11/6 - DESCENDING CONTROL OF MOVEMENT Flashcards
MOTOR CONTROL COMPONENTS
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.
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
flaccid paralysis
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
spastic paralysis
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.
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.
_______ play vital role in the choice, design and monitoring of movement but have NO Direct Effect on lower motor neurons.
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.
Motor neurons in the spinal cord are capable of activating muscles through _____
(e.g., extensor reflex, flexor withdrawal reflex).
Motor neurons in the spinal cord are capable of activating muscles through various reflex loops
(e.g., extensor reflex, flexor withdrawal reflex).
The function of _____ is to regulate the activity of these reflex loops and ultimately the ____ of motor neurons in the spinal cord.
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.
DESCENDING TRACTS
LATERAL CORTICOSPINAL
VENTRAL (ANTERIOR) CORTICOSPINAL
RUBROSPINAL
DESCENDING CONTROL OF MOVEMENT:
Cells of origin
Cells of origin are located in primary motor, premotor, and supplementary motor cortices.
Primary Motor Cortex:
Location
Most of the Primary Motor Cortex is buried in the central sulcus; it forms the anterior wall of the sulcus.
MOTOR CIRCUIT:
Output
Premotor and Supplementary Motor Cortex project to Primary Motor Cortex
Primary Motor Cortex projects to ______ .
Primary Motor Cortex projects to Brainstem and Spinal Cord
Multiple Areas Of The Brain Are Involved In Regulating ____ .
Effect is mediated through circuitry that activates ____ of the ___ lobe.
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.
Primary Motor Cortex (M1)
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
M1 IS ACTIVE DURING EXECUTION OF A VOLUNTARY MOVEMENT
Most M1 activity occurs while movement is underway
Few cells in M1 are active during motor planning
M1 PROJECTIONS ALLOW FOR SPECIFIC MOTOR CONTROL
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.
____ cells from MI have focused projections to motor pools for hand and finger muscles
Single corticospinal cells from MI have focused
projections to motor pools for hand and finger
muscles
PREMOTOR CORTICAL AREAS
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.
PREMOTOR AREAS HAVE PREFERENCES AND ARE PREPARED
Externally Guided
PREMOTOR AREA
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.
SUPPLEMENTARY MOTOR AREA (SMA)
Internally guided movements, including complex sequences and well-learned movements, routine, and speech (motor)
Bimanual coordination
Heavily interconnected with basal ganglia
M1
Primary Motor Cortex
Random movements
Random movements result in Activation of primary motor cortex (M1)
Movement that is planned and carried out in specific sequence
When movement is planned and carried out in specific sequence, supplementary
motor cortex also active.
Movement that is only mentally planned and
rehearsed
When movement is mentally planned and rehearsed, only supplementary motor cortex is active.
Cortical Motor Area Information Flow
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.
Primary Sensory Cortex
Areas 1, 2, and 3
Primary Sensory Cortex (1,2,3) directly project to _____ .
Primary Sensory Cortex (1,2,3) directly project to Primary Motor Cortex (4).
Primary Motor Cortex
Area 4
Association Areas of Parietal Lobe
Areas 5 and 7
Premotor Motor Region
Area 6
Supplementary Motor Region
Area 8
Association areas of Parietal Lobe (5,7) project to _____ .
Association areas of Parietal Lobe (5,7) project to Premotor (6) and Supplementary (8) Motor Regions .
Premotor and Supplementary Motor Regions project to _____.
Premotor and Supplementary Motor Regions project to Primary Motor Cortex.
APRAXIA
The inability to execute a voluntary motor movement despite being able to demonstrate normal muscle function.
CORTICOSPINAL TRACT
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.
CORTICOSPINAL (PYRAMIDAL) TRACT:
Function
classically defined as mediating voluntary
movement, especially of the digits
CORTICOSPINAL (PYRAMIDAL) TRACT:
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).
CORTICOSPINAL (PYRAMIDAL) TRACT:
Course
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.
lateral corticospinal tract
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.
anterior corticospinal
tract (ACT)
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.
CORTICOBULBAR TRACT
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
CORTICOSPINAL/ CORTICOBULBAR TRACT
COURSE
Internal Capsule ----> Cerebral Peduncle (Midbrain) ----> Medulla's Pyramids
CORTICOBULBAR TRACT Nuclei
Facial Motor Nucleus
-Making Faces
Motor Nucleus of V
Nucleus Ambiguus Muscles Of Larynx, Pharynx (IX, X).
-Swallowing, talking
Hypoglossal Nucleus (XII)
In the ____, the CORTICOSPINAL TRACT occupies the middle part of the _____ .
The remaining part is occupied by ____ fibers.
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.
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.
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.
In the pons, the CORTICOSPINAL TRACT is broken up into fascicles that course between collections of neurons forming ____ .
In the pons, the CORTICOSPINAL TRACT is broken up into fascicles that course between collections of neurons forming pontine nuclei.
Many cortical axons, not contributing to the corticospinal tract, project to brainstem nuclei in the
midbrain, pons, and medulla, especially _____ and ____.
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.
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 ____.
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.
15% of the fibers in the _____ remain on the ipsilatral side in the same ____ position. This is now called the _____.
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.
LATERAL CST AXONS TERMINATE ON:
Motor Neurons Located Laterally (Upper Limbs &
Digits)
Interneurons That Project To Motor Neurons
ANTERIOR CST AXONS TERMINATE ON:
Motor Neurons Located Medially (Axial, Trunk Muscles).
Some Cross To Contralateral Side.
End In Cervical & Thoracic Segments.
Lateral corticospinal tract
In spinal cordrtex
Axons Synapse on interneurons, alpha, and gamma motor neurons.
It will synapse directly onto motor neurons involved in digital movement for precise control.
THE CORTICOSPINAL TRACT HAS STRONG INFLUENCE ON MOTOR NEURONS THAT CONTROL DIGITS.
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).
RUBROSPINAL TRACT
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
RUBROSPINAL TRACT:
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
RUBROSPINAL TRACT:
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.
RUBROSPINAL TRACT:
Course
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.
RUBROSPINAL TRACT:
Crossing
Originate in contralateral red nucleus.
Axons cross at level of origin in midbrain.
RUBROSPINAL TRACT:
Spinal Projections
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.
AFFERENTS TO RED NUCLEUS
Primarily from cerebellum and a few from cerebral cortex
OTHER DESCENDING PATHWAYSATE ON:
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.
corticobulbar
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.
In monkeys, transection of the corticospinal tract at the level of the pyramids show ____.
Major motor deficit is permanent inability to ____.
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).
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.
If other parts of the brainstem are involved (reticular formation) are included there is a severe disability to move proximal and axial muscles.
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.
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.
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.
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.
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.
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.
Babinski test
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.
Vestibulospinal reflexes
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
tectospinal tract
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.
reticulospinal tract
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.
