Nsp Week 1: Descending Motor Pathways (Blair)

Front 1

What are the 3 main levels of the motor system?

Back 1

Lowest level --> spinal cord and a-motoneurons in cranial nerves

Middle level --> all pathways that impact the lowest level (descending pathways from brainstem; corticospinal pathway from primary motor cortex)

Highest level --> regions containing motor programs and instructions (basal ganglia, cerebellum, and cortex)

Front 2

Alpha-motoneurons receive input from which two principal sources in the brain?

Back 2

1. Cerebral cortex (direct activation pathway)
2. Brainstem pathways (indirect activation pathway)

Front 3

Brainstem pathways receive input from which to regions of the brain?

Back 3

1. Cerebral cortex
2. Cerebellum

Front 4

Which control circuit influences movements of ipsilateral muscles through its connections to the cerebral cortex and brainstem?

Back 4

Cerebellar control circuit

Front 5

Which control circuit influences movements of contralateral muscles through connections with the cerebral cortex?

Back 5

Basal ganglia

Front 6

What type of control do medial systems mainly provide?

Back 6

Posture and balance, including orienting movements
(involuntary movements that do not reach consciousness)

Front 7

With one exception, the medial systems pathways course through which portions of the spinal cord?

Back 7

Ventromedial portions

Front 8

The lateral vestibulospinal tract excites and inhibits which motoneurons?

Back 8

Excites alpha and gamma- motoneurons to EXTENSOR muscles in proximal and axial muscles

Inhibits alpha- and gamma- motoneurons to flexor muscles

*Courses throughout the length of the spinal cord

Front 9

Which vestibulospinal tract courses throughout the length of the spinal cord?

Back 9

Lateral vestibulospinal tract

(Medial vestibulospinal tract does not descend past the portion of the spinal cord containing the neurons that innervate neck muscles)

Front 10

Which motoneurons are excited by the medial vestibulospinal tract?

What kind of movements are coordinated by this pathway?

Back 10

Alpha- and gamma- motoneurons that innervate neck muscles

*Coordinates head movements in response to stimulation of semicircular canals

Front 11

What is the function of the medial (pontine) reticulospinal tract?

Back 11

(functions similarly to lateral vestibulospinal tract)

Excites alpha- and gamma- motoneurons to extensor muscles in proximal limbs and axial muscles

Inhibits alpha- and gamma- motoneurons to flexor muscles

Front 12

Which reticulospinal tract courses throughout the length of the spinal cord-- Medial (pontine) or Lateral (medullary)?

Back 12

Medial (pontine)

Front 13

Which descending pathway provides a counterbalance to the lateral vestibular and medial reticulospinal tracts?

Back 13

Lateral (medullary) reticulospinal tract

Front 14

What is the function of the Lateral (medullary) reticulospinal tract?

Back 14

Excites alpha- and gamma- motoneurons to flexor muscles in proximal limbs and axial muscles
Inhibits alpha- and gamma- motoneurons to extensor muscles

*Courses throughout the length of the spinal cord

*Opposes actions of lateral vestibulospinal and medail (pontine) reticulospinal tracts

Front 15

What is the only medial systems pathway that courses in the ventrolateral portion of the spinal cord, and overlaps with the ascending spinothalamic tract?

Back 15

Lateral (medullary) reticulospinal tract

Front 16

Which tract primarily functions to coordinate head and eye movements?

Back 16

Tectospinal tract
(from superior colliculus)

Front 17

What do the lateral systems mainly control?

Back 17

Fractionated, skilled, dexterous movements

*Excite flexors and inhibit extensors of upper limb, but excite flexors and extensors of distal muscles (fine control of finger muscles)

Front 18

What is the function of the corticospinal tract?

Back 18

Excites alpha- and gamma- motoneurons of flexors in proximal limbs
Inhibits alpha- and gamma- motoneurons of extensors in proximal limbs
In the distal limbs and digits, it excites alpha- and gamma- motoneurons to both flexors and extensors

Front 19

What is the function of the Rubrospinal tract?

