7 Motor System

Question 1

What type of motor neurons innervate extrafusal muscle fibers?

Answer 1

alpha motorneurons

Question 2

What sensory structures are connected in parallel with extrafusal fibers?

Answer 2

muscle spindles

Question 3

What types of fibers and motor neurons exist in muscle spindles?

Answer 3

intrafusal fibers and gamma motorneurons

Question 4

supraspinal activation causes what?

Answer 4

stimulation of alpha motor neurons to contract extrafusal fibers AND GAMMA MOTOR NEURONS TO CONTRACT ASSOCIATED MUSCLE

Question 5

loss of corticospinal fiber innervation to inhibitory interneurons explains what?

Answer 5

exaggerated stretch reflex after UMN lesions

Question 6

Medial motor groups of the ventral horn innervate?

Answer 6

axial muscles

Question 7

Lateral motor groups in the ventral horn innervate?

Answer 7

intrinsic limb muscles originating in trunk

Question 8

Lateral-most motor neurons in the ventral horn innervate what?

Answer 8

distal muscles

Question 9

Dorsal groups of motor neurons innervate what?

Answer 9

flexors

Question 10

ventral groups of motor neurons innervate what?

Answer 10

extensors

Question 11

Is the spinal reticular core essential for motor function?

Answer 11

Yes- central pattern generator

Question 12

What do spinal interneurons do?

Answer 12

generate stereotypic movements

Question 13

what is the name for neurons contained entirely within the spinal cord

Answer 13

propriospinal fibers

Question 14

What are the 2 main things spinal interneurons effect?

Answer 14

specific gaits and upper/lower limb coordination

Question 15

Pontine and medullary reticular formations contain interneurons which interact with>

Answer 15

bulbar motor neurons

• -centers for stereotypic head and neck movements
• -saccades

Question 16

what reticular formations directly involved in saccades?

Answer 16

paramedian pontine reticular formation

Question 17

What are the 3 major types of movements?

Answer 17

voluntary, stereotypic and postural control

Question 18

What movement is willed, purposefully and fractioned?

Answer 18

voluntary-limbs, eyes and orofacial (language)

Question 19

What movement is hard-wired movements of the head and limbs and eyes and tongue involving coordination of several muscle groups?

Answer 19

stereotypic

Question 20

Are stereotypic movements present at birth?

Answer 20

yes

Question 21

What movement is because humans are upright and extensors play the principal role?

Answer 21

postural

Question 22

Postural movements is dominated by what system?

Answer 22

vestibular [may control mostly gamma motor neurons to increase muscle tone]

Question 23

Where does the corticospinal and corticobulbar system originate?

Answer 23

cerebral cortex-

[mostly motor cortex, but also premotor, somatosensory cortex an adjacent parietal cortex]

Question 24

What contains a representation of the opposite side of the body (homunculus)

Answer 24

M1 motor cortex

Question 25

How much of motor cortex is dedicated to hand and the jaw/lowerface?

Answer 25

40%

Question 26

T-F---Corticospinal fibers have its strongest influence on extensor muscle groups?

Answer 26

False--flexor muscle groups

Question 27

About what percentage of cortico spinal fibers synapse on Alpha motor neurons?

Answer 27

20%- [particularly in dorsal part of the ventral horn in the cervical enlargement]

Question 28

Where are motor neurons for intrinsic hand muscles located?

Answer 28

dorsal part of the ventral horn C7-T1

Question 29

What is thought to allow individual and fractioned movements of the hand and forearm?

Answer 29

direct innervation by corticospinal fibers on intrinsic hand muscle motor neurons

Question 30

If only 20 % of corticobulbar fibers contact motor neurons what do the remainder connect to?

Answer 30

pre-motor neurons in the pontine and medullary reticular formation

Question 31

What is thought to mediate voluntary control over posture?

Answer 31

anterior corticospinal pathway

Question 32

Where does the rubrospinal pathway originate?

Answer 32

red nucleus of the midbrain

Question 33

Does the rubrospinal pathway have a huge significance in humans?

Answer 33

no- but in all mammals it facilitates next and upper limb flexors [non-human primates over time the pathway can take over much of the function of the corticospinal tract after a lesion]

Question 34

What is the reticulospinal pathway involved in?

Answer 34

maintenance of posture and in the modulation of muscle tone--[other may include visceromotor activity and pain modulation]

Question 35

Where does the medial reticulospinal pathway originate?

Answer 35

pontine tegmentum

Question 36

Where does the lateral reticulospinal pathway originate?

