11/6 - DESCENDING CONTROL OF MOVEMENT

Question 1

MOTOR CONTROL COMPONENTS

Answer 1

ALPHA OR LOWER MOTOR NEURONS
Motor neurons in spinal cord and cranial nerve nuclei that project to skeletal muscles.
Final common pathway to innervate muscles.
When lost = flaccid paralysis

UPPER MOTOR NEURONS
Neurons in cortex and other areas of brainstem that project to motor neurons in spinal cord or cranial nerve nuclei with somatic motor component.
Damage results in spastic paralysis as reflexes go
“unchecked.”

Basal ganglia, cerebellum, association areas of motor cortex play vital role in the choice, design and monitoring of movement but have NO direct effect on lower motor neurons.

Question 2

ALPHA OR LOWER MOTOR NEURONS

Answer 2

Motor neurons in spinal cord and cranial nerve nuclei that project to skeletal muscles.

Final common pathway to innervate muscles.

When lost = flaccid paralysis

Question 3

flaccid paralysis

Answer 3

an abnormal condition characterized by the weakening or the loss of muscle tone. It may be caused by disease or by trauma affecting the lower motor nerves associated with the involved muscles.

Paralysis characterized by limp, unresponsive muscles.

*Botulism

Question 4

spastic paralysis

Answer 4

A chronic pathological condition in which the muscles are affected by persistent spasms and exaggerated tendon reflexes because of damage to the CNS (upper motor neurons).

an abnormal condition characterized by the involuntary contraction of one or more muscles with associated loss of muscular function.

Question 5

UPPER MOTOR NEURONS

Answer 5

Neurons in cortex and other areas of brainstem that project to motor neurons in spinal cord or cranial nerve nuclei with somatic motor component.

Damage results in spastic paralysis, as reflexes go
unchecked.

Question 6

_______ play vital role in the choice, design and monitoring of movement but have NO Direct Effect on lower motor neurons.

Answer 6

Basal ganglia, cerebellum, association areas of motor cortex play vital role in the choice, design and monitoring of movement but have NO Direct Effect on lower motor neurons.

Question 7

Motor neurons in the spinal cord are capable of activating muscles through _____
(e.g., extensor reflex, flexor withdrawal reflex).

Answer 7

Motor neurons in the spinal cord are capable of activating muscles through various reflex loops
(e.g., extensor reflex, flexor withdrawal reflex).

Question 8

The function of _____ is to regulate the activity of these reflex loops and ultimately the ____ of motor neurons in the spinal cord.

Answer 8

The function of descending tracts is to regulate the activity of these reflex loops and ultimately the firing rate of motor neurons in the spinal cord.

Question 9

DESCENDING TRACTS

Answer 9

LATERAL CORTICOSPINAL

VENTRAL (ANTERIOR) CORTICOSPINAL

RUBROSPINAL

Question 10

DESCENDING CONTROL OF MOVEMENT:

Cells of origin

Answer 10

Cells of origin are located in primary motor, premotor, and supplementary motor cortices.

Question 11

Primary Motor Cortex:

Location

Answer 11

Most of the Primary Motor Cortex is buried in the central sulcus; it forms the anterior wall of the sulcus.

Question 12

MOTOR CIRCUIT:

Output

Answer 12

Premotor and Supplementary Motor Cortex project to Primary Motor Cortex

Question 13

Primary Motor Cortex projects to ______ .

Answer 13

Primary Motor Cortex projects to Brainstem and Spinal Cord

Question 14

Multiple Areas Of The Brain Are Involved In Regulating ____ .

Effect is mediated through circuitry that activates ____ of the ___ lobe.

Answer 14

Multiple Areas Of The Brain Are Involved In Regulating Cortical Control of Lower Motor Neurons

Effect is mediated through circuitry that activates neurons in the precentral gyrus of the frontal lobe.

Question 15

Primary Motor Cortex (M1)

Answer 15

Projects widely to other motor areas of the brainstem and spinal cord

Inputs from premotor cortical areas, primary sensory cortex, basal ganglia, and cerebellum

Specialized for voluntary control

Responsible for fine control of distal muscles

Is somatotopically organized similar to sensory cortex

Question 16

M1 IS ACTIVE DURING EXECUTION OF A VOLUNTARY MOVEMENT

Answer 16

Most M1 activity occurs while movement is underway

Few cells in M1 are active during motor planning

Question 17

M1 PROJECTIONS ALLOW FOR SPECIFIC MOTOR CONTROL

Answer 17

Single corticospinal cells from M1 have focused
projections to motor pools for hand & finger muscles.

