Cranial Nerves

Question 1

Cranial Nerve 1

Answer 1

Function: sense of small (special sense)
Pathway: leads from superior part of nasal cavity and goes to cortex frontal and temporal lobe (associated with smells coming from memory)
Olfactory nerve attaches to form olfactory bulbs…nerves pass through holes of cribriform plate (ethmoid bone) to upper part of nasal cavity with olfactory receptors

How to test it:
-Peppermint essential oils, see if patients can smell it (eyes closed)
-or can use Coffee (best smell ever 😊 )
Anosmia: loss of smell
COVID made that famous- loss of sense of smell (head injury can also cause it)

Question 2

Where are cranial nerves located, and what are the different types

Answer 2

ALL Cranial nerves are found in the brain stem EXCEPT 1 and 2:
1) Olfactory nerve projects to cortex
2) Optic nerve Projects to thalamus and then cortex
All others are found in the brainstem
3-4=midbrain
5-8=pons
9-12 = Medulla
BRAIN STEM= Midbrain, pons and medulla
Cranial nerve 8 used to be called auditory but now vestibulocochlear because has 2 functions (
The vestibular nerve is primarily responsible for maintaining body balance and eye movements, while the cochlear nerve is responsible for hearing.)

Types of cranial nerves
1) Special sensory senses=sight, smell, sound, taste, balance
Somatic sensory information: Skeletal muscles (think before you do)
Somatic sensory: not special sense (pain, light touch, vibration, pressure, temperature)
Autonomic NS if cannot control or perceive them
Some cranial nerves are sensory, some motor, and some are both

Question 3

Cranial Nerve 2

Answer 3

Function = vision (special sense); responsible for transmitting visual information.
Goes from back of eye (retina which has rods and cones)

How to test it?
1) Snellen eye chart
2) Peripheral field test -see of can see finger moving (do with both eyes) - close 1 eye
3) Ophthalmoscope to assess (blood vessels, plaque for macular degeneration, blood vessel can tell if there is hypertension if torturous)

Question 4

What are Cranial nerves 3,4 and 6 and how do you test them?

Answer 4

Function: Controls the movements of the eye; issues with any of these cranial nerves can cause nystagmus

How to test:
H test is the perfect test for these 3 cranial nerves. The PERRLA test cranial nerve 3

Question 5

How many cranial nerves are there and name all of them

Answer 5

remember the mnemonic OOOTTAFAGVAH; Oh Oh Oh To Touch And Feel Ah Girls Vagina AHHHHH

1. Olfactory
2. Optic
3. Oculomotor
4. Trochlear
5. Trigerminal
6. Abducens
7. Facial
8. Auditory (vestibulocochlear)
9. Glossopharyngeal
10. Vagus
11. Auxillary
12. Hypoglossal

Question 6

What cranial nerves will cause Nystagmus?
A. CN 3,4 and 6
B. CN 2,3 and 7
C. CN 1 and 12
D. CN 2, 6 and 9

Answer 6

Correct answer is A below is why
Cerebellum: The cerebellum is the region of your brain that controls balance. Damage to the cerebellum, such as from a tumor or stroke, may cause nystagmus. Additionally, the antibodies in paraneoplastic syndromes cause nystagmus by targeting the cerebellum.

Cranial nerves: Three pairs of cranial nerves control eye movement muscles (each eye is controlled by one nerve of each pair). Damage to these nerves can interfere with eye muscles, causing nystagmus.

The oculomotor nerve (cranial nerve three) controls several muscles that move your eyes: the superior rectus muscle, the medial rectus muscle, the inferior rectus muscle, and the inferior oblique muscle. These muscles move your eyes straight up and down and toward your nose.
The trochlear nerve (cranial nerve four) controls the superior oblique muscle that moves your eye in a direction that is down and away from your nose.
The abducens nerve (cranial nerve six) controls the lateral rectus muscle, which moves your eye outward and away from your nose.
The vestibulocochlear nerve (cranial nerve eight) mediates your sense of sound and balance. It does not control eye movement, but a deficit in this nerve can impair balance to a degree that causes nystagmus.
Brainstem: The cranial nerve fibers and the nerve fibers of the cerebellum run through the brainstem, an area of the brain that links the brain with the spinal cord. For this reason, a disease that involves the brainstem (such as bleeding or stroke) may cause nystagmus.

Inner ear: The inner ear contains many tiny structures that control hearing and help mediate balance. Inflammation, infections, and tumors involving the inner ear can cause nystagmus.

Question 7

What is cranial nerve 5, what type of nerve is it, and it’s function?

Answer 7

Trigerminal

Cranial Nerve 5= both sensory and motor! 3 branches

Opthalmic branch: sensation of touch/pain/balance and proprioception around eye/forehead/scalp/cornea/eyelids/nasal mucosa

Maxillary branch: maxillary part of face and maxillary teeth

Mandibular branch: mandible/lower jaw, proprioception for tongue but not involved in taste
Exit from pons and go through superior orbital fissure for Opthalmic
Foramen rotundum for maxillary
Foramen ovale for mandibular part

Motor function: mastication and chewing (temporalis, masseters, pterygoids) and neck/middle ear muscles ..mandibular nerve innervates these muscles and exits through foramen ovale

How to test
-Can use sharp and dull touch test (cotton for soft part and can break it for sharp part)
Forehead
Maxillary
Mandibular region

**Can test mandible by asking to open and clench it

image showing regions in red provided by https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Ftse2.mm.bing.net%2Fth%3Fid%3DOIP.ElHID3HEHWS0A6jBFI7n8AHaGg%26pid%3DApi&f=1&ipt=c8ea48cf3114353f4e64ca75ec8b60830fd679c9a86b7a14eaf598014a461c53&ipo=images

