Ch. 14: Cranial Nerves Flashcards
How many pairs of cranial nerves are there?
- 12 pairs
- 11 exit anterior, 1 exits posterior…relative to brainstem
What do the cranial nerves innervate?
Innervate head, neck, thorax, upper abdomen
(not lower abdomen)
What are the 4 basic functions of cranial nerves?
- Motor innervation.
- Somatosensory and special sensory innervation.
- Parasympathetic innervation
- Head, neck, thorax, upper abdomen
- Corticobrainstem tracts: UMN’s of cranial nerve motor fxn
- For those that innervate muscle - they are THEMSELVES the LMN’s
What is the name of Crainal Nerve I?
Olfactory
Is Cranial Nerve I sensory, motor or mixed?
Sensory
Where is the Olfactory NERVE itself contained?
Within the roof of the nasal sinus
Where is the Olfactory TRACT located?
Starts above the nasal sinus and travels back to the olfactory centers of the brain
(seen in gross disection)
What effect does traumatic brain injury of shaking have on Cranial Nerve I?
- Can disconnect the nerve from the tract
- Creates lack of smell
- Can also lead to altered or lack of taste
What is the possible link between smell loss and Parkinson’s Alzheimer’s disease?
Could be an early sign of these diseases
What is the name of Cranial Nerve II?
Optic
Is Cranial Nerve II sensory, motor or mixed?
Sensory
What is the function of Cranial Nerve II?
Lets in light info from retina of eyeball
What is the path Cranial Nerve II (Optic) takes from the eye back to the brain?
Nerve → Chiasm → Tract
- Nerve: Direct backward projection from the eye ball
- Chiasm: Both cranial nerves come together at the mid line
- Tract: Split apart again
In Cranial Nerve II (Optic), what information is sent from the optic tract to the occipital cortex?
Conscious vision
In Cranial Nerve II (Optic), what information is sent from the optic tract to the superior colliculus?
Uncoscious reflex responses
What dysfunctions are present with complete damage to Cranial Nerve II (Optic)?
- Blindness
- Disruption of pupillary light reflex
- Shine light in eyes, no conscious or reflex function to constrict pupil
What are the names and numbers of the Cranial Nerves that are “Extraocular?”
- Cranial Nerve III (Oculomotor)
- Cranial Nerve IV (Trochlear)
- Cranial Nerve VI (Abducens)
How many “extraocular” muscles are there?
6, three around each eye
What do the muscles innervated by CN III (Oculomotor) do?
Elevates, depresses and adducts eye
(everything the other two CN’s do not do)
[Dont need to know: Medial rectus, Superior rectus, Inferior rectus, Inferior oblique]
What do the muscles innervated by CN IV (Trochlear) do?
Move eye down toward tip of the nose
[Do not need to know: Superior Oblique]
What do the muscles innervated by CN VI (Abducens) do?
ABducts eye away from midline
[Do not need to know: Lateral Rectus]
What is the Medial Longitudinal Fasciculus?
- Interconnects CN III, IV, & VI, vestibular nuclei, and spinal accessory nerve nuclei in brainstem
- Connects all cranial nerve nuclei’s that move the eyes and connects all of those cranial nerves to vestibular nuclei or inner ear
What nucleus is responsible for Parasympathetic contribution to CN III?
Edinger-Westphal nucleus
What are the somatic actions of CN III?
- adduct eyes
- adjust pupil
The parasympathetic innervation of the eye that travels with CN III innervates what two things to affect the eye?
- Pupillary Sphincter -> constricts pupil
- Ciliary Muscle -> Increase curvature of lens for near vision
What is the Pupillary Light Reflex?
- Constricts pupil to light
- Relfex only
- Optic (afferent) and occulomotor (efferent) nerves
- Retina → brain stem (through midbrain) CN II → synapses w/ CN III → then goes right back to the eye
What is the Consensual Light Reflex?
- Light in one eye will constrict both pupils
- Reflex only
- Optic (afferent) and occulomotor (efferent) nerves
- Retina → brain stem (through midbrain) CN II → synapses (parasympathetic) w/ CN III → then goes right back to the eye
What is the Accommodation Reflex?
