Spinal Cord II

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White matter of spinal cord including how tract stated and course of each tracts.

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Spinal Cord II:

Spinal Cord II Dr Pankaj Maheria

White matter :

White matter Surrounds the central H -shaped mass of grey matter Contain : Nerve fibres Types of f ibres Sensory fibres Motor fibres Association fibres

Divisions of white matter:

Divisions of white matter Divided into three columns ( funiculi ) Ventral Dorsal Lateral White commissure Made up of tracts

Arrangement of fibers in the funiculi:

Arrangement of fibers in the funiculi Anterior funiculi : Peripheral fibres are descending Intermediate fibres are ascending Deep fibres are both ascending and descending

Arrangement of fibers in the funiculi:

Arrangement of fibers in the funiculi Lateral funiculi Peripheral fibres are ascending Intermediate fibres are descending Deeper fibres are both ascending and descending. Dorsal funiculi Ascending

Arrangement of fibers in the Funiculi:

Arrangement of fibers in the Funiculi In general, the posterior white column is sensory, the anterior column is motor and lateral column is mixed (i.e. motor as well as sensory). Further, the ascending tracts are located at the periphery and the descending tracts in the centre.

Tracts of Spinal Cord:

Tracts of Spinal Cord Collections of nerve fibres within the central nervous system, which have same origin, course and termination. Fasciculi or Lemnisci Name : masses of grey matter connected by them. Two components : First : origin Second : termination Classification : Descending Ascending Intersegmental

Descending tracts :

Descending tracts

Corticospinal tract Pyramidal tract :

Corticospinal tract Pyramidal tract Origin : From areas 4, 6, 3, 1, 2 and probably from other areas of cerebral cortex Course Corona radiata  posterior limb of internal capsule  middle two-third of basis pedunculi of midbrain  pons  pyramid of the medulla oblongata.

Corticospinal tract (Pyramidal tract): At Lower medulla :

Corticospinal tract (Pyramidal tract): At Lower medulla 90% fibres : lateral cortico -spinal tract (crossed pyramidal tract) 8% fibres : anterior cortico-spinal tract 2% fibres : uncrossed in lateral cortico -spinal tract.

Corticospinal tract (Pyramidal tract ): Position in spinal cord :

Corticospinal tract (Pyramidal tract ): Position in spinal cord Lateral corticospinal tract Lateral white column In front of the posterior horn and medial to the posterior spinocerebellar tract . Anterior corticospinal tract: Anterior white column Close to the anterior median fissure. separated from it by the sulcomarginal fasciculus

Corticospinal tract (Pyramidal tract ): termination :

Corticospinal tract (Pyramidal tract ): termination Laminae IV to VII of spinal grey A few fibres , directly synapse with the alpha and gamma neurons of lamina IX. They provide stimulating fibres to the flexor muscles and inhibitory fibres to the extensor muscle of the trunk .

Points of special interest:

Points of special interest Cortico -spinal tract extends uninterruptedly from the cortex to the spinal grey, unlike the other descending pathway. It is named as 'pyramidal tract ', since it occupies the pyramid of the medulla. It is one of the essential components of upper motor neuron and is concerned with the skilful , non -postural, volitional movements of the flexor muscles of the trunk and distal parts of the extremities . It modulates the sensory input and helps in smooth performance of movements. Myelination of cortico -spinal tracts starts about 3 years after birth and is completed by puberty.

Rubro-spinal tract:

Rubro -spinal tract Origin : Both Magnocellular and Pervo -cellular parts of red nucleus in the midbrain tegmentum . Course : Decussate immediately and descend through the contralateral rubro -spinal tracts. ( Ventral tegmental decussation )

Rubro-spinal tract:

Rubro -spinal tract Termination : Laminae V to VII of spinal grey, similar to the termination of corticospinal tract. Function : Facilitates flexor muscles and inhibits extensor muscles of the body.

