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PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
General Senses
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
13c
Peripheral Nervous System (PNS)
 PNS – all neural structures outside the brain and spinal cord
 Includes sensory receptors, peripheral nerves, associated
ganglia, and motor endings
 Provides links to and from the external environment
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Sensory Receptors
 Structures specialized to respond to stimuli
 Activation of most sensory receptors results in
depolarizations (electrical activations) that trigger impulses
to the CNS
 The realization of these stimuli, sensation and perception,
occur in the brain
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From Sensation to Perception
 Survival depends upon sensation and perception
 Sensation is the biological awareness of changes in the
internal and external environment
 Perception is the conscious interpretation of those stimuli
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Receptor Classification by Location
1. exteroreceptors - respond to external environment
2. enteroreceptors - respond to internal environment
3. proprioreceptors - respond to body position/motion
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Receptor Class by Location: Exteroceptors
 Respond to stimuli arising outside the body
 Found near the body surface
 Sensitive to touch, pressure, pain, and temperature
 Include the special sense organs
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Receptor Class by Location: Interoceptors
 Respond to stimuli arising within the body (pH, CO2, O2,
salts)
 Found in internal viscera and blood vessels
 Sensitive to chemical changes, stretch, and temperature
changes
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Receptor Class by Location: Proprioceptors
 Respond to degree of stretch of the organs they occupy
 Found in skeletal muscles, tendons, joints, ligaments, and
connective tissue coverings of bones and muscles
 Constantly “advise” the brain of one’s movements
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Receptor Classification by Stimulus Type
1. mechanoreceptors - any mechanical deviation
a. touch, pressure, vibration, proprioception etc.
2. thermoreceptors - changes in temperature
3. nocireceptors - pain; physical or chemical damage
4. photoreceptors - light; rods & cones of the eye
5. chemoreceptors - shapes of different molecules
a. taste, smell, chemicals of blood
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Simple Receptors
 Meissner’s corpuscles
 Pacinian corpuscles
 Muscle spindles
 Golgi tendon organs
 Ruffini’s corpuscles
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Simple Receptors: Unencapsulated
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Table 13.1.1
Simple Receptors: Encapsulated
Table 13.1.2
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Simple Receptors: Encapsulated
Table 13.1.3
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Adaptation of Sensory Receptors
Adaptation occurs when sensory receptors are subjected to an
unchanging stimulus
 Receptor membranes become less responsive
 Receptor potentials decline in frequency or stop
 Receptors responding to pressure, touch, and smell adapt
quickly
 Pain receptors and proprioceptors do not exhibit adaptation
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
Special Senses
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
15
I. Chemical Senses
Chemical senses – gustation (taste) and olfaction (smell)
Their chemoreceptors respond to chemicals in aqueous solution
 Taste – to substances dissolved in saliva
 Smell – to substances dissolved in fluids of the nasal
membranes
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Taste Buds
 Most of the 10,000 or so taste buds are found on the tongue
 Taste buds are found in papillae of the tongue mucosa
 Papillae come in three types: filiform, fungiform, and
circumvallate
 Fungiform and circumvallate papillae contain taste buds
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Taste Buds
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Figure 15.1
Gustatory Pathway
Figure 15.2
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Influence of Other Sensations on Taste
 Taste is 80% smell
 Thermoreceptors, mechanoreceptors, nociceptors also
influence tastes
 Temperature and texture enhance or detract from taste
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Sense of Smell
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Figure 15.3
II. Eye and Associated Structures
- 70% of all sensory receptors are in the eye
- Most of the eye is protected by a cushion of fat and the bony orbit
Accessory structures include:
 eyebrows
 eyelids
 conjunctiva
 lacrimal apparatus
 extrinsic eye muscles
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Palpebrae (Eyelids)
1
2
3
4
5
6
7
8
9
Figure 15.5b
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Conjunctiva
Transparent membrane that:
