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Functional Components of the Facial Nerve Human Gross Anatomy at

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					 The Facial Nerve:
Functional Components and
        Anatomy
Brief overview of cranial nerve functional components
•   The 12 cranial nerves participate in a total of seven neural functions. Each of
    these seven functions is designated by a three letter acronym.
•   The first letter is either G (General) or S (Special).
     – General refers to primitive and/or external structures of the body.
     – Special refers to senses unique to the head (taste, olfaction, hearing, vision, and
       balance) and to muscles of branchial arch derivatives.
•   The second letter is either S (Somatic) or V (Visceral).
     – Somatic refers to non-visceral structures including skin, muscles, tendons, joints,
       retina (vision), basilar membrane (hearing), and utricle/saccula (balance).
     – Visceral refers to organs of the body cavity, smooth muscle, vessels, and glands.
•   The third letter is either A (Afferent) or E (Efferent).
     – Afferent refers to flow of neural information toward the brain (sensation)
     – Efferent refers to flow of neural information toward the periphery (motor).
•   Knowledge of the functional components and the deficits that follow damage
    to each provides the basis of the thorough neurological exam.
            The Seven Functional Components
• GSA – General Somatic Afferent
   – Touch, temperature, and pain from non-visceral structures
• GSE – General Somatic Efferent
   – Motor to skeletal muscle
• GVA – General Visceral Afferent
   – Touch (distention), temperature, and pain from the viscera
• GVE – General Visceral Efferent
   – Motor to viscera, smooth muscle, and glands
• SSA – Special Somatic Afferent
   – Vision, hearing, and balance
• SSE – Doesn’t exist
• SVA – Special Visceral Afferent
  – Taste and olfaction
• SVE – Special Visceral Efferent
   – Motor to muscles derived from the branchial arches
The remainder of this tutorial focuses on the
functional nerve components contained within the
facial nerve:
  SVE
  GVA
  SVA
  GVE
  GSA

  These components, either alone or in combination, make up the
  facial nerve and its branches. An understanding of these
  components can serve as a template for understanding the other
  functional components. In addition, an understanding of the facial
  nerve and its components can be applied in clinical situations to
  help localize a patient’s defect.
  Functional Components Within Branches of the
                 Facial Nerve:

• Greater Superficial Petrosal Nerve (GSPN)
   – GVA, GVE, SVA
• Stapedial Nerve
   – SVE
• Chorda Tympani Nerve
   – GVE, SVA
• Posterior Auricular Nerve
   – SVE, GSA
• Facial Nerve (terminal branch)
   – SVE
          Anatomy of Facial Nerve Branches
• The facial nerve exits the posterior cranial fossa (PCF) at the internal
  acoustic meatus.
• Within the internal acoustic meatus the facial nerve enters the facial
  canal.
• The first branch of the facial nerve, the greater superficial petrosal nerve
  (GSPN) branches from the geniculate ganglion within the genu of the
  facial canal and enters the middle cranial fossa by way of the hiatus of
  the canal for the GSPN.
• The second branch of the facial nerve, the stapedial nerve, branches
  from the descending portion of the facial nerve and enters the middle
  ear.
• The third branch of the facial nerve, the chorda tympani nerve, branches
  from the descending portion of the facial nerve and enters the middle
  ear. Within the middle ear the chorda tympani nerve crosses the medial
  surface of the tympanic membrane. It then passes through the
  petrotympanic fissure to enter the infratemporal fossa.
• The descending portion of the facial nerve continues into the parotid
  region by way of the stylomastoid foramen.
The facial nerve exits the posterior cranial
fossa (PCF) at the internal acoustic
meatus.
Within the internal acoustic meatus the
facial nerve enters the facial canal.
The first branch of the facial nerve, the
greater superficial petrosal nerve (GSPN)
branches from the geniculate ganglion
within the genu of the facial canal and
enters the middle cranial fossa by way of
the hiatus of the canal for the GSPN.
The second branch of the facial nerve, the
stapedial nerve, branches from the
descending portion of the facial nerve and
enters the middle ear.
The third branch of the facial nerve, the
chorda tympani nerve, branches from the
descending portion of the facial nerve and
enters the middle ear. Within the middle
ear the chorda tympani nerve crosses the
medial surface of the tympanic membrane.
It then passes through the petrotympanic
fissure to enter the infratemporal fossa.
The descending portion of the facial nerve
continues into the parotid region by way of
the stylomastoid foramen.
         Functional components of the
            Facial Nerve (CN VII)
1.   • SVE (Special Visceral Efferent) — Motor to
       striated muscles derived from the 2 nd branchial
       arch.
2.   • GVA (General Visceral Afferent) — Sensory
       from visceral touch, temperature, and pain.
3.   • SVA (Special Visceral Afferent) — Taste
4.   • GVE (General Visceral Efferent) — Autonomic
       innervation to mucosal, lacrimal, and salivary
       glands.
5.   • GSA (General Somatic Afferent) — Sensory
       from somatic touch, temperature, and pain.
          SVE Component of the
              Facial Nerve
     The next 11 slides demonstrate innervation to
        muscles derived from the 2nd branchial arch:
1.   Stapedius muscle -- dampens movement of the
     ossicles (inserts on stapes of middle ear)
2.   Posterior auricular muscle -- posterior movement
     of pinna
3.   Stylohyoid muscle -- elevates hyoid bone
4.   Posterior belly of digastric -- elevates hyoid
     bone, depresses mandible
5.   Muscles of facial expression -- blinking, smiling,
     frowning, facial movements
1. The Stapedius muscle dampens movement of the ossicles
                              \
When a loud noise is heard by the ear:

