Cranial Nerves Flashcards
Cranial Nerves
- Peripheral nerves that exit / enter the central nervous system
- 31 pairs of spinal nerves
- Some: special sensory or parasympathetic component
- CNs can be motor, sensory, or mixed
Cranial Nerves – Origin
12 pair of cranial nerves
- CNs III - XII exit from the brain stem
- CN I projects directly to the telencephalon
- CN II is an outgrowth of the diencephalon
Spinal Nerves & CNs
Spinal Nerves
• Somatic sensory fibers conveying information from skin, muscle and joint on pain, temperature, and touch
• Visceral sensory information from blood vessels (for BP and chemistry) or visceral structures such as the digestive tract
**• Visceral motor ** autonomic motor to viscera (peristalis, secretion)
**• Somatic motor ** voluntary skeletal muscle
Cranial Nerves
- CNs have somatic sensory, visceral sensory, visceral motor, somatic motor, and a special sensory component (ex: smell, taste, equilibrium).
- Some CNs: parasympathetic function.
Cranial Nerve Nuclei
- Nuclei = Brain of the nerve
- Nuclei are a collection of neuronal cell bodies located within the central nervous system
- Function: Sensory (afferent) axons enter and synapse onto neural cell bodies and motor (effernt) axons originate centrally at nuclei and project to peripheral structures
- The bundles of effernt and afferent axons associated with CN nuclei are the cranial nerves
Cranial Nerve Composition
• Sensory – I, II, VIII • Motor – II, IV, VI, XI, XII • Mixed – V, VII, IX, X
Parasympathetic Function (calming) • CN III Occulomotor Nerve • CN VII Facial Nerve • CIX Glossopharyngeal • CN X Vagus
Functional Components
• Somatic Motor - Striated muscle of tongue and eze
**• Branchial Motor ** - Muscles of mastication, face, larynx, pharynx
**• Visceral Motor ** - Parasympathetic to smooth muscle and glands
**• Visceral Sensory ** - unconsious visceral sensations
• Somatic Sensory - General sensation may or may not be consious in nature
• Special Sensory - taste, smell, hearing, vision, and balance
Name all the Cranial Nerves.
• CN I Olfactory
• CN II Optic
• CN III Oculomotor
• CN IV Trochlear
• CN V Trigeminal
- CN V1 Opthalmic division
- CN V2 Maxillary division
- CN V3 Mandibular division
• CN VI Abducens
• CN VII Facial
• CN VIII Vestibulocochlear
• CN IX Glossopharyngeal
• CN X Vagus
• CN XI Accessory
• CN XII Hypoglossal
CN I Olfactory
Special sensory visceral afferent
Function: Smell
- Communicates with the temporal lobe (Uncus and etorhinal cortex)
- Olfaction: Sesation of odors that results from detection of odorous substances aerosolized in the environment
- Olfactory epithelium: roof of nasal cavity, contains cells whose axons constitute the olfactor nerves (approx. 25 million neurosensory cells per side of nose).
- Nerves pass through the cribiform plate of the ethmoid bone and synapse onto the olfactory bulb
- Axons extend from the bulb to form the olfactory tract which communicates with the medial temporal lobe
• Exit: Foramen of cribiform plate
• Location of Nuclei: Telencephalon
CN I Olfactory – Injufry & Test
- Resulst in Anosmia - loss of sense of smell
- Facture of cribiform plate (CSF leakage)
- Tumor of frontal lobe or anterior meninges may compress olfactory bulb or tract
- Temporal lobe tumor
- Viral or allergic rhinitis
CN I Olfactory – Test
- Unilateral test that must be performed bilaterally
- Block one nostril + place something pungent under the other nostril (coffee). Ask the patient when they smell it.
