15. The Spinal Cord.pdf

THE SPINAL CORD DR NADINE RAMPF | PHD [email protected] LECTURE OUTLINE Overview 04 Gray matter 07 White matter 16 Spinal nerves 23 Spinal meninges 27 Blood supply 29 02 OBJECTIVES Name the regions of the spinal cord Briefly exp...

THE SPINAL CORD DR NADINE RAMPF | PHD [email protected] LECTURE OUTLINE Overview 04 Gray matter 07 White matter 16 Spinal nerves 23 Spinal meninges 27 Blood supply 29 02 OBJECTIVES Name the regions of the spinal cord Briefly explain the concept of segmentation of the spinal cord, and the course of a normal spinal nerve Describe the position, relationships and coverings of the spinal cord. Include the spaces associated with the coverings and their contents, where applicable, as well Differentiate between the parts of the spinal cord on a transverse section at the level of C5, T5 and L5, respectively Name and demonstrate the position of the major afferent and efferent nerve pathways in the spinal cord Name the elements of the grey matter horns, as well as which body parts are represented by each Describe a dermatome and the dermatomal pattern of the body 03 LECTURE OUTLINE Overview Gray matter White matter Spinal nerves Spinal meninges Blood supply 04  OVERVIEW Elongated, cylindrical, suspended in the vertebral canal Surrounded by the meninges and cerebrospinal fluid (CSF) Extends from the foramen magnum to the second lumbar vertebra Body Continuous superiorly with the medulla oblongata The tapered inferior end forms conus medullaris It is connected to the coccyx by a non-neuronal cord called filum terminale Gives rise to 31 pairs of spinal nerves The bundle of spinal nerves extending inferiorly from lumbosacral enlargement and conus medullaris surround the filum terminale and form cauda equina Segmented Cervical Thoracic Lumbar Sacral Has two enlargements Cervical enlargement: supplies upper limbs Lumbosacral enlargement: supplies lower limbs 05 CROSS-SECTION OF THE SPINAL CORD The spinal cord is incompletely divided into two equal parts: Anteriorly by a short, shallow median fissure Posteriorly by a deep narrow septum, the posterior median sulcus Composed of gray matter in the centre surrounded by white matter supported by neuroglia Commissures: Connections between left and right halves Gray with the central canal in the centre White Roots: Spinal nerves arise as rootlets then combine to form roots Dorsal (posterior) root has a ganglion Ventral (anterior) Two roots merge laterally and form the spinal nerve 06 LECTURE OUTLINE Overview Gray matter White matter Spinal nerves Spinal meninges Blood supply 07  Posterior horn Central canal GRAY MATTER Gray commissure Consists of nerve cell bodies and their processes, PWC neuroglia, and blood vessels The nerve cells are multipolar, and are of 3 main categories: Sensory neurons Located in the dorsal horn Receive impulses from the periphery of the body White Gray matter matter LWC Axons constitute the ascending fasciculi of the white matter Lower motor neurons Located in the ventral horn Transmit impulses to the skeletal muscles AWC Interneurons (connector neurons) Link sensory and motor neurons, at the same or different levels, which form spinal reflex arcs Anterior horn 08 GRAY MATTER NEURONAL ARCHITECTURE Cells of the same type are clustered into groups, which occur in long columns In transverse section, these columns appear as layers, especially within the dorsal horn These layers are called the laminae of Rexed, that are numbered consecutively by Roman numerals, starting from the tip of the dorsal horn and moving ventrally into the ventral horn 09 DORSAL HORN NUCLEAR GROUPS 4 MAIN GROUPS Substantia gelatinosa Nucleus proprius Nucleus dorsalis (Clark’s column, nucleus thoracis) Visceral afferent nucleus 10 DORSAL HORN NUCLEAR GROUPS Substantia Gelatinosa Rexed lamina II Located at the apex of the horn Composed of large neurons Extends throughout the length of the spinal cord Afferents: Dorsal root fibres concerned with pain, temperature and touch Nucleus Proprius Rexed lamina IV Located anterior to substantia gelatinosa Composed