Neuro Lecture 9 (pt. 2): CN VIII, IX, X, XI, XII

What are the 2 divisions of the ear (CN VIII)?

- Bony labyrinth

- Membranous labyrinth

What does the bony labyrinth contain (CN VIII)?

Perilymph

What does the membranous labyrinth contain (CN VIII)?

Endolymph

What are the 3 components that the membranous labyrinth contains (CN VIII)?

- Cochlea

- Semicircular canals

- Otolith organs

What does the cochlea contain (CN VIII)?

Hair cells (receptors) for hearing

What do the semicircular canals contain (CN VIII)?

Hair cells that respond to angular accelerations

What do the otolith organs contain (CN VIII)?

Hair cells that respond to linear accelerations

What does higher frequency sound/pitch activate (CN VIII)?

- Hair cells near oval window

- Birds, children, alarms

What does lower frequency sound/pitch activate (CN VIII)?

Hair cells near apex of cochlea

Where does the cochlear nerve synapse (CN VIII)?

Dorsal/ventral cochlear nuclei

How does auditory pathway cross (CN VIII)?

- Bilaterally at multiple points

- No unilateral hearing loss with lesions above cochlear nuclei

What are the 2 auditory pathways of the cochlear nerve (CN VIII)?

- Primary lemniscal

- Non-lemniscal

What is the primary lemniscal pathway responsible for (CN VIII)?

- Carries information from both ears to primary auditory cortex

- Conscious hearing and recognition of sounds

What is the first step of the primary lemniscal pathway (CN VIII)?

Primary sensory neurons in spinal ganglion send axons in cochlear division

What is the second step of the primary lemniscal pathway (CN VIII)?

Dorsal/ventral cochlear nuclei

What is the third step of the primary lemniscal pathway (CN VIII)?

Superior olivary nucleus

What is the fourth step of the primary lemniscal pathway (CN VIII)?

Inferior colliculus

What is the fifth step of the primary lemniscal pathway (CN VIII)?

MGN of thalamus

What is the sixth step of the primary lemniscal pathway (CN VIII)?

Auditory cortex (Heschl's gyrus)

What is the non-lemniscal pathway responsible for (CN VIII)?

- Unconscious perception of attention, awareness, auditory reflexes, emotional responses

- Via reticular formation

- Orients head and eye to location of sound

- Alerts to impending danger

What causes unilateral hearing loss (CN VIII)?

- Abnormalities of external auditory canal, middle ear, cochlea

- Injury of CN VIII, dorsal/ventral cochlear nuclei

What are 2 types of unilateral hearing loss (CN VIII)?

- Conductive

- Sensorineural

What is conductive hearing loss (CN VIII)?

Abnormalities of external auditory canal or middle ear

What causes conductive hearing loss (CN VIII)?

- Otitis

- Tympanic membrane perforation

What is sensorineural hearing loss (CN VIII)?

Disorders of cochlea or CN VIII

What causes sensorineural hearing loss (CN VIII)?

- Exposure to loud sounds

- Meniere's disease

- Tumor

Where can you find the vestibular anatomy (CN VIII)?

- Posterior to the cochlea

- Filled with endolymph

What does the vestibular anatomy consist of (CN VIII)?

- 3 semicircular canals

- Otolith organ

- Utricle and saccule

What structures are a part of the semicircular canals (CN VIII)?

Anterior/posterior/lateral semicircular canals

What sensory organ is a part of the semicircular canals (CN VIII)?

Ampulla

What is the function of the semicircular canals (CN VIII)?

- Sensing angular head motion in different directions

- Helps keep eyes steady when head is moving

- Vestibular ocular reflex (VOR)

What is the ampulla (CN VIII)?

The structure in which hair cells are located

What is seen with increased activity in semicircular canals (CN VIII)?

- Complimentary

- Increased activity in one ear inhibits activity in the other

- Allows for better balance and stable vision

What structures are a part of the otolith organs (CN VIII)?

Utricle and saccule

What sensory organ is a part of the otolith organs (CN VIII)?

- Macula

- Hair cells sensitive to movement in straight lines

What is the function of the otolith organs (CN VIII)?

Sense position of the head with respect to gravity (linear acceleration)

What is the utricle sensitive to (CN VIII)?

Vertical acceleration, orientation, balance

What is the saccule sensitive to (CN VIII)?

Horizontal acceleration, deceleration of head in horizontal plane

What is benign paroxysmal positional vertigo (CN VIII)?

- Inner ear disorder

- Feeling that everything is spinning in/around

What causes benign paroxysmal positional vertigo (CN VIII)?

Otolith move out of place and enter semicircular canals

How do you test for benign paroxysmal positional vertigo (CN VIII)?

- Dix-Hallpike (Nylén-Bárány) Test

- +ve with nausea and nystagmus

- -ve if dizzy but no nystagmus

What characteristics set apart peripheral vertigo (CN VIII)?

- Sudden and memorable onset

- Client will be able to give you a date/time

What characteristics set apart central vertigo (CN VIII)?

- Slow onset

- Client will not be able to tell you when symptoms started

What are the functions of the vestibular system (CN VIII)? (6)

- Proprioception

- Muscle tone and postural control

- Head positioning and movement in relation to gravity

- Balance

- Bilateral integration

- Alertness and arousal

What is proprioception responsible for (CN VIII)?

