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SPECIAL SENSES

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Special Senses

General Senses• receptors that are widely distributed throughout the body• skin, various organs, and joints• receive stimulation of touch, temperature, pain

Special Senses• specialized receptors confined to structures in the head • eyes and ears•Allow vision, hearing, equilibrium, taste, and smell

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Senses

Sensory Receptors• specialized cells or multicellular structures that collect information from the environment

• stimulate neurons to send impulses along sensory fibers to the brain

Sensation• a feeling that occurs when brain becomes aware of sensory impulse

Perception• a person’s view of the stimulus; the way the brain interprets the information

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Receptor Types

Chemoreceptors• respond to changes in chemical concentrations

Pain receptors (Nociceptors)• respond to tissue damage• respond to intense stimuli of any kind

Thermoreceptors• respond to changes in temperature

Mechanoreceptors• respond to mechanical forces• touch/pressure

Photoreceptors• respond to light

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Referred Pain

• May occur due to sensory impulses from two regions following a common nerve pathway to brain

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Special Senses

• Sensory receptors are within large, complex sensory organs in the head

• smell in olfactory organs

• taste in taste buds

• hearing and equilibrium in ears

• sight in eyes

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Sense of Smell

Olfactory Receptors• chemoreceptors• respond to chemicals dissolved in liquids

Olfactory Organs• contain olfactory receptors and supporting epithelial cells• cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

Sensory Adaptation• when an odor seems to fade away after you have been exposed to it

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Olfactory Receptors

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Sense of Taste-Gustatory Senses

Taste Buds• organs of taste• located on papillae of tongue, roof of mouth, linings of cheeks, and walls of pharynx

Taste Receptors• chemoreceptors• taste cells – modified epithelial cells that function as receptors• taste hairs – microvilli that protrude from taste cells; sensitive parts of taste cells

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Gustatory Sense OrgansGustatory Sense Organs

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Tongue MapTongue Map

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Taste Receptors

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Taste Sensations

Four Primary Taste Sensations• sweet – stimulated by carbohydrates• sour – stimulated by acids• salty – stimulated by salts• bitter – stimulated by many organic compounds

Spicy foods activate pain receptors

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Hearing

Ear – organ of hearing

Three Sections• External• Middle• Inner

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External Ear

• Auricle• Collects sounds waves• Flap on the side of the head

• External auditory meatus• Ear canal• Carries sound to tympanic membrane• Terminates with tympanic membrane

• Tympanic membrane • Ear drum• Vibrates in response to sound waves• Separates external from middle ear

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Middle Ear

• Tympanic cavity• Air-filled space in temporal bone

• Three auditory ossicles• Vibrate in response to tympanic membrane• Malleus, incus, and stapes

• Oval window • Opening in wall of tympanic cavity• Stapes vibrates against it to move fluids in inner ear

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Auditory Tube

• Eustachian tube • Connects middle ear to throat• Helps maintain equal pressure on both sides of tympanic membrane• Usually closed by valve-like flaps in throat• Pathway for infection

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Inner Ear

Three Parts of Labyrinths• Cochlea

• Functions in hearing• Semicircular canals

• Functions in equilibrium• Vestibule

• Functions in equilibrium

Range of Human Hearing• 20 – 20,000 vibrations per second

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Sight

Visual Accessory Organs• Eyelids• Lacrimal apparatus• Extrinsic eye muscles

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Eyelid

• Palpebra• Composed of four layers

• skin• muscle • connective tissue• conjunctiva

• Orbicularis oculi - closes• Levator palperbrae superioris – opens• Tarsal glands – secrete oil onto eyelashes• Conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball

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Lacrimal Apparatus

• Lacrimal gland• lateral to eye• secretes tears

• Canaliculi• collect tears

• Lacrimal sac• collects from canaliculi

• Nasolacrimal duct• collects from lacrimal sac• empties tears into nasal cavity

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Coats of the Eyeball - Outer Tunic

Cornea• anterior portion• transparent• No blood vessels

Sclera• posterior portion• opaque• protection

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Middle Tunic

Iris • anterior portion• pigmented• controls light intensity

Ciliary body• anterior portion• pigmented• holds lens• moves lens for focusing

Choroid coat• provides blood supply• pigments absorb extra light

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Anterior Portion of Eye

• Filled with aqueous humor (thick watery substance

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Lens

• transparent• biconvex• lies behind iris• largely composed of lens fibers• elastic• held in place by suspensory ligaments of ciliary body

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Accommodation• changing of lens shape to view objects

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Iris

• composed of connective tissue and smooth muscle• pupil is hole in iris• dim light stimulates radial muscles and pupil dilates• bright light stimulates circular muscles and pupil constricts

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Inner Tunic

• Retina• contains visual receptors - Rods and Cones• continuous with optic nerve• ends just behind margin of the ciliary body• composed of several layers

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Posterior Cavity

• Contains vitreous humor – thick gel that holds retina flat against choroid coat

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Layers of the Eye

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Visual Receptors

Rods• long, thin projections• contain light sensitive pigment called rhodopsin• hundred times more sensitive to light than cones• provide vision in dim light• produce colorless vision• produce outlines of objects

Cones• short, blunt projections• contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe• provide vision in bright light• produce sharp images• produce color vision

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Rods and Cones