Spinal Cord Part 2 White Matter PDF

Spinal cord Part II White matter  White Matter Columns Contains columns of axons Ascending tracts (afferent) Carry sensory information to the brain Descending tracts (efferent) Carry motor signals from brain to body Funiculus means column (b...

Spinal cord Part II White matter  White Matter Columns Contains columns of axons Ascending tracts (afferent) Carry sensory information to the brain Descending tracts (efferent) Carry motor signals from brain to body Funiculus means column (bundles of nerve fibers Look at slide 22 to see matching column names. Fasciculus small bundles of nerve fibers (axons) Tract Bundles of upper motor neuron axons that travel together in the white matter of the brainstem and spinal cord. Learning objective: Describe the location and pathways of the major sensory and motor tracts of the spinal cord.  Spinal Cord Tracts For this unit know the Descending Tracts Ascending Tracts Descending Tracts (Motor) (Somatosensory) Lateral Pathways Anterolateral Corticospinal Spinothalamic Dorsal Column Medial Rubrospinal Lemniscus Ventromedial Pathways Fasciculus Cuneatus Reticulospinal (Medullary and Pontine) Fascicilus Gracilis Vestibulospinal Spinocerebellar Tectospinal We will come back to ascending when we do the somatosensory system later in the course Organization of Spinal Cord Cross Section Dorsal column Lateral Motor system  Ascending Pathways Compare and contrast Dorsal Column and the Anterolateral pathways Similarity- innovate contralateral thalami nuclei and somatosensory cerebral cortex Different pathways Synapsing structures Crossing over Pathway locations Look at Location of pathway at the various levels the pathways go through. Where the pathways cross over. Know the location of neurons in the pathways often referred to as 1st order, 2nd order and 3 order neurons. Again we will come back to the ascending pathways  Dorsal Column Medial Lemniscus Function: Proprioception and Discriminative Touch Dorsal column in the Spinal cord as two parts Fasciculus gracilis (medial) lower extremity Fasciculus cuneatus (lateral) upper extremity (go back to slide 69) Dorsal Column nuclei in medulla have same names Pathway from medulla changes name to medial lemniscus Key concept of information organization: Somatotopic organization  Anterolateral Spinothalamic Function: pain, temperature and crude touch Sensory neurons enter spinal cord and synapse on interneurons in the dorsal horn Immediate decussation of axons in spinal cord at level Fibers project upward directly to thalamus  Spinocerebellar Tract Conveys unconscious proprioceptive information See Cerebellar lectures! Descending (motor) pathways Contain upper motor neurons Descending Pathways Descending Pathways Lateral System Fine, precise motor skills in distal extremities Lateral Corticospinal Tract (Upper and Lower extremities) Rubrospinal Tract (Upper extremities) Compare and contrast the two motor systems! Medial System Trunk movement and proximal muscles for holding and postures Reticulospinal Tracts Vestibulospinal Tracts Tectospinal Tract Lateral system tracts Corticospinal Tract 90% of Fibers form Lateral Corticospinal Tract Part of Lateral system 10% of Fibers form the Anterior/Medial Corticospinal Tract Part of medial system Lateral Corticospinal Tract Fine Control of distal extremities and coarse regulation of proximal flexors Allows fractionation of movement Enables us to tie knots, press individual keys of a piano, pick up small objects. Longest, largest tract in the spinal cord Lateral Corticospinal Tract Pathway Pathway: Arise Primary Motor, Premotor, and Supplementary motor cortex Course through internal capsule Through Basis Pedunculi of Midbrain, Basis Pontis of Pons, and Pyramid of medulla DECUSSATES at pyramidal decussation of cervicomedullary junction Courses through lateral white matter of spinal cord and synapses in Lateral intermediate zone and motor neurons in the lateral region of Lamina IX in ventral horn Medial (Anterior) Corticospinal Tract Originates in Motor Cortex (frontal lobe) and