 Lines the eyelids as the palpebral conjunctiva
 Covers the whites of the eyes as the ocular conjunctiva
 Lubricates and protects the eye
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Lacrimal Apparatus
- Consists of the lacrimal gland and associated ducts
- Lacrimal glands secrete tears
Tears:
 Contain mucus, antibodies, and lysozyme
 Enter the eye via superolateral excretory ducts
 Exit the eye medially via the lacrimal punctum
 Drain into the nasolacrimal duct
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Lacrimal Apparatus
1
2
3
4
5
6
Figure 15.6
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Extrinsic Eye Muscles
 Six straplike extrinsic eye muscles
 Enable the eye to follow moving objects
 Maintain the shape of the eyeball
 Four rectus muscles originate from the annular ring
 Two oblique muscles move the eye in the vertical plane
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Extrinsic Eye Muscles
Figure 15.7a, b
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Summary of Cranial Nerves and Muscle Actions
 Names, actions, and cranial nerve innervation of the
extrinsic eye muscles
Figure 15.7c
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Structure of the Eyeball
 A slightly irregular hollow sphere with anterior and posterior
poles
 The wall is composed of three tunics – fibrous, vascular, and
sensory
 The internal cavity is filled with fluids called humors
 The lens separates the internal cavity into anterior and
posterior segments (chambers)
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Structure of the Eyeball
9
1
10
2
11
3
12
4
5
13
6
7
8
14
Figure 15.8a
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A. Fibrous Tunic
Forms the outermost coat of the eye and is composed of:
 Opaque and white sclera (posteriorly)
 Clear cornea (anteriorly)
 The sclera protects the eye and anchors extrinsic muscles
 The cornea lets light enter the eye
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B. Vascular Tunic (Uvea)
Has three regions: choroid, ciliary body, and iris
1. Choroid region:
 A dark brown membrane that forms the posterior portion
of the uvea
 Supplies blood to all eye tunics
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2. Ciliary body:
 A thickened ring of tissue surrounding the lens
 Composed of smooth muscle bundles (ciliary muscles)
 Anchors the suspensory ligament that holds the lens in
place
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3. Iris:
 The colored part of the eye
 Pupil – central opening of the iris
- Regulates the amount of light entering the eye
during:
-- Close vision and bright light – pupils constrict
-- Distant vision and dim light – pupils dilate
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Pupil Dilation and Constriction
Figure 15.9
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C. Sensory Tunic: Retina
Retina: A delicate two-layered membrane
1. Pigmented layer – the outer layer that absorbs light and
prevents its scattering
2. Neural layer - which contains:
 photoreceptors that transduce light energy
 bipolar cells
 ganglion cells
 amacrine and horizontal cells
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Sensory Tunic: Retina
Figure 15.10a
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The Retina: Ganglion Cells and the Optic Disc
 Ganglion cell axons leave the eye as the optic nerve
The optic disc:
 Is the site where the optic nerve leaves the eye
 Lacks photoreceptors (the blind spot)
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The Retina: Ganglion Cells and the Optic Disc
Figure 15.10b
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The Retina: Photoreceptors
Rods:
 Respond to dim light
 Are used for peripheral vision
Cones:
 Respond to bright light
 Have high-acuity color vision
 Are found in the macula lutea
 Are concentrated in the fovea centralis
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Cones and Rods
Figure 15.10a
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Rods
Functional characteristics:
 Sensitive to dim light and best suited for night vision
 Absorb all wavelengths of visible light
 Sum of visual input from many rods feeds into a single
ganglion cell
 Results in fuzzy and indistinct images
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Cones
Functional characteristics:
 Need bright light for activation (have low sensitivity)
 Have pigments that furnish a vividly colored view
 Each cone synapses with a single ganglion cell
 Vision is detailed and has high resolution
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Inner Chambers and Fluids
- The lens separates the internal eye into anterior and
posterior segments
- The posterior segment is filled with a clear gel called
vitreous humor that:
 Transmits light
 Supports the posterior surface of the lens
 Holds the neural retina firmly against the pigmented layer
 Contributes to intraocular pressure
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Anterior Segment
Composed of two chambers:
 Anterior – between the cornea and the iris
