Anat 6.4 Pyramidal Tract_Calilao

Anatomy 6.4

February 7, 2012 Dr. Melissa Calilao

Pyramidal System I. II. A. B. C. D. E. III. A. B. C. D. IV. A. B. V. A. B. VI. A. B.

OUTLINE Motor System Pyramidal Tract Two Main Pathways Origin of Fibers Motor Homunculus Supplementary Motor Area Descending Pathways: Anatomical Organization Corticospinal Tract Pathway Lateral Corticospinal Tract Anterior Corticospinal Tract Termination of Pyramidal Tract Upper Motor Neuron vs Lower Motor Neuron Paralysis Upper Motor Neuron Lower Motor Neuron Corticobulbar Tract Facial Motor Nucleus Lower Motor Nucleus Other Descending Tracts Midbrain Pons/Medulla

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TWO MAIN PATHWAYS 1. Corticospinal tract  Lateral Corticospinal Tract  Anterior /Ventral Corticospinal Tract 2. Corticobulbar tract

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ORIGIN OF FIBERS 

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 of cerebral 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

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

2.Postcentral gyrus (Brodmann’s area 3, 1, 2)  Primary sensory cortex  1/3 of the axons  Fibers are not involved in voluntary movement but they are responsible in controlling sensory inputs

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 wellcoordinated movements  Influence lower motor neurons indirectly through modulation of the cerebral cortex and brainstem

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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

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

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  

Group 17 | Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

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

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Figure 1. Reflex Arc III. CORTICOSPINAL TRACT A.

PATHWAY

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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 contralateral side) There is better motor control on the upper extremities and body because more fibers terminate at this area

 Figure 2. Motor Homunculus D.

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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

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DESCENDING PATHWAYS: ANATOMICAL ORGANIZATION  

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1 order of neuron(N1) o Nerve cell body in the cerebral cortex nd 2 order of neuron(N2) o Internuncial neuron (connecting neuron) in anterior gray column of spinal cord o Has short axon rd 3 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

Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

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Origin: Cerebral cortex (1 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

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Corona radiata  Where descending fibers from cerebral cortex will converge  Afferent and efferent fibers situated deep in the medullary substance

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Internal capsule  From corona radiata, it will pass through the posterior 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 cervical 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 Page 2 of 7

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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 Cerebral peduncles (middle 3/5)  Cervical portions of the body: Fibers located more medially  Lower extremities: Fibers located more laterally 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 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 Pyramidal decussation (caudal medulla)  Crossing over of fibers at the junction of medulla oblongata and the spinal cord 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 ventromedian fissure)  They will eventually cross before terminating on anterior horn cells in cervical and upper thoracic regions  Formed by the 10-15% uncrossed fibers B.   

Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

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

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UPPER MOTOR NEURON (UMN) o

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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

The pyramidal tracts normally tend to increase muscle tone, while extrapyramidal tracts inhibit muscle tone In clinical practice, it is rare to find a lesion that is limited solely to the pyramidal tract or extrapyramidal tract 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 Complete paralysis (complete loss of action, since main innervations of muscles are severed) Flaccidity - due to atonia

Arreflexia (reflex arc is damaged)

Muscles undergo marked atrophy

No Clonus Figure 3. Motor Neurons Lesions

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LOWER MOTOR NEURON (LMN)

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3 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

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No Babinski sign

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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

Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

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UMN LESION Paresis (muscle weakness) Spasticity due to marked hypertonia increase in muscle tone lesion is on extrapyramidal tract Hyperreflexia (LMN over discharge there is an absence of suppressor action on LMN related to increase in tone lesion on extrapyramidal tract) No muscle atrophy minor in chronic state in time, it will have disused atrophy Clonus manifested rapid, strong muscle contraction when paralyzing limb is grasped firmly lesion on extrapyramidal tract (+) 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

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 the lateral 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 aspect 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. Page 4 of 7

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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, laughing o 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

FACIAL MOTOR NUCLEUS 

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Dorsal part o 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 inability to move the left half of the face but can still wrinkle both eyebrows Type of lesion? UMN Where is the lesion? Right Supranuclear PRACTICE PROBLEM 2

Case Scenario: A patient upon waking up in the morning is unable to move the entire right half of his face. PHHx: had chicken pox 2 weeks prior Type of lesion? LMN Diagnosis? Bell’s Palsy Where is the lesion? Right Nucleus of Facial Nerve Prognosis? Excellent; 85% or more recover B.

HYPOGLOSSAL NUCLEUS

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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 at 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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Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

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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

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Function: Mediate reflex postural movements in response to visual and auditory stimuli (head turning and eye movement)

RUBROSPINAL TRACT  

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Origin: Red nucleus (mesencephalic structure seen at the level of superior colloculus) FIbers: Crosses immediately in the ventral tegmental 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 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 to the LEFT Type of lesion? LMN Where is the lesion? LEFT Hypoglossal Nucleus PRACTICE PROBLEM 4 Caes Scenario: The resident noted that the tongue of a post-stroke patient is NOT atrophied and deviated to the LEFT Type of lesion? UMN Where is the lesion? Right Corticobulbar Fibers

VII. OTHER DESCENDING TRACTS MIDBRAIN A.

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. 

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) Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

Interstitiospinal tract o Origin: Interstitial nucleus of Cajal o Uncrossed and forms part of the MLF o Termination: Anterior horn of upper cervical levels of spinal cord including laminae VII and VIII o Function: modulates reflex postural movements in response to visual and vestibular stimuli PONS/MEDULLA

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VESTIBULOSPINAL TRACT

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Concerned with postural activity associated with balance (maintains balance) Page 6 of 7

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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 th the floor of the 4 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

o o o o B.

Reticulospinal Tract

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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 motor 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

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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”

Termination: rexed laminae VII and VIII on alpha and gamma motor neurons on all cervical cord segments Afferents: primary vestibular, mesencephalic and cerebellar Excites motor neurons innervating neck and back “bilaterally short”

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Pontine(Medial) Reticulospinal Tract Origin: Pons Descends into the spinal cord mostly uncrossed Descends through the anterior white column (anterior funiculus of SC) – all cord levels, laminae VII and VIII o Facilitate extensor motor neurons o “ipsilaterally long” o o o

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Medullary (Lateral) Reticulospinal Tract Origin: medulla Fibers project bilaterally to spinal levels Descends into the spinal cord crossed and uncrossed Descends through the lateral white column (lateral funiculus) – all cord levels, laminae VII and IX o Inhibit extensor motor neurons o o o o

Figure 8. Lateral Vestibulospinal Tract

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Medial Vestibulospinal Tract o Origin: medial vestibular nucleus o Descend in MLF  anterior funiculus of SC (until midthoracic level only)

Group 17|Esguerra, Eslao, Esling, Espelimbergo, Esternon, Estevanez, Estrada, Estrellado

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