Corticospinal

Question 1

___________ movements are carried out by means of the corticospinal tract for the body and corticobulbar (corticonuclear) tracts for the cranial nerve motor nuclei that innervate muscles of the______.

Answer 1

Volitional

face

Question 2

The corticospinal tract and corticobulbar tracts (pathways) arise in the cerebral cortex; descend through the _____________ to end in ___________________ or the ventral horn of the spinal cord.

Answer 2

internal capsule

brainstem motor nuclei

Question 3

Most of the fibers descending to the spinal cord cross in the ___________________ at the _____________ decussation. The remainder of the fibers descend ipsilaterally to individual segments and then cross.

Answer 3

lower medulla

pyramidal

Question 4

This organization describes how volitional movement on the left side of the body is controlled by the ____________________; and the right side of the body to be controlled by the ______________________.

Answer 4

right side of the brain

left side of the brain

Question 5

REMEMBER, the sensory information from the left side of the body crossed and ascended to end in the right side of the brain; and all of the information from the right side of the body crossed and ascended to end in the left side of the brain. Makes for a pretty efficiently organized system!!

Answer 5

REMEMBER, the sensory information from the left side of the body crossed and ascended to end in the right side of the brain; and all of the information from the right side of the body crossed and ascended to end in the left side of the brain. Makes for a pretty efficiently organized system!!

Question 6

Corticospinal tract =

Answer 6

voluntary motor pathway for the body

Question 7

Primary cells of origin are located in the _____________ (primary motor cortex; area 4). There are also neurons found in area 6 (________________________________________________), area 8 (____________) and also to a lesser extent in the ______________________ (areas 3,1, 2) whose axons travel in the corticospinal tract.

Answer 7

precentral gyrus

premotor region; lateral premotor and supplementary motor

frontal eye fields

primary somatosensory cortex

Question 8

The fibers that make up the corticospinal tract exit the gray matter of the cortex and travel through the __________________ (the fiber bundles underlying the cortex).

Answer 8

medullary white matter

Question 9

List some of the structures that the fibers travel through in the medullary white matter:

Answer 9

(in sequence):

• corona radiata
• posterior limb of the internal capsule
• cerebral peduncles
• corticospinal fibers in the ventral pons
• pyramids.

Question 10

At the lower end of the medulla, ____of the fibers cross at the pyramidal decussation and continue their descent as the _____________________________ (located in the lateral funiculus).

Answer 10

85%

lateral corticospinal tract

Question 11

The remaining fibers that do not cross descend as the ______________________________ (located in the anterior funiculus). These latter fibers then cross at the __________ level where they innervate the _______________________________

Answer 11

anterior corticospinal tract

segmental

lower motor neuronal pool.

Question 12

The organization of the fibers as they descend is __________________ arranged.

Answer 12

topographically

Question 13

The termination of the corticospinal tract fibers is primarily on ____________________ (97%).

Answer 13

interneurons

Question 14

The majority of the corticospinal fibers terminate in the _________________ (55%) and lesser numbers in the _______________ (20%) and _____________ (25%) regions.

Answer 14

cervical region

thoracic region

lumbosacral

Question 15

It is the ____________ that then excite or inhibit the lower motor neurons (neurons in the ventral horn that make up the ventral root) to influence the activity of a given motor unit.

Answer 15

interneurons

Question 16

Lower motor neurons that are responsible for activation of extrafusal muscle fibers (volitional movements) are termed ___________ neurons and are the final _______________________ to the muscle or effecter organ.

Answer 16

alpha () motor

common pathway

Question 17

___________________ neurons are also lower motor neurons. They innervate the _______________ muscle fibers of the muscle spindle. (Think about this distribution and what parts of the body have the most delicate and fine motor movements.)

Answer 17

Gamma () motor

intrafusal

Question 18

Corticoreticulospinal pathway runs __________ to the corticospinal tract.
The cells giving rise to these fibers are located in the ______________________________________ areas.

Answer 18

parallel

supplementary motor and lateral premotor

Question 19

The axons descend along with the corticospinal fibers to the level of the ___________________________________, where they synapse bilaterally. Reticulospinal fibers then descend into the spinal cord where they synapse in the __________________ on the lower motor neuron pool; primarily interneurons.

