Neuroanatomy #4. Cranial nerves

VIII, IX, XI and XII Aygul Shafigullina

Department of Morphology and General Pathology

CN VIII – Vestibular cochlear nerve – Nervus vestibulocochlearis

CN VIII – Vestibulocochlear nerve – Nature and nuclei

Nature Nucleus

Ganglion and receptors

Function

Sensory (specific sensitivity)

Vestibular: - Superior (Bekhterev) - Lateral (Deiters) - Medial (Schwalbe) - Inferior (Roller)

Vestibular ganglion (g.Scarpae) Receptor – hair cells of internal ear vestibulum

Equilibrium

Sensory (specific sensitivity)

Cochlear: - Ventral - Dorsal

Spiral ganglion Hair cells of cochlea

Hearing

CN VIII – Vestibulocochlear nerve – Cochlear part

• malleus (hammer) • incus (anvil) • stapes (stirrup)

The INNER EAR consists of a maze of fluid-filled tubes, running through the temporal bone of the skull. The bony tubes, the bony labyrinth, are filled with a fluid called perilymph. There are three major sections of the bony labyrinth: 1. The front portion, the

snail-shaped cochlea, functions in hearing.

2. The rear part, the semicircular canals, helps maintain balance.

3. Interconnecting the cochlea and the semicircular canals is the vestibule, containing the sense organs responsible for balance, the utricle and saccule.

Within this bony labyrinth is a second series of delicate cellular tubes, called the membranous labyrinth, filled with the fluid called endolymph. The membranous labyrinth within the cochlea houses the Organ of Corti, containing the inner and outer hair cells that generate the nerve impulses required for hearing.

Epithelial cells of the bony labyrinth produce perilymph: Scala tympani and scala vestibuli contain perilymph

Sensory cells – hair cells (Organ of Corti) 1st neuron cell bodies – in spiral ganglion

Irritation of hair cells (organ of Corti) – transform irritation to nerve impulse

Sound waves

External acoustic meatus

Tympanic membrane (its vibration)

Middle ear ossicles (malleus-incus-stapes) – intensify the vibrations and transmit it to oval window of cochlear

Vibration of perilymph in cochlear

Vibration of endolymph

Primary sensory neurons (spiral ganglion)

Diagram of relationship of nerves in the internal acoustic meatus: VII = facial nerve NI = nervus intermedius VIIIc = cochlear nerve VIIIvs = superior division of vestibular nerve VIIIvi = inferior division of vestibular nerve

2nd neuron – Cochlear nuclei of CN VIII:

- Ventral - Dorsal

Superior olivary nucleus (ipsi- and contralateral sides, axons arise with lateral lemniscus) – determine sound localization

1st neuron

2nd neuron

2nd neuron 3rd neuron

•4th neuron Inferior colliculus of midbrain, medial geniculate bodies, nucleus of thalamus – subcortical auditory center

Cortical auditory center (Heschl gyrus)

Conductor (external air pathway) and neurosensory (cochlear) components of the CNVIII

Sing a sound and, while singing, close one of the ears. Normally, the sound`s volume in closed ear increases.

Ludwig van Beethoven (1770-1827)

CN VIII – Vestibulocochlear nerve – Vestibular part

Vestibular apparatus – sensory hair cells in 5 structures: utricle, saccule, 3 semicircular canals

1st neuron cell bodies – in vestibular (Scarpa`s) ganglion

2nd neuron Vestibular nuclei of CN VIII: - Superior (Bekhterev) - Lateral (Deiters) - Medial (Schwalbe) - Inferior (Roller)

1st neuron

2nd neuron

3rd neuron

Ascending medial longitudinal fascicule (reticular formation)

- to nuclei of CN III, CN IV, CN VI

Descending medial longitudinal fascicule (reticular formation)

and vestibulospinal tract

Otolith organs react to gravity!

Sea sickness

Romberg's test, Romberg's sign, or the Romberg maneuver is a test used in an exam of neurological function for balance, and also as a test for drunken driving.

• there are more compartments and ducts within the membranous labyrinth than there are regions of the bony labyrinth

• it is important to recognize that the membranous labyrinth is completely enclosed, therefore there are no connections between the spaces containing endolymph and those containing perilymph

• beginning at the oval and round windows, the first part of the membranous labyrinth is the cochlear duct (= scala media); it extends anteriorly before coiling around the modiolus

Membranous labyrinth

• branching off the cochlear duct is the narrow ductus reuniens that connects to the saccule, the most anterior and inferior of the vestibular system components

• the saccule connects to the utricle, which occupies the rest of the vestibule • the saccule and utricle have a Y-shaped connection with each other, and with the

endolymphatic duct, which travels through the vestibular aqueduct to a blind end called the endolymphatic sac (not shown in the picture)

