ALL ABOUT THE SPINAL CHORDFunctions of Spinal CordSlide 3Motor NeuronsSpinal Cord and Spinal NervesOverview of Spinal CordFunctions of the Spinal CordAnatomy of the Spinal CordGross Anatomy of Lower Spinal CordMeninges of the Spinal CordMeninges of Vertebra and Spinal CordCross-Sectional Anatomy of the Spinal CordGray Matter in the Spinal CordWhite Matter in the Spinal CordSpinal TractsOrganization of Somatosensory SystemDorsal Column Ascending PathwaySpinothalamic PathwaySpinoreticular TractSpinocerebellar PathwayCorticospinal TractDescending Motor TractsPoliomyelitis and ALSAnatomy of a NerveAnatomy of Ganglia in the PNSSpinal Nerve Roots and PlexusesThe Spinal NervesBranches of a Spinal NerveRami of Spinal NervesShinglesNerve PlexusesThe Cervical PlexusThe Brachial PlexusThe Lumbar PlexusThe Sacral and Coccygeal PlexusesSome FactsCutaneous Innervation and DermatomesSlide 38ALL ABOUT THE SPINAL CHORD13-1Functions of Spinal Cord•Final common pathway for the somatomotor system•Conveys somatosensory information from the body•Autonomic neurons•Reflexes•Central pattern generators for rhythmic movementsSensory vs motor rootsVentral: somatic motor + visceral motorMotor Neurons•Alpha and gamma motor neurons•aka ventral horn cells, anterior horn cells•Very elaborate dendritic tree•Neurotransmitter=Ach•Alpha: extrafusal fibers•Gamma: intrafusal fibers13-5Spinal Cord and Spinal Nerves•Spinal cord•Spinal nerves13-6Overview of Spinal Cord•Information highway between brain and body•Extends through vertebral canal from foramen magnum to L1•Each pair of spinal nerves receives sensory information and issues motor signals to muscles and glands•Spinal cord is a component of the Central Nervous System while the spinal nerves are part of the Peripheral Nervous System13-7Functions of the Spinal Cord•Conduction–bundles of fibers passing information up and down spinal cord•Locomotion–repetitive, coordinated actions of several muscle groups–central pattern generators are pools of neurons providing control of flexors and extensors (walking)•Reflexes–involuntary, stereotyped responses to stimuli (remove hand from hot stove)–involves brain, spinal cord and peripheral nerves13-8Anatomy of the Spinal Cord•Cylinder of nerve tissue within the vertebral canal (thick as a finger)–vertebral column grows faster so in an adult the spinal cord only extends to L1•31 pairs of spinal nerves arise from cervical, thoracic, lumbar and sacral regions of the cord–each cord segment gives rise to a pair of spinal nerves•Cervical and lumbar enlargements•Medullary cone (conus medullaris) = tapered tip of cord•Cauda equinae is L2 to S5 nerve roots resemble horse’s tail13-9Gross Anatomy of Lower Spinal Cord13-10Meninges of the Spinal Cord•3 Fibrous layers enclosing spinal cord•Dura mater–tough collagenous membrane surrounded by epidural space filled with fat and blood vessels•epidural anesthesia utilized during childbirth•Arachnoid mater–layer of simple squamous epithelium lining dura mater and loose mesh of fibers filled with CSF(creates subarachnoid space)•Pia mater–delicate membrane adherent to spinal cord–filium terminale and denticulate ligaments anchor the cord13-11Meninges of Vertebra and Spinal Cord13-12Cross-Sectional Anatomy of the Spinal Cord•Central area of gray matter shaped like a butterfly and surrounded by white matter in 3 columns•Gray matter = neuron cell bodies with little myelin•White matter = myelinated axons13-13Gray Matter in the Spinal Cord•Pair of dorsal or posterior horns–dorsal root of spinal nerve is totally sensory fibers•Pair of ventral or anterior horns–ventral root of spinal nerve is totally motor fibers•Connected by gray commissure punctured by a central canal continuous above with 4th ventricle13-14White Matter in the Spinal Cord•White column = bundles of myelinated axons that carry signals up and down to and from brainstem•3 pairs of columns or funiculi–dorsal, lateral, and anterior columns•Each column is filled with named tracts or fasciculi (fibers with a similar origin, destination and function)13-15Spinal Tracts•Ascending and descending tract head up or down while decussation means that the fibers cross sides•Contralateral means origin and destination are on opposite sides while ipsilateral means on same sideOrganization of Somatosensory System•Touch•Fine, discriminitive touch•Presssure and vibration sense•Conscious proprioception•Unconscious proprioception•Pain•Temperaturehttp://thalamus.wustl.edu/course/body.html13-17•Deep touch, visceral pain, vibration, and proprioception•Fasciculus gracilis and cuneatus carry signals from arm and leg •Decussation of 2nd order neuron in medulla•3rd order neuron in thalamus carries signal to cerebral cortexDorsal Column Ascending Pathway13-18Spinothalamic Pathway•Pain, pressure, temperature, light touch, tickle and itch•Decussation of the second order neuron occurs in spinal cord•Third order neurons arise in thalamus and continue to cerebral cortex13-19Spinoreticular Tract•Pain signals from tissue injury•Decussate in spinal cord and ascend with spinothalamic fibers•End in reticular formation (medulla and pons)•3rd and 4th order neurons continue to thalamus and cerebral cortex13-20Spinocerebellar Pathway•Proprioceptive signals from limbs and trunk travel up to the cerebellum•Second order nerves ascend in ipsilateral lateral column13-21•Precise, coordinated limb movements•Two neuron pathway–upper motor neuron in cerebral cortex–lower motor neuron in spinal cord•Decussation in medulla Corticospinal Tract13-22Descending Motor Tracts•Tectospinal tract (tectum of midbrain)–reflex turning of head in response to sights and sounds•Reticulospinal tract (reticular formation)–controls limb movements important to maintain posture and balance•Vestibulospinal tract (brainstem nuclei)–postural muscle activity in response to inner ear signals13-23Poliomyelitis and ALS•Diseases causing destruction of motor neurons and skeletal muscle atrophy•Poliomyelitis caused by poliovirus spread by fecally contaminated water–weakness progresses to paralysis and respiratory arrest•Amyotrophic lateral sclerosis–sclerosis of spinal cord due to astrocyte failure to reabsorb glutamate neurotransmitter–paralysis and muscle atrophy13-24Anatomy of a Nerve•A nerve is a bundle of nerve fibers