• SVE sends a signal from the motor nucleus of the facial
  nerve, through the internal acoustic meatus, traveling
  through the facial canal until exiting into the middle ear
  via the stapedial nerve.

• In the middle ear the stapedius muscle dampens
  movement of the ossicles, protecting the inner ear from
  damage from loud noises.
2. The Posterior Auricular nerve innervates the posterior
                              \
auricular muscle, pulling the pinna posteriorly.

• SVE sends a signal from the motor nucleus of the facial
  nerve, through the internal acoustic meatus, traveling
  through the facial canal until exiting at the stylomastoid
  foramen.

• After exiting the stylomastoid foramen the posterior
  auricular nerve branches from the facial nerve and via
  the SVE component of the posterior auricular nerve the
  posterior auricular muscle pulls the pinna posteriorly.
3. The Stylohyoid muscle elevates the hyoid bone
                              \
• SVE sends a signal from the motor nucleus of the facial
  nerve, through the internal acoustic meatus, traveling
  through the facial canal until exiting at the stylomastoid
  foramen.

• After exiting the stylomastoid foramen the stylohyoid
  branch of the facial nerve innervates the stylohyoid
  muscle.

• The Stylohyoid muscle elevates the hyoid bone.
4. The Posterior belly of digastric muscle elevates the
   hyoid bone                 \
• SVE sends a signal from the motor nucleus of the facial
  nerve, through the internal acoustic meatus, traveling
  through the facial canal until exiting at the stylomastoid
  foramen.

• After exiting the stylomastoid foramen the Posterior belly
  of the digastric branch of the facial nerve innervates the
  posterior belly of the digastric muscle.

• The posterior belly of digastric muscle elevates the hyoid
  bone
5. The next six slides demonstrate SVE innervation to
the muscles of facial expression*
   A.    Temporal branch (with zygomatic branch) innervates orbicularis
        oculi--closes eyelids

   B.   Zygomatic branch (with buccal branch) innervates zygomaticus
        major--smiling

   C.   Buccal branch innervates
        buccinator--tenses cheek

   D.   Mandibular branch innervates depressor angularis oris--frowning

   E.   Cervical branch innervates platysma -- lowers mandible, tenses
        skin of anterior neck

   *These are key innervations to the muscles of facial expression.
   However, each nerve branch innervates multiple muscles and each
   muscle receives multiple nerve branches.
A. The temporal and zygomatic branches of the facial
                                \
  nerve provide SVE nerve fibers that innervate the
  ipsilateral orbicularis oculi, the muscle responsible for
  closing the eyelid.

