Anatomy Module 10

cranial nerves

part of PNS. Sensory, motor, and parasympathetic nerve fibers that innervate the head and viscera.

The cranial nerves originate at brain or brainstem. Named in order from anterior to posterior where they emerge from the brain

3 pairs of sensory nerves, 5 pairs of motor nerves, 4 pairs of mixed nerves

old orange octopuses track tired ass fat vaquitas going very slow happily

Olfactor and optic nerves attach to the forebrain, the rest are attached at the brainstem. Only the vagus extends past head and neck

olfactory nerve

olfaction/smell

origin: olfactory epithelium of nose (terminale in posterior olfactory cortex)

optic nerve

technically not a nerve, rather a brain tract, but it is still refered to as a nerve.

sensory: vision

origin: retina of the eye (terminale in primary visual cortex)

vestibulocochlear

sensory: hearnig and balance (equilibrium)

origin: inner ear, enters brain stem at pons

3 sensory cranial nerves

olfactory, optic, vestibulocochlear

innervation for special sensory structures (smell, vision, equilibrium and hearing)

5 motor cranial nerves

oculomotor, trochlear, abducens, spinal accessory

somatic motor fibers to skeletal muscles of eye, neck/back and tongue

oculomotor nerve

origin: midbrain

motor nerves to extrinsic eye muscles

also parasympathetic

[explain better]

trochlear nerve

origin midbrain

motor nerves to extrinsic eye muscles

abducens

origin: pons

extrinsic eye muscles motor inervation

strabismus

eyes not parallel

ptosis

drooping eyelidsd

diplopia

double vision

spinal accessory nerve

motor nerve to trapezius and sternocleidomastoid muscles

origin: roolets at cervical region of spinal cord

lets you shrug your shoulders

hypoglossal

motor to tongue muscles

origin: medulla oblongata

mixed nerve

mixed nerves: sensory innervation to the face, mouth, and viscera and also motor innervation to pharyngeal arch muscles (chewing, facial expression)

includes: trigeminal, facial, glossopharyngeal, vagus

trigeminal nerve

three branches: v1 (ophthalmic), v2 (maxillary), v3 (mandibular)

motor: V3 only

sensory for all 3 - somatic sensory for face, oral cavity, nasal cavity, anterior 2/3 tongue

origin: sensory receptors to pons

if a bug landed on your forehead, this would allow you to feel it

facial nerve

somatic motor: muscles of facial expression (5 motor branches)

visceral motor (parasympathetic): lacrimal gland, submandibular and sublingual salivary glands (digestion), nasal and palatine glands

sensory: taste of anterior 2/3 of tongue, small patch at ear for somatic sensory

origin: pons

glossopharyngeal

somatic motor: stylopharyngeus muscle

visceral motor (parasympathetic): parotid salivary gland (involved with digestion)

sensory: general visceral sensory, taste of posterior 1/3 of tongue

origin: medulla oblongata

vagus nerve

somatic motor: larynx and pharyngeal muscles

visceral motor (parasympathetic): thoracoabdominal viscera through 2/3 of the intestines; regulates heartrate, breathing, and digestive system activity

sensory: external auditory meatus and laryngopharynx. also visceral sensory from most thoracoabdominal viscera

origin: medulla oblongata

only cranial nerve to extend beyond head/neck

two types of senses

general: receptors throughout the body, can be somatic (body) or visceral (organ walls), includes tactile (touch, itch, pressure), thermal, pain, proprioception (knowing where our body and body parts are)

special: receptors are located in one specific place: gustatory (taste), olfactory, vision, hearing and equilibrium (balance)

olfaction

olfactory nerves travel through cribriform plate to superior nasal cavity

transmitted by olfactory cranial nerve

gustation

receptors located in papillae on tongue

transmitted by facial and glossopharyngeal

3 sections of ear

external, middle, inner

external ear

auricle gathers sound waves and funnels into external auditory meatus. Auricle is mostly elastic cartilage covered with skin

external auditory meatus (EAM): is short tube running from auricle to tympanic membrane (eardrum). EAM lined with hairs, sebaceous glands and ceruminous glands (produce earwax) to keep dust and insects out

tympanic membrane

eardrum

the boundary between external and middle ear

sound waves entering external auditory meatus travel to tympanic membrane, cause it to vibrate

middle ear

air-filled space medial to tympanic membrane

located inside petrous portion of temporal bone

holes in bony wall between middle and inner ear are the round window and oval window

auditory ossicles (bones)

lateral to medial: malleus (hammer), incus (anvil), stapes (stirrup)

smallest bones in the body

transmit vibrations from tympanic membrane across middle ear cavity to inner ear (eardrum vibrates against malleus; stapes vibrates against oval window)

middle ear muscles

two muscles help dampen loud sounds by reducing the movement of the ossicles. This helps protect the inner ear during loud noises

tensor tympani muscle - attached to malleus

stapedius muscle - attached to stapes

pharyngotympanic tube

aka auditory/ Eustachian tube

connects middle ear to nasopharynx

allows equalization of pressure on both sides of the tympanic membrane (the reason for ears popping on planes)

ottis media

middle ear infection from nasopharynx via pharyngotympanic tube

fluid builds up in middle ear, causes tympanic membrane to bulge

common in babies and children, because pharyngotympanic tube is more horizontal

inner ear

aka labyrinth

bony labyrinth is a cavity made of semicircular canals, vestibule and cochlea

membranous labyrinth is the walls and sacs inside the bony labyrinth

cochlea

hearing

looks like a snail shell

cochlear nerve (part of vestibulocochlear nerve) runs through center of modiolus (axis of cochlea)

the membranous portion is called the cochlear duct

vestibule

equilibrium (acceleration such as starting and stopping)

vestibule has the utricle and saccule

when you tilt your head, gelatinous otolithic membrane moves and bends the stereocilia of the macula

semicircular canals

equilibrium (rotation)

three semicircular canals are at right angles to each other

expansion at the end of each canal is the ampulla (receptor for movement)

when head rotates, endolymph (fluid) in canals moves, cupula within ampulla bends, triggering stereocilia

spiral organ

spiral organ is the receptor organ for hearing. It has stereocilia (hair cells). It is inside the cochlear duct

spiral organ is supported by the basilar membrane

pressure waves travel through cochlea, moving basilar membrane.

