THE BACK THE SPINAL CORD THE SPINAL CORD The structures in the - PowerPoint PPT Presentation

THE BACK THE SPINAL CORD

THE SPINAL CORD The structures in the vertebral canal: • the spinal cord • spinal nerve roots • spinal meninges • the neurovascular structures

THE SPINAL CORD

THE SPINAL CORD The spinal cord occupies the superior 2/3 of the vertebral canal In adults, the spinal cord is 42–45 cm long It is conHnuous cranially with the medulla oblongata , just below the level of the foramen magnum , at the upper border of the atlas . It terminates caudally as the conus medullaris . At the level of the disc between vertebrae LI and LII in adults. It can end as high as vertebra TXII or as low as the disc between vertebrae LII and LIII The lumbar and sacral nerve roots are the longest, extending far beyond the terminaHon of the adult spinal cord at approximately the L2 level to reach the remaining lumbar, sacral, and coccygeal IV foramina.

THE SPINAL CORD The terminaHon of the spinal cord - the cauda equina . In neonates , the spinal cord extends approximately to vertebra LIII but can reach as low as vertebra LIV . Grows much more slowly than the bony vertebral column during fetal development. The distal end of the cord, the conus medullaris is cone shaped.

THE SPINAL CORD The spinal cord is not uniform in diameter along its length. It has two major enlargements in regions associated with the origin of spinal nerves that innervate the upper and lower limbs . • cervical enlargement • lumbosacral enlargement A cervical enlargement occurs in the region associated with the origins of spinal nerves C4 to T1 , which innervate the upper limbs. A lumbosacral enlargement occurs in the region associated with the origins of spinal nerves T11 to S1 , which innervate the lower limbs.

THE SPINAL CORD The anterior rami of the spinal nerves arising from this enlargement make up the: • lumbar plexuses • sacral plexuses of nerves that innervate the lower limbs.

THE SPINAL CORD The external surface of the spinal cord is marked by a number of fissures and sulci: • The anterior median fissure extends the length of the anterior surface. • The posterior median sulcus extends along the posterior surface. • The posterolateral sulcus on each side of the posterior surface marks where the posterior rootlets of spinal nerves enter the cord.

THE SPINAL CORD Internally, the cord has a small central canal surrounded by gray and white maSer: • The gray maRer is rich in nerve cell bodies , which form longitudinal columns along the cord, and in cross secHon these columns form a characterisHc H-shaped appearance in the central regions of the cord. • The white maRer surrounds the gray maSer and is rich in nerve cell processes , which form large bundles or tracts that ascend and descend in the cord to other spinal cord levels or carry informaHon to and from the brain.

THE SPINAL NERVES

THE SPINAL CORD The spinal nerves consist of 31 pairs of nerves: • 8 cervical (1 st between skull and C1) • 12 thoracic • 5 lumbar • 5 sacral • 1 coccygeal The first cervical C1 nerves lack dorsal roots in 50% of people . The coccygeal nerve may be absent.

THE SPINAL CORD Spinal nerves iniHally arise from the spinal cord as rootlets - the rootlets converge to form two nerve roots Spinal nerves iniHally arise from the spinal cord as rootlets - the rootlets converge to form two nerve roots : • anterior (ventral) nerve root • posterior (dorsal) nerve root

THE SPINAL CORD An anterior (ventral) nerve root , consisHng of motor (efferent) fibers passing from nerve cell bodies in the anterior horn of spinal cord gray maSer to effector organs located peripherally. A posterior (dorsal) nerve root , consisHng of sensory (afferent) fibers from cell bodies in the spinal (sensory) or posterior (dorsal) root ganglion (DRG) that extend peripherally to sensory endings and centrally to the posterior horn of spinal cord gray maSer.

THE SPINAL CORD The posterior and anterior nerve roots unite , within or just proximal to the intervertebral foramen, to form a mixed (both motor and sensory) spinal nerve . The spinal nerve immediately divides into two rami: • posterior (dorsal) ramus • anterior (ventral) ramus

THE SPINAL CORD The spinal nerve, the posterior and anterior rami carry both motor and sensory fibers . The terms motor nerve and sensory nerve are almost always relaHve terms . Nerves supplying muscles of the trunk or limbs (motor nerves) also contain about 40% sensory fibers , which convey pain and propriocepHve informaHon. The cutaneous (sensory) nerves contain motor fibers, which serve sweat glands and the smooth muscle of blood vessels and hair follicles.

