Post on 06-Jul-2018
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
1/7
Anatomy 6.4 February 7, 2012
Pyramidal System Dr. Melissa Calilao
Group 17 | Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 1 of 7
OUTLINE
I. Motor System
II. Pyramidal Tract
A. Two Main Pathways
B. Origin of Fibers
C. Motor Homunculus
D. Supplementary Motor Area
E. Descending Pathways: AnatomicalOrganization
III. Corticospinal Tract
A. Pathway
B. Lateral Corticospinal Tract
C. Anterior Corticospinal Tract
D. Termination of Pyramidal Tract
IV. Upper Motor Neuron vs Lower Motor
Neuron Paralysis
A. Upper Motor Neuron
B. Lower Motor Neuron
V. Corticobulbar Tract
A. Facial Motor Nucleus
B. Lower Motor Nucleus
VI. Other Descending Tracts
A. Midbrain
B. Pons/Medulla
Objectives:
Enumerate the tracts that constitute the pyramidal system
Trace the pathway of the pyramidal tracts
Locate the position of the lateral and anterior corticospinal tracts in a
section of the spinal cord
Differentiate an upper motor vs. a lower motor neuron lesion
Describe briefly the other descending tracts
I. MOTOR SYSTEM
MOTOR SYSTEM
1. Pyramidal system
The primary control of voluntary movement
thru:a. Corticospinal
b. Corticobulbarparthways
2. Extrapyramidal system
a. Basal Ganglia (nuclei)
b. Cerebellum
Supporting role in the production of well-
coordinated movements
Influence lower motor neurons indirectly
through modulation of the cerebral cortex and
brainstem
II. PYRAMIDAL TRACT
Longest and largest descending fiber tract of human CNS
Fibers are responsible for the formation of pyramids
(swellings)
Fibers pass through the medullary pyramids (in upper
medulla)
Concerned with voluntary, discrete, skilled movements of
the distal musculature of the limbs and control of muscles
involved in speech and vocalization
A.
TWO MAIN PATHWAYS
1. Corticospinal tract
Lateral Corticospinal Tract
Anterior /Ventral Corticospinal Tract
2. Corticobulbar tract
B.
ORIGIN OF FIBERS
Known as the Sensorimotor Cortex because it is comprised
of three areas from which the fibers arise
1. Precentral gyrus
2. Postcentral gyrus
3.Premotor cortex and Frontal eye field
1. Precentral gyrus (Brodmann’s area 4)
Primary motor cortex
1/3 of the axons
Pyramidal cells of Betz
o 10% or 3% of CST fibers
o Large motor neurons located at the 5th layer ocerebral cortex of areas 4 and 6
o Unique since their axons are sent directly to the
anterior horn cells (monosynaptic connection)
o Responsible for the highly skilled movements
2.Postcentral gyrus (Brodmann’s area 3, 1, 2)
Primary sensory cortex
1/3 of the axons
Fibers are not involved in voluntary movement bu
they are responsible in controlling sensory inputs
3. Premotor cortex and Frontal eye field (Brodmann’s area 6)
1/3 of the axons
Secondary motor cortex For controlling the posture
Some also arise from the frontal eye field (BA 8)
Figure 1. Sensorimotor Cortex
C.
MOTOR HOMUNCULUS
The body has somatotopic representation on the primary
motor and premotor cortex. at the precentral gyrus
Each body is represented in specific portion
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
2/7
Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 2 of 7
Paracentral lobule is represented by the lower extremities,
feet, and the perineum
Most lateral, close to Sylvian fissure is represented by the
tongue and larynx
Hands, face, and lips occupy large areas since they are
involved in fine and highly skilled movements
Figure 2. Motor Homunculus
D.
SUPPLEMENTARY MOTOR AREA
Located at BA 6, in front of paracentral lobule
Has a special role in controlling movement that are
performed simultaneously on both sides of the body
Together with premotor, they are concerned with planning
movements
E.