of large neurons Extends throughout the length of the spinal cord Afferents: Dorsal root fibres concerned with senses of position and movement 11 DORSAL HORN NUCLEAR GROUPS Nucleus Dorsalis Rexed lamina VII Located at the base of the dorsal horn Composed mostly of large neurons Extends from C8 to L3-4 segments Afferents: Dorsal root fibres concerned with information from muscle spindles and tendon organs Visceral Afferent Nucleus Rexed lamina VII Located lateral to nucleus dorsalis Composed mostly of medium size neurons Extends from T1 to L3 segments Afferents: Visceral afferents 12 VENTRAL HORN MOTOR NEURONS a.k.a. lower motor neurons A special type of interneurons, the Renshaw cells, whose branched axons form inhibitory synaptic junctions on motor neurons Two types Large multipolar cells Axons pass out in the ventral roots of spinal nerves as alpha efferents Innervate extrafusal muscle fibres of skeletal muscles Less numerous smaller multipolar cells Axons pass out in the ventral roots of spinal nerves as gamma efferents Innervate intrafusal muscle fibres of neuromuscular spindles Both alpha and gamma motor neurons are under the influence of descending pathways from the brain 13 VENTRAL HORN MOTOR NEURONS Motor neurons are organized into 3 groups: Medial: Present in most segments Innervates muscles of neck and trunk (including intercostal and abdominal muscles) Central: Smallest, present in some cervical (phrenic C3-5, spinal accessory C1-6) and lumbosacral (L2-S1) segments Lateral: Present in cervical and lumbosacral segments Innervates muscles of the limbs Neurons supplying flexor muscles are located dorsal to neurons for extensor muscles 14 LATERAL HORN NEURONAL GROUPS Small column composed of small neurons Extends from T1 to L2-3 segments: Give rise to preganglionic sympathetic fibres Extends from S2-4 segments: Give rise to preganglionic parasympathetic fibres 15 LECTURE OUTLINE Overview Gray matter White matter Spinal nerves Spinal meninges Blood supply 16 WHITE MATTER Consists of a mixture of nerve fibres, neuroglia and blood vessels White colour is due to a high proportion of myelinated nerve fibres The white matter of the spinal cord is arranged in columns/funiculi: Anterior Posterior Lateral The nerve fibres are arranged as bundles, running vertically through the cord A group of nerve fibres (axons) that share a common origin, termination and function form a tract or fasciculus These tracts are formed by sensory nerve fibres ascending to the brain, motor nerve fibres descending from the brain and fibres of interneurons Tracts are often named according to their points of origin and destination, e.g. spinothalamic, corticospinal 17 ASCENDING AND DESCENDING TRACTS CLICK TO PLAY 18 19 COMMISSURES OF THE SPINAL CORD Gray commissure Gray commissure PWC Transverse bridge of grey matter connecting the anterior and posterior gray horns on each side Is pierced by the central canal that divides it into anterior and posterior parts White Gray LWC White commissure matter matter Lies ventral to the gray commissure Mainly contains decussating nerve fibres AWC White commissure 20 CENTRAL CANAL OF THE SPINAL CORD The cerebrospinal-filled space that runs PWC longitudinally through the entire length of the spinal cord Lined by ependyma (ciliated columnar epithelium) Continuous with the ventricular system of the brain White Gray Superiorly opens into the 4th ventricle matter matter LWC Inferiorly in the conus medullaris, it expands into the fusiform terminal ventricle and terminates below at the root of filum terminale AWC 21 REGIONAL DIFFERENCES Although the general pattern of gray matter is the same throughout the spinal cord, regional differences are apparent in transverse sections The amount of white matter increases in a caudal-to- cranial direction because fibres are added to ascending tracts and fibres leave descending tracts The gray matter increases in volume in the cervical and lumbosacral enlargements for innervation of upper and lower limbs The lateral horn is characteristic of thoracic and upper lumbar segments 22 LECTURE