Cranial Nerves (VII-XII) (Viva)
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FACIAL NERVE
Q.1 What is the origin of facial nerve?
By two roots in the lateral part of the groove between the lower border of pons and the upper border of the medulla.
Q.2 What are the functional components of the facial nerve?
Special visceral efferent:
Motor to muscles of facial expression and elevation of the hyoid bone, which arise from the mesoderm of the second branchial arch.
General visceral efferent:
Secretomotor to submandibular and sublingual glands, lacrimal glands, and glands of nose, palate, and pharynx.
Special visceral afferent:
Carries taste sensation from anterior 2/3 of tongue and palate.
General somatic afferent:
For proprioceptive impulses from muscles supplied.
Q.3 What is nervus intermedius?
Sensory root of the facial nerve because it is attached between the motor root (medially) and vestibulocochlear nerve (laterally).
Q.4 What is the position of geniculate ganglion?
It is present in the course of facial nerve through the substance of petrous temporal bone.
Q.5 What is the position of the facial nerve nucleus?
In reticular formation of pons, medial to the spinal nucleus of the trigeminal nerve.
Q.6 What is the position, connections, and branches of pterygopalatine ganglion?
It is the peripheral autonomic ganglion of the cranial parasympathetic outflow.
Position:
Present in the pterygopalatine fossa and is suspended from the maxillary nerve by two ganglionic branches.
Connections:
– Motor (Parasympathetic) root: Nerve of pterygoid canal.
– Sympathetic root: From internal carotid plexus pass through ganglion without relay.
– Sensory root: From the maxillary nerve several branches pass through it without relay.
Branches:
– Secretomotor fibers to lacrimal gland and glands of nasal and palatine mucosa from postganglionic fibers of nerve of pterygoid canal.
– Orbitalis muscle by orbital branch by sympathetic nerves.
– Sensory root: From palate, nose, and pharynx. Taste fibers from the soft palate.
Q.7 What is the position, connections, and branches of submandibular ganglion?
It is a peripheral autonomic ganglion of the cranial parasympathetic outflow.
Position:
It lies over the hyoglossus muscle suspended from the lingual nerve by two or more roots.
Connections:
– Parasympathetic root: Lingual nerve
– Sympathetic root: From facial artery plexus, pass through ganglion without relay
Branches:
– Secretomotor fibers to submandibular and sublingual salivary glands by parasympathetic fibers.
– Blood vessels of submandibular and sublingual glands by sympathetic plexus.
Q.8 What are the branches of facial nerve and structures supplied?
- Within the facial canal.
– Greater petrosal nerve:
Arises from geniculate ganglion.
Joins deep petrosal nerve at foramen lacerum, to form nerve of pterygoid canal.
Supply glands of nose, palate, and pharynx, and lacrimal gland. Also carries taste sensation from the palate.
– Nerve to stapedius muscle.
– Chorda tympani:
Joins lingual nerve.
Supplies:
– Secretomotor fibres to submandibular and sublingual glands.
– Carries taste sensation from anterior 2/3 of the tongue.
- At exit from Stylomastoid foramen.
– Posterior auricular: Supplies auricularis posterior, occipitalis, and intrinsic muscles on the back of the auricle.
– Digastric branch: To posterior belly of digastric.
– Stylohyoid branch: To stylohyoid muscle.
- Terminal branches within the parotid gland.
– Temporal branches: Supply auricularis anterior and superior, intrinsic muscles on the lateral side of the ear, frontalis, orbicularis, and corrugator supercilli.
– Zygomatic branches: To orbicularis oculi.
– Buccal branches: To buccal muscles.
– Mandibular branch: To muscles of lower lip and chin.
– Cervical branch: Supplies platysma.
– Communicating branches: To trigeminal and vagus nerve to supply part of the skin of auricle.
Q.9 What is Bell’s palsy?
It is the infranuclear lesion of the facial nerve, in which the whole of the face is paralyzed on the same side. The face becomes asymmetrical and is drawn to the normal side.
Q.10 Why in the supranuclear lesion of the facial nerve, only the lower part of the face is paralyzed?
Because the lower facial muscles have a unilateral cortical representation through the opposite pyramidal tract but the upper facial muscles have a bilateral representation through pyramidal tracts of both sides.
VESTIBULOCOCHLEAR NERVE
Q.1 Name the nuclei of origin of the vestibulocochlear nerve.
- Dorsal and ventral cochlear nuclei, situated in relation to the inferior cerebellar peduncle.
- Superior, inferior, medial, and lateral vestibular nuclei, situated laterally in pons and medulla.
