Brain and Cranial Nerves

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					    BIOLOGY 2401
       PART I
   CHAPTER 12 &13
 The Brain and the Cranial Nerves
Regions and Organization of the Brain
  • The basic parts of the brain are as follows:
     – The cerebrum
     – The diencephalon
     – The brain stem
     – The cerebellum
  • The brain is organized into groupings of cell bodies
    (the gray matter) and fibers (the white matter).
  • The cerebrum & the cerebellum contain gray matter
    on the outer edges w/white matter below this surface.
  • While the diencephalon & brain stem have the white
    matter superficially surrounding internal pockets of
    gray matter
• More than 80% of the human brain’s weight is the
• The cerebrum is divided into left and right hemispheres
  by the longitudinal fissure.
• The cell bodies in the outer cortex require more surface
  area than the underlying white matter which results in
  much folding.
   – The upfoldings are called gyri (gyrus, singular).
   – The infoldings are called sulci (sulcus, singular).
• A few of the sulci divide the the hemispheres further into
  four major lobes named for neighboring cranial bones:
   – The frontal lobe
   – The parietal lobe
   – The occipital lobe
   – The temporal lobe
Lateral View of the Cerebrum
            Other parts:
• The diencephalon:
  – The epithalamus
  – The thalamus
  – The hypothalamus
• The brain stem
  – The midbrain
  – The pons
  – The medulla oblongata
• The cerebellum
Protection of the Central Nervous System
• The brain and spinal cord are a very delicate set of
  organs which are easily damaged by pressure or blows.
• The CNS is protected by a set of structures:
   – The axial skeleton
      • cranium and vertebrae
   – The meninges
   – The cerebrospinal fluid
   – The blood brain barrier
                   The Meninges
• The meninges are a set of three connective tissue layers
  that surround the brain and spinal cord.
   – The dura mater – toughest and outermost
   – The arachnoid mater – middle layer containing most
     major blood vessels and cerebrospinal fluid.
   – The pia mater – innermost layer with fine blood vessels.
      Cerebrospinal Fluid (CSF)
• Cerebrospinal Fluid is produced from blood plasma.
• CSF is found within and all around the brain to protect
  it and make it more buoyant.
• Because the CSF circulates through and around both
  the brain and the spinal cord, samples may be
  retrieved using a lumbar puncture (spinal tap).
• The CSF is produced by the choroid plexus withing the
  ventricles of the brain.
Ventricles of the Brain
Cranial Nerves (PNS from the neck up)
  • 12 major nerves leave the brain before the spinal cord
  • These are part of the Peripheral Nervous System (PNS)
  • They are numbered I-XII
                Cranial Nerves
•   I. Olfactory      •   VII. Facial
•   II. Optic         •   VIII. Vestibulocochlear
•   III. Oculomotor   •   IX. Glossopharyngeal
•   IV. Trochlear     •   X. Vagus
•   V. Trigeminal     •   XI. Accessory
       • Ophthalmic   •   XII. Hypoglossal
       • Maxillary
       • Mandibular
• VI. Abducens
      Cranial Nerve I: Olfactory
• Function: purely sensory - carrying afferent impulses for
  the sense of smell
• Exit: Cribriform Foramina
         Cranial Nerve II: Optic
• Arises from the
  retina of the eye
• Function:
  sensory - solely
  for vision
• Exits through
  optic canal
     Cranial Nerve III: Oculomotor
• Function: primarily motor
  - raises the eyelid,
  directs the eyeball,
  constricts the iris, and
  controls lens shape
• Exit: superior orbital
      Cranial Nerve IV: Trochlear
• Function: Primarily a motor nerve that directs the eyeball
• Exit: superior orbital fissure
    Cranial Nerve V: Trigeminal
• Trigeminal means the three twins
• It is composed of 3 divisions:
         • ophthalmic (V1)
         • maxillary (V2)
         • mandibular (V3)
• Function: both sensory and motor
   – Conveys sensory impulses from various areas of the
       face (V1) and (V2), and supplies motor fibers (V3) for
• Exits:
         superior orbital fissure (V1)
         foramen rotundum (V2)
         foramen ovale (V3)
Cranial Nerve V: Trigeminal
      Cranial Nerve VI: Abducens
• Function: Primarily a motor nerve innervating the lateral
  rectus muscle (abducts the eye)
• Exit: superior orbital fissure

                                                 Figure VI from Table 13.2
           Cranial Nerve VII: Facial
• Function: both sensory and motor
   – Motor functions include facial expression, and the
     transmittal of autonomic impulses to lacrimal and salivary
   – Sensory function is in taste
• Exits: internal acoustic meatus and the stylomastoid foramen
  Cranial Nerve VIII: Vestibulocochlear
• Function: Purely Sensory
• Sensory fibers arise from the equilibrium and hearing apparatus
  of the inner ear
• Two divisions – vestibular (balance) and cochlear (hearing)
• Exit: internal acoustic meatus
   Cranial Nerve IX: Glossopharyngeal
• Function: Both motor and
   – Motor – innervates part of
     tongue & pharynx, and
     provides motor fibers to
     the parotid salivary gland
   – Sensory – fibers conduct
     taste and general sensory
     impulses from the tongue
     and pharynx
• Exit: jugular foramen
         Cranial Nerve X: Vagus
• The only cranial nerve that extends beyond the head and
  neck – the “wanderer”
• The vagus is a mixed nerve
   – Most motor fibers are parasympathetic fibers to the
     heart, lungs, and visceral organs
   – Its sensory function is in taste
• Exit: jugular foramen
Cranial Nerve X:
    Cranial Nerve XI: Accessory
• Primarily a motor nerve
   – Supplies fibers to the larynx, pharynx, & soft palate
   – Innervates the trapezius and sternocleidomastoid,
     which move the head and neck
• Exit: jugular foramen
      Cranial Nerve XII: Hypoglossal
• Function: primarily motor
• Innervates muscles of the tongue, which contribute to
  swallowing and speech
• Exit: hypoglossal canal
Practice Questions
Which of the following cranial nerves is not
   involved with the eye?
A. Oculomotor
B. Trochlear
C. Optic
D. Abducens
E. Trigeminal
Which of the following cranial nerves is
   purely sensory?
A. Accessory
B. Vagus
C. Trigeminal
D. Optic
E. Hypoglossal
Which of the following cranial nerves has a
   name that means "the wanderer"?
A. Vestibulocochlear
B. Glossopharyngeal
C. Trochlear
D. Trigeminal
E. Vagus
Cranial nerves are formed by fusion of
 sensory and motor roots.

Nerves are either sensory or motor but not

The cranial nerves serve structures only in
 the head and neck.

               Frontal lobe
               Parietal lobe
               Temporal lobe
               Occipital lobe


Diencephalon   Thalamus



 Brain Stem    Pons

               Medulla Oblongata

S   I. Olfactory           Cribriform foramina
S   II. Optic              Optic Canal
M   III. Oculomotor        Superior Orbital Fissure
M   IV. Trochlear          Superior Orbital Fissure
B   V. Trigeminal          S.O.F., F. Rotundum, F. Ovale
M   VI. Abducens           Superior Orbital Fissure
    VII. Facial            Internal acoustic meatus, Stylomastoid
S   VIII.Vestibulocochlear Internal Acoustic Meatus
B   IX. Glossopharyngeal Jugular Foramen
B   X. Vagus               Jugular Foramen
M   XI. Accessory          Jugular Foramen
M   XII. Hypoglossal       Hypoglossal

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