OUTLINE Overview Gray matter White matter Spinal nerves Spinal meninges Blood supply 23 SPINAL NERVES Rootlets Posterior root 31 pairs of spinal nerves Anterior root 1st pair exit vertebral column between skull and atlas Spinal nerve Last 4 pairs exit via the sacral foramina Others exit through intervertebral foramina 8 pair cervical, 12 pair thoracic, 5 pair lumbar, 5 pair sacral, 1 pair coccygeal DRG Each spinal nerve arises as rootlets which then combine to form dorsal (posterior) and ventral (anterior) roots Two roots merge laterally and form the spinal nerve Dorsal (posterior) root has a ganglion (dorsal root/sensory ganglion) that contains the cell bodies of the sensory neurons Each spinal nerve then divides into a smaller dorsal and a larger ventral ramus 24 BRANCHES SPINAL NERVES Dorsal ramus: Innervate deep muscles of the trunk responsible for movements of the vertebral column and skin near the midline of the back Ventral ramus: Structures innervated depends upon which part of the spinal cord is considered Thoracic region: Form intercostal nerves that innervate the intercostal muscles and the skin over the thorax Remaining spinal nerve ventral rami (roots of the plexus): Form 5 plexuses (intermingling of nerves) Ventral rami of C1-C4 = cervical plexus Ventral rami of C5-T1 = brachial plexus Ventral rami of L1-L5 = lumbar plexus Ventral rami of L4-S4 = sacral plexus Ventral rami of S4-S5 = coccygeal plexus 25 DERMATOMES Areas of cutaneous innervation that are supplied by a single spinal nerve or cord level (with the exception of cranial nerves V1–3) While there is some overlap in the general distribution of dermatomes each individual spinal cord level supplies a distinct zone of skin Testing touch or sensory perception in these areas can be used to localize lesions of the spinal cord to a specific cord level or spinal nerve Dermatomes and distribution: C2 - Posterior half of skull C3 - Upper neck, directly inferior to mandible C4 - Above the clavicle, including upper shoulders and trapezius C5 - Below the clavicle, including lower shoulders bilaterally and medial biceps C6 - Lateral aspect of forearms and thumbs C7 - Middle triceps and mid-palm, including index and middle fingers C8 - Medial triceps and medial palm, including ring and small fingers T4 - Level of the nipples T7 - Xiphoid process T10 - Umbilicus L1 - Inguinal ligament L4 - Patella and large toe L5 - Dorsal web space between first and second toes S2-S4 - Penile and anal regions 26 LECTURE OUTLINE Overview Gray matter White matter Spinal nerves Spinal meninges Blood supply 27 SPINAL MENINIGES Connective tissue membranes surrounding the spinal cord Continuous with cranial meninges Dura mater: Outermost layer Continuous with epineurium of the spinal nerves Arachnoid mater: Middle layer Thin and wispy Pia mater: Innermost layer Bound tightly to the surface of the spinal cord Forms the filum terminale, which anchors the spinal cord to the coccyx and the denticulate ligaments that attach the spinal cord to the dura mater Spaces Pia mater Epidural: Contains blood vessels, connective tissue and fat Subdural: Contains serous fluid Arachnoid mater Subarachnoid: Contains CSF and blood vessels within web-like Dura mater strands of arachnoid tissue 28 LECTURE OUTLINE Overview Gray matter White matter Spinal nerves Spinal meninges Blood supply 29 BLOOD SUPPLY Arteries Supplied by branches of the vertebral and segmental arteries The vertebral artery gives rise to anterior and posterior spinal arteries Segmental arteries, such as the deep cervical, ascending cervical, and posterior intercostal give rise to 31 pairs of radicular arterial branches which supply the roots of spinal nerves Veins Similarly named veins accompany the arteries Anterior and posterior spinal veins drain into radicular veins, which then empty into the (internal and external) vertebral venous plexus This network eventually empties into the vertebral (neck) and segmental (trunk) veins 30  THANK YOU FOR YOUR ATTENTION Content for this lecture: Chapter 4 | Snell's Clinical Neuroanatomy, 8th Edition