NEUROLOGICAL SYSTEM PART II

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NEUROLOGICAL SYSTEMPART II

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

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CEREBRALANATOMY AND PHYSIOLOGY

• OBJECTIVES
• Identify gross anatomical features of the brain.
• Discuss functions associated with membranes of
  the cranial meninges.
• Describe significant aspects of arterial cerebral
  vascularization.
• Explain cerebral perfusion pressure and
  autoregulation associated with cerebral blood
  flow.
• List divisions of the brain and specific
  functions related to each division.
• Discuss significant differences between gray and
  white matter.

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CEREBRALANATOMY AND PHYSIOLOGY

• INTRODUCTION
• Brain weighs 1300 Gms
• Divided into four principle parts
• Brain stem
• Diencephalon
• Cerebrum
• Cerebellum
• Brain is protected by cranial bones, cranial
  meninges, and CSF

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CEREBRALANATOMY AND PHYSIOLOGY

• INTRODUCTION
• Brain stem consists of the medulla oblongata,
  pons, and midbrain. Lower end is a continuation
  of the spinal cord.
• Diencephalon consists primarily of the thalamus
  and hypothalamus
• Cerebrum spreads over the diencephalon and
  occupies most of the cranium
• Inferior to the cerebrum and posterior to the
  brain stem is the cerebellum
• Cranial meninges surround the brain and are
  continuous with the spinal meninges

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL BONES
• Frontal bone forms the forehead, roofs of the
  orbits, and most of the anterior portion of the
  cranial floor
• Parietal bones form greater portion of the sides
  and roof of the cranial cavity
• Temporal bones form inferior sides of cranium and
  part of the cranial floor

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL BONES
• Occipital bone forms posterior part and
  significant portion of the base of the cranium
• Sphenoid bone is situated at the middle part of
  the base of the skull and articulates with all
  other cranial bones
• Ethmoid bone is principle supporting structure of
  the nasal cavities. Forms part of the anterior
  portion of the cranial floor, medial wall of the
  orbits, superior portions of the nasal septum,
  and most of the sidewalls of the nasal roof

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL BONES
• Four prominent skull sutures are immovable joints
  found only between skull bones and contain very
  little connective tissue
• Coronal suture
• Sagittal suture
• Lambdoidal suture
• Squamosal suture

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL BONES
• At birth fontanels, membrane-filled spaces found
  between cranial bones, will eventually be
  replaced by bone
• Anterior (frontal) fontanel
• Posterior (occipital) fontanel
• Anterolateral (sphenoidal) fontanel
• Posterolateral (mastoid) fontanel

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL MENINGES
• Three membranes envelope the brain
• Dura (outermost layer)
• Arachnoid
• Pia (innermost layer)

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL MENINGES
• Dura
• Tough fibrous structure containing an inner
  (meningeal) layer and outer (periosteal) layer
• Most of the duras venous sinuses lie between the
  dural layers
• Dural layers are generally fused, except where
  they separate to provide space for the venous
  sinuses and where the inner layer forms septa
  between the brain portions
• Outer layer firmly attached to inner surface of
  cranial bones inner layer continuous with spinal
  dura

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL MENINGES
• Arachnoid
• Delicate avascular membrane covers the
  subarachnoid space
• Between the arachnoid and dura mater lies the
  subdural space
• Arachnoid granulations project into the superior
  sagittal sinus
• Subarachnoid space between the arachnoid and the
  pia is relatively narrow over the surface of the
  cerebral hemisphere and is much wider at areas at
  the base of the brain

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CEREBRALANATOMY AND PHYSIOLOGY

• CRANIAL MENINGES
• Pia
• Thin connective tissue membrane that covers the
  brain surface and extends into sulci and fissures
  and around blood vessels throughout the brain
• Invaginations of the pia form choroid plexuses of
  the ventricles
• Clinical considerations
• Various types of lesions, malformations, or
  pathology may present in one or more intracranial
  compartments

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CEREBRALANATOMY AND PHYSIOLOGY

• CEREBRAL VASCULARIZATION
• 18 of total blood volume circulates in the
  brain
• Brain is responsible for 20 of total body oxygen
  consumption
• Constant flow of oxygen must be maintained
• Loss of consciousness occurs in less than 15
  seconds
• Irreparable damage occurs within 5 minutes
• Cerebrovascular disease occurs as a result of
  vascular compromise or hemorrhage in the central
  nervous system

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CEREBRALANATOMY AND PHYSIOLOGY

• ARTERIAL SUPPLY OF THE BRAIN
• Extra cerebral vessels R carotid artery arises
  from R subclavian, L carotid artery arises from
  aortic arch
• Intracranial cerebral vessels internal carotid
  artery divides into anterior cerebral and middle
  cerebral arteries
• Two vertebral arteries (arising from the
  subclavian arteries) join to form the basilar
  artery which gives rise to the posterior cerebral
  artery supplying occipital lobes and brain stem

