Anatomical Cranial Nerve Sensory Pathways
The Bright Light Effect – Pupillary Reflex:
Sensing the light
- retinal ganglion
- optic nerve
- optic canal
- optic chiasm
- optic tract
- lateral geniculate ganglia and midbrain
Constricting the pupil
- somatic complex of Oculomotor nerve sends parasympathetic fiber toward left AND right eye
- superior orbital fissure
- ciliary ganglion
- short ciliary nerves of V1
- sphincter muscle of pupil
Sensing particles touching cornea
- cornea sends afferent fibers through long ciliary nerve and short ciliary nerves (which pass through the ciliary ganglion without snapping)
- all join the nasociliary nerve
- superior orbital fissure
- trigeminal ganglion
- synapses in ganglion in the brain
Blinking the eye-VII
- superior orbital fissure, bypassing geniculate ganglion
- stylomastoid foramen
- temporal branch
- orbicularis oculi, palpebral part
Tearing-VII
- superior orbital fissure
- geniculate ganglion in facial canal
- first branch is Greater Petrosal Nerve
- hiatus for Greater Petrosal Nerve
- groove of the Greater Petrosal Nerve
- (joins with Deep Petrosal Nerve)
- petrotympanic fissure
- pterygoid canal/Vidian’s canal
- nerve now called “nerve of pterygoid canal/Vidian’s nerve”
- pterygopalatine fossa
- pterygopalatine ganglion
- Zygomatic Neve-V2
- communicating branch
- Lacrimal Nerve-V1
- lacrimal gland
- tearing
Taste
Smelling the steak
- airborne particles of food bind to the olfactory epithelium
- olfactory nerve travels through cribriform plate
- through olfactory bulb
- along olfactory tract
- synapses in olfaction nuclei in the brain
Anterior 2/3 of tongue-VII
- fungiform, filiform, and foliate taste buds
- Chorda Tympani
- lingual nerve-V3
- passes through or near submandibular ganglion without snapping
- petrotympanic fissure
- facial canal
- passes through geniculate ganglion without snapping
- internal acoustic meatus
- synapses in brain
Posterior 1/3 of tongue-IX
- circumvallate/vallate, fungiform, filiform, and foliate papillae
- Glossopharyngeal nerve
- jugular foramen
- synapses in brain
Gag reflex
- Glossopharyngeal nerve sends afferent fibers back through jugular foramen to synapse in the brain.
- IX and X are responsible for the muscular contraction of the pharynx as follows:
Pharynx Innervation by IX
- through jugular foramen
- descends posterior to stylopharyngeus muscle (innervating it)
- reverse peristalsis of pharynx
Pharynx Innervation by X
- through jugular foramen
- through carotid sheath
- Reverse peristalsis is by visceral motor innervation of the middle and inferior constrictors by three nerve branches of X: external branch of the superior laryngeal nerve, recurrent laryngeal nerve, and the pharyngeal branch. There is some debate as to the innervation of the superior constrictor; rumor has it that Dr. Cleary wants us to consider it innervated by the pharyngeal branch of X, not XI fibers carried by X (Moore p. 649).
Visceral Salivation
Salivation-IX
- through jugular foramen
- branch of tympanic nerve
- through tympanic canuliculus
- through tympanic plexus
- becomes Lesser Petrosal Nerve
- through hiatus for Lesser Petrosal Nerve (in tegmen tympani)
- groove for Lesser Petrosal Nerve
- foramen ovale
- synapses in otic ganglion
- wraps around middle meningeal artery (with Auriculotemporal Nerve-IX)
- parasympathetic innervation of the parotid duct (Stenson’s duct, which empties lateral to uppers second molar)
Salivation-VII
1. through internal acoustic meatus
2. passes through geniculate ganglion without synapsing
3. through facial canal
4. becomes the chorda tympani
5. passes between the malleus and the incus
6. through the petrotympanic fissure
7. joins the Lingual Nerve-V3
8. synapses in the submandibular ganglion
9. provides parasympathetic innervation to the submandibular and sublingual glands
Involvement of the ear-VIII
Detecting Acceleration
- movement of endolymph moves the cupula within the ampullae of each semicircular canal
- the kinocilium and multiple stereocilia protruding into the gelatinous cupula, which are attached to the cristae at the base, trigger special sensory nerve impulses
- these nerves travel to the vestibular ganglion of semicircular ducts and join IX proper
- through internal acoustic meatus
- synapse in vestibular nuclei in brain
Global Proprioception – Detecting your head is temporarily abducted-VIII
- the position of the otolith shifts on top of the maculae in the saccule
- this triggers special sensory impulses that travel to the vestibular ganglion
- these join IX proper
- through the internal acoustic meatus
- synapse in the vestibular nuclei in the brain
Hearing the steak hit your head
- Conduction vibrations resonate in the mastoid air cells and some compression sound waves cause your tympanic membrane to vibrate overcoming the attenuative action of the tensor tympani muscle, under the control of V3, and the stapedius muscle, under the control of VII.
- the malleus, incus, and stapes oscillate, in turn vibrating the oval window
- the sound wave travels in the tympanic duct through the endolymph spirally toward the tip
- The sound wave reaches the tip, called the helicotrema, and comes backward through the spiral in the cochlear duct. The very end of the pathway that a given sound wave takes is near the round window, which helps absorb and end the wave.
- The organ of Corti lies laterally in the spiral, but interfaces with the vestibular and cochlear ducts on the basilar membrane.
- the movement of endolymph distorts the kinocilia and stereocilia against the overlying tectorial membrane (internal roof) of the organ of Corti
- sensation of this distortion travels to the spiral ganglion
- VIII travels through the internal acoustic meatus on its way to synapse in the brain.
Tags: chorda tympani, cornea sensation, corneal reflex, endolymph, geniculate ganglion, Lesser Petrosal Nerve, mastoid air cells, otolith, parasympathetic innervation, parotid duct, petrotympanic fissure, proprioception, pupillary reflex, smell pathway, sound wave, sublingual gland, submandibular gland, taste pathway, tympanic membrane, tympanic plexus, vestibular ganglion
