SPINAL TRACTS

SPINAL TRACTS

DR.KRISHNA MADHUKAR

DEPT. OF ORTHOPAEDICS

BHARATI HOSPITAL

STRUCTURE OF THE SPINAL CORD Anterior surface has a deep furrow –

Anterior median fissure

Lateral to anterior median fissure there is anterolateral sulcus – exit of anterior nerve root.

Posterior depression – posterior median sulcus.

Continues into the spinal cord as posterior median septum

On either side lateral to PMS – posterointermediate sulcus and posterolateral sulcus.

Posterolateral sulcus – denotes exit of posterior nerve root.

INTERNAL STRUCTURE OF THE SPINAL CORD

The neural substance of the spinal cord is divided into :

GREY MATTER Dorsal horn Lateral horn Ventral horn

WHITE MATTER Ventral funiculus Lateral funiculus Dorsal funiculus

INTERNAL STRUCTURE OF THE SPINAL CORD Exactly at the center of the

grey matter there is a canal – spinal canal

Part of grey matter anterior to spinal canal – Anterior grey commissure.

Part to grey matter posterior to spinal canal – Posterior grey commissure.

Part of white matter between the anterior median sulcus and the anterior grey commissure – anterior white commissure

INTERNAL STRUCTURE OF THE SPINAL CORD NEURONS IN THE GREY MATTER

o Anterior grey matter – involved in motor function

1. Alpha motor neurons : multipolar cells –axons leave spinal cord through anterior root and end in skeletal muscle fibre.

2. Gamma motor neurons : smaller cells which are scattered among alpha motor neurons which send axons to the intrafusal fibres of the muscle spindle.

3. Renshaw cells : also smaller cells which are inhibitory neurons

INTERNAL STRUCTURE OF THE SPINAL CORD Neurons in the

lateral grey matter

Clusters of nerve cells called intermediolateral horn cells which give rise to sympathetic preganglionic fibers, which leave the spinal cord through the anterior nerve root.


Neurons in the posterior grey horn – receive impulses from various receptors of the body through posterior nerve root.

1. Substantia Gelatinosa of Rolando : cap of gelatinous material at the apex of the posterior horn – small nerve cells.

2. Marginal cells : cover the substantia gelatinosa ot the tip of the posterior horn.

3. Chief sensory cells : situated in the remaining parts of the posterior horn.

4. Clarke’s column of cells : occupy the inner part of the posterior horn


White matter is a collection of myelinated and non myelinated nerve fibers.

SPINAL TRACTS

ASCENDING TRACTS : Carry sensory impulses from spinal cord to brain.

DESCENDING TRACTS : Carry motor impulses from brain to spinal cord.

SPINAL TRACTS

ASCENDING TRACTS OF SPINAL CORD

WHITE FUNICULUS TRACT

Anterior funiculus 1. Anterior spinothalamic tract

Lateral funiculus 2. Lateral spinothalmic tract3.Ventral spinocerebellar tract4. Dorsal spinocerebellar tract5. Spinotectal tract6. Spinoreticular tract7. Spino-olivary tract8. Spinovestibular tract

Posterior funiculus 9. Fasiculus gracilis10. Fasiculus cuneatus11. Comma tract of Schultze

ANTERIOR SPINOTHALAMIC TRACT

SITUATION : Anterior white funiculus

ORIGIN : Fibers arise from chief sensory cells of posterior grey horn – second order neurons for crude touch pathway. First order neurons are situated in the posterior nerve root ganglion

ANTERIOR SPINOTHALAMIC TRACT COURSE : After taking origin the

fibers ascend for 2 -3 segments in the same side and then cross obliquely to enter the anterior white funiculus of the opposite side . From here the fibers ascend through other segments of spinal cord and brainstem ( medulla, pons and midbrain) to reach the thalamus.

TERMINATION : Ventral posterolateral nucleus of the thalamus . The third order neurons from the thalamic nucleus carry impulses to sensory cortex of the cerebral cortex.

ANTERIOR SPINOTHALAMIC TRACT

FUNCTION : This tract carries impulses of crude touch.

EFFECT OF LESION : A unilateral lesion of this tract causes loss of crude touch sensation in the opposite side below the level of the lesion.