DESCENDING PATHWAYS: ANATOMICAL ORGANIZATION
1st
order of neuron(N1)
o Nerve cell body in the cerebral cortex
2nd
order of neuron(N2)
o Internuncial neuron (connecting neuron) inanterior gray column of spinal cord
o Has short axon
3rd
order of neuron(N3)
o Lower motor neuron
o In the anterior gray column of the spinal cord
o Axon directly innervates the skeletal muscles
through the anterior root of spinal nerves
o Lower Motor Neurons (Alpha motor neuron) -
the final common pathway
Reflex
o Involuntary response to a stimulus and requires
fast action
o Higher centers of the brain is not needed
Reflex arcs
o Important in maintaining muscle tone for
posture
o Components:
1. Receptor organ
2. Afferent neuron
3. Efferent neuron
4. Effector organ
Figure 1. Reflex Arc
III. CORTICOSPINAL TRACT
A.
PATHWAY
It forms pathways concerned with speed and agility to
voluntary movements and is used in performing rapid skilled
movements. (Lesion will not abolish movement but will become
slow and less agile)
Majority of corticospinal fibers are myelinated and are
relatively slow-conducting, small fibers Most fibers synapse with internuncial neurons, which, in turn
synapse with alpha motor neurons and some gamma motor
neurons
Corticospinal tract is believed to control the prime mover
muscles while the other descending tracts are important in
controlling basic movements
Corticospinal tract is a crossed tract, thus, the right sensory
motor cortex controls the left side of the body and vice versa
(Lesion on one side will be manifested on the contralatera
side)
There is better motor control on the upper extremities and
body because more fibers terminate at this area
1.
Origin: Cerebral cortex (1st order neuron)
1/3 from primary motor complex (area 4)
1/3 from secondary motor complex (area 6)
1/3 from parietal lobe (area 3, 1, 2)
OR
2/3 from precentral gyrus
1/3 from postcentral gyrus (fibers do not control motor
activity but influence sensory input to the nervous system
2.
Corona radiata
Where descending fibers from cerebral cortex wil
converge
Afferent and efferent fibers situated deep in the
medullary substance
3.
Internal capsule
From corona radiata, it will pass through the posterio
limb of the internal capsule
V-shaped on horizontal view, with the anterior and
posterior limb joined at the genu
Fibers closest to the genu are concerned with cervica
portions of the body, while the those situated posteriorly
are concerned with lower extremity
A broad, compact band which separates lentiform
nucleus from thalamus and caudate nucleus
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
3/7
Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 3 of 7
Descending fibers : Grouped closely at the genu and in
the anterior 2/3 of posterior limb
Motor fibers of upper extremity:
o At the rostral part of posterior limb
o Behind these are the lower extremity fibers
Anterior limb: Made up of fibers passing to and from the
frontal lobe
Posterior limb: Fibers from the parietal lobe
4.
Cerebral peduncles (middle 3/5)
Cervical portions of the body: Fibers located more
medially Lower extremities: Fibers located more laterally
5. Pons
Fibers will leave the mesencephalon to continue at this
site
Tract will then break up into many bundles or numerous,
smaller fascicles in basilar portion of pons by the
transverse pontocerebellar fibers
Scattered in these fascicles are pontine nuclei and
pontocerebellar fibers
6.
Medulla oblongata
From Pons, the bundles will group together along the
anterior border to form a swelling known as Pyramids
(upper medulla)
Collects into a discrete bundle, some fibers cross
7.