CN II Optic
• Special Sensory
- *• Function:**
- Visual acuity
- Intactness of visual fields
• Surrounded by meninges and subarachnoid space (CSF)
• Optic Nerve: Formed by retinal ganglion cells that pierce the sclera dep tot he otpic disc
• Optic Chiasm:
Point where optic nerve axons from retinal ganglia cells int he nasal half of each retina decussate – for binocular vison
• Optic Tracts: Ipsilateral temporal retinal axon fibers and crossed contralateral nasal axon fibers
• Left and right tracts terminate in the corresponding lateral geniculate body of the thalamus and is relayed to visual cortices
• Enter: Optic Canal
• Location of Nuclei: Diencephalon
CN II Optic – Injury
Papilledema
- Edema of Papilla (optic disc)
- Caused by increased intracranial pressure (CSF pressure) surrounding optic nerve
- Pressure is placed on vein and prevents return of venous blood form retina
Optic Neuritis
- Inflammation due to exposure to toxic sustances
- Degenration
- De-myelinating Disorder
CN II Optic – Test
**Test: **
• with Snellen Chart • Placed 6 m away
• close one eye and read the smallest line they can make out
→ 1 miss is fine; 3-4 move up one line
CN III Occulomotor
• Motor
- *• Function:**
- Pupil constriction
- Upward / Downward / Medial gaze
- Eyelid elevation
- Somatic and Visceral Efferent
- Motor to 4 of 6 extra-occular eye striated muscles → Superior, medial, and inferiro rectus → Inferiror oblique
• Motor to upper eyelid (striated mm)
→ Levator palpebrae superioris
- Motor to sphincter of pupil, the smooth muscle of the iris (parasympathetic, visceral) → Constriction of pupil (smooth mm)
- Motor to ciliary muscles of lens → Produces accomodation of lens (smooth mm)
• Exit: Superior orbital fissure
• Location of Nuclei: brain stem
CN III Occulomotor – Eye Muscles
- Superior rectus - elevate + add
- Inferior rectus - depress + add
- Medial rectus - add
- Inferior obplique - elevate + add(no direct pull → coming from behind the eye, loops around → attaches to eye → elevates + add)
CN III Occulomotor – Injury
• Ptosis: drooping of upper eyelid
• No pupillary reflex
• Dialation of the pupil (interruption of Parasymp)
• Eyeball abducted and inferior
• Increased ICP (intercranial pressure) → Can compress CN III → Result: decreased / slow pupillary light reflex ipsilateral
• Aneurysm of PCA or SCA (post & sup cerebral arteries)
CN III Occulomotor – Test
Pupil constriction (direct & consensual)
• Shine a light in patients eye. Look to see if the pupil of the eye the light is shone in constricts; also look if the contralateral pupil constricts.
Eyelid elevation
- Look for symmetry of the eyelids
- Ptosis (droopy eyelid)
CN IV Trochlear
• Motor
• Function: ** ** Somatic Motor + proprioception to one extra-occular eye muscule → Superior Oblique (moves the eyeball inferiorly and laterally) → “Down + Out” (cute shoes)
- Travels the longest distance intercranially (subarachnoid)
- Smallest cranial nerve
- Only nerve to emerge dorsally (posterior surface) from the midbrain
- Exit: Superior Orbital Fissure
- Location of nuclei: Midbrain - exit from brain stem
CN IV Trochlear – Injury
- Rarely paralyzed alone
- Can be tron in severe head injuries
- Diplopia (double vision) when looking inferiorly + medially
CN V Trigemninal – Test
• Test:
• Sensory component:
- Sensation to face (hot/cold, sharp/dull)
- Corneal reflex:touch cornea w/ a paper towel
–> blinking
• Motor component:
- Palpate masseter muscles
CN V Trigeminal
Mixed: Motor & Sensory • General Sensory w/ Somatic Afferents
- *Function:** • Sensory:
- face, cornea, nasal & oral cavity, upper & lower teeth
- Ophthalmic, Maxillary, Mandibular division
• Motor:
- Muscles of Mastication - Mandibular division
3 Divisions • Ophthalmic - Sensory • Macillary - Sensory • Mandibular - Sensory + Motor
• Location of Nuclei: Pons and Medulla
CN V Trigemnial – Opthalmic Division
Somatic Sensory for:
- Cornea: transparent covering for the eyes
- Forehead
- Scalp
- Eyelids
- Nose
- Nasal Mucosa
Exit: Superior Orbital Fissure
CN V Trigeminal – Maxillary Division
Somatic sensry for:
- Skin over Maxilla
- Upper Lip
- Maxillary teeth
Exit: Foramen rotundum