LATERAL SPINOTHALAMIC TRACT

SITUATION : Lateral white funiculus towards the medial side

ORIGIN : Fibers arise from the Substantia Gelatinosa of Rolando in the posterior grey horn – second order neurons for pain and temperature pathway

LATERAL SPINOTHALAMIC TRACT COURSE : After taking origin the

fibers cross to the lateral white funiculus of the opposite side of the same segment after which they ascend through medulla, pons and midbrain to reach the thalamus along with the fiber of the anterior spinothalamic tract.

The fibers of the lateral spinothalamic tract form spinal lemniscus along with fibers of the anterior spinothalamic tract at the lower part of medulla.

TERMINATION : Ventral posterolateral nucleus of the thalamus from where third order neurons relay impulses to the sensory cortex of the cerebral cortex.

LATERAL SPINOTHALAMIC TRACT

FUNCTION : This tract carries impulses of pain and temperature.

EFFECT OF LESION : A unilateral lesion of this tract causes loss of pain and temperature in the opposite side below the level of the lesion.

VENTRAL SPINOCEREBALLAR TRACT (Gower’s tract)

SITUATION : Lateral white funiculus along the periphery.

ORIGIN : Marginal cells of posterior gray horn – second order neurons of proprioception

VENTRAL SPINOCEREBALLAR TRACT COURSE : Fibers cross

the midline and ascend in the lateral white funiculus of the opposite side through the other spinal segments, medulla ,pons and midbrain to reach the superior cerebellar peduncle.

TERMINATION : Cortex of the anterior lobe of the cerebellum

VENTRAL SPINOCEREBALLAR TRACT

FUNCTION : This tract carries impulses of proprioception from muscles tendons and joints.

EFFECT OF LESION : A unilateral lesion causes loss of proprioception in the opposite side below the level of lesion.

DORSAL SPINOCEREBELLAR TRACT (Flechsig’s tract)

SITUATION : Lateral white funiculus toward the posterolateral periphery of spinal cord.

ORIGIN : Clarke’s column of cells in the posterior grey horn – second order neurons of proprioception.

DORSAL SPINOCEREBELLAR TRACT

COURSE : After taking origin the fibers reach the lateral white funiculus of the same side from where they ascend through other spinal segments and medulla to reach the inferior cerebellar peduncle.

TERMINATION : Cortex of the anterior lobe of cerebellum.

DORSAL SPINOCEREBELLAR TRACT

FUNCTION : This tract relays impulses of proprioception.

EFFECT OF LESION : A unilateral lesion of this tract causes loss of proprioception on same side as the fibers do not cross.

SPINOTECTAL TRACT

This tract is considered as a component of anterior spinothalamic tract.

SITUATION : Lateral white funiculus , bound anteriorly by anterior nerve root.

ORIGIN : Chief sensory cells of posterior grey horn.

This tract is very prominent in cervical segments of the spinal cord.

SPINOTECTAL TRACT COURSE : After taking

origin the fibers cross to the opposite side lateral white funiculus from where they ascend to the midbrain along with anterior spinothalamic tract

TERMINATION : Superior colliculus of tectum in midbrain.

SPINOTECTAL TRACT

FUNCTION : This tract is concerned with spinovisual reflex.

SPINORETICULAR TRACT It is formed by fibers of second order

neurons.

SITUATION : Anterolateral white funiculus.

ORIGIN : Intermediolateral cells in the lateral grey horn.

SPINORETICULAR TRACT COURSE : After taking origin the

fibers ascend in the same side without crossing

TERMINATION : terminate in the reticular formation of brain stem in 3 ways

I. Some fibers terminate in the nucleus reticularis gigantocellularis and lateral reticular nucleus of medulla on the same side.

II. Some terminate in the nucleus reticularis pontis caudalis of pons in the same side.

III. Very few fibers terminate in the midbrain.

SPINORETICULAR TRACT

FUNCTION : This tract is concerned with consciousness and awareness.

SPINO-OLIVARY TRACT

SITUATION : Anterolateral part of the white funiculus.

Origin of fibers of this tract are not specific.

SPINO-OLIVARY TRACT COURSE : After

taking origin the fibers cross to the opposite side and ascend to terminate in the olivary nucleus of medulla from where neurons project into the cerebellum on the same side.

SPINO-OLIVARY TRACT

FUNCTION : This tract is concerned with proprioception.