Pyramidal decussation (caudal medulla)
Crossing over of fibers at the junction of medulla
oblongata and the spinal cord
8.
a. Lateral CST
From the decussation of fibers, it will enter the lateral
white column of the spinal cord (lateral funiculus) to form
this tract
Formed by the decussation of 75-90% of fibers at the
caudal medullary level
Termination: Anterior gray column of all spinal cord
segments
Figure 2. Lateral Corticospinal Tract
8.b. Anterior / Ventral CST
Some fibers do not cross in the decussation but descend in
the anterior white column of the spinal cord to form this
tract (anterior funiculus of spinal cord close to the ventro
median fissure)
They will eventually cross before terminating on anterio
horn cells in cervical and upper thoracic regions
Formed by the 10-15% uncrossed fibers
B. TERMINATION OF PYRAMIDAL TRACT FIBERS
Cervical spinal cord level – 55%
Thoracic level – 20%
Lumbar/sacral level – 25%
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
4/7
Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 4 of 7
IV. UPPER MOTOR NEURON VS LOWER MOTOR NEURON
PARALYSIS
A.
UPPER MOTOR NEURON (UMN)
1st order neuron (N1) located in motor area of cerebral cortex
Processes connect with motor nuclei in anterior horn of spinal
cord (N2)
UMN from precentral gyrus initiate impulses to skeletal
muscles
o Those that originate in other areas do not initiate
impulses. Rather, they suppress or inhibit lower motor
neurons
Figure 3. Motor Neurons Lesions
B.
LOWER MOTOR NEURON (LMN)
3rd
order neurons (N3) located in anterior horns of spinal cord,
their axons passing via peripheral nerve to skeletal muscle
When suppressor upper motor neurons have lesions, the LMN
will discharge at will, producing hyperreflexia or spasticity
Figure 4. A cross section of the spinal cord, dorsal and ventral
roots, and peripheral nerve [Important: Lesion 4, anterior horn
cells]
Notes:
o The ”pyramidal tract” is used by physicians to refer
specifically to the corticospinal tract
o The pyramidal tracts normally tend to increase muscle
tone, while extrapyramidal tracts inhibit muscle tone
o In clinical practice, it is rare to find a lesion that is limited
solely to the pyramidal tract or extrapyramidal tract
o Usually, both sets of tracts are affected to a variable
extent, producing both groups of clinical signs
Table 1. Differentiation of LMN from UMN Lesion
LMN LESION UMN LESION
Complete paralysis (complete loss of action,
since main innervations
of muscles are severed)
Paresis
(muscle weakness)
Flaccidity - due to atonia
Spasticity
due to marked hypertonia
increase in muscle tone
lesion is on extrapyramidal tract
Arreflexia
(reflex arc is damaged)
Hyperreflexia
(LMN over discharge
there is an absence of suppressor
action on LMN
related to increase in tone
lesion on extrapyramidal tract )
Muscles undergo marked
atrophy
No muscle atrophyminor in chronic state
in time, it will have disused
atrophy
No Clonus
Clonus manifested
rapid, strong muscle contraction
when paralyzing limb is grasped
firmly
lesion on extrapyramidal tract
No Babinski sign
(+) Babinski sign
dorsiflexion of big toe and
fanning out of other toes
lesion on corticospinal tract
Loss of certain superficial
reflexes
lesion on pyramidal tract
a. Superficial abdominal reflex
b. Cremasteric reflex
Notes:
Areas exhibiting clonus:
- Flexors of fingers
- Gastrocnemius
- Quadriceps femoris
Babinski’s reflex (Extensor plantar reflex)is normally
present in children of about 1 year of age because the
corticospinal tract fibers are not yet fully myelinated
Stimulation is through the application of pressure on thelateral border of the sole of the foot from the back of the
heel to the base of the toes.
Superficial abdominal reflex is elicited by
scratching/stroking the skin of the abdomen. Normally, the
muscles should contract.
Cremasteric reflex is elicited by stroking the inner aspec
of the thigh, normally causing the scrotum and testis to
retract on the same side.
Babinski’s reflex, superficial abdominal, and cremasteric
reflexes are specific for a lesion on the pyramidal tract .
