The Seventh Cranial Nerve


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The Seventh Cranial Nerve

  1. 1. ANATOMY AND PHYSIOLOGY  The facial nerve consists of a motor and a sensory part, the latter being frequently described under the name of the nervus intermedius (pars intermedii of Wrisberg).  The two parts emerge at the lower border of the pons in the recess between the olive and the inferior peduncle, the motor part being the more medial, immediately to the lateral side of the sensory part is the acoustic nerve. Plan of the facial and intermediate nerves and their communication with other nerves.
  2. 2. THE MOTOR PORTION  The motor root arises from a nucleus which lies deeply in the reticular formation of the lower part of the pons. This nucleus is situated above the nucleus ambiguus, behind the superior olivary nucleus, and medial to the spinal tract of the trigeminal nerve.  From this origin the fibers pursue a curved course in the substance of the pons. They first pass backward and medialward toward the rhomboid fossa, and, reaching the posterior end of the nucleus of the abducent nerve, run upward close to the middle line beneath the colliculus fasciculus.  At the anterior end of the nucleus of the abducent nerve they make a second bend, and run downward and forward through the pons to their point of emergence between the olive and the inferior peduncle.
  3. 3. THE MOTOR PORTION  The facial nerve is a predominantly motor nerve that innervates the muscles of facial expression and the muscles of the scalp and ear, as well as the buccinator, platysma, stapedius, stylohyoid, and posterior belly of the digastric.  It contains parasympathetic secretory fibers to the submandibular and sublingual salivary glands, the lacrimal gland and to the mucous membranes of the oral and nasal cavities which are conveyed through the chorda tympani nerve.
  4. 4. THE SENSORY PORTION  The sensory root arises from the genicular ganglion, which is situated on the geniculum of the facial nerve in the facial canal, behind the hiatus of the canal. The cells of this ganglion are unipolar, and the single process divides in a T- shaped manner into central and peripheral branches.  The central branches leave the trunk of the facial nerve in the internal acoustic meatus, and form the sensory root; the peripheral branches are continued into the chorda tympani and greater superficial petrosal nerves.  Entering the brain at the lower border of the pons between the motor root and the acoustic nerve, the fibers of the sensory root pass into the substance of the medulla oblongata and end in the upper part of the terminal nucleus of the glossopharyngeal nerve and in the fasciculus solitarius.
  5. 5. SENSORY FUNCTIONS:  It mediates taste from the anterior two-thirds of the tongue.  It also conveys exteroceptive sensation from the eardrum and external auditory canal, proprioceptive sensation from the muscles it supplies, and general visceral sensation from the salivary glands and mucosa of the nose and pharynx.
  7. 7. Branches of Communication  In the internal acoustic meatus……………………..  At the genicular ganglion…………………  In the facial canal……..  At its exit from the stylomastoid foramen……  Behind the ear…………  On the face……….  In the neck…………  With the acoustic nerve.  With the sphenopalatine ganglion by the greater superficial petrosal nerve.  With the otic ganglion by a branch which joins the lesser superficial petrosal nerve.  With the sympathetic on the middle meningeal artery.  With the auricular branch of the vagus.  With the glossopharyngeal.  With the vagus.  With the great auricular.  With the auriculotemporal.  With the lesser occipital.  With the trigeminal.  With the cutaneous cervical.
  8. 8. Branches of Distribution  With the facial canal………  At its exit from the stylomastoid foramen………  On the face…  Nerve to the Stapedius muscle.  Chorda tympani.  Posterior auricular.  Digastric.  Stylohyoid.  Temporal.  Zygomatic.  Buccal.  Mandibular.  Cervical.
