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The Senses• Help to maintain homeostasis

• General senses – receptors located throughout the body

� Within the skin, organs & joints

� Sense of touch

• Special senses – receptors in the head

�Sight

�Smell

�Taste

�Hearing

�Equilibrium

Receptors• Receptors – specialized cells that collect info from

the environment & pass info to the nervous system

• Chemoreceptors – receptors for smell & taste; respond to chemicals in solution

• Pain receptors (nociceptors) –

• Thermoreceptors – respond to temp.

• Mechanoreceptors –

• Proprioceptors sense changes in tension of muscles & tendons

• Baroreceptors detect changes in pressure

• Stretch receptors detect changes in length or volume

• Photoreceptors respond to patterns made by light; sight

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Chemical Senses – Taste & Smell

• Chemoreceptors; respond to chemicals in a solution

•Chemicals dissolved in saliva & fluids in nasal membranes

• Both senses complement each other; 80% of taste depends on smell

Olfaction –• Olfactory receptors are located in the roof

of the nasal cavity

•Chemicals must be dissolved in mucus

•Sniffing intensifies smell; pulls molecules across olfactory receptor cells

•Olfactory cells surrounded by supporting cells

•Olfactory hairs increase the surface area of receptor cells

•Olfaction closely related to taste & memories

Olfaction

•Impulses are transmitted from receptor cells to the olfactory nerve

•Olfactory nerve passes thru ethmoid bone to the olfactory bulb.

•Interpretation of smells is made in the cortex but passes through the limbic system, the part of the brain that stores memories and emotions

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The Sense of Taste

• Gustation –

• Taste buds – receptor organs for taste

• Location of taste buds

• Most are on the tongue

• Hard & soft palate

• Cheeks

The Tongue and Taste• Tongue is covered w/projections called

• Taste buds are found on the sides of papillae

• Taste buds are constantly being replaced due to wear and tear

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Structure of Taste Buds• Taste buds consist of 3 types of cells;

gustatory cells, supporting cells, & basal cells

�Gustatory cells (taste cells) are the receptors

�Supporting cells surround taste cells

�Gustatory hairs (long microvilli) protrude from TASTE PORE

− Hairs are stimulated by chemicals dissolved in saliva

�Basal cells are located at the base & are the source for new taste cells

Anatomy of Taste Buds

Taste Sensations• Sweet receptors –

�Sugars, carbohydrates

• Sour receptors –

�Acids (lemon, vinegar)

• Salty receptors –

�Metal ions (NaCl)

• Bitter receptors –

�Alkaloids (aspirin), many poisons

• Umami

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Taste Pathway• Impulses are carried to the gustatory

complex by several cranial nerves because taste buds are found in different areas

• Facial nerve – transmits impulse from taste buds in anterior 2/3 of tongue

• Glossopharyngeal nerve – from taste buds in posterior 1/3 of tongue

• Vagus nerve - from the few taste buds at the base of the tongue & pharynx

The Ear

• Houses 2 senses

� Hearing

� Equilibrium

• Receptors are mechanoreceptors –respond to vibrations & movement of fluids in ear

• Different organs house receptors for each sense

Anatomy of the Ear

• The ear is divided into 3 areas

• Outer (external) ear

• Middle ear

• Inner ear

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The External Ear• Involved in hearing only

• Structures of the external ear

• Pinna (auricle) – shell shaped structure; directs sound waves into canal

• External auditory canal –w/in temporal bone external acoustic meatus

• Tympanic membrane –transfers sound waves

The External Auditory Canal

• Ceruminous glands secrete ear wax (cerumen)

• External ear ends at the tympanic membrane or eardrum

Middle Ear or Tympanic Cavity

• Air-filled cavity within the bone

• Only involved in the sense of hearing

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Middle Ear or Tympanic Cavity

• 2 tubes are associated with the middle ear

• The opening from the auditory canal is covered by the tympanic membrane

• The auditory tube or eustachian tube connects middle ear w/throat

• Allows for equalizing air pressure during yawning, swallowing or flight

• This tube is otherwise collapsed

Bones of the Tympanic Cavity• 3 bones of the

cavity (ossicles)

