Chapter 17: Peripheral region Flashcards
PNS
all neural structures distal to the spinal nerves (median nerve, ulnar nerve, etc.).
-Cranial nerves are “peripheral” by definition, but are covered in chapters 19-21
everything that is distal to the spinal nerve
CNS
All structures enclosed by bone.
Spinal region- Nerve roots
nerve roots- motor and sensory, ventral and dorsal (dorsal root ganglion)
Spinal nerve
where sensory, motor, and autonomic come together.
Peripheral region: rami
3 rami branches from spinal nerve as it progresses distally.
- Anterior- has all of the axons that feed arms and legs in front of me
- Posterior- has the sensory and motor and autonomic to the backside of us
- Communicating branches (SNS)- autonomic neurons to and from the synapse.
Peripheral region: plexus
Plexus- cervical, brachial, lumbar, and sacral= all get input only from anterior ramus of every spinal level.
- plexus is distal to spinal nerve and proximal to peripheral nerve.
- Posterior rami just goes back and strip you like a barber pole.
Damage to one spinal nerve
a spinal level is damaged proximal to plexus- dermatomal sensory loss (one whole dermatome), many muscles will be weak but non should be paralyzed (every muscles gets input from many spinal levels).
Damage to one peripheral nerve
Damage to one peripheral nerve- sensory loss- medial nerve completely crushed- thumb, index, middle finger all on palmer side sensory loss (section of dermatome, some but not all of C6 dermatome)
Muscle loss- paralyzed muscle, the final pathway to muscle is cut.
peripheral nerves
Bundles of axons (sensory, motor, autonomic))
3 kinds of connective tissue:
- Endoneurium- surrounds individual axons
- Perineurium- surrounds bundles of axons
- Epineurium- surrounds bundles of fascicles.
around all axons is the perineurium gathers a bundle of axons together and is called a fascicle= a bundle of axons in a peripheral nerve.
-Epineurium is a thick connective tissue coating that gathers all fascicles together in a peripheral nerve.
- a peripheral nerve is a “bundle of bundles” axons- nerve is a whole bunch of axons
- axons is one fiber out of a whole nerve.
Peripheral nerve: fascicle
a bundle of neurons that all have a common destination, fascicle is part of the nerve.
Peripheral nerves-blood supply
Rich blood supply alongside every peripheral nerve.
-Arterial branches following every nerve.
myelinated vs. unmyelinated axons
One simple wrapping is unmyelinated
Cinnamon role is myelinated
Peripheral nerves- cutaneous vs muscular branches
Axons that go to skin (superficial) and muscle (deep)
Axons of peripheral nerves
A- alpha (efferent-extrafusal muscle)- motor neurons
Ia, Ib, II (afferent- proprioception)- tell us about how we are moving
A-beta (afferent- exteroception)- discriminative touch from surface of skin
A-gamma (efferent- intrafusal muscle)- keep spindle sensitie
A-delta (afferent-pain, temperature, viscera)- Sharp and stinging types of pain and cause us to move away (fast pain)
B (efferent-presynaptic autonomic)- preganglionic autonomic efferent)
C (afferent-pain, temperature, viscera)- dull and aching chronic pain (slow pain)
C- (efferent- postsynaptic autonomic)- postganglionic autonomic efferent
nerve plexuses
Cervical plexus- C1 to C4
Brachial plexus- C5-T1
Lumbar plexus- L1-L4
Sacral plexus- L4-S4
- The only plexus that contains parasympathetic nervous system fibers in it.
- At S2-S4 parasympathetic in perineum
Principles of a plexus
- One peripheral nerve gets axons from many different spinal levels
- One spinal level sends axons to many different peripheral nerves.
Peripheral nerves
All peripheral nerves have axons of:
- Motor function
- Sensory function
- Autonomic function
- Usually SNS (trunk, arms, legs)
- PNS in peripheral nerves of perineum
Autonomic is only arms, trunk, and legs
movement is essential for nerve health
- improves blood flow
- facilitates gliding of fascicles and nerves
- facilitates axoplasmic transport
- Anterograde
- Retrograde
- “wrinkling” of axons within endoneurium
- Lack of movement leads to physical stress on neural membrane
Contracture
loss of sarcomere and nerves get trapped in connective tissue. When try and move the connective tissue squeezes nerves and activates them (neuropathic pain) neural tension.
Neuromuscular junction
- voluntary effort generates action potentials
- release Ach (only a gas pedal)
- only excitatory
- “Miniature end-plate potential:
- -at rest
- -muscle health
- “atrophy of denervation
- evidence that our A-alpha motor neurons lack a bit of Ach even when not contracting them, doesn’t cause muscle to contract at all but affects the health of the muscle membrane. Lack of leaking that leads muscle fiber to wither away. When muscle fiber is denervated. Becomes unhealthy= atrophy of denervation.