  9. 9. Muscles of the Face, Their Actions, and Innervations
  10. 10. NERVE BRANCH MUSCLE INNERVATIONS MUSCLE ACTION Temporal branch FRONTALIS Raises eyebrows and skin over the root of the nose; draws scalp forward, throwing forehead into transverse wrinkles CORRUGATOR (CORRUGATOR SUPERCILII) Draws eyebrow down and medially, produces vertical wrinkles in the forehead (the frowning muscle) UPPER PART OF THE ORBICULARIS OCULI (ORBICULARIS PALPEBRARUM) Eyelid sphincter; palpebral portion narrows palpebral fissure and gently closes eyelids; orbital portion draws skin of forehead, temple, and cheek toward medial orbit, pulls eyebrow down, draws skin of cheek up; closes eye firmly OCCIPITALIS Draws scalp backwards PROCERUS (PYRAMIDALIS NASI) Draws medial eyebrow downward, produces transverse wrinkles over bridge of nose
  11. 11. NERVE BRANCH MUSCLE INNERVATIONS MUSCLE ACTION Zygomatic Lower and lateral orbicularis oculi Eyelid sphincter Buccal Orbicularis oculi Buccinator Zygomaticus Nasalis Levator anguli oris Levator labii superioris (quadratus labii superioris) Eyelid sphincter. Compresses cheeks, , keeps food under pressure of cheeks in chewing. Draws mouth backward and upward. Depresses cartilaginous portion of nose, draws the ala toward septum. Raises angle of mouth. Elevates upper lip, dilates nostril
  12. 12. NERVE BRANCH MUSCLE INNERVATIONS MUSCLE ACTION Mandibular LOWER PART OF THE ORBICULARIS ORIS Sphincter of the mouth; closes lips; superficial fibers protrude lips; deep fibers draw lips in and press them against teeth. MENTALIS Protrudes lower lip, wrinkles skin of chin. RISORIUS Retracts angle of mouth TRIANGULARIS DEPRESSOR LABII INFERIORIS. Depresses angle of mouth Draws lower lip downward and lateralward. Cervical PLATYSMA Pulls lower lip and angle of mouth down; depresses lower jaw; raises and wrinkles skin of neck
  13. 13. CLINICAL EXAMINATION  Examination of the Motor Functions  Examination of facial nerve motor functions centers on assessment of the actions of the muscles of facial expression.  Note the tone of the muscles of facial expression, and look for atrophy and fasciculations.  Note the resting position of the face and whether there are any abnormal muscle contractions.  Note the pattern of spontaneous blinking for frequency and symmetry. A patient with parkinsonism may have infrequent blinking and an immobile, expressionless, “masked” face. Facial dystonia causes an abnormal fixed contraction of a part of the face, often imparting a curious facial expression. Progressive supranuclear palsy may cause a characteristic facial dystonia with knitting of the brows and widening of the palpebral fissures.
  14. 14.  Synkinesias are abnormal contractions of the face, often subtle, synchronous with blinking or mouth movements; they suggest remote facial nerve palsy with aberrant regeneration. Spontaneous contraction of the face may be due to hemifacial spasm (HFS). Other types of abnormal involuntary movements that may affect the facial muscles include tremors, tics, myoclonic jerks, chorea, and athetosis.  Observe the nasolabial folds for depth and symmetry and note whether there is any asymmetry in forehead wrinkling or in the width of the palpebral fissures with the face at rest. A flattened nasolabial fold with symmetric forehead wrinkles suggests a central (upper motor neuron) facial palsy; a flattened nasolabial fold with smoothing of the forehead wrinkles on the same side suggests a peripheral (lower motor neuron) facial nerve palsy. Eyelid position and the width of the palpebral fissures often provide subtle but important clinical clues. A unilaterally widened palpebral fissure suggests a facial nerve lesion causing loss of tone in the orbicularis oculi muscle, the eye closing sphincter; this is sometimes confused with ptosis of the opposite eye. It is a common misconception that facial nerve palsy causes ptosis.
  15. 15.  Examples of primarily neurologic conditions include parkinsonism and related extrapyramidal disorders (masked facies), progressive supranuclear palsy (facial dystonia, omega sign), Möbius' syndrome, myotonic dystrophy (hatchet face, myopathic face), facioscapulohumeral muscular dystrophy (myopathic face, transverse smile), general paresis (facies paralytica), myasthenia gravis (myasthenic snarl), facial nerve palsy (unilateral or bilateral), and Wilson's disease (risus sardonicus). These are discussed in the sections dealing with these particular diseases. There are of course numerous congenital syndromes that cause distinctively dysmorphic facies.  Observe the movements during spontaneous facial expression as the patient talks, smiles, or frowns. Certain upper motor neuron facial palsies are more apparent during spontaneous smiling than when the patient is asked to smile or show the teeth. In infants, facial movements are observed during crying.  Have the patient grin, vigorously drawing back the angles of the mouth and baring the teeth. Note the symmetry of the expression, how many teeth are seen on each side and the relative amplitude and velocity of the lower facial contraction. Have the patient close eyes tightly and note the symmetry of the upper facial contraction. How completely the patient buries the eyelashes on the two sides is a sensitive indicator of orbicularis oculi strength.
