233 Chapter 13
The Spinal Cord, Spinal Nerves, and Spinal Reflexes
Spinal Cord
Gross Anatomy of the 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 – on posterior side
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
Gross Anatomy of the Spinal Cord
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
Cauda equine - Nerve roots extending below conus medullaris
31 Spinal Cord Segments
Based on vertebrae where spinal nerves originate
Positions of spinal segment and vertebrae change with age
Cervical nerve - Named for inferior vertebra (vertebra below them)
All other nerves - Named for superior vertebra (vertebra above them)
Roots - Two branches of spinal nerves
Ventral root - Contains axons of motor neurons
Dorsal root - Contains axons of sensory neurons
Dorsal root ganglia - Contain cell bodies of sensory neurons
The Spinal Nerve - Each side of spine (bilateral)
Dorsal and ventral roots join to form a spinal nerve
Mixed Nerves - Carry both afferent (sensory) and efferent (motor) fibers
The Spinal Meninges - Specialized membranes isolate spinal cord from surroundings
Functions include:
Protecting spinal cord
Carrying blood supply
Continuous with cranial meninges
Meningitis - Viral or bacterial infection of meninges
The Three Meningeal Layers
Dura mater - Outer layer of spinal cord
Arachnoid mater - Middle meningeal layer
Pia mater - Inner meningeal layer
, The Dura Mater - 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, blood vessels
Anesthetic injection site
The Arachnoid Mater - Middle meningeal layer
Arachnoid membrane
Simple squamous epithelia
Covers arachnoid mater
The Interlayer Spaces of Arachnoid Mater
Subdural space - Between arachnoid mater and dura mater
Subarachnoid space - Between arachnoid mater and pia mater
Contains collagen/elastin fiber network (arachnoid trabeculae)
Filled with cerebrospinal fluid (CSF)
Cerebrospinal Fluid (CSF)
Carries dissolved gases, nutrients, and wastes
Lumbar puncture or spinal tap withdraws CSF
The Pia Mater - Is the innermost meningeal layer
Is a mesh of collagen and elastic fibers
Is bound to underlying neural tissue
Spinal Cord
Structures of the Spinal Cord
Paired denticulate ligaments - Extend from pia mater to dura mater
Stabilize side-to-side movement
Blood vessels along surface of spinal pia mater, within subarachnoid space
Gray Matter and White Matter
Sectional Anatomy of the Spinal Cord
White matter - Is superficial, contains myelinated and unmyelinated axons
Gray matter - Surrounds the central canal of spinal cord
Contains neuron cell bodies, neuroglia, unmyelinated axons
Has projections (gray horns)
Organization of Gray Matter
The gray horns
Posterior gray horns contain somatic and visceral sensory nuclei
Anterior gray horns contain somatic motor nuclei
Lateral gray horns are in thoracic and lumbar segments; contain visceral motor nuclei
Gray commissures - Axons that cross from one side of cord to the other before reaching
gray matter
The cell bodies of neurons form functional groups called nuclei
Sensory nuclei - Dorsal (posterior), Connect to peripheral receptors
Motor nuclei - Ventral (anterior), Connect to peripheral effectors
The Spinal Cord, Spinal Nerves, and Spinal Reflexes
Spinal Cord
Gross Anatomy of the 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 – on posterior side
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
Gross Anatomy of the Spinal Cord
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
Cauda equine - Nerve roots extending below conus medullaris
31 Spinal Cord Segments
Based on vertebrae where spinal nerves originate
Positions of spinal segment and vertebrae change with age
Cervical nerve - Named for inferior vertebra (vertebra below them)
All other nerves - Named for superior vertebra (vertebra above them)
Roots - Two branches of spinal nerves
Ventral root - Contains axons of motor neurons
Dorsal root - Contains axons of sensory neurons
Dorsal root ganglia - Contain cell bodies of sensory neurons
The Spinal Nerve - Each side of spine (bilateral)
Dorsal and ventral roots join to form a spinal nerve
Mixed Nerves - Carry both afferent (sensory) and efferent (motor) fibers
The Spinal Meninges - Specialized membranes isolate spinal cord from surroundings
Functions include:
Protecting spinal cord
Carrying blood supply
Continuous with cranial meninges
Meningitis - Viral or bacterial infection of meninges
The Three Meningeal Layers
Dura mater - Outer layer of spinal cord
Arachnoid mater - Middle meningeal layer
Pia mater - Inner meningeal layer
, The Dura Mater - 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, blood vessels
Anesthetic injection site
The Arachnoid Mater - Middle meningeal layer
Arachnoid membrane
Simple squamous epithelia
Covers arachnoid mater
The Interlayer Spaces of Arachnoid Mater
Subdural space - Between arachnoid mater and dura mater
Subarachnoid space - Between arachnoid mater and pia mater
Contains collagen/elastin fiber network (arachnoid trabeculae)
Filled with cerebrospinal fluid (CSF)
Cerebrospinal Fluid (CSF)
Carries dissolved gases, nutrients, and wastes
Lumbar puncture or spinal tap withdraws CSF
The Pia Mater - Is the innermost meningeal layer
Is a mesh of collagen and elastic fibers
Is bound to underlying neural tissue
Spinal Cord
Structures of the Spinal Cord
Paired denticulate ligaments - Extend from pia mater to dura mater
Stabilize side-to-side movement
Blood vessels along surface of spinal pia mater, within subarachnoid space
Gray Matter and White Matter
Sectional Anatomy of the Spinal Cord
White matter - Is superficial, contains myelinated and unmyelinated axons
Gray matter - Surrounds the central canal of spinal cord
Contains neuron cell bodies, neuroglia, unmyelinated axons
Has projections (gray horns)
Organization of Gray Matter
The gray horns
Posterior gray horns contain somatic and visceral sensory nuclei
Anterior gray horns contain somatic motor nuclei
Lateral gray horns are in thoracic and lumbar segments; contain visceral motor nuclei
Gray commissures - Axons that cross from one side of cord to the other before reaching
gray matter
The cell bodies of neurons form functional groups called nuclei
Sensory nuclei - Dorsal (posterior), Connect to peripheral receptors
Motor nuclei - Ventral (anterior), Connect to peripheral effectors