 • SVE sends a signal from the motor nucleus of the facial
   nerve, through the internal acoustic meatus, traveling
   through the facial canal until exiting at the stylomastoid
   foramen.

 • After exiting the stylomastoid foramen the temporal and
   zygomatic branches of the facial nerve innervate the
   orbicularis oculi muscle.

 • Contraction of orbicularis oculi causes the eyelid to
   close.
B. The zygomatic and buccal branches of the facial nerve
                               \
  innervate the ipsilateral zygomaticus major muscle, the
  main muscle responsible for smiling.


 • SVE sends a signal from the motor nucleus of the facial
   nerve, through the internal acoustic meatus, traveling
   through the facial canal until exiting at the stylomastoid
   foramen.

 • After exiting the stylomastoid foramen the zygomatic and
   buccal branches of the facial nerve innervate the
   zygomaticus major muscle.

 • Contraction of the zygomaticus major muscle causes
   smiling.
C. The buccal branch of the facial nerve innervates the
                               \
  buccinator muscle, the muscle responsible for holding
  the cheek against the teeth, thus positioning food for
  chewing.

 • SVE sends a signal from the motor nucleus of the facial
   nerve, through the internal acoustic meatus, traveling
   through the facial canal until exiting at the stylomastoid
   foramen.

 • After exiting the stylomastoid foramen the buccal branch
   of the facial nerve innervates the buccinator muscle.

 • Contraction of the buccinator muscle causes tensing of
   the cheek which helps position food within the occusal
   plane for chewing
D. The mandibular and buccal branches of the facial nerve
                               \
  innervate the ipsilateral depressor angularis oris muscle,
  a muscle responsible for frowning.


 • SVE sends a signal from the motor nucleus of the facial
   nerve, through the internal acoustic meatus, traveling
   through the facial canal until exiting at the stylomastoid
   foramen.

 • After exiting the stylomastoid foramen the mandibular
   branch of the facial nerve innervates the depressor
   angularis oris muscle.

 • Contraction of the depressor angularis oris muscle
   causes frowning.
E. The cervical branch of the facial nerve innervates the
                               \
  platysma muscle, a muscle partly responsible for
  depressing the mandible.


 • SVE sends a signal from the motor nucleus of the facial
   nerve, through the internal acoustic meatus, traveling
   through the facial canal until exiting at the stylomastoid
   foramen.

 • After exiting the stylomastoid foramen the cervical
   branch of the facial nerve innervates the platysma
   muscle.

 • Contraction of the platysma muscle results in depression
   of the mandible.
E. The cervical branch of the facial nerve innervates the
                                \
   platysma muscle (the ―shaving muscle‖), a muscle
   responsible for tightening the skin of the anterior neck.


 • SVE sends a signal from the motor nucleus of the facial
   nerve, through the internal acoustic meatus, traveling
   through the facial canal until exiting at the stylomastoid
   foramen.

 • After exiting the stylomastoid foramen the cervical
   branch of the facial nerve innervates the platysma
   muscle.