• the semicircular canals are connected to the utricle; the anterior and posterior canals form a common duct at the end opposite their ampullae

Membranous labyrinth

CN IX – Glossopharyngeal nerve – Nervus glossopharyngeus

Nature Nucleus Ganglia and receptor cells

Area of innervation

Somatic motor Nucleus ambiguus - - m.stylopharyngeus

Parasympathetic (visceral motor)

Nucleus salivatorius inferior

Ganglion oticum - Secretory innervation of parotid salivary gland

Visceral sensory Nucleus (tractus) solitarius

Ganglion inferior - Sensitivity from carotid glomus (chemoreceptors) and carotid sinus (baroreceptors)

General somatic sensory Nucleus (tractus) solitarius

Ganglion inferior

- skin of the external ear, internal surface of the tympanic membrane, upper pharynx, tonsils, soft palate, and the posterior 1/3 of the tongue.

Special sensory Nucleus (tractus) solitarius

Ganglion inferior

- Taste sensitivity of the posterior 1/3 (root) of the tongue

CN IX – Glossopharyngeal nerve – Nervus glossopharyngeus

CN IX – Glossopharyngeal nerve – Nervus glossopharyngeus

Emerge from brain: sulcus dorsolateralis retroolivaris medullae oblongatae

CN IX – Glossopharyngeal nerve – Nervus glossopharyngeus

The glossopharyngeal fibers travel just anterior to the cranial nerves X and XI which also exit the skull via the jugular foramen.

1st neuron cell bodies – in superior and inferior (petrosal)

ganglia

1st sensory nucleus – superior/inferior ganglia

Otic ganglion: - parasympathetic - 2nd parasympathetic

neuron cell bodies - Secretory innervation of

ipsilateral parotid salivary gland

- Postganglionic fibers from the otic ganglion travel with the auriculotemporal branch of CN V3 to enter the substance of the parotid gland.

CN IX

SM - Somatic motor PS – Parasympathetic S - Sensory

S, PS

PS

SM

S

S

S - taste

S

CN IX - central course - visceral sensory component

• From the nucleus solitarius, connections are made with several areas in the reticular formation and hypothalamus to mediate cardiovascular and respiratory reflex responses to changes in blood pressure, and serum concentrations of CO2 and O2.

CN IX - Clinical correlation

• The general sensory fibers of CN IX mediate the afferent limb of the pharyngeal reflex in which touching the back of the pharynx stimulates the patient to gag (i.e. the gag reflex). The efferent signal to the musculature of the pharynx is carried by the branchial motor fibers of the vagus nerve.

CN XI – Accessory nerve – Nervus accessorius

Nature Nucleus Ganglia and receptor cells

Area of innervation

Somatic motor Nucleus spinalis nervi accessorius

- - m. sternocleidomastoideus - m. trapezius

CN XI – Accessory nerve – Nervus accessorius

CN XI – Accessory nerve – Nervus accessorius

CN XI – Accessory nerve

CN XII – Hypoglossal nerve – Nervus hypoglossus

Nature Nucleus Ganglia and receptor cells

Area of innervation

Somatic motor Nucleus nervi hypoglossi - - Skeletal muscles of the tongue - Infrahyoid group of muscles

(together with branches of cervical plexus)

CN XII – Hypoglossal nerve – Nervus hypoglossus

CN XII – Hypoglossal nerve – Nervus hypoglossus

Hypoglossal nerve (XII) – only contralateral side (total decussation)

Normal

Deviate to damaged side

Cranial nerves: I – Olfactory II – Optic III – Oculomotor IV – Trochlear V – Trigeminal VI – Abducens VII – Facial VIII – Vestobulocochlear IX – Glossopharyngeal X – Vagus XI – Accessory XII – Hypoglossal

Tests to check cranial nerves

CN I – Olfactory nerve

CN II – Optic nerve

CN III – Oculomotor nerve CN IV – Trochlear nerve CN VI – Abducens nerve

CN III – Oculomotor nerve, parasympathetic component

CN V – Trigeminal nerve

Corneal reflex

Test masticatory muscles

Test skin sensitivity

CN VII – Facial nerve

Test taste sensitivity

Test mimic muscles

Don’t forget! - Dry eye - Dry mucous of nasal and oral cavity

CN VIII – Vestibulocochlear nerve

Tests of Rinne

Romberg's test

Tests of Weber

CN IX – Glossopharyngeal nerve

The gag reflex

Don’t forget! - Parotid salivary gland

CN X – Vagus nerve

Uvula turned to healthy side

Descent of left side of soft palate

CN XI – Accessory nerve

Test m. sternocleidomastoideus Test m. trapezoideus

CN XII – Hypoglossal nerve