-Down A-alpha motor neurons
dysfunction of peripheral nerves
Sensory changes:
- Decreased
- Absent
- Abnormal (allodynia)
Sensory changes (order of sensory loss)
- Conscious proprioception and discriminative touch
- Cold
- Fast pain (sharp)
- Heat
- Slow pain (dull)
order of sensation return after compression is relieve is in opposite order of loss.
Dysfunction of peripheral nerves: Autonomic changes
- Loss of sweating
- Loss of “shunting” in superficial arterioles
- Loss of “capacitance” (leads to orthostatic hypotension)
- other
-leaves us to be red indicating there is a lot of blood right underneath the skin.
Dysfunction of peripheral nerves: motor changes
- Paresis
- Paralysis
- If denervation
- -atrophy of denervation
- -fibrillations
atrophy of denervation will have fibrillation potentials ( a single muscle fiber that lost its nerve supply) is a signal of their irritation. cannot see on surface of skin.
Dysfunction of peripheral nerves: trophic changes (after denervation) due to:
- blood supply changes
- Loss of autonomic innervation
- loss of sensation
- loss of movement
-changes in tissue health (lost peripheral nerve supply, trophic changes include: -shiny, thin, fragile, hairless skin -redness -lack of sweating -poor nail growth
Classification of neuropathies
Classified by:
-how many nerves are affected (one, several, many)
-How severe is the damage
(traumatic myelinopathy, traumatic axonopathy, severance)
classification of neuropathies: how many
Mononeuropathy (one)- unilateral carpal tunnel, APB denervated
Multiple mononeuropathy (several)- bilateral carpal tunnel syndrome, median nerve on each side (damage) -reduced blood flow due to vasculitis.
Polyneuropathy (many)- many nerves are affected at once- stocking and gloves (lose sensation of the feet, ankles, and calves as well as the fingers, hands, and forearms bilaterally). Multiple dermatomes and multiple peripheral nerves have been simultaneously affected.
- symmetrical involvement of sensory, motor, and autonomic axons.
- often progresses distal to proximal (very often caused by diabetes)
- many nerves are sick.
- Other toxic, metabolic, autoimmune, or hereditary causes (idiopathic, Guillain-Barre Syndrome, Charcot-Marie).
classification of neuropathies: how severe?
Traumatic myelinopathy- first level of severity. we have experienced mild (crossed legs and foot fell asleep- fibular nerve ischemic and all the axons within it fell asleep)
One axon nerve. damage typically compression and ischemia causes a part of the axon to fail to conduct. Prolonged ischemia may lead to myelin dying around the axon (recovery takes longer to occur). prognosis is not as good and it will take days to maybe a couple of weeks to recover. (3 pics- top is normal, middle is not myelin around axon, 3rd is myelin regenerates if blood is restored in time).
-It is possible that the axon will insert modality or ligand gated channels into demyelinated space which can lead to mikels sign-can cause action potentials off of mechanical stimuli.
Classification of neuropathies: how severe-axonopathy
Traumatic axonopathy- the axon dies and degenerates distal to the point of injury (Wallerian degeneration).
-prognosis is good, recovery in weeks to months (1 inch per month regeneration).
Classification of neuropathies: how severe- severance
Axon and connective tissue is cut all together. Avulsion injury will separate the axon and its tissue.
- Proximal axon will try and regrow but because the tube is disrupted it may not find the way back to regrow correctly. May find the wrong tube.
- prognosis is guarded.
Diabetic polyneuropathies
Blood vessel damage in the feet may cause tissue damage such as sores or lesions, poor circulation that can lead to amputation.
-Peripheral nerves need blood supply and so they start to fail and lose sensation and function as worsens.
*Wont feel stimulus that is big enough to hurt them. Loss of sensation
Dysfunction neuromuscular junction
Occurs when Ach receptors start to disappear at the neuromuscular junction. (starts out strong and fades over time).
Myasthenia Gravis- degeneration of Ach receptors on postsynaptic membrane
Botulism- Impaired release of Ach from presynaptic-
- Inject it into a muscle that is overactive hoping to cause muscle to relax and not over constrict. Ach doesn’t get pushed out corticospinal, tonic contraction/ (botox- helps muscle relax, brain still sending contract signals that muscle cannot respond to them)
- Botox typically lasts about 2 to 4 months (average is 3)
peripheral nerve growth
nothing makes peripheral nerve growth go any faster (1 inch per month)
What do we do in the mean time? educate them about what is going on and the process, how to care for themselves in this period while stuff is happening. (edema reduction, don’t let contractures form ROM, Joint range, joint protection, make sure the tissue is healthy so when the nerve gets back it can hook up.
