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PowerPoint® Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham
C H A P T E R
Copyright © 2011 Pearson Education, Inc.
Part 1
Senses
Copyright © 2011 Pearson Education, Inc.
Basic Structural Components of the PNS
• INPUT: Sensory receptors—pick up stimuli from inside or outside the body
• Nerves and ganglia – connecting structures • Nerves—bundles of peripheral axons • Ganglia—clusters of peripheral neuronal cell
bodies • OUTPUT: Motor endings—axon terminals of
motor neurons • Innervate effectors (muscle fibers and glands)
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Peripheral Sensory Receptors
• …Are structures that pick up sensory stimuli and initiate signals in sensory axons
• Two main categories of sensory receptors • 1. Free nerve endings of sensory neurons • Monitor general sensory information
• 2. Complete receptor cells—specialized epithelial cells or small neurons • Monitor most types of special sensory
information
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Peripheral Sensory Receptors
• Sensory receptors also classified according to • Location • Type of stimulus detected • Structure
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Classification by Location • Exteroceptors—sensitive to stimuli arising from outside the body
• Located at or near body surfaces • Include receptors for touch, pressure, pain, and temperature
• Interoceptors—receive stimuli from internal viscera • Located in digestive tube, bladder, and lungs • Monitor a variety of stimuli
• Changes in chemical concentration • Taste stimuli • Stretching of tissues • Temperature
• Proprioceptors • Located in skeletal muscles, tendons, joints, and ligaments • Monitor degree of stretch • Send inputs on body movement to the CNS
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Classification by Stimulus Detected • Mechanoreceptors—respond to mechanical forces
• Touch, pressure, stretch, vibration, and itch • Baroreceptors monitor blood pressure
• Thermoreceptors—respond to temperature changes • Chemoreceptors
• Respond to chemicals in solution • Photoreceptors—respond to light
• Located in the eye • Nociceptors
• Respond to harmful stimuli that result in pain
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Classification by Structure • (Discussion here of General sensory
receptors only, not special senses) • General senses are widely distributed • General senses include nerve endings of sensory neurons that
monitor: • Touch • Pressure • Vibration • Stretch • Pain • Temperature • Proprioception
• So, classification of General Sensory Receptors by structure …. • Divided into two groups
• Free nerve endings • Encapsulated nerve endings
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Free Nerve Endings (or ‘unencapsulated’)
• Abundant in epithelia and underlying connective tissue • Respond to pain and temperature • Monitor affective senses • Two specialized types of free nerve endings
• Epithelial tactile complexes (Merkel discs) • Consist of tactile epithelial cell innervated by
sensory nerve ending • Slowly adapting receptors for light touch
• Hair follicle receptors—wrap around hair follicles • Rapidly adapting receptors
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Unencapsulated Nerve Endings
Table 14.1 (1 of 4) Copyright © 2011 Pearson Education, Inc.
Encapsulated Nerve Endings • Consist of one or more end fibers of sensory
neurons • Enclosed in connective tissue • Mechanoreceptors • Include four main types • Tactile (Meissner’s) corpuscles • Lamellar (Pacinian) corpuscles • Bulbous corpuscles (Ruffini endings) • Proprioceptors
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Encapsulated Nerve Endings • Tactile (Meissner’s) corpuscles
• Spiraling nerve ending surrounded by Schwann cells • Occur in the dermal papillae • Rapidly adapting receptors for discriminative touch • Occur in sensitive, hairless areas of the skin
• Lamellar Corpuscles • Single nerve ending surrounded by layers of flattened Schwann
cells • Occur in the hypodermis • Sensitive to deep pressure—rapidly adapting receptors
• Bulbous Corpuscles • Located in the dermis and respond to pressure • Monitor continuous pressure on the skin—adapt slowly
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Tactile Corpuscles
Table 14.1 (2 of 4)
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Lamellar Corpuscles and Bulbous Corpuscles
Table 14.1 (3 of 4) Copyright © 2011 Pearson Education, Inc.
More Encapsulated Nerve Endings • Proprioceptors
• Monitor stretch in locomotory organs • Three types of proprioceptors:
• Muscle spindles— measure the changing length of a muscle • Imbedded in the perimysium between muscle
fascicles • Golgi tendon organs— monitor tension within tendons
• Located near the muscles/tendon junction • Joint kinesthetic receptors--- monitor stretch within
synovial joints • Sensory nerve endings within the joint capsules
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Proprioceptors
Table 14.1 (4 of 4) Copyright © 2011 Pearson Education, Inc.
