Senses, Equilibrium, and hearing

What are the accessory structures of the eye

• Extrinsic muscles

• Eyelids

• Canthi

• Lacrimal

• Caruncle

• Conjustiva

• Lacrimal apparatus

What is the function of the conjuctiva

Lines the eyelids and anterior; it does not cover the cornea

What is the function of the lacrimal apparatus

Produces, collects and drains tears to lubricate the anterior eye

What is the correct pathway of tears

Lacrimal gland → canaliculi → lacrimal sac → nasolacrimal duct

What are the three tunics of the eye

• Fibrous tunic

• Vascular tunic

• Retina

What structures make up the fibrous tunic

Cornea and sclera

What is the function of cornea

Transparent anterior portion of the fibrous tunic; helps refract light

What is the function of sclera

Tough, white outer layer that protects and supports the eye

What are the three regions of the vascular tunic

• Choroid

• Ciliary body

• Iris

What is the function of the choroid

Contains capillaries that supply oxygen and nutrients to the retina

What is the function of the ciliary body

Changes the shape of the lens

What is the functions of the iris

Pigmented part of the eye that controls pupil size and incoming light

What does the sphincter pupillae muscle do

Circular muscle that constricts the pupil

What does the dilator pupillae muscle do

Radial muscle that dilates the pupil

Where is the lens located, and what is it’s shape

Behind the iris and pupil; transparent and biconvex

What attaches the lens to the ciliary body

Suspensory ligaments

What is accommodation

Changing lens shape to focus images on the retina

What is the anterior cavity

Space in front of the lens containing circulating aqueous humor

What is the posterior cavity

Space behind the lens containing permanent vitreous humor

How do aqueous and vitreous humor differ

Aqueous humor circulates in the anterior cavity; vitreous humor permanently fills the posterior cavity

What is glaucoma

A condition associated with increased intraocular pressure that can damage the optic nerve

What is retina

The internal eye layer containing photoreceptors and neurons that convert light into nerve impulses

What are the three neural layers of the retina

• Photoreceptors

• Bipolar cells

• Ganglion cells

What are the two types of photoreceptors

Rods and cones

What are the functions of rods

Dim-light and night vision; shades of gray; low visual activity

What are the functions of cones

Color vision, daylight vision, and precise detail; high visual acuity

Which photoreceptors are more numerous

Rods: approximately 120 million per retina; cones: approximately 6 million

Where are rods and cones concentrated

Rods are more numerous in the periphery; cones are concentrated in the fovea

What is the function of bipolar cells

Connect photoreceptors with ganglion cells

What do ganglion cell axons form

The optic nerve (cranial nerve II)

What is the optic disc

The retinal blind spot where ganglion cell axons exit; it lacks photoreceptors

What is the fovea centralis

Depression in the macula lutea with many cones and almost no rods, sharpest vision

What is the pathway of light through the eye

Cornea → aqueous humor → pupil → lens → vitreous humor → retina

What is the pathway of visual nerve impulses

Retina → optic nerve → optic chiasm → optic tract → thalamus → optic radiation → occipital lobe

What happens at the optic chiasm

Some retinal nerve fibers cross to the opposite side

What is visual acuity

The ability to distinguish fine details

What do 20/20, 20/15, and 20/40 vision mean

• 20/20: is normal

• 20/15: is better than normal

• 20/40 is worse than normal

What are the three anatomical regions of the ear

• External ear

• Middle ear

• Inner ear

What structures make up the external ear

• Auricle

• External acoustic meatus

• Tympanic membrane

What is cerumen

A waxlike secretion produced by glands in the external auditory meatus

What structures make up the middle ear

• Auditory ossicles

• Malleus incus

• Stapes

What is the function of the auditory ossicles

Transmit sound vibrations to the inner ear

What does the auditory tube connect

The middle ear to the nasopharynx

Where is the inner ear located

Within the petrous portion of the temporal bone

Which inner ear structures are responsible for equilibrium

• Utricle

• Saccule

• Semicircular ducts

Which inner ear structures is responsible for hearing

Cochlea

What is equilibrium

Awareness of head postion

What is static equilibrium

Detects head postion when stationary and linear acceleration

Which structures detect static equilibrium

Maculae within the utricle and saccule

What does maculae contain

Hair cells embedded in a gelatinous layer containing otoliths

What are otoliths

Particles in the gelatinous layer that shift with head movement and bend hair cells

What happens when macula hair cells bend

Electrical activity is sent to the brain through the vestibular nerve

What is dynamic equilibrium

Detects rotational or angular acceleration of the head

Which structures detect rotational movement

The three semicircular ducts

• Anterior

• Posterior

• Lateral

What is an ampulla

An expanded region within each semicircular canal

What the crista ampullaris

Elevated sensory region in the ampulla covered with hair cells

What is the cupula

Gelatinous dome over the crista ampullaris into which hair cells extend

What happens during head rotation

Endolymph pushes against the cupula, bending stereocilia and changing hair cell transmitter release

What is the cochlea

Inner ear organ responsible for hearing

What fills the cochlear duct

Endolymph

What membrane is associated with cochlear duct

The basilar membrane

What is the function of the spiral organ (organ of corti)

Contains sensory hair cells responsible for hearing

What is the tectorial membrane

A membrane that interacts with the hair cells of the spiral organ

What is the pathway of sound vibrations through the inner ear

Oval window → scala vestibuli → cochlear duct → basilar membrane → spiral organ

What happens when hair cells in the spiral organ stimulated

They convert mechanical vibrations into nerve signals

Which nerve carries hearing information to the brain

The cochlear branch of the vestibulocochlear nerve (CN VII)

Where does the brain interpret sound

The auditory cortex in the temporal lobe

What determines the pitch of sound

The frequency of sound waves

What determines the loudness of a sound

The amplitude of sound waves

What is tinnitus

Ringing or other sounds perceived in the ears

What is conductive hearing loss

Hearing loss caused by problems transmitting sound through the external or middle ear

What is otitis externa

Inflammation or infection of the external ear canal

What is otitis media

Inflammation of infection of the middle ear

What is otitis interna

Inflammation or infection of the inner ear

What is the function of the auditory tube

Connects the middle ear to nasopharynx and helps equalize pressure

What is the function of the semicircular ducts

Detect rotational or angular acceleration

What is the function the utricle and saccule

Detect head position and linear acceleration

What is the function of cochlea

Hearing

What is the difference between static and dynamic equilibrium

Static detects head position and linear acceleration; dynamic detects rotational movement

What is the difference between the scala vestibuli and scala tympani and the cochlear duct

The scala vestibuli and scala tympani contain perilymph; the cochlear duct contains endolymph

Where are the sensory hair cells for hearing located

In the spiral organ (organ of corti)