Motor Systems

Question 1

Cortical areas involved in movement:

Answer 1

Premotor cortex (PMC) and supplementary motor area (SMA) – Brodmann’s area 6
Primary motor cortex (M-I) – Brodmann’s area 4
Posterior parietal cortex – Brodmann’s area 7
Primary somatosensory cortex (S-I) – Brodmann’s areas 3, 1, 2

Question 2

Premotor cortex (PMC) and supplementary motor area (SMA)

Answer 2

Complex movements are designed and sequenced here, then transmitted to the primary motor cortex; controls axial and proximal, upper and lower limbs

Question 3

Primary motor cortex (M-I)

Answer 3

Execution of distinct, well-defined movements; controls the opposite side of the body

Question 4

Posterior parietal cortex

Answer 4

Sensory integration and visual guidance of movement

Question 5

Primary somatosensory cortex (S-I)

Answer 5

Influences movement via sensory input from visceral and somatic structures to the spinal cord

Question 6

Describe layer V of corticospinal tract

Answer 6

Upper motor neurons; contain large, pyramidal-shaped cell bodies that give rise to axons that form the descending motor pathways

Question 7

Origin of anterior/lateral corticospinal tracts

Answer 7

1/3 of fibers from each of the following:

• -Brodmann’s area 4
• -Brodmann’s area 6
• -Brodmann’s area 5, 7 and 3, 1, 2

Question 8

Course of anterior/lateral corticospinal tracts

Answer 8

Descends through the corona radiata, posterior limb of the internal capsule, basis pedunculi, pons, and medulla (where they assemble and descend in the pyramid – layer V)

Question 9

Decussation of anterior/lateral corticospinal tracts

Answer 9

In the caudal medulla, almost all the fibers decussate in the pyramidal decussation and the remaining do not and remain on the same side of origin

Question 10

Termination of lateral corticospinal tract

Answer 10

These are the fibers that decussated, and they travel in the lateral funiculus, as well as terminate and synapse, at all spinal cord levels; the majority of fibers terminate in the cervical region; controls distal muscles of the upper limb (skilled/manipulative finger movements)

Question 11

Termination of anterior corticospinal tract

Answer 11

The fibers that did not decussate and travel in the anterior funiculus, as well as terminate and synapse, at the cervical and upper thoracic spine; these fibers decussate at level of termination (ONLY UMN to decussate in the spinal cord); control axial muscles

Question 12

Upper and lower motor neuron – descriptions

Answer 12

UMN – cell bodies reside in the motor cortex or brainstem that influence LMNs in the brainstem or spinal cord

LMN – control movement of the body, reside in the ventral horn of the spinal cord, axons run in peripheral nerves that terminate in and innervate skeletal muscles

Question 13

Deficits following UMN lesion in corticospinal tract

Answer 13

Spastic paralysis, hyperreflexia, muscle atrophy, and Babinski’s sign

Initially, temporary muscle weakness, hypotonia, and hyporeflexia –> hypertonicity develops because the gamma motor neurons become overstimulated due to lack of appropriate tone control via the cerebellum, causing the alpha-gamma loop being overstimulated, resulting in hypertonicity

Deficits will appear on the CONTRALATERAL side of the body

Question 14

Deficits following lesion in corticospinal tract at spinal cord level

Answer 14

Same as UMN lesion (spastic paralysis, hyperreflexia, muscle atrophy, and Babinski’s sign)

Deficits will appear on IPSILATERAL side of body

Question 15

Deficits following a spinal LMN lesion in corticospinal tract

Answer 15

Affects ipsilateral side and results in muscle becoming denervated

Hypotonia, hyporeflexia, flaccid paralysis, muscle atrophy, fibrillations, fasciculations

Question 16

Arterial blood supply to corticospinal tracts

Answer 16

Anterior cerebral artery = medial M-I cortex (CONTRALATERAL lower limb)
Middle cerebral artery = lateral M-I cortex (CONTRALATERAL UL and face)
Lenticulostriate arteries (off middle cerebral) = supply anterior and posterior limbs of the internal capsule
Anterior spinal artery = anterior corticospinal tract, medulla, cervical spinal cord
Posterior spinal artery =   dorsal column
Posterior cerebral artery and basilar artery = midbrain
Pontine arteries (off basilar artery) = pons
Vertebral artery = rostral medulla

Question 17

Origin of corticotectal tract

Answer 17

Visual association cortex

Question 18

Termination of corticotectal tract

Answer 18

Oculomotor accessory nuclei in the midbrain, projecting via the MLF to nuclei that innervate extraocular muscles

Superior colliculus in the rostral midbrain, which gives rise to:

TECTOSPINAL tract – axons cross, and then terminate in the cervical and thoracic spinal cord levels

Question 19

Function of corticotectal tract

Answer 19

Responsible for reflexes associated with responses to startling stimuli (loud auditory, cutaneous, etc.); elicit head/eye turning to see stimuli source

Question 20

Origin of corticorubral tract

Answer 20

Sensorimotor cortex

Question 21

Termination of corticorubral tract

Answer 21

Red nucleus of midbrain, which gives rise to:

RUBROSPINAL tract – axons terminate in upper spinal cord

Question 22

Function of corticorubral tract

Answer 22

Facilitates/inhibits motor neurons that innervate the distal flexor/extensor muscles of the UL and supplements the activity of the corticospinal tract

Question 23

Origin of corticoreticular tract

Answer 23

Sensorimotor cortex

Question 24

Termination of corticoreticular tract

Answer 24

RF of the pons and medulla, which gives rise to:

