Term
| Transition from CNS to PNS |
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Definition
| Segements of afferent and efferent nerve fibers are located in both. The boundary between the CNS and PNS is defined as the location where the nerve fibers exit the spinal cord/brain stem and where glia cells of the CNS (oligodendrocytes) give way to those of the PNS (Schwann cells). |
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Term
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Definition
| Merging of spinal nerves after emerging from dorsal and ventral roots. Most peripheral nerves are mixed nerves. |
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Term
| Where are the cell bodies for afferent neurons? |
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Definition
| Outside CNS in the DRG or Cranial Ganglia. |
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Term
| Where are the cell bodies of the efferent neurons? |
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Definition
| In the ventral and medial horn of the spinal cord. |
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Term
| Epineurium is contiguous with? |
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Definition
| Dura mater of spinal cord. |
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Term
| Which layer of a nerve sheath forms the blood-nerve barrier? |
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Definition
| Perineurium. Tight junctions of perineurium contribute to this. |
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Term
Extrinsic Circulation
Intrinsic? |
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Definition
Extrinsic: Epineurial space - Outside fascicles. Vessels controlled by sympathetics.
Intrinsic: Run within the endoneurial space (penetrate perineurium). Vessels not controlled by sympathetics. |
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Term
| Proportion of myelinated vs unmyelinated. |
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Definition
| 1:4 - but myelinated do make up most area. |
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Term
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Definition
| 5-20 unmyelinated axons ensheathed by a single Schwann cell (ensheathed does not mean myelinated). |
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Term
Small diameter (.2-2um are unmyelinated). Small diameter+lack of sheath makes these sloooow.
The larger the diameter of an axon, the thicker the myelin sheath |
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Definition
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Term
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Definition
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Term
| What percent of axons in a peripheral nerve are myelinated? |
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Definition
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Term
| Can Schwann cells myelinate more than one axon? Long distance between Nodes of Ranvier does what to axons? |
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Definition
| No. Increases rapid saltatory conduction. |
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Term
| Compound Action Potential |
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Definition
| Summation of all the action potentials of an entire nerve. Therefore they are graded (different nerve fibers in a nerve will have different stimulus intensity). |
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Term
| Which has a lower threshold for extracellular stimulation, large or small fibers? |
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Definition
| Large fibers (larger x-sectional area and lower resistance). |
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Term
| Which is first recruited, large or small fibers? |
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Definition
| Large rapidly conducting (Aalpha, Bbeta). Further increasing the stimulis recruits small diameter Adelta and C fibers. |
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Term
| Which has larger membrane resistances, small or large cells? |
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Definition
| Small - mostly due to differences in surface area. Therefore with direct INTRACELLULAR stimulation, the small fibers are actually recruited first. |
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Term
| Classification of Peripheral Nerve Fibers |
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Definition
The letter system A, B, and C are based on conduction velocity (in order of CV)
Roman Numerals - Fibers grouped according to size (I>II>III>IV). |
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Term
| Letter system of peripheral nerves: |
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Definition
A - myelinated sensory and motor nerve fibers (Aalpha, Abeta, Agamma, and Adelta).
B - myelinated visceral fibers (preganglionic efferents)
C - unmyelinated fibers (nociceptors, thermal, touch, postganlgionic) |
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Term
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Definition
I>II>III>IV. I,II,III represent myelinated axons. Group Ia - muscle spindle. Group Ib - Golgi tendon
Group IV are unmyelinated axons. |
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Term
What would the following be classified as (letter system used for MYELINATED EFFERENT FIBERS):
Skeletal muscle extrafusal fibers
Intrafusal muscle fibers
Autonomic preganglionic fibers |
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Definition
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Term
Roman Numerals Used for MYELINATED AFFERENTS:
Muscle afferents (Spindle, GTO)
Secondary muscle spindles, mechanoreceptors of skin and joints.
Free endings, mechanoreceptors, thermoreceptors, noiciceptors |
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Definition
I (Ia and Ib)
II - Abeta
III - Adelta |
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Term
| Unmyelinated fibers - Group C or IV |
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Definition
| Free endings, thermoreceptors, mechanoreceptors, postganglionic fibers. |
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Term
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Definition
| Damage to a single peripheral nerve. Carpal tunnel. Accidents fall common. |
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Term
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Definition
| Disorder of more than one nerve. Accounts for greatest number of peripheral neuropathy cases. One of the most common forms of chronic polyneuropathy is DIABETIC neuropathy |
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Term
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Definition
| CMT is most common. Progressive loss of axons from peripheral nerve. Longest are first to be affected (so feet, legs, and hands). Caused by Connexin mutation (component of gap junction of Schwann cells). |
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