Unit27spinalcord.ppt

The central nervous system The spinal cordThe location and external features:1.Location:In vertebral canal,it extends from foramen magnum to lower border of first lumbar vertebra(adult).2.External features:1.)cervical and lumbosacral enlargements:associate with brachial plexus and lumbosacral plexus.2.)conus medullaris 3.)filum terminale 4.)anterior median fissure,posterior median sulcus,posteriolateral and anterolateral sulci.5.)cauda equina 6.)most segments of spinal cord are located above similarly numbered vertebral body The internal structure of spinal cordGrey matter:posterior,anterior horn.grey commissure,lateral horn(T1L3)the central canalWhite matter:posterior,lateral,anterior funiculi,anterior white commissure The main nuclei of spinal cord1.Three main kinds of neuron in anterior horn:1.)-motor neuron:axon reaches to skeletal muscle.2.)-motor neuron:axon reaches to skeletal muscle to play role in reflex regulation of muscle tonus.3.)local circuit neurons 2.The anterior horn cells are organized into medial and lateral groups.The nuclei in the intermediate zone1.The intermediolateral nucleus:Its axons form the sympathetic preganglionic fibers.2.The sacral parasympathetic nucleus(S24):Its axons form the pelvic visceral nerve.3.The intermediomedial nucleus:It receives branches of posterior root fibers and gives rise to fibers that constitute spinocerebellar tract.The nuclei in the posterior horn1.The nucleus posteromarginalis:Its axons form intersegmental pathways.2.The substantia gelatinosa:They may be excited by the nociceptive stimuli.3.The nucleus proprius:Its axons cross then contribute to the spinothalamic tracts.4.The nucleus thoracicus:Its axons contribute fibers to the posterior spinocerebellar tract of ipsilateral side.The laminas Based on neuronal size,shape,cytological feature,ten laminas have been distinguished:Lamina I:To respond to noxious stimuli and send axons to the contralateral psinothalamic tractLamina II:To respond to noxious stimuli.Lamina III and IV:Their main input is from fibers that convey position and light touch sense.Lamina V:To respond to both noxious and visceral afferent stimuli.Lamina VI:To respond to mechanical signals from joints and skin.Lamina VII:A large area that contains the nucleus thoracicus,the intermediolateral nucleus etcLamina VIII and IX:To represent motor neuron groups the medial and lateral portions of the ventral horn.Lamina X:around the central canal.The spinal white matterThe long ascending tracts(carry sensory impulses)1.Fasciculus gracilis and fasciculus cuneatus:1.)They are formed by fibers of posterior root entering ipsilateral posterior funiculus of spinal cord.2.)Fasciculus gracilis is from sacral,lumbar,lower eight thoracic segnents of spinal cord.3.)Fasciculus cuneatus is from upper four thoracic,cervical segments.4.)They terminate upon nuclei gracilis and cuneatus.5.)They conduct discriminating tactile and kinesthetic sense.2.The posterior spinocerebellar tract:1.)It arises from ipsilateral nucleus thoracicus.2.)It conveys subconscious proprioceptive impulses to the cerebellum.3.The anterior spinocerebellar tract:1.)It arises from intermediate zone of spinal cord,2.)Its function is same as that of the posterior spinocerebellar tract.4.The spinothalamic tract:1.)It includes the lateral and anterior spinothalamic tracts.2.)The nucleus proprius gives rise to axons and forms opposite spinothalamic tracts.3.)A small number of uncrossed fibers may ascend in ipsilateral anterior spinothalamic tract.4.)They transmit impulses associated with pain and thermal sense,rough touch sense.The long descending tracts1.The corticospinal tract:1.)It arises from cerebral cortex then divided into two tracts.2.)Lateral corticospinal tract decussates in medulla oblongata,then terminates in anterior horn.3.)Anterior corticospinal tract is ipsilateral descending tract.In spinal cord,most fibers decussate and then terminate jn the anterior horn.2.The tectospinal tract:1.)Fibers arise from neurons in superior colliculus.2.)It innervates anterior horn cells indirectly mediate reflex postural movements.3.The rubrospinal tract:1.)Fibers arise from red nucleus of the midbrain.2.)It increases the flexor muscle tone.4.The vestibulospinal tract:1.)Fibers arise from lateral vestibular nucleus of same side.2.)It increases the extensor muscles tone and inhibit motor neuron of flexors