Neural activity in M1 cells can be specifically related
to facilitation of certain muscles.

Question 18

____ cells from MI have focused projections to motor pools for hand and finger muscles

Answer 18

Single corticospinal cells from MI have focused
projections to motor pools for hand and finger
muscles

Question 19

PREMOTOR CORTICAL AREAS

Answer 19

Area rostral to precentral sulcus

All have activity well before movement starts, even during mental rehearsal

Differences are in what context they plan for and how directly they can control the movement once it’s underway

Most project to M1; there is a small projection to the spinal cord.

Question 20

PREMOTOR AREAS HAVE PREFERENCES AND ARE PREPARED

Answer 20

Externally Guided

Question 21

PREMOTOR AREA

Answer 21

Externally guided movement (esp. vision).

Movement elicited by external stimulus (like someone tossing a ball to you).

Heavily connected with Cerebellum and Association areas of parietal lobe (areas 5-7)

Projects to M1, basal ganglia, and spinal cord.

Important for planning, preparation, and learning.

Question 22

SUPPLEMENTARY MOTOR AREA (SMA)

Answer 22

Internally guided movements, including complex sequences and well-learned movements, routine, and speech (motor)

Bimanual coordination

Heavily interconnected with basal ganglia

Question 23

M1

Answer 23

Primary Motor Cortex

Question 24

Random movements

Answer 24

Random movements result in Activation of primary motor cortex (M1)

Question 25

Movement that is planned and carried out in specific sequence

Answer 25

When movement is planned and carried out in specific sequence, supplementary
motor cortex also active.

Question 26

Movement that is only mentally planned and

rehearsed

Answer 26

When movement is mentally planned and rehearsed, only supplementary motor cortex is active.

Question 27

Cortical Motor Area Information Flow

Answer 27

Primary Sensory Cortex (1,2,3) directly project to Primary Motor Cortex (4).

Association areas of Parietal Lobe (5,7) project to Premotor (6) and Supplementary (8) Motor Regions.

Premotor and Supplementary Motor Regions project to Primary Motor Cortex.

Question 28

Primary Sensory Cortex

Answer 28

Areas 1, 2, and 3

Question 29

Primary Sensory Cortex (1,2,3) directly project to _____ .

Answer 29

Primary Sensory Cortex (1,2,3) directly project to Primary Motor Cortex (4).

Question 30

Primary Motor Cortex

Answer 30

Area 4

Question 31

Association Areas of Parietal Lobe

Answer 31

Areas 5 and 7

Question 32

Premotor Motor Region

Answer 32

Area 6

Question 33

Supplementary Motor Region

Answer 33

Area 8

Question 34

Association areas of Parietal Lobe (5,7) project to _____ .

Answer 34

Association areas of Parietal Lobe (5,7) project to Premotor (6) and Supplementary (8) Motor Regions .

Question 35

Premotor and Supplementary Motor Regions project to _____.

Answer 35

Premotor and Supplementary Motor Regions project to Primary Motor Cortex.

Question 36

APRAXIA

Answer 36

The inability to execute a voluntary motor movement despite being able to demonstrate normal muscle function.

Question 37

CORTICOSPINAL TRACT

Answer 37

PYRAMIDAL TRACT

Function: classically defined as mediating voluntary movement, especially of the digits

Cells of origin: pyramidal cells in motor regions of
frontal lobe.

Axons course through posterior limb internal capsule (large fiber tract located lateral to thalamus).

Axons descend ipsilaterally through cerebral peduncle
in the midbrain, basilar pons and rostral pyramidal tract in the medulla.

On reaching caudal medulla 85% cross to the
contralateral side in the pyramidal decussation to form lateral corticospinal tract.

15% remain ipsilateral to form anterior corticospinal
tract.

Terminate either directly on motor neurons or on
interneurons that contact motor neurons.