Answer 19

pontine and medullary reticular formation

ventral horn

Question 20

Functionally, this system has a dual purpose. The premotor and secondary motor areas provide the information to primary motor cortex for ______________ movement.

Answer 20

voluntary

Question 21

The information from primary motor cortex then descends for fine motor control distally on the extremities, i.e., the fingers. This precise individual movement is termed __________________ movement.

Answer 21

fractionated

Question 22

At the same time, these premotor areas are activating the __________________ and subsequently the reticulospinal fibers. This information is transferred to the spinal cord for initiation of _____________________________of axial and proximal limb musculature – it sets the platform for movement in anticipation of the fractionated movement.

Answer 22

reticular formation

complementary activation

Question 23

Pontine (medial) reticulospinal pathway =

Answer 23

primarily ipsilateral and facilitory to axial and limb musculature, especially the extensors and works with the medial vestibulospinal tract.

Question 24

Medullary (lateral) reticulospinal pathway =

Answer 24

bilateral (greater ipsilateral) and is facilitory to flexor musculature and inhibitory to axial and limb extensor musculature.

Question 25

Lateral vestibulospinal pathway =

Answer 25

ipsilateral and excitatory on extensors of lower extremity musculature (inhibits flexor musculature).

Question 26

Medial vestibulospinal pathway =

Answer 26

projects bilaterally and descends only to cervical and upper thoracic levels. Control of neck and upper thoracic musculature.

Question 27

Tectospinal pathway =

Answer 27

descends only to cervical levels and coordinates neck movement toward a stimulus.

Question 28

Rubrospinal pathway =

Answer 28

contralateral and described as descending the entire length of cord.

Question 29

However, in bipedal locomotion this tract (rubrospinal pathway) has diminished in importance and functions mostly at the _____________. Current thinking is that in humans this pathway is involved in ________________________ of the upper extremity, primarily distal musculature and plays a role in fractionated movements.

Answer 29

cervical level

flexor activation

Question 30

Medial vs Lateral Activation Systems: This differentiation is defined primarily by the location of the axons of the upper motor neurons. Medial activation pathways are involved in more ______________ movements and activities. They are named for both their ___________ in the cord and their ___________. The lateral activation system is more involved with the _________________________, i.e., fractionated movement.

Answer 30

postural

POSITION in the cord and their FUNCTION

distal limb musculature

Question 31

The _____________ activation system is located in the anterior funiculus and consists of the anterior corticospinal, medial reticulospinal, medial and lateral vestibulospinal, and tectospinal pathways.

Answer 31

medial

Question 32

The _______ activation system is located in the lateral funiculus and consists of the lateral corticospinal, rubrospinal, and lateral reticulospinal pathways.

Answer 32

lateral

Question 33

Primary somatosensory cortex sends axons caudally through the ________________ pathway. These axons terminate in the ________________ and are thought to function as a feedback mechanism that integrates cortical understanding of sensation with incoming sensory information.

Answer 33

lateral corticospinal

dorsal horn

Question 34

_______________ and ____________ pathways (originate in reticular formation nuclei – ____________ and ______________) are also involved in modification of afferent sensory information at the dorsal horn level.

Answer 34

Raphespinal and
Cerulospinal

Raphe nuclei and
Locus Ceruleus

Question 35

___________________ and _________________ pathways activate a number of reticular system components. These descending components play a role in the modulation of incoming _____ stimuli.

Answer 35

Spinomesencephalic and spinoreticular

pain

Question 36

The entire motor component of cranial nerves (both sides) receives bilateral corticobulbar input. What does this mean with respect to strokes damaging the descending control?

Answer 36

???

Question 37

EXCEPTION:
Cortical control of Facial Motor Nucleus (muscles of facial expression) and Hypoglossal Nucleus (muscles controlling tongue movement).

Answer 37

EXCEPTION:
Cortical control of Facial Motor Nucleus (muscles of facial expression) and Hypoglossal Nucleus (muscles controlling tongue movement).