  16. 16.  Other useful movements include having the patient raise the eyebrows, singly or in unison, and noting the excursion of the brow and the degree of forehead wrinkling; close each eye in turn; corrugate the brow; puff out the cheeks; frown; pucker; whistle; alternately smile and pucker; contract the chin muscles; and pull the corners of the mouth down in an exaggerated frown to activate the platysma. The platysma can also be activated by having the patient open the mouth against resistance or clinch the teeth. The patient may smile spontaneously after attempting to whistle, or the examiner may make an amusing comment to assess emotional facial movement. Because of their paucity of facial expression, patients with Parkinson's disease may fail to smile after being asked to whistle: the whistle- smile (Hanes) sign.  Trying to gently push down the uplifted eyebrow may detect mild weakness. It is difficult to pry open the tightly shut orbicularis oculi in the absence of weakness. Vigorously pulling with the thumbs may sometimes crack open a normal eye. If the examiner can force the eye open with her small fingers, then the orbicularis oculi is definitely weak. Likewise, it is difficult to force open the tightly pursed lips in a normal individual. When the orbicularis oris sphincter is impaired, the examiner may be able to force air out of the puffed cheek through the weakened lips. Testing ear and scalp movements is seldom useful. The stylohyoid muscle and posterior belly of the digastric cannot be adequately tested. With stapedius weakness, the patient may complain of hyperacusis, especially for low tones.
  17. 17. DISORDERS OF FUNCTION FACIAL WEAKNESS PERIPHERAL FACIAL PALSY  Lower motor neuron lesion.  Peripheral facial palsy (PFP) may result from a lesion anywhere from the CN VII nucleus in the pons to the terminal branches in the face.  Results from an ipsilateral lesion. CENTRAL FACIAL PALSY  Upper motor neuron lesion.  Central facial palsy (CFP) is due to a lesion involving the supranuclear pathways before they synapse on the facial nucleus.  Results from a contralateral lesion.
  18. 18. Peripheral Facial Palsy  There is flaccid weakness of all the muscles of facial expression on the involved side, both upper and lower face, and the paralysis is usually complete (prosopoplegia).  The affected side of the face is smooth; there are no wrinkles on the forehead.  The eye is open; the inferior lid sags;.  The nasolabial fold is flattened; and the angle of the mouth droops.  The patient cannot raise the eyebrow, wrinkle the forehead, frown, close the eye, laugh, smile, bare the teeth, blow out the cheeks, whistle, pucker, retract the angle of the mouth, or contract the chin muscles or platysma on the involved side.  The cheek is flaccid and food accumulates between the teeth and the paralyzed cheek.  The patient may bite the cheek or lip when chewing. Food, liquids, and saliva may spill from the corner of the mouth. The cheek may puff out on expiration because of buccinator muscle weakness.  As shown in the picture she talks and smiles with one side of the mouth, and the mouth is drawn to the sound side on attempted movement. A patient with a peripheral facial nerve palsy on the right patient is attempting to retract both angles of mouth. Patient attempting to raise both eyebrows.
  19. 19.  The facial asymmetry may cause an apparent deviation of the tongue to the affected side.  A patient with an incomplete PFP may be able to close the eye, but not with full power against resistance. Inability to wink with the involved eye is common. The palpebral fissure is open wider than normal, and there may be inability to close the eye (lagophthalmos).  BELL’S PHENOMENON: During spontaneous blinking, the involved eyelid tends to lag behind, sometimes conspicuously. Attempting to close the involved eye causes a reflex upturning of the eyeball. The iris may completely disappear upwardly.  To elicit the levator sign of Dutemps and Céstan, have the patient look down, then close the eyes slowly; because the function of the levator palpebrae superioris is no longer counteracted by the orbicularis oculi, the upper lid on the paralyzed side moves upward slightly.  Akin to Bell's phenomenon is Negro's sign, where the eyeball on the paralyzed side deviates outward and elevates more than the normal one when the patient raises the eyes. Infranuclear paralysis of right trigeminal, facial and hypoglossal nerves in a patient with metastatic carcinoma.