Answer 36

central and ventral medulla

Question 37

Does the medial or lateral reticulospinal pathway run in the anterior funiculus?

Answer 37

Medial---lateral runs with the lateral corticospinal funiculus

Question 38

Where do reticulospinal neurons receive input from?

Answer 38

cortico-reticular fibers and fastigial nucleus of the deep cerebellar nuclei

Question 39

Where do most medial reticulospinal fibers end?

Answer 39

bilaterally on interneurons in the ventral horn---some alpha motor neurons for axial muscles

Question 40

Do medial or lateral reticulspinal fibers excite or inhibit axial and proximal limb extensors?

Answer 40

medial through influence on interneurons and gamma motor neurons [lateral generally inhibit same groups]

Question 41

T-F--medial reticulospinal neurons are involved in activation compound limb movements and stereotypic limb movements?

Answer 41

True- also may be involved in steering head and trunk movements

Question 42

What may be important command systems for complex stereotypic movements?

Answer 42

descending monoaminergic pathways from locus ceruleus and pontine/midbrain raphe

Question 43

IS the pontine and midbrain raphe use noradrenaline or serotonin for command systems?

Answer 43

serotonin---locus ceruleus uses noradrenaline

Question 44

does the medial reticulospinal system have a component that sends fibers to the phrenic and accessory respiratory motor nuclei?

Answer 44

Yes--arise in the medulla and influence by pontine and medullary respiratory centers

Question 45

Where does the tectospinal pathway arise? end?

Answer 45

middle and deep layers of superior colliculus---only extends to cervical spinal levels

Question 46

What does the tectospinal pathway innervate? what is it's effect?

Answer 46

contralateral ventral horn---excites motorneurons of contralateral neck and inhibits ipsilateral muscles

Question 47

Where does the lateral vestibulospinal pathway originate? where does it descend?

Answer 47

-lateral vestibular nucleus | ipsilateraly through the whole length of the spinal cord

Question 48

Where does the lateral vestibulospinal pathway end on? what are the effects?

Answer 48

- medial part of ventral horn mostly on interneurons | - excitatory to axial muscles and proximal limb extensors

Question 49

Damage to the brain above the pons leads to decerebrate rigidity how?

Answer 49

no antagonism to the lateral vestibulospinal tract by corticospinal fibers

Question 50

T-F---damage to the cortex excluding motor cortex can lead to decorticate rigidity?

Answer 50

True--lower limbs and back are extended but arms and neck are flexed

Question 51

Where does the medial vestibule spinal tract arise? goes where?

Answer 51

medial vestibular nucleus----> mostly crossed and extends to mid-thoracic level

Question 52

What does the medial vestibule spinal tract facilitate?

Answer 52

extensor muscles for head and neck movements leading to an upright level position for the head

Question 53

What is in charge of planning and preparation for movement?

Answer 53

Frontal lobe

Question 54

What is the premotor cortex mostly concerned with?

Answer 54

planning movements in response to external cues

Question 55

Do lesions affecting premotor areas have less impact on motor function than motor cortex lesions?

Answer 55

Yes--patients can reach for something despite damage to that area in the pre-motor cortex

Question 56

Most corticospinal neurons send off side-branches to where?

Answer 56

striatum component of the basal ganglia

Question 57

Neurons in the striatum are capable of what?

Answer 57

learning and storing complex motor actions

Question 58

Is the output of the basal ganglia inhibitory or excitatory to the ventral anterior thalamic nucleus?

Answer 58

inhibitory

Question 59

What does the ventral anterior thalamic nucleus innervate?

Answer 59

premotor cortex---and brainstem reticular formations

Question 60

The frontal lobe effects release of what in the basal ganglia?

Answer 60

dopamine

Question 61

Lesions of basal ganglia can produce?

Answer 61

reduction in movement or uncontrollable movement

Question 62

Almost all cortical areas send axons where?

Answer 62

to the pontine nuclei-

Question 63

do corticopontine fibers outnumber corticospinal fibers?

Answer 63

yes 7:1

Question 64

What are the largest source of input to the cerebellum?

Answer 64

pontine nuclei

Question 65

Through what nuclei does the cerebellum exert its major influence on the motor cortex?

Answer 65

deep cerebellar nuclei and ventrolateral thalamic nucleus

Question 66

What tracts provide continuous information about body and limb position?

Answer 66

spinocerebellar tracts and vestibular system

Question 67

What provides the motor cortex with continuous feedback about body and limb position?

Answer 67

cerebellum

Question 68

What deficit usually involves degradation of fine movements and postural difficulties?

Answer 68

cerebellar