The Special Senses

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The Senses
Anatomy & Physiology II
Chapter 11
The Senses
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Sensory receptors detect and respond to
stimuli (environmental change)
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Activation of receptors initiates nerve
impulse (signal)
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Signal interpreted by cerebral cortex
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Sensation experienced
Sensory Receptors
Distribution of sense receptors
 Special senses in sense organ
◦ Vision
◦ Hearing
◦ Equilibrium
◦ Taste
◦ Smell
 General senses throughout body
◦ Pressure, temperature, pain, touch
◦ Sense of position
Sensory Receptors
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Sensory receptors
◦ Nociceptors – respond to tissue damage (painful
stimuli)
◦ Chemoreceptors - respond to chemicals
◦ Photoreceptors - respond to light
◦ Thermoreceptors - respond to heat
◦ Mechanoreceptors - respond to movement
The Eye and Vision
Eye protection structures
 Eye cavity bones
 Eyelids
 Eyelashes and eyebrow
 Conjunctiva
 Lacrimal glands
Coats of the Eyeball
Eyeball has three separate coats (tunics)
 Sclera
 Choroid
 Retina
The Eye
Note the three tunics, the refractive parts of the
eye (cornea, aqueous humor, lens, vitreous
body), and other structures involved in vision.
Pathway of Light Rays and Refraction
Transparent parts of the eye that refract
light
 Cornea
 Aqueous humor
 Lens
 Vitreous body
Function of the Retina
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Pigmented layer
◦ Sensitive to light
Rods
◦ Function in dim light
◦ Shades of gray
◦ Blurred images
Cones
◦ Function in bright light
◦ Color sensitive
◦ Sharp images
Connecting neurons
Structure of the Retina
Rods and cones form a deep layer of the retina, near the
choroid. Connecting neurons carry visual impulses toward
the optic nerve.
Muscles of the Eye
Two muscle groups adjust eye so retina can
receive clear image
The Extrinsic Muscles
Outer surface of eyeball
 Voluntary
 Control convergence for threedimensional vision
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Extrinsic Muscles of the Eye
The medial rectus is not shown.
ZOOMING IN • What characteristics are used in naming the extrinsic eye muscles?
The Intrinsic Muscles
Within eyeball
 Iris regulates amount of light entering eye
 Ciliary muscle shapes lens for near and
far vision
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Ciliary Muscle and Lens
Contraction of the ciliary muscle relaxes tension on the suspensory
ligaments, allowing the lens to become more round for near vision.
Nerve Supply to the Eye
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Optic nerve (cranial nerve II)
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Oculomotor nerve (cranial nerve III)
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Trigeminal nerve (cranial nerve V)
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Trochlear (cranial nerve IV)
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Abducens (cranial nerve VI)
Nerve Supply to the Eye
ZOOMING IN
• Which of the nerves shown moves the eye?
Errors of Refraction
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Hyperopia (farsightedness) – difficulty
focusing on objects near the face.
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Myopia (nearsightedness) – difficulty focusing
on distant objects.
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Astigmatism - An irregular shaped cornea or
lens prevents light from focusing properly on the
retina. Images focus at muliple points on retina
Eye Disorders

Strabismus – inability to align both eyes
simultaneously due to a lack of muscle
coordination
◦ Convergent (cross-eyed) – affected eye deviates toward
nose
◦ Divergent – affected eye deviates laterally

Amblyopia (lazy eye) – loss of vision in a healthy
eye due to inadequate muscle balance
◦ not correctable by glasses or contact lenses
◦ The brain, for some reason, does not fully acknowledge
the images seen by the amblyopic eye.
Other Eye Disorders
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Infections
◦ Conjunctivitis
◦ Inclusion conjunctivitis
◦ Ophthalmia neonatorum
Injuries
 Cataract
 Glaucoma
 Disorders involving the retina