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The cortico - rubro spinal tract thus formed may act as alternate route of pyramidal system to exert influence on lower motor neurons. The rubro -spinal tract is somatotopically arranged so that the dorsal fibres are confined to the cervico -thoracic segments and ventral fibres extend to the lumbo -sacral segments of the cord. Red nucleus receives input from the cerebellum and from the globus pallidus . Therefore, the rubrospinal tract, in general, stimulates the flexor tone and inhibits extensor tone.

Tecto-spinal tract:

Tecto -spinal tract Origin : Neurons in the superior colliculus (midbrain ). Course : The fibres cross to the opposite side in the upper part of the tegmentum of the midbrain . The crossing fibres form the dorsal tegmental decussation Pons Medulla Anterior funiculus of the spinal cord. Termination : Synapsing with ventral horn cells in cervical segments of the cord. Internuncial neurons located in laminae VI to VIII of the spinal grey matter.

Reticulo-spinal tract : Medial reticulo-spinal tract:

Reticulo -spinal tract : Medial reticulo -spinal tract Origin : Medial part of the reticular formation of both the pons and the medulla (mainly from the nucleus gigantocellularis reticularis of the medulla, and the oral and caudal reticular nuclei of the pons ). Course : The fibres which are crossed and uncrossed descend in the anterior funiculus (near the anterior median fissure). The fibres reach all levels of the spinal cord. Termination : They end directly, or through interneurons , on alpha and gamma motor neurons. Function : The tract is facilitatory to muscles of the trunk and limbs, but some fibres are inhibitory to neck muscles. The tract is concerned with postural adjustments of the head, trunk and limbs.

Reticulo-spinal tract : Lateral reticulo-spinal tract:

Reticulo -spinal tract : Lateral reticulo -spinal tract Origin : Ventrolateral tegmental field of the pons . Course : The fibres cross in the rostral medulla oblongata and project, with a high degree of collateralization, throughout the length of the spinal cord. Position in Spinal cord : lateral funiculus of the spinal cord, Closely associated with the rubrospinal and lateral corticospinal tracts Termination : Laminae I, V and VI, and also bilaterally in the lateral cervical nucleus. Function : Evidence suggests that this pathway is involved in the control of pain perception and in motor functions.

Vestibulo-spinal tracts:

Vestibulo -spinal tracts Vestibular nuclear complex Situation : upper medulla, comprises four groups of nuclei- lateral, medial , superior and inferior. Afferent : From the vestibular From the flocculonodular lobe of the cerebellum. Efferents : To the archicerebellum ; To the nuclei of third, fourth and sixth cranial nerves via the medial longitudinal fasciculus To the lower motor neurons of spinal anterior grey columns through the vestibulo - spinal tract

Lateral vestibulo-spinal tract:

Lateral vestibulo -spinal tract Uncrossed tract, somatotopically arranged extends upto caudal segments of the cord . Origin : lateral vestibular nucleus Course : Medulla Termination : Laminae VIII and VII of spinal grey

Lateral vestibulo-spinal tract:

Lateral vestibulo -spinal tract Position in spinal cord Anterior funiculus ventral to the anterior spino -thalamic tract , and intervenes between the tecto -spinal tract medially and the olivo -spinal tract · Iaterally . Function : facilitates extensor motor neurons and inhibits the flexors.

Medial vestibulo-spinal tract:

Medial vestibulo -spinal tract extends upto the mid-thoracic level. Uncrossed Origin : Medial vestibular nucleus Course : Medulla Termination : Laminae VII and VIII

Medial vestibulo-spinal tract:

Medial vestibulo -spinal tract Position in spinal cord Side of the anterior median sulcus as the sulco -marginal fasciculus, just lateral to the anterior cortico -spinal tract. Function : Still remains unsettled.