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
5/7
Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 5 of 7
V. CORTICOBULBAR TRACT
Arise from the face region of the primary motor cortex (BA
4), also from BA 6 and 3, 1, 2
End at the midbrain
Project to:
o Motor nuclei of CN III, IV, V, VI, VII, IX, X, XI and XII
(every CN EXCEPT 1, 2, 8 which are sensory)
o Parts of reticular formation (Corticoreticular fibers) in
pons and medulla – for controlling the movements of
emotions such as smiling, laughingo Sensory relay nuclei (nucleus gracilis, nucleus
cuneatus, sensory trigeminal nuclei, nucleus of
solitary fasciculus) – controls the sensory inputs that
arrive at CNS
Projections are bilateral – receive innervations from both
contralateral and ipsilateral cortex EXCEPT:
o Facial motor nucleus
o Hypoglossal nucleus
Also pass through the internal capsule, located at the genu
A. FACIAL MOTOR NUCLEUS
Dorsal parto Innervates upper half of the face
o Receives innervations from both contralateral and
ipsilateral cerebral cortex
Ventral part
o Innervates lower half of the face
o Only receives innervations from the contralateral
cerebral cortex
Central facial paralysis
o UMN/supranuclear lesion of the corticobulbar tract
o Dorsal part still receives innervations from the same
side of cerebral cortex thus, some functions are still
retained (able to wrinkle forehead muscle)
Peripheral facial paralysis (Bell’s Palsy)
o LMN lesion of facial nerve or motor nucleus o Complete paralysis of half of the face on the same
side of the lesion (ipsilateral)
Figure 5. Shaded areas of the face show the distribution of facial
muscles paralyzed after a supranuclear lesion of the corticobulbar
tract & a lower motor neuron lesion of the facial nerve
PRACTICE PROBLEM 1
Case Scenario: A post-stroke patient with inabilityto move the left half of the face but can still wrinkleboth eyebrowsType of lesion? UMN
Where is the lesion? Right Supranuclear
PRACTICE PROBLEM 2
Case Scenario: A patient upon waking up in themorning is unable to move the entire right half of hisface.PHHx: had chicken pox 2 weeks priorType of lesion? LMNDiagnosis? Bell’s Palsy Where is the lesion? Right Nucleus of Facial NervePrognosis? Excellent; 85% or more recover
B. HYPOGLOSSAL NUCLEUS
Controls genioglossus muscle of the tongue: draws the
root of the tongue forward to the opposite side Corticobulbar projections are largely contralateral
If the patient is normal (no lesion) – tongue is protruded a
the midline
UMN lesion
o Tongue would point or deviate to the opposite side of
the lesion
o Without atrophy
o Example: if there is left UMN lesion, it will affect right
genioglossus muscle; thus, ability to draw the tongue
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
6/7
Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 6 of 7
to the left is defective, the tongue will then be drawn
to the right
LMN lesion
o Ipsilateral
o Tongue will be pushed on the same side of the lesion
o With atrophy
Figure 6. Lesion on Hypoglossal Nucleus
PRACTICE PROBLEM 3
Caes Scenario: The resident noted that the tongue
of a post-stroke patient is atrophied and deviated tothe LEFTType of lesion? LMNWhere is the lesion? LEFT Hypoglossal Nucleus
PRACTICE PROBLEM 4
Caes Scenario: The resident noted that the tongueof a post-stroke patient is NOT atrophied anddeviated to the LEFTType of lesion? UMNWhere is the lesion? Right Corticobulbar Fibers
VII.
