Download 8-5 The brain and spinal cord are surrounded by three layers of

8-5 The brain and spinal cord
are surrounded by three
layers of membranes called
the meninges
The Central Nervous System
• The central nervous system (CNS) consists of the:
» Brain
» Spinal Cord
• The organs in the CNS…
» Require abundant nutrients and consistent supply of
oxygen
» Must be protected from blood-borne compounds
» Must be protected from contacting surrounding bone
(in the cranium)
The Central Nervous System
• The CNS receives physical stability and shock
absorption from the meninges
» Consist of three layers of specialized tissue
surrounding brain and spinal cord
• Blood vessels within meninges
deliver oxygen and nutrients
• Three layers:
» Dura mater
» Arachnoid
» Pia mater
The Three Meningeal Layers
• The Dura Mater  Brain
• Tough and fibrous outermost layer of the CNS
• Consists of two layers in the brain
– Cranially:
» Fuses with periosteum of occipital bone
– Caudally:
» Tapers to dense cord of collagen fibers
The Three Meningeal Layers
• The Dura Mater  Brain
• At several locations, the inner layer of the dura
mater extend deep into the cranial cavity
» Called dural folds
» Hold the brain in position
The Three Meningeal Layers
The Three Meningeal Layers
• The Dura Mater  Spinal Cord
• Outer layer is not fused to bone
• Space found between spinal cord and vertebral
canal is called the epidural space:
» Contains loose connective and adipose tissue
» Anesthetic injection site to affect spinal nerves in
immediate area of injecetion (aka: epidural)
The Three Meningeal Layers
• The Arachnoid
• Middle meningeal layer
• Space contains small amount of lymphatic fluid
» Reduces friction between opposing surfaces
• Subarachnoid space:
» Simple squamous epithelia
» Contain collagen and elastic fibers
» Filled with cerebrospinal fluid
that acts as a shock absorber
and transfers nutrients and
waste
The Three Meningeal Layers
The Three Meningeal Layers
• The Pia Mater
• Is the innermost meningeal layer
• Is a mesh of collagen and elastic fibers
• Is bound to underlying neural tissue
• Highly vascular region
» Provide blood and nutrients to the superficial areas
of the neural cortex
The Three Meningeal Layers
8-6 The spinal cord contains
gray matter surrounded by
white matter and connects to
31 pairs of spinal nerves
Gross Anatomy
• The Spinal Cord
• Serves as the information “highway” for the
passage of sensory and motor impulses
• Integrates information on its own
• Controls spinal reflexes
» Automatic motor responses
Gross Anatomy
• 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
Gross Anatomy
• 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
Gross Anatomy
• Spinal Cord
• Central canal
» Narrow internal passageway filled with cerebrospinal
fluid (CSF)
• Posterior surface
» Shallow groove called the posterior median sulcus
• Anterior surface
» Deeper groove called the anterior median fissure
Gross Anatomy
Gross Anatomy
Gross Anatomy
• 31 Spinal Cord Segments
• Based on vertebrae where spinal
nerves originate (letter and number)
• Positions of spinal segment and
vertebrae change with age:
» Cervical nerves are named for inferior
vertebra
» All other nerves are named for
superior vertebra
Gross Anatomy
• Every spinal segment is associated with a pair of
dorsal root ganglia (singular: ganglion)
» Contain cell bodies of sensory neurons
• Ventral roots: (anterior)
» Contains axons of motor neurons
» Send information to PNS
• Dorsal roots: (posterior)
» Contains axons of sensory neurons
» Bring information to CNS
Gross Anatomy
Gross Anatomy
• Distal to each dorsal root ganglion, the sensory
(dorsal) and motor (ventral) roots are bound
together into a single spinal nerve
• All spinal nerves are considered mixed nerves:
» Carry both afferent (sensory) and efferent (motor)
fibers
Sectional Anatomy
• Left and right sides of spinal cord are created by
the…
» Anterior median sulcus
» Posterior median fissure
Sectional Anatomy
• Gray matter
» Surrounds central canal of spinal cord
» Contains neuron cell bodies, neuroglia, unmyelinated
axons
» Has projections (gray horns) that extend into the
white matter
Sectional Anatomy
• Organization of Gray Matter
• Gray matter contains cell bodies of motor and sensory
neurons
• Horns have specific functions
» Posterior gray horn  sensory nuclei
» Anterior gray horn  motor control of skeletal muscles
» Lateral gray horn  visceral motor neurons
» Gray commissures  connect horns on both sides
Sectional Anatomy
Sectional Anatomy
• White matter
» Is superficial; surrounds the gray matter
» Contains myelinated and unmyelinated axons
Sectional Anatomy
• Organization of White Matter
• White matter is divided into 3 columns (or regions)
» Posterior white columns
» Anterior white columns
» Lateral white columns
• Each column contain tracts whose axons carry
sensory or motor information
» Ascending Tract  sensory info to the brain
» Descending Tract  convey motor commands into
spinal cord
Sectional Anatomy