How far does the pathway descend down the spinal cord?

Back 19

Excites alpha- and gamma- motoneurons of flexors in upper arm down to the writs
Inhibits alpha- and gamma- motoneurons that innervate extensors

*Does not project below the level of the cord that innervates the arms

Front 20

List the 2 lateral system tracts.

Back 20

1. Corticospinal tract
2. Rubrospinal tract

Front 21

List the 5 medial system tracts

Back 21

1. Lateral vestibulospinal tract
2. Medial vestibulospinal tract
3. Medial (pontine) reticulospinal tract
4. Lateral (medullary) reticulospinal tract
5. Tectospinal tract

Front 22

Which medial systems tract descends from the superior colliculus?

Back 22

Tectospinal tract

Front 23

Where does the corticospinal tract originate?

Back 23

Cerebral cortex

Front 24

Where does the Rubrospinal tract originate?

Back 24

Red nucleus

Front 25

Which descending tract is also termed the direct activation pathway? Why is it termed this?

Back 25

Corticospinal tract
It only has one synapse, so it is the most direct pathway from the cortex to alpha motor neurons

Front 26

Which tract has features common to both medial and lateral systems?

Back 26

Lateral (medullary) reticulospinal tract
(courses in the lateral spinal cord and facilitates flexors, but is mainly used in postural control)

Front 27

Which tracts do the cerebral cortex activate first-- reticulospinal or corticospinal tracts?

Back 27

Reticulospinal tract

*Postural muscles are affected before the muscles that make skilled voluntary movements

Front 28

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

Back 28

Vestibular apparatus

Front 29

Which pathways are primarily involved with feedforward adjustments of posture in the anticipation of movements?

Back 29

Reticulospinal pathways

Front 30

Which pathways are primarily involved with feedback adjustments to posture?

Back 30

Vestibulospinal pathways

Front 31

Which tracts provide excitatory drive to proximal extensor muscles in the arms?

Back 31

1. Medial (pontine) reticulospinal
2. Lateral vestibulospinal

Front 32

From which 2 regions does input to the lateral vestibulospinal tract originate?

Back 32

1. Vestibular apparatus in inner ear
2. Cerebellum

Front 33

List 3 inputs that are received by the Medial (pontine) reticulospinal tract

Back 33

1.Cerebellum
2. Somatosensory input from anterolateral system (spinoreticular and spinothalamic tracts)
3. Cerebral cortex (corticoreticular tract)

Front 34

Which tract provides inhibitory drive to proximal extensor muscles of the arm?

Back 34

Lateral (medullary) reticulospinal tract

Front 35

What is the primary input to the lateral reticulospinal tract?

Back 35

Corticoretular tract

Front 36

What is the primary input to the Rubrospinal tract?

Back 36

Cerebellum

(Input also arises from the cortex)

Front 37

A lesion placed between the superior and inferior colliculi in the midbrain causes what problem?

How does this affect extensor and flexor motoneurons?

Back 37

Decerebrate rigidity
(rigidity in arm extensor muscles)

Axons of the corticoreticular tract are disturbed, removing the excitatory cortical influence of the medullary reticulospinal tract--> Inhibitory drive on extensor motoneurons is removed

Rubrospinal tract is damaged --> removes excitation of flexor motoneurons

Front 38

Decerebrate rigidity results from damage to which 2 tracts?

Back 38

1. Corticoreticular tract (negatively affects medullary reticulospinal tract)
2. Rubrospinal tract

Front 39

Which tracts are minimally affected by a lesion between the superior and inferior colliculi?

Back 39

1. Lateral vestibulospinal pathway (unaffected)
2. Medial (pontine) reticulospinal tract (minimally affected -- cortical influence removed, but is still activated by cerebellar input and somatosensory sources)

Front 40

What kind of rigidity ensues when a lesion occurs more rostrally than the corpora quadragemina, so that the red nucleus is undamaged?

