- Motor changes: paresis, paralysis, and if denervated: atrophy of denervation and fibrillations
What trophic changes might be present following denervation of a peripheral nerve?
Trophic changes can occur due to:
- Blood supply changes
- Loss of autonomic innervation
- Loss of sensation
- Loss of movement
- Muscle will eventually turn to fat if it can no longer contract
What is an avulsion?
- Nerve pulls away from root
What is a laceration?
- Partial or complete cut of nerve fibers (fun shot wound, glass, or knife wound)
Why does nerve compression sometimes occur?
My be due to:
- ganglions
- osteophytes
- tumors
- crush injury
How does edema or ischemia affect nerves?
- It prevents the nerve from gliding
What is traction of a nerve?
- Stretch
How can radiation affect nerves?
- Radiation can cause burns and/or scarring
- Doctors do not always educate their patients on the effects of radiation treatment
How does chemotherapy affect nerves?
- It attacks all cells, including nerves
How are neuropathies classified?
- The number of nerves affected
- The severity of damage
- The type of damage
How are neuropathies categorized by number?
- One: mononeuropathy (ex: carpal tunnel in one wrist)
- Multiple (ex: carpal tunnel and cupital tunnel in one side, aka double crush injury because two different things are cooccurring)
- Poly (ex: diabetic neuropathy: symmetric involvement of sensory, motor, and autonomic axons. Often progresses from distal to proximal)
How are neuropathies categorized by severity of damage?
- Myelinopathy: the myelin sheath is affected. The severity can be determined by Tinel’s Sign
- Axonopathy/Axonotmesis: the myelin sheath and axon are affected
- Severance/Neurotmesis: the axon is severed
What are Seddon’s three degrees of nerve injury?
- Neuropraxia: nerve problems with light tingling and numbness, reversible because axon is preserved and there is no wallerian degeneration. There is local demylenation and a local conduction block
- Axonotmesis: only a few axons affected, deep cut with Wallerian degeneration but good prognosis. Healing occurs through axonal sprouting guided by the neural tube
- Neurontmesis: most severe, loss of axon and endoneurial tube continuity, nerve is completely severed and may require surgical intervention. If muscle does not fire during surgery then there is a worse prognosis. Muscles will atrophy and develop fatty striations and fibrosis
What is Sunderland’s Classification of nerve injury?
- Five degrees of nerve injury
- Add two more categories to neurotmesis
What is neuropraxia?
- A mild injury
- The nerve is intact but conduction is impaired
- Excellent recovery prognosis
- There may be some sensory loss but it is minimal
- May not have a positive Tinel sign
- Therapy implications: short-term and focused. A good response to conservative treatment
What is axonotmesis?
- A moderate injury
- Recovery rate is 1”/month or 1-2 mm/day
- Good prognosis
- Therapy implications: education (it is going to take time to heal), moderate intervention (tendon and nerve glides, splinting, etc.), and good PROM is maintained
- An example is Saturday Night Palsy because it there is a wrist drop due to damage to the radial nerve
What is neurotmesis?
- A severe nerve injury
- Spontaneous recovery is impossible and medical intervention is required
- There is Wallerian degeneration
- There will be loss of sensory, motor, and sympathetic function
- Prognosis is better for sensory return than for motor return
- Therapy implications: long-term comprehensive care
What are some interesting facts about nerve regeneration?
- Nerve regeneration does not involve mitosis and multiplication of nerve cells
- The cell body restores nerve continuity by growing a new axon
- Axon sprouting can begin as early as 24 hours following nerve transection
When do muscles typically begin to atrophy post nerve injury/compression?
- 3 months
How quickly do motor plates degrade following a nerve injury?
- 1% a week
When does muscle fibrosis occur after a nerve injury?
- 24 months
How quickly will a nerve conduction produce a contraction if the neuromuscular junction is re-established?
- 18 day delay following neuromuscular junction re-establishment
- It generally takes an addition five days for functional reflexes to occur
What is Thoracic Outlet Syndrome?
- Nerve compression that involves the brachial plexus
- The plexus crosses underneath the clavicle
- Pain can occur between the 1st and 2nd ribs and in the scapula
What direction do the pectoralis minor fibers run?
- Up and down
- Do not stretch pectoralis minor to the side because it will pull on the brachial plexus
T/F: Thoracic Outlet Syndrome symptoms can resemble carpal tunnel symptoms
True!
How can posture be corrected?
- Through gentle stretching
- Progressive stretching is best
- Improve forward rounded posture
- Improve pelvic alignment
- Strengthen abdominal muscles
- Use foam roller or towel between shoulder blades while lying supine on the floor
T/F: The ulnar nerve is both motor and sensory in function
True
- Sensory to ring and pinky fingers
What are cubital tunnel syndrome?
Cubital tunnel - compression of ulnar nerve between the medial epicondyle and olecranon
Interesting fact: there are 5 areas of compression in the elbow alone
Subluxation: the ulnar nerve pops in and out of canal during elbow flexion and extension
Symptoms: numbness and tingling in pinky finger and half of the ring finger, pain at inside of elbow, medial forearm, and in severe cases the thenar regions (causes loss of motor function)
What are therapeutic interventions for cubital tunnel syndrome?
- Activity modification and pathology education
0-6 weeks:
- Elbow pad for protection
- Static night elbow splint with elbow at 35 to 60 degrees flexion (worn 3 months)
- Pt education to avoid repetitive flexion/extension of elbow, prolonged flexion of elbow, and direct pressure to medial-posterior aspect of elbow
What is Guyon’s Canal Syndrome?
- Compression of ulnar nerve between the hook of hamate and the volar carpal ligament
Symptoms: tenderness over pisiform, pain with wrist extension, numbness and tingling in the ring and small finger, decreased grip/pinch strength, and weakness in finger abduction and adduction
What are therapeutic interventions for Guyon’s Canal?
- Splinting in wirst neutral
- ACUTE: rest, ice elevation
- Sub-acute: gentle AROM and ulnar nerve gliding
What is ulnar nerve palsy or an ulnar nerve lesion?
- Deformity produced by imbalance of the intrinsic and extrinsic muscles. The intrinsics do not work and are unopposed by the extensors
- Results in clawing of the ring and small fingers. But intrinsic must be markedly weakened or paralyzed to produce claw deformity. The long extensor muscles hyperextend the MCP joint and the long flexor muscles flex the PIP and DIP joints
- Accounts for 18% of nerve injuries
What is the splinting procedure following ulnar nerve palsy?
- Hand-based splint to block MP hyperextension
- Maintains transmetacarpal arch
- Pt and therapist want to try and facilitate MCP fexion
What muscles are affected by wrist level injury of the ulnar nerve?
- Abductor digiti minimi
- Flexor digiti minimi (superficialis)
- Opponens digiti minimi
- Lumbricals 4 and 5
- Dorsal and palmer interossei
- Flexor pollicis brevis (deep head)
- Adductor pollicis