Q.2 What are the parts of the VIII cranial nerve?
- Cochlear nerve: Nerve of hearing.
- Vestibular nerve: Nerve of equilibrium (balance).
Q.3 Trace the auditory and balance pathways.
- Auditory pathway:
Receptors: Hair cells of organ of Corti.
First-order sensory neuron:
Spiral ganglion of bipolar cells (in a canal around modiolus).
Central processes of ganglion form cochlear nerve, which terminate in dorsal and ventral cochlear nuclei.
Second-order neuron:
Neurons in cochlear nuclei.
Axons of these pass to the dorsal part of the pons and most of them cross to the opposite side. The crossing fibers of two sides form a trapezoid body. These end in the superior olivary complex.
Third-order neuron:
Arise from the superior olivary complex and form an ascending bundle called lateral lemniscus and end in the inferior colliculus of the midbrain from which fibers reach the medial geniculate body.
From it, acoustic radiations pass to the acoustic area of the cerebral cortex (Area 41,42) via the sublentiform part of the internal capsule. The fibers from the superior olivary complex also reach dorsal and ventral cochlear nuclei of the inferior cerebellar peduncle.
- Equilibrium pathway:
Receptor: Hair cells in the macula of saccule, utricle, and crista of ampullae of semicircular canals.
First-order neuron:
Vestibular ganglion of bipolar neurons.
Central processes of ganglion forms vestibular nerve.
Second-order neuron:
Vestibular nuclei.
These send fibers to:
– Archicerebellum
– Motor nuclei of the brainstem (of III, IV, and VI nerve).
– Anterior horn cells of the spinal cord.
Q.4 Why the unilateral injury to the cochlear nerve do not greatly affect auditory acuity?
Because auditory radiations to the cortex are bilaterally distributed.
Q.5 What is the effect of the lesion of the vestibular nerve?
Vertigo, ataxia and nystagmus.
GLOSSOPHARYNGEAL NERVE
Q.1 Name the functional components of the IX cranial nerve.
Special visceral efferent:
Motor to stylopharyngeus. This muscle develops from the mesoderm of the third branchial arch
General visceral efferent:
Secretomotor to parotid.
General visceral afferent:
Sensory to the mucous membrane of the pharynx, tonsil, soft palate, and posterior 1/3 of the tongue.
Special visceral afferent:
Taste sensation from posterior 1/3 of the tongue.
General somatic afferent:
Proprioceptive impulses from stylopharyngeus and skin of the auricle.
Q.2 Name the nuclei of origin of the ninth nerve?
- Nucleus ambiguus.
- Nucleus of tractus solitarius
- Inferior salivatory nucleus.
Q.3 What are branches of the IX cranial nerve?
| Tympanic: To middle ear, auditory tube, mastoid air cells, and lesser petrosal nerve to parotid gland via otic ganglion. |
| Carotid: To carotid body and carotid sinus |
| Pharyngeal: Forms pharyngeal plexus |
| Muscular: To stylopharyngeus |
| Tonsillar: Supply palatine tonsils and soft palate |
| Lingual: Taste and general sensations from posterior 1/3 of the tongue. |
Q.4 What is the position, connections, and branches of otic ganglion?
It is a peripheral autonomic ganglion of the cranial parasympathetic outflow.
Position:
Present just below the foramen ovale medial to the trunk of the mandibular nerve. It is connected to the nerve to the medial pterygoid muscle.
Connections:
– Parasympathetic root: Lesser petrosal nerve, part of the tympanic branch.
– Sympathetic root: From plexus on middle meningeal artery and pass through ganglion without relay.
– Motor root: Through nerve to medial pterygoid, branch of mandibular nerve and pass through ganglion without relay.
Branches:
– Secretomotor fibers to the parotid gland via a branch connecting otic ganglion to the auriculotemporal nerve, which itself gives a parotid branch.
– Sympathetic fibers to parotid gland through auriculotemporal nerve.
– Motor fibers to tensor tympani and tensor palati muscles.
VAGUS NERVE
Q.1 Name the functional components of the X cranial nerve.
| General somatic afferent: To skin of auricle. |
| Special visceral efferent: To musculature of the pharynx, larynx, and soft palate, derived from branchial arches. Superior laryngeal branch is the nerve of the fourth arch and the recurrent laryngeal branch is the nerve of the sixth arch. |
| General visceral afferent: Branches to pharynx, larynx, trachea, and esophagus and thoracic and abdominal viscera |
| Special visceral afferent: Carries taste sensation from the posterior-most part of the tongue and epiglottis. |
| General somatic afferent: To skin of auricle. |
Q.2 Name the nuclei of the vagus nerve.