MEDIAL (PONTINE) RETICULOSPINAL tract – originates from the pontine nuclei, descends in the anterior funiculus, and terminate at all spinal cord levels in the gray matter (with interneurons and gamma motor neurons); standing muscles

LATERAL (MEDULLARY) RETICULOSPINAL tract – originates from medullary nuclei, descends in the anterior funiculus, and terminate at all spinal cord levels in the gray matter (with interneurons and gamma motor neurons); laying down muscles

Question 25

Function of medial (pontine) reticulospinal

Answer 25

Inhibits paravertebral/limb flexors and excites extensors

Question 26

Function of lateral (medullary) reticulospinal tract

Answer 26

Excites paravertebral/limb flexors and inhibits extensors

Question 27

Origin of vestibulospinal tract

Answer 27

Vestibular nuclei in the medulla and pons; gives rise to two tracts (lateral and medial)

Question 28

Medial vestibulospinal tract: origin, termination, and function

Answer 28

Origin – medial and inferior vestibular nuclei

Termination – bilaterally at cervical and upper thoracic spinal levels (alpha and gamma motor neurons innervating neck muscles)

Function – maintain balance in response to vestibular input and control head movement to keep an image on the retina

Question 29

Lateral vestibulospinal tract: origin, termination, and function

Answer 29

Origin – lateral vestibular nucleus

Termination – ipsilaterally at all spinal cord levels (interneurons and alpha motor neurons)

Function – excite paravertebral and limb extensor muscles, inhibit flexors

Question 30

Deficits of lesion in corticorubral/rubospinal tracts

Answer 30

UMN signs; not significant since these tracts simply supplement the corticospinal tract (receive dual innervation)

Question 31

Corticoreticular/reticulospinal lesions

Answer 31

UMN signs

Question 32

Brown-Sequard syndrome

Answer 32

Group of symptoms that occurs as a result to a hemisection of the spinal cord:

• -UMN lesion signs (ipsilateral)
• -LMN signs (ipsilateral)
• -Loss of reflex activity at the level of the lesion (ipsilateral)
• -Loss of fine touch/vibration/discrimination (ipsilateral)
• -Loss of pain/temperature sensation (contralateral about 2 levels below lesion)

Question 33

Combined systems disease (subacute combined degeneration)

Answer 33

Deficiency in vitamin B12 that causes degeneration in:

Dorsal funiculus – sensory fibers of FG and FC; results in loss of discriminative touch, two-point discrimination, vibratory sense, proprioception, and sensory ataxia

Lateral funiculus – corticospinal motor fibers; results in UMN signs

Question 34

Deficits with occlusion of anterior spinal artery

Answer 34

Loss of anterolateral pathways, causing loss of pain and temperature sensation several levels below the lesion

Damage to anterior horn cells, producing LMN weakness

Produces a lesion that affects the lateral corticospinal tracts, producing UMN signs

Damages descending pathways that control sphincter function, causing incontinence

Question 35

Neurological deficits with occlusion of posterior spinal artery

Answer 35

Loss of proprioception, vibratory sense, and tactile (fine touch) discrimination

Question 36

Origin of corticonuclear (corticobulbar) tract

Answer 36

Motor cortex

Question 37

Course and pattern of termination of corticonuclear fibers in motor nuclei of cranial nerve V

Answer 37

Fibers travel (along with corticospinal fibers) to the brainstem, where they terminate bilaterally in the RF of the pons next to CN V

Question 38

Course and pattern of termination of corticonuclear fibers in motor nuclei of cranial nerve VII

Answer 38

Superior half – receives UMNs bilaterally; innervates superior half of face

Inferior half – receives UMNs contralaterally; innervates inferior half of face

Question 39

Course and pattern of termination of corticonuclear fibers in nucleus ambiguus (IX, X, XI)

Answer 39

IX and X (receives fibers bilaterally) sends fibers to the soft palate, larynx, and pharynx
XI (receives fibers ipsilaterally) sends fibers to the SCM and trapezius’

Question 40

Course and pattern of termination of corticonuclear fibers in motor nuclei of cranial nerve XII

Answer 40

To all muscles of the tongue (except genioglossus) – receives fibers bilaterally

To genioglossus – receives fibers contralaterally

Question 41

Cortical projections that influence motor nuclei of cranial nerves III, IV, and VI

Answer 41

The frontal and parietal motor eye fields send separate axons that terminate in the RF, which then projects into the CN III, IV, and VI nuclei

Question 42

Deficits of UMN lesion with fibers of corticonuclear tract terminating in facial nucleus

Answer 42

The upper half of the face is unaffected – since the UMN fibers are bilateral, there are “backup” fibers if there is a unilateral lesion

The side of the lower half of the face contralateral to the lesion is affected – the lower face receives contralateral UMNs

Since corticonuclear and corticospinal fibers run very closely together (internal capsule, basis pedunculi, basilar pons, medullary pyramid), if the corticonuclear fibers are damaged then the corticospinal are likely damaged as well; often, there will be muscle weakness in the extremities on the same side as the facial weakness

Question 43

Deficits of UMN lesion with fibers of corticonuclear tract terminating in hypoglossal nucleus

Answer 43

Unilateral lesion to the XII UMN would result in a deviation of the tongue to the same side as the lesion because the genioglossus receives contralateral input, so this muscle on the contralateral side of the lesion would be weakened

Question 44

Arterial blood supply of corticonuclear tract

Answer 44

Middle cerebral artery = lateral surface of precentral gyrus
Lenticulostriate arteries (off middle cerebral) = supply GENU and posterior limb of the internal capsule
Anterior spinal artery = medulla
Posterior cerebral artery and basilar artery = midbrain
Pontine arteries (off basilar artery) = pons
Vertebral artery = rostral medulla