OTHER DESCENDING TRACTS
MIDBRAIN
A. TECTOSPINAL TRACT and TECTOBULBAR TRACT
Origin: Superior colliculus
Fibers:
o Level of midbrain: Crosses at the tegmental
decussation
o Level of medulla: Incorporated in the Median
Longitudinal Fasciculus (MLF)
Termination: Anterior gray column in the upper cervical
spinal cord in Rexed laminae VI, VII and VIII (Tectospinal)
Function: Mediate reflex postural movements in response
to visual and auditory stimuli (head turning and eye
movement)
B. RUBROSPINAL TRACT
Origin: Red nucleus (mesencephalic structure seen at the
level of superior colloculus)
FIbers: Crosses immediately in the ventral tegmenta
decussation -> Diffuses as it descend through the
brainstem -> Enter the lateral funiculus of the spinal cord
and lie anterior and lateral to the lateral corticospinal tract
Termination: Internuncial neurons (anterior gray column)
Functions:
o Influences both alpha and gamma anterior horn cells
o Influences control of tone in flexor muscle groups
o Activates contralateral flexor motor neurons while
inhibiting contralateral extensor fibers
Figure 7.Rubrospinal Tract
NOTE: Red nucleus receives afferent fibers from cerebral cortex
and cerebellum which influences the activity of the alpha and
gamma motor neuron of the spinal cord.
Interstitiospinal tract
o Origin: Interstitial nucleus of Cajal
o Uncrossed and forms part of the MLFo Termination: Anterior horn of upper cervical levels o
spinal cord including laminae VII and VIII
o Function: modulates reflex postural movements in
response to visual and vestibular stimuli
PONS/MEDULLA
A.
VESTIBULOSPINAL TRACT
Concerned with postural activity associated with balance
(maintains balance)
8/17/2019 Anat 6.4 Pyramidal Tract_Calilao
7/7
Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado Page 7 of 7
Acts on the motor neurons in the anterior grey columns,
facilitating the activity of the extensor muscles and inhibiting
the flexor muscles
o Vestibular nuclei:
Situated in the pons and medulla oblongata beneath
the floor of the 4th
ventricle
Receive afferent fibres from the inner ear through the
vestibular nerve and from the cerebellum
Axons give rise to the vestibulospinal tract
Tract descends through the medulla and spinal cord
uncrossed to the anterior white column Terminate by synapsing with the internuncial neurons
of the anterior grey column of the spinal cord
1.
Lateral Vestibulospinal Tract
o Origin: lateral vestibular nucleaus
o Descend in anterolateral funiculus
o Extends the length of the spinal cord
Termination: rexed laminae VII and VIII on alpha and
gamma motor neurons on all cervical cord segments
Afferents: vestibular nerve and cerebellum
Excites motor neurons innervating neck, back, limb
muscles
“ipsilaterally long”
Figure 8. Lateral Vestibulospinal Tract
2. Medial Vestibulospinal Tract
o Origin: medial vestibular nucleus
o Descend in MLF anterior funiculus of SC (until
midthoracic level only)
o Termination: rexed laminae VII and VIII on alpha and
gamma motor neurons on all cervical cord segments
o Afferents: primary vestibular, mesencephalic and
cerebellar
o Excites motor neurons innervating neck and back
o “bilaterally short”
B.
Reticulospinal Tract
Tracts enter the anterior grey columns of the spinal cord to gain
access to alpha and gamma motor neurons
Facilitate and inhibit activity of the alpha and gamma moto
neurons in the anterior grey columns, influencing voluntary
movement and reflex activity
Includes the descending motor fiber; allows access from the
hypothalamus to the sympathetic and sacral parasympathetic
outflows
Reticular Formation: groups of scattered nerve cells and nerve
fibres scattered throughout the midbrain, pons, and medulla
oblongata
Example: respiration, circulation, dilation, sweating, shivering
sphincter control of GIT and urinary tract
1. Pontine(Medial) Reticulospinal Tract
o Origin: Pons
o Descends into the spinal cord mostly uncrossed
o Descends through the anterior white column (anterio
funiculus of SC) – all cord levels, laminae VII and VIII
o Facilitate extensor motor neurons
o “ipsilaterally long”
2. Medullary (Lateral) Reticulospinal Tract
o Origin: medulla
o Fibers project bilaterally to spinal levels
o Descends into the spinal cord crossed and uncrossed
o Descends through the lateral white column (latera
funiculus) – all cord levels, laminae VII and IX
o
Inhibit extensor motor neurons