The Spinal Cord & Spinal Nerves PDF

The Spinal Cord & Spinal Nerves Images from Human Anatomy 8th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. Images from Neuroanatomy: An Atlas of Structures, Sections, and Systems, 7th ed., by Dua...

The Spinal Cord & Spinal Nerves Images from Human Anatomy 8th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. Images from Neuroanatomy: An Atlas of Structures, Sections, and Systems, 7th ed., by Duane E. Haines, © 2007 indicated by “HA”. Cerebrum CNS = Brain + Spinal Cord Brain enclosed in cranium, consists of the: Brain stem Cerebellum 1. Cerebrum Spinal cord • bilaterally paired, anatomically symmetrical cerebral hemispheres 2. Brainstem • contains nuclei, white matter tracts, vital centers • continuous with spinal cord 3. Cerebellum Mc14.1 • bilaterally paired cerebellar hemispheres • concerned with coordination of movement, etc. Spinal Cord the elongated continuation of the brainstem enclosed in the vertebral column 2 PNS = Cranial Nerves, Spinal Nerves & Ganglia Cranial Nerves Cranial Nerves Spinal Nerves • arise from the brain & brainstem Ganglia • special senses: vision, hearing, balance, smell, taste • general sensation from the face • voluntary motor control of striated muscle in the face • parasympathetic outflow to targets in face (eyes, glands) as well as thoracic and abdominal viscera Spinal Nerves • arise from the spinal cord • general sensation from body and back of head • voluntary motor control of striated muscle in the body • all sympathetic outflow (thoracic and abdominopelvic viscera, skin, AND targets in face) • parasympathetic outflow to visceral organs of pelvis Ganglia Mc14.1 • associated with both cranial and spinal Ns 3 Dermatomes & Myotomes C2–C3 NV Dermatomes C2–C3 C2 C3 T2 C6 C8 C7 L1 L2 T1 L3 L4 L5 C4 C5 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 S2 • dermatome: the area of skin innervated by a given spinal level C3 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L4L3 L5 C4 C5 T2 C6 T1 C7 • myotome: the group of muscles supplied by a given spinal level SS 43 L1 S1L5 S5 C8 L2 S2 • lesion of a given spinal nerve results in a stereotyped loss of sensory input and motor output L3 S1 L4 ANTERIOR Ma14.7 POSTERIOR 4 The Meninges Gray matter • within bony coverings, CNS enclosed in meninges White matter Spinal nerve • composed of three layers: Pia mater Arachnoid mater Dura mater – dura mater – arachnoid mater – pia mater • subarachnoid space contains cerebrospinal fluid (CSF) Ma14.2 5 VERTEBRAE Spinal nerves C1-C8 Spinal nerves T1-T12 Spinal nerves L1-L5 Spinal nerves S1-S5 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 1 2 3 4 5 Rostrocaudal Subdivisions of the Spinal Cord Cervical spinal segments C1-C8 • bilaterally paired spinal nerves are named according to their associated vertebra Thoracic spinal • C1 spinal nerves emerge from segments T1-T12 above the atlas…… • axons within a spinal nerve (or peripheral nerve arising from it) come from cell bodies located at a prescribed spinal level or segment Lumbar spinal segments L1-L5 Sacral spinal segments S1-S5 • the naming of a spinal segment corresponds to its spinal nerve 6 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 1 2 3 4 5 The Cauda Equina & Dural Sac A. spinal cord ends as the conus medullaris at vertebral level L2 • more caudal nerves must descend to exit between appropriate vertebrae B. mass of nerves below vertebral level L2 referred to as the cauda equina A B C • spinal cord (like the rest of the CNS) enclosed in meninges: dura, arachnoid & pia maters • pia covers the spinal cord faithfully C. dura & arachnoid form the dural sac which extends to vertebral level S2 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 1 2 3 4 5 The Lumbar Cistern A. subarachnoid space lies between arachnoid and pia maters, contains cerebrospinal fluid (CSF) B. pial filum terminale interna extends caudally from conus medullaris A C. at S2, filum terminale takes layers from sac forming filum terminale externa which extends to the coccyx B D. expanded subarachnoid space between vertebral D levels L2 & S2, is the lumbar cistern C • CSF sampled in a lumbar puncture 8 CONUS MEDULLARIS CAUDA EQUINA HA2.4 DURAL SAC FILUM TERMINALE INTERNA 9 Ma14.1 Cervical spinal nerves Thoracic spinal nerves C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T9 T11 Lumbosacral enlargement L1 Conus medullaris T12 L2 L3 L4 L5 Sacral spinal nerves Coccygeal nerve (Co1) S1 S2 S3 S4 S5 • here, the vertebral laminae have been cut, thus opening the spinal canal • the dural sac is open, exposing the spinal cord in situ from the dorsal aspect T8 T10 Lumbar spinal nerves Cervical enlargement The Spinal Cord in Situ Cauda equina inc. filum terminale interna Filum terminale externa • the cauda equina & filum terminale interna are within the lumbar cistern • nerves arising from the spinal cord extend toward the intervertebral foramina to exit 10 between adjacent vertebra Fat and BVs Fill the Epidural Space • this is the site of injection of an epidural anesthetic • arachnoid held against dura by hydrostatic pressure of CSF • spinal nerves formed by the union of a dorsal and ventral root Epidural space POSTERIOR Spinous process of vertebra Dura mater Arachnoid Subarachnoid space Pia mater Spinal cord Ma14.2 