10: motor descending tract Flashcards
what do you find in layers I-VI of Rexed’s laminae?
intermediate sensory neurons
what do you find in layers VII-VIII of rexed’s laminae?
local circuit, autonomic and commisural neurons
what do you find in Layer IX of rexed’s laminae?
lower motor neurons
name a human muscle that is considered fast fatigable
gastrocnemius
name a human muscle that is considered slow fatigue resistant
soleus
term for a group of muscle fibers innervated by a single lower motor neuron
motor unit
the size of the motor neuron is proportional to what
the number of muscle fibers it innervates (big motor neurons innervate more muscle fibers)
this type of motor unit has many mitochondria, more capillaries, more myoglobin
slow motor units (aka Type I muscle)
this type of motor unit has less myoglobin, fewer mitochondria, and fewer capillaries
fast fatigable (Type II muscle)
what kind of nerve fibers do golgi tendon organs use?
Type Ib
what kind of nerve fibers to muscle spindles use?
Type I: encodes both length and velocity
Type II: encodes length
____________ motor neuron activity reflects positive bias or gain on muscle tone; the higher the gain the greater the muscle tone and force of contraction.
gamma motor neuron
what are 2 components of the nervous system that alter gamma motor neuron gain?
local reflex circuitry and upper motor neuron input
what kind of structures monitor muscle tension and protect the muscles against excessive contraction?
golgi tendon organ activity
what 2 components of the nervous system alter golgi tendon organ activity?
local sensory circuitry and upper motor neuron input
term for contractions of a small number of motor units causing visible worm-like contractions of muscle
fasciculations
will you have atrophy in an UMN lesion?
no
will you have atrophy in a lower motor neuron lesion?
yes
UMN lesions have ___________ reflexes while LMN lesions have ___________ reflexes
UMN lesion–>increased reflexes
LMN lesion–>decreased reflexes
Do you find fasciculations in an UMN lesion or a LMN lesion?
LMN lesion
muscle tone is _____ in UMN lesion while it is ___________ in LMN lesions
UMN lesion–> increased muscle tone
LMN lesion–> decreased muscle tone
where do you find the Betz cells?
broadmann area 4, the primary motor cortex (large motor neurons)
what is in Brodmann area 6?
has premotor area and the supplementary motor area
what is in brodmann areas 3,1,2?
primary somatosensory cortex
what is in brodmann areas 5,7?
parietal association cortex
name the tract: this tract travels closely with the lateral corticospinal tract and participates in the control of arm muscles
rubrospinal tract
name the tract: this tract terminates largely at the cervical spinal cord level to innervate neck muscles and that this innervation provides information coming from the superior colliculus to coordinate head movements with eye movements
colliculospinal (Tecto) tract
name the 2 tracts that fit this description: terminate at the cervical and thoracic spinal cord levels to innervate neck and trunk muscles and that this innervation provides information coming from the vestibular formation to control coordinated movements of neck and trunk muscles
vestibulospinal tract and reticulospinal tract
what is the term for repetitive plantar extension of the foot when the foot is forcefully flexed upward?
clonus (reflects the muscle stretch reflex that is unchecked and continues to operate through a feedback loop)
Clonus is a finding you will see in what kind of motor neuron lesion?
upper motor neuron lesions have clonus (repetitive plantar extension of the foot when the foot is forcefully flexed upward)
what kind of motor neuron lesion has a positive Babinski sign?
UMN lesion
which disease classically affects both upper and lower motor neurons?
ALS
