Spinal Nerves Lecture Notes PDF

Figure 13-1 An Overview of Chapters 13 and 14. CHAPTER 14: The Brain Sensory input Motor output over cranial over cranial nerves Reflex nerves Effectors...

Figure 13-1 An Overview of Chapters 13 and 14. CHAPTER 14: The Brain Sensory input Motor output over cranial over cranial nerves Reflex nerves Effectors Sensory centers in Muscles receptors brain CHAPTER 13: The Spinal Cord Glands Sensory input Motor output over Reflex over spinal nerves spinal nerves Sensory centers in receptors spinal cord Adipose tissue  13-2 The Spinal Cord ▪ Spinal cord – Housed within: Protective membranes (meninges) Vertebral column – Carries sensory and motor information between brain and most other parts of body – Gives rise to spinal nerves 2 © 2018 Pearson Education, Inc.  13-2 The Spinal Cord ▪ Gross anatomy of the spinal cord – From brain only to vertebrae L1 and L2 Stops lengthening around age 4 vertebral column still grows – 4 regions: Cervical, thoracic, lumbar, sacral – Bilateral symmetry – 31 segments Give rise to spinal nerves – Grooves divide spinal cord into left and right Posterior median sulcus Anterior median fissure (deeper groove) ▪ Central canal contains cerebrospinal fluid (CSF) 3 © 2018 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord. Posterior median sulcus C3 Dorsal root Cervical enlargement - Nerves Dorsal root ganglion White matter of shoulders and upper limbs Gray C1 matter Central canal C2 Cervical spinal C3 Lumbar enlargement - Nerves nerves C4 C5 Spinal Ventral C6 of pelvis and lower limbs C7 Cervical enlargement nerve root Anterior median fissure C8 T1 CSF fills the central T2 T3 T4 canal; acts as shock T5 T6 absorber and T7 exchange of material Thoracic T8 Posterior spinal T9 median sulcus nerves KEY Spinal cord regions = Cervical T10 T3 = Thoracic T11 Lumbar enlargement = Lumbar T12 = Sacral L1 Conus medullaris L2 Conus medullaris Lumbar L3 Inferior tip of spinal cord Thin, conical spinal cord spinal L4 Cauda equina nerves below lumbar enlargement L5 L1 More Gray matter Cauda equina Sacral spinal nerves S1 S2 (“enlargements”) = Nerve roots extending S3 S4 dedication to sensory below conus medullaris S5 Coccygeal Filum terminale S2 and motor control nerve (Co1) (in coccygeal ligament) b Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. a The superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The adult spinal cord extends from the brain only to the level of vertebrae L1–L2; the spinal segments found at representative locations are indicated in the cross sections. Figure 13-2 Gross Anatomy of the Adult Spinal Cord (Part 4 of 4). Cauda equina Nerve roots extending below conus medullaris Inferior Filum terminale tip of spinal Thin thread of fibrous tissue at cord end of conus medullaris Cauda equina Attaches to coccygeal ligament S1 Sacral spinal nerves S2 S3 S4 S5 Filum terminale S2 Coccygeal nerve (Co1) (in coccygeal ligament) b Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. a The superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The adult spinal cord extends from the brain only to the level of vertebrae L1– L2; the spinal segments found at representative locations are indicated in the cross sections. Naming of Segments Cervical nerves named based on the cervical vertebrae immediately inferior to it. Thoracic, lumbar ad sacral nerves named based on the vertebrae immediately superior to it. © 2013 Pearson Education, Inc. https://radiopaedia.org/articles/spinal-cord?lang=us  13-2 The Spinal Cord ▪ Spinal nerves – Formed by union of posterior and anterior roots – Pairs—one from each side at each vertebral level – Each has a white ramus communicans and a gray ramus communicans that innervate glands and smooth muscle – Mixed nerves—contain both afferent and efferent fibers – Each spinal nerve quickly divides into rami: Posterior ramus supplies skin/muscles of back Anterior ramus supplies most of body wall, skin, limbs 7 © 2018 Pearson Education, Inc. Figure 13–2c Gross Anatomy of the Adult Spinal Cord. 8 © 2018 Pearson Education, Inc. Figure 13-3a The Spinal Cord and Spinal Meninges. White matter Gray matter Ventral rootlets of spinal nerve Dorsal root ganglion Ventral root Spinal nerve Dorsal root Dorsal rootlets of Meninges Dorsal spinal nerve Pia mater - sensory Arachnoid mater Ventral Dura mater - control somatic and visceral effectors intervertebral foramen a A posterior view of the Pedicle spinal cord, showing the meningeal layers, superficial landmarks, and distribution Every segment has pair of spinal of gray matter and white matter ganglia, that contain cell bodies of sensory neurons. Figure 13-3b The Spinal Cord and Spinal Meninges. White Rami- myelinated axons Meninges Gray Rami- unmyelinated; nerves for glands and smooth muscles Dura mater