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Stack #215313

Neuro Unit II Lecture 7

Define: Lower motor neuron under the direct influence of CNS and neurons that live in the cerebral cortex
Define: Upper motor neuron Projections of the brain cortex that influence the activity of the LMNs
Define: Interneurons A series of nerves that transfer the signal between UMN and LMN in the spinal cord.
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)
Where are the first cell bodies of LMN's located? Ventral horn, lamina 9
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
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
What is a motor unit? An alpha motor neuron and all the fibers that it innervates
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
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
What excites a GTO? A Spindle? GTO: tension produced during passive stretch. Spindle: passive stretch (change in length)
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
What happens to GTOs during muscle twitch? firing increased b/c of increased tension on the tendon during contraction
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
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
What are the reflexes that we need to know for the test? Myotatic, Inverse Myotatic, Flexor Reflex
What does the myotatic stretch reflex regulate? Give an example of a myotatic relfex Length! Patellar reflex
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
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
Why don't GTO's fire during myotatic reflex? B/c their threshold is too high
What does the inverse myotatic reflex regulate? Tension
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
What is autogenic inhibition? A muscle group inhibited by its own sensory input. Muscle tension leads to inhib of its own motor neurons!
Is the myotatic reflex tested clinically? What about the inverse myotatic reflex? Yes myotatic, no inverse myotatic
What does the flexor reflex do? what is another name for it? Guards against noxious stimuli (ie glass on the floor) aka withdrawl reflex
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!
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
What is promoted in UMN lesions? What are the signs? Disinhibition! Signs: initial flaccid paralysis below injury, development of spasticity, changes in muscle reflexes
What are the changes in muscle reflexes due to UMN lesion? hypertonia, hyperreflexia, Clasp knife, clonus
Define hypertonia increased resistance to passive manipulation (evidence of spasticity)
Define hyperreflexia velocity/intensity of stretch reflex exaggerated (loss of inhib. input, so get gamma loop!)
Define: Clasp knife resistance to flexion and extension of joint -> @ a pt, resistance dissappears and snaps like a pocket knife
Define: Clonus oscillating contraction and relaxation of a joint due to loss of inhibition of Ia fibers! (increased stretch)
Created by: StudyBuddies