10: motor descending tract

Question 1

what do you find in layers I-VI of Rexed’s laminae?

Answer 1

intermediate sensory neurons

Question 2

what do you find in layers VII-VIII of rexed’s laminae?

Answer 2

local circuit, autonomic and commisural neurons

Question 3

what do you find in Layer IX of rexed’s laminae?

Answer 3

lower motor neurons

Question 4

name a human muscle that is considered fast fatigable

Answer 4

gastrocnemius

Question 5

name a human muscle that is considered slow fatigue resistant

Answer 5

soleus

Question 6

term for a group of muscle fibers innervated by a single lower motor neuron

Answer 6

motor unit

Question 7

the size of the motor neuron is proportional to what

Answer 7

the number of muscle fibers it innervates (big motor neurons innervate more muscle fibers)

Question 8

this type of motor unit has many mitochondria, more capillaries, more myoglobin

Answer 8

slow motor units (aka Type I muscle)

Question 9

this type of motor unit has less myoglobin, fewer mitochondria, and fewer capillaries

Answer 9

fast fatigable (Type II muscle)

Question 10

what kind of nerve fibers do golgi tendon organs use?

Answer 10

Type Ib

Question 11

what kind of nerve fibers to muscle spindles use?

Answer 11

Type I: encodes both length and velocity

Type II: encodes length

Question 12

____________ motor neuron activity reflects positive bias or gain on muscle tone; the higher the gain the greater the muscle tone and force of contraction.

Answer 12

gamma motor neuron

Question 13

what are 2 components of the nervous system that alter gamma motor neuron gain?

Answer 13

local reflex circuitry and upper motor neuron input

Question 14

what kind of structures monitor muscle tension and protect the muscles against excessive contraction?

Answer 14

golgi tendon organ activity

Question 15

what 2 components of the nervous system alter golgi tendon organ activity?

Answer 15

local sensory circuitry and upper motor neuron input

Question 16

term for contractions of a small number of motor units causing visible worm-like contractions of muscle

Answer 16

fasciculations

Question 17

will you have atrophy in an UMN lesion?

Answer 17

no

Question 18

will you have atrophy in a lower motor neuron lesion?

Answer 18

yes

Question 19

UMN lesions have ___________ reflexes while LMN lesions have ___________ reflexes

Answer 19

UMN lesion–>increased reflexes

LMN lesion–>decreased reflexes

Question 20

Do you find fasciculations in an UMN lesion or a LMN lesion?

Answer 20

LMN lesion

Question 21

muscle tone is _____ in UMN lesion while it is ___________ in LMN lesions

Answer 21

UMN lesion–> increased muscle tone

LMN lesion–> decreased muscle tone

Question 22

where do you find the Betz cells?

Answer 22

broadmann area 4, the primary motor cortex (large motor neurons)

Question 23

what is in Brodmann area 6?

Answer 23

has premotor area and the supplementary motor area

Question 24

what is in brodmann areas 3,1,2?

Answer 24

primary somatosensory cortex

Question 25

what is in brodmann areas 5,7?

Answer 25

parietal association cortex

Question 26

name the tract: this tract travels closely with the lateral corticospinal tract and participates in the control of arm muscles

Answer 26

rubrospinal tract

Question 27

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

Answer 27

colliculospinal (Tecto) tract

Question 28

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

Answer 28

vestibulospinal tract and reticulospinal tract

Question 29

what is the term for repetitive plantar extension of the foot when the foot is forcefully flexed upward?

Answer 29

clonus (reflects the muscle stretch reflex that is unchecked and continues to operate through a feedback loop)

Question 30

Clonus is a finding you will see in what kind of motor neuron lesion?

Answer 30

upper motor neuron lesions have clonus (repetitive plantar extension of the foot when the foot is forcefully flexed upward)

Question 31

what kind of motor neuron lesion has a positive Babinski sign?

Answer 31

UMN lesion

Question 32

which disease classically affects both upper and lower motor neurons?

Answer 32

ALS