Arachnoid mater ANTERIOR Pia mater Subarachnoid space Vertebral body Autonomic (sympathetic) ganglion Rami communicantes Ventral root of spinal nerve Ventral ramus Dorsal Spinal cord ramus Adipose tissue Denticulate Dorsal root in epidural space ligament ganglion POSTERIOR b A sectional view through the spinal cord and meninges, showing the relationship of the meninges, spinal cord, and spinal nerves 13-2 Spinal Cord Spinal Meninges – Specialized membranes isolate spinal cord from surroundings Including bony walls of vertebral column – Functions of the spinal meninges include: Protecting spinal cord – Physical stability and shock absorption Provide blood supply Continuous with cranial meninges – Meningitis Viral or bacterial infection of meninges 13-2 Spinal Cord The Three Meningeal Layers 1. Dura mater Outer layer of spinal cord 2. Arachnoid mater Middle meningeal layer 3. Pia mater Inner meningeal layer  13-2 Spinal Cord Dura Mater – Tough and fibrous collagen – Cranially: Fuses with periosteum of occipital bone Is continuous with cranial dura mater – Caudally: Tapers to dense cord of collagen fibers Joins filum terminale in coccygeal ligament Longitudinal stability 13-2 Spinal Cord Arachnoid Mater – Middle meningeal layer – Arachnoid membrane Simple squamous epithelia Pia Mater – Innermost meningeal layer – Mesh of collagen and elastic fibers – Bound to underlying neural tissue Note: Subarachnoid space contains CSF. 13-2 Spinal Cord – The epidural space Between spinal dura mater and walls of vertebral canal Contains loose connective and adipose tissue Anesthetic injection site 13-2 Spinal Cord The Interlayer Spaces of Arachnoid Mater – Subdural space Between arachnoid mater and dura mater – Subarachnoid space Between arachnoid mater and pia mater Contains collagen/elastin fiber network (arachnoid trabeculae) Filled with cerebrospinal fluid (CSF) Site for lumbar punctures 13-2 Spinal Cord The Interlayer Spaces of Arachnoid Mater Cerebrospinal Fluid (CSF) – Carries dissolved gases, nutrients, and wastes – Lumbar puncture or spinal tap withdraws CSF – Why lumbar region? 13-2 Spinal Cord Structures of the Spinal Cord – Paired denticulate ligaments Extend from pia mater to dura mater Stabilize side-to-side movement – Blood vessels Along surface of spinal pia mater Within subarachnoid space Provide nutrients/oxygen and waste exchange Figure 13-4 The Spinal Cord and Associated Structures. Spinal cord Anterior median fissure Pia mater Denticulate ligaments Dorsal root Ventral root, formed by several “rootlets” from one cervical segment Arachnoid mater (reflected) Dura mater (reflected) Spinal blood vessel Figure 13-3b The Spinal Cord and Spinal Meninges. Meninges Dura mater Arachnoid mater ANTERIOR Pia mater Subarachnoid space Vertebral body Autonomic (sympathetic) ganglion Rami communicantes Ventral root of spinal nerve Ventral ramus Dorsal Spinal cord ramus Adipose tissue Denticulate Dorsal root in epidural space ligament ganglion POSTERIOR b A sectional view through the spinal cord and meninges, showing the relationship of the meninges, spinal cord, and spinal nerves © 2013 Pearson Education, Inc.  13-3 Gray Matter and White Matter ▪ Functional organization of gray matter – Masses of gray matter within CNS are called nuclei and are organized into regions called horns Posterior horns – Somatic and visceral sensory nuclei Incoming information from receptors Anterior horns – Somatic motor nuclei Outgoing information to effectors Lateral horns – Thoracic and lumbar segments Visceral motor nuclei 22 © 2018 Pearson Education, Inc.  13-3 Gray Matter and White Matter ▪ Structural organization of white matter – Three columns Posterior white columns – between posterior horns and posterior median sulcus Anterior white columns – between anterior horns and anterior median fissure – Anterior white commissure—where axons cross from one side of spinal cord to the other Lateral white columns – on each side of spinal cord, between anterior and posterior columns 23 © 2018 Pearson Education, Inc.  13-3 Gray Matter and White Matter ▪ Functional organization of white matter – Tract—bundle of axons in CNS Relay same type of information in same direction Ascending tracts—sensory information up toward the brain Descending tracts—motor commands down to the spinal cord 24 © 2018 Pearson Education, Inc. 13.3 Gray and White Matter Organization “commissures”- bridge posterior and anterior sides to central canal. “Tracts” - bundles of axons in white matter in CNS; ascending and descending Posterior Posterior Posterior gray white column median sulcus commissure Functional Organization of Gray Matter From posterior root The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Posterior Somatic horn Sensory nuclei (Up to brain) Lateral Visceral Spinal