Descending Tracts ending in the Brainstem:

Descending Tracts ending in the Brainstem Corticonuclear tracts Cortico-ponto-cerebellar pathway

Ascending Tracts:

Ascending Tracts

Fibers of dorsal nerve roots and their termination:

Fibers of dorsal nerve roots and their termination

Fibers of dorsal nerve roots and their termination:

Fibers of dorsal nerve roots and their termination Medial division Thickly myelinated group I and group II fibres

Fibers of dorsal nerve roots and their termination:

Fibers of dorsal nerve roots and their termination Lateral division Thinly myelinated Group III fibres Unmyelinated group IV fibres .

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Spinal cord reflexes Ascending tracts to the cerebellum and brain stem nuclei Ascending tracts to the thalamus

Ascending tracts to the thalamus:

Ascending tracts to the thalamus For conscious integration the sensory system obeys the following principles : Environment (in which sensations generate) is represented on the contralateral side of sensory cortex (3, I, 2) of the brain. Three neuron concept of conscious sensory pathway is, however, violated by the olfactory system Thalamus appreciates the quality of consciousness (crude), but is unable to analyze the details of sensations. Pain and temperature are primarily appreciated by thalamus which imparts some emotional behavior. Sensory cortex handles detailed process of consciousness, and localizes, discriminates and analyses different modalities of exteroceptive and proprioceptive sensations. Ascending tracts which fail to reach the thalamus , cannot induce consciousness .

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach):

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach ) Unique in that they are formed predominantly by central processes of neurons located in dorsal nerve root ganglia. first order sensory neurons: The fibres derived from the lowest ganglia are situated most medially; while those from the highest ganglia are most lateral.

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach):

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach ) Second order sensory neurons ( Medial Lemniscus ) Neurons of the gracile and cuneate nuclei Internal arcuate fibres Medial lemniscus Medulla  P ons  midbrain to end in the thalamus (ventral posterolateral nucleus).

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach):

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach ) Third order sensory neurons Located in the thalamus Internal capsule  corona radiata  somatosensory areas of the cerebral cortex.

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach):

Fasciculus gracilis (tract of Gall) Fasciculus cuneatus (tract of Burdach ) Function : Some components of the sense of touch . These include deep touch and pressure, tactile localization, tactile discrimination, and stereognosis . Proprioceptive impulses that convey the sense of position and of movement of different parts of the body. The sense of vibration.

Applied anatomy :

Applied anatomy Tabes dorsalis Loss of sense of position Romberg's sign

Spinothalamic tract : Anterior and Lateral spinothalamic tracts:

Spinothalamic tract : Anterior and Lateral spinothalamic tracts First order neurons Spinal ganglia Second order neurons Located mainly in laminae IV, V, VI and VII. Cross to the opposite side of the spinal cord in the white commissure . Tracts also carry some uncrossed fibres (about 10 per cent).

Spinothalamic tract : Anterior and Lateral spinothalamic tracts:

Spinothalamic tract : Anterior and Lateral spinothalamic tracts Second order neurons Position in spinal cord Medulla Tracts separate Anterior spinothalamic tract : Medial lemniscus lateral spinothalamic tract: S pinal lemniscus Thalamus Ends in ventral posterolateral nucleus.

Spinothalamic tract : Anterior and Lateral spinothalamic tracts:

Spinothalamic tract : Anterior and Lateral spinothalamic tracts Third order neurons located in the thalamus Internal capsule  corona radiata  somatosensory areas of the cerebral cortex.

Spinothalamic tract : Anterior and Lateral spinothalamic tracts:

Spinothalamic tract : Anterior and Lateral spinothalamic tracts Function: Lateral spinothalamic tract carries pain and temperature sensations Anterior spinothalamic tract carries sensations of crude touch and pressure

Applied anatomy:

Applied anatomy Lateral spinothalamic tract The pain fibres become very superficial in the lateral white column of the cord in the cervical region. Therefore cordotomy can be performed safely at this level to relieve pain in the opposite half of the body. Syringomyelia Anterior spinothalamic tract loss of light touch and pressure on the opposite of the body below the level of the lesion.

