Neuro Unit II Lecture 7
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| Define: Lower motor neuron | under the direct influence of CNS and neurons that live in the cerebral cortex
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| Define: Upper motor neuron | Projections of the brain cortex that influence the activity of the LMNs
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| Define: Interneurons | A series of nerves that transfer the signal between UMN and LMN in the spinal cord.
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| Sensory receptors | Muscle, Tendon and Joint receptors. These structures feed back sensory input to the spinal cord and other parts of the CNS. (spindles/GTOs/Ruffinis)
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| Where are the first cell bodies of LMN's located? | Ventral horn, lamina 9
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| What is in each nucleus located in lamina 9 and what are they called? | the nerves to innervate a SINGLE muscle. Called a motor pool
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| What do alpha motor neurons innervate? What do they look like? | Extrafusal fibers (the normal skeletal muscle fibers that do the contracting work); massive dendritic trees
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| What is a motor unit? | An alpha motor neuron and all the fibers that it innervates
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| Each motor unit has how many nerves stimulating it? How do motor units vary? | Just one; vary in amt of fibers innervated, ability to sustain contraction, amt of force generated
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| How is contraction regulated by the alpha motor neuron of a single motor unit? | By firing rate of the neuron and the recruitment of different motor neurons
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| What excites a GTO? A Spindle? | GTO: tension produced during passive stretch. Spindle: passive stretch (change in length)
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| What happens to spindles during muscle twitch (contraction)? What can be a problem? | Spindles: decrease firing during muscle shortening. Can get so short, that gives a period of CNS blindness
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| What happens to GTOs during muscle twitch? | firing increased b/c of increased tension on the tendon during contraction
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| What do gamma motor neurons innervate? Why is this weird for a sensory organ? What type of fiber is used? | spindles; spindles are the only sensory receptor to recieve efferent connections from NS. Fiber type: Ia
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| What is gamma recalibration? | during muscle contraction, alpha and gamma motor neurons fire. spindles contract w/ the muscle so as to get rid of possibility of CNS silence
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| What are the reflexes that we need to know for the test? | Myotatic, Inverse Myotatic, Flexor Reflex
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| What does the myotatic stretch reflex regulate? Give an example of a myotatic relfex | Length! Patellar reflex
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| Give the series of events for a patellar reflex | Hit tendon -> stretches tend/muscle (quadr) -> change in length activates spindles that activates Ia neurons -> dorsal root of spine -> transfer signal to alpha motor neuron and out ventral root ->contract quads
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| Why don't the antagonist muscles in the leg contract as well during a myotatic reflex? | Reciprocal inhibition: When one side is contracting, inhibitory neurons stop the antagonist muscles from contracting
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| Why don't GTO's fire during myotatic reflex? | B/c their threshold is too high
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| What does the inverse myotatic reflex regulate? | Tension
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| Steps in inverse myotatic reflex | contraction of quads stims GTO's -> send sign via Ib to dorsal root -> inhib interneuron to alpha mn for quads, AND excit interneuron to the antagonist muscles
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| What is autogenic inhibition? | A muscle group inhibited by its own sensory input. Muscle tension leads to inhib of its own motor neurons!
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| Is the myotatic reflex tested clinically? What about the inverse myotatic reflex? | Yes myotatic, no inverse myotatic
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| What does the flexor reflex do? what is another name for it? | Guards against noxious stimuli (ie glass on the floor) aka withdrawl reflex
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| Where does the flexor reflex initiate? How is this different from myotatic? | Initiates at sens. recept. (nocicoceptor that activates due to stepping on glass!) Myotatic activates by length change/stretch!
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| Sequ. of events for flexor reflex | step on glass -> activ. nocic.(Adelta) in lft foot -> stim same side flexors, inhib same side extensors -> ALSO stim opp side extensors and inhib opp side flexors
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| What is promoted in UMN lesions? What are the signs? | Disinhibition! Signs: initial flaccid paralysis below injury, development of spasticity, changes in muscle reflexes
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| What are the changes in muscle reflexes due to UMN lesion? | hypertonia, hyperreflexia, Clasp knife, clonus
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| Define hypertonia | increased resistance to passive manipulation (evidence of spasticity)
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| Define hyperreflexia | velocity/intensity of stretch reflex exaggerated (loss of inhib. input, so get gamma loop!)
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| Define: Clasp knife | resistance to flexion and extension of joint -> @ a pt, resistance dissappears and snaps like a pocket knife
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| Define: Clonus | oscillating contraction and relaxation of a joint due to loss of inhibition of Ia fibers! (increased stretch)
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