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

• f spinal nerves that innervate the upper and lower limbs.
• cervical enlargement
• lumbosacral enlargement

A cervical enlargement occurs in the region associated with the

• rigins of spinal nerves C4 to T1, which innervate the upper limbs.

A lumbosacral enlargement occurs in the region associated with the

• rigins 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
• f 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 (1st 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

• ther (do not merge to form major somaHc nerve plexuses).

THE SPINAL CORD

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 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.

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

THE SPINAL CORD

The spinal pia mater, the innermost membrane, closely follows all the surface features of the spinal cord. The spinal pia also directly covers the roots of the spinal nerves and the spinal blood vessels. The spinal cord is suspended in the dural sac by the filum terminale and the right and le] denHculate ligaments.

THE SPINAL CORD

The subarachnoid space is located between the arachnoid and pia mater and is filled with CSF. SUBARACHNOID SPACE The lumbar cistern - the enlargement of the subarachnoid space in the dural sac, caudal to the conus medullaris and containing CSF and the cauda equina.

THE SPINAL CORD

ARTERIES OF SPINAL CORD AND NERVE ROOTS

THE SPINAL CORD

The arteries supplying the spinal cord are branches of the:

• vertebral
• ascending cervical
• deep cervical
• intercostal
• lumbar
• lateral sacral arteries

Three longitudinal arteries supply the spinal cord:

• anterior spinal artery
• paired posterior spinal arteries.

THE SPINAL CORD

These arteries run longitudinally from the medulla of the brainstem to the conus medullaris of the spinal cord. The anterior spinal artery, formed by the union of branches of the vertebral arteries, runs inferiorly in the anterior median fissure. The posterior spinal artery is a branch of either the vertebral artery or the posteroinferior cerebellar artery.

THE SPINAL CORD

The anterior and posterior segmental medullary arteries are derived from spinal branches of the:

• ascending cervical
• deep cervical
• vertebral
• posterior intercostal
• lumbar arteries.

They enter the vertebral canal through the IV foramina. The posterior and anterior roots of the spinal nerves and their coverings are supplied by posterior and anterior radicular arteries.

THE SPINAL CORD

VEINS OF SPINAL CORD

THE SPINAL CORD

There are usually three anterior and three posterior spinal veins The veins of the spinal cord join the internal vertebral (epidural) venous plexuses in the epidural space. The internal vertebral venous plexuses pass superiorly through the foramen magnum to communicate with dural sinuses and vertebral veins in the cranium. The internal vertebral plexuses also communicate with the external vertebral venous plexuses.

CERVICAL SPINAL CORD INJURY

CERVICAL SPINAL CORD INJURY

A 45-year-old man was involved in a serious car accident. On examinaHon he had a severe injury to the cervical region of his vertebral column with damage to the spinal cord. In fact, his breathing became erraHc and stopped.

CERVICAL SPINAL CORD INJURY

If the cervical spinal cord injury is above the level of C5, breathing is likely to stop.

CERVICAL SPINAL CORD INJURY

The phrenic nerve takes origin from

• C3,
• C4,
• and C5

and supplies the diaphragm.

CERVICAL SPINAL CORD INJURY

Breathing may not cease immediately if the lesion is just below C5, but does so as the cord becomes edematous and damage progresses superiorly.

CERVICAL SPINAL CORD INJURY

In addiHon, some respiratory and venHlatory exchange may occur by using neck muscles plus the sternocleidomastoid and trapezius muscles, which are innervated by the accessory nerve [XI].

CERVICAL SPINAL CORD INJURY

The paHent was unable to sense or move his upper and lower limbs.

CERVICAL SPINAL CORD INJURY

The paHent has paralysis of the upper and lower limbs and is therefore quadriplegic.

CERVICAL SPINAL CORD INJURY

If breathing is unaffected, the lesion is below the level of C5 or at the level of C5.

CERVICAL SPINAL CORD INJURY

The nerve supply to the upper limbs is via the brachial plexus, which begins at the C5 level.

CERVICAL SPINAL CORD INJURY

The site of the spinal cord injury is at or above the C5 level.

CERVICAL SPINAL CORD INJURY

It is important to remember that although the cord has been transected in the cervical region, the cord below this level is intact.

CERVICAL SPINAL CORD INJURY

Reflex acHvity may therefore occur below the injury, but communicaHon with the brain is lost.