Applied anatomy:

Applied anatomy Thalamic syndrome Threshold for appreciation of touch pain or temperature is lowered. Sensation that are normal may appear to be exaggerated or unpleasant. There may be spontaneous pain. Emotions may be abnormal. Cordotomy

Spinocerebellar tracts:

Spinocerebellar tracts Located in the lateral white column of the cord Division Posterior spinocerebellar tract Anterior spinocerebellar tract Function : Unconscious proprioceptive sensations from cord to the cerebellum Important role in muscular coordination .

Posterior ( Dorsal ) spinocerebellar tract:

Posterior ( Dorsal ) spinocerebellar tract First order sensory neurons Dorsal root ganglia of the spinal nerves. Nucleus dorsalis (Clarke's column).

Posterior ( Dorsal ) spinocerebellar tract:

Posterior ( Dorsal ) spinocerebellar tract Second order neuron : Spinal cord :Axons of the tract originate ipsilaterally from the larger neurones of Clarke's column, in lamina VII throughout spinal segments T1–L2 Medulla:  inferior cerebellar peduncle  Termination : ipsilaterally in the rostral and caudal parts of the cerebellar vermis .

Anterior ( Ventral ) spinocerebellar tract:

Anterior ( Ventral ) spinocerebellar tract First order sensory neurons Dorsal root ganglia of the spinal nerves. Nucleus dorsalis (Clarke's column).

Anterior ( Ventral ) spinocerebellar tract:

Anterior ( Ventral ) spinocerebellar tract Second order neuron : Spinal cord : ventral to the dorsal tract Most of the axons forming the tract decussate, but some remain ipsilateral . The tract begins in the upper lumbar region and ascends Medulla oblongata Upper pontine level Descends in the dorsal part of the superior cerebellar peduncle Termination : mainly contralaterally , in the anterior cerebellar vermis .

Cuneocerebellar tract (posterior external arcuate fibres):

Cuneocerebellar tract (posterior external arcuate fibres ) Clarke's column is located only from C8 to L3 spinal segments. first order neuron : Proprioceptive sensations from upper limb and entering the spinal cord above C8 segment  ipsilateral dorsal funiculus  terminate A ccessory cuneate nucleus of the medulla. Second order semory neurons Ipsilateral cerebellum  inferior cerebellar peduncle.

Applied anatomy:

Applied anatomy

Syringomyelia:

Syringomyelia A fluid cavity (or cavities) develops near the centre of the spinal cord usually in the cervical segments the destruction of the cord involving central canal and its surrounding area. Dissociated sensory loss.

Hemisection of Cord ( Brown-Se quard syndrome):

Hemisection of Cord ( Brown-Se quard syndrome) ON THE SIDE OF THE LESION Following damage of posterior funiculus loss of position and vibratory senses , disturbances of stereognosis and tactile discrimination, below the level of lesion. Involvement of the pyramidal tract produces spastic paralysis with exaggerated tendon reflexes and positive Babinski sign. Due to paralysis, the ataxia is not demonstrated.

Hemisection of Cord ( Brown-Se quard syndrome):

Hemisection of Cord ( Brown-Se quard syndrome) ON CONTRALATERAL SIDE OF THE LESIONS Damage of the lateral spino -thalamic tract produces loss of pain and temperature, one or two segments below the level of lesion.

Hemisection of Cord ( Brown-Se quard syndrome):

Hemisection of Cord ( Brown-Se quard syndrome) Due to Local Damage of Spinal segment and Nerve root Irritation of dorsal root produces radicular pain and occasional paresthesia like prickling and numbness, over the affected areas of dermatomes. In complete injury of the dorsal root, there will be segmental and ipsilateral loss of all modalities of sensations, along with areflexia and atonia . Destruction of ventral root produces flaccid paralysis of the muscles supplied by the affected half of the corresponding spinal segment.

TRANSECTION OF THE CORD:

TRANSECTION OF THE CORD Spinal fracture or dislocation Loss of all sensations and voluntary movement Above the fifth cervical cord segment Unable to survive due to paralysis of respiratory muscles following involvement of phrenic nerve nucleus below the level of lesion.

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