CRANIAL NERVE: COMPONENT, ORIGIN, AND INSERTION, FUNCTION AND EXAMINATION: PART 3(in this part facial nerve and vestibulocochlear nerve)
FACIAL NERVE – the facial nerve is 7th nerve
• COMPONENT: facial nerve is a Mixed nerve that is consist of a motor and sensory component.
• FUNCTION: function is divided into motor, sensory and secretomotor and functions given below are following-
o Muscles of face and scalp
o Stapedius muscle
o Posterior belly of digastric
o Stylohyoid muscles
o Taste from anterior 2/3rd of tongue
o From the floor of mouth and palate
o Submandible and sublingual salivary glands
o Lacrimal gland
o Glands of nose and palate
4. ORIGIN: facial nerve originated from Medulla oblongata
5. OPENING TO THE SKULL: opening to the skull supply these parts –
o Internal acoustic meatus
o Facial canal
o Stylomastoid foramen
EXAMINATION- for examination of facial nerve following can be done-
Observe patient as he talks and smiles, watching for:-
-asymmetrical elevation of mouth
-flattening of nasolabial fold
The patient is then instructed to:-
-wrinkled forehead(frontalis muscle)by looking upward.
-close eyes while examiner attempts to open them (orbicularis oculi)
-Purse lips while examiner presses cheeks. (buccinator)
-show teeth (orbicularis oris)
For the taste sensation, it may be tested by sugar, tartaric acid or salt. A small quantity of each substance is placed anteriorly on the appropriate side of the protruded tongue.
VESTIBULOCOCHLEAR NERVE- the vestibulocochlear nerve is 8th nerve
• COMPONENT: Vestibular nerve is the sensory nerve.
• FUNCTIONS: the function of the vestibulocochlear nerve divided into the vestibular and cochlear component and function is given below-
o In vestibular:
supplies saculae, saccule, semicircular canal
Maintains position of head
o In cochlear:
Supplies organ of Corti
• ORIGIN: medulla oblongata
• OPENING TO THE SKULL: Internal acoustic meatus
• Examination- for examination of vestibulocochlear nerve
For balance, the testing patient is asked to do march past.
For hearing –
Cochlear component test- test by whispering numbers into one ear while another ear is closed. if a hearing is impaired, examine external meatus and tympanic membrane with auroscope to exclude wax or other infection.
Differentiate conductive deafness from perceptive(nerve) deafness by :
1.weber’s test- hold the base of tuning fork (256 or 512 Hz) against the vertex. Ask the patient if a sound is heard louder in one ear.
In conductive deafness, a sound is louder in the affected ear.
Nerve deafness sound is louder in the normal ear.
2. Rinne’s test- hold the base of vibrating tuning fork against the mastoid bone. Ask the patient if a note is heard. When note disappears- hold tuning fork near the external auditory meatus. A patient should hear the sound again since air conduction via the ossicles is better than bone conduction.
In conductive deafness, bone conduction is better than air conduction.
In nerve deafness, both bone and air conduction are impaired.
Further auditory testing and examination of the vestibular component require specialized investigation.
In this part, two nerve that is facial nerve and vestibulocochlear nerve along with examination is described. Next part is the last part and remaining cranial nerve is described in the last part.