 • Contraction of the platysma muscle causes the skin of
   the anterior neck to tighten.
                        Summary of SVE
1. A nerve signal is transmitted from the facial nucleus, through the internal
    acoustic meatus, to the middle ear where stapedius muscle contraction
    dampens movement of the ossicles.
2. A nerve signal is transmitted from the facial nucleus, through the internal
    acoustic meatus, through the stylomastoid foramen to the temporal
    (orbicularis oculi closes eyelids), zygomatic (zygomaticus major muscle
    partly responsible for smiling), buccal (buccinator tenses cheek), mandibular
    (depressor angularis oris responsible for frowning), and cervical (platysma
    helps lower mandible and tightens skin of neck) branches of the facial
    nerve.
3. A nerve signal is transmitted from the facial nucleus, through the internal
    acoustic meatus, through the stylomastoid foramen, to the posterior belly of
    the digastric muscle, which elevates the hyoid bone.
4. A nerve signal is transmitted from the facial nucleus, through the internal
    acoustic meatus, through the stylomastoid foramen, to the stylohyoid
    muscle, which elevates the hyoid bone.
5. A nerve signal is transmitted from the facial nucleus, through the internal
    acoustic meatus, through the stylomastoid foramen, to the posterior
    auricular muscle, which is responsible for posterior displacement of the
    pinna.
    GVA Component of the
        Facial Nerve
The next slide demonstrates that GVA is
   responsible for providing:
1. Light touch, temperature, and pain
   sensation from the soft palate via the
   greater superficial petrosal nerve
   (GSPN).
1. GVA provides sensation of light touch,
temperature, and pain from the soft palate.
    When the soft palate encounters an extreme temperature,
    is touched lightly, or is subject to a painful stimulus:
•   A nerve signal is sent via the GVA component through
    the lesser palatine canal. The GVA component then
    becomes part of the GSPN.
•   As part of the GSPN the GVA component travels to the
    lacerate foramen, and then through the hiatus of the
    canal of the GSPN.
•   At the geniculate ganglion, the GVA component
    becomes part of the facial nerve.
•   The nerve signal travels along the GVA component of
    the facial nerve and passes through the internal acoustic
    meatus. After passing through the internal acoustic
    meatus the nerve signal from the soft palate reaches the
    brainstem.
                  Summary of GVA

• A nerve signal is transmitted through the lesser palatine
  canal, to the lacerate foramen, through the hiatus of the
  canal of the greater superficial petrosal nerve, and
  through the internal acoustic meatus to provide light
  touch, temperature, and pain from the soft palate.
   SVA Component of the
       Facial Nerve
The next two slides demonstrate that SVA
   is responsible for providing:
1. Taste from the hard and soft palate via
   the greater superficial petrosal nerve
   (GSPN).
2. Taste from the anterior 2/3 of the
   tongue via the chorda tympani nerve.
1. SVA provides taste sensation from the hard and
            soft palate via the GSPN.
     When food or drink, such as coffee sweetened with
     sugar, comes in contact with the hard and soft
     palate:
 •   A nerve signal is sent via the SVA component
     through the lesser palatine canal. The SVA
     component then becomes part of the GSPN.
 •   As part of the GSPN the SVA component travels to
     the lacerate foramen, and then through the hiatus of
     the canal of the GSPN.
 •   At the geniculate ganglion, the SVA component
     becomes part of the facial nerve.
 •   The nerve signal travels along the SVA component of
     the facial nerve and passes through the internal
     acoustic meatus. After passing through the internal
     acoustic meatus the nerve signal from the hard and
     soft palate reaches the brainstem.
2. SVA provides taste to the anterior 2/3 of the
    tongue via the chorda tympani nerve.
    When a drink or food item, such as a lollipop, comes
    in contact with the anterior 2/3 of the tongue:
•   A nerve signal is sent via the SVA component.
•   Fibers from the SVA component then join with fibers
    from the GVE component to form the chorda tympani
    nerve.
•   The chorda tympani nerve passes through the
    petrotympanic fissure and across the medial surface
    of the tympanic membrane.
•   The chorda tympani nerve fibers then become part of
    the facial nerve. As part of the facial nerve the SVA
    fibers pass through the internal acoustic meatus.
    After passing through the internal acoustic meatus
    the nerve signal from the anterior 2/3 of the tongue
    reaches the brainstem.
         Summary of SVA Pathways

1.   A nerve signal is transmitted through the greater and
     lesser palatine canals, to the lacerate foramen,
     through the hiatus of the canal of the greater
     superficial petrosal nerve, and through the internal
     acoustic meatus to provide taste from the hard and
     soft palate.
2.   A nerve signal is transmitted through the
     petrotympanic fissure and through the internal
     acoustic meatus to provide taste from the anterior 2/3
     of the tongue.
     GVE Component of the
         Facial Nerve
1. Via   the pterygopalatine ganglion GVE provides:
    A.   Lacrimation (tearing of the eye)
    B.   Mucus secretions of the nasal cavity
    C.    Mucus secretions of the oral cavity

2. Via innervation of the submandibular ganglion
    GVE provides:
    A. Salivation of the oral cavity
1. The GVE component of the facial nerve transmits preganglionic
fibers to the pterygopalatine ganglion via the GSPN. From the
pterygopalatine ganglion postganglionic fibers cause ipsilateral
lacrimation and mucus secretions of the nasal and oral cavities.