THE SPINAL CORD The unilateral area of skin innervated by the sensory fibers of a single spinal nerve is called a dermatome . The unilateral muscle mass receiving innervaHon from the fibers conveyed by a single spinal nerve is a myotome .

THE SPINAL CORD As they emerge from the intervertebral foramina, spinal nerves are divided into two rami : • posterior (primary) rami of spinal nerves • anterior (primary) rami of spinal nerves Posterior (primary) rami of spinal nerves supply nerve fibers to the: • synovial joints of the vertebral column, • deep muscles of the back, • overlying skin in a segmental paSern. Posterior (primary) rami of spinal nerves remain separate from each other (do not merge to form major somaHc nerve plexuses).

THE SPINAL CORD Anterior (primary) rami of spinal nerves supply nerve fibers to the much larger remaining area, consisHng of the anterior and lateral regions of the trunk and the upper and lower limbs. Anterior (primary) rami of spinal nerves are distributed exclusively to the trunk generally remain separate from each other, also innervaHng muscles and skin in a segmental paSern

THE SPINAL CORD The majority of anterior rami merge with one or more adjacent anterior rami, forming the major somaHc nerve plexuses . The most peripheral nerves arising from the plexus contain fibers from mulHple spinal nerves . The spinal nerves lose their idenHty as they split and merge in the plexus .

THE SOMATIC AND VISCERAL FIBERS

THE SPINAL CORD The types of fibers conveyed by spinal nerves are: 1. SomaHc fibers a. General sensory fibers b. SomaHc motor fibers 2. Visceral fibers a. Visceral sensory fibers b. Visceral motor fibers

THE SPINAL CORD General sensory fibers (general somaHc afferent [ GSA ] fibers) transmit sensaHons from the body to the CNS. They may be exterocepHve sensaHons from the skin (pain, temperature, touch, and pressure) or pain and propriocepHve sensaHons from muscles, tendons, and joints. SomaHc motor fibers (general somaHc efferent [ GSE ] fibers) transmit impulses to skeletal (voluntary) muscles .

THE SPINAL CORD Visceral sensory fibers (general visceral afferent [GVA] fibers) transmit pain or subconscious visceral reflex sensaHons (informaHon concerning distension, blood gas, and blood pressure levels) from hollow organs and blood vessels to the CNS. Visceral motor fibers (general visceral efferent [GVE] fibers) transmit impulses to smooth (involuntary) muscle and glandular Hssues. Visceral motor fibers (general visceral efferent [GVE] fibers) Two varieHes of fibers, presynapHc and postsynapHc, work together to conduct impulses from the CNS to smooth muscle or glands.

THE SPINAL CORD Both types of sensory fibers: visceral sensory and general sensory, are processes of pseudounipolar neurons with cell bodies located in spinal sensory ganglia . The motor fibers of nerves are axons of mulHpolar neurons . The cell bodies of somaHc motor and presynapHc visceral motor neurons are located in the gray maRer of the spinal cord .

SPINAL MENINGES AND CEREBROSPINAL FLUID (CSF)

THE SPINAL CORD The spinal dura mater, arachnoid mater, and pia mater surrounding the spinal cord consHtute the spinal meninges . The spinal meninges : • spinal dura mater • arachnoid mater • pia mater

THE SPINAL CORD The spinal dura is separated from the periosteum - covered bone and the ligaments that form the walls of the vertebral canal by the epidural space . This space is occupied by the internal vertebral venous plexus embedded in a faSy matrix ( epidural fat ). The spinal dura forms the spinal dural sac , a long tubular sheath within the vertebral canal. The spinal dural sac is evaginated by each pair of posterior and anterior roots.

THE SPINAL CORD INNERVATION OF DURA MATER Nerve fibers are distributed to the spinal dura by the (recurrent) meningeal nerves

THE SPINAL CORD The spinal arachnoid mater is a delicate, avascular membrane that lines the spinal dural sac and its dural root sheaths. The spinal arachnoid mater encloses the CSF-filled subarachnoid space containing the spinal cord, spinal nerve roots, and spinal ganglia. The spinal arachnoid is not aRached to the spinal dura but is held against its inner surface by the pressure of the CSF.

THE SPINAL CORD In a lumbar spinal puncture , the needle traverses the spinal dura and arachnoid. Bleeding into this layer creates a pathological space at the dura - arachnoid juncHon in which a subdural hematoma is formed.

THE SPINAL CORD The spinal arachnoid is separated from the pia mater on the surface of the spinal cord by the subarachnoid space containing CSF. The arachnoid trabeculae , span the subarachnoid space connecHng the spinal arachnoid and pia.