◦ Diabetic retinopathy
◦ Macular degeneration
The Ear
Sense organ for hearing and equilibrium
 Outer ear
 Middle ear
 Inner ear
The ear. Structures in the outer, middle, and
inner divisions are shown
The Outer Ear
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Pinna (auricle)
◦ Directs sound waves into ear
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External auditory canal (meatus)
◦ Ceruminous glands
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Tympanic membrane
◦ Vibrates as sound waves enter ear
The Middle Ear and Ossicles
Middle ear cavity contains ossicles (small
bones) that amplify sound waves and
transmit sounds to inner ear
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrup)
Eustachian Tube
Connects middle ear cavity with throat
(pharynx)
 Allows pressure to equalize on both sides
of tympanic membrane
 Continuous mucous membrane from
pharynx to middle ear cavity
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The Inner Ear
 Bony
labyrinth
◦ Vestibule
◦ Semicircular canals
◦ Cochlea
◦ Perilymph fluid
 Membranous
labyrinth
◦ Vestibule
◦ Semicircular canals
◦ Cochlea
◦ Endolymph fluid
The Inner Ear
The vestibule, semicircular canals, and cochlea are made of a bony shell
(labyrinth) with an interior membranous labyrinth. Endolymph fills the
membranous labyrinth and perilymph is around it in the bony labyrinth.
Hearing
Organ of Corti
 Located in membranous cochlea
(cochlear duct)
 Ciliated receptor cells
 Tectorial membrane
Cochlea and the
organ of Corti.
The arrows show
the direction of
sound waves in the
cochlea.
Equilibrium
Ciliated equilibrium sensory receptors are
located in vestibule and semicircular
canals
 Types of equilibrium
◦ Static
 Maculae receptors
 Otoliths fluid
◦ Dynamic
 Cristae receptors
Action of the receptors (maculae) for static equilibrium. As the head moves,
the thick fluid above the receptor cells, weighted with otoliths, pulls on the
cilia of the cells, generating a nerve impulse.
Action of the receptors (cristae) for dynamic equilibrium.
As the body spins or moves in different directions, the
cilia bend as the head changes position, generating
nerve impulses.
Otitis and Other Disorders of the Ear
Otitis media
 Otitis externa
 Hearing loss
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◦ Conductive hearing loss
◦ Sensorineural hearing loss
◦ Presbycusis
Other Special Sense Organs
Taste and smell sense organs respond to
chemical stimuli
Sense of Taste
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Taste receptors
(buds) on tongue
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◦ Stimulated by
substance in solution
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Basic tastes
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Sweet
Salty
Sour
Bitter
Other tastes
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Water
Alkaline
Metallic
Umami
Cranial nerves
◦ Facial (VII)
◦ Glossopharyngeal (IX)
Special senses that respond to chemicals.
(A)Organs of taste (gustation) and smell (olfaction).
(B) A taste map of the tongue.
Sense of Smell
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Smell receptors in nasal cavity
◦ Stimulated by substances in solution in nasal
fluids
◦ Smells stimulate appetite and flow of digestive
juices
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Olfactory nerve (cranial nerve I)
The General Senses
Receptors scattered throughout the body
sense
 Touch
 Pressure
 Heat
 Cold
 Position
 Pain
Sense of Touch
Tactile corpuscles
 Found mostly in dermis of skin and around hair
follicles
 Sensitivity varies with the number of receptors
 Baroreceptors in walls of large arteries monitor
blood pressure and trigger responses that control
BP as vessels stretch.
Sense of Pressure
Receptors for deep touch located
 In subcutaneous tissues
 Near joints, muscles, and other deep tissues
Sense of Temperature
Temperature receptors
 Are free nerve endings
 Are widely distributed in the skin
 Are separate for heat and cold
 Occur in hypothalamus of brain
◦ Help to adjust body temperature according to
temperature of circulating blood
Sense of Position
Proprioceptors (position receptors)
 Are located in muscles, tendons, joints
 Relay impulses of body parts in relation to
each other
 Send impulses to the cerebellum for
coordination
Sense of Pain
 Pain
receptors
◦ Are free nerve endings
◦ Are found in skin, muscles, joints and (to a
lesser extent) in most internal organs
 Pain
relief
◦ Analgesic drugs
◦ Anesthetics
◦ Endorphins
◦ Heat or cold
◦ Relaxation or distraction techniques
Sensory Adaptation
Occurs when receptors are exposed to
continuous stimulus
 Some receptors can adjust themselves so
sensation becomes less acute
 Receptors adapt at different rates
 Pain receptors do not adapt
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End of Presentation

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