Nsp: Descending Motor Pathways - Blair

Front 1

What two principal sources in the brain do alpha motorneurons receive input from?

Back 1

1. Cerebral Cortex (direct)

2. brainstem pathways (indirect)

Front 2

the cerebellar control circuit influences movements of ______________ muscles through its connections to the _____________ and ____________.

Back 2

the cerebellar control circuit influences movements of IPSILATERAL muscles through its connections to the CEREBRAL CORTEX and BRAINSTEM

Front 3

The basal ganglia control circuit influences movements of _________ muscles through connections with the ____________

Back 3

The basal ganglia control circuit influences movements of CONTRALATERAL muscles through connections with the CEREBRAL CORTEX

Front 4

Medial Systems mainly provide control of what?

Back 4

posture and balance, including orienting movements

Front 5

With one exception, medial system pathways course in what part of the spinal cord?

Back 5

ventromedial

Front 6

What tract excites alpha & gamma motorneurons to extensor muscles in the proximal limbs and axial muscles and inhibits alpha/gamma motorneurons to flexor muscles?

Back 6

lateral vestibulospinal tract

Front 7

The lateral vestibulospinal tract excites what muscles & inhibits what muscles?

Back 7

excites extensor muscles in proximal limbs and axial muscles

inhibits flexor muscles

Front 8

True or False:

The vestibulospinal tract courses through the length of the spinal cord

Back 8

True

Front 9

The medial vestibulospinal tract mainly excites alpha/gamma motoneurons that innervate what muscles?

Back 9

neck muscles

Front 10

True or False:

the medial vestibulospinal tract courses throughout the length of the spinal tract?

Back 10

False

The medial vestibulospinal tract (MVS) does not descend paths the portion of the spinal cord containing neurons that innervate neck muscles

Front 11

What tract coordinates head movements in response to stimulation of the semicircular canals?

Back 11

The medial Vestibulospinal tract (MVS)

Front 12

The Medial (Pontine) Reticulospinal tract originates where?

Back 12

pontine reticular formation

Front 13

What muscles does the Medial Reticulospinal tract excite and inhibit?

Back 13

excites extensor muscles in proximal limbs and axial muscles

inhibits flexor muscles

(much like the lateral vestibulospinal tract)

Front 14

True or False

the Medial (pontine) Reticulospinal Tract courses throughout the length of the spinal cord?

Back 14

True

Front 15

Which tract provides a counterbalance to the lateral vestibulospinal and medial reticulospinal tracts because it mainly excites alpha/gamma motoneurons to flexor muscles in proximal limbs and axial muscles and inhbits extensor muscles?

Back 15

the Lateral (Medullary) Reticulospinal Tract

Front 16

Where does the Lateral Reticulospinal tract originate?

Back 16

medullary reticular formation

Front 17

Which tract is the only medial system that courses in the ventrolateral portion of the spinal tract, overlapping with the spinothalamic tract?

Back 17

the Lateral (medullary) reticulospinal tract

Front 18

What does the tectospinal tract do?

Back 18

it excites alpha/gamma motoneurons in the cervical cord that innervate muscles that move the head.

It's primary function is to coordinate head and eye movements

Front 19

The lateral systems provide what?

Back 19

control of fractionated, skilled, dextrous movements

They mainly excite flexors and inhibit extensors of upper limb, but excite both flexors and extensors of the distal muscles

Front 20

Where does the corticospinal tract originate?

Back 20

cerebral cortex

Front 21

What does the corticospinal tract do?

Back 21

excites alpha/gamma motoneurons in flexors and inhibits extensors of proximal limbs but excites both in distal limbs and digits

Front 22

What is unique and important about the Corticospinal tract?

Back 22

it's the only tract that coordinates movement of the fingers

Front 23

Where does the rubrospinal tract originate?

Back 23

red nucleus of the midbrain

Front 24

What does the Rubrospinal tract do?

Back 24

excites alpha/gamma motoneurons of the flexor muscles in upper arms down to the wrists

and inhibits extensors

Front 25

True or False

The Rubrospinal tract courses throughout the length of the spinal cord?

