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