somatosensory area of parietal lobe Pathway: Motor Cortex Internal Capsule Base of cerebral peduncle (Midbrain) 10 % of total corticospinal Tract Part of medial activation system) Pons Medulla Does not Cross in the pyramids Anterior (ventral) column of Spinal Cord Synapse on medial intermediate zone and medial motor neurons in lamina IX Medial Corticospinal Tract Medial (Anterior) Corticospinal Track Anterior (Medial) Corticospinal Tract - Function Axons of Anterior (Medial) Corticospinal Tract synapse cervical and thoracic regions only. Conveys info to Lower motor neurons that control neck, shoulder, and trunk muscles. Part of the Medial Activation system Rubrospinal Tract Originates red nucleus of midbrain Rubro Latin for Red Axons decussate in the pons and join with axons of corticospinal tract in lateral column of spinal cord Part of lateral activation system Rubrospinal Tract  Lateral Corticospinal/Rubrospinal Impairments Poor Fractionated Movements of arms and hands – use all fingers at once (lateral Corticospinal also distal Lower extremity) Voluntary movements slower – less accurate Medial Tracts Ventromedial Pathways Reticulospinal (Medullary and Pontine) Vestibulospinal Tectospinal Medial Corticospinal Tract (discussed previously)  Advanced knowledge Reticular formation (System)- Reticulospinal Tract A network of neurons(nuclei) in brainstem with multiple functions including arousal and pain modulation Arise form reticular formation of brain stem Pontine Tract (Ipsilateral) Facilitates Extensor Motor Neurons Enhances antigravity reflexes of spinal cord Helps maintain standing posture Lateral (Medullary) Tract (Bilateral) Facilitates Flexor Motor Neurons Liberates antigravity muscles from reflex control Reticulospinal Tract Green  Advanced Knowledge Vestibular Nuclei integrate Sensory Vestibulospinal Tract information on head position and movement from CN VIII Responds to stimuli from the vestibular apparatus (in the inner ear) Medial Vestibulospinal Tract Controls neck and upper back muscles for positioning Keeps head (eyes) stable when the head is moving Lateral Vestibulospinal Tract Facilitates extensors and inhibits flexors for balance Damage to these tracts leads to ataxia and balance problems Vestibulospinal Tract  Advance knowledge- Tectum process visual and auditory Tectospinal Tract information and contributes to automatic (reflective) head movements Originates Midbrain – superior colliculus – which receives direct input from the retina and projections from visual cortex Directs head movements toward novel visual and auditory stimuli Course: Superior Colliculus Crosses at tectobulbospinal junction Travels with vestibulospinal tract ending cervical region Tectospinal Tracts Somatotopic organization of Tracts Vascular Supply to Spinal Cord Longitudinal vascular supply 1 anterior spinal artery and 2 posterior arteries spinal artery plexus Segmental vascular supply spinal artery plexus and anterior and posterior segmental medullary arteries. Clinical application Spinal cord injury Trauma Loss of blood supply Will cause spinal cord injuries. There are several stereotypic spinal cord injury syndromes Objective is to match injury to the clinical signs and symptoms  Central Cord Syndrome What are the impairments here? Symptoms are different depending on size Consider: If white mater is involved, What pathways? If pathway is only partly involved, consider somatotopic organization All deficits are below the level of injury If grey matter involved symptoms Usually caused by a syrinx of the spinal cord are just at the level of injury An opening of the central canal. See Blum. Fig 7.5 for MRI Anterior Cord Syndrome What are the impairments here? Usually caused by occlusion of anterior spinal artery Brown-Sequard syndrome Usually caused by a penetrating injury Posterior Cord Syndrome Can be caused by penetrating or posterior spinal artery occlusion.  If a tract is covered (lesioned) then everything below the injury level is involved Figure 7.10 Blumenfeld. The keys to understanding is knowing where tracts cross over