Back 25

False

The Rubrospinal tract does not project below the level of the cord that innervates the arms

Front 26

Why is the corticospinal tract terms the direct activation pathway?

Back 26

because it is the most direct (one synapse) pathway from cortex to alpha motor neuron

Front 27

What part of the cord do the lateral systems pathways course?

Back 27

posterior (dorsal) half of cord

Front 28

Both reticulospinal tracts receive input from what higher level?

Back 28

cerebral cortex

Front 29

What mechanism ensures postural muscles will be affected before the muscles that are needed to make skilled voluntary movements?

Back 29

The cerebral cortex activates the Reticulospinal tracts slightly before the Corticospinal tracts

Front 30

What pathways are primarily involved with feedfoward adjustments of posture in the anticipation of movements, so that the movement does not destabilize you?

Back 30

the Reticulospinal pathways

Front 31

Where does the major input to the vestibular nuclei originate from?

Back 31

the vestibular apparatus of the inner ear

Front 32

Which tracts adjust posture following an alteration of postural stability that is detected by the vestibular apparatus?

Back 32

vestibulospinal tracts

Front 33

Which pathways are primarily involved with feedback adjustments to posture?

Back 33

Vestibulospinal tracts

Front 34

Input to the lateral vestibulospinal tracts originates from the vestibular apparatus and the _______________

Back 34

cerebellum

Front 35

Where does the medial pontine reticulospinal tract receive input from? (3)

Back 35

1. cerebellum

2. Cerebral cortex (corticoreticular tract)

3. Somatosensory (nociceptive) input via the anterolateral system; the sources of this input are the spinoreticular tracts and axon collaterals of the spinothalamic tracts

Front 36

What is the primary input to the lateral reticulospinal tract?

Back 36

the corticoreticular tract

Front 37

The Rubrospinal tract receives primary input from where? and also from where?

Back 37

primary - cerebellum

also from the cerebral cortex (corticorubral system)

Front 38

Which tracts of the medial/lateral systems are not important to proximal muscle coordination?

Back 38

corticospinal tract (not as important as the others)

Medial vestibulospinal tract and tectospinal tracts do not descend to the level of the cord that innervates the muscles

Front 39

Decerebrate rigidity is caused by a lesion from where?

Back 39

between the superior and inferior colliculi in the midbrain

Front 40

What pathways are cut in decerebrate rigidity?

Back 40

Corticoreticular tract (thereby removing the excitatory cortical influence on the medullary reticulospinal tract)

rubrospinal tract

Cortical influence to the pontine reticulospinal tract (but is still activated by cerebellar input and somatosensory sources)

Front 41

What is the net result in decerebrate rigidity?

Back 41

rigidity in arm extensor muscles

Front 42

What is the affect of a more rostral lesion in decorticate rigidity?

Back 42

The red nucleus is undamaged (rubrospinal tract) thereby leaving the excitatory influence of flexors and inhibitory influence of extensors leading to flexion of the arms

Front 43

Which is more overpowering when both have excitatory input? Flexion or extenstion?

Back 43

flexion

the reason for this is unknown

Front 44

Why are the legs still extended in decorticate rigidity?

Back 44

The legs do not receive input from the red nucleus; therefore they remain extended

Front 45

What is an antigravity muscle?

Leg ___
Foot ___
Toe ___
Arms: ____
Wrist and finger ____
Neck ____

Back 45

any muscle that resists gravity during the routine activities of the species- i.e. when standing

Leg extensors
Foot extensors
Toe Flexors
Biceps
Wrists and finger flexors
Neck Extensors

Front 46

What muscles become rigid in decorticate posture?

Back 46

antigravity muscles

Front 47

The brainstem motor mechanisms mainly regulate when?

Back 47

involuntary responses (most notably postural)

Front 48

Loss of the corticospinal tracts prevents what, while the preservation of indirect activation pathways permits a person to still do what?

Back 48

Loss of the corticospinal tracts prevents a person to make SKILLED, FRACTIONATED MOVEMENTS OF THE EXTREMITIES, white the preservation of indirect activation pathways permits a person to still make CRUDE MOVEMENTS OF THE DISTAL LIMBS

Front 49

The cerebral cortical motor regions control what?