Question 38

CORTICOSPINAL (PYRAMIDAL) TRACT:

Function

Answer 38

classically defined as mediating voluntary

movement, especially of the digits

Question 39

CORTICOSPINAL (PYRAMIDAL) TRACT:

Cells of origin

Answer 39

pyramidal cells in motor regions of frontal lobe.

Axons course through posterior limb internal capsule (large fiber tract located lateral to thalamus).

Question 40

CORTICOSPINAL (PYRAMIDAL) TRACT:

Course

Answer 40

Axons course through posterior limb internal capsule (large fiber tract located lateral to thalamus).

Axons descend ipsilaterally through cerebral peduncle
in the midbrain, basilar pons and rostral pyramidal tract in the medulla.

On reaching caudal medulla 85% cross to the
contralateral side in the pyramidal decussation to form lateral corticospinal tract (LCT).

15% remain ipsilateral to form anterior corticospinal
tract (ACT).

Terminate either directly on motor neurons or on
interneurons that contact motor neurons.

Question 41

lateral corticospinal tract

Answer 41

The larger of the 2 corticospinal tracts comprising the 85% of the fibers in each medullary pyramid that cross the midline in the pyramidal decussation to reach the opposite lateral funiculus.

The axons of this tract end on spinal lower motor neurons or (more often) on smaller interneurons that in turn synapse on motor neurons.

Question 42

anterior corticospinal

tract (ACT)

Answer 42

The smaller of the 2 corticospinal tracts consisting of the fibers (~15%) in each medullary pyramid that continue directly into the anterior funiculus of the spinal cord without decussating; many fibers eventually cross in the anterior white commissure of the cord before terminating, but some end uncrossed.

Fibers of the anterior corticospinal tract end (mainly in the cervical and thoracic spinal cord) on spinal motor neurons or nearby interneurons in medial parts of the anterior horn, affecting motor neurons for axial muscles.

Question 43

CORTICOBULBAR TRACT

Answer 43

Neurons in the cerebral cortex also project to motor nuclei related to cranial nerves.

Arise from face region of
precentral gyrus.

Although shown as bilateral input, cranial nerve nuclei primarily receive crossed projection; analagous to corticospinal tract

Question 44

CORTICOSPINAL/ CORTICOBULBAR TRACT

COURSE

Answer 44

Internal Capsule 
---->
Cerebral Peduncle (Midbrain)
---->
Medulla's Pyramids

Question 45

CORTICOBULBAR TRACT Nuclei

Answer 45

Facial Motor Nucleus
-Making Faces

Motor Nucleus of V

Nucleus Ambiguus Muscles Of Larynx, Pharynx (IX, X).
-Swallowing, talking

Hypoglossal Nucleus (XII)

Question 46

In the ____, the CORTICOSPINAL TRACT occupies the middle part of the _____ .

The remaining part is occupied by ____ fibers.

Answer 46

In the midbrain, the CORTICOSPINAL TRACT occupies the middle part of the cerebral peduncle (CP)

The remaining part is occupied by corticopontine and corticobulbar fibers.

Question 47

In the medulla, CORTICOSPINAL TRACT axons form the pyramidal tract (pyramid).

However, there is a significant decrease in size of this fiber tract compared to that of the cerebral peduncle.

Answer 47

Comparison of size of cerebral peduncle (before pons) and pyramid (after pons) show how many axons leave the tract in the pons and rostral medulla.

Question 48

In the pons, the CORTICOSPINAL TRACT is broken up into fascicles that course between collections of neurons forming ____ .

Answer 48

In the pons, the CORTICOSPINAL TRACT is broken up into fascicles that course between collections of neurons forming pontine nuclei.

Question 49

Many cortical axons, not contributing to the corticospinal tract, project to brainstem nuclei in the
midbrain, pons, and medulla, especially _____ and ____.

Answer 49

Many cortical axons, not contributing to the corticospinal tract, project to brainstem nuclei in the
midbrain, pons and medulla, especially cranial nerve nuclei with a motor component and neurons
in the pontine nuclei.

This is why size comparison of cerebral peduncle (before pons) and pyramid (after pons) show that many axons leave the tract in the pons and rostral medulla.

This occurs above the Decussation.

