Anatomy & Physiology: Special Senses

Anatomy & Physiology: Special Senses

1. The Eye & Vision

1. Accessory Structures of the Eye

1. Orbital Cavity

1. Frontal, maxilla, ethmoid, sphenoid, lacrimal, & palatine bones.
2. Optic foramen –

1. Superior orbital foramen –

1. Fat pad -

1. Eyebrow – ridge of frontal bone that is covered by coarse hair. Provides shade and prevents perspiration from dripping into the eye.
2. Eyelids – thin, skin covered folds that protect the eye from foreign objects and helps keep eyes moist. The blinking reflex occurs every 3 – 7 seconds.
3. Conjunctiva –

1. Lacrimal Apparatus

1. Lacrimal gland – located on the area of the eye.
2. Lacrimal secretion (tears) – dilute saline, mucus, & enzyme solution that keeps eye moist, pH balanced, and free of germs.
3. Blinking washes tears across the eyes.
4. Nasolacrimal duct – drains excessive tears from the eye into the nasal cavity.

1. Extrinsic Eye Muscles – ____ muscles that control the movement of the eyes.

a.

b.

c.

d.

e.

f.

1. Structure of the Eyeball (three layers: Vascular Tunic, Fibrous Tunic, Nervous Tunic)

1. Fibrous Tunic – outermost layer of the eye

1. Sclera (White of the eye)

1. Cornea –

2. Vascular Tunic – middle layer of the eye that has many blood vessels

1. Choroid - Black to brown tissue that lines the back 5/6 of the eye. Functions to supply nutrients and blood to the inner tissues of the eye and t absorb excess light.
2. Ciliary body –

1)Ciliary Muscles –

2)Suspensory ligament –

1. Lens –

1. Iris – colored part of the eye. Composed of circular and radial arranged smooth muscles that function to regulate the amount of light that enters the eye from its center opening (pupil).

1)Iris dilates to let in more light and constricts to decrease the amount of light.

2)Colors are brown, blue, green, or gray depending upon the amount of brown pigment.

1. Aqueous Humor –

1. Nervous (Sensory) Tunic – innermost layer of the eye

1. Retina – layer that contains visual receptor cells.

1)rods – responsible for black & white vision. Stimulated in dim light.

2)Cones – responsible for color vision. Stimulated in bright light.

a)concentrated near the center of the retina

b)three colors: red, blue, & green.

1. Macula lutea (yellow spot) –

1. Optic disc (blind spot) –

1. Vitreous Humor – clear, jelly-like fluid that functions to support the shape of the eyeball and to hold the retina against the surface of the eye ball.

1. Vision Physiology

1. Refraction & lenses

a.

b .A lens is a transparent object that is curved on one or both sides such that

light is bent as it passes through.

1)convex lens – cause light waves to converge

2)concave lens – cause light waves to diverge

c. Focal point – the point at which convergent light rays meet.

d. The thicker the lens, the more the light rays will be bent.

1. Real image – the image formed by a convex lens will be upside down and backwards.

1. Visual focusing

1. As light reaches the eyeball the cornea refracts it towards the lens. Most of the refraction of the light occurs at the cornea.

1)Distant objects require less focusing, thus the lens is stretched by the ciliary muscles into a thinner shape.

2)Near objects need more focusing thus the ciliary body relaxes and allows the lens to recoil back to its shorter, fatter shape that refracts the light more. (accommodation)

1. ______vision is normal vision and requires NO accommodation or change in lens shape (usually 20 feet.)

1. Refraction problems

1. Myopia (nearsightedness)

1. Hyperopia (farsightedness)

1. Astigmatism – unequal curvature of the lens that causes unequal focusing of objects back on the retina. Correction involves special cylindrically ground lenses.
2. Presbyopia (farsightedness due to age)

1. Disorders of the Eyes

1. Cataracts – thickening and hardening of the lens that causes it to cloud over and eventually blindness. Due to age (normally), UV light, smoking, diabetes. Lens replacement surgery is only cure.
2. Glaucoma – a buildup of aqueous humor in the anterior chamber of the eye that eventually can cause blindness. Due to decreased drainage of the aqueous humor past the age of 40. If detected early on, it can be corrected using eye drops that increase drainage.
3. Colorblindness – sex-linked hereditary condition that results in the absence of one or more types of cones.

1. Monochromates – black & white only
2. Dichromates – blue-yellow or red-green

1. The Ear, Hearing and Equilibrium

1. Structure of the Ear (divided into three parts: outer ear, middle ear, & inner ear)

1. Outer Ear

1. Auricle / Pinna – funnel shaped elastic cartilage that directs sound into the ear canal.
2. External Auditory Meatus (canal) – short (2.5 cm) curved tube that connects the auricle and the eardrum.

1)Ceruminous glands line the tube and secrete a yellow, sticky wax (cerumen) that traps dirt & debris

2)Lined with hairs that point out to capture dirt.

1. Tympanic membrane (eardrum) – membrane that converts air vibrations into mechanical vibrations.

1. Middle Ear

1. Air filled space (tympanic chamber) that connects the outer & inner ears.
2. Pharyngotympanic tube (Eustachian tube)

1. Auditory ossicles –

1)Smallest bones of the body.

2)

3)Transmit and amplify the vibrations from the eardrum to the inner ear.

1. Tensor tympani & Stapedius –

1. Inner Ear

1. Labyrinth – maze of canals and chambers in the temporal bone (behind the eye). Two major divisions: Bony Labyrinth & Membranous Labyrinth.

1)Bony Labyrinth –

2)Membranous Labyrinth

3)Perilymph –

4)Endolymph –

5) The three structures of the inner ear are the

a)Cochlea –

b)Vestibule -

c)Semicircular Canals –

1. The Cochlea and Hearing

1. Structure of the Cochlea (from Latin for snail)

1. The cochlea is divided into three ducts

1)Scala Vestibuli - upper duct. Contains perilymph.

2)Scala Tympani – lower duct. Contains perilymph.

3)Scala Media (Cochlear duct) – middle duct. Contains endolymph and has the Organ of Corti.

1. Oval window –

1. Tectoral membrane –

1. Basilar membrane –

1. Organ of Corti –

1. Physiology of Hearing

1. Mechanical vibrations of the stapes put pressure on the oval window of the s. vestibuli. This pressure is transferred to the perilymph, which is continuous throughout the s. vestibuli and s. tympani.
2. The frequency of the vibration causes a localized distortion of the basilar membrane.
3. Movement of the basilar membrane presses the hair cells of the organ of Corti up against the tectoral membrane.
4. The hair cells are neural receptors that transfer the stimuli into an impulse that travels to the brain via the Auditory nerve.
5. The location of the basilar membrane distortion depends upon the frequency of the sound.

1)High pitch sound will cause a distortion closer to the oval window.

2)Low pitch sounds will cause a distortion closer to the center of the shell.

1. The volume of the sound will cause a greater or lesser distortion in the basilar membrane. The louder the sound, the more distortion and the greater the number of hair cells will be stimulated.

1. Sound – two physical properties: frequency & amplitude

1. Frequency –

c.

1. Amplitude –

b.

1. Deafness

1. Conductive deafness – interference in the transmission of vibrations to the inner ear.

1. Sensorineural deafness – damage to the organ of Corti or auditory nerve that prevents transmission of the nerve impulse to the brain.

1. Presbycusis –

1. Vestibule, Semicircular canals, & Equilibrium

1. Vestibule – two sacs of the inner ear that sense static equilibrium.

c.

1. Semicircular canals – three canals that sense dynamic equilibrium.

a.

b.

c.

d.