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BIO 156

Chapter 11

Chapter 17: The Special Senses

The special senses include:

Taste

Smell

Vision

Hearing

Balance

The Special Senses

Taste

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Taste buds respond to chemicals

dissolved in food.

Taste buds respond to five flavors: salty, bitter, sweet, sour, and umami.

Taste buds are preferentially responsive to one flavor.

Located principally on the upper surface of the tongue.

Food molecules dissolve in the saliva and bind to the membranes of the microvilli of the receptor cells.

Smell

The olfactory epithelium is a patch of receptor cells that detects odors.

The molecules bind to membrane receptors on the olfactory hairs, stimulating nerve impulses that are transmitted to the brain via the olfactory nerve.

Located in the roof of the nasal cavities.

The receptor cells respond to thousands of different molecules.

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Vision

The Visual Sense: The Eye

The middle layer consists of the choroid, the ciliary body, and the iris.

The innermost layer is the retina, the light-sensitive layer,

Human eye consists of three distinct layers. The

The outermost layer consists of the sclera and the cornea.

The retina contains two types of photoreceptors: rods and cones.

Rods function in dim light and provide black-and-white vision Cones operate in bright light and provide color vision. Cones are also responsible for visual acuity.

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The lens and cornea focus light on the retina.

Alterations in the shape of the lens and eyeball cause the most common visual problems.

Overlapping visual fields give us depth perception.

Figure11-8

Accommodation

Extrinsic Eye Muscles

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Hearing and Balance: The Cochlea and Middle Ear

The ear consists of three anatomically separate

portions: the outer, middle, and inner ears.

The inner

ear contains

the cochlea

where the

receptors for

sound are

located

The outer ear consists of the auricle and external auditory

canal, both of which direct sound to the eardrum.

The middle ear consists of the eardrum and three small

bones, the ossicles, which transmit vibrations to the inner ear.

The Structures of the Ear

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Hearing requires the participation of several structures.

The vestibular apparatus houses receptors that detect body position and movement.

The utricle

and saccule

contain

receptors that

respond to

linear

acceleration

and tilting of

the head.

The semicircular canals, utricle, and saccule.

Fluid movement inside the semicircular canals deflects the

cupula lying over the receptor cells, alerting the brain to

head movements.

End of Chapter 17