Spinal nerve Intervertebral foramen Body of vertebra ANTERIOR 11 CSF is Sampled in a Lumbar Puncture Position of lumbar puncture needle in interspinous space L3 Cauda equina L4 Subarachnoid space Filum terminale interna Vertebral canal MIDSAGITTAL SECTION OF VERTEBRAL COLUMN AND LUMBAR CISTERN 12 CSF is Sampled in a Lumbar Puncture Conus medularis Subarachnoid space containing cerebrospinal fluid and spinal nerve roots Cauda eqina and filum terminale interna L5 vertebra Filum terminale externa Ma14.2 MRI, lateral view A Cross Section Through the Spinal Cord POSTERIOR Ma14.5 ANTERIOR Organization of the Spinal White Matter • located superficially, runs longitudinally • carries sensory info upward, motor info downward Sulci Delineate the White Matter into Columns Dorsal median sulcus White matter Dorsal funiculus (column) Lateral funiculus (column) Ventral funiculus (column) Mc16.5 Ventral median fissure Dorsal lateral sulcus (dorsal rootlets enter) Ventral lateral sulcus (ventral rootlets enter) 15 Organization of the Spinal Grey Matter • deep, forms a continuous column extending the length of the cord • at all levels, grey matter forms a butterfly in XS, divided into: – dorsal horns: primarily sensory Ns – ventral horns: primarily motor Ns • at certain levels, intermediolateral cell column (IML) present (next slide…) Grey matter Dorsal horn Ventral horn Mc16.5 LOWER CERVICAL Regional Variations in the Spinal Cord The ventral horns are enlarged at cervical and lumbar levels • cervical enlargement: ventral horns from C5 – T1 contain somatic motor Ns innervating the arms THORACIC • lumbosacral enlargement: ventral horns from L2 – S2 contain somatic motor Ns innervating the legs IML cell columns form lateral horns from T1 to L2 • contain cell bodies of sympathetic preganglionic Ns LUMBOSACRAL IML cell columns are present from S2 – S4 • contain cell bodies of parasympathetic preganglionic Ns • their axons form the pelvic splanchnic nerves S2 – S4 • because of large ventral horns, does not form a distinct “lateral horn” White matter • amount of white matter ↓ in rostrocaudal direction 17 Dorsal Roots Carry Sensory Information Neurons of the dorsal horn are sensory. • Neurons of the dorsal horn receive sensory information from body wall, limbs, viscera • cell bodies of sensory Ns located in dorsal root ganglia, DRG • sensory input conveyed by dorsal roots • in a lesion of a the dorsal root, sensory signs seen in a dermatomal distribution Dorsal root ganglion Sensory axon DH Dorsal root LH VH 18 Ventral Roots Carry Motor Information Neurons of the ventral horn are somatic motor. • Somatic motor Ns control striated muscle of the body wall & limbs Neurons of the IML cell column are visceral motor. • Visceral motor Ns control visceral targets • both somatic & visceral motor output conveyed by ventral roots • a lesion of a ventral root will manifest with motor signs in a myotomal distribution Dorsal root ganglion Sensory axon DH Dorsal root IML VH Ventral root Visceral motor axon Somatic motor axon 19 Spinal Nerves are Mixed Nerves • spinal nerves formed by union of dorsal & ventral roots • thus contain both sensory and motor fibres; i.e. they are mixed nerves • in a lesion of a spinal nerve, both sensory and motor signs may be seen Dorsal root ganglion DH Sensory axon Dorsal root Spinal nerve LH VH Ventral root Visceral motor axon Somatic motor axon 20 The Spinal Cord and Spinal Nerves in Context Deep muscles of back POSTERIOR Spinous process Dorsal root Dorsal root ganglion Spinal cord Dorsal ramus Ventral ramus Spinal nerve Ventral root Body of vertebra Rami communicantes Sympathetic Trunk ganglion Mc16.5 ANTERIOR 21 Spinal Cord: Anterior View Pia mater Denticulate ligaments Dorsal root of C4 Ventral root of C4 Spinal blood vessel Dura and Arachnoid mater (reflected) Ma14.2 Herniated Disc Compressed area of spinal nerve Area of distortion Nucleus pulposus Mc8.9 Spinal nerve Spinal cord Anulus fibrosus Herniated disc, superior view 23 Somatic Nerve Plexuses • a plexus is a “braid” • recall, dorsal & ventral rami are mixed nerves • ventral rami of some spinal nerves blend to create compound nerves carrying axons from 2 or more spinal segments • the overlapping network between the ventral rami and the final compound peripheral nerve is called a nerve plexus Ma14.8 • ∴ a muscle innervated by a compound nerve is controlled by more than one spinal segment 24 eg. the Brachial Plexus Ma14.10 25 Visceral Nerve Plexuses • viscera are controlled by the balance between the sympathetic and parasympathetic inputs at any point in time • sympathetic and parasympathetic outflow originate from different regions of the CNS • they overlap, prior to innervating their target, in a visceral plexus Ma17.9 26 Reflexes • reflex: an involuntary motor response (output) evoked by a specific stimulus (input) • stimulus (input) may be external or internal – external stimuli: – internal stimuli: • motor response (output) may involve skeletal, cardiac or smooth muscle – skeletal muscle – cardiac muscle – smooth muscle • thus, reflexes occur in both the somatic and visceral nervous systems • reflexes function to maintain homeostasis or the status quo • pathway from receptor to effector is a reflex arc • great variation in complexity between different reflex arcs 27