- Compensation to focus in near vision
- Driven by consciousness vision (routes from occipital region)
- Pupils constrict
- Eye converge (adduct)
- Lens becomes more convex
What are the dysfunctions associated with damage to CN III?
What does it look like?
- Ptosis - Drooping of eyelid
- Affected eye looks down and out - When CN III not working, CN VI ABducts the eye out
- Diplopia - Double vision - 2 images superimposed on top of each other
- Difficulty moving eye medially, downward and upward.
- Dilation of pupil - CN III has parasympathetic - if it is gone, SNS wins and dilates pupil with out any
- Loss of pupillary light reflex and consensual light reflex - Loss of near vision
- Loss of constriction of pupil for focus on near object.
What are the dysfunctions associated with damage to CN IV?
What does it look like?
- Cannot look down and in.
- Extorsion (“tilted head”) due to unopposed action of inferior oblique - Eye rolls lateral to left so patient tilts head to right
What are the dysfunctions associated with damage to CN VI?
What does it look like?
- Inability to abduct eye - Cranial nerve II wins
- Resting position of the eye drifts medially.
What is the name of CN V?
Trigeminal Nerve
What does CN V (trigeminal) do?
- SENSORY
- for tongue but not taste on tongue
- for face and jaw movement
How many branches does the Trigeminal N (CN V) have?
- 3 branches (like Kenny’s hood)
- Opthalamic - above eye (forehead)
- Maxillary - cheek bone
- Mandibular
What messages are sent through the Afferent pathways of the Trigeminal N (CN V)?
- Discriminative touch: face, eye, tounge
- Proprioception
- Nociception: fast pain & slow pain
(bottom picture)
What messages are sent through the Efferent pathways of the Trigeminal N (CN V)?
Muscles of mastication
(top picture)
What are the reflexes for Trigeminal N (CN V)?
-
Blink reflex - touch eyeball
- CN V sensory (in), CN VII motor (out) - better ways to test CN VII out
-
Jaw jerk reflex - finger on chin, hit metacarpal, quick stretch jaw and it closes fast
- Tests CN V (in and out) on reflex level
What signs and sx’s are present with CN V (Trigeminal) Dysfunction?
-
Loss of touch, pain, temperature on face
- Wont be able to feel all or part of their face
-
Possible loss of blink reflex
- Cant feel eye
- Possible loss of jaw jerk reflex (with jaw deviation toward the involved side on active opening).
-
Trigeminal Neuralgia (neuropathic pain in trigeminal nerve).
- Deep dull aching (its going to kill me pain)
- Breeze hitting skin can cause pain
What signs and sx’s are present with CN V II (Facial) Dysfunction?
- Motor function: muscles of facial expression.
-
Parasympathetic function: Salivary, nasal and lacrimal glands.
- Helps you cry, mouth water, nose run
-
Sensory function: Taste sensation from anterior 2/3 of tongue.
- Sweet, salty and sour
How do you test CN VII (Facial)?
- Squeeze tightly closed
- Open eyes wide
- Smile real big and show all teeth
- Lips together, puff out cheeks
What signs and sx’s are present with CN V II (Facial) Dysfunction?
- Paralysis or paresis of all ipsilateral muscles of facial expression (Bell’s Palsy).
- Traumatic mylenopathy - Not working short term
- Traumatic axonopathy - Not working long term (couple weeks to months)
- Lack of closing eye lid, does not produce enough tears -> may have dry eye
What are the functions of CN VIII?
- Sensory
-
2 divisions
- Vestibular division (head movement and position)
- Cochlear division (hearing)
-
Transduction of sound
- Sound waves created by water waves
-
Frequency Coding
- Wide at one end, narrow at other
- Auditory fxn within CNS
What three places does sound travel too?
-
Inferior Colliculus
- Orientation of head and eyes toward sound
-
Reticular Formation
- Sounds can inc or dec arousal (ex: tires screeching)
-
Conscious awareness and recognition of sounds
- Conscious identification & add meaning to sound
- From ear to temporal lobe
What are the dysfunctions of CN VIII?
- Dizzines/Disequilibrium
- Hearing loss
- Difficulty locating sounds in space
What are the types of hearing loss?
