Anat 6.4 Pyramidal Tract_Calilao

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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


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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


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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%


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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 .


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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


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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)


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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

Anat 6.4 Pyramidal Tract_Calilao

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