•   GVE fibers send a signal from the lacrimal nucleus,
    through the internal acoustic meatus. The nerve signal
    travels along the GVE component of the facial nerve

•   At the geniculate ganglion the nerve signal travels
    along preganglionic GVE fibers of the GSPN to the
    Vidian nerve and to the pterygopalatine ganglion.

•   From the pterygopalatine ganglion postganglionic GVE
    fibers carry the nerve signal to cause ipsilateral tearing
    of the eye, mucus secretions of the nasal cavities, and
    mucus secretions of the hard and soft palate.
2. The GVE component of the facial nerve transmits preganglionic
fibers to the submandibular ganglion via the chorda tympani nerve.
From the submandibular ganglion postganglionic fibers innervate the
submandibular and sublingual glands, causing salivation.
•   GVE sends a signal from the superior salivary nucleus,
    through the internal acoustic meatus. The nerve signal
    travels along the GVE component of the facial nerve.
•   At the point that the chorda tympani nerve branches
    from the facial nerve the nerve signal travels along
    preganglionic GVE fibers of the chorda tympani nerve,
    through the petrotympanic fissure, to the
    submandibular ganglion.
•   From the submandibular ganglion postganglionic GVE
    fibers carry the nerve signal to cause salivation from
    the submandibular and sublingual glands.
                    Summary of GVE
1.   From the superior salivary and lacrimal nucleus a nerve
     signal is transmitted through the internal acoustic meatus,
     through the hiatus of the canal of the GSPN, to the lacerate
     foramen, and through the pterygoid canal to the
     pterygopalatine ganglion. From the pterygopalatine
     ganglion postganglionic GVE fibers provide lacrimation of
     the eyes and mucus secretion of the nasal cavity and oral
     cavity.
2.   From the superior salivary and lacrimal nucleus a nerve
     signal is transmitted through the internal acoustic meatus
     and through the petrotympanic fissure to the submandibular
     ganglion. From the submandibular ganglion postganglionic
     GVE fibers provide salivation in the oral cavity.
     GSA Component of the
         Facial Nerve
GSA is responsible for providing:

  1. Touch, temperature, and pain sensation from
  part of the external acoustic meatus via the
  posterior auricular nerve.
    1. GSA provides touch, temperature, and pain
     sensation from the external acoustic meatus.
    When the external acoustic meautus encounters an
    extreme temperature, is touched, or is subject to a
    painful stimulus:
•   A nerve signal is sent via the GSA component of the
    posterior auricular nerve.
•   The nerve signal continues to travel along the GSA
    component as part of the descending portion of the facial
    nerve and passes through the stylomastoid foramen.
•   From the stylomastoid foramen the nerve signal
    continues to travel along the GSA component of the
    facial nerve and passes through the internal acoustic
    meatus.
•    After passing through the internal acoustic meatus the
    nerve signal from the external acoustic meatus reaches
    the brainstem.
              Summary of GSA

• A nerve signal is transmitted from the external
  acoustic meatus, through the stylomastoid
  foramen, and through the internal acoustic
  meatus to provide touch, temperature, and pain
  sensation from the external acoustic meatus.
Summary of functional components
• Each of the five functional components of the
  facial nerve SVE, GVA, SVA, GVE, and GSA
  have a unique function. Knowledge of these
  functional components can be applied to clinical
  observations to aid in localizing lesions of nerve
  branches or at anatomical landmarks.
• The following slides provide examples of how
  lesions at different locations can effect function.
              Lesion #1

One effect of a lesion located between the
branching of of the stapedial nerve and the
branching of the chorda tympani nerve would be
paralysis of facial muscles.
              Lesion #2

Another effect of a lesion located between the
branching of the stapedial nerve and the
branching of the chorda tympani nerve would be
loss of taste of anterior 2/3 of the tongue.
                Lesion #3

