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Chapter 14

BISC 3221 Chapter Notes - Chapter 14: Muscle Spindle, Commissure, Postganglionic Nerve Fibers

Biological Sciences
Course Code
BISC 3221
Craig Frank

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Chapter 14: The Spinal Cord and Spinal Nerves
14.1 Gross Anatomy of the Spinal Cord
Posterior median sulcus: shallow longitudinal groove on dorsal surface of cord
Anterior median fissure: deep crease along ventral surface of cord
Each region of cord has tracts involved with it
More grey matter in segments of cord concerned with sensory and motor innervation of limbs;
contain interneurons for sending sensory info and coordinating limb movements
Cervical enlargement: supplies nerves to pectoral girdle and upper limbs
Lumbosacral enlargement: supplies nerves to structures of pelvis and lower limbs
Conus medullaris: conical tip of spinal cord, at/inferior to first lumbar vertebra
Filum terminale: fibrous tissue from tip of conus medullaris to dorsum coccyx, supports spinal
cord as component of coccygeal ligament
Cord has 31 segments
Dorsal root ganglia: every segment has one, contains cell bodies of sensory neurons (exceptions
in some people: C1 and CO1)
Dorsal root: contains axons of sensory neurons in dorsal root ganglion, thicker than ventral
Ventral root: contains axons of somatic motor neurons, visceral motor neurons
Spinal nerve: mixed nerves containing sensory and motor fibers (afferent and efferent)
Spinal cord extends only to first or second lumbar vertebra; spinal cord S2 is at vertebra L1
Cauda equina: filum terminal + long ventral and dorsal rots extending caudal to conus medullaris
14.2 Spinal Meninges
Spinal meninges: specialized membranes that provide protection, physical stability, shock
absorption for spinal cord; cover spinal cord, surround spinal nerve roots; blood vessels in them
deliver O2 and nutrients to spinal cord
3 layers
Cranial meninges: surround the brain, 3 layers
The Dura Mater
Tough, fibrous, outermost layer
Dense irregular CT, outer and inner surfaces covered by simple squamous epithelium
Outer epithelium not bound to bony walls of vertebral canal
Epidural space: between outer epithelial layer and vertebral canal; contains areolar tissue, blood
vessels, adipose tissue
Localized attachments to edge of foramen magnum of skull, 2nd and 3rd cervical vertebrae,
sacrum, posterior longitudinal ligament; all helps stabilize spinal cord
Coccygeal ligament: cord of collagen from spinal dura + parts of filum terminale; extends along
sacral canal
The Arachnoid Mater
Subdural space separates dura mater from deeper layers
Arachnoid mater: middle meningeal layer, simple squamous epithelium
Separated from pia mater by subarachnoid space that contains CSF (shock absorber, diffusion of
gases/nutrients/chemical messengers/waste products)
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Arachnoid trabeculae: extend form inner surface of arachnoid mater to outer surface of pia mater
Subarachnoid space can be accessed between L3 and L4, important for CSF
examination/anesthetic dose
The Pia Mater
Innermost meningeal layer
Elastic and collagen fibers, interwoven with those of arachnoid trabeculae
Contains blood vessels supplying spinal cord
Bound to underlying neural tissue by connecting with spinal cord astrocytes
Denticulate ligaments: along length of spinal cord, extensions of spinal pia mater, connects pia
mater and spinal arachnoid mater to dura mater; prevent side to side and inferior movement of
Meningeal membranes are continuous with CT surrounding spinal nerves
14.3 Sectional Anatomy of the Spinal Cord
Grey matter: H shape in cross section, dominated by cell bodies, glial cells
Central canal: in horizontal bar of H
Horns: grey matter extending towards outer surface of cord
White matter: outer region, contains myelinated and unmyelinated axons in tracts and columns
Organization of Grey Matter
Nuclei: groups of cell bodies of neurons in grey matter
Sensory nuclei: receive and relay sensory info from peripheral receptors
Motor nuclei: send info to peripheral effectors
Posterior/dorsal grey horns: contain somatic and visceral sensory nuclei
Anterior/ventral grey horns: contain somatic motor neurons
Lateral grey horns: contain axons crossing from one side of cord to the other
Motor nuclei organized so that nerves of proximal structures are located more medially than those
innervating more distal structures
Size of anterior horns depends on number of muscles innervated by that segment (largest in
cervical and lumbar regions, control limb muscles)
Organization of White Matter
Columns: regions of white matter
Posterior white columns: between posterior grey horns and posterior median
Anterior white columns: between anterior grey horns and anterior median fissure
Anterior white commissure: interconnects posterior and anterior white columns
Lateral white columns: white matter on either side between anterior and posterior columns
Tracts: AKA fasiculi, sections of columns containing axons with shared functional and structural
characteristics; conveys sensory info/motor commands, axons in it are uniform in diameter,
myelination, conduction speed, relay info in same direction
Smaller tracts carry sensory or motor signals between segments of spinal cord
Larger tracts connect spinal cord with brain
Ascending tracts: carry sensory info toward brain
Descending tracts: convey motor commands into spinal cord
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