TRACTS OF THE SPINALCORD Definition of Tract – A collection of nerve fibres that connects two masses Grey matter within the central nervous system is called a tract. Some tracts are called fascicul...
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DR.KRISHNA MADHUKAR DEPT.. OF ORTHOP DEPT ORTHOPAEDIC AEDICS S BHARA BHAR ATI HOSPITAL HOS PITAL
STRUCTURE STRUC TURE 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 STRUCTURE OF THE SPINAL CORD y
The neural substance of the spinal cord is divided into :
GREY MATTE MATTER R Dorsal horn Lateral horn Ventral horn
WHITE MA MATTER TTER Ventral funiculus Lateral funiculus Dorsal funiculus
INTERNAL STRUCTURE 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 ± 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 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.
INTERNAL STRUCTURE OF THE SPINAL CORD 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
INTERNAL STRUCTURE STRUCTURE OF THE SPINAL CORD White matter is a collection of myelinated myelinate d and non myelinate myelinated d nerve nerv e fibers.
SPINAL TRACTS ASCENDING TRACTS : Carry sensory impulses from spinal cord to brain.
DESCENDING TRACTS : Carry motor impulses from brain to spinal cord.
SPINAL TRA TRACTS CTS
ASCENDING TRACTS TRACTS OF SPINAL CORD WHITE FU F UNICULUS
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 unilater unilateral al 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 spinothalam ic 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 L ESION : A unilatera unilaterall 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 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 unilater unilateral al lesion causes loss of proprioception in the opposite side below the level of lesion.
DORSAL SPINOCEREBELLAR TRACT (Flechsig·s tract) (Flechsig·s 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 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 L ESION : A unilatera unilaterall 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 spinothalami spinot halamic c 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 : TERMINATION Superior colliculus of tectum in midbrain.
SPINOTECTAL TRACT
FUNCTION : This tract is concerned with with spinovisual reflex.
SPINORETICULAR TRACT It is formed by fibers of second s econd 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
I.
II.
III.
TERMINATION : terminate in the reticular formation of brain stem in 3 ways Some fibers terminate in the nucleus reticularis gigantocellularis and lateral reticular nucleus of medulla on the same side. Some terminate in the nucleus reticularis pontis caudalis of pons in the same side. Very few fibers terminate in the midbrain.
SPINORETICULAR TRACT
FUNCTION : This tract is concerned with consciousness and awareness.
SPINO--OLI SPINO -OLIVARY TRACT SITUATION : Anterolateral part of the white funiculus. Origin of fibers of this tract are not specific.
SPINO--OLI 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 cerebellu m on the same side.
SPINO--OLI SPINO -OLIVARY TRACT
FUNCTION : This tract is concerned with proprioception.
FASCICULUS DORSOLATERALIS (Tract (T ract of o of f Lissauer Liss Lissauer) auer) 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 (T FASICULUS ((Tract Tract of of Goll Goll)) & FASICULUS CUNEA CUNEATUS TUS (T (Tract ract of of Burdach) Both the tracts are constituted by fibers of first order neurons of sensory pathway pathway.. SITUATION : Posterior white funiculus divided by posterior intermediate septum. ORIGIN : Cell bodies in the posterior root ganglion .
FASICULUS GRACILIS (T FASICULUS ((Tract Tract of of Goll Goll)) & FASICULUS CUNEA CUNEATUS TUS (T (Tract ract of of Burdach 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 FASICULUS (Tract of o off Goll) Goll) & FASICULUS CUNEA CUNEATUS TUS (T (Tract ract of of Burdach 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 (T FASICULUS ((Tract Tract of of Goll Goll)) & FASICULUS CUNEA CUNEATUS TUS (T (Tract ract of of Burdach Burdach))
FUNCTIONS
Fine sensation
Tactile localiza localization tion
Tactile discrim discrimination ination
Sensation of vibration
Proprioception
Stereognosis
FASICULUS GRACILIS (T FASICULUS ((Tract Tract of of Goll Goll)) & FASICULUS CUNEA CUNEATUS TUS (T (Tract ract of of Burdach 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 propriocept proprioception ion
COMMA TRACT OF SCHULTZE This tract is situated between 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 :
There are 2 pyramidal tracts Anterior and lateral corticospinal corticos pinal 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 TRA TRACTS CTS 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 Somatosensory the parietal lobe of cerebral cortex.(areas 3,1,2) 40%
PYRAMIDAL TRA TRACTS CTS 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 TRA TRACTS CTS 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 TRA TRACTS CTS FUNCTIONS :
Voluntary movements of the body
Fine and skilled movements
PYRAMIDAL TRA TRACTS CTS 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 FASICU ASICULUS LUS 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 FASICU ASICULUS LUS 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 t he upper cervical segments of the spinal cord. TERMINATION : Anterior 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 t horacic segments of the spinal cord. COURSE : Run down uncrossed from the medulla into the anterior white funiculus. TERMINATION : Anterior Anterior motor neurons of the spinal cord. 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. TERMINATION : Anterior Anterior motor neurons of the spinal cord. FUNCTION : Concerned with adjustment of head and body during angular and linear accelaration.
RETICULOSPINAL TRAC TRACT T SITUATION : Two tracts
Medial RST ± Anterior white funiculus
Lateral RST ± Lateral white funiculus.
RETICULOSPINAL TRAC TRACT T ORIGIN ±
Medial RST ± Uncrossed fibers arising from pons
Lateral RST ± Uncrossed fibers arising from medulla
RETICULOSPINAL TRAC TRACT T EXTENT : Fibers of this tract extend upto the thoracic segments of the spinal cord. TERMINATION : Gamma motor neurons of anterior grey horn
RETICULOSPINAL TRAC TRACT T FUNCTION
PONTINE
MEDULLARY
RETICUL RETICULAR AR FIBERS FIBERS
RETICUL RETICULAR AR FIBERS FIBERS
Facilitates
Inhibits
Control of muscle tone Facilitates through gamma motor neurons
Inhibits
On respiration
Favors expiration
Favors inspiration
On blood vessels
Vasoconstriction
Vasodilatation
Control of voluntary and reflex movements
TECTOSPINAL TRACT SITUATION : Anterior white funiculus ORIGIN : Superior colliculus of midbrain
TECTOSPINAL TRACT COURSE : After origin origin the fibers cross in the dorsal tegmental decussation decussation and descend to the anterior white funiculus. EXTENT : Only upto lower cervical segments of the spinal cord. TERMINATION : Anterior Anterior motor neurons 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 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 Anterior motor neurons of spinal cord. FUNCTION : Influence the flexor f lexor muscle tone.
OLIVOSPINAL TRACT SITUATION : Lateral white funiculus of spinal cord. ORIGIN : Inferior olivary nucleus in the medulla. TERMINATION : Anterior Anterior motor neurons of the spinal cord. FUNCTION : Reflex movements m ovements arising from propriocept proprioceptors. ors.
