PNS Flashcards
What are fascicles enclosed by?
Perineurium
Name the 2 types of somatic sensory (primary afferents)
C fibres (unmylinated, slow) A delta (myelinated, faster)
What holds fascicles together?
Epineurium
What else is contained in the epineurium?
White adipocytes (protection)
Blood vessels (many anastomoses)
Describe what happens to the blood vessels in diabetic neuropathy
Endothelial cells & smooth muscle cells lining the vessels hypertrophy
Closes lumen
Restricts blood flow
Describe the strength of the perineurium and the only thing that can transverse it
Tough
Resistant to pressure
Blood vessels
What allows nerves to pass through infected areas of the body unaffected?
Perineurium
Forms a barrier to infection
What is the endoneurium made of?
Collagen & ECF
Where are macrophages found in peripheral nerves?
Epineurium & endoneurium
What is the difference between oligodendrocytes & Schwann cells?
Oligo= CNS, myelinate several axons
Schwann= PNS, myelinate one axon
What do Schwann cells secrete?
A glycoprotein called Laminin
Laminin is important in nerve regeneration. How?
Provides a surface along which to grow.
Angiogenesis must occur- Laminin provides surface for new blood vessels to grow.
What organelles are responsible for axonal transport?
Neurotubules, held together by tau
Over expression/ destruction of tau will stop what?
Axonal transport
Molecules produced in the cell body are unable to leave, neurone dies
Happens in Alzheimer’s
Name the 2 types of axonal transport
Orthograde (cell body–>terminal/synapse)
Retrograde (terminal/synapse–>cell body)
Name the molecular motors involved in orthograde & retrograde axonal transport
O= Kinesin
R= Dynein
Name the 2 types of orthograde axonal transport & what each transports
Fast- small molecules (enzymes required for NT production.
Slow- larger structures.
Name the 3 categories of peripheral nerve damage
Contusion/bruising (temporary)
Crushing (distal axons will degen)
Severing (distal axons will degen)
Describe Wallerian degeneration & the regeneration that follows
Axons distal to injured nerve degenerate but M sheath remains = friendly environment, encourages growth of new As. As from prox side of injury sprout, grow towards empty Schwann cell tubes. Sprout grows into intact endoneurium, attempt to form new A.
What helps the axon sprouts proximal to an injury grow towards empty Schwann cell tubes after ‘Wallerian degeneration’
Growth factors produced by Schwann cells
What 3 factors affect how good regeneration is?
1) How clean the damage is
2) Whether there is adequate blood supply
3) Age
What IS neuropathic pain?
A pain experienced when regeneration is not complete/perfect. Spontaneous/evoked by movement. Tenderness/burning/tingling.
What CAUSES neuropathic pain?
Regenerated axon may form a swelling = neuroma, on sensory fibres regenerating into skin. New section of axon has a new mem but distribution of ion channels isn’t perfect = As generate abnormal APs, go to chord, cannot interpret abnormal info, consequence = NP!