Question 50

At the junction of the spinal cord and medulla, 85% of the axons in the ____ tract cross to the contralateral
side. They also move ____. This becomes the ____.

Answer 50

At the junction of the spinal cord and medulla, 85% of the axons in the corticospinal tract cross to the contralateral
side. They also move dorsally and laterally. This is now the lateral corticospinal tract.

Question 51

15% of the fibers in the _____ remain on the ipsilatral side in the same ____ position. This is now called the _____.

Answer 51

15% of the fibers in the corticospinal tract remain on the ipsilatral side in the same ventral position. This is now called the anterior corticospinal tract.

Question 52

LATERAL CST AXONS TERMINATE ON:

Answer 52

Motor Neurons Located Laterally (Upper Limbs &
Digits)

Interneurons That Project To Motor Neurons

Question 53

ANTERIOR CST AXONS TERMINATE ON:

Answer 53

Motor Neurons Located Medially (Axial, Trunk Muscles).

Some Cross To Contralateral Side.

End In Cervical & Thoracic Segments.

Question 54

Lateral corticospinal tract

In spinal cordrtex

Answer 54

Axons Synapse on interneurons, alpha, and gamma motor neurons.

It will synapse directly onto motor neurons involved in digital movement for precise control.

Question 55

THE CORTICOSPINAL TRACT HAS STRONG INFLUENCE ON MOTOR NEURONS THAT CONTROL DIGITS.

Answer 55

Squirrel Monkey does not use individual digits.

Cebus monkey does use individual digits to manipulate objects

There is a strong projection of corticospinal tract to most lateral part of ventral horn in Cebus monkey (area where digits
are represented).

Question 56

RUBROSPINAL TRACT

Answer 56

Function: alternate route for mediation/modulation of movements.
Primary effect is on flexor muscles, but also can have an effect on extensors.
May excite flexor and inhibit extensor.
Also an important source of afferents to the inferior olivary nucleus

Cells of origin: red nucleus in the midbrain.
Receives input from cerebral cortex and cerebellum and
modulates activity of motor neurons in the spinal cord.

Axons cross midline to form the rubrospinal tract (RST) in midbrain.
Most terminate in cervical spinal cord but others will
traverse the entire length of the spinal cord.

In spinal cord, axons are located just ventral to lateral
corticospinal tract

Question 57

RUBROSPINAL TRACT:

Function

Answer 57

alternate route for mediation/modulation of movements.

Primary effect is on flexor muscles, but also can have an effect on extensors.

May excite flexor and inhibit extensor.

Also an important source of afferents to the inferior olivary nucleus

Question 58

RUBROSPINAL TRACT:

Cells of origin

Answer 58

red nucleus in the midbrain

Receives input from cerebral cortex and cerebellum and modulates activity of motor neurons in the spinal cord.

Question 59

RUBROSPINAL TRACT:

Course

Answer 59

Axons cross midline to form the rubrospinal tract (RST) in midbrain.

Most terminate in Cervical spinal cord, but others will
traverse the entire length of the spinal cord.

In spinal cord, axons are located just ventral to lateral corticospinal tract.

Receives input from cerebral cortex & cerebellum and modulates activity of motor neurons in the spinal cord.

Question 60

RUBROSPINAL TRACT:

Crossing

Answer 60

Originate in contralateral red nucleus.

Axons cross at level of origin in midbrain.

Question 61

RUBROSPINAL TRACT:

Spinal Projections

Answer 61

In the spinal cord, individual axons terminate at specific levels (minimal collateralization).

In humans, few extend below cervical cord.

Terminate medially and more dorsally where they are excitatory to proximal upper limb flexors.

Question 62

AFFERENTS TO RED NUCLEUS

Answer 62

Primarily from cerebellum and a few from cerebral cortex

Question 63

OTHER DESCENDING PATHWAYSATE ON:

Answer 63

In addition to the cortiospinal and rubrospinal
tracts, other areas of the brainstem give rise to axons that descend to influence alpha motor neurons either directly or through interneurons.

These include:
Reticulospinal
Tectospinal
Vestibulospinal

These nuclei receive input from motor neurons as they descend through the brainstem:
corticobulbar projections.