Awareness of body position and movement in space

What are muscle tone and postural control responsible for (CN VIII)?

- Influences proprioception

- Via medial/lateral vestibular spinal tract

What is head positioning and movement in relation to gravity responsible for (CN VIII)?

Head stability and midline orientation

What falls under the responsibilities of balance (CN VIII)?

- Gaze stability

- Gait stability

- Spatial awareness

What signs are associated with dysfunction of alertness and arousal in the vestibular system (CN VIII)?

- Nausea

- Vomiting

- Altered consciousness

What muscle does the branchial motor neuron associated with the glossopharyngeal nerve innervate (CN IX)?

Stylopharyngeus muscle

What gland is associated with the parasympathetic aspect of the glossopharyngeal nerve (CN IX)?

Parotid gland (salivation)

What does the general sensory neuron associated with the glossopharyngeal nerve innervate (CN IX)?

- Posterior 1/3 of tongue

- Pharynx

- Auditory meatus

What is the special sensory neuron associated with the glossopharyngeal nerve responsible for (CN IX)?

Taste from posterior 1/3 of tongue

What receptors make up visceral sensory neurons associated with the glossopharyngeal nerve innervate (CN IX)?

Chemoreceptors and baroreceptors of carotid body

What are the important functions of CN IX?

- Special sensory

- Visceral sensory

- Other: gag reflex

Which cranial nerve is also known as the "wandering nerve"?

CN X (vagus nerve)

What parts of the body are affected by CN X? (8)

- Larynx

- Trachea

- Bronchi

- Lungs

- Heart

- GI tract

- Liver

- Pancreas

Which organs receive parasympathetic innervation from the vagus nerve (CN X)?

- Heart

- Lungs

- Digestive tract

- Down to splenic flexure

Which muscles receive motor innervation from the vagus nerve (CN X)?

Pharyngeal and laryngeal muscles

Which areas receive general sensory innervation from the vagus nerve (CN X)?

- Pharynx

- Meninges

- External auditory meatus

What is the special sensory innervation from the vagus nerve responsible for (CN X)?

Taste for the epiglottis and posterior pharynx

What makes up the visceral sensory innervation from the vagus nerve (CN X)?

Baroreceptor and chemoreceptor of aortic arch

What tests can an OT do for CN IX and CN X?

- Palate elevation

- Gag reflex

What is dyspnea?

- Difficulty breathing if visceral branch of vagus nerve is damaged

- CN X pathology

What is dysphonia?

Hoarse voice

What is dysphagia?

Difficulty swallowing

What is dysarthria?

Difficulty enunciating words

What is the first step of the pathway of the spinal accessory nerve (CN XI)?

Arises in medulla and upper 5-6 cervical segments

What is the second step of the pathway of the spinal accessory nerve (CN XI)?

Ascend through foramen magnum to reach intracranial cavity

What is the third step of the pathway of the spinal accessory nerve (CN XI)?

Exits cranium via jugular foramen

What is the function of the branchial motor neurons associated with the spinal accessory nerve (CN XI)?

- Elevation of larynx with swallowing

- SCM for turning head in opposite direction

- Upper trapezius elevates shoulder and maintain head extension

Is the lower portion of the trapezius supplied by CN XI?

No, mainly supplied by cervical nerve roots C3 and C4

What are signs and symptoms of CN XI pathology? (5)

- Dysphasia

- Laryngeal elevation

- Weakness rotating head contralaterally

- Weakness flexing/extending head

- Difficulty elevating shoulder or involved arm above 90º

What is the function of the hypoglossal nerve (CN XII)?

- Somatic motor

- Tongue movement

What is the first step of the pathway of the hypoglossal nerve (CN XII)?

Motor pathway decussates and then synapses on hypoglossal nucleus

What is the second step of the pathway of the hypoglossal nerve (CN XII)?

Exits between pyramid and inferior olivary nucleus

What does an UMN lesion of the hypoglossal nerve affect (CN XII)?

- Primary cortex

- Internal capsule (corticobulbar)

- Contralateral weakness of tongue

What does a LMN lesion of the hypoglossal nerve result in (CN XII)?

- Ipsilateral weakness of tongue

- Fasciculations

- Atrophy

What is an OT testing for with CN XII pathology?

- Tongue protrusion

- Unilateral weakness

- Tongue deviates toward weak side when protruded

What are signs and symptoms of CN XII pathology?

- Dysarthria

- Dysphagia

What are causes of dysarthria with CN XII pathology? (4)

- Infarct

- MS

- Brainstem lesions

- Lesions of cerebellar and basal ganglia pathways

What are causes of dysphagia with CN XII pathology? (5)

- Infarcts

- Neoplasms

- Esophageal strictures (narrowing)

- Neural components

- Aspiration pneumonia (serious!)

What is the cranial nerve combination involved in dysphagia?

- CN V

- CN VII

- CN XI (head control)

- CN X

- CN XII

What is the cranial nerve combination for innervation of the face?

- CN V (sensation)

- CN VII (movement of facial expression)

What is the cranial nerve combination for functions of the tongue and mouth?

- CN V mandibular division (general sensory)

- CN IX (general sensory)

- CN VII (special sensory)

- CN IX (special sensory)

- CN X (epiglottis and posterior pharynx)