NEUROLOGICAL SYSTEM PART I

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NEUROLOGICAL SYSTEMPART I

• DENNIS STEVENS CRNA, MSN, ARNP
• SEPTEMBER 2007
• FLORIDA INTERNATIONAL UNIVERSITY
• ADVANCED BIOSCIENCE IN ANESTHESIOLOGY II
• NGR 6145

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• OBJECTIVES
• Describe the principle divisions of the nervous
  system.
• Discuss significant differences of the afferent
  and efferent systems of the peripheral nervous
  system.
• Explain the three stages of gestation regarding
  CNS development and identify major milestones
  associated with each stage.
• Describe embryonic formation of the spinal cord
  including development of white and gray matter.
• State major malformations and abnormalities and
  their causes associated with the central nervous
  system.

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• INTRODUCTION
• The nervous system may be divided into two
  principle divisions
• Central nervous system (CNS)
• Peripheral nervous system (PNS)
• CNS consists of the brain and spinal cord, is
  enclosed in bone and wrapped in protective
  coverings (meninges) and fluid filled spaces
• PNS is formed by the cranial nerves and spinal
  nerves and may be divided into
• Afferent system
• Efferent system

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• INTRODUCTION
• Efferent system is subdivided into
• Somatic nervous system (SNS) consists of
  efferent neurons that conduct impulses from the
  CNS to skeletal muscle tissue. The SNS is under
  conscious control and therefore voluntary
• Autonomic nervous system (ANS) consists of
  efferent neurons that conduct impulses from the
  CNS to smooth muscle tissue, cardiac muscle
  tissue, and glands. Produces responses in
  involuntary muscles and glands

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• CENTRAL NERVOUS SYSTEM
• Consists of the brain and spinal cord

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• PERIPHERAL NERVOUS SYSTEM
• Formed by the cranial and spinal nerves
• Divided into afferent and efferent systems
• Further subdivided into somatic nervous system
  and autonomic nervous system

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• INTRODUCTION
• Viscera receive nerve fibers from the two
  divisions of the ANS that have largely opposing
  actions
• Sympathetic (thoracolumbar) nervous system
  division
• Parasympathetic (craniosacral) nervous system
  division
• Developmental anatomy of the CNS
• Human CNS is a complex computing device capable
  of a wide array of interrelated functions and
  actions
• Development of the nervous system begins in the
  third week of gestation

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• KEY TERMS
• Neuron nerve cell body extending from nerve
  cell body
• Axon single axon arises from most neurons.
  Conducts electrical signals from the initial
  segment to synaptic terminals. Many axons covered
  by myelin
• Dendrite receive incoming synaptic information
  from the environment (sensory neurons) or other
  neurons

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• KEY TERMS
• White matter refers to the aggregations of
  myelinated axons from many neurons
• Gray matter contains either nerve cell bodies
  and dendrites, or bundles of unmyelinated axons
• Tract bundle of fibers in the CNS. May run long
  distances along the spinal cord. Also exist in
  the brain connecting parts of the brain with each
  other and with the spinal cord.
• Ascending tracts
• Descending tracts
• Major tracts are often composed of myelinated
  fibers

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• PRE-EMBRYONIC PERIOD
• Zygote rapidly develops to form a hallow ball of
  cells (blastocyst) within the first week
• Blastocyst is differentiated into
• Trophectoderm
• Inner cell mass
• Blastocoel
• Blastocyst remains free within the cavity of the
  uterus from 2-4 days prior to attaching to the
  uterine lining

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• PRE-EMBRYONIC PERIOD
• Attachment of the blastocyst to the endometrium
  (implantation) occurs 7-8 days following
  fertilization
• Following implantation inner cell mass of the
  blastocyst begins to differentiate into three
  primary germ layers from which all tissues and
  organs of the body will develop
• Endoderm
• Mesoderm
• Ectoderm

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• EMBRYONIC PERIOD
• Development of the nervous system begins with a
  thickening of the ectoderm (neural plate)
• Plate folds inward and forms a longitudinal
  groove (neural groove)
• Neural tube is formed and eventually separates
  from the ectoderm (22-23 days)
• Cells of the wall that enclose the neural tube
  differentiates into three kinds of cellular layers

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• EMBRYONIC PERIOD
• When the neural tube is formed the anterior
  portion develops into three enlarged areas called
  vesicles
• Prosencephalon
• Mesencephalon
• Rhombencephalon
• The posterior portion does not expand and
  eventually becomes the spinal cord
• Ventricular system eventually develops

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• EMBRYONIC PERIOD
• As development progresses subdivision of the
  three primary vesicles results in five secondary
  vesicles
• Prosencephalon anterior telencephalon and
  posterior diencephalon
• Mesencephalon remains unchanged
• Rhombencephalon anterior metencephalon and
  posterior myelencephalon

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• EMBRYONIC PERIOD
• Ultimately
• Telencephalon develops into the cerebral
  hemispheres and basal ganglia
• Diencephalon develops into the thalamus,
  hypothalamus, and pineal gland
• Mesencephalon develops into the midbrain
• Metencephalon develops into the pons and
  cerebellum
• Myelencephalon develops into the medulla oblongata

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• EMBRYONIC PERIOD
• Brain folds or flexes on itself as it develops,
  resulting in the cerebral hemispheres eventually
  covering the midbrain, diencephalon, and
  hindbrain
• Cavities within the vesicles develop into the
  ventricles of the brain, whereas the fluid within
  them is cerebrospinal fluid
• Area of the neural tube posterior to the
  myelencephalon forms the spinal cord
• Embryonic period is also a period for development
  of basic organs and body systems formation

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• FETAL PERIOD
• Onset organ functions
• Time of growth and changes in proportion
• Maturation of organ functions

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• SPINAL CORD
• Area of the neural tube posterior to the
  myelencephalon thickens and gives rise to the
  spinal cord
• Initially, neural tube consists of
  neuroepithelium which gives rise to
• Neuroblasts
• Glioblasts
• Ependymal cells

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• SPINAL CORD
• Cells of the wall that encloses the neural tube
  eventually differentiates into
• Marginal layer (outer)
• Mantle layer
• Ependymal layer (inner)
• Two columns of cells extend cephalad and caudad
  in each plate becoming dorsal and ventral horns
  of gray matter
• Spinal cord initially fills entire length of
  vertebral canal, dura and spinal canal develop
  more quickly
• Nerve roots fill the lumbar and sacral vertebral
  canal
• Conus medullaris is anchored by an extension of
  pia to coccyx

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• CENTRAL NERVOUS SYSTEM MALFORMATIONS
• Most major CNS abnormalities and malformations
  result from defective neural tube formation
• Causes may be chromosomal or environmental
  resulting in mental retardation and other
  developmental problems
• CNS most vulnerable before many females are aware
  of pregnancy
• Malformations
• Meningocele, myelocele
• Hydrocephalic, ancephalic

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CENTRAL NERVOUS SYSTEM DEVELOPMENT

• REFERENCES
• Morgan, G.E., Mikhail, M.S., and Murray, M.J.
  (2006).
• Clinical Anesthesiology. (4th Ed.) New York, NY
• McGraw-Hill.
• Nagelhout, J.J. and Zaglaniczny, K.L. (2005).
  Nurse
• Anesthesia. (3rd Ed.) St. Louis, MO Elsevier-
• Saunders.
• Waxman, S.G. (2000). Correlative Neuroanatomy
  (24th ed.). New York, NYMcGraw-Hill.