Lecture 6 - LMNs Flashcards
Where do LMNs start?
In the spinal cord
What is the myotactic reflex?
pre-programmed response by the body to something that causes the muscle to stretch
Regarding the face, if the left hemisphere is damaged, then what might result?
the right upper face will experience weakness, since it receives impulses from the right hemisphere. right lower face will be damaged, since it receives impulses from the left hemisphere
If there’s LMN damage on the left side of the brain, then what might happen to one’s face?
left side of the face is droopy, since LMNs innerve ipsilaterally
If the tongue is deviated, fasciculates are present, and hemifacial droop, then what cranial nerve is damaged?
CN VII
If an individual has a right UMN stroke, then what are the symptoms?
tongue deviation to the left; lower part of the face is intact, but the upper part of the face may experience weakness
Alpha LMNs innervate _________.
voluntary muscles
Gamma LMNs deal with _______
stretch and tension
LMN start in the ________
brainstem and spinal cord
UMN start in the ______
cerebral cortex, particularly PMA and primary somatosensory cortex
What is the purpose of the gamma loop?
to maintain muscle tone
Alpha LMNs activate ______ , whereas gamma LMNS activate ________
extrafusal fibers; intrafusal fibers
What pathway innervates the gamma loop?
the indirect pathway, particularly reticulospinal tract
What is the final common pathway consist of?
Lower motor neurons of PNS; 12 pairs of cranial nerves and 31 pairs of spinal nerves
UMN lesions are characterized by
spasticity, no atrophy, no fasciculations, weakness, increased muscle tone, ataxia, babinski sign, hypo or hyperkinesia
LMN lesions are characterized by
flaccidity, atrophy, fasciculations, weakness, decreased muscle tone, paresis, paralysis, fibrillations
The final common pathway has two important sensory receptors. They are ____ and _____
1a and 1b
The sensory receptor _____ is responsible for stretch, whereas the sensory receptor _____ is responsible for tension.
1A and 1B
What inputs do alpha LMNs receive?
spinal interneurons, upper motor neurons, and sensory input from muscle spindles
What inputs do alpha LMNs receive for proprioception?
monosynaptic A.K.A myotactic; multisynaptic; direct activation pathways
What are the components of the gamma loop?
alpha LMN, gamma LMN, intrafusal fibers, input from the indirect activation pathway (most likely the reticulospinal tract), sensory receptors i muscle spindles
There are more muscle spindles in the ______ tract than in the _______ tract
corticospinal; corticobulbar
What parts of the body have many muscle spindles?
jaw muscles, especially the masseter; recurrent and superior laryngeal; pharyngeal muscles; optic-oculomotor muscles; stapedius muscle
What parts of the body have few muscle spindles?
tongue, lips, face (except for eyes and jaw)
For tension, golgi tendon organs fire and then what happens?
golgi tendon organs fire and stimulate 1b sensory receptors in the muscle spindles. Then 1b sensory receptors stimulate interneurons. The interneurons stimulate alpha LMNs which then contracts the extrafusal fibers in the muscle.
For stretch, gamma LMNs fire and then what happens?
intrafusal fibers contract; this signals to alpha LMNs to innervate extrafusal fibers to contract and match the length of the intrafusal fibers
What are fasciculations?
brief local twitching
What are fibrillations?
a consequence of a LMN lesion; regular contractions caused by slow repetitive action potentials