stereocilia bend and trigger nerve impulses

hearing pathway

1. sound enters ear, make tympanic membrane vibrate

2. ossicles move

3. stapes makes pressure waves at oval window

4. waves displace basilar membrane, bending hair cells and sending nerve impulses via vestibucochlear

   1. remaining wave exits cochlea at round window

two types of hearing loss

conductive hearing loss: results from issues with external and middle ear. Sounds like volume was turned down: earwax buildup, fluid in middle ear, etc

sensorineural hearing loss: results from issues with inner ear, vestiblucochlear nerve and possible brain. sounds like things aren’t “tuned” correctly. Damage to hair cells in cochlea is usual cause

vision

dominant sense in humans: 70% of sensory receptors are in eyes, 40% of cerebral cortex devoted to processing visual information.

5 cranial nerves involved with eye, lacrimal system and eye muscles: cn II (optic) cn III (oculomotor) cn iv (trochlear) cn vi (abducens) cn vii (facial)

external structures of the eye

eyelids protect eyeball from excessive light and injury

inside of eyelids is covered in conjunctiva, which keeps the cornea moist by spreading lacrimal fluid (tears)

conjuctiva

mucus membrane covering inner eyelids and sclera

the ocular conjunctiva doesn’t cover the cornea, but still helps moisten the eyeball

lacrimal apparatus

lacrimal glands located in supero-lateral corner of orbit and supply eyes with lacrimal fluid (tears)

lacrimal fluid has immune functions (mucus, antibodies, enzymes)

drains into lacrimal sac and then nasolacrimal duct and nasal cavity = runny nose when you cry

lateral rectus

abduct eyes, innervated by abducens (VI) nerve

medial rectus

adducts eye, innervated by oculomotor nerve (III)

superior rectus

elevates and adducts eye, innervated by oculomotor nerve (III)

inferior rectus

depresses and adducts eye, innervated by oculomotor nerve (III)

inferior oblique

elevate and abduct eye, innervated by oculomotor nerve (III)

superior oblique

depresses and abducts eye, innervated by trochlear nerve (IV)

fibrous layer of eye

most external layer or tunic

sclera = tough outer covering of eye (white of the eye), it protects the eyeball

cornea = continuation of sclera, is transparent, allows light into eye, acts as fix lens for focusing. it is avascular, but contains lots of nerve endings. (covers like the iris part)

vascular layer

middle layer/tunic of the eyeball

choroid - heavily pigmented vascular layer. melanin helps absorb light. posterior 2/3rds of eyeball

ciliary body/muscles - surround the lens and control lens shape for precise focusing (adapting for near/far vision)

iris - colored part of the eye, regulates light entering eye. controls pupil diameter. anterior portion of this layer.

the pupil is a space, not a structure, which allows light to enter eye

pupil size

two sets of muscles control the size of the pupil. In bright light, the sphincter pupillae contracts to make the pupil smaller. This is controlled by the PNS.

In low light or high stress, the dilator pupillae contracts to make the pupil larger. Sympathetic innervation.

retinal layer

deepest layer/tunic of eyeball

retina = converts light to nerve impulses

optic nerve (CN II) - transmits nerve impulses to brain

retina

innermost layer of eyeball, photosensitive

two layers

1. pigmented layer: contains melanocytes. absorbs light and keeps it from scattering. pigments layer is superficial to neural layer

   1. neural layer is nervous tissue with photoreceptor cells (rods and cones)

two kinds of photoreceptor cells

rod - work best in dim light. Rod-shaped. more rods than cones in body

cones - used for bright light and color vision (perceive red, blue, green), cone-shaped

macula lutea

area of concentrated cone cells at posterior pole

fovea centralis

area of only cone cells in center of macula lutea. region with highest visual acuity

optic disc

blind spot, location where optic nerve attaches. no photoreceptive cells here

lens

avascular, transparent disk, its shape can be changed to adjust focus (deformable)

the lens divides into eye anterior cavity, containing aqueous humor (fluid), which removes wastes.

poesterior cavity has vitreous humor (gelatinous), which is the most volume of the eye. vitreous humors help maintain intraocular pressure and the shape of the eyeball

lens and focusing disorders

distance vision is our natural state. In order to focus on near objects, the lens adjusts to become more spherical (this process is called accommodation.) the contraction of ciliary muscles is what allows the lens to change shape

as we age, the lens becomes less flexible = presbyopia which makes pts need reading glasses

binocular vision and vision pathway

humans have binocular vision which = good depth perception

lens of eye is convex, so the images it perceives are upside-down and reversed

visual cortex (occipital cortex) flips image back to “normal” so we can see it properly

your pt injured the obturator nerve. what action would be affected?

adduction of the thigh