Back 49

voluntary movements

Front 50

What requires low intensity electrical stimulation in order to produce focal movements?

Back 50

Primary motor cortex

Front 51

What constitutes the premotor cortex?

Back 51

lateral premotor cortex
supplementary and cingulate motor cortices on medial portion of brain

Front 52

How can the premotor cortex evoke movement?

& which muscle group is generall excited?

Back 52

by electrical stimulation w/ intensity that is greater than the primary motor cortex

larger muscle groups

Front 53

What, although considered to be motor cortex, does not connect w/ the primary motor cortex?

Back 53

the frontal eye fields

instead they project to the regions controlling the saccadic eye movements

Front 54

What cortical regions can influence movements through synaptic connects w/ the motor area?

Back 54

Somatosensory and parietal regions

Front 55

The primary motor cortex is what broadmann's area #?

Back 55

4

Front 56

Where is the primary motor cortex located?

Back 56

Anterior to the central sulcus
in the precentral gyrus

On the medial surface, the primary motor cortex is located on the anterior portion of the paracentral lobule

Front 57

from medial to lateral, list the parts of the body innervated by the primary motor cortex

Which body parts have larger representation?

Back 57

foot, leg, trunk, arm, hand, face

Larger representation: fingers and thumb, and muscles used in speech

Front 58

What describes the primary motor cortex in regards to the body:

ipsilateral or contralateral?

Back 58

Contralateral; it's also unilateral

Front 59

Major thalamic input to the primary motor cortex comes from where?

Back 59

posterior portion of the ventral lateral nucleus (which relays information from the cerebellum)

Front 60

Where do the major cortical input to the primary motor cortex come from?

Back 60

the premotor cortex: supplementary motor cortex, lateral premotor cortex, and the somatosensory cortex

Front 61

Output from the primary motor cortex goes where? (3)

Back 61

1. striatum
2. brainstem
3. spinal cord

Front 62

What permits the primary cortex to rapidly respond to sensory stimuli?

Back 62

input to the primary motor cortex from the complementary region of the somatosensory cortex

Front 63

What Brodmann's number is the supplementary motor cortex?

Back 63

6

Front 64

Where is the supplementary motor cortex located?

Back 64

anterior to the primary motor cortex on the medial surface of the brain

it is located in parts of the paracentral gyrus and superior frontal gyrus

Front 65

Is the supplementary motor cortex somatotopically organized like the primary motor cortex?

Back 65

yes, but less so

the leg region is more posterior and the head region is more anterior

Front 66

Which describes the supplementary motor cortex?

unilateral or bilateral

Back 66

bilateral

Front 67

What is the thalamic input of the supplementary motor cortex?

Back 67

the anterior portion of the ventral lateral nucleus (VLa) and the ventral anterior nucleus (VA)

both of these nuclei relay information from the basal ganglia

Front 68

Where does the supplementary cortex receive major cortical input from? (4)

Back 68

1. lateral premotor cortex
2. somatosensory cortex
3. prefrontal cortex
4. posterior parietal cortex

Front 69

The supplementary motor cortex projects to what? (4)

Back 69

1. primary motor cortex
2. lateral premotor cortex
3. spinal cord
4. motor regions of the brainstem

Front 70

What are the 4 functions of the supplementary motor cortex?

Back 70

1. coordinates movements on both sides of the body (esp. bimanual)
2. learns new movement sequences and mentally rehearses sequences
3. adjusts posture for movement (provides input to the reticulospinal pathways for feedfoward regulation of posture)
4. controls the selection of movements generated from memory (tying shoes)

Front 71

What is an apraxia and how is it diagnosed?

Back 71

An apraxia is the inability to perform learned skilled movements

to diagnose, the physician must determine that the patient has no sensory deprivation, no spasticicty, paralysis or altered tone & demonstration that the pt. can understand the command

Front 72

What Brodmann's number is the lateral premotor cortex?

Back 72

6 (along w/ the supplemental motor cortex)

Front 73

Where is the Lateral Premotor Cortex located?

Back 73

anterior to the primary motor cortex on the lateral convexity

Front 74

Is the Lateral Premotor Cortex somatotopically organized?

