Cranial Nerves, Special Senses, and Auditory Pathways

Sixty question-and-answer style flashcards covering cranial nerves, vision, olfaction, gustation, hearing, balance, and the auditory pathway.

What is Cranial Nerve I and its primary function?

Cranial Nerve I is the Olfactory nerve; it conveys special sensory information for smell.

How is Cranial Nerve I clinically tested?

Ask the patient to identify familiar odors (e.g., coffee) with each nostril separately while eyes are closed.

What is Cranial Nerve II and its primary function?

Cranial Nerve II is the Optic nerve; it carries special sensory information for vision.

Which bedside exams assess Cranial Nerve II function?

Visual acuity testing, visual field testing, and fundoscopic examination.

What is Cranial Nerve III and its overall role?

Cranial Nerve III is the Oculomotor nerve; it supplies somatic motor fibers to most extra-ocular muscles and parasympathetic fibers for pupil constriction and lens accommodation.

Which eye muscles are innervated by Cranial Nerve III?

Superior, inferior, and medial recti; inferior oblique; and levator palpebrae superioris.

What classic eye appearance suggests an Oculomotor nerve palsy?

‘Down and out’ eye position with ptosis and a dilated, non-reactive pupil.

What is Cranial Nerve IV and its primary function?

Cranial Nerve IV is the Trochlear nerve; it provides somatic motor innervation to the superior oblique muscle.

Which single muscle does the Trochlear nerve control?

The superior oblique muscle of the eye.

How is Cranial Nerve IV tested clinically?

Ask the patient to look down and in; inability or vertical diplopia indicates dysfunction.

Name Cranial Nerve V and its three major divisions.

The Trigeminal nerve; its divisions are ophthalmic (V1), maxillary (V2), and mandibular (V3).

What sensory modalities are carried by the Trigeminal nerve?

General somatic sensation (touch, pain, temperature) from the face, cornea, nasal cavity, oral cavity, and anterior two-thirds of the tongue.

What motor function is provided by the Trigeminal nerve?

Motor innervation to muscles of mastication (masseter, temporalis, pterygoids) via V3.

How do you test the Trigeminal nerve clinically?

Assess facial sensation in all three divisions and test jaw clench or jaw opening strength.

What is Cranial Nerve VI and its function?

Cranial Nerve VI is the Abducens nerve; it supplies the lateral rectus muscle to abduct the eye.

What sign indicates an Abducens nerve palsy?

Inability to abduct the affected eye, leading to medial deviation (esotropia) and horizontal diplopia.

What is Cranial Nerve VII and its composite functions?

Cranial Nerve VII is the Facial nerve; it provides motor to facial expression muscles, taste from anterior 2/3 tongue, parasympathetics to lacrimal and salivary glands, and some general sensation from ear canal.

Which bedside tests evaluate Cranial Nerve VII?

Ask the patient to raise eyebrows, close eyes tightly, smile, and puff cheeks; also test taste on the anterior tongue if needed.

What is Cranial Nerve VIII and its two main branches?

Cranial Nerve VIII is the Vestibulocochlear nerve; branches are the cochlear (hearing) and vestibular (balance) nerves.

How can Cranial Nerve VIII function be tested?

Perform hearing tests (whisper or tuning fork) and vestibular tests such as the head-impulse or caloric test.

Identify Cranial Nerve IX and list two key functions.

Cranial Nerve IX is the Glossopharyngeal nerve; it provides taste and general sensation to the posterior 1/3 of the tongue and supplies motor fibers to the stylopharyngeus muscle; also carries parasympathetics to the parotid gland.

Which clinical exam checks Glossopharyngeal nerve integrity?

Elicit the gag reflex (afferent limb via CN IX) and test taste on the posterior tongue.

Name Cranial Nerve X and its broad roles.

Cranial Nerve X is the Vagus nerve; it supplies motor to pharyngeal/laryngeal muscles, parasympathetic output to thoracic and most abdominal organs, and sensory input from viscera.

What finding suggests a Vagus nerve lesion?

Deviation of the uvula away from the lesion side and hoarse voice due to vocal-cord paralysis.

What is Cranial Nerve XI and which muscles does it innervate?

Cranial Nerve XI is the Spinal Accessory nerve; it motor-innervates the sternocleidomastoid and trapezius muscles.