  20. 20.  Labials and vowels are produced by pursing the lips; patients with peripheral facial weakness have a great deal of difficulty in articulating these sounds.  Because of weakness of the lower lid sphincter, tears may run over and down the cheek (epiphora), especially if there is corneal irritation because of inadequate eye protection. A lack of tearing may signal very proximal involvement, above the origin of the greater superficial petrosal nerve. With severe weakness, the eye never closes, even in sleep.
  21. 21. BELL’S PALSY  The most common cause of PFP is Bell's palsy.  Idiopathic facial paralysis (Bell's palsy) frequently follows a viral infection or an immunization.  Symptoms often begin with pain behind the ear, followed within a day or two by facial weakness. There is peripheral facial weakness involving both upper and lower face. The paralysis is complete in approximately 70% of patients.
  22. 22.  The most common symptoms accompanying Bell's palsy are increased tearing, pain in or around the ear, and taste abnormalities like Dysgeusia and ageusia occurs.  There may be drooling and difficulty speaking due to the slack facial muscles.  Patients are often unable to close the eye;  Liquids and saliva may drool from the affected corner of the mouth and tears may spill down the cheek.
  23. 23. Facial Weakness of Central Origin  In a supranuclear, upper motor neuron or central facial palsy (CFP), there is weakness of the lower face, with relative sparing of the upper face. The upper face has both contralateral and ipsilateral supranuclear innervation, and cortical innervation of the facial nucleus may be more extensive for the lower face than the upper. The paresis is rarely complete.  A lesion involving the corticobulbar fibers anywhere prior to their synapse on the facial nerve nucleus will cause a CFP. Lesions are most often in the cortex or internal capsule. Occasionally, a lesion as far caudal as the medulla can cause a CFP because of involvement of the aberrant pyramidal tract.  The upper face is not necessarily completely spared, but it is always involved to a lesser degree than the lower face.  There may be subtle weakness of the orbicularis oculi, the palpebral fissure may be slightly wider on the involved side, and there may be a decrease in palpable lid vibrations.  Involvement of the corrugator and frontalis is unusual, and the patient should be able to elevate the eyebrow and wrinkle the forehead with no more than minimal asymmetry.
  24. 24.  Lesions are most often in the cortex or internal capsule. There is considerable individual variation in facial innervation, and the extent of weakness in a CFP may vary from the lower half to two- thirds of the face.  The upper face is not necessarily completely spared, but it is always involved to a lesser degree than the lower face.  There may be subtle weakness of the orbicularis oculi, the palpebral fissure may be slightly wider on the involved side, and there may be a decrease in palpable lid vibrations.  However, involvement of the corrugator and frontalis is unusual, and the patient should be able to elevate the eyebrow and wrinkle the forehead with minimal asymmetry.  Inability to independently wink the involved eye may be the only demonstrable deficit.
  25. 25.  Even if there is some degree of upper facial involvement in a CFP, the patient is always able to close the eye, Bell's phenomenon is absent, the corneal reflex is present, and the orbicularis oculi reflex may be exaggerated.  In CFP the lower face is weak, the nasolabial fold is shallow, and facial mobility is decreased. However, the lower face weakness is never as severe as with a PFP, which suggests that there may be some direct cortical innervation to the lower face as well as the upper.  There are two variations of CFP: (a) volitional, or voluntary; and (b) emotional, or mimetic. In most instances of CFP, the facial asymmetry is present both when the patient is asked to smile or show the teeth, and during spontaneous facial movements such as smiling and laughing. However, spontaneous movements and deliberate, willful movements may show different degrees of weakness (Figure 16.7). When asymmetry is more apparent with one than the other, the facial weakness is said  to be dissociated. Facial asymmetry more apparent with spontaneous expression, as when laughing, is called a mimetic, emotive or emotional facial palsy (EFP), see Figure 16.7C; weakness more marked on voluntary contraction, when the patient is asked to smile or bare her teeth, is called a volitional facial palsy (VFP)
  26. 26. Panels A-C. Patient with left thalamic tumor with face at rest (A), on voluntarily baring the teeth (B), and on reflex smiling (C); there is right facial paresis on smiling but not on voluntary contraction, an emotional facial palsy. Panels D-F. Patient with a lesion of the corticobulbar fibers in the genu of the left internal capsule with face at rest (D), on voluntarily baring the teeth (E), and on reflex smiling (F); there is right facial paresis on voluntary contraction but not on smiling, a volitional facial palsy.