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Nervous System Injury and Repair
N/A
49
Anatomy
Graduate
01/20/2012

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Cards

Term
What makes up a peripheral nerve?
Definition
Axon, myelinating schwann cells, connective tissue, vascular supply
Term
What is the first action taken by neurons in response to injury?
Definition
Axon retracts proximal to the site of injury, usually to the first node of ranvier
Term
What is the initial reaction an injured nerve undertakes in preparation for the metabolic requirements of axonal regeneration?
Definition
Dispersion of ribosomal RNA in the Nissl substance (chromatolysis), movement of the nucleus to one side of the cell (eccentricity)
Term
What is the duration of the retrograde reaction in the cell body of an injured neuron?
Definition
Begins 2-3 days after injury, reaches peak at about 2 weeks after injury
Term
Why might the loss of an axon result in cell body death?
Definition
Axons contain up to 95% of the cytoplasm of a neuron
Term
The degeneration and phagocytosis of a severed axon following injury is a process known as what?
Definition
Anterograde or Wallerian degeneration
Term
How do Bands of Bungner cells develop?
Definition
Shwann cells in the axon distal to the injury rebsorb their myelin and remain in the connective tissue tubes
Term
What is the function of Bands of Bugner?
Definition
Synthesize trophic factors that can attract and support the growth of axons and are essential to the regeneration process
Term
What occurs at the proximal stump of a lesioned axon as it attempts to regenerate?
Definition
Forms sprouts that grow out to find the distal stump and enter the empty columns of Swhann cells (bands of Bugner)
Term
What determines the ability of proximal lesioned axons reaching their destination on the distal stump during regeneration of nerves?
Definition
The extent and type of damage to the nerve and distance to the distal stump
Term
What is the first degree of nerve injury and how is its defined?
Definition
Neuropraxia - the function of the axon may be disrupted without physical injury of the axon
Term
What are examples some of neuropraxia?
Definition
Nerve pressure block, foot falling asleep, compression during alcohol intoxication
Term
What is the second degree of nerve injury and how is it defined?
Definition
Axonotmesis - axons within a nerve are disrupted but the connective tissue scaffold (endoneurium, perineurium, epineurium) is intact
Term
What is an example of axonotmesis?
Definition
Nerve traction, crush injuries, compression
Term
What is the third degree of nerve injury and how is it defined?
Definition
Neurotmesis - Axons and the connective tissue structure of the nerve are both disrupted
Term
What might cause neurotmesis?
Definition
Cutting injuries or other severe trauma
Term
What happens to muscle tissue and sensory peripheral tissues that loose innervation?
Definition
Degeneration until either reinnervation occurs or the degeneration becomes irreversible
Term
What is the response by muscles that have lost innervation?
Definition
Flaccid paralysis, relatively rapid loss of muscle mass, physiological changes in the muscle including denervation supersensitivity and the spread of receptors over its surface
Term
How are changes in denervated muscles reversed?
Definition
Reverses if reinnervation occurs
Term
What causes muscle atrophy in denervated muscles?
Definition
Loss of trophic factors that maintain muscle metabolism
Term
How long does it take for denervated muscle tissue to atrophy to the point where it is no longer functional when innervation is restored?
Definition
12-24 months
Term
What is the rate of regeneration of axons?
Definition
1 inch/month
Term
Which sensory response is generally lost over a larger area in response to injury, light and discriminative touch or pain?
Definition
Light and discriminative touch
Term
How long does it take for specialized sensory structures such as pacinian corpuscles and merkel endings to degenerate to the point of permanent loss?
Definition
About 6 months
Term
What tends to regenerate faster, sensory axons or motor axons?
Definition
Sensory axons
Term
What are the consequences of interruption of postganglionic sympathetic axons that are severed along with a damaged peripheral nerve?
Definition
Loss of vascular control, sudomotor control, denervation of large areas (plexuses cam result in bone decalcification from disuse and loss of circulatory control
Term
In what order are sensory functions restored during functional recovery?