• Malleus ( )

• Incus ( )

• Stapes ( )

• Vibrations from eardrum moves the malleus

• Bones transfer sound to the inner ear

Inner Ear or Labyrinth

• Includes organs for hearing & balance

• Osseous labyrinth – bony canal in temporal bone

• Membranous labyrinth – within osseous labyrinth

• Perilymph – inner ear fluid between osseous & membranous labyrinth

• Endolymph – fluid within the membranous labyrinth

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Inner Ear

Inner Ear• A maze of bony chambers within the

temporal bone

• Cochlea – snail shell organ used in hearing

• Semicircular canals –

• Vestibule – contains oval & round window, saccule, & utricle for hearing & equilibrium

Inner Ear

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Cochlea

• Organ of Corti

• Located within the cochlea

• Receptors or hair cells on the basilar membrane

• Gel-like tectorial membrane is capable of bending hair cells

• Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of Hearing

Figure 8.13

Mechanisms of Hearing

• Vibrations from sound waves move tectorial membrane

• Hair cells are bent by the membrane

• Continued stimulation can lead to adaptation

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Organs of Equilibrium

• Receptor cells are in 2 structures

• Vestibule

• Semicircular canals

Organs of Equilibrium

• Equilibrium has 2 functional parts

• Static equilibrium-

• Dynamic equilibrium –

Static Equilibrium

• Maculae – receptors in the vestibule

• Report on the position of the head

• Send information thru vestibular nerve

• Anatomy of the maculae

• Hair cells are embedded in the otolithicmembrane

• Otoliths ( ) float in a gel around the hair cells

• Movements cause otoliths to bend the hair cells

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Function of Maculae

Hair cells

Sensory (afferent) nerve fiber Supporting cells

Otoliths

(a) Head upright (b) Head bent forward

Macula

of utricle

Hairs of

hair cells bend

Gelatinous

material sags

Gravitational

force

Dynamic Equilibrium

• Crista ampullaris – receptors in the semicircular canals

• Tuft of hair cells

• Cupula (gelatinous cap) covers the hair cells

• With angular head movements, the cupula stimulates the hair cells

• An impulse is sent via the vestibular nerve to the cerebellum

Dynamic Equilibrium

• Action of angular head movements

• The cupula stimulates the hair cells

• An impulse is sent via the vestibular nerve to the cerebellum

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The Eye

• Visual perception based on photoreceptors that sense patterns made by

• Eye Protection

• Enclosed in a bony orbit

• Fat surrounds & cushions eye

Accessory Structures of the Eye• Eyebrow –prevent sweat from entering eye

• Eyelids –

• Thinnest skin in the body

• Protects & lubricates

• Medial canthus – inner corner

• Lateral canthus – outer corner

• Eyelashes –

• Blinking protects eye from foreign objects

Accessory Structures of the Eye

• Tarsal glands –produces an oily secretion to lubricate the eye& eyelid

• Ciliary glands – modified sweat glands between the eyelashes;

• Sty – inflammation of ciliary gland

• Conjunctiva

• Membrane lining eyelids

• Connects to the surface of the eye

• Secretes mucus to lubricate the eye

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Accessory Structures of the Eye

•Conjunctivitis – inflammation of conjunctiva;

Accessory Structures of the Eye

Accessory Structures of the Eye

• Lacrimal apparatus

• Lacrimal gland – produces tears (saline solution)

• Lacrimal puncta – pore that tears drain into

• Superior & inferior lacrimal canaliculi – drains lacrimal fluid from eyes to lacrimal sac

• Lacrimal sac – empties lacrimal fluid into nasal ducts

• Nasolacrimal duct – empties lacrimal fluid into the nasal cavity

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Function of Lacrimal Apparatus

• Properties of lacrimal fluid (tears)