-
Conductive hearing loss (e.g., excessive wax or otitis media).
- Air waves cant create water waves
-
Sensorineural hearing loss (e.g., damage to receptor cells or cochlear nerve).
- Peripheral nerve (e.g., acoustic neuroma causing hearing loss and tinnitus) → Damage to cranial nerve itself
- Cochlear nuclei/central pathways (e.g., brainstem stroke) → Hearing cells inside brain stem
What are the functions of CN IX (Glosopharyngeal)?
- Back of tounge and top of throat
- Mixed sensory, motor and autonomic
-
Sensory component: Somatosensation from post tongue, soft palate and pharynx
- Taste sensation from post 1/3 tongue → Bitter
- Starts gag reflex (sensation)
What are the dysfunctions of CN IX (Glosopharyngeal)?
- Loss of afferent limb of gag reflex.
- Loss of afferent limb of swallow reflex.
What are the functions of CN X (Vagus)?
- Mixed Sensory, Motor and Autonomic.
- Sensory component: entire throat & upper abdominal viscera
-
Motor component: throat
- Motor component of:
- Gag reflex ->muscles to spit it out
- Swallow reflex -> muscles to swallow
- Motor component of:
-
Autonomic component: head, throat, thorax & upper abdomen
- Voluntary muscles of throat, wind pipe and voice box (pitch/tone/inflection of speech)
What are the dysfunctions of CN X (Vagus)?
- Difficulty speaking
- Hoarse voice - cant get vocal cord to come together
-
Difficulty swallowing - motor component of swallow reflex - wind pipe doesn’t get closed - can lead to aspiration
- Elect not to eat
- Drool all the time
-
Asymmetric elevation of soft palate - when you go to dr and they have you say “ah”
- If have sore throat and suspect nerve damage you can do the “ah” test to look for asymmetries
- Loss of efferent limb of gag reflex.
- Loss of efferent limb of swallow reflex.
- Poor digestion & may get constipated
What are the functions of CN XI (Accessory)?
-
Motor: Traps & SCM
- Turn head and elevate soulders
What are the functions of CN XII (Hypoglossal)?
-
Motor: Intrinsic & extrinsic muscle of the tounge
- Chew: moves food around in mouth
- Swallow: “scoop” loader dumps food in back of throat
- Speak: constant sounds
What are the dysfunctions of CN XII (Hypoglossal)?
-
Atrophy of ipsilateral tongue
- Atrophy of denervation
- Tongue drifts toward side of lesion when “stuck out” asymmetrically (ipsilateral)
-
Difficulty speaking and swallowing
- Softening of hard constants
What are the CN’s involved in the Oral Stage of swallowing?
- CN V, VII, XII [5,7,12]
- V: Moves jaw
- VII: Closes lips
- XII: Stirs around so you can chew
What are the CN’s involved in the Laryngeal/Pharyngeal Stage of swallowing?
- CN IX, X [9,10]
- IX: Sense food at back of throat
- IX: yummy = swallow OR yucky = spit out
- X: food down throat into stomach
What are the CN’s involved in the Esophageal Stage of swallowing?
- CN X
- If not working = aspiration is a potentail problem
What cranial nerves are involved in speaking?
-
CN X (Vagus)
- Larynx - Control throat and vocal cords
- Soft palate - Raise/lower for resonance of speech
-
CN VII (Facial)
- Lips - Especially the lips to produce “B,” “P,” “M”
-
CN V (Trigeminal)
- Jaw - Moves jaw to put teeth in right place OR open jaw to allow sound to come out
-
CN XII
-
Tongue - Moves tongue - where tongue presses against hard palate or the teeth
- Dysfunction: dysarthria - mechanical aspects of speech not good
-
Tongue - Moves tongue - where tongue presses against hard palate or the teeth
What is the Corticobrainstem Tract?
Upper motor neurons that control motor function of all cranial nerves
What nerves are affected with a swallowing dysfunction?
May indicate problems with UMN or LMN of CN V, VII, IX, X and/or XII
What nerves are affected with dysarthria?
May indicate problems with UMN or LMN of CN V, VII, X, and/or XII.