Structure of Proprioceptors
Figure 14.3
Secondary sensory endings (type II fiber)
γ Efferent (motor) fiber to muscle spindle
Primary sensory endings (type Ia fiber)
Connective tissue capsule
Muscle spindle
Tendon
Sensory fiber
Tendon organ
α Efferent (motor) fiber to extrafusal muscle fibers Extrafusal muscle fiber
Intrafusal muscle fibers
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The Special Senses
• Taste, smell, sight, hearing, and balance • Characteristics of Special sensory receptors
• Localized—confined to the head region • Receptors are not free endings of sensory neurons • Special receptor cells
• Are neuron-like epithelial cells or small peripheral neurons • Transfer sensory information to other neurons
in afferent pathways (i.e., cranial nerves)
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The Chemical Senses: Taste and Smell
• Taste—gustation • Smell—olfaction • Receptors—classified as chemoreceptors • Respond to chemicals • Food dissolved in saliva • Airborne chemicals that dissolve in fluids of
the nasal mucosa
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Taste—Gustation
• Taste receptors • Occur in taste buds • Most are found on the surface of the tongue • Located within tongue papillae
• Two types of papillae (with taste buds) • Fungiform papillae • Vallate papillae
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Taste Buds
• Collection of 50–100 epithelial cells • Contain two major cell types • Gustatory epithelial cells • Basal epithelial cells
• Contain long microvilli—extend through a taste pore to the surface of the epithelium
• Cells in taste buds replaced every 7–10 days
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Taste Buds
Figure 16.1
(a) Taste buds associated with fungiform and vallate papillae (b) Enlarged section of a
vallate papilla
Fungiform papillae Taste bud
Vallate papilla
Epiglottis
Palatine tonsil Lingual tonsil
Taste fibers of cranial nerve
Connective tissue
Gustatory epithelial
cells Taste pore
Gustatory hair
Stratified squamous epithelium of tongue
(c) Enlarged view of a taste bud (micrograph, 160X)
Basal epithelial
cells
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Taste Sensation and the Gustatory Pathway
• Five basic qualities of taste • Sweet, sour, salty, bitter, and umami • “Umami” is elicited by glutamate
• The “taste map” is a myth • All taste modalities can be elicited from all
areas containing taste buds
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Gustatory Pathway
• Taste information reaches the cerebral cortex • Primarily through the facial (VII) and
glossopharyngeal (IX) nerves • Some taste information through the vagus nerve (X) • Sensory neurons synapse in the medulla
• Relay neurons located in the solitary nucleus • Impulses are then transmitted to the thalamus and
ultimately to the gustatory area of the cerebral cortex in the insula
• Smell contributes to taste perception
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Gustatory Pathway from Taste Buds
Figure 16.2
Gustatory cortex (in insula)
Thalamic nucleus (ventral posteromedial nucleus) Pons Solitary nucleus
in medulla oblongata
Facial nerve (VII) Glossopharyngeal nerve (IX)
Vagus nerve (X)
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Smell (Olfaction)
• Olfactory receptors are part of the olfactory epithelium
• Olfactory epithelium is pseudostratified columnar and contains three main cell types: • Olfactory sensory neurons • Supporting epithelial cells • Basal epithelial cells
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Smell (Olfaction)
• Cell bodies of olfactory sensory neurons • Located in olfactory epithelium • Have an apical dendrite that projects to the epithelial
surface • Ends in a knob from which olfactory cilia radiate
• Olfactory cilia act as receptive structures for smell • Mucus captures and dissolves odor molecules
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Smell (Olfaction)
• Axons of olfactory epithelium • Gather into bundles— these are the filaments/axons
of the olfactory nerve (C.N. I) • These axons pass through the cribriform plate of the
ethmoid bone • Attach to the olfactory bulbs and synapse with
mitral cells • Mitral cells transmit impulses along the olfactory
tract to 1. Limbic system 2. Piriform lobe of the cerebral cortex
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Olfactory Receptors
Figure 16.3
Mitral cell (output cell)
Olfactory gland
Olfactory tract
Olfactory epithelium
Filaments of olfactory nerve
Cribriform plate of ethmoid bone
Lamina propria connective tissue Basal cell
Supporting cell Dendrite Olfactory cilia
Olfactory bulb Glomeruli
Axon
