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Lecture 10

BLG 700 Lecture Notes - Lecture 10: Dura Mater, Filum Terminale, Pia Mater

5 pages17 viewsFall 2016

Department
Biology
Course Code
BLG 700
Professor
Nancy Woodley
Lecture
10

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Chapter 14: Spinal Cord and Spinal Nerves
(Sections 14.1-14.5)
central nervous system (CNS) = brain and spinal cord
peripheral nervous system = nerves and ganglia outside of CNS
o central role in communication between brain and rest of body
o 12 pairs of cranial nerves and 31 pairs of spinal nerves and their ganglia
Spinal Cord
extends from the foramen magnum to the 2nd lumbar vertebra (Fig 14.1)
composed of cervical, thoracic, lumbar and sacral segments named according to portion of vertebral
column from which the nerves enter and exit
cervical and lumbosacral enlargements = associated with nerves that supply upper and lower limbs
conus medullaris = immediately inferior to lumbosacral enlargement
o filum terminale = slender connective tissue extending to dorsum of coccyx
provides longitudinal support to spinal cord
cauda equine = numerous roots (origins) of spinal nerves extending inferiorly from the lumbosacral
enlargement and conus medullaris
meninges (Fig 14.2) = specialized membranes surrounding brain and spinal cord
o provided protection, physical stability and shock absorption
o dura mater = most superficial tough fibrous membrane
dense irregular connective tissue
external and internal surfaces covered with simple squamous epithelium
caudal end blends with filum terminale
lateral extensions cover spinal nerve roots
epidural space = space between dura mater and the periosteum of the vertebral canal
contains spinal nerve roots, blood vessels, areolar connective tissue and adipose tissue
epidural anesthesia (often during childbirth) = injection of anesthetics into epidural space
o needle does not penetrate dura mater and takes time for drug to diffuse to CFS
o provides mainly sensory anaesthesia
o drugs can be administered via catheter to maintain longer anesthesia
o arachnoid mater = middle layer thin and wispy = simple squamous epithelium
subdural space = space between dura and arachnoid maters and contains small amount of serous
fluid
o pia mater = deepest layer that is bound tightly to surface of spinal cord
contains elastic and collagen fibers and thin layer of astrocytes
denticulate ligaments = extensions of pia mater that connect pia mater and arachnoid mater to
dura mater
help prevent side-to-side movement of spinal cord
subarachnoid space = space between arachnoid and pia maters
contains cerebrospinal fluid (CSF) and blood vessels
clinical procedures introducing needle into subarachnoid space at L3/L4 or L4/L5 level
o does not puncture spinal cord because it terminals at L2 and pushes nerves aside
o spinal anesthesia (spinal block) drug blocks action potential transmission
advantages = delivered directly to CSF, stronger and takes effect faster
o lumbar puncture (spinal tap) (Clinical Note p.381) CSF fluid is removed in order to
examine it for infectious agents (meningitis) or blood (haemorrhage) or to measure CSF
pressure
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Cross Section of Spinal Cord (Fig 14.4)
superficial and peripherally located white matter consists of myelinated and unmyelinated axons that
form nerve columns and tracts
o ventral (anterior), dorsal (posterior), and lateral columns
tracts (fasciculi) = subdivision of columns
collection of axons within CNS (nerve = collection of axons outside CNS)
all axons within a tract relay information in the same direction
ascending tracts carry sensory information toward the brain
descending tracts carry motor commands from the brain to motor neurons of spinal cord
deep centrally-located grey matter = contains cell bodies of glial cells and neurons, dendrites, axon
terminals and unmyelinated axons
o organized in butterfly (H-)pattern
o nuclei = clusters of nerve cell bodies in the grey matter of the central nervous system
o thin dorsal (posterior) horns contain somatic and visceral sensory nuclei
o larger ventral (anterior) horns contain somatic motor nuclei
o small lateral (intermediate) horns associated with autonomic nervous system (visceral motor nuclei)
anterior median fissure (crack) and posterior median sulcus (groove) = longitudinal landmarks that
partially separate two halves of spinal cord
grey and white commissures = axons that cross from one side of the spinal cord to the other
central canal contains CSF and located in the center of the grey matter
6-8 rootlets combine to form roots (Fig 14.2, 14.4)
o dorsal root = sensory (afferent) information that enters the dorsal side of the spinal cord
dorsal root ganglion = swelling on dorsal root that contains the cell bodies of sensory neurons
no synapses here axons extend into CNS and synapse with interneurons
o ventral root = motor (efferent) axons that exits the ventral side of the spinal cord
o extend laterally from the spinal cord
o dorsal and ventral roots pass through subarachnoid space and pierce arachnoid and dura maters
spinal nerve = distal to dorsal and ventral roots = combined sensory and motor fibers (mixed nerves)
spinal cord injury leading causes: automobile and motorcycle accidents, gunshot wounds, falls and
swimming accidents
o spinal shock = period of sensory and motor paralysis following severe injury of spinal cord
resulting loss in function may be temporary or permanent
o spinal concussion = injury caused by blow usually due to bone or disk displacement into the cord
no visible damage to spinal cord and period of spinal shock temporary with complete recovery in
few hours
o spinal contusion = injury resulting in hemorrhage within meninges often resulting from whiplash or
falls
pressure rises in cerebrospinal fluid and white matter of cord may degenerate at site of injury
gradual recovery over period of weeks and may leave some functional loss
o spinal laceration = tear or cut produced by vertebral fragments or foreign bodies
o spinal compression = spinal cord physically squeezed or distorted within vertebral canal
o spinal transection = complete severing of spinal cord
o often involve some combination of compression, laceration, contusion and partial transection
treatment = relieving pressure and stabilizing area
o most occur in the cervical region or at the thoracolumbar junction
cervical region most severe and can result in paralysis of all four limbs (quadriplegia) with
abdominal and chest muscles also affected
below T1 can result in varying degrees of paralysis of the legs (paraplegia) and abdomen
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