Back 40

Decorticate rigidity
(arms flexed at the elbows, but the legs are extended)

Front 41

It appears that in humans, if there are strong competing influences from both flexors and extensors in the arms, then which muscle group will "win"?

Back 41

Flexors

Front 42

The muscles that become rigid in the decorticate posture are the ones that are considered to be _________ muscles.

Back 42

Antigravity

*Muscles that resist gravity when you stand

Front 43

Which muscles of the legs, feet, and toes are antigravity muscles?

Back 43

Extensors in legs (allow standing)
Extensors in feet ("resist" the ground and makes you taller)
Flexors in toes (moves foot away from ground)

Front 44

Which muscles of the arms, wrist, fingers, and neck are antigravity muscles?

Back 44

(think about doing a chin-up)

Biceps (flexor)
Wrist flexors
Finger flexors
Neck extensors

Front 45

Which muscles primarily become spastic with upper motor neuron lesions?

Back 45

Antigravity muscles

Front 46

Loss of which descending tract will prevent the ability to make skilled, fractionated movements in the extremities?

Back 46

Corticospinal tract
(direct activation pathway)

Front 47

Loss of the corticospinal tract with preservation of the indirect activation pathways, will still permit a person to make crude movements in which portion of the limbs?

Back 47

Distal limbs
(Ex: hand can still be moved, but discrete control of fingers is lost)

Front 48

What are the two major conceptual divisions of the motor cortex?

Back 48

1. Primary motor cortex
2. Premotor cortex (lateral premotor cortex, supplementary, and cingulate motor cortices)

Front 49

What is the difference between the required electrical intensity and muscle groups excited by the primary motor cortex and the premotor cortex?

Back 49

Primary motor cortex --> low intensity stimulation; focal movements produced (single muscles can be stimulated)

Premotor cortex --> greater intensity required; larger muscle groups stimulated

Front 50

Do frontal eye fields connect with the primary motor cortex?

Back 50

No.
Instead, they project to regions controlling saccadic eye movements

Front 51

Which cortex is located just anterior to the central sulcus?

Back 51

Primary motor cortex

Front 52

Describe where nearly the entire face region of the primary motor cortex is located?

Back 52

Located along the lateral convexity of the brain in the precentral gyrus
*Mostly buried in the anterior wall of the central suclus

Front 53

Where is the primary motor cortex located on the medial surface of the brain?

Back 53

Anterior portion of the paracentral lobule

Front 54

Where is the leg represented in the primary motor cortex?

Back 54

Medial surface
(with the foot most inferior)

Front 55

Where are the arm, hand, and face represented in the primary motor cortex?

Back 55

On the lateral convexity
(the arm is most superior and the face is most inferior)

Front 56

Major cortical input to the primary motor cortex comes from which regions of the cortex?

Back 56

1. Supplementary motor cortex
2. Lateral premotor cortex
3. Somatosensory cortex

Front 57

Major thalamic input to the primary motor cortex comes from which region of the thalamus?

Back 57

Ventral lateral nucleus (VLp)

Front 58

Which region of the brain is primary involved in the execution of voluntary movements and in controlling fractionated movements?

Back 58

Primary motor cortex

Front 59

Where is the supplementary motor cortex located?

Back 59

Anterior to the primary motor cortex on the medial surface of the brain
Parts of the paracentral lobule and superior frontal gyrus

Front 60

What is the main difference between the somatotopical organization of the primary motor cortex and the supplementary motor cortex?

Back 60

In the supplementary cortex, the head is located more anterior and the leg more posterior

Front 61

Major thalamic input to the supplementary motor cortex comes from which regions of the thalamus?

Back 61

1. Anterior portion of the ventral lateral nucleus
2. Ventral anterior nucleus

(Both of these nuclei relay information from the basal ganglia)

Front 62

The supplementary motor cortex receives its major cortical input from which regions?

