Normal Nerve Anatomy Flashcards
What is subconscious processing?
- Subconscious functions
- Emotion
- Involuntary functions
What is cortical processing?
- Voluntary functions
- Higher order processing
What is the difference between afferent and efferent nerves in the PNS?
Afferent = sensory, towards CNS
Efferent = motor, away from CNS
What is the difference between the somatic and autonomic nervous system?
Somatic
- Voluntary motor functioning
Autonomic
- Involuntary motor functioning
- Sympathetic - fight or flight
- Parasympathetic - rest and repair
What makes conduction quicker at nodes of ranvier?
Increased conc of VG Na + K channels
How does local anaesthetic work?
- No sensory conduction
- Reversibly binds to Na channel
What are commonly used preparations of local anaesthetic?
- Lidocaine - rapid onset, short duration
- Bupivicaine - slower onset, lasts longer
How do non-depolarising neuromuscular blocking drugs work?
- e.g. Atracurium
- Competitive antagonist
- Block action of Ach
- Not broken down
- No fasciculations
How do depolarising neuromuscular-blocking drugs work?
- 1 type = Suxamethonium
- Competitive agonist
- Act in addition to Ach
- Slowly broken down
- Fasciculations
How does Botulinium work?
Blocks Ach release
What are the different classifications of nerve injury?
- Neurapraxia (I)
- Axonotmesis (II, III, IV)
- Neurotmesis (V, VI)
How is neurapraxia described?
- Myelin damage
- Conduction slowed
How is axonotmesis described?
I
- Loss of axonal continuity
- Endoneurium intact
- No conduction
- Advancing tinels present
III
- Loss of axonal + endoneurial continuity
- Perineurium intact
- No conduction - wallerian degeneration combined with scarring within endoneurium
- Advancing tinels present
IV
- Loss of axonal, endoneurial + perineurial continuity
- No conduction - complete scar block
- Advancing tinels absent
How is neurotmesis described?
V
- Nerve trink divided
- No conduction
VI (mixed)
- Injury varies fascicle to fascicle
Summarise Wallerian Degeneration
- Injury
- Breakdown - Ca = release of proteases by Schwann
- Phagocytosis
- Slower centrally compared to peripherally
- End result = shrunken nerve skeleton with intact CT + perineurial sheaths + multiplying Schwann cells - Regeneration
- Severe injuries regeneration only begins once wallerian degeneration complete
- Genes upset to produce proteins/lipids for axonal growth
- NISSL reaction = chromatolysis (= apoptosis)
- Nucleus migrates to peripheral and Nissl granules disperse (chromatolysis)
- Schwann extend to engage with filopodia