Definition
Deep sensation -> localized superficial cutaneous pain and vasomotor control -> heat and cold sensory -> light touch and discriminative touch (often incomplete)
Term
What test can be used to evaluate the progress of sensory regeneration?
Definition
Tinel's sign
Term
What are the two primary methods used for surgical repair of cut nerves?
Definition
Epineural nerve suture and nerve grafting
Term
Describe the process of epineural nerve suturing
Definition
The epineurium is thick enough to provide an anchor for sutures to join ends of severed nerves. The fascicles of the nerves are aligned as closely as possible to avoid blockage of axon growth by connective tissue
Term
What is group fascicular suture repair?
Definition
Repair of nerves via suturing of individual fascicles, though this can be difficult due to the high number of fascicles
Term
What is a common mistake that occurs during suture repairs?
Definition
Mismatching of sensory and motor axons which can diminish the chance of axons reaching their appropriate targets
Term
What can form on the end of a severed nerve when a large gap is present between cut ends as in a gunshot wound?
Definition
Knot of axons and connective tissue known as neuroma. Removal is required and nerve grafts are used to close the gap
Term
What nerves are usually used as donor nerves for nerve grafting?
Definition
Sensory nerves such as sural antebrachial cutaneous
Term
With larger nerves, allografts (transplants from a different person)can be performed. What must be used alongside an allograft to avoid rejection of the donor nerve?
Definition
Immunosuppressive agents
Term
What factors lead to a different response to cellular injury in the CNS as opposed to what is seen in the PNS?
Definition
Axons are myelinated by oligodendrocytes instead of Schwann cells, blood brain barrier and astrocyte barrier, presence of microglia and gitter cells
Term
What is the function of microglia?
Definition
Activated by tissue injury in the CNS< they proliferate and activate to phagocytize dying and necrotic tissue
Term
What is the function of gitter cells?
Definition
Peripheral microphages that enter the brain when blood vessels are disrupted, these cells phagocytize damaged tissue and dissolve necrotic tissue
Term
What is the function of astrocytes in response to injury?
Definition
Walls off isolated damaged areas from intact tissue to create a barrier known as a glial scar that replaces tissue
Term
What causes autolysis in the CNS in response to injury?
Definition
Cytokines, glutamate, and other factos secreted by activated macrophages, may worsen some injuries of the CNS
Term
What are some methods used to curb the detrimental of effects of autolysis in cases of CNS injury?
Definition
Large doses of methylprednisolone after a spinal cord injury, lowering body temp, drug induced coma
Term
Autolysis prevents what repair technique in the CNS that is viable in the PNS?
Definition
Suturing of severed ends of the spinal cord
Term
What is the difference between retrograde neuronal reactions in the CNS and the PNS?
Definition
CNS neurons do not produce the metabolic stimulation associated with axonal regeneration in the peripheral nervous system and instead result in slow neuronal atrophy and loss
Term
What is abortive regeneration and where is it seen?
Definition
Severed CNS axons undergo a small transient outgrowth shortly after injury that is then retracted without undergoing a true regenerative response
Term
What can happen to CNS neurons that are directly innervated by an injured neuron?
Definition
May also undergo degeneration (ex. optic nerve lesions = induced neuronal loss int he lateral geniculate and visual cortex)
Term
What is the difference between Wallerian degeneration in the CNS compared to the PNS?
Definition
Occurs very slowly (months to years)and is accomplished by astrocytes and resident microglia rather than Shwann cells
Term
What can be used to detect long term degeneration of tissue and tracts in the CNS?
Definition
MRI
Term
What are some recent techniques that are being researched that may aide in CNS axon repair?
Definition
Transplantation of stem cell precursors to oligodendrocytes to enhance remyelination, transplantation of different tissues into sites of CNS lesions, fetal brain transplants, results have been limited
Term
Transplantation of fetal tissue into the brain has been attempted most frequently with what disease?
Definition
Parkinson's disease
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