Assessment of Cranial Nerves mnemonic, cranial nerves function, cranial nerves test

 

1st Cranial nerve

 

Smell, which is controlled by the 1st (olfactory) cranial nerve, is normally assessed only after a head injury or when lesions of the anterior fossa (e.g., meningioma) are suspected or when patients report irrelevant smell or taste. 

 

While one nostril is closed, the patient is asked to identify smell (such as soap, coffee, or cloves) delivered to each nostril. When malingering is suspected, irritants such as alcohol, ammonia, and other irritants are used to test the nociceptive receptors of the 5th (trigeminal) cranial nerve.

 

2nd Cranial nerve

 

Visual performance is examined for the second (optic) cranial nerve using a Snellen chart for distance vision or a portable chart for near vision; each eye is assessed separately, with the other eye covered. 

Standard pseudoisochromatic Ishihara or Hardy-Rand-Ritter plates with numbers or figures placed in a field of specially colored dots are used to evaluate color perception. 

Direct confrontation is used to examine visual fields in all four visual quadrants. The pupillary responses are assessed both directly and indirectly. In addition, a funduscopic examination is performed.

 

3rd, 4th, and 6th Cranial nerves

 

Eyes are examined for symmetry of movement, globe position, asymmetry or drooping of the eyelids (ptosis), and twitches or flutters of the globes or lids for the 3rd (oculomotor), 4th (trochlear), and 6th (abducens) cranial nerves. The patient is asked to follow a moving target (e.g., examiner's finger, penlight) across all four quadrants (including across the midline) and toward the tip of the nose; this test can reveal nystagmus and ocular muscle palsies. End-lateral gaze nystagmus with a fine amplitude is normal. 

In a dimly light space, anisocoria (Anisocoria is unequal pupil size) in pupillary size should be noted. The symmetry and briskness of the pupillary light response are assessed.

5th Cranial nerve

 

The 3 sensory divisions (ophthalmic, maxillary, and mandibular) of the 5th (trigeminal) nerve are assessed using a pinprick to test facial sensibility and a wisp of cotton against the lower or lateral cornea to assess the corneal reflex. The angle of the jaw should be evaluated if face sensation is gone; sparing of this area (innervated by spinal root C2) suggests a trigeminal deficit. Depressed or absent corneal sensation, which is frequent in contact lens wearers, should be separated from a weak blink due to face weakness (e.g., 7th cranial nerve paralysis). Even if the blink rate is reduced, a patient with facial weakness feels the cotton wisp on both sides normally. 

 

The masseter muscles are palpated as the patient clenches his or her teeth, and the patient is asked to open his or her mouth against opposition. The jaw deviates to that side if a pterygoid muscle is weak.

7th Cranial nerve

 

Hemifacial weakness is used to assess the 7th (facial) cranial nerve. The nasolabial fold is depressed and the palpebral fissure is widened on the weakened side of the face during spontaneous conversation, especially when the patient smiles or, if obtunded, grimaces at a noxious stimulus; on the weakened side, the nasolabial fold is depressed and the palpebral fissure is widened. The etiology of 7th nerve weakness is central rather than peripheral if the patient only displays lower facial weakness (i.e., furrowing of the forehead and eye closure are retained). 

Sweet, sour, salty, and bitter solutions placed with a cotton swab on one side of the tongue, then the other, can be used to assess taste in the anterior two thirds of the tongue. 

 

A vibrating tuning fork held adjacent to the ear can identify hyperacusis ( a disorder in loudness perception)f, which indicates stapedius muscle weakness.

8th Cranial nerve

 

Because the 8th cranial nerve (vestibulocochlear, acoustic, auditory) conveys both auditory and vestibular input, a thorough examination is required. 

 

Hearing evaluations 

Tests of vestibular function 

Hearing is first checked in each ear by whispering something into one ear while occluding the other. Formal audio-logic testing should be performed on any suspected hearing loss to validate findings and distinguish conductive hearing loss from sensorineural hearing loss. To separate the two, the Weber and Rinne tests can be performed at the bedside, although they are difficult to do efficiently outside of specialized facilities. 