Question 8

Cranial nerve 7 what is its name, what type of nerve and its function

Answer 8

1. Facial nerve
2. Trickiest nerve it is both sensory and motor
3. Sensory: anterior 2/3 of tongue (taste special sense); think its closest to the face and the glossopharyngeal senses the posterior 1/3
   Somatic sensory (vibration/pressure/pain) of ear (auricle and ear canal…along with mandibular)
   Motor: many skeletal muscles of the body (more than any other nerve) …other than tongue/eye muscles or muscles of mastication
   Controls eye opening, pursed lips, raising eyebrows
   Salivary (sublingual, submandibular and parotid), tear gland (AKA lacrimal gland), nasal mucosa

Question 9

Cranial NERVE 8 What is the name, what type of nerve is it

Answer 9

1. vestibulocochlear (auditory)
2. sensory
   3.Transmits sound waves.
   a)Sound waves–>tympanic membrane–>Malleus, incus and stapes–>transmits vibration into cochlea –>vibrations in cochlear fluid move hairs and transmit electrical impulses which is carried by CN8
   There is one nerve going to cochlea and another nerve going to the vestibule
   Inner ear infection throws off balance and get nauseated

Inner ear–>internal acoustic meatus–>pons –> thalamus –>temporal lobe for sound perception

4.Stand behind patient and whisper things “baseball”, come closer until they hear you
Or can use tuning fork to test if they have better air or bone conduction (can transmit sound with end of tuning fork on area of skull like mastoid bone). You hit hit tuning fork and place end on mastoid bone and wait until they can’t hear it anymore…then bring next to ear (without striking it again) and should hear again…If bone conduction is greater than ear conduction, it indicates conductive hearing loss…indicates issues with ear canal, bones, tympanic membrane

Question 10

What is Cranial Nerve 9

Answer 10

1. Glossopharyngeal
2. Sensory and motor (comes from medulla)
   a) Motor Functions: Swallowing: The glossopharyngeal nerve helps control muscles involved in swallowing. Parotid Gland Secretions: It stimulates the parotid gland, which is the largest salivary gland. Saliva is necessary for lubricating food and making swallowing easier. Without saliva, food would be dry, and it would be hard to swallow. This also helps prevent saliva from pooling in the mouth.
   b) Sensory Functions: Pharynx Sensation: The glossopharyngeal nerve provides sensory input from the pharynx (throat). This includes sensations of pain, pressure, and temperature.
   Ear Sensation: It also picks up sensory information from part of the ear (pain, pressure, temperature).
   c) Chemoreceptors and Baroreceptors in the Carotid Artery:
   Chemoreceptors: These receptors detect levels of oxygen (O2) and carbon dioxide (CO2) in the blood. They play a role in regulating respiratory rate by signaling the brain when the levels of O2 or CO2 in the blood are abnormal.
   Baroreceptors: These receptors monitor blood pressure by sensing the stretch of the carotid artery walls. If blood pressure rises or falls, baroreceptors send signals through the glossopharyngeal nerve to the brain, which helps regulate heart rate and blood vessel constriction to maintain stable blood pressure.
   d) Taste: The glossopharyngeal nerve carries taste sensations from the posterior one-third of the tongue (the back of the tongue). In contrast, the facial nerve (cranial nerve VII) is responsible for taste from the anterior two-thirds (front) of the tongue.
   Why Chemoreceptors and Baroreceptors Are Important:
   These receptors are part of the body’s homeostatic mechanisms that regulate key physiological functions, such as breathing rate and blood pressure. The glossopharyngeal nerve helps relay these signals to the brainstem, where the body makes necessary adjustments (e.g., increasing or decreasing respiration or heart rate) to keep conditions stable.

This makes the glossopharyngeal nerve critical not only for functions like swallowing and taste but also for essential involuntary processes like maintaining proper blood pressure and respiration.

How to test it?
Gag reflex (same as strep test) - swab back of throat (some hypersensitive)
Some can swap uvula and tonsils with minimal reflex
Want soft palate and tongue elevate

Question 11

What is Cranial nerve 10, type of nerve is it, its function, and how to test it

Answer 11

Vagus nerve –cranial nerve 10 =autonomic nervous system

-visceral organs (lungs, heart, liver, GI tract)
-Both sensory and motor
MOTOR: pharyngeal muscles (also swallowing) but also laryngeal muscles
PNS - Rest and digest – peristalsis
Sensory: internal organs, pharynx, external ear
-Sensory input from aortic baroreceptors and chemoreceptors

How to test it?
Listen to patients voice and see if its hoarse (ask to say ahhh) - want to see upper palate elevate
Don’t really test visceral organ function at physical exam this way

Question 12

What is cranial nerve 11

Answer 12

1. Accesory Nerve
2. Cranial Nerve 11- motor only
   Spinal accessory nerve
   
   • Innervates SCN and trapezius
   • Cell bodies more in cervical spinal cord than brain stem BUT travels thorugh foramen magnum and out via jugular foramen
3. How to test it?
   Turn head against resistance (try rotation as rotation requires both of these muscles)
   Shrugging shoulders (for trapezius)

Question 13

Cranial Nerve 12; What is the name, what type of nerve, its function, and how do you test it?

Answer 13

1. Hypoglossal
2. ONLY motor
   
   • Tongue but not taste
   • Key for speech and swallowing
   • Exits medulla and enters hypoglossal canal – tongue falls back when relaxes and closes airway when sleep and leads to breathing obstruction!
3. How to test?
   Ask to stick out tongue and move side to side. See if there is a natural deviation when asked to keep the tongue straight (could be damage to nerve, medulla or cortex)