- Nucleus ambiguus
- Nucleus of tractus solitarius
- Dorsal nucleus of the vagus
Q.3 Name the ganglia on the vagus and what are their connections.
Superior ganglion: In jugular foramen. Connected to IX and XI nerves and Superior cervical ganglion of the sympathetic chain.
Inferior ganglion: Near base of skull. Connected to XII nerve, superior cervical ganglion, and Loop between C1 and C2 nerves.
Q.4 Name the branches of the vagus. What are the structures supplied by these?
| From superior ganglion: |
| Meningeal: Dura of posterior cranial fossa. |
| Auricular: Conchae and root of auricle. Posterior ½ of the external auditory meatus and Outer surface of the tympanic membrane. |
| In Neck (From inferior ganglion:) |
| Pharyngeal: Has mainly fibers of the cranial accessory nerve. Forms pharyngeal plexus. Supplies muscles of the pharynx and soft palate except tensor palati. |
| Carotid: To carotid body. |
| Superior laryngeal nerve: It divides into External laryngeal: Inferior constrictor and cricothyroid muscle. Internal laryngeal: Sensory to larynx up to vocal fold. |
| Right recurrent laryngeal nerve: To intrinsic muscles of the larynx except cricothyroid. Sensory to larynx below the vocal fold. Sensory branches to trachea, esophagus, and inferior constrictor. To deep cardiac plexus. |
| Cardiac: To superficial and deep cardiac plexus. |
| In the abdomen: The two vagus nerves are distributed to the stomach and coeliac, hepatic and renal plexuses. |
Q.5 What is the effect of the lesion of the vagus nerve?
- Nasal regurgitation of swallowed liquids
- Nasal twang in voice
- Hoarseness of voice
- Flattening of palatal arch
- Cadaveric position of vocal cord and
- Dysphagia.
ACCESSORY NERVE
Q.1 Name the roots of the accessory nerve.
Two roots: Cranial and spinal roots
Q.2 Where do the roots of accessory nerve arise?
The cranial root arises from the lower part of nucleus ambiguus. The spinal root arises from the lateral part of the anterior grey column of the cervical part, C1-5 of the spinal cord.
Q.3 What is the functional component of the IX cranial nerve?
Special visceral efferent: Supplies the muscles derived from branchial arches.
Q.4 How does the spinal root enter the cranial cavity?
The spinal rootlets of the accessory nerve unite to form a trunk which ascends in the vertebral canal and enters the cranial cavity through the foramen magnum.
Q.5 Why is accessory nerve called ‘accessory’?
It is an accessory to the vagus nerve, hence the name. The cranial root is in fact a part of the vagus nerve.
Q.6 What is the distribution of the cranial accessory nerve?
It is distributed via branches of the vagus to the muscles of the soft palate (except the tensor palati), pharynx (except the stylopharyngeus), and intrinsic muscles of the larynx.
Q.7 What is the distribution of the spinal accessory nerve?
It supplies the sternomastoid and trapezius muscles.
Q.8 What will be the effects of a complete lesion of the spinal accessory nerve?
There will be paralysis of the sternomastoid and trapezius muscles (lower motor neuron type of paralysis).
The patient will not be able to rotate his head to the healthy side (due to paralysis of sternomastoid) and he will not be able to shrug the affected shoulder nor will he be able to raise the arm above the head (due to paralysis of trapezius).
HYPOGLOSSAL NERVE
Q.1 What is the position of the hypoglossal nucleus?
It is present in the medulla extending into both open and closed parts of the medulla.
Q.2 What is the distribution of the hypoglossal nerve?
- Hypoglossal is a motor nerve to all muscles of the tongue except the palatoglossus.
- Branches of hypoglossal nerve containing fibers of the C1 nerve.
– Meningeal branch: To meninges of posterior cranial fossa.
– Descending branch: Upper root of ansa cervicalis.
– To thyrohyoid and geniohyoid.
Q.3 What will be the effects of cutting this nerve on one side?
There will be ipsilateral lower motor neuron type of paralysis of muscles of the tongue. On asking the patient to protrude his tongue, it will deviate to the paralyzed side.
Q.4 How will you differentiate a nuclear lesion from an infranuclear lesion of the hypoglossal nerve?
In addition to features of the infranuclear lesion (flaccid paralysis and wasting of muscles), there will also be fasciculations in the muscles of the tongue on the affected side. There will be wrinkling of the mucous membrane of the tongue due to the wasting of muscles and their fasciculations.
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