Lateral horn white Visceral ganglion column Anterior Motor nuclei (Down spinal cord) horn Somatic To anterior root Anterior root Anterior gray commissure Anterior white commissure Anterior white column Anterior median fissure a The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior horns. The red arrows represent sensory input from the posterior root and motor output to the anterior root. Lateral horn only in thoracic/lumbar sections of spinal cord; controls visceral motor nuclei 25 13-4 Spinal Nerves and Plexuses Anatomy of Spinal Nerves – Each spinal cord segment: Is connected to a pair of spinal nerves – Each spinal nerve: Is surrounded by three connective tissue layers That support structures and contain blood vessels 13-4 Spinal Nerves and Plexuses Three Connective Tissue Layers of Spinal Nerves 1. Epineurium Outer layer Dense network of collagen fibers 2. Perineurium Middle layer Divides nerve into fascicles (axon bundles) 3. Endoneurium Inner layer Surrounds individual axons Figure 13-6a A Peripheral Nerve. Blood vessels Connective Tissue Layers Epineurium covering peripheral nerve Perineurium (around one fascicle) Endoneurium Schwann cell Myelinated axon Fascicle a A typical peripheral nerve and its connective tissue wrappings  13-4 Spinal Nerves and Plexuses ▪ Spinal nerves – Pair of spinal nerves emerges laterally from each spinal cord segment – Form by junction of anterior and posterior roots – All are mixed nerves ▪ Peripheral nerves – Form from branching and re-sorting of spinal nerves. – All are mixed nerves (sensory and motor) – Same connective tissue layers as spinal nerves (continuous with each other) 29 © 2018 Pearson Education, Inc. 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves Motor nerves – Distribute motor commands from motor nuclei to thoracic/ lumbar segments of spinal cord. – Rami Communicantes: White ramus – Carries visceral motor fibers – To sympathetic ganglion of autonomic nervous system Gray ramus – Unmyelinated nerves – From sympathetic ganglion 13-4 Spinal Nerves and Plexuses Motor nerves cont. – Dorsal ramus Contains somatic and visceral motor fibers Innervates the back – Ventral ramus Larger branch Innervates ventrolateral structures and limbs Figure 13-8 Peripheral Distribution of Spinal Nerves (Part 1 of 2). From interoceptors of From exteroceptors, 4 Sensory Info back proprioceptors of back The dorsal root of each spinal nerve carriers 3 sensory information to the The dorsal ramus carries sensory spinal cord. information from the skin and skeletal muscles of the back. Somatic sensory nuclei 2 The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body, wall, and the limbs. Dorsal root From exteroceptors, ganglion proprioceptors of body wall, limbs From interoceptors of body wall, limbs Rami communicantes Visceral sensory Ventral root nuclei KEY = Somatic sensations (eyes, ears, tongue, skin) 1 = Visceral The sympathetic nerve carriers sensations sensory information from the From interceptors of (internal organs) visceral organs. visceral organs Figure 13-8 Peripheral Distribution of Spinal Nerves (Part 2 of 2). Postganglionic fibers to Motor Commands To skeletal muscles of back smooth muscles, glands, etc., of back 2 The spinal nerve forms just lateral to the intervertebral 3 foramen, where the dorsal and The dorsal ramus contains somatic ventral roots unite. motor and visceral motor fibers that innervate the skin and skeletal muscles Dorsal root of the back. Dorsal root ganglion 4 The axons in the relatively large 1 ventral ramus supply the The ventral root of each spinal nerve ventrolateral body surface, contains the axons of somatic motor structures in the body wall, and and visceral motor neurons. the limbs. Visceral motor nuclei To skeletal muscles of body wall, limbs Somatic motor nuclei Rami communicantes Postganglionic fibers to KEY smooth muscles, and = Somatic motor commands glands of body wall, limbs Sympathetic ganglion = Visceral motor commands 5 The white ramus communicans is the first branch from the spinal nerve and carries visceral motor fibers to a nearby sympathetic ganglion. Because these preganglionic axons are myelinated, this Postganglionic fibers to branch has a light color and is therefore known as the white ramus. smooth muscles, White rami are only found between T1 and L2. glands, visceral organs in thoracic cavity 7 A sympathetic nerve 6 contains preganglionic and The gray ramus communicans contains preganglionic fibers that Preganglionic fibers to postganglionic fibers innervate glands and smooth muscles in the sympathetic ganglia innervating structures in the body wall or limbs. These fibers are unmyelinated and have innervating thoracic cavity. abdominopelvic viscera 1 a dark gray color. Gray rami are associated with each spinal nerve.