Question 64

corticobulbar

Answer 64

Strictly defined, a large collection of fibers originating in the cerebral cortex and descending through the internal capsule (immediately anterior to the corticospinal fibers) to terminate in the “bulb” (an old term for the medulla, or for the entire brainstem) on neurons of sensory relay nuclei, the reticular formation, and motor nuclei of cranial nerves.

In common usage, the term refers only to the last fibers of this group.

Basically, the equivalent of the corticospinal tract for cranial nerve nuclei.

Question 65

In monkeys, transection of the corticospinal tract at the level of the pyramids show ____.

Major motor deficit is permanent inability to ____.

Answer 65

In monkeys, transection of the corticospinal tract at the level of the pyramids show little chronic motor deficits.

Major motor deficit is permanent inability to use fingers individually (pick up small object).

Question 66

LESIONS OF THE CORTICOSPINAL TRACT:

If other parts of the brainstem are involved (reticular formation) are included, there is a severe disability to move ___ muscles.

Answer 66

If other parts of the brainstem are involved (reticular formation) are included there is a severe disability to move proximal and axial muscles.

Question 67

In humans, lesions of the pyramids cause less pronounced weakness compared to lesions of the _____ .

As in monkeys, primary loss is ability to move digits.

Answer 67

In humans, lesions of the pyramids cause less pronounced weakness compared to lesions of the motor cortex.

As in monkeys, primary loss is ability to move digits.

Question 68

Damage to the pyramids only affects _____ .

However, lesions of the motor cortex involve corticospinal and
corticobulbar to areas of the brainstem that also influence motor neurons.

Shows the importance of these other parts of the brainstem in controlling ____ and their ability to “take over” when corticospinal axons are lost.

Answer 68

Damage to the pyramids only affects corticospinal axons.

However, lesions of the motor cortex also involve
corticospinal and
corticobulbar to areas of the brainstem that also influence motor neurons.

Shows the importance of these other parts of the brainstem in controlling alpha motor neurons and their ability to “take over” when corticospinal axons are lost.

Question 69

Damage to motor cortex produces ___ of muscles due to loss of control of ____.

Small movements of the muscle cause ____ .

Also see a positive Babinski sign.

Answer 69

Damage to motor cortex produces spastic paralysis of muscles due to loss of control of stretch reflex.

Small movements of the muscle cause strong activation of the sensory-motor loop.

Also see a positive Babinski sign.

Question 70

Babinski test

Answer 70

Stroke the sole of the foot.

Normally, in adults toes curl downward.

With damage to upper motor neurons, the toes extend and fan out.

This fanning out reflex is normal in infants before corticospinal tract is functional. It is not normal in adults.

Question 71

Vestibulospinal reflexes

Answer 71

PURPOSE: coordinate head & neck movement with the trunk & body, with the goal of maintaining the head in an upright position

can act in synergy or opposition to neck muscle stretch reflexes which work to keep the neck upright

2 systems that have distinctly different pathways and functions:

LATERAL VESTIBULOSPINAL: postural changes to compensate for tilts and movements of the body

MEDIAL VESTIBULOSPINAL: stabilizes head position during walking

Question 72

tectospinal tract

Answer 72

a tract of myelinated nerve fibers that mediate various visual and auditory reflexes and that originate in the superior colliculus, cross to the opposite side, and descend in the anterior funiculus of the spinal cord to terminate in the ventral horn of gray matter in the cervical region of the spinal cord

a bundle of thick, heavily myelinated fibers originating in the deep layers of the Superior Colliculus, crossing to the opposite side in the dorsal tegmental decussation, descending along the median plane, between the medial longitudinal fasciculus dorsally and the medial lemniscus ventrally, and into the anterior funiculus of the spinal cord. The tract ends in the medial region of the anterior horn of the cervical spinal cord, and appears to be involved in head movements during Visual and Auditory Tracking. Throughout its course in the brainstem, it is accompanied by fibers of the tectobulbar tract.

Question 73

reticulospinal tract

Answer 73

Any of several fiber tracts descending to the spinal cord from the reticular formation of the pons and medulla oblongata.

Some fibers conduct impulses from the neural mechanisms regulating cardiovascular and respiratory functions to the spinal cord; others form links in extrapyramidal motor mechanisms affecting muscle tonus and somatic movement.