 

The presence of nystagmus can be used to assess vestibular function. The existence of nystagmus and its characteristics (such as direction, duration, and triggers) can help detect vestibular diseases and distinguish central from peripheral vertigo. Vestibular nystagmus is made up of two parts: 

Vestibular input causes a sluggish component. 

A quick-acting, reversible component that induces movement in the opposite direction (called beating).

9th and 10th Cranial nerves

 

Typically, the 9th (glossopharyngeal) and 10th (vagus) cranial nerves are assessed simultaneously. It is recorded whether the patient's palate raises symmetrically when he or she says "ah." The uvula is lifted away from the paretic side if one side is paretic. A tongue blade can be used to touch one side of the posterior pharynx, then the other, to see if the gag reflex is symmetrical; bilateral absence of the gag response is frequent among healthy persons and is unlikely to be relevant. 

Suctioning the endotracheal tube generally causes coughing in an intubated, unconscious patient. 

 

The vocal chords are examined if hoarseness is detected. Isolated hoarseness (with normal gag and palate elevation) should initiate a search for lesions compressing the recurrent laryngeal nerve (e.g., mediastinal lymphoma, aortic aneurysm).

11th Cranial nerve

 

The muscles supplied by the 11th (spinal accessory) cranial nerve are tested: 

 

The patient is asked to turn the head against resistance provided by the examiner's hand as the examiner palpates the active muscle for the sternocleidomastoid (opposite the turned head). 

The patient is instructed to raise their shoulders against the examiner's resistance for the upper trapezius.

12th Cranial nerve

 

By asking the patient to extend their tongue and evaluating it for atrophy, fasciculations, and weakness, the 12th (hypoglossal) cranial nerve is assessed (deviation is toward the side of a lesion).

Origin of Cranial Nerves, Dysfunctions, Different Mnemonics

 

Origin of the Cranial Nerves

There are a total of twelve cranial nerves. The cerebrum gives rise to the olfactory nerve (CN I) and the visual nerve (CN II). 

The brain stem gives rise to the cranial nerves III–XII. They can come from a specific portion of the brain stem (midbrain, pons, or medulla), or from a point where two parts meet.

The trochlear nerve (IV) originates from the midbrain's posterior side. Of all the cranial nerves, it has the longest intracranial length. 

Oculomotor(III) - midbrain-pontine junction.

Trigeminal (V) - pons. 

Abducens, facial, and vestibulocochlear (VI-VII-VIII) - Pontine-Medulla Junction. 

Glossopharyngeal, vagus, and accessory (IX-X-XI)-medulla oblongata : posterior to the olive.

Hypoglossal(XII) : anterior to the olive.

 

I. Olfactory nerve (Smell)

The olfactory nerve sends sensory information about smells to your brain.

II. Optic nerve (Vision)

The optic nerve is the vision-related sense nerve.

III. Oculomotor nerve (Move eyes, Pupil)

Muscle function and pupil response are two motor functions of the oculomotor nerve. 

Muscle function is a term that refers to the ability of a muscle to perform a four of the six muscles around your eyes are controlled by the oculomotor nerve. These muscles aid in the movement and focus of your eyes. 

It also aids in the management of your pupil's size as it responds to light.

IV. Trochlear nerve (Move eyes)

The superior oblique muscle is controlled by the trochlear nerve. The downward, outward, and inward eye motions are controlled by this muscle.

V. Trigeminal nerve (Face sensation)

The largest of your cranial nerves, the trigeminal nerve serves both sensory and motor tasks. 

The trigeminal nerve is divided into three sections: 

•Ophthalmic. 

Sensory information from the upper half of your face, such as your forehead, scalp, and upper eyelids, is sent to the ophthalmic division. 

•Maxillary. 

The sensory information from the middle area of your face, including your cheeks, upper lip, and nasal cavity, is communicated through this division. 

•Mandibular. 

The sensory and motor functions of the mandibular division are both present. Your ears, lower lip, and chin all provide sensory information to it. It also regulates the movement of your jaw and ear muscles.

VI. Abducens nerve (Move eye)

The lateral rectus muscle, which is related with eye movement, is controlled by the abducens nerve. Outward eye movement is controlled by this muscle. For example, You might use it to look to the side.

