LEC 21 - Cranial nerves

Question 1

What cranial nerves are exclusively motor

Answer 1

3, 4, 6, 11, 12

Question 2

Describe the origin and pathway of the oculomotor nerve.

Answer 2

The oculomotor nerve, also known as the 3rd cranial nerve, originates from the midbrain and passes through the superior orbital fissure.

Question 3

Define the primary functions of the oculomotor nerve.

Answer 3

The oculomotor nerve innervates 4 of the 6 extraocular muscles (excluding the superior oblique and lateral rectus), the levator palpebrae superioris muscle of the upper eyelid, and 2 intrinsic smooth muscles of the eye.

Question 4

Describe the origin and pathway of the trochlear nerve.

Answer 4

The trochlear nerve, also known as the 4th cranial nerve, is unique as it is the only nerve that emerges from the dorsal part of the midbrain and passes through the superior orbital fissure.

Question 5

Define the primary function of the trochlear nerve.

Answer 5

The primary function of the trochlear nerve is to innervate the superior oblique muscle of the eye, which is a motor nerve responsible for moving the eye down and out.

Question 6

Describe the origin and pathway of the abducens nerve.

Answer 6

The abducens nerve, also known as the 6th cranial nerve, originates from the anterior border of the pons and medulla oblongata, and it passes through the superior orbital fissure to enter the orbit.

Question 7

Define the primary function of the abducens nerve.

Answer 7

The primary function of the abducens nerve is to innervate the lateral rectus muscle of the eye, which is responsible for abducting the eye.

Question 8

How does a lesion of the right abducens nerve affect eye movement?

Answer 8

Results in right lateral rectus palsy, difficulty in moving eye to the right

Question 9

Describe the origin and function of the trigeminal nerve.

Answer 9

The trigeminal nerve (CN 5) originates from the pons and serves as the principal pathway for sensation from the head and face.

Question 10

How many major branches does the trigeminal nerve have and what are they called?

Answer 10

The trigeminal nerve has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).

Question 11

Define the unique characteristic of the mandibular nerve among the trigeminal nerve branches.

Answer 11

The mandibular nerve (V3) is the only branch of the trigeminal nerve that contains both sensory and motor fibers.

Question 12

How does damage to the trigeminal nerve affect mastication?

Answer 12

Damage to the trigeminal nerve causes ipsilateral paralysis of mastication muscles, with jaw deviation toward the injury. Bilateral upper motor neuron lesions lead to a low-hanging mandible, impairing speech sounds.

Question 13

Define the jaw-jerk reflex and its relation to the trigeminal nerve.

Answer 13

The jaw-jerk reflex, or masseter reflex, is normally absent and is mediated by cranial nerve V (CN V), which transmits sensory feedback to its motor nucleus.

Question 14

Describe the primary function of the ophthalmic nerve (V1).

Answer 14

The ophthalmic nerve (V1) carries only sensory fibers, supplying sensation to the forehead, eyelids, eyebrow, nose, eye, and upper nasal cavity. It enters the orbit through the superior orbital fissure.

Question 15

How does the ophthalmic nerve contribute to the corneal reflex?

Answer 15

The ophthalmic nerve (V1) provides the afferent sensory component of the corneal/blink reflex, while the efferent motor part is supplied by CN VII.

Question 16

Define the major branches of the ophthalmic nerve (V1) in the orbit.

Answer 16

The ophthalmic nerve (V1) branches into three major nerves in the orbit: the frontal nerve, nasociliary nerve, and lacrimal nerve.

Question 17

Describe the function of the maxillary nerve (V2) in the trigeminal nerve system.

Answer 17

The maxillary nerve (V2) carries only sensory fibers, supplying sensation to the middle face, nasal cavity mucosa, palate, upper jaw teeth, and maxillary sinus.

Question 18

How does the maxillary nerve (V2) enter the pterygopalatine fossa?

Answer 18

The maxillary nerve (V2) enters the pterygopalatine fossa by passing through the foramen rotundum.

Question 19

Define the major branches of the maxillary nerve (V2) and their continuation.

