SPINAL CORD, SPINAL NERVES, AND REFLEXES

•          IS A ROPELIKE BUNDLE OF NERVOUS TISSUE

•          BEGINS AT FORAMEN MAGNUM AND PASSES THROUGH VERTEBRAL CANAL AS FAR AS L1-L2

•          IS CONTINUOUS WITH THE MEDULLA OF THE BRAIN.

•          IT IS ABOUT AS THICK AS A FINGER

•          DIAMETER IS NOT CONSTANT ALONG ITS LENGTH , TWO SWOLLEN OCCUR WHERE SPINAL NERVES OF LIMBS JOINT THE SPINAL CORD                        (  CERVICAL AND LUMBOSACRAL ENLARGEMENTS )

•          THE CORD EXHIBITS LONGITUDINAL GROOVES ON ITS ANTERIOR AND POSTERIOR SIDES- ANTERIOR MEDIAN FISSURE AND POSTERIOR MEDIAN SULCUS.

•          INFERIOR TO LUMBAR ENLARGEMENT SPINAL CORD NARROWS AND TERMINATES AT THE CONUS MEDULLARIS.

•          SPINAL NERVES FAN OUT FROM CONUS MEDULARIS IN A GROUP CALLED THE CAUDA EQUINA.

•          THE FILUM TERMINALE EXTENDS PAST THE CONUS TO ANCHOR SPINAL CORD IN THE SACRUM

FUNCTIONS

•          CONDUCTION – CONDUCT INFORMATION UP AND DOWN THE CORD

•          LOCOMOTION – BRAIN INITIATE WALKING, BUT THE SIMPLE REPETITIVE MUSCLE CONTRACTIONS ARE COORDINATED BY THE CORD

•          REFLEXES

SPINAL CORD IS ORGANIZED INTO 31 SEGMENTS.

EACH SEGMENT HAS A PAIRED SPINAL NERVE FORMED BY THE JOINING OF TWO LATERAL EXTENSIONS, DORSAL AND VENTRAL ROOTS.

THERE ARE 31 PAIRS OF SPINAL NERVES AND ROOTS

•          8 CERVICAL ( C1 – C8 )

•          12 THORACIC ( T1 – T12 )

•          5 LUMBAR ( L1 – L5 )

•          5 SACRAL ( S1 – S5 )

•          1 COCCYGEAL ( Co1 )

SPINAL CORD IS PROTECTED BY THE BONE, MENINGES, AND CEREBROSPINAL FLUID

THE MENINGES SURROUND, PROTECT, AND STABILIZE THE CNS

CONSIST OF THREE LAYERS:

•          DURAMATER

•          ARACHNOID

•          PIAMATER

DURAMATER

•          OUTERMOST LAYER OF SPINAL CORD

•          ATTACHES TO THE COCCYX VIA THE COCCYGEAL LIGAMENT, AND TO THE PERIOSTEUM OF SKULL AROUND FORAMEN MAGNUM.

•          BETWEEN DURA AND VERTEBRAL CANAL LIES THE EPIDURAL SPACE

ARACHNOID

•          MIDDLE MENINGEAL LAYER

•          INNER SURFACE OF DURA IS IN CONTACT WITH OUTER SURFACE OF ARACHNOID

•          BETWEEN ARACHNOID AND OUTER SURFACE OF PIAMATER IS THE SUBARACHNOID SPACE WHICH IS FILLED WITH CEREBROSPINAL FLUID

PIAMATER

•          INNERMOST MENINGEAL LAYER

•          ATTACH TO THE DURA ( AND ARACHNOID ) VIA THE DENTICULATE LIGAMENTS. THESE LIGAMENTS PREVENT LATERAL MOVEMENT.

CROSS-SECTIONAL ANATOMY

•          THE CORD IS COMPOSED OF AN OUTER LAYER OF WHITE MATER AND A CENTRAL AREA OF GRAY MATTER.

•          WHITE MATTER CONTAINS MYELINATED AND UNMYELINATED FIBERS

•          GRAY MATTER CONTAINS CELL BODIES OF NEURONS, NEUROGLIA, AND UNMYELINATED FIBERS

•          SPINAL NERVES ORIGINATE AS A PAIR OF NERVE ROOTS ( ONE DORSAL ROOT AND ONE VENTRAL ROOT )

•          SPINAL NERVES ALSO HAVE 2-WAY CONDUCTION – BOTH SENSORY AND MOTOR INFORMATION IS CARRIED IN THE NERVES

SPINAL NERVES ARE CLASSIFIED AS MIXED NERVES

( CONTAIN AFFERENT-SENSORY AND EFFERENT-MOTOR FIBERS )

THE SEGMENTAL DISTRIBUTION OF THE DORSAL RAMUS CAN BE SEEN IN THE SENSORY DERMATOMES OF THE SKIN

IN THE CERVICAL, LUMBAR, AND SACRAL REGIONS, GROUPS OF SPINAL NERVES JOIN IN A NETWORK CALLED A PLEXUS

NERVE PLEXUS

THERE ARE FOUR MAJOR PLEXUSES:

CERVICAL

BRACHIAL

LUMBAR

SACRAL

CERVICAL PLEXUS

•          CONSISTS OF BRANCHES OF C1 –C4, AND PARTS OF C5.

•          SUPPLY STRUCTURES OF THE NECK, SHOULDER, ARM, AND DIAPHRAGM.

•          PHRENIC NERVE IS THE MAJOR NERVE OF THE PLEXUS

BRACHIAL PLEXUS

•          CONSISTS OF BRANCHES OF C5-T1

•          INNERVATES PECTORAL GIRDLE AND UPPER LIMBS

•          INCLUDES: MUSCULOCUTANEOUS NERVE, MEDIAN NERVE, RADIAL NERVE, ULNAR NERVE.

LUMBAR PLEXUS

•          INCLUDE BRANCES FROM T12 – L4

•          INNERVATE PELVIC GIRDLE AND LOWER LIMBS.

•          INCLUDE: GENITOFEMORAL NERVE AND FEMORAL NERVE.

SACRAL PLEXUS

•          CONTAINS BRANCHES FROM L4 –S4.

•          THE TWO MAJOR NERVES ARE THE SCIATIC NERVE AND PUDENDAL NERVE.

REFLEXES

•          REFLEXES ARE QUICK, INVOLUNTARY,   STEREOTYPED REACTIONS OF GLANDS OR MUSCLES TO STIMULATION.

•          REFLEXES REQUIRE STIMULATION

REFLEXES HAVE SPECIFIC PATHWAYS CALLED REFLEX ARCS, WHICH CONSIST OF THE FOLLOWING

•          RECEPTOR

•          SENSORY NEURON

•          INTEGRATION CENTER

•          MOTOR NEURON

•          EFFECTOR