Block II: CC1 Flashcards
WHta is the endoneurium?
is a supporting structure around individual axons within each fascicle.
WHat is a fascicle?
number of axons together in a circular structure surrounded by perineurium
WHta is the perineurium?
Collagenous tissue binding each fascicle with elastic fibers and mesothelium cells
Whta si the epineurium?
Collagen, elastic fibers and fatty tissue binding individual fascicles together. Outmost layer of supportive tissue. Contains vasa nervorum.
Rate nerve fibers by size (um)
Aa > AB > Ay > Ag > B >C
Rate nerve fibers by conduction speed (ms-1)
Aa > AB > Ay > Ag > B >C
Which fibers are myelinated?
Aa (thickest)
AB
Ay
Ag (thinnest)
B
Which fibers are NOT myelinated?
C
General functions of Aa?
Motor, propioception
General functions of AB?
Touch, pressure, vibration
General functions of Ay
Motor to muscle spindle
General functions of Ag
Touch, coldness, fast pain
General functions of B
Pre-ganglionic autonomic
General functions of C
Touch, warmth, itch, slow pain; post-ganglionic autonomic
What is slow transport in axonal transport?
0.5-10mm/day
-unidirectional always anterograde
-moves enzymes, cytoskeletal components and new axoplasm down the axon during repair and regeneration of damaged axons
-Damaged nerve fibers regenerate at a speed governed by slow axonal transport
what is fast transport in axonal transport?
20-400mm/day
-bi-directional
-anterograde transport: organelles, enzymes, synaptic vesicles and small molecules
-Retrograde: for recycle material and pathogens- rabies, herpes simplex, tetanus, polio viruses.
What is wallerian degeneration?
Following focal interruption of axons (as trauma or vasculitis). From injury downward. atrophic muscle
What is axonal degeneration?
Dying -back phenomenon from metabolic derangement of the neuron. Injuty occurs in the whole nerve, but dies from distal to proximal. atrophic muscle.
What is segmental demyelination?
affects myelin, slowing the conduction velocity. patched pattern
What is neuraplaxia?
Class I nerve injury
-milder form of damage
-nerve does not suffer major changes after injure, myelin regenerates
-cause:compression or ischemia
-good prgnosis
What is axonotmesis?
-class II nerve injury
-axonal damage results in loss of continuity and wallerian degeneration distally.
-Basal lamina and endoneurial tissue is intact
-recovery depends on nerve regeneration (1-3mm/d)
What is neuronotmesis?
Class III nerve injury
-results in separation of entire nerve including supportive tissue, ranging from endoneurial and schwann cell tube transection to total nerve serverance
-limited axonal regeneration
-neuroma formation and aberrant regeneration is common
What type of fibers are injured in patient has trouble with motor and sensory axons responsible for propioception, vibration and light tough?
Large myelinated axons
What type of fibers are injured in patient has trouble with sensory fibers responsible for light touch, pain, temperature, and preganglionic autonomic fucntions?
thinly myelinated axons
What type of fibers are injured if the patient has trouble with pain, temperature and postganglionic autonomic factors?
small unmyelinated fibers
what is diffuse (symemtric spatial distribution?
polyradiculopathu ex. sensory/motor diabetic neuropathy
what is focal spatial distribution?
mononeuropathies, ex. entrapment neuropathies as in carpal tunnel or local trauma
what is multifocal-lower spatial distribution?
usually assymetric; multiple mononeuropathy; ex. vasculitis
What are symptoms of large fiber neuropathy?
-lower motor neuron pattern of weakness
-muscle loss, atrophy
-loss of tendon reflexes
-impaired propioception
-abnormal romberg test
What are symptoms of large fiber neuropathy?
Contact hyperalgesia
-burning, aching, stabbing pain (non specific)
-mild distal disturbance in sharp dull discrimination
-normal DTR’s
-Orthostatic hypotension
Axonal neuropathy pathologic features include:
-Impaired axonal transport
-failure of impulses generation in nerve terminal
-atrophy
clinicopathologic correlation of axonal neuropathy
-initial findings in lower limbs
-sensory and motor loss
-tingling and pinprick
-decresed or loss ankle reflexes
-normal CSF protein level
-slow recovery
what is demyelinating neuropathies?
-acquired conditions generally result of an immune mediated attack to PNS myelin
-primary myelin destruction sheath leaving axon intact
-begins at nodes of ranvier
-spinal roots involved
-schwann cells remyelinates the axon
-no atrophy
demyalinated neuropathy clinicopathology correlationa
-fast (days)
-cranial nerves invovled
-weakness with mild sensory loss
-absent DTRs
-elevated CSF protein
-may recover
-segmental (multifocal) almost always acquired
-uniform - hereditary
What is an evaluation method for patients with peripheral neuropathy?
EMG and nerve conduction
Which is th emost commeon clinical neuropathy?
diabetes
What are some characteristics of clinical diabetic neuropathy?
-majority have distal symmetric fiber-lenth-dependent pattern
-sensory and autonomic manifestations
-progressive distal axonopathy
-can develop focal and multifocal neuropathies
What are cranial neuropathies?
-unilateral oculomotor nerve palsies
-third CN (pupillary reflex spared, pain 5%)
-6th cranial nerve
What is proximal diabetic neuropathy of lower limbs?
-pain and sensory loss with unilateral proximal muscles weakness and atrophy
-acute onset
-burning type of pain in thigh
-good prognosis
What is an example of demyelinating polyneuropathy?
guillain barre syndrome
explain guullian barre
-bilateral acute, ascending, symmetric peripheral neuropathy
-progression may continue up to 4 weeks
-areflexia
-mild sensory symtoms
-bilateral facial weakness
-may require ventilator
-infection or gastroenteritis may be a predisposing factor (CMV, Campilobacter jejuni)
-csf protein elevated after first week
-elcectrodiagnostic studies (lumbar punction)
What is molecular mimicry?
when there is a pathogen or unknown substance, the perivascular lymphocytic macrophages infiltrates causing a segmental inflammatory demyelination and edema by error attacks myelin from nerve since antibodies of virus seem similar to those of the nerve.
What is vasculitic neuropathies?
A diverse group of disorders characterized by the acute-to-subacute onset of painfulsensory and motor deficits that result from inflammatory destruction of nerve blood vessels and subsequent ischemic injury.
what are the two main pathways that lead to sichemic vasculitic nerve damage?
-Immune complex deposition within the vessel walls with complement deposition and release of proinflammatory cytokines.
-Cell-mediated immunity occurs when antigen-presenting cells present relevant antigens to circulating T cells producing proinflammatory cytokines and other inflammatory mediators that cause neutrophils and lymphocytes to adhere to and injure the blood vessel.
Examples of primary vasculitis?
large vessel: giant cell (temporal) arteritis
-medium and small vessel vasculitis: polyarteritis nodosa, churg0strauss syndrome, wegner’s granulomatosis, microscopic polyaniitus, isolated angiitis of NS)
Examples of secondary vasculitis?
-connective tissue disorder: RA, SLE
-Malignancies: small cell CA lung, lymphoma
-infections: herpes varicella zoster, CMV, HIV, hepatitis
-cryoglobulinemia
example of focal neuropathies?
carpal tunnel syndrome
peroneal neuropathy
tarsal tunnel
meralgia parestehtica
