Spinal Cord Internal Structure Cervical Lumber Thoracic Structure

Spinal Cord Internal Structure Cervical

Lumber

Thoracic

Structure of White Mater The tracts are divided into: 1. Short Tracts =Associative tracts: • Containing short ascending & descending fibers which coordinate the function of the different regions of spinal cord. - They begins and end in the spinal cord. They are found close to the gray matter. 2. Long Tracts: • Ascending tracts. • Descending tracts. The white mater contains nerve fibers =Tract definite origin, termination& function. 1. Ascending tracts of the SC: Carrying sensory impulses from the SC to the brain: e. g. lateral spinothalamic tract. 2. Descending tracts of the SC: Carrying motor impulses from the brain to the SC: e. g. pyramidal tract “corticospinal tract, corticobulber

Short Tracts

long ascending Tracts • Finally to sub- cortical level (4) 1 - Posterior &Anterior spinocerebellar Ts. 2 -Spinoreticular 3 - Spino- olivary T. 4 - Spinotectal T. • Finally to Cerebral cortex: sensory area(4) 1 - Gracile T. 2 - Cuneate T. 3 - Lateral & 4 - ventral spinothalamic Ts.

Ventral spinothalamic T. First order neuron. Impulses from touch receptors ----dorsal root ganglia--sensory cells in the posterior horn (Main sensory nucleus) Second order neuron. Arise from the sensory cells in the posterior horn(main sensory N), crosses the midline in front of the central canal and ascend in the opposite side of the spinal cord as the ventral spinothalamic tract to reach the posteroventral nucleus of the thalamus (PVN). Third order neuron. Arises from the PVN of the thalamus ascend in the posterior limb of the internal capsule to reach the sensory area of the cerebral cortex

Lateral spinothalamic tract First order neuron. Impulses from temperature receptors –dorsal root ganglia--- Lissauer, s tract on the same side to end on the cells of substentia gelatenosa of rolandi. Second order neuron. It arises from the cells of substentia gelatinosa of rolandi, crosses the midline in front of the central canal and ascends in the opposite side of the spinal cord as Lateral Spinothalamic tract to reach the PVN of the thalamus. Third order neuron. Neuron arises from PVN of the thalamus and ascends in the posterior limb of the internal capsule to reach the sensory area of the cerebral cortex.

Gracilis & Cuneatus tract • Posterior White Column-Medial Lemniscal Modality: Discriminative Touch Sensation (include Vibration) and Conscious Proprioception (Position Sensation) • Receptor: Most receptors except free nerve endings • Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion) Posterior Root - Posterior White Column • 2 nd Neuron: Dorsal Column Nuclei (Nucleus Gracilis & Cuneatus) Medulla oblongata • Internal Arcuate Fiber - Lemniscal Decussation Medial Lemniscus • 3 rd Neuron: Thalamus Internal Capsule ----- Corona Radiata Termination: Primary Somesthetic Area

Spinocerebellar Tract Posterior Spinocerebellar Tract posterior spinocerebellar fibers receive muscle joint information from the muscle spindles, tendon organs and joint receptors of the trunk and lower limbs. • • 1 st order : Posterior (dorsal) root ganglion 2 nd order : neurons nucleus dorsalis (Clarke’s N). • posterior spinocerebellar tract -----inferior cerebellar peduncle and terminates in the cerebellar cortex Anterior Spinocerebellar Tract The anterior spinocerebellar tract conveys muscle joint information from upper part & upper limb. • 1 st order : posterior root ganglion • 2 nd order: neurons in the nucleus dorsalis anterior spinocerebellar tract in the lateral white column of the same side enter the cerebellum through the superior cerebellar peduncle and terminate in the cerebellar cortex.

Spino-olivary Tract Spino-tectal Tract The spino-olivary tract conveys This pathway provides afferent information to the cerebellum from information for spinovisual reflexes and cutaneous and proprioceptive organs. brings about movements of the eyes and v The axons enter the spinal cord from the head toward the source of the stimulation. posterior root ganglion Ø The axons enter the spinal cord from the posterior root ganglion v unknown second-order neurons in the posterior gray column Ø unknown second-order neurons • The axons from the second-order. neurons cross the midline and ascend as Ø The axons of the second-order neurons the spino-olivary tract in the white cross the median plane and ascend as matter at the junction of the anterior the spino-tectal tract in the and lateral columns. anterolateral white column lying v third-order neurons in the inferior close to the lateral olivary nuclei in the medulla oblongata spinothalamic tract. • The axons of the third-order neurons cross the midline and enter the cerebellum through the inferior cerebellar peduncle. Ø terminate in the superior of the midbrain colliculus

Spino-reticular tract Spinoreticular tract provides an afferent pathway for the reticular formation, which plays an important role in influencing levels of consciousness. • The axons enter the spinal cord from the posterior root ganglion • unknown second-order neurons in the gray matter • The axons from these second order neurons ascend the spinal cord as the spinoreticular tract in the lateral white column mixed with the lateral spinothalamic tract. • Most of the fibers are uncrossed and terminate by synapsing with neurons of the reticular formation in the medulla oblongata, pons, and midbrain. The spinoreticular tract provides an afferent pathway for the reticular formation , which plays an important role in influencing levels of consciousness.

Long tracts: II- Descending (Motor) Ts. • Pyramidal. Ts. • Corticospinal • Extra-Pyramidal Ts. 3 - Rubrospinal T. 4 - Lateral tecto, reticulo, 1 - Lateral corticospinal T. vestibulo spinal Ts. 2 - Ventral corticospinal T. 5 - Ventral tecto, reticulo, vestibulo spinal Ts. Corticobulbar T 6. Olivospinal

Corticobulbar tract • • • The motor fibers descend from the cortex to the motor cranial nerve nuclei. Origin: Lower parts of areas 4 and 6 Course: The fibers travels in corona radiata – the genu of the internal capsule on reaching the brain stem the fibers cross to the opposite side to terminate at motor nuclei of the cranial nerves. Some fibers not cross to the opposite side. The motor nuclei of the cranial nerves receive fibers from both sides (direct and indirect) with some exceptions as the lower face division of the facial nucleus which receives only unilateral innervation from the opposite side. Thus in upper motor neuron bulbar lesion only the lower face is affected.

Extra-Pyramidal Ts. It include all descending tracts other than the pyramidal tract, they descend to AHC after passing through many relay steps. • Origin: • Motor areas of the cortex in front and behined area 4. • Pathway. • The fibers relay in the basal ganglia, subthalamus, red nucleus, superior and inferior colliculi, reticular formation and Vestibular nuclei, and then the impulses are carried to the spinal cord along the following tracts. 1 -Rubrospinal tract: from red nucleus in midbrain. 2 -Tectospinal tracts: from tectum of midbrain, they are v Lateral Tectospinal tracts: from superior colliculus for visual reflexes. v Ventral Tectospinal tract: from inferior colliculus for auditory reflexes. 3 -Reticulospinal tracts: from reticular formation to give lateral and ventral reticulospinal tracts. 4 - Vestibulospinal tracts: Lateral and ventral vestibulospinal tracts from Vestibular nucleus.