One effect of a lesion located at the stylomastoid
foramen would be partial loss of sensation of the
external acoustic meatus.
              Lesion #4

A lesion located between the branching of the
GSPN and the branching of the stapedial nerve
will spare taste of the hard palate.
               Lesion #5

A lesion located between the branching of the
GSPN and the branching of the stapedial nerve
will also spare light touch sensation from the soft
palate.
                Thank You
Return to SVE     Return to GVA        Return to SVA




          Return to GVE      Return to GSA



                   Return to Lesions
                      Incorrect
The GVA component of the GSPN, which is spared by this lesion,
   is responsible for providing sensation from the soft palate.




                         Please try again
                        Incorrect
   The stapedial nerve (SVE), which is spared by this lesion, is
responsible for protecting the ear from increased sensitivity to loud
                               noises.




                            Please try again
                     Incorrect
The SVA component of the GSPN, which is spared by this lesion,
    is responsible for providing taste from the hard palate.




                        Please try again
                      Incorrect
The GVA component of the GSPN, which is spared by this lesion,
   is responsible for providing light touch from the soft palate.




                          Please try again
                     Incorrect
The SVA component of the GSPN, which is spared by this lesion,
     is responsible for providing taste from the soft palate.




                        Please try again
                     Incorrect
The GVA component of the GSPN, which is spared by this lesion,
    is responsible for providing temperature sensation from
                          the soft palate.




                         Please try again
                      Incorrect
The GVA component of the GSPN, which is spared by this lesion,
   is responsible for providing light touch from the soft palate.




                          Please try again
                     Incorrect
The GVE component of the chorda tympani nerve, which is spared
      by this lesion, is responsible for providing salivation
                          of the oral cavity.




                         Please try again
                        Incorrect
   The stapedial nerve (SVE), which is spared by this lesion, is
responsible for protecting the ear from increased sensitivity to loud
                               noises.




                            Please try again
                       Incorrect
This lesion will not spare taste to the anterior 2/3 of the tongue,
which is supplied via the SVA component of the chorda tympani
                              nerve.




                           Please try again
                      Incorrect
This lesion will not spare salivation of the oral cavity, which is
supplied by the GVE component of the chorda tympani nerve.




                          Please try again
                      Incorrect
This lesion will not spare ipsilateral facial expression, which is
supplied by the temporal, zygomatic, buccal, mandibular, and
          cervical branches of the facial nerve (SVE).




                          Please try again
                        Incorrect
This lesion will not spare the ability to smile, which is supplied by
         the zygomatic branch of the facial nerve (SVE).




                           Please try again
                         Incorrect
This lesion will not spare the ability to taste from the anterior 2/3 of
the tongue, which is supplied by the SVA component of the chorda
                            tympani nerve.




                             Please try again
                        Incorrect
This lesion will not spare the ability to smile, which is supplied by
         the zygomatic branch of the facial nerve (SVE).




                           Please try again
                      Incorrect
This lesion will not spare the ability to protect the ear from loud
    noises, which is supplied by the stapedial nerve (SVE).




                          Please try again
                Correct!
A lesion here will cause paralysis of facial muscles due
        to its disruption of the SVE component.




        Go back to question 1        Next question
                     Correct!
A lesion here will cause a loss of taste to the anterior 2/3 of the
     tongue due to the disruption of the SVA component of
                    the chorda tympani nerve.




           Go back to question 2          Next question
                      Correct!
   A lesion here will cause partial loss of sensation (light touch,
  temperature, and pain) of the external acoustic meatus due to
disruption of the GSA component of the posterior auricular nerve.




           Go back to question 3        Next question
                         Correct!
 A lesion here will spare a person’s ability to taste on the hard and soft
palate because the SVA component of the Greater Superficial Petrosal
                      Nerve (GSPN) remains intact.




               Go back to question 4         Next question
                        Correct!
A lesion here will spare the sensation of light touch of the soft palate
     because the GVA component of the GSPN remains intact.




              Go back to question 5           Continue

				
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