How is Cranial Nerve XI tested?

Ask the patient to shrug shoulders against resistance and turn head against resistance.

What is Cranial Nerve XII and its function?

Cranial Nerve XII is the Hypoglossal nerve; it provides motor innervation to intrinsic and extrinsic tongue muscles.

What tongue sign indicates a Hypoglossal nerve lesion?

Tongue deviates toward the side of a lower motor neuron lesion upon protrusion.

Which ocular structure provides most of the eye’s refractive power?

The cornea.

What is the primary role of the lens?

Fine-tunes focus by changing shape to accommodate near or distant objects.

What is the functional role of the retina?

It houses photoreceptors that convert light into neural signals for vision.

Which muscles control pupil diameter?

Sphincter pupillae (constriction) and dilator pupillae (dilation).

Describe the parasympathetic pathway that constricts the pupil.

Edinger-Westphal nucleus → CN III → ciliary ganglion → short ciliary nerves → sphincter pupillae muscle.

Outline the sympathetic pathway for pupil dilation.

Hypothalamus → spinal cord (T1-T2) → superior cervical ganglion → long ciliary nerves → dilator pupillae muscle.

Which cranial nerve carries parasympathetic fibers to the sphincter pupillae?

The Oculomotor nerve (CN III).

List the six extra-ocular muscles.

Superior, inferior, medial, and lateral recti; superior and inferior obliques.

State the classic innervation rule for extra-ocular muscles.

LR6 SO4 AO3: Lateral rectus by CN VI, Superior oblique by CN IV, All others by CN III.

What is the primary action of the lateral rectus muscle?

Abduction of the eyeball (moves it laterally).

What is the primary action of the superior oblique muscle?

Depression and intorsion of the eye when adducted; overall helps look down and in.

Which retinal cells perform phototransduction?

Rods and cones.

What is the role of bipolar cells in the retina?

They relay signals from photoreceptors to ganglion cells.

What is the function of retinal ganglion cells?

Their axons form the optic nerve, carrying visual information to the brain.

Where in the visual pathway does partial decussation occur?

At the optic chiasm.

What visual defect results from a lesion at the optic chiasm?

Bitemporal (heteronymous) hemianopia.

A right optic tract lesion produces which visual field loss?

Left homonymous hemianopia.

Which cells detect odorants in the nasal cavity?

Olfactory sensory neurons (bipolar receptor cells).

Where is the olfactory epithelium located?

In the superior nasal concha and upper part of the nasal septum.

Name the three principal cell types of the olfactory epithelium.

Olfactory sensory neurons, supporting (sustentacular) cells, and basal stem cells.

Where is the first synapse of the olfactory pathway?

In the olfactory bulb, within structures called glomeruli.

Where is the primary olfactory cortex found?

In the ipsilateral piriform cortex of the temporal lobe.

Which cranial nerve carries taste from the anterior two-thirds of the tongue?

Facial nerve via the chorda tympani (CN VII).

Which cranial nerve conveys taste from the posterior one-third of the tongue?

Glossopharyngeal nerve (CN IX).

Which cranial nerve carries taste sensation from the epiglottis and lower pharynx?

Vagus nerve (CN X).

Outline the central gustatory pathway.

Taste fibers → solitary nucleus (medulla) → ventral posteromedial nucleus of thalamus → gustatory cortex in the insula and frontal operculum.

List two factors that influence taste perception.

Age (loss of taste buds) and olfactory input (smell enhances flavor).

What is the function of the tympanic membrane?

Transforms airborne sound waves into mechanical vibrations of the ossicles.

Why are the auditory ossicles important?

They amplify and transmit vibrations from the tympanic membrane to the oval window of the cochlea.

Where are auditory hair cells located?

Within the organ of Corti on the basilar membrane of the cochlea.

How do semicircular canals differ from otolithic organs?

Semicircular canals detect angular (rotational) acceleration; otolithic organs (utricle and saccule) detect linear acceleration and head position relative to gravity.

Trace the central auditory pathway from the cochlea to the cortex.

Cochlear nerve → cochlear nuclei → superior olivary complex → lateral lemniscus → inferior colliculus → medial geniculate nucleus → primary auditory cortex in the superior temporal gyrus.