VII. Facial nerve (Move face)

The facial nerve controls both sensory and motor processes, including the muscles that move your face and several muscles in your jaw. 

Supplying flavor to the majority of your tongue 

providing glands in your head or neck, such as salivary glands and tear-producing glands, that communicate feelings from your ear's outer parts

VIII. Vestibulocochlear nerve (Hearing and Balance)

Hearing and balance are sensory capabilities of the vestibulocochlear nerve. There are two parts to it: the cochlear portion and the vestibular portion: 

Cochlear part:

Sound vibrations are detected by specialized cells in your ear based on the intensity and pitch of the sound. This causes nerve impulses to be generated, which are then sent to the cochlear nerve.

Vestibular part: 

This section also has a collection of unique cells that can track both linear and rotational head movements. The vestibular nerve receives this information and uses it to change your balance and equilibrium.

IX. Glossopharyngeal nerve (Taste, Gag reflex)

The glossopharyngeal nerve serves both motor and sensory tasks, delivering sensory information from your sinuses, back of your throat, sections of your inner ear, and the back part of your tongue. 

Producing a feeling of taste for the rear part of your tongue by activating voluntary movement of the stylopharyngeus muscle in the back of your throat.

X. Vagus nerve (Parasympathetic innervation)

The vagus nerve has a wide range of functions. It performs both sensory and motor functions, such as: 

Communicating sensation information from your ear canal and parts of your throat.

Sending sensory information from organs in your chest and trunk, such as your heart and intestines; allowing motor control of muscles in your throat.

Stimulating the muscles of organs in your chest and trunk, including those that move food through your digestive tract (peristalsis); and providing a sense of taste near the root of your tongue.

XI. Accessory nerve (Shoulder Shrug)

The motor neuron that controls the muscles in your neck is known as the accessory nerve. Your neck and shoulders can rotate, flex, and extend thanks to these muscles. 

There are two elements to it: spinal and cranial. The top part of your spinal cord is where the spinal portion begins. The medulla oblongata is where the cranial part begins.

XII. Hypoglossal nerve (Swallowing)

The hypoglossal nerve is the 12th cranial nerve, and it controls the majority of the muscles in your tongue. It begins in the medulla oblongata and travels down into the jaw, eventually reaching the tongue.

 

Two different mnemonics to help you remember the cranial nerves. 

First mnemonic goes like this on occasion our trusty truck acts funny very good vehicle anyhow now the first letter of each word corresponds to the first letter of that cranial nerve.

Mnemonics	Nerves
On	Olfactory
Occasion	Optic
Our	Oculomotor
Trusty	Trochlear
Truck	Trigeminal
Acts	Abducens
Funny	Facial
Very	vestibular cochlear
Good	Glossopharyngeal
Vehicle	vagus
Any	Accessory
How	Hypoglossal

 

 

Second mnemonics goes like this some say Mary money but my brother says big brains matter more. just like this where S stands for sensory M stands for motor and B stands for both sensory and motor.

Mnemonics	Nerve
Sensory	Olfactory
Sensory	Optic
Motor	Oculomotor
Motor	Trochlear
Both	Trigeminal
Motor	Abducens
Both	Facial
Sensory	vestibular cochlear
Both	Glossopharyngeal
Both	vagus
Motor	Accessory
Motor	Hypoglossal

 

 

 

Dysfunction of Cranial nerves

Certain cranial nerve disorders can impact the eye, pupil, optic nerve, or extra ocular muscles and their nerves, and are thus classified as cranial nerve disorders, neuro-ophthalmologic disorders, or both. 

Smell, vision, chewing, facial feeling or expression, taste, hearing, balance, swallowing, phonation, head tilting and shoulder elevation, or tongue movements can all be affected by cranial nerve diseases . It's possible that one or more cranial nerves are impacted. 

Tumors, inflammation, trauma, systemic illnesses, and degenerative or other processes can cause vision loss, diplopia, ptosis, pupillary irregularities, periocular pain, face pain, or headache, among other symptoms.

 Assessment of Cranial Nerves

 

 Sixth ( Abducens) Nerve Palsy