Back 62

1. Lateral premotor cortex
2. Somatosensory cortex
3. Prefrontal cortex
4. Posterior parietal cortex

Front 63

The supplementary motor cortex projects to which 4 regions?

Back 63

1. Primary motor cortex
2. Lateral premotor cortex
3. Spinal cord
4. Motor regions of the brainstem

Front 64

Which region of the brain coordinates movements on both sides of the body, particularly movements that require both hands (bimanual movements)?

Back 64

Supplementary motor cortex

Front 65

Which region of the brain learns new movement sequences, and mentally rehearses these sequences?

Once you become adept at a new sequence, activity in which area of the brain increases?

Back 65

Supplementary motor cortex

*Once routine is memorized, activity in the primary motor cortex increases and activity in the supplementary motor cortex decreases

Front 66

Which region of the brain provides input to the reticulospinal pathways for feedforward regulation of posture?

Back 66

Supplementary motor cortex

Front 67

Damage to the supplementary motor cortex results in what kinds of problems?

Back 67

1. Problems in either the programming or selection of complex sequences
(apraxias-- the command can be understood, but not performed)
2. Reduces spontaneous movements and speech

Front 68

Where is the lateral premotor cortex located?

Back 68

Anterior to the primary motor cortex on the lateral convexity of the cerebral hemisphere.

Front 69

How does the somatotopic organization of the lateral premotor cortex compare to that of the primary motor cortex?

Back 69

They are very similar. Both are arranged so that the leg region is superior and the head region is inferior.
They are different in that the lateral premotor cortex:
1. Less organized that the primary motor cortex
2. Leg region is on the convexity rather than the medial surface

Front 70

What kind of movement is the lateral premotor cortex primary involved with?

Back 70

Unilateral movements among multiple muscles

Front 71

The major thalamic input to the lateral premotor cortex comes from which regions of the thalamus?

Back 71

1. Anterior portion of the ventral lateral nucleus
2. Ventral anterior nucleus

(same as the supplementary motor cortex)

Front 72

Which 3 regions does the lateral premotor cortex project to?

Back 72

1. Primary motor cortex
2. Spinal cord
3. Motor regions of the brainstem

Front 73

Which region of the brain is involved in selecting movements based on environmental cues?

Back 73

Lateral premotor cortex

Front 74

Which region of the brain contain mirror neurons, which become active when you watch someone else do something that you could do yourself?

Back 74

Lateral premotor cortex

Front 75

Where is the cingulate motor cortex located?

Back 75

In the cingulate sulcus, inferior to the supplementary motor cortex

Front 76

Which region of the brain is involved in controlling involuntary movements associated with emotional responses?

Back 76

Cingulate motor cortex

Front 77

A lesion in the frontal eye field will produce eye deviation toward which side?

Back 77

Towards the same side of the lesion

Front 78

Which region of the brain controls voluntary saccadic eye movements?

Back 78

Frontal eye field

Front 79

Where are Betz cells found?

Back 79

Only in the primary motor cortex

Front 80

The corticospinal system is composed of which fibers?

Back 80

1. Primary motor cortex (30%)
2. Premotor areas (30%)
3. Postcentral gyrus (40%)

Front 81

Which regions of the midbrain, pons, and medulla are occupied by the corticospinal tract?

Back 81

Crus cerebri in the midbrain
Ventromedial regions of the pons and medulla

Front 82

In which portion of the spinal cord does the corticospinal tract descend?

Back 82

Dorsolateral portion

Front 83

The Anterior cerebral artery provides blood supply to which region of the corticospinal tract?

Where is this artery located?

Back 83

Lower extremity region (foot, leg, hip)

*Located on medial surface of precentral gyrus

Front 84

The Middle cerebral artery provides blood supply to which region of the corticospinal tract?

Where is this artery located?

Back 84

Trunk, upper extremity, and head regions

*Located on lateral surface of precentral gyrus

Front 85

The internal capsule receives blood supply from which arterial branches?