FASCICULUS DORSOLATERALIS (Tract of Lissauer)

SITUATION : Lateral white funicular on the posterior aspect

ORIGIN : Fibers arise from cells of posterior root ganglia and enter the spinal cord through lateral division of posterior nerve root – fibers of first order neurons

Considered a component of lateral spinothalamic tract.

FASCICULUS DORSOLATERALIS COURSE : Synapse

with the cells of substantia gelatinosa which form the second order neurons of lateral spinothalamic tract.

FUNCTION : This tract carries impulses of pain and temperature.

FASICULUS GRACILIS (Tract of Goll) &

FASICULUS CUNEATUS (Tract of Burdach)

Both the tracts are constituted by fibers of first order neurons of sensory pathway.

SITUATION : Posterior white funiculus divided by posterior intermediate septum.

ORIGIN : Cell bodies in the posterior root ganglion .

FASICULUS GRACILIS (Tract of Goll) & FASICULUS CUNEATUS (Tract of Burdach) COURSE :

After entering the spinal cord the fibers ascend through the posterior white funiculus with fasiculus gracilis carrying fibers from the sacral, lumbar and lower thoracic ganglia and fasiculus cuneatus carrying fibers from the upper thoracic and cervical ganglia of the posterior nerve root.

FASICULUS GRACILIS (Tract of Goll) & FASICULUS CUNEATUS (Tract of Burdach)

TERMINATION : Nucleus gracilis and nucleus cuneatus in the medulla respectively.

The cells of these medullary nucleii form the second order neurons which form the internal arcuate fibers after crossing the midline .

The fibers then ascend through pons and midbrain as medial lemniscus.

Fibers of the medial leminiscus terminate in the ventral posterolateral nucleus of the thalamus.

From here the third order neurons relay to sensory area of cerebral cortex.

FASICULUS GRACILIS (Tract of Goll) & FASICULUS CUNEATUS (Tract of Burdach) FUNCTIONS

Fine sensation Tactile localization Tactile discrimination Sensation of vibration Proprioception Stereognosis

FASICULUS GRACILIS (Tract of Goll) & FASICULUS CUNEATUS (Tract of Burdach) EFFECT OF LESION – Symptoms appear

on the same side of below the level of lesion.

Loss of fine sensation Loss of tactile localization Loss of tactile discrimination Loss of vibratory sense. Astereognosis Loss of proprioception

COMMA TRACT OF SCHULTZE This tract is situated between fasiculus

gracilis and fasiculus cuneatus.

Fibers arise from the medial division of the posterior nerve root.

The function of this tract is to establish intersegmental communications and to form short reflex arc.

DESCENDING TRACTS OF THE SPINAL CORD These tracts are formed by motor nerve

fibers arising from brain and descend into the spinal cord.

Two types : Pyramidal tracts Extrapyramidal tracts

DESCENDING TRACTS OF THE SPINAL CORD

TYPE TRACT

Pyramidal tracts 1. Anterior corticospinal tract2. Lateral corticospinal tract

Extrapyramidal tracts 1. Medial longitudinal fasiculus2. Anterior vestibulospinal tract3. Lateral vestibulospinal tract4. Reticulospinal tract5. Tectospinal tract6. Rubrospinal tract7. Olivospinal tract

PYRAMIDAL TRACTS

There are 2 pyramidal tracts Anterior and lateral

corticospinal tracts.

While running from the cerebral cortex towards the spinal cord ,the fibers of these two tracts give the appearance of a pyramid on the upper part of anterior surface of medulla.

The fibers of these tracts are axons of upper motor neurons

PYRAMIDAL TRACTS

ORIGIN :

i. Gaint cells or Betz cells in precentral gyrus of motor cortex.(area 4) 30%

ii. Premotor area (area 6) of motor cortex. 30%

iii. Other parts of frontal lobe

iv. Somatosensory areas of the parietal lobe of cerebral cortex.(areas 3,1,2) 40%

PYRAMIDAL TRACTS COURSE : After taking origin ,the nerve

fibers converge to form a fan like structure – corona radiata.

From the corona radiata the fibers descend down the internal capsule, midbrain and pons to reach the medulla.

At the lower border of the medulla the pyramidal tracts on each side are divided into two unequal bundles.