Answer 19

The maxillary nerve (V2) gives off several major branches in the pterygopalatine fossa, with the major nerve continuing as the infraorbital nerve.

Question 20

Mandibular Nerve (V3) - What is Sensory Function

Answer 20

Mandibular nerve (V3) is a mixed nerve supplying sensory fibres to:

Skin of the lower face

All lower jaw teeth

General sensation (pain, temperature, touch) of the anterior 2/3 of the tongue (excluding taste)

Question 21

Mandibular Nerve (V3) - What is the Motor Function

Answer 21

Mandibular nerve (V3) provides motor fibers to:

Muscles of mastication (e.g., masseter, temporalis, lateral and medial pterygoids)

Middle ear muscle (tensor tympani)

Oral diaphragm muscles (mylohyoid and anterior belly of digastric)

Palate muscle (tensor veli palatini)

Question 22

How do the main and spinal trigeminal nuclei differ in their functions?

Answer 22

The main trigeminal nucleus relays touch and mechanical sensation, while the spinal trigeminal nucleus receives input from small fibers related to pain, temperature, and itch.

Question 23

Define the unique characteristic of the mesencephalic trigeminal nucleus.

Answer 23

The mesencephalic trigeminal nucleus uniquely contains primary sensory neurons and receives input from jaw proprioceptors.

Question 24

Describe Facial Nerve (7th Cranial Nerve) - Pathway

Answer 24

The facial nerve (7th cranial nerve) travels through the internal acoustic meatus and exits via the stylomastoid foramen.

Question 25

Describe Facial Nerve - Motor & Parasympathetic Components

Answer 25

Motor (branchial): Controls facial expression, scalp muscles, posterior digastric, stylohyoid, stapedius, and contributes to the corneal/blink reflex.

Parasympathetic: Innervates tear, submandibular, sublingual, and nasal glands.

Question 26

Describe Facial Nerve - Sensory Component

Answer 26

Provides special visceral afferents for taste sensation from the anterior 2/3 of the tongue, via the chorda tympani nerve and geniculate ganglion.

Question 27

Describe the major branches of the facial nerve responsible for facial expression.

Answer 27

The major branches of the facial nerve that supply the muscles of facial expression are: temporal, zygomatic, buccal, marginal mandibular, and cervical.

Question 28

How does the facial nerve interact with the parotid gland?

Answer 28

The facial nerve gives motor branches to the posterior digastric and stylohyoid muscles, forming a plexus in the parotid gland, and exits to supply facial expression muscles.

Question 29

Describe Bell’s Palsy - Motor and Sensory Effects

Answer 29

Definition: Unilateral paralysis of facial muscles

(e.g., inability to close the eye, difficulty with food intake, lips parted at rest).

Impaired articulation of labial and labiodental sounds.

Sensory Loss: Loss of taste in the anterior 2/3 of the tongue

Question 30

Describe Bell’s Palsy - Gland and Hearing Effect

Answer 30

Gland Dysfunction:

Eyes: Excessive dryness or tearing due to issues with the lacrimal gland and inability to close the eye.

Mouth: Dry mouth or reduced saliva from submandibular and sublingual glands.

Hearing: Hyperacusis (increased sensitivity to sound) due to lack of stapedius muscle innervation, which normally dampens sound.

Question 31

How does an upper motor neuron injury affect facial muscle strength?

Answer 31

An upper motor neuron injury, such as from a stroke, results in weakness of the contralateral lower face only.

Question 32

Define the effects of a lower motor neuron injury on facial muscles.

Answer 32

A lower motor neuron injury, like Bell’s palsy, causes weakness in both the ipsilateral upper and lower face.

Question 33

Define the anatomical pathway of the glossopharyngeal nerve.

Answer 33

The glossopharyngeal nerve emerges from the medulla and exits the skull via the jugular foramen.

Question 34

Describe Glossopharyngeal Nerve (9th Cranial Nerve) - Sensory Functions

Answer 34

Special Sensation: Taste from the posterior 1/3 of the tongue to the solitary nucleus.

