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Spinal cord motor & sensory Spinal nerves -31 pairs 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal -C1 & C2 exception to rule below they are not mixed, one is principally motor the other sensory *Dorsal roots sensory; cell bodies live in dorsal root ganglia *Ventral roots motor; cell bodies live in gray matter of ventral horn (cell bodies actually in spinal cord itself) Spinal vasculature -arteries arise from 2 sources vertebral arteries & radicular arteries -vertebral arteries *give off branches in upper cervical region that will give rise to 3 spinal arteries 1 anterior & 2 posterior *these arteries course the entire length of the spinal cord -radicular arteries *arise from regional arteries, such as the posterior intercostal & lumbar branches of the descending aorta *feed into the longitudinal arteries at various points along the spinal cord -all these arteries do not supply enough blood to keep cord alive if you accidently clip a small artery, you can kill off a large portion of spinal cord *takes a ton of blood to keep it alive! -venous drainage numerous veins – longitudinal veins anterior & posterior to cord *connect to veins paralleling the dorsal & ventral roots *drain into internal vertebral plexus found in epidural fat Spinal sensory pathways -5 separate modalities of sensation proprioception & touch (mechanical senses) and temperature, pain, itch (“protective” senses) *different pathways in the spinal cord -different sensory modalities end the cord in different areas all still enter via dorsal root but at different spots *this is b/c spinal cord is laminar & it has a somatotopic organization clinically, this makes it easier to figure out where lesions are located on the spinal cord; but takes very little damage to take out a large region of sensory/motor -sensory homunculus of the parietal cortex (postcentral gyrus) Mechanical senses -touch mechanoreceptors; Pacinian corpuscles; myelinated A-beta fibers -proprioception mechanoreceptors; myelinated A-alpha & -beta fibers *joints help you realize where you are/where muscles are -dorsal column – medial lemniscus pathway (back of spinal column) -primary neuron in DRG receiving information -first synapse in brain stem dorsal column nucleus -receptors in peripheral tissue input to soma in DRG; enter cord via dorsal horn; ascend in dorsal columns; synapse in nuclei of dorsal column -secondary neurons “decussate” or cross midline to opposite side of CNS Protective senses -temperature thermoreceptors; myelinated A-delta & unmyelinated C fibers -pain nociceptors; myelinated A-delta fibers (fast) & unmyelinated C fibers (slow) -itch histamine; unmyelinated C fibers -anterolateral pathway -primary neuron in DRG -first synapse in dorsal horn of spinal cord at level it enters -receptors in peripheral tissue (bare nerve endings) input to soma in DRG; enter cord via dorsal horn; SYNAPSE at or near level of entry to dorsal horn; secondary neurons in dorsal horn -“decussate” via ventral commissure in spinal cord *MOST NEURONS DECUSSATE AFTER FIRST SYNPASE NO MATTER WHERE LOCATED! -ascend in anterolateral columns Sensory lesions -cut spinal cord on L, L4 going to lose protective sensation on R lower side; lose L mechanical senses from that point down -Brown-Sequard Syndrome Spinal motor pathways -originate from 2 regions of CNS cortical (frontal lobe, premotor & motor cortex, precentral gyrus) & brain stem motor nuclei *cortical (voluntary movements mainly) lateral corticospinal tract; ventral corticospinaltract; corticobulbar tract *brain stem (nonvoluntary movements & coordinated movements mainly) rubrospinal tract; reticulospinal tract; tectospinal tract; vestibulospinal tract (orienting self in space) MOTOR INPUTS -Brain stem nuclei - Mainly “automatic” stuff -Primary motor cortex - Mainly voluntary movements -Basal Ganglia and Cerebellum - Fine tuning, automatic actions *No direct input to spinal motor neurons -Secondary motor neurons and interneurons - Directly affect muscles; axons travel to PNS as the motor portion of spinal nerves *interneurons – linked sensory & motor neurons gives you reflexes -motor portion of spinal cord is somatotopicaly organized (precentral gyrus) -motor homunculus Motor tracts -two separate pathways *lateral columns (black circle); usu. contralateral; decussate in brainstem *ventral columns (red circle); usu. ipsilateral; decussate in spinal cord CORTICOSPINAL TRACTS -lateral *frontal cortex to ventral horn neurons *decussates in pyramids – junction of medulla & cord *primary motor pathway for most muscles *contralateral in cord -ventral *primary motor cortex to ventral horn of cervical & upper thoracic region only! *ipsilateral in cord until it reaches terminal level – many fibers decussate in ventral commissure – bilateral motor function -corticobulbar *terminated primarily in motor nuclei in pons & medulla *principally associated with cranial nerve motor function -rubrospinal red nucleus to ventral horn of cervical spine ONLY; decussates in midbrain -reticulospinal *from reticular regions of pons & medulla to ventral horn *descend in ipsilateral cord; but exert bilateral motor control *branches or interneurons at terminal level *mainly function to control “automatic functions” such as walking or posture -tectospinal *from superior colliculus to ventral horn of cervical region *decussates at level of colliculus *only functions in upper limb/neck *tectum is associated with visual movements also- coordination of muscle with visual input? Changes in spinal cord -vestibulospinal *coordinate head & eye movements *two separate nuclei lateral – balance (ipsilateral path, but interneurons decussate); medial – head/neck position (bilateral path) -spinal cord varies in diameter depending on what region you observe *cervical & lumbar portions are larger, & have much larger ventral horns d/t presence of motor neurons for limbs Motor nerve damage -damage to lateral tracts tends to lead to loss of function from level of damage down-contralateral (b/c decussate at level enter spinal cord) *leads to initial flaccid paralysis *later patients will develop spastic paralysis & inappropriate reflexes -damage to ventral tracts does not usu. present as severely, have some loss of function from level of damage down- ipsilateral AND contralateral *why does this not have as much effect as lateral tract damage? b/c some decussate & some do not on either side!