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Spinal cord and Pathways Roosindu Peris Year 5Vertebrae in all its glory!Vertebrae Facts • Made up of 24 separate vertebrae, sacrum and coccyx • 7 C, 12 T, 5 L, 5 S, 3 or 4Coccyx • It’s 3 main functions include • Protection • Attachment • Articulate articulatePicking up a typical vertebrae - !!!Picking up a typical vertebrae - !!Cervical VertebraeC1 and C2 aren’t typicalAtlas (C1) and Axis (C2)Atlas (C1) and Axis (C2) OrientationC7 – another odd one! • Doesn’t have a bifid spinous process • Spinous process tends to be longerThoracic VertebraeThey don’t look the same - just similar!Lumbar VertebraeSacrum”Typical” Body Vertebral Neural arch Spinous Upper Lower Transverse Foramina process articular articular process facets facets Cervical Small, Curved Large, Largely Short and Up and Back Down and Arise from Traingular Lamina, Bifid forward side of body, Pedicles are containing a short hole known as transverse foramen Thoracic Increase in Circular / Downwards Backwards, Forwards, Sideways, size as you go (almost vertical vertical articulates down, overlapping with ribs. NO articulates the one FORAMINA with a pair of below). NOT ribs (demi BIFID. facet) Lumbar Kidney shape, Traingle / Shorter than Inward Outward Small very large thoracic, doesn’t extend past the body, broad and points backwardsLigaments of the SpineTypes of Joints • Vertebral body jointscartilaginous hyaline joints • Posterior joints– zygapophyseal joints surrounded by a capsular ligament covered with hyaline.Synovial joint • Costovertebral joints • Craniovertebral joints • Sacro-iliac joints – synovial jointFunction of the spinal cord • Receives afferent fibre from sensory receptors • Provides a pathway for descending motor nerves • Controls movements of trunk and limbs • Provides autonomic innervation to internal organs (viscera)Gross structure of spinal cord • Cord terminates at the L1/L2 IV disc level, forming the conus medullaris • The cord consists of two enlargements which are found at thecervical (C4-T1) and lumbar (L1-L2) parts of the cord • These give rise to the brachial and lumbosacral plexus respectivelySpinal nerves • There are 31 pairs of spinal nerves • Fascicle >> Root >> Nerve • Dorsal nerve roots have primary afferent neurones (sensory nerves) • Ventral roots have efferent fibres (motor neurones) • C1 –C7 exit at the level of their corresponding vertebrae, except C8 which exits below the C7 vertebrae • Below this, the spinal nerve exit at increasingly lower levels to their corresponding vertebrae due to lengthening of vertebrae even after the spinal cord has stopped growingSpinal meningesInternal structure of spinal cordVariations…A step further – Grey Matter of SC As an alternative to spinal cord nuclei, Bror Rexed(1950s) identified layers, or laminae, within the spinal cord where cells were grouped according to their structure and function, rather than solely on locationSubstantia Gelatinosa – the bit of GM you should know • Substantia Gelatinosa (RexedLamiae II) is where nociceptive fibers terminate • These neurons release glutamic acid and substance P • These then interact with multiple sites at the same level of the spinal cord before allowing pain sensations to be modulated, and to relay info up the ascending tracts • Most ascending tract cell bodies are found at the nucleus proprius (lamiae III) – Gate theory of painAscending Tracts – White Matter of SC • These transmit sensory information to the CNS • They can be classified into conscious and unconscious tracts depending on what sort of information they carry • Conscious tracts = dorsal columnar medial leminiscal (dorsal columns) + Anterolateral system • Unconscious tracts = spino-cerebellar tracts • First order neurons – begin at the receptor and end at the spinal cord/midbrain (cell body in dorsal root ganglion) • Second order neurons – begin at the spinal cord/midbrain and end at the thalamus region (cell body in medulla) • Third order neurons – thalamus to brain (cell body in thalamus)Dorsal column-medial leminiscal pathway • Relay info regardingproprioception, fine touchand