Back 85

Lenticulostriate branches of the M1 segment of the middle cerebral artery

Front 86

The midbrain receives its blood supply from which arteries?

Back 86

1. Posterior cerebral artery
2. Branches of the Posterior communicating artery

Front 87

The pons receives its blood supply by branches of which artery?

Back 87

Paramedian branches of the basilar artery

Front 88

The medulla receives its blood supply from branches of which artery?

Back 88

Anterior spinal artery

Front 89

The spinal cord receives its blood supply by branches of which arteries?

Back 89

1. Arterial vasocorona
2. Sulcal branches of Anterior spinal artery

Front 90

Lesions to the corticobulbar pathway above the level of the facial nucleus will have what effect?

Back 90

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

Front 91

Lesion of the facial nerve produces what kind of problem?

Back 91

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

Front 92

Lesions of the corticobulbar pathway above the level of the nucleus ambiguus has what kind of affect on the uvula?

Back 92

Causes the uvula to deviate towards the side of the lesion

Front 93

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

Back 93

Mostly bilateral, except for motor neurons innervating part of the soft palate and uvula, which receive contralateral input

Front 94

Lesions to the corticobulbar pathway above the level of the hypoglossal nucleus have what effect on the tongue?

Back 94

Upon protrusion, the tongue deviates AWAY from the side of the lesion

Front 95

Is input to the hypoglossal nucleus (XII) contralateral or bilateral?

Back 95

Contralateral

Front 96

Is input to the accessory nucleus (XI) contralateral or bilateral?

Back 96

Mainly contralateral
(can vary in different people)

Front 97

Lesions of the accessory nucleus (XI) usually result in what problems?

Back 97

1. Difficulty shrugging shoulders
2. Difficulty turning head TOWARD the side of lesion

Front 98

Which system coordinates corticospinal and rubrospinal functions?

Back 98

Corticorubral system

Front 99

Where does the corticorubral system originate?

Where does it project?

Back 99

Originates:
1. Primary motor cortex
2. Supplementary motor cortex
3. Lateral premotor cortex

Projects:
Ipsilateral red nucleus

Front 100

Where does the corticoreticular system originate?

Where does it project?

Back 100

Originates:
1. Lateral premotor cortex (mainly
2. Supplementary motor cortex

Projects:
Pontine and medullary reticulospinal tracts

Front 101

Which system communicates cortical information to cerebellum?

Back 101

Corticopontine system

Front 102

"Lower motor neuron" refers to what type of neurons?

Back 102

1. Spinal motoneurons or nerves
2. Cranial nerve motor neurons

Front 103

"Upper motor neuron" refers to what type of neurons

Back 103

1. Corticospinal neurons
2. Other descending neurons

Front 104

List 5 characteristic signs of lower motor neuron damage.

Back 104

1. Decreased muscle tone
2. Neurogenic muscle atrophy
3. Muscle fasciculations or fibrillations of single fibers
4. Reduction of tendon reflexes (hyporeflexia)
5. No Babinski sign

Front 105

List 5 characteristic signs of upper motor neuron damage

Back 105

1. Decreased muscle tone intially, increased muscle tone with time
2. Rarely have muscle atrophy
3. Affects groups of muscles
4. Enhanced stretch reflexes (hyperreflexia)
5. Babinski sign

Front 106

List 3 characteristics of spasticity

Back 106

1. Unidirectional (resistance to movement is greater in antigravity muscles)
2. Velocity dependent
3. Hyperreflexive tendon jerk

Front 107

List 3 characteristics of clinical rigidity

Back 107

1. Bidirectional
2. Less velocity dependent than spasticity
3. No hyperactive tendon jerk

Front 108

What is the difference in stiffness seen with spasticity and clinical rigidity?

Back 108

Spasticity --> unidirectional stiffness
Clinical rigidity --> bidirectional stiffness

Front 109

Is decerebrate (and decorticate) rigidity more similar to spasticity or clinical rigidity?

Back 109

Spasticity