CNS – The Spinal Cord, Spinal Nerves & Spinal
Reflexes
Spinal Cord & Spinal Nerves
Spinal cord Truly the pathway between body and mind
Conducts impulses to and from the brain
Carries out spinal reflexes
Spinal nerves31 pairs
All 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) long
1/2 inch (14 mm) wide
Ends 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 segment
involvement 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 medullaris
attaches to coccygeal ligament
Meninges of the Spinal Cord
The Meninges
Specialized membranes isolate spinal cord from surroundings
Spinal meninges:protect spinal cord
carry 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 fibrous
Cranially:fuses with periosteum of occipital bone
is continuous with cranial dura mater
Caudally:tapers to dense cord of collagen fibers
joins filum terminale in coccygeal ligament
The Epidural Space
Between spinal dura mater and walls of vertebral canal
Contains loose connective and adipose tissue
Anesthetic injection site
Arachnoid Mater
Middle meningeal layer
Arachnoid membrane:simple squamous epithelia
covers arachnoid mater
Inter-Layer Spaces
filled with cerebrospinal fluid (CSF)
Cerebrospinal Fluid (CSF)
Is found in subarachnoid space
Carries dissolved gases, nutrients, and wastes
Spinal tap:withdraws CSF
Pia Mater
Is the innermost meningeal layer
Is a mesh of collagen and elastic fibers
Is bound to underlying neural tissue
Spinal Cord Meninges
Sectional Anatomy of the Spinal Cord
Consists of….
White matter
Gray matter
Gray hornsPosterior gray horns
contain somatic and visceral sensory nuclei
Anterior gray hornscontain somatic motor nuclei
Lateral gray hornsare in thoracic and lumbar segments
contain 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