vibration Key words: 1. Internal arcuate fibers 2. Fasciculus cuneatus 3. Fasciculus Gracillis 4. Thalamus 5. Medial leminiscus 6. Post central gyrus of parietal 7. DecussateDCML bit you need to knowFrom your lecture on the brainstem…Anterolateral Spinothalamic pathway • Contain two tracts; theanterior and lateral spinothalamic tracts • Anterior relays information on crude touchand pressure • Lateral relays pain and temperature Key Words: 1. Decussate 2. Substantia Gelatinosa 3. Dorsal horn of SC 4. Lateral Spinothalamic 5. Anterior SpinothalamicWhat we learnt so far (hopefully)…Spinocerebellar Tracts • The “unconscious” one • Relays information regarproprioceptionSpinocerebellar Tracts • Carry information from receptors found in muscles and tendons • Helps control posture and co-ordinate movement • They only contain two neurons (primary and secondary, no tertiary) • Ventral and dorsal spinocerebellar tracts – carry information from lower limbs • Dorsal spinocerebellar tracts: T1- L12 spinocerebellar originates from Laminae VII, aka Clarkes segment • Ventral spinocerebellar tracts : nerves from lumbosacral levels • Rostral spinocerebellar and cuneospinocerebellar carry info from upper limbs • Spinocerebellar tracts terminate in the neocerebellum zone of the cerebellumSpinocerebellar TractsDescending Tracts – White Matter SC • Corticospinal tracts • Rubrospinal • Tectospinal • Reticulospinal • VestibulospinalCorticospinal TractsCorticospinal Tracts • Controls conscious movements of the limbs • Pathway : Precentral gyrus (primary motor cortex) >>> corona radiata and pyramids (medulla) >>> lateral and ventral corticospinal tracts >>> musclehe • Lateral corticospinal tracts contain fibers from the contraletralside of the brain • Ventral corticospinal tracts contain fibers from the ipsilateral side of he brain HOWEVER lower down when the VENTRAL fibers exit, they decussate to the other side • So overall fibers o the corticospinal tract innervate the contralateral side of the body • Large Betz Cells found in the cortex give rise to the largest diameter corticospinal neuronsCorticospinal Tracts • Large Betz Cells found in the cortex give rise to the largest diameter corticospinal neuronsOther Descending Tracts • Rubrospinal – originates from red nucleus, associated with controlling tone of flexor muscles • Tectospinal tractarise from superior colliculus, mediates reflex movements associated with visual stimuli • Vestibulospinal trac–sarise from vestibular nuclei, coordinating head and eye movement + controlling tone of extensor muscles • Reticulospinal tracts– modulate voluntary movement, reflexes and muscle tone + control of breathing + modulate circulatory systemSpinal VasculatureStretch reflex • Muscle spindles are stretched • These forces are detected by Ia afferent fibers • Impulses travel in a- motorneurones, which synapse in the spinal cord and travel to the pair of muscles where one is inhibited and its antagonistic pair flexes • Gamma motor neurons mediate the sensitivity of the reflexReferences 1. https://www.visiblebody.com/blog/3d-skeletal-system-atlas-axis-and-the-atlanto-axial-relationship 2. https://www.anatomystandard.com 3. https://www.spine-health.com/conditions/spine-anatomy/c1-c2-vertebrae-and-spinal-segment 4. https://anatomycorner.com/main/2015/10/06/atlas-and-axis/ 5. https://teachmeanatomy.info/back/bones/vertebral-column/ 6. https://www.kenhub.com/en/library/anatomy/thoracic-vertebrae 7. https://www.researchgate.net/figure/Illustration-of-thoracic-vertebrae-showing-vertebral-body-pedicles-facets- transverse_fig2_323804926 8. https://www.istockphoto.com/photo/lumbar-vertebrae-l5-gm636179512-112710859 9. https://en.wikipedia.org/wiki/Epidural_blood_patch 10. http://biodrawing.com/Neurology_modules/NervousSystemSite/Neuroanatomy/meninges/Spinal_meninges.html 11. https://pocketdentistry.com/15-the-structure-of-the-central-nervous-system/ 12. https://teachmeanatomy.info/neuroanatomy/pathways/ascending-tracts-sensory/ 13. https://quizlet.com/293626317/medullamyelencephalon-flash-cards/ 14. https://teachmeanatomy.info/neuroanatomy/pathways/ascending-tracts-sensory/