CN V Trigeminal – Mandibular Division
Somatic sensory for:
- Skin over Mandible, lower lip, side of head
- Mandibular Teeth
- Temporomandibular Joint (TMJ)
- Somatic sensation anterior 2/3 of tongue
Motor for muscles of mastication:
- Masseter
- Pytegoids (Medial + Lateral)
- Mylohyoid
- Anterior Belly Digastric
- Tensor Tympani
Exit: Foramen ovale
CN V Trigeminal – Injury
Injury:
- Tumors or lesions of pons and medulla
- Aneurysms
- Meningeal Infections
** Paralysis** to mm of mastication
→ loss of thermal/painful sensation to face, loss of corneal reflex
CN VI Abducens
Motor
Function: Pure lateral eye movement
• Somatic Motor ot one extra-occular eye muscle → Lateral Rectus: abducts / moves eye laterally
Exit: Superior Orbital Fissure
Location of Nuclei: Pons, Nerve emerges from bainstem between pons and medulla and runs alongside basilar artery then bends sharply over petrous part of temporal bone
CN VI Abducens – Injury
Eye rests medially deviated b/c lateral rectus is pralyzed and can cause diplopia
- Increased ICP stretches the nerve
- Brain tumor may compress the nerve
- Aneurysm of the Circle of Willis
CN VI Abducens – Test
III, IV, VI tested together
- Smooth pursuits:
Check for smooth tracking (“follow my pen”)
- Saccades:
Accuracies (no jumping or overshooting; “look at my nose, look at my pen”)
CN VII Facial
Mixed: Sensory + Motor
Sensory Function: = special visceral and general somatic afferent
- Taste: anterior 2/3rds of tongue, soft palate
- Somatic sencory to external ear
- Parasympathetic to several salivary glands, lacrimal glands
Motor Function: = brachial/somatic & parasympathetic general visceral efferent
• Muscles of facial expression, throat muscles, and auricular muscles (stapedius)
Exit: Internal Acoustic Meatus (Stylomastoid Foramen)
Emergence: Junction of pons and medulla
Location of Nuclei: Pons
CN VII Facial – Injury
Most frequently injured CN
• Sensory: loss of tste ant 2/3rds of tongue
• Motor: Facial muscle paralysis
• Location of injury determines sequela with altered salivation and tear production, facial muscle paralysis and tst loss. Each being possible.
• Belly Palsy: Unilateral paralysis of some or all facial muscles secondary to a lesion of facial nerve CN VII
• Idopathic
CN VII Facial – Test
• Sensory component:
- Taste test: ID sweet or salty
• Motor component:
- Corneal reflex:touch cornea w/ a paper towel
- -\> blinking
- "Make faces"
CN VIII Vestibulocochlear
Sensory
Function:
• Special Sensory for hearing and equilibrium (balance issues)
2 Divisions • Vestibular: Equilibrium and balance w/ 4 Nuclei at pons and medulla juncture • Cochlear: Hearing with 2 nuclei located in the medulla
Entrance: Internal Acoustic Meatus ⇒ seperates into vestibular and cochlear Ns
Cochlear Nerve: • Information Relay • Medial geniculate body of thalamus • Auditory aspect of cerebral cortex (superior region of temporal lobe near lateral sulcus)
Cochlear function: Hearing acuity
Vestibular function: position in space related to position & movement of head and balance
CN VIII Vestibulocochlear – Injury
MOI: • Acoustic Neuroma • Trauma • Middle Ear Infection • Labyrinthine artery damage
Injury: • Tinitus (ring, buzz) • Vertigo (diyyy, loss of balance • Altered hearing
Deafness • conductive (external and / or middle ear) (oritis media)
• sensorineural (disease of cochlea, or cochlea to brain)
Acoustic neuroma (neurofibroma)
- Slow growing B9 tumor Schwann cells (neurolemma, the outer most layer of Schwann cells) in cochlear nerve
- Leads to loss of hearing, probable dysequilibrium and tinnitus in 70% of patients
Vertigo (hallucinogenic movement)
- Spinning vs. swaying back & forth
- Meniere Syndrome - all ages, sually middle to older age
CN VIII Vestibulocochlear – Test
• Hearing tests:
- Rine Test (Air): tuning fork through air
- Weber Test (Bone): tuning fork on bony promnence: mastoid process, cranium
• Vestibular testing:
- cold/warm stimulus
- -> SHOULD cause vertigo/nystagmus
- -> direction of nystagmus or eye beating
- -> COWS: cold opposite, warm same
• Vestibulo-ocular reflex
- Reflex test for III, VI & VIII
- Eyes should stay on examiners nose while head thrust performed.