Back 74

yes, but not as much as the primary motor cortex

Superior - leg
Inferior - head

Front 75

Which of the following describes the premotor cortex?

unilateral or bilateral
single muscle or multiple muscles

Back 75

unilateral
multiple muscles

Front 76

What is the major thalamic input to the Lateral premotor cortex?

Back 76

Anterior portion of the ventral lateral nucleus (VLa)
Ventral anterior nucleus

(same as supplemental cortex)

Front 77

Where does the Lateral Premotor Cortex receive input primarily from? (4)

Back 77

1. Somatosensory Cortex
2. Supplementary Cortex
3. Posterior Parietal cortex
4. Prefrontal cortex

Front 78

Where does the Lateral premotor cortex primarily project to?

Back 78

1. Primary Motor Cortex
2. Spinal Cord
3. Motor regions of the brainstem

Front 79

What are the functions of the Lateral Premotor Cortex? (3)

Back 79

1. Movements reacting to environment
2. adjusts posture for a movement (via the reticulospinal feedfoward)
3. Mirroring

Front 80

What Brodmann's number is the cingulate motor cortex?

Back 80

24

Front 81

What Brodmann's number is the Frontal Eye Field?

Back 81

ventral portion of 8

Front 82

Where is the cingulate motor cortex located?

Back 82

in the cingulate sulcus inferior to the supplementary cortex

Front 83

What does the cingulate motor cortex do?

Back 83

involved in controlling the involuntary movements associated w/ emotional responses (laughing at a joke or motor control of crying)

Front 84

What does the Frontal eye Field do?

Back 84

controls voluntary saccadic eye movements (the fast eye movements)

Front 85

Does stimulation of the frontal eye field causes saccadic eye movements on the same side or toward the opposite side

Back 85

toward the opposite side

Front 86

A lesion produced in the Frontal Eye Fields causes the eyes to deviate.....
toward side of lesion
or away from side of lesion

Back 86

toward side of lesion

Front 87

What percentage of Corticospinal fibers orginate in the primary motor cortex?
in the premotor areas?
in the postcentral gyrus?

Back 87

primary - 30%
premotor - 30%
postgentral - 40%

Front 88

What are the largest neurons conducting at 70 m/s only found in the primary motor cortex that were orginally thought to make up the entire corticospinal system but acutally make up 3%?

Back 88

Betz cells

Front 89

Where do the premotor corticospinal tracts project to?

Back 89

mainly the spinal areas controlling postural movement

Front 90

Where do the postcentral corticospinal fibers terminate & what do movemetns do they modulate?

Back 90

terminates in the dorsal horn (not alpha motor neuron)

modulates propioceptive and somatosensory transmission

Front 91

Describe the pathway of the corticalspinal tract from the cortex to spinal cord including location in the midbrain, pons, medulla, and Spinal cord

Back 91

cortex through corona radiata to posterior limb of internal capsule

midbrain: central region of crus cerebri
pons: ventromedial regions
pons: medulla
90% dessucates in pyramids then travels in the dorsolateral portion of SC

10% doesn't cross over until it reaches its destination in the spinal cord (fibers destined to influence medial system pathways)

Front 92

What is the blood supply to the corticospinal tract lower extremity area on the MEDIAL SURFACE OF PRECENTRAL GYRUS?

Back 92

Anterior cerebral artery (A2 segment)

Front 93

What is the blood supply that provides blood to the trunk, upper extremity, and head portion of the corticospinal tract mostly on the LATERAL SURFACE OF PRECENTRAL GYRUS

Back 93

Middle Cerebral Artery (M2)

Front 94

What is the blood supply of the internal capsule?

Back 94

Lenticulostriate branches of the M1

Front 95

What is the blood supply of the midbrain portion of the corticospinal tract?

Back 95

Paramedian branches of the Posterior Cerebral Artery (P1)

& brahnces of Posterior communicating artery (most lateral parts-leg and trunk)

Front 96

What is the blood supply to the corticospinal tract of the pons?

Back 96

paramedian branches of the basilar artery

Front 97

What is the blood supply to the medulla oblongata portion of the corticospinal tract?

Back 97

branches of the anterior spinal artery

Front 98

What is the blood supply to the spinal cord's portion of the corticospinal tract?

