LEC 21 - Cranial nerves Flashcards
What cranial nerves are exclusively motor
3, 4, 6, 11, 12
Describe the origin and pathway of the oculomotor nerve.
The oculomotor nerve, also known as the 3rd cranial nerve, originates from the midbrain and passes through the superior orbital fissure.
Define the primary functions of the oculomotor nerve.
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.
Describe the origin and pathway of the trochlear nerve.
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.
Define the primary function of the trochlear nerve.
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.
Describe the origin and pathway of the abducens nerve.
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.
Define the primary function of the abducens nerve.
The primary function of the abducens nerve is to innervate the lateral rectus muscle of the eye, which is responsible for abducting the eye.
How does a lesion of the right abducens nerve affect eye movement?
Results in right lateral rectus palsy, difficulty in moving eye to the right
Describe the origin and function of the trigeminal nerve.
The trigeminal nerve (CN 5) originates from the pons and serves as the principal pathway for sensation from the head and face.
How many major branches does the trigeminal nerve have and what are they called?
The trigeminal nerve has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).
Define the unique characteristic of the mandibular nerve among the trigeminal nerve branches.
The mandibular nerve (V3) is the only branch of the trigeminal nerve that contains both sensory and motor fibers.
How does damage to the trigeminal nerve affect mastication?
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.
Define the jaw-jerk reflex and its relation to the trigeminal nerve.
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.
Describe the primary function of the ophthalmic nerve (V1).
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.
How does the ophthalmic nerve contribute to the corneal reflex?
The ophthalmic nerve (V1) provides the afferent sensory component of the corneal/blink reflex, while the efferent motor part is supplied by CN VII.
Define the major branches of the ophthalmic nerve (V1) in the orbit.
The ophthalmic nerve (V1) branches into three major nerves in the orbit: the frontal nerve, nasociliary nerve, and lacrimal nerve.
Describe the function of the maxillary nerve (V2) in the trigeminal nerve system.
The maxillary nerve (V2) carries only sensory fibers, supplying sensation to the middle face, nasal cavity mucosa, palate, upper jaw teeth, and maxillary sinus.
How does the maxillary nerve (V2) enter the pterygopalatine fossa?
The maxillary nerve (V2) enters the pterygopalatine fossa by passing through the foramen rotundum.
Define the major branches of the maxillary nerve (V2) and their continuation.
The maxillary nerve (V2) gives off several major branches in the pterygopalatine fossa, with the major nerve continuing as the infraorbital nerve.
Mandibular Nerve (V3) - What is Sensory Function
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)
Mandibular Nerve (V3) - What is the Motor Function
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)
How do the main and spinal trigeminal nuclei differ in their functions?
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.
Define the unique characteristic of the mesencephalic trigeminal nucleus.
The mesencephalic trigeminal nucleus uniquely contains primary sensory neurons and receives input from jaw proprioceptors.
Describe Facial Nerve (7th Cranial Nerve) - Pathway
The facial nerve (7th cranial nerve) travels through the internal acoustic meatus and exits via the stylomastoid foramen.
Describe Facial Nerve - Motor & Parasympathetic Components
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.
Describe Facial Nerve - Sensory Component
Provides special visceral afferents for taste sensation from the anterior 2/3 of the tongue, via the chorda tympani nerve and geniculate ganglion.
Describe the major branches of the facial nerve responsible for facial expression.
The major branches of the facial nerve that supply the muscles of facial expression are: temporal, zygomatic, buccal, marginal mandibular, and cervical.
How does the facial nerve interact with the parotid gland?
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.
Describe Bell’s Palsy - Motor and Sensory Effects
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
Describe Bell’s Palsy - Gland and Hearing Effect
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.
How does an upper motor neuron injury affect facial muscle strength?
An upper motor neuron injury, such as from a stroke, results in weakness of the contralateral lower face only.
Define the effects of a lower motor neuron injury on facial muscles.
A lower motor neuron injury, like Bell’s palsy, causes weakness in both the ipsilateral upper and lower face.
Define the anatomical pathway of the glossopharyngeal nerve.
The glossopharyngeal nerve emerges from the medulla and exits the skull via the jugular foramen.
Describe Glossopharyngeal Nerve (9th Cranial Nerve) - Sensory Functions
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
Describe Glossopharyngeal Nerve - Motor and Parasympathetic Functions
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.
Describe Vagus Nerve (10th Cranial Nerve) - Overview and Pathway
Definition: The only cranial nerve extending beyond the head and neck to reach distant body parts
Describe Vagus Nerve - General Visceral Sensory Component
Function: creates a pathway that interfaces with the parasympathetic control of the heart, lungs and digestive tract
Describe Vagus Nerve - Special Visceral Sensory Component
Function: Carries taste sensation from the pharyngeal area.
Describe Vagus Nerve - Motor Component
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.”
Describe Vagus Nerve - Parasympathetic Component
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.
Describe Effects of Vagus Nerve Lesions on Reflexes and Autonomic Functions
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).
Describe Effects of Vagus Nerve Lesions on Pharyngeal Branch
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.
Describe Effects of Recurrent Laryngeal Nerve Lesions
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.
Describe accessory Nerve (11th Cranial Nerve) - Structure
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.
Describe Accessory Nerve - Innervation
Innervates two neck muscles: trapezius and sternocleidomastoid.
Effects of Accessory Nerve Damage
Trapezius Paralysis: Causes ipsilateral shoulder sagging and inability to raise the shoulder.
Sternocleidomastoid Paralysis: Limits head movement to the opposite side of the lesion.
Describe Hypoglossal Nerve (12th Cranial Nerve) - Pathway
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.
Describe Hypoglossal Nerve - Function and Innervation
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.
What are the cranial nerves involved in swallowing?
5, 7,9,10,12
Describe Lesions affecting the hypoglossal nerve
• When (left) hypoglossal nerve is damaged, the tip of the tongue is deviated to the affected side
• Tongue becomes flaccid and wrinkled
