SPINAL CORD INTERNAL STRUCTRE BY DR SHIVRAM BHAT

SPINAL CORD INTERNAL STRUCTRE BY DR SHIVRAM BHAT

TRANSVERSE SECTION

AT DIFFERENT LEVELS

INTERNAL STRUCTURE • H shaped Grey matter in the centre & white matter in the periphery. GREY MATTER • It consists of nerve cells, neuroglia & blood vessels. • The grey matter presents a pair of anterior grey column (ventral horns) & posterior grey column (dorsal horns. Lateral grey column – in some parts. Grey matter White matter LGC PGC AGC • The grey matter of right & left halves are connected across in the midline by grey commissure & traversed by central canal.

NUCLEI OF SPINAL CORD- Columnar arrangement Anterior grey column: Lower motor neurons (α, β, ) are arranged in 3 groups of longitudinal columns in cervical & lumbosacral enlargements. Medial, lateral &central. • Medial – whole length – VM, DM- skeletal Retro dorso muscles of the trunk. lateral N • Lateral – Cervical & Dorso lumbosacral lateral N enlargements- VL, DL Ventro & RDL. Limb muscles. lateral N • Central – Cervical & lumbosacral- phrenic Dorsomedial N Trunk Central N nerve nucleus muscles Ventromedial N

Posterior grey column: 4 main sets of nuclei are seen. • Postero marginal nuclei: Receives some incoming dorsal root fibers. • Substantia gelatinosa of Rolando: Present through the entire length of spinal cord- Relay station for pain and temperature fibers. The axons give rise to lateral spino thalamic tract. ` • Nucleus proprius: Present through the entire length of the cord. Concerned with sensory associative mechanisms. • Nucleus dorsalis: C 8 - L 3 segments – unconscious proprioceptive impulses to the cerebellum- post spino cerebellar tract. Visceral afferent Nu.

Lateral grey column: • Intermediolateral: Acts as both efferent and afferent nuclear columns. Seen at 2 levels T 1 L 2 segments (pregang. Symp fib, thoracolumbar outflow) and S 2 -S 4 segments (pregang. Symp fib, for pelvic viscera). • Intermedio medial: Mostly internuncial neuronal column.

LAMINAR CONCEPT OF SPINAL GREY MATTER: • LAMINA I : post marginal nucleus • LAMINA II: Substantia gleatinosa of Rolando • LAMINA III & IV: Nucleus proprius. • LAMINA V & VI: Corresponds to base of dorsal column. • LAMINA VII: Between dorsal & ventral – intermedio medial and lateral • LAMINA VIII: Ventral horn (DMN, VMN) • LAMINA IX: Lateral group of nuclei. Supply the skeletal muscle. • LAMINA X: Surrounds the central canal. Contains decussating axons.

SENSORY RECEPTORS: Peripheral endings of • • afferent fibers which receive impulses. Exteroceptors: Respond to stimuli from external environment – pain, temp, touch and presure. Proprioceptors: Respond to stimuli from in deeper tissues – contraction of muscles, movements, position and pressure. Interoceptors: From viscera, gland, blood vessel, carotid sinus. Special sense receptors: Concerned with vision, hearing, smell and taste.

NUCLEI & FUNCTIONS

TRANSVERSE SECTION

ARRANGEMENTS OF FIBERS IN THE FUNICULI IN THE ANTERIOR FUNICULI: • Peripheral • Intermediate • Deep Medial reticulospinal tract Spino-olivary Anterior spino thalamic Olivo spinal Anterior cortico spinal Tectospinal Lat. vestibulo spinal

IN THE LATERAL FUNICULI: • Peripheral • Intermediate Lateral cortico spinal Post. Spino cerebellar Rubro spinal Ant. Spino cerebellar Lateral spino thalamic Lateral reticulo spinal

IN THE DORSAL FUNICULI: • Fasciculus gracilis • Fasciculus cuneatus. Fasciculus gracilis They convey the axons of Fasciculus cuneatus first order sensory neurons from the cells of the dorsal root ganglia.

Fibers of dorsal root and their termination: • All modalities of sensations (Exteroceptive, proprioceptive and interoceptive) reach the spinal cord by way of dorsal nerve roots. • Dorsal root presents near the intervertebral foramen a spinal ganglion which contains T shaped unipolar neurons with peripheral and central process. SPINAL GANGLION/DORSAL ROOT GANGLION CENTRAL PROCESS PERIPHERAL PROCESS

TRACTS: Connection of nerve fibers that connects two masses of grey matter within the CNS. DESCENDING TRACTS: 1. PYRAMIDAL: Lateral corticospinal tract Anterior cortico spinal tract 2. EXTRAPYRAMIDAL TRACT: Rubro spinal Medial & lateral reticulo spinal Olivospinal Vestibulospinal tectospinal

Pyramidal/ Lateral corticospinal • Formed by the axons of pyramidal cells in the motor area of the cerebral corterx + cells of premotor area also. Posterior limb of internal capsule midbrain pons medulla 80% cross to the opposite side (Pyramidal decussation) enter the lateral column of white matter & form the lateral corticospinal. • Most of the fibers terminate at the anterior horn cells INTERNAL CAPSULE MIDBRAIN PONS MEDULLA CROSSING

