Anatomy of Spinal Cord PDF

Spinal cord Lebanese University Faculty of public health sciences-Branch VI Dr. Nada Basbous-Hafez  The central nervous system (CNS) consists of: The brain The spinal cord  Anatomically connected but the brain and SC show significant degree of functional independence ...

Spinal cord Lebanese University Faculty of public health sciences-Branch VI Dr. Nada Basbous-Hafez  The central nervous system (CNS) consists of: The brain The spinal cord  Anatomically connected but the brain and SC show significant degree of functional independence  The SC is more than a highway for information - integrates and processes information  The SC is more than a highway for information: Integrates and processes information Can function with the brain Can function independently of the brain  Features of the Spinal Cord ◦ Measures 45 cm in length ◦ Passes through the foramen magnum ◦ Extends from the brain (foramen magnum) to inferior border of the first lumbar vertebra (L1)  Features of the spinal cord ◦ Consist of:  cervical region  thoracic region  Lumbar region  Sacral region  Coccygeal region  Features of the spinal cord ◦ Consist of:  Cervical enlargement  Lumbosacral enlargement  Conus medullaris  Cauda equina  Filum terminale: becomes a component of the coccygeal ligament  Posterior and anterior median sulci  Features of the spinal cord ◦ Dorsal and posterior surface of the SC  posterior median sulcus  anterior median fissure ◦ Gray matter is increased in segments of the SC  involved with sensory and motor innervation of the limbs  contain interneurons (relay sensory input & motor output)  cervical enlargement (pectoral girdle and upper limbs)  lumbosacral enlargement (pelvis and lower limbs)  Features of the spinal cord ◦ Spinal cord tapers to a conical tip: conus medullaris ◦ Filum terminale (‘terminal thread’) provides longitudinal support as part of coccygeal ligament ◦ Divided into 31 segments associated with a pair of dorsal root ganglia  Contain cell bodies of sensory neurons lies between pedicles of adjacent vertebrae  Dorsal root contains axons of the sensory neurons  Ventral root contains axons of somatic motor neurons  Dorsal and ventral roots enter and leave between adjacent vertebrae at the intervertebral foramina  Features of the spinal cord ◦ Distal to each dorsal root ganglion sensory and motor fibers form a single spinal nerve  classified as mixed nerves, contain both afferent (sensory) and efferent (motor) fibers ◦ Spinal cord enlarges and elongates until 4 years old  adult spinal cord extends only to the 1st or 2nd lumbar vertebra (L1 & L2) ◦ Cauda equina: complex of the filum terminale and long ventral and dorsal roots  Features of the spinal cord ◦ Transverse view  White matter  Gray matter  Central canal  Dorsal root and ventral root: merge to form a spinal nerve  Dorsal root is sensory: axons extend from the soma within the dorsal root ganglion  Ventral root is motor  Features of the spinal nerves ◦ Sensory nerves (afferent nerves): transmit impulses toward the spinal cord ◦ Motor nerves (efferent nerves): transmit impulses away from the spinal cord  Features of the spinal meninges ◦ Specialized membranes that provide protection, physical stability, and shock absorption ◦ Continuous with the cranial (cerebral) meninges ◦ Denticulate ligaments help anchor the spinal cord in position ◦ Made of three layers:  Dura mater: tough, fibrous outermost layer  Arachnoid mater: middle layer  Pia mater: innermost layer ◦ Made of three layers:  Dura mater: tough, fibrous outermost layer  Arachnoid mater: middle layer  Pia mater: innermost layer  Dura mater: dense irregular CT whose outer and inner surfaces are covered by simple squamous epithelium outer epithelium not bound to walls of the vertebral canal intervening epidural space contains areolar tissue, BVs and adipose tissue  Arachnoid mater: consists of a simple squamous epithelium separated from pia mater by the subarachnoid space that contains cerebrospinal fluid (CSF) arachnoid trabeculae bundles of fibers  Pia mater: elastic and collagen fibers interwoven with the arachnoid trabeculae contains the BVs supplying the SC paired denticulate ligaments are extensions of the pia mater  Spinal taps: a) The needle The needle punctures the dura and withdraws CSF - position of the needle is in the subarachnoid space, near the nerves of the cauda equina but below the SC  Myelography: b) introduction of a radiopaque (opaque to x- rays) dye into the CSF - CSF appears white on a radiograph - tumors, inflammation, adhesions that distort or divert CSF will be shown  Surrounds the central canal and contains cell bodies of neurons and glial cells  Groups of nuclei (sensory or motor) with specific functions  Posterior gray horns contain somatic and visceral sensory nuclei; anterior gray horns contain somatic motor nuclei  Lateral gray horns contain visceral motor neurons  Gray commissures contain the axons of interneurons that cross from one side of the cord to the other  Divided into 6 columns (funiculi, sing. funiculus) - contain tracts or fasiculi that convey sensory information or motor commands  Ascending tracts relay information from the SC to the brain  Descending tracts carry information from the brain to the SC  31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal - each peripheral nerve has 3 layers of CT  Epineurium: outer tough fibrous sheath - dense irregular CT, 1° of collagen fibers and fibrocytes - forms the blood-nerve barrier  Perineurium: composed of collagenous fibers, elastic fibers, and fibrocytes - divides the nerve into fascicles (bundle of axons)  Endoneurium: loose irregular CT - capillaries from the perineurium provide oxygen and nutrients ot the axons and Schwann cells of the nerve Anatomy of a Peripheral Nerve  Each spinal nerve forms through fusion of dorsal and ventral nerve roots  Distally all spinal nerves form 2 branches - a dorsal ramus and a ventral ramus  Spinal nerves T1 to L2 contain 4 branches - a dorsal ramus and a ventral ramus - a white ramus and a gray ramus known as rami communicantes (‘communicating branches’)  Carry visceral motor fibers to and from a nearby autonomic ganglion associated with the sympathetic division of the ANS  White ramus: carries fibers to the ganglion - contains preganglionic myelinated axons  Gray ramus: innervate glands and smooth muscles - 2 groups of unmyelinated postganglionic fibers that leave the ganglion  Carry visceral motor fibers to and from a nearby autonomic ganglion associated with the sympathetic division of the ANS  White ramus: carries fibers to the ganglion - contains preganglionic myelinated axons  Gray ramus: innervate glands and smooth muscles - 2 groups of unmyelinated postganglionic fibers that leave the ganglion Peripheral Distribution of Spinal Nerves (Motor Fibers  Dorsal ramus provides sensory innervation from, and motor innervation to, a specific segment of the skin and muscles of the neck and back  Ventral ramus supplies the ventrolateral body surface, structures in the body wall, and the limbs  Distribution of sensory fibers within these rami illustrates the segmental division of labor - each pair of spinal nerves monitors a specific region of the body surface known as a dermatome Peripheral Distribution of Spinal Nerves (Sensory Fibers)  Dermatomes  Each pair of spinal nerves monitors specific surface areas (dermatomes)  These are clinically important areas regarding surgery : damage to a spinal nerve or dorsal root ganglion produces a loss of sensation  Complex network of nerves  Occurs in segments that control skeletal musculature of the neck and limbs o peripheral distribution of the ventral rami do not directly proceed to their peripheral targets  Ventral rami of adjacent spinal nerves blend their fibers to produce compound nerve trunks o formed during development when small skeletal muscles fuse to form larger muscles with compound origins o compound muscles contain sensory and motor fibers o ventral rami converge and branch to form compound nerves  There are four nerve plexuses o Cervical plexus o Brachial plexus o Lumbar plexus o Sacral plexus  Sometimes the lumbar and sacral are combined to form the lumbosacral plexus  Peripheral nerves and Nerve Plexuses  The Cervical Plexus (C1–C5) o Consists of cutaneous and muscular branches  Cutaneous branch innervates: o Head o Neck o Chest  Muscular branches innervate muscles of the neck and shoulder  Muscular branch innervates: o Omohyoid, sternohyoid, geniohyoid, thyrohyoid o Sternothyroid o Scalenes o Sternocleidomastoid o Levator scapulae o Trapezius o Diaphragm (controlled by the phrenic nerve of the cervical plexus)  Major nerve of this plexus the phrenic nerve provides the entire nerve supply to the diaphragm  The Brachial Plexus (C4–T1) The immediate nerves emerging from C4 to T1 are the: o Superior trunk o Middle trunk o Inferior trunk  These trunks all merge to form the posterior cord  Larger and more complex innervates the pectoral girdle and upper limb  Formed by the ventral rami of spinal nerves C4- T1 o converge to form the superior, middle, and inferior trunks o trunks divide into anterior and posterior divisions o all 3 posterior divisions unite to form the posterior cord o anterior divisions of the superior and middle trunks unite to form the lateral cord o medial cord is formed by continuation of the anterior division of the inferior trunk  Nerves arise from one or more trunks or cords  The cords of the brachial plexus o Lateral cord: merging of the superior and middle trunks o Medial cord: an extension of the inferior trunk o Posterior cord: merging of all trunks The Trunks and Cords of the Brachial Plexus  The cords of the brachial plexus o Lateral cord: extends to form the musculocutaneous nerve o The lateral cord and medial cord extend to form the median nerve o Medial cord extends to form the ulnar nerve o Posterior cord: branches to form the radial nerve and axillary nerve The Trunks and Cords of the Brachial Plexus The Trunks and Cords of the Brachial Plexus  The Lumbar and Sacral Plexuses (T12–S4)  Arise from the lumbar and sacral segments of the SC. Also called the lumbosacral plexus o Lumbar plexus nerves  Genitofemoral nerve  Lateral femoral cutaneous nerve  Femoral nerve o Sacral plexus nerves  Sciaticnerve (branches to form the common fibular nerve and the tibial nerve)  Pudendal nerve  Ventral rami of these nerves supply the pelvis and lower limb  ventral rami of both plexuses are distributed to the lower limb (often referred to as the lumbosacral plexus)  Major nerves of the lumbar plexus  genitofemoral, lateral femoral cutaneous, and femoral nerve  Major nerves of the sacral plexus - the Sciatic nerve which branches into the common fibular nerve and the tibial nerve and the pudendal nerve  Summary of the spinal nerves: o Cervical spinal nerves emerge from C1–C8 o Thoracic spinal nerves emerge from T1–T12 o Lumbar spinal nerves emerge from L1–L5 o Sacral spinal nerves emerge from S1–S5 o Coccygeal spinal nerves emerge from Co1 o Cervical plexus nerves emerge from C1–C5 o Brachial plexus nerves emerge from C5–T1 o There is not a thoracic plexus o Lumbar plexus nerves emerge from T12–L4 o Sacral plexus nerves emerge from L4–S4 o There is not a coccygeal plexus