cns – the spinal cord, spinal nerves & spinal reflexes

CNS – The Spinal Cord, Spinal Nerves & Spinal

Reflexes

Spinal Cord & Spinal Nerves

Spinal cord Truly the pathway between body and mindConducts impulses to and from the brainCarries out spinal reflexes

Spinal nerves31 pairsAll are mixed nerves

Mixed Nerves?

Dorsal rootsGanglion containing axons of sensory neurons (afferent)

Ventral rootsAll motor fibers (axons) leave the cord by the ventral roots (efferent)

General Organization

Highly organized, very efficient

Spinal Reflexes

Rapid, automatic nerve responses triggered by specific stimuli Controlled by spinal cord alone; not the brain

Gross Anatomy of the Spinal Cord

The Adult Spinal Cord

About 18 inches (45 cm) long1/2 inch (14 mm) wideEnds between vertebrae L1 and L2

Bilateral Symmetry

Grooves divide the spinal cord into left and right

Posterior median sulcus:Shallow

Anterior median fissure:deeper groove on anterior side

Enlargements of the Spinal Cord

Caused by:amount of gray matter in segmentinvolvement with sensory and motor nerves of limbs

Cervical enlargement:nerves of shoulders and upper limbs

Lumbar enlargement:nerves of pelvis and lower limbs

The Distal End

Conus medullaris: thin, conical spinal cord below lumbar enlargement

Filum terminale:thin thread of fibrous tissue at end of conus medullarisattaches to coccygeal ligament

Meninges of the Spinal Cord

The Meninges

Specialized membranes isolate spinal cord from surroundingsSpinal meninges:

protect spinal cordcarry blood supply continuous with cranial meninges

Meningitis:viral or bacterial infection of meninges

The 3 Meningeal Layers

Dura mater:outer layer of spinal cord

Arachnoid mater:middle meningeal layer

Pia mater:inner meningeal layer

Spinal Dura Mater

Are tough and fibrousCranially:

fuses with periosteum of occipital boneis continuous with cranial dura mater

Caudally:tapers to dense cord of collagen fibersjoins filum terminale in coccygeal ligament

The Epidural Space

Between spinal dura mater and walls of vertebral canalContains loose connective and adipose tissueAnesthetic injection site

Arachnoid Mater

Middle meningeal layerArachnoid membrane:

simple squamous epitheliacovers arachnoid mater

Inter-Layer Spaces

filled with cerebrospinal fluid (CSF)

Cerebrospinal Fluid (CSF)

Is found in subarachnoid spaceCarries dissolved gases, nutrients, and wastes Spinal tap:

withdraws CSF

Pia Mater

Is the innermost meningeal layerIs a mesh of collagen and elastic fibersIs bound to underlying neural tissue

Spinal Cord Meninges

Sectional Anatomy of the Spinal Cord

Consists of….

White matterGray matterGray horns

Posterior gray hornscontain somatic and visceral sensory nuclei

Anterior gray hornscontain somatic motor nuclei

Lateral gray hornsare in thoracic and lumbar segmentscontain visceral motor nuclei

Spinal cord is so highly organized:

it is possible to predict results of injuries to specific areas

Spinal NervesThe roots unite into the spinal nerve

Spinal nerves exit through intervertebral foramen

Split into branches, or rami.

DermatomesSpecific bilateral region of the skin surface monitored by a single pair of spinal nerves

Nerve PlexusesPlexus = “braid”Nerves supplying the limbs form plexuses when they leave the spinal cord

Cervical plexusBrachial plexusLumbar plexusSacral plexus