• Dilute salt solution

• Contains antibodies & lysozymes to reduce eye infections

• Protects, moistens, & lubricates the eye

Extrinsic Eye Muscles

• Muscles attached to the outer surface of eye

• Control eye movements

• 4 rectus muscles originate from annular ring located in back of orbit

– Superior rectus – top muscle, upward movement

– Inferior rectus – lower muscle, downward movement

– Lateral rectus – outer muscle, outward movement

– Medial rectus – inner muscle, inner movement

• Superior Oblique – originates at annular ring & runs through trochlea loop; attaches to top; helps rotate eye down & out

• Inferior Oblique – originates at medial orbit; runs laterally to inferior surface; helps rotate eye up & out

• Trochlea – loop supporting superior oblique

Extrinsic Eye Muscles

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Eyelid Muscles

• Orbicularis occuli –

• Levator palpebrae –

Structure of the Eye

• The eye is a fluid filled sphere surrounded by several layers called tunics

• Humors – fluids that help maintain shape of eye

• 3 Tunics (layers)

• Fibrous tunic – outside layer

• Vascular tunic– (uvea) middle layer

• Sensory tunic – (retina) inside layer

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Fibrous Tunic – outer layer� 1. Cornea

• Transparent window; bulges from sclera

• Allows light to pass through

• Repairs itself easily

• The only human tissue that can be transplanted without fear of rejection

� 2. Sclera

• White connective tissue layer

• Site of muscle attachment

• Optic nerve emerges from back of sclera

Vascular Tunic - middle layer • Choroid - highly vascular layer that is loosely

attached to sclera

� Dark pigment helps absorb light

• Ciliary body – smooth muscles that control lens shape; secretes aqueous humor

� Suspensory ligaments – hold the lens in place & may change the shape of the lens as the eye focuses on near or far objects.

• Accommodation –

Lens Accommodation

• Light must be focused to a point on the retina for optimal vision

• The eye is set for distance vision (about 20 ft away)

• The lens must change shape to focus for closer objects; suspensory ligaments contract

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Vascular Tunic - middle layer • Iris - gives eye color; located between cornea

& lens; smooth muscles control size of pupil

• Pupil – opening in the iris; allows light to enter the circulation of aqueous humor

� Smooth muscles of iris act as diaphragm to change size of pupil

� Bright light – pupil

� Dim light – pupil

Sensory Tunic (Retina) – inner layer• Retina - contains photoreceptors – cells that

respond to light

� Thin, delicate inner lining of the eye

� Rods – dim light vision & peripheral vision; grays

� Cones –

� Signals pass from photoreceptors via a 2-neuron chain

� Bipolar neurons – receive impulse from cones & rods

� Ganglion cells – receives impulse from bipolar cells; sends message to optic nerve

3 parts of Retina

• Optic nerve – carries impulse to brain for interpretation

• Fovea centralis – area of greatest visual acuity; point of sharpest vision; contains only cones

• Optic disc – blind spot; no photoreceptors are present

•Site of where

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Neurons of the Retina

Lens

• Biconvex crystal-like structure

• Held in place by suspensory ligaments attached to ciliary body

Internal Eye Chamber Fluids

• Anterior cavity – in front of lens,contains aqueous humor

• Watery fluid

• Helps maintain proper pressure

• Provides nutrients for the lens & cornea

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Internal Eye Chamber Fluids

• Vitreous humor –

• Gel-like substance behind the lens

• Keeps the eye from collapsing

• Helps hold retina against chroid coat

• Helps transmit light

• Emmetropic –

• Astigmatism – unequal curves w/in lens; object

appears clear in some areas and blurry in others

• Hyperopic – far sighted

– Eye too short

– Objects focused behind retina

– Corrected w/ convex lens

• Myopic – nearsightedness

– Eye too long

– Objects focused in front of retina

– Corrected w/concave lens

Visual Diorders

• Presbyopia – deterioration of lens as one ages

• Amblyopia – lazy eye

• Strabismus – crossed eye

• Colorblindness – lack of certain cones

• Retinal detachment – retinal & neural layers separate

• Caused by traumatic blows, diabetes

• May cause blindness

• Glaucoma –increase pressure to eye

• Due to excess aqueous fluid

• Compresses retina & optic nerve

• Cataracts – clouding of lens

• Lens transplants

Visual abnormalities