 Posterior – between the iris and the lens
 Aqueous humor
 A plasma like fluid that fills the anterior segment
 Drains via the canal of Schlemm
 Supports, nourishes, and removes wastes
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Anterior Segment
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Figure 15.12
Lens
 A biconvex, transparent, flexible, avascular structure that:
- Allows precise focusing of light onto the retina
 Lens epithelium – anterior cells that differentiate into lens
fibers
 With age, the lens becomes more compact and dense and
loses its elasticity
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Visual Pathways
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Figure 15.23
Visual Pathways
 Ganglion cells of the retina make up optic nerves
 Left and right optic nerves (II) into brain via optic foraminae
 Optic chiasma (nasal side fibers cross to contralateral brain)
 Optic tracts (carry fibers back to the thalamsus)
 Ganlion cell axons terminate in lateral geniculate n. of thalamus
 Optic radiations carry fibers back to occipital cortex (Area 17)
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The Ear: Hearing and Balance
The three parts of the ear are the inner, outer, and middle ear
 The outer and middle ear are involved with hearing
 The inner ear functions in both hearing and equilibrium
 Receptors for hearing and balance:
- Respond to separate stimuli
- Are activated independently
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Outer Ear
The auricle (pinna) is composed of:
 The helix (rim)
 The lobule (earlobe)
External auditory canal
 Short, curved tube
Tympanic membrane (eardrum)
 Thin connective tissue membrane that vibrates in response to
sound
 Transfers sound energy to the middle ear ossicles
 Boundary between outer and middle ears
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A. External Ear
Figure 15.25a
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B. Middle Ear
 A small, air-filled, mucosa-lined cavity
 Flanked laterally by the eardrum
 Flanked medially by the oval and round windows of the
cochlea
 Pharyngotympanic tube – connects the middle ear to the
nasopharynx
- Equalizes pressure in the middle ear cavity with the
external air pressure
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Middle Ear (Tympanic Cavity)
Figure 15.25b
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Ear Ossicles
The tympanic cavity contains three small bones: the malleus,
incus, and stapes
 Transmit vibratory motion of the eardrum to the oval
window
 Dampened by the tensor tympani and stapedius muscles
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Ear Ossicles
Figure 15.26
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Inner Ear
Bony labyrinth:
 Tortuous channels worming their way through the
temporal bone
 Contains the cochlea, the vestibule, and the
semicircular canals
 Filled with perilymph
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Inner Ear
Figure 15.27
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The Vestibule
The central egg-shaped cavity of the bony labyrinth
 Suspended in its perilymph are two sacs: the saccule and
utricle
 The saccule extends into the cochlea
 The utricle extends into the semicircular canals
These sacs:
 House equilibrium receptors called maculae
 Respond to gravity and changes in the position of the
head, especially linear movements
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The Semicircular Canals
Three canals that each define two-thirds of a circle and lie in
the three planes of space
 Membranous semicircular ducts line each canal and
communicate with the utricle
 The ampulla is the swollen end of each canal and it houses
equilibrium receptors in a region called the crista
ampullaris
- These receptors respond to angular movements of the head
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The Semicircular Canals
Figure 15.27
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The Cochlea
 A spiral, conical, bony chamber that:
 Extends from the anterior vestibule
 Contains the cochlear duct, which ends at the cochlear
apex
 Contains the organ of Corti (hearing receptor)
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The Cochlea
The cochlea is divided into three chambers:
 Scala vestibuli
 Scala media
 Scala tympani
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The Cochlea
 The scala tympani terminates at the round window
 The scalas tympani and vestibuli are filled with perilymph
 The scala media is filled with endolymph
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The Cochlea
 The “floor” of the cochlear duct is composed of:
 The bony spiral lamina
 The basilar membrane, which supports the organ of
Corti
 The cochlear branch of nerve VIII runs from the organ of
Corti to the brain
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The Cochlea
Figure 15.28
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Simplified Auditory Pathways
Figure 15.34
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