Semester 1 Review

• Anatomical directional terms• Cells and tissues• Skin and the integumentary system• Nervous system

Special Senses

Eye and Ear

Eye and Vision

Quick Facts about the Eye

• 70% of all sensory receptors are in the eye• Approx. 1 inch in diameter• Uses light to gather information about

environment

External Eye

• Eyelid• Eyelashes• Medial canthus• Lateral canthus

Accessory Structures of the Eye• Tarsal glands (within

eyelids)• Conjuctiva• Lacrimal apparatus

– Lacrimal glands Lacrimal canals and lacrimal sac Nasolacrimal duct nasal cavity

– Lacrimal secretions are made up of a dilute salt solution and lysozyme (antibiotic)

Internal Eye Anatomy (from above)

Eye Overview

• Made of tunics and humors• Tunics: layers surrounding the eye and it’s

parts• Humors: fluid areas within the tunics to give

eye pressure and keep it’s shape

Tunics

• Sclera: outermost tunic– Thick, white covering– Anterior portion modified into cornea• No blood vessels

Tunics

• Vascular tunic: middle tunic– Supplies blood to eye– 2 parts: • Choroid (posterior)• Ciliary body (anterior) attaches lens using ciliary

zonule

• Iris• Pupil

Tunics

• Sensory tunic: innermost tunic• Retina: contains photoreceptors– Rods: black, white and shades of gray in dim light,

peripheral vision– Cones: color receptors

• Signals sent from retina to optic nerve to brain

Retina

• Macula lutea: yellowish area near back of the eye– Fovea Centralis: depression in the center of

Macula lutea• High concentration of cones• Produces sharpest vision

• Optic disc: nerve fibers and blood vessels enter and leave the eye– Contains a blind spot

Humors

• Humors: fluid filled areas in eye• Aqueous humor– Anterior to lens– Constantly replaced to bring nutrients to areas without

blood supply• Secreted by choroid• Scleral vernous sinus (canal of Schlemm) – at junction of sclera

and cornea

• Vitreous humor– Posterior to lens– Constant pressure to give eye shape (intraocular pressure)

Lens

• Biconvex structure• Behind cornea, iris, pupil• Bends to focus on objects

Muscles of the Eye (right eye)

Muscles of the Eye (front)

How does the eye work?

• Light is refracted by each layer it moves through– Humors, lens, cornea

• Image is shown on retina (upside-down) and sent to brain

• Brain flips the image and uses other cues to make sense of image

How does the eye work?

• Nerve impulses from the retina leave the eye through the optic nerve.

• Optic nerves from each eye meet at the optic chiasma.

How does the eye work?

• At the optic chiasma, the impulses from the medial portion of each retina cross over to the opposite side;

• Leaving the optic chiasma are the optic tracts, which fuse in the thalamus;

• Leaving the thalamus are the optic radiations, which then join to the occipital lobe (visual cortex) of the brain where interpretation occurs;

How does the eye work?

• Result is that each side of the brain receives input from both eyes.

• Binocular vision – each eye sends an image to the brain, resulting in 3-dimensional vision.

Problems within the Eye

• Cateracts• Conjunctivitis• Nearsightedness – distant objects are blurry• Farsightedness – close objects are blurry• Astigmatism• Glaucoma

The Ear, Hearing, and Balance

Overview of the Ear

• 3 parts: outer, middle, inner• Mechanoreceptor: respond to physical forces

(sound vibrations, movement of the head)

Outer Ear

• Pinna or auricle – external ear– Surrounds auditory canal into ear canal

• External acoustic meatus (external auditory canal) – skin lined canal between outside of the head and the eardrum– Glands in skin (ceruminous canals) secrete

cerumen to protect ear

Middle Ear• Tympanic membrane• Tympanic cavity• Ossicles (hammer/malleus,

anvil/incus, stirrup/stapes)• Oval window• Round window• Pharyngotympanic tube

(auditory/Eustachian tube)– connects ear and throat and will open and close to keep pressure within ear the same as external pressure

Inner Ear • Made up of bony chambers called the osseous (bony) labyrinth

• 3 divisions:– Cochlea– Vestibule– Semicircular canals

• Filled with fluid called perilymph

• Within labyrinth are membranes (membranous labyrinth)– Filled with endolymph

Hearing

• Organ of Corti– Within the cochlea– Contain hair cells to detect vibrations which cause

cochlear fluid to move• Send sound signals along cochlear nerve to the

temporal lobe (auditory cortex)• Two ears help us determine where sounds are coming

from • Over-stimulation of cochlear nerve allows us to “tune

out” certain sounds

Hearing Video

• http://www.youtube.com/watch?v=ahCbGjasm_E

Equilibrium and Balance

• Vestibular Apparatus: equilibrium detectors in the vestibule and semicircular canals– Static equilibrium – detects up and down

• Maculae: otolithic membrane with a gel-like material with otoliths (calcium salt stones) detect movement of head

– Dynamic equilibrium – movement in all directions• Crista ampularis – tuft of hair cells with cupula (gel cap)

– Movement bends hairs and cupula

• All send signals to brain through vestibular nerve to cerebellum