Pyramidal/ Anterior corticospinal • 20% of the fibers which donot cross enter anterior white column to form anterior corticospinal tract. • The fibers also cross at appropriate levels and reach grey matter of opposite half of spinal cord. • Found only in primates including man. INTERNAL CAPSULE MIDBRAIN PONS MEDULLA CROSSING

Functional significance of pyramidal tract: • Concerned with the skillful, voluntary movements of non-postural type affecting mainly the flexor muscles of distal part of upper and lower extremities. • Controls voluntary movements of opposite half of the body through anterior horn cells. • Facilitatory for flexors and inhibitory for extensors. • LESION: Above the level of decussation cause contralateral paralysis. Below the level- ipsilateral. UMN type: loss of power of voluntary movements. hypertonia, exaggerated tendon reflexes, superficial reflexes are lost.

Extrapyramidal tracts: Rubrospinal tract: From red nucleus in midbrain -ant horn cells in the spinal cord (X). Reticulospinal tracts: 1. Medial reticulospinal : reticular formation in pons, uncrossed terminate in spinal cord. 2. Lateral reticulospinal : reticular formation in the medulla oblongata, crossed & uncrossed, spinal cord. Olivospinal tract: From inferior olivary nucleus in medulla oblongata, uncrossed to anterior horn cells of spinal cord.

Vestibulospinal tract: From vestibular nucleus in the pontomedullary junction uncrossed to anterior horn cells of spinal cord. Tectospinal tract: From superior colliculus in the midbrain, cross (dorsal teg decussation)to anterior horn cells of spinal cord.

Descending tracts

Ascending tracts: • The 1 st order neurons start in the dorsal root ganglia which has pseudounipolar cells. • The peripheral process of these cells from the sensory fibers of peripheral nerves which carry various types of sensations from sensory end organs. • The central process of the neurons in the dorsal root ganglia enters the spinal cord through dorsal nerve root and terminate either by synapsing with cells in posterior grey column of spinal cord / at higher level in the medulla i. e. nucleus gracilis/cuneatus. • The 2 nd order neuron starts from here and end in thalamus or cerebellum. • 3 rd order starts from here and ends projects into sensory areas in the cerebral cortex.

Lateral spinothalamic tract: sensation of pain &temp • 1 st order neuron - dorsal root ganglia- synapse with neurons in the grey matter of lamina II & III. • 2 nd order neuron cross to opp side and ascend as lateral spinothalamic tract. • Lesion of lateral spino thalamic tract produces contralateral loss of pain and temp of the body below the lesion. Thalamus Dorsal root ganglia Crossing

Anterior spinothalamic tract: crude touch &pressure • 1 st order neuron - dorsal root ganglia- synapse with neurons in the grey matter of lamina III & IV. • 2 nd order neuron cross to opp side and ascend as anterior spinothalamic tract. ANTERIOR SPINOTHALAMIC CROSS DORSAL ROOT GANGLIA

Fasc. gracilis (Tract of Goll): conscious proprioception, & discriminatory touch(lower thoracic, lumbar, sac, cocc) • 1 st order neuron - dorsal root gangliado not synapse with neurons in the grey matter. Ascend in the posterior column of white matter, synapse with Nucleus neurons of nucleus gracilis • 2 nd order neuron , cross, ascend and relay in the thalamus. • 3 rd order neuron goes to the sensory area in the cerebral cortex.

Fasc. Cuneatus (Tract of Burdach): unconscious proprioception, & exteroceptive touch(upper thoracic, cervical segment) • 1 st order neuron - dorsal root ganglia- do not synapse with neurons in the grey matter. Ascend in the posterior column of white Nucleus matter, and synapse with neurons ofcuneatus nucleus cuneatus • 2 nd order neuron , cross and relay in the thalamus. Proprioceptive goes to the cerebellum • 3 rd order neuron goes to the sensory area in the cerebral cortex.

• Spino tectal. • Spino reticular. • Spino cerebellar- anterior and posterior.

Ascending tracts

LESIONS: ( AFFERENT SYSTEM) • Dorsal nerve roots: slip disc, extramedullary tumour, inflammation. Complete destruction – ipsilateral and segmental loss of all modalities of sensation. • Posterior white funiculus: Complete lesion – loss of position sense, vibratory sense, discriminative touch on the same side. Patient walks with legs apart and eyes fixed to the ground. • Spinothalamic tracts: involvement of lateral –loss of pain and temp on the opp side below the lesion. • Syringomyelia: Cavitation of the central canal affecting the cervical enlargement of the cordbilateral and segmental loss of pain and temperature.

LESIONS: ( EFFERENT SYSTEM) • LMN lesion: results in hypoactive muscle, and reduction in muscle tone ---no stretch reflex. Muscle fasciculation, twitching or contractions of groups of muscle fibers. Muscle undergoes wasting or atrophy. (FLACCID PARALYSIS) • UMN lesion: Have a net overall inhibitory effect on muscle stretch reflex. ----Paralysis of skeletal muscle with muscle stretch or deep tendon reflex that are hypertonic/ hyperactive. (SPASTIC PARALYSIS). Disuse atrophy of muscles