- Conjugate horizontal gaze: coordinated eye movement
CN IX Glossopharyngeal
Mixed: Motor, Sensory & Parasympathetic
• Gag reflex
Sensory Function:
• Taste on posterior 1/3rd of tongue, somatic sensaton on 1/3rd of tongue, auditory tube & middle ear, carotid bodies (on bifurcation of arteries)
Motor Function:
• Stylopharyngeus (elevates pharynx w/ swalloing)
Parasympathetic Function: • Parotid Gland (Salivary gland arond the mandibular ramus
Exit: Jugular Foramen
Location of Nuclei: Medulla • 2 sensory • 2 motor • Share nuclei w/ CN X Vagus & CN XI Accessory
CN IX Glossopharyngeal Nerve – Injury
Tumors
- Loss of taste posterior 1/3rd of tongue
- Absent gag reflex
- Often includes involvement of CN X Vagus and CN XI Accessory
CN IX – Glossopharyngeal Nerve – Test
• Sensory component:
- Taste test: Does it taste bitter? - Gag reflex: lightly stimulate back of throat
• Motor component:
- Have patient swallowing a liquid
CN X Vagus
Mixed
Sensory Function:
• General somatic, special cisceral (taste, carotid bodies/sinus), general visceral • Heart, lungs, trachea, pharynx, larynx, bronchi, GI tract, external ear
Motor Function:
• Visceral (parasympathetic) to thoracic and abdominal viscera • Somatic motor to soft palate, pharynx (post. Tongue, mouth), laryngeal muscles • Motor: heart, lungs, trachea, palate, pharynx, larynx, bronchi, GI tract (ex: constricts bronchioles, decreases HR, increases GI motility)
Parasympathetic Function: • Thoracic and abdominal viscera, to level of left colic flexure
Exit: Jugular Foramen
Emergence: from a sercies of rootlets in Medulla
- Travels through the neck in the carotid sheath with the internal carotid and internal jugular vein
- Travel down the thorax in the esophageal hiatus of the diaphragm to the abdominal cavity
Location of Nuclei: Medulla + Cranial Spinal Cord • 2 sensory • 2 motor
CN X Vagus – Injury
• Dysphagia: Difficulty swallowing - Injury to pharyngeal branches -
• Dysphonie: Difficulty speaking
• Aphonia: Loss of voice
• Inspirator stridor: high pitch harsh respiratory sound
CN X Vagus – Test
• Say Ahhh - Test
–> examine symmetry of uvula
If lesion –> uvula deviates contralaterally
(strong side is pulling)
–> listen for hoarsness
- -> If both severed –> aphonia (unable to talk)
- -> if one severed –> deviates from affected side
CN XI Accessory
Also called Spinal Accessory Nerve
Motor
Function:
• Sternocleidomastoid (SCM) - somatic
• Trapezius • Striated mm of soft palate, pharynx, and larynx via connections with CN X Vagus
• Cranial and spinal nerve roots form the first 5 cranial levels
Exit: Jugular foramen
CN XI Accessory Nerve – Injury
- Lymph node biospy
- Surgical procedures ot intenal carotid or internal jugular veins
⇒ Resultant weakness of SCM and Traps
CN XI Accessory – Test
- Shoulder shrug test: Trapezius
- Head turn test: Sternocleidomastoid
CN XII Hypoglossal
Motor
Function: • Intrinsic + extrinsic muscles of tongue • Motor nerves carry proprioceptive info
• Tongue movement, symmetry & shape
Exit: through hypoglossal canal
Location of Nuclei: Medulla
• Branches off Medulla
CN XII Hypoglossal Nerve – Injury
- Paralysis of ½ of tongue, ipsilateral to side of injury
- Deviates toward side of paralysis (pushing)
CN XII Hypoglossal Nerve – Test
• Let me see your tongue test:
–> examine resting tongue
• Stick out your tongue test:
–> examine tongue movement, strength & coordination
–> if lesion –> tongue deviates ipsilaterally (strong side pushing)
Anatomical Origin Summary
Forebrain: CN I + II
Midbrain: CN III + IV
Brainstem:
- Pons: CN V
- Junction between Pons & Medulla: CN VI + VII + VIII
• Medulla: CN IX + X + XII
Superior Spinal Cord: CN XI