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CEREBRALANATOMY AND PHYSIOLOGY

• ARTERIAL SUPPLY OF THE BRAIN
• Circle of Willis is a confluence of vessels that
  gives rise to all major cerebral arteries
• It is fed by the paired internal carotid arteries
  and the basilar artery
• When the circle is complete, it contains a
  posterior communicating artery on each side and
  an anterior communicating artery
• Each major artery supplies a certain territory
• Sudden occlusion affects its territory
  immediately, sometimes irreversibly

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CEREBRALANATOMY AND PHYSIOLOGY

• REGULATION OF CEREBRAL BLOOD FLOW
• Cerebral perfusion pressure is the difference
  between mean arterial pressure and intracranial
  pressure
• CPP MAP ICP
• CPP is normally 80-100 mm Hg
• CPP values less than 50 mm Hg often show slowing
  on EEG
• CPP values between 25-40 mm Hg typically flat EEG
• Sustained CPP less than 25 mm Hg results in
  irreversible damage

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CEREBRALANATOMY AND PHYSIOLOGY

• REGULATION OF CEREBRAL BLOOD FLOW
• Autoregulation
• CBF remains nearly constant between MAP of 60-160
  mm Hg
• Pressures greater than 150-160 mm Hg can disrupt
  the blood brain barrier
• Extrinsic mechanisms influencing cerebral blood
  flow
• Respiratory gas tensions
• Temperature
• Viscosity
• Autonomic influences

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CEREBRALANATOMY AND PHYSIOLOGY

• VENOUS DRAINAGE
• Venous drainage of the brain and coverings
  includes veins of the brain itself, dural venous
  sinuses, duras meningeal veins, and diploic
  veins
• Eventual cerebral venous drainage is the internal
  jugular vein
• Cerebral veins contain no valves

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CEREBRALANATOMY AND PHYSIOLOGY

• DIVISIONS OF THE BRAIN
• Develop from embryonic brain vesicles that form
  from the cranial end of the neural tube
• Consists of
• Brain stem
• Diencephalon
• Cerebrum
• Cerebellum

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CEREBRALANATOMY AND PHYSIOLOGY

• BRAIN STEM
• Medulla
• Relays motor and sensory impulses between other
  parts of the brain and spinal cord (some tracts
  decussate)
• Reticular formation functions in consciousness
  and arousal
• Contains vital reflex centers (heartbeat,
  breathing, and blood vessel diameter)
• Nonvital reflex centers coordinate swallowing,
  vomiting, coughing, sneezing, and hiccupping
• Contains nuclei of origin for CNs VIII, IX, X,
  XI, and XII
• Vestibular nuclear complex helps maintain
  equilibrium

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CEREBRALANATOMY AND PHYSIOLOGY

• BRAIN STEM
• Pons
• Relays impulses within the brain and between
  parts of the brain and the spinal cord
• Contains nuclei of origin for CNs V, VI, VII, and
  VIII
• Pneumotaxic and apneustic areas help regulate
  breathing
• Midbrain
• Relays motor impulses from cerebral cortex to
  pons and spinal cord and relays sensory impulses
  from spinal cord to thalamus
• Coordinates movement of eyeballs and head and
  trunk
• Contains nuclei of origin for CNs III and IV

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CEREBRALANATOMY AND PHYSIOLOGY

• DIENCEPHALON
• Thalamus
• Serves as relay station for all sensory impulses,
  except smell, to cerebral cortex
• Relays motor impulses from cerebral cortex to
  spinal cord
• Interprets pain, temperature, light touch, and
  pressure sensations
• Functions in emotions and memory
• Hypothalamus
• Controls and integrates the ANS, articulates with
  the pituitary gland, center for mind-over-body
  phenomena, rage and aggression, controls normal
  body temperature, food intake and thirst,
  maintains waking state and sleep

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CEREBRALANATOMY AND PHYSIOLOGY

• CEREBRUM
• Functional areas of cerebral cortex divided into
  sensory, motor, and association areas
• Sensory areas interpret sensory impulses, motor
  areas control muscular movement, and association
  areas function in emotional and intellectual
  processes
• Basal ganglia control gross muscle movements and
  regulate muscle tone
• Limbic system functions in emotional aspects of
  behavior related to survival
• Language contained in the left hemisphere in 90
  of the population, located in frontal (Brocas
  area), parietal, and temporal lobes

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CEREBRALANATOMY AND PHYSIOLOGY

• CEREBELLUM
• Second-largest portion of the brain, occupies
  inferior and posterior aspects of the cranial
  cavity
• Separated from the cerebrum by the transverse
  fissure and the tentorium cerebelli
• Controls subconscious skeletal muscle
  contractions required for coordination, posture,
  and balance
• Assumes a role in emotional development,
  modulating sensations of anger and pleasure

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CEREBRALANATOMY AND PHYSIOLOGY

• 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.