Back 98

branches of the arterial vasocorona and sulcal branches of anterior spinal artery

Front 99

Input to trigeminal (V) and facial (VII) nuclei is....

unilateral or bilateral

Back 99

bilateral

except muscles on the lower half of the face which are innervated mainly CONTRALATERALLY

Front 100

Cortical input to the upper half of the face originates from where?

Cortical input to the lower half of the face originates where?

Back 100

upper half - anterior cingulate gyrus

lower half- motor homunculus

Front 101

Lesions to the corticobulbar pathway above the level of the facial nucleus produces what?

Back 101

Contralateral drooping of the corner of the mouth and lower face (central seven)

Front 102

Lesion of the facial nerve produces what?

Back 102

ipsilateral drooping of the whole side of the face (Bell's palsy)

Front 103

Is input to the nucleus ambiguus in the medulla unilateral or bilateral?

Back 103

bilateral except for motor neurons innervating the soft palate and uvula (contralateral)

Front 104

Lesions of the corticobulbar pathway above the level of the nucleus ambiuguus causes what to happen to the uvula?

Back 104

to deviate toward the side of the lesion (due to unopposed contraction of ipsilateral muscles)

Front 105

Input to the hypoglassal nuclues (XII) is ipsilateral or contralateral?

Back 105

contralateral

Front 106

What happens to the tongue in a lesion in the corticobulbar pathway above the level of the hypoglossal nucleus?

Back 106

the tongue deviates away from the leasion due to unopposed action of the ipsilateral genioglossus muscle)

Front 107

Is input to the accessory muscle (XI) ipsilateral or contralateral?

What do you see in lesions of this pathway?

Back 107

contralateral

difficulty shrugging shoulders or turning head toward the side of the lesion

Front 108

Where does the corticorubral system originate?

Where does it project?

Back 108

primary motor cortex, supplementary motor cortex, lateral premotor cortex, some posterior parietal cortex

projects to the ipsilateral red nuclues

Front 109

The corticorubral system coordinates which two functions/pathways?

Back 109

the corticospinal and rubrospinal fxns

Front 110

Where does the Corticoreticular system originate?

Where does it project

Back 110

lateral premotor cortex and supplemental motor cortex

pontine (medial) and medullary (lateral) reticulospinal tracts

Front 111

What does the corticopontine system consist of?

Back 111

pathways from nearly all regions of the cortex that project to ipsilateral pontine nuclei which then project to the cerebellum

this system communicates cortical info to cerebellum

Front 112

What is a lower motor neuron?

Back 112

spinal motoneurons or nerves, or cranial nerve motor neurons

Front 113

What does damage to the lower motor neurons cause? (5)

Back 113

1. decreased muscle tone
2. Neurogenic muscular atrophy (not as strong as muscle size)
3. Muscle fasciculations or fibrillations of single fibers
4. Reduction of tendon reflexes (hyporeflexia)
5. No babinski sign

Front 114

What is an upper motor neuron?

Back 114

corticospinal neurons and other descending neurons

Front 115

What does damage to the upper motor neurons cause? (5)

Back 115

1. decreased muscle tone initially, becoming increased muscle tone w/ time
2. Rarely have muscle atrophy
3. Affects groups of muscles (instead of single muscle)
4. Enhanced stretch reflexes (hyperreflexia - indirect pathway)
5. Babinski sign

Front 116

What is spasticity?

What are the characteristics?

Back 116

condition of hypertonic and hyperreflexive muscles in which there is enhanced resistance to passive movements

1. Unidirectional - resistance is greater in antigravity muscles
2. Velocity dependent - resistance to movement depends on speed
3. Hyperreflexive tendon jerk

Front 117

What probably causes spasticity?

Back 117

changes in functional synaptic connections related to stretch reflex

There is reduction in inhibitory influences on motor pathways due to abnormal fxn of the INDIRECT activation pathways, not the direct activation pathway

Front 118

What is clinical rigidity and what is it associated with?

Back 118

Assoc. w/ Parkinsonism

It's
1. Bidirectional: resistance to movement in any direction
2. Less velocity dependent
3. No hyperactive tendon jerk