Cranial Nerves (Ch 15) Flashcards
Cranial Nerve Summary
- part of PNS
- sensory, motor, and parasympathetic nerve fibers that innervate the HEAD and VISCERA
Where do cranial nerve originate?
brain and brainstem
- olfactory/optic attach to forebrain
- only vagus extends past head/neck
How many pairs of cranial nerves are there?
12
- 3 pairs of sensory nerves
- 5 pairs of motor nerves
- 4 pairs of mixed nerves
Cranial Nerve List
CN 1: Olfactory CN 2: Optic CN 3: Oculomotor CN 4: Trochlear CN 5: Trigeminal CN 6: Abducens CN 7: Facial CN 8: Vestibulocochlear CN 9: Glossopharyngeal CN 10: Vagus CN 11: Spinal Accessory CN 12: Hypoglossal
Mnemonic for remembering the order of cranial nerves
On On On They Traveled And Found Voldemort Guarding Very Secret Horcruxes
What are the Sensory Cranial Nerves?
–> innervate for special sensory structures (smell, vision, equilibrium, and hearing)
CN 1: Olfactory Nerve
CN 2: Optic Nerve
CN 8: Vestibulocochlear
Olfactory Nerve
CN 1
sensory: olfaction (smell)
origin: olfactory epithelium of nose (terminate in post olfactory cortex)
Optic Nerve
CN 2
- -> not technically a nerve, but a brain tract
sensory: vision
origin: retina of eye (terminate in primary visual cortex)
Vestibulocochlear Nerve
CN 8
sensory: hearing and balance (equilibrium)
origin: inner ear, enters brainstem at pons
What are the Motor Cranial Nerves?
--> somatic motor fibers to skeletal muscles of eye, neck/back, and tongue CN 3: Oculomotor CN 4: Trochlear CN 6: Abducens CN 11: Spinal Accessory Nerve CN 12: Hypoglossal
Oculomotor Nerve
CN 3
motor: extrinsic eye muscle
origin: midbrain
- -> also parasympathetic
Trochlear Nerve
CN 4
motor: extrinsic eye muscle
origin: midbrain
Abducens Nerve
CN 6
motor: extrinsic eye muscles
origin: pons
Spinal Accessory Nerve
CN 11
motor: innervates trapezius + sternocleidomastoid muscle
origin: rootlets at cervical region of spinal cord
Hypoglossal Nerve
CN 12
motor: tongue muscles
origin: medulla oblongata
What are the conditions of damaged eye innervation?
Strabismus (eyes not parallel)
Ptosis (drooping eyelids)
Diplopia (double vision)
What are the Mixed Cranial Nerves?
- -> sensory innervation of the face, mouth, viscera
- -> motor innervation to pharyngeal arch muscles (chewing/facial expression)
CN 5: Trigeminal
CN 7: Facial
CN 9: Glossopharyngeal
CN 10: Vagus
Trigeminal Nerve
Three Branches:
V1- ophthalmic
V2- maxillary
V3- mandibular
motor: V1 only, muscles of mastication
sensory: V1/V2/V3, somatic sensory for face, oral cavity, nasal cavity, anterior 2/3 of tongue (not taste)
origin: sensory receptor to pons
Facial Nerve
CN 7
somatic motor: muscles of facial expression
visceral motor: parasympathetic, lacrimal glands (tears), submandibular/sublingual salivary glands (digestion), and nasal/palatine glands
sensory: taste, anterior 2/3 of tongue, small patch at ear for somatic sensory
origin: medulla oblongata (posterior 1/3 of tongue)
Vagus Nerve
CN 10
somatic motor: larynx/pharyngeal muscles
visceral motor: parasympathetic, thoracolumbar viscera through 2/3 of intestines (regulates HR, breathing, digestive system)
sensory: external auditory meatus and laryngopharynx, also visceral sensory from most thoracoabdominal viscera
- -> mostly visceral sensory
origin: medulla oblongata
a. k.a. “the wanderer” - only cranial nerve to extend beyond head/neck
What are the Visceral Motor Nerves?
CN 3: Oculomotor - pupils
CN 7: Facial - lacrimal/salivary glands
CN 9: Glossopharyngeal - salivary glands (parotid)
CN 10: Vagus - thoracoabdominal organs
What are the three main parts of the ear?
External, Middle, and Inner Ear
External Ear
- auricle gathers sound waves and funnels into external auditory meatus
- mostly elastic cartilage
External Acoustic Meatus
short tube running from auricle to eardrum, lined with hairs, sebaceous glands, and ceremonious glands to keep dust/insects out
Tympanic Membrane
a. k.a. eardrum
- boundary between external and middle ear
- sound waves entering EAM hits eardrum, causes vibration
Middle Ear
- air filled space medial to eardrum
- located inside petrous part of temporal bone
- holes in bony wall between middle and inner ear = round and oval window
Middle Ear Ossicles
- Malleus
- Incus
- Stapes
- -> smallest bones in body
- transmit vibrations from eardrum across middle ear cavity and to inner ear (eardrum vibrates against malleus, stapes vibrates against oval window)
What are the two muscles of the middle ear?
- Tensor Tympani: attached to malleus
2. Stapedius: attached to stapes
Pharyngotympanic Tube
a. k.a. Auditory Meatus
- -> connects middle ear to pharynx –> allows equalization of pressure on both sides of tympanic membrane
Otitis Media
“ear infection”
- infection from throat (via pharyngotympanic tube)
- fluid buildup
Inner Ear
a.k.a. Labyrinth
Two parts:
1. Bony Labyrinth: cavity consisting of semicircular canals, vestibule, and cochlea
2. Membranous Labyrinth: walls/sacs within the bony labyrinth
What are the three parts of the inner ear?