General/Visceral Sensation: Sensation to the intraoral region, pharynx, posterior 1/3 of the tongue, carotid body, and carotid sinus

Reflex: Sensory component of the pharyngeal (gag) reflex

Question 35

Describe Glossopharyngeal Nerve - Motor and Parasympathetic Functions

Answer 35

Motor Component: Innervates the stylopharyngeus muscle from the nucleus ambiguus.

Parasympathetic Component: From the inferior salivatory nucleus to the parotid gland via the otic ganglion.

Question 36

Describe Vagus Nerve (10th Cranial Nerve) - Overview and Pathway

Answer 36

Definition: The only cranial nerve extending beyond the head and neck to reach distant body parts

Question 37

Describe Vagus Nerve - General Visceral Sensory Component

Answer 37

Function: creates a pathway that interfaces with the parasympathetic control of the heart, lungs and digestive tract

Question 38

Describe Vagus Nerve - Special Visceral Sensory Component

Answer 38

Function: Carries taste sensation from the pharyngeal area.

Question 39

Describe Vagus Nerve - Motor Component

Answer 39

Function: Innervates muscles of the larynx, pharynx, and upper esophagus, including:

Levator veli palatini, salpingopharyngeus, palatoglossus, palatopharyngeus

All muscles of the pharynx and larynx

Additional Role: Provides the motor component of the pharyngeal or gag” reflex.”

Question 40

Describe Vagus Nerve - Parasympathetic Component

Answer 40

Function: Supplies parasympathetic innervation to all visceral organs in the neck, thorax, upper abdomen, and parts of the intestine derived from the foregut and midgut.

Question 41

Describe Effects of Vagus Nerve Lesions on Reflexes and Autonomic Functions

Answer 41

Impairments: Lesions in the vagus nerve can disrupt reflexes involved in swallowing, gagging, coughing, sneezing, vomiting, breathing, and heart rate.

Associated Nerves: Lesions may involve other cranial nerve nuclei, such as glossopharyngeal (IX) and hypoglossal (XII).

Question 42

Describe Effects of Vagus Nerve Lesions on Pharyngeal Branch

Answer 42

Pharyngeal Branch Lesion: Causes paralysis of the pharynx and soft palate, leading to swallowing difficulty.

Signs: Soft palate droops on the affected side, and the uvula shifts toward the unaffected side.

Question 43

Describe Effects of Recurrent Laryngeal Nerve Lesions

Answer 43

Unilateral Lesions: Affect vocal folds, leading to a breathy voice and hoarseness, with minimal impact on phonation.

Bilateral Lesions: Cause aphonia (loss of voice) and impaired air flow.

Question 44

Describe accessory Nerve (11th Cranial Nerve) - Structure

Answer 44

Type: Pure motor nerve with two parts.

Cranial Part: Originates from the brainstem, merges with the vagus nerve.
Spinal Part: Emerges from the spinal cord, enters the skull via the foramen magnum, joins the cranial part, and exits through the jugular foramen.

Question 45

Describe Accessory Nerve - Innervation

Answer 45

Innervates two neck muscles: trapezius and sternocleidomastoid.

Question 46

Effects of Accessory Nerve Damage

Answer 46

Trapezius Paralysis: Causes ipsilateral shoulder sagging and inability to raise the shoulder.

Sternocleidomastoid Paralysis: Limits head movement to the opposite side of the lesion.

Question 47

Describe Hypoglossal Nerve (12th Cranial Nerve) - Pathway

Answer 47

Origin: Fibers arise from the medulla and exit the skull via the hypoglossal canal.
Location: The only cranial nerve exiting anteriorly from the medulla, located between the pyramids and olives.

Question 48

Describe Hypoglossal Nerve - Function and Innervation

Answer 48

Type: Pure motor nerve.

Innervation: Supplies all muscles of the tongue (both intrinsic and extrinsic) except the palatoglossus muscle.

Function: Crucial for tongue movements, including protrusion.

Question 49

What are the cranial nerves involved in swallowing?

Answer 49

5, 7,9,10,12

Question 50

Describe Lesions affecting the hypoglossal nerve

Answer 50

• When (left) hypoglossal nerve is damaged, the tip of the tongue is deviated to the affected side

• Tongue becomes flaccid and wrinkled