The Special Senses

Chapter 17

Objective

• Describe the structure of vertebrate sensory organs and relate structure to function in vertebrate sensory systems.

The 5 Special Senses

1. Olfaction

2. Gustation

3. Vision

4. Equilibrium

5. Hearing

Vision - Eye Anatomy

• Cornea – clear protective layer of eye (also refracts light)

• Iris – colored muscle of eye which protects retina by changing pupil size

• Pupil – allows light into eye

• Aqueous humor – watery fluid filled substance that gives the front of eye its shape

• Lens – refracts light onto retina

• Vitreous humor – jelly like fluid that gives eye it’s shape

Eye Anatomy • Retina – back part of eye that contains rods & cones for detecting

light

• Fovea centralis – contains cones for color vision

• Optic nerve – impulses sent via this nerve to the occipital lobe of the brain

• Blind spot – part of the retina where the optic nerve attaches (lacks rods & cones)

• Sclera – White part of external eye (Outermost protective layer)

• Choroid – middle layer in eye with blood vessels

LASIK

Eyelashes

Sclera

(covered by

conjunctiva)

Site where

conjunctiva

merges with

cornea

Lateral

commissure

Iris

Medial

commissure

Lacrimal

caruncle

Eyelid

Eyelid

Eyebrow

Pupil

Palpebral

fissure

(a) Surface anatomy of the right eye

Problems of Refraction

• Myopia (nearsightedness)—focal point is in front of the retina, e.g. in a longer than normal eyeball • Corrected with a concave lens

• Hyperopia (farsightedness)—focal point is behind the retina, e.g. in a shorter than normal eyeball • Corrected with a convex lens

• Astigmatism—caused by unequal curvatures in different parts of the cornea or lens • Corrected with cylindrically ground lenses, corneal

implants, or laser procedures

Figure 15.14 (1 of 3)

Focal

plane

Focal point is on retina.

Emmetropic eye (normal)

Figure 15.14 (2 of 3)

Concave lens moves focal

point further back.

Eyeball

too long

Uncorrected

Focal point is in front of retina.

Corrected

Myopic eye (nearsighted)

Figure 15.14 (3 of 3)

Eyeball

too short

Uncorrected

Focal point is behind retina.

Corrected

Convex lens moves focal

point forward.

Hyperopic eye (farsighted)

Cataracts

Diabetic retinopathy

Glaucoma

Macular degeneration

Olfactory Organs

• Sensory organs of smell

• Organs have 2 layers:

• Olfactory epithelium

• Lamina propria

• Contains olfactory glands – secretions absorb water, form a thick, pigmented mucus

Special Senses of the Ear

• Special senses of equilibrium and hearing are provided by the inner ear

• Equilibrium

• Position of the head in

space

• Hearing

• Detect and determine

sound waves

Anatomy of the Ear

• 3 regions:

• External ear

• Detects sound waves towards middle ear

• Middle ear

• Collects sound waves

• Inner ear

• Contains sensory

organs

External Ear

• Fleshy and cartilagenous auricle (pinna)

• Provides directional sensitivity

• Ends at the tympanic membrane

• Ear drum

• Thin, semitransparent sheet

• Delicate

• Protected by cerumen

Middle Ear

• Air-filled chamber

• Auditory tube permits equalization on both sides of the tympanic membrane

• 3 tiny bones: • Malleus

• Hammer

• Incus • Anvil

• Stapes • Stirrup

Inner Ear

• Labyrinth of dense bones • 3 subdivisions:

• Vestibule • Saccule • Utricle

• Sensations of gravity and linear acceleration

• Cochlea • Snail shell • Sense of hearing

Equlibrium

• Hair cells receive signals

• Provide info about the direction and strength of stimuli

Hearing

• Receptors can detect frequency and intensity of sounds

• Intensity is measured in decibels (dB) • Normal conversation 60-70dB

• Telephone dial tone 80dB

• Sustained exposure resulting in hearing loss: 90dB

• Rock concert 115dB

• Loudest recommended with protection: 140dB

• Gun blast 140dB

Olfactory Discrimination

• Olfactory system can distinguish thousands of chemical stimuli

• Olfactory

receptors

decline with

age

Gustatory Receptors

• Taste receptors

• Aka taste buds

• An adult has ~3000 taste buds

• 3 types of projections:

• Filiform

• Fungiform

• Circumvallate

Filiform Papillae

• Provide friction

• Help the tongue move around the mouth

• Do not contain taste buds

Fungiform Papillae

• Each contains about 5 taste buds

Circumvallate Papillae

• Contain ~100 taste buds each

• Form a V near the posterior region of the tongue

Aging and Taste

• 10,000 taste buds when born

• # declines dramatically by age 50

• ** olfactory stimuli has a powerful effect on mood & behavior

• ** if we cannot smell the food, we believe it is more bland