- Cochlea (hearing)
- Vestibule (equilibrium/acceleration)
- Semicircular Canals (equilibrium/rotation)
Cochlea
- hearing
- looks like snail shell
- cochlear nerve: runs through center of modulus (axis of cochlea (part of vestibulocochlear nerve)
Cochlear Duct
part of membranous labyrinth of inner ear consisting of sensory receptors for hearing
roof: vestibular membrane
floor: basilar membrane
Basilar membrane
floor of cochlea
-supports spiral organ (organ of Corti)
Spiral Organ
-has hair cells (cilia) –> when basilar membrane moves, cilia bend/distort –> triggers impulses
Vestibule
- has a utricle and saccule (expansions of labyrinth)
- -> these have maculae: when head tilts, otoliths (small crystals) embedded in gelatinous layer of maculae move, and hairs bend)
- sense of balance when nodding
Semicircular Canal
are at right angle from each other
- expansion at end of ampulla (receptor for movement)
- when head rotates, endolymph in canals move, cupola within ampulla bends, triggering cilia
- sense of balance when rotating head
Vision
dominant sense in humans
- 70% of sensory receptors are in eyes
- 40% of cerebral cortex devoted to processing visual info
What are the four cranial nerves that affect vision?
CN 2: Optic
CN 3: Oculomotor
CN 4: Trochlear
CN 6: Abducens
What are the external structures of the eye?
- superior/inferior palpebrum (eyelid)
- lateral/medial angles
- lacrimal caruncle
- eyelashes
Conjunctiva
mucus membrane covering inner eyelids and sclera (not the cornea)
Two Types: palpebrum and ocular conjunctiva
Lacrimal Apparatus
- lacrimal glands supply eyes with lacrimal fluid (tears)
- lacrimal fluid has immune functions (mucus, antibodies, and enzymes)
- drains into lacrimal sac and then nasolacrimal duct/nasal cavity (runny nose when crying)
Extrinsic Eye Muscles
- Lateral Rectus (abducts) - CN 6
- Medial Rectus (adducts) - CN 3
- Superior Rectus (elevates/adducts) - CN 3
- Inferior Rectus (depresses/adducts) - CN 3
- Inferior Oblique (elevates/abducts) - CN 3
- Superior Oblique (depresses/abducts) - CN 4
What are the layers of the eye?
- Fibrous
- sclera
- cornea - Vascular
- choroid
- ciliary body/muscles
- iris - Inner
- retina
- optic nerve
Fibrous Layer
- most external
- ->composed of sclera and cornea
Sclera
*fibrous layer
tough outer covering of eye (white), protects eyeball
Cornea
*fibrous layer
continuation of sclera, transparent, allows light into the eye, acts as fixed lens for focusing
-avascular, but lots of nerve endings
Vascular Layer
- middle layer
- ->composed of choroid, ciliary body/muscles, iris, and pupil (space)
Choroid
*vascular layer
heavily pigmented vascular layer, melanin helps to absorb light
Ciliary Body/Muscles
*vascular layer
encircle lens, control shape for precise focusing
Iris
*vascular layer
colored part of the eye, regulates light entering the eye
Pupil
*vascular layer
a space, NOT a structure –> allows light to enter eye
pupillary constriction
bright light –> sphincter papillae contracts (parasympathetic innervation)
pupillary dilation
low light –> dilator papillae contracts (sympathetic innervation)
Inner Layer
- innermost layer
- ->composed of retina and optic nerve
Retina
- inner layer
- converts light to nerve impulses
- photosensitive
Two layers: pigmented and neural layer
Composed of:
- macula lutea
- fovea centralis
- optic disc
Pigmented Layer of retina
melanocytes, absorb light and keep it from scattering
Neural Layer of retina
nervous tissue with photoreceptive cells
Photoreceptor cells
rods: work best in dim light
cones: work best in bright light, perceive red, blue, green (good for color vision)
- -> absorption spectra overlap, so combo of stimulations of the cones = different colors
Macula Lutea
*in retina
area of concentrated cone cells at posterior pole
Fovea Centralis
- in retina
- area of ONLY cone cells in center of macula lute
- highest visual acuity
Optic Disc
- in retina
- blind spot
- location where optic nerve attaches
- NO photoreceptor cells
Lens
avascular, transparent disc
-shape can be changed to adjust focus
Two chambers:
- Anterior Chamber: in front of lens, has aqueous humor
- Posterior Chamber: behind lens, has vitreous humor, most volume of eye
Humor
Aqueous Humor: CSF-like
Vitreous Humor: jelly-like
–> help maintain interocular pressure
Images coming into eye
lens is convex (images are upside-down and reverse) –> cerebral cortex flips image back to normal
Benign Paroxysmal Positional Vertigo (BPPV)
- room spinning = vertigo (not dizziness)
- fluid disrupted in ear (semicircular canal)
- -> Epsley Maneuver
Cataracts
buildup of proteins in the lens
-one of the most common causes of blindness
Glaucoma
increased interocular pressure that can affect the optic nerve (vision)
Glossopharyngeal Nerve
sensory: posterior 1/3 of tongue, general visceral sensory
motor: stylopharngeus muscle (swallowing), parotid salivary gland (digestion)
origin: medulla oblongata