Question 38

EXCEPTION:

Cortical control of extraocular eye muscles (specific circuitry will be discussed with the oculomotor system).

Answer 38

EXCEPTION:

Cortical control of extraocular eye muscles (specific circuitry will be discussed with the oculomotor system).

Question 39

Lower motor neurons are located in either the _________ horn of the spinal cord or in a _________________ nucleus.

Answer 39

ventral

cranial nerve motor

Question 40

The ________ of this lower motor neuron cell body leaves the spinal cord or brainstem to innervate motor units of __________________. These axons along with the sensory axons make up the ________________________ we dissected in anatomy.

Answer 40

axon

skeletal muscle

peripheral nerves

Question 41

Lesions of lower motor neurons (damage to axon or cell body) classically are described as resulting in the following symptoms:

Answer 41

• Flaccid paralysis (atonia or hypotonia)
• Areflexia or hyporeflexia
• Atrophy of muscle (muscle wasting)
• Fasciculations and fibrillations

Question 42

Flaccid paralysis (atonia or hypotonia) =

Answer 42

flaccid paralysis = weakness or paralysis and reduced muscle tone w/o obvious cause.
Atonia or hypotonia = tone is not velocity dependent

Question 43

Areflexia or hyporeflexia =

Answer 43

below normal or absent reflexes

Question 44

Fasciculations and fibrillations =

Answer 44

fasci curation= brief, spontaneous contraction affecting a small number of muscle fibers, often causing a flicker of movement under the skin.

Question 45

Upper motor neurons are the neurons whose cell bodies are located at __________________ levels of the CNS with axons that end in the ________________ or cranial nerve motor nucleus. These UMN synapse on interneurons or  or  motor neurons.

Answer 45

suprasegmental

ventral horn

Question 46

Upper motor neuron lesions (damage to descending fiber tracts classified as UMN) classically are described as resulting in the following symptoms:

Answer 46

-Initial flaccid paralysis followed by:
-Abnormal cutaneous reflexes (Babinski sign)
-Abnormal reflexes: clonus, clasp knife)
-Spasticity – velocity dependent hypertonia
-Abnormal timing of muscle activation (slower onset, prolonged contraction)
Paresis or plegia (weakness)

Question 47

Paralysis =

Answer 47

total loss of motor function

Question 48

-plegia =

Answer 48

A loss of activation of voluntary motor activity sometimes incorrectly referred to as paralysis; i.e., hemiplegia is a loss of accurate activation of muscle activity over half of the body.

Question 49

-paresis =

Answer 49

weakness; small strokes can result in a paresis or weakness, as opposed to the (plegia of a major stroke)

Question 50

Brown-Sequard Syndrome:

Answer 50

This lesion is a hemisection of the spinal cord. It is not a common occurrence, but is useful in understanding the distribution of symptoms as they relate to the ascending and descending pathways. We have already discussed this with respect to ascending somatosensory systems.

Question 51

Syringomyelia:

Answer 51

A lesion caused by cavitation of the central canal, the remnant of the lumen of the neural tube. This lesion encroaches upon the anterior white commissure. Further ventral and lateral enlargement of the cavity will then encroach upon the ventral horn, effecting LMNs of axial then appendicular musculature.

Question 52

Poliomyelitis:

Answer 52

Disease that attacks LMNs in the ventral horn of the spinal cord or cranial nerve nuclei. This has been almost eradicated with vaccine treatment. Flu-like symptoms followed by weakness (flaccid) of muscles and fasciculations. Post-Polio syndrome is now a clinical concern due to overuse of intact motor units.

Question 53

Amyotrophic Lateral Sclerosis (ALS; Lou Gehrig’s disease):

Answer 53

ALS is a chronic and progressive disease of unknown origin. It destroys LMNs in the ventral horn and brainstem nuclei. Slow in onset. This disease also destroys white matter pathways.

Question 54

Multiple Sclerosis:

Answer 54

Multifocal disease (can have more than one site of lesion). Thought to be an autoimmune attack on myelin. Develops in the spinal cord, brainstem and optic nerve. Disease of upper motor neurons and central myelinated pathways, as well as sensory pathways.