80% of fibers cross to the opposite side forming the pyramidal decussation giving rise to lateral corticospinal tract.

20% of fibers do not cross and descend down to form the anterior corticospinal tract.

PYRAMIDAL TRACTS TERMINATION :

Both crossed and uncrossed fibers terminate in the motor neurons of the anterior grey matter, axons of which leave the spinal cord through the anterior nerve root.

PYRAMIDAL TRACTS

FUNCTIONS :

Voluntary movements of the body

Fine and skilled movements

PYRAMIDAL TRACTS

EFFECTS OF LESION : UMN lesion

Loss of voluntary movements Spastic paralysis Superficial reflexes are lost Deep reflexes are exaggerated. Positive Babinski’s sign

EXTRAPYRAMIDAL TRACTS

Descending tracts other than the pyramidal tracts are called extrapyramidal tracts.

MEDIAL LONGITUDINAL FASICULUS

SITUATION : Posterior part of anterior white funiculus.

ORIGIN : 4 different areas of the brain stem

Vestibular nuclei Reticular formation Superior colliculus Interstitial cells of Cajal.

MEDIAL LONGITUDINAL FASICULUS COURSE : After origin the fibers descend in the

posterior part of anterior white funiculus on the same side of the spinal cord.

EXTENT : Fibers of this tract extend up to the upper cervical segments of the spinal cord.

TERMINATION : Anterior motor neurons of the spinal cord.

FUNCTION : Coordination of reflex ocular movements and integration of ocular and neck movements.

ANTERIOR VESTIBULOSPINAL TRACT

SITUATION : Anterior white funiculus along the periphery of the spinal cord.

ORIGIN : Medial vestibular nucleus in medulla.

ANTERIOR VESTIBULOSPINAL TRACT EXTENT : The fibers run upto the thoracic

segments of the spinal cord.

COURSE : Run down uncrossed from the medulla into the anterior white funiculus.


FUNCTION : Concerned with adjustment of head and body during angular and linear accelaration.

LATERAL VESTIBULOSPINAL TRACT

SITUATION : Anterior part of lateral white funiculus.

ORIGIN : Lateral vestibular nucleus in medulla

LATERAL VESTIBULOSPINAL TRACT EXTENT : The fibers run through out the spinal

cord.

COURSE : Run down uncrossed from the medulla into the anterior white funiculus.


FUNCTION : Concerned with adjustment of head and body during angular and linear accelaration.

RETICULOSPINAL TRACT

SITUATION : Two tracts

Medial RST – Anterior white funiculus

Lateral RST – Lateral white funiculus.

RETICULOSPINAL TRACT ORIGIN –

Medial RST – Uncrossed fibers arising from pons

Lateral RST – Uncrossed fibers arising from medulla


EXTENT : Fibers of this tract extend upto the thoracic segments of the spinal cord.

TERMINATION : Gamma motor neurons of anterior grey horn


FUNCTION PONTINE RETICULAR FIBERS

MEDULLARY RETICULAR FIBERS

Control of voluntary and reflex movements

Facilitates Inhibits

Control of muscle tone through gamma motor neurons

Facilitates Inhibits

On respiration Favors expiration Favors inspiration

On blood vessels Vasoconstriction Vasodilatation

TECTOSPINAL TRACT

SITUATION : Anterior white funiculus

ORIGIN : Superior colliculus of midbrain

TECTOSPINAL TRACT COURSE : After origin the fibers cross in the dorsal

tegmental decussation and descend to the anterior white funiculus.

EXTENT : Only upto lower cervical segments of the spinal cord.


FUNCTION : Movement of head in response to visual and auditory stimuli

RUBROSPINAL TRACT

SITUATION : Lateral white funiculus

ORIGIN : Large cells of red nucleus in mid brain

RUBROSPINAL TRACT COURSE : After origin the fibers cross in ventral

tegmental decussation and descend into spinal cord through reticular formation in pons and medulla.

EXTENT : Only upto the thoracic segments of the spinal cord.

TERMINATION : Anterior motor neurons of spinal cord.

FUNCTION : Influence the flexor muscle tone.

OLIVOSPINAL TRACT SITUATION : Lateral white funiculus of spinal

cord.

ORIGIN : Inferior olivary nucleus in the medulla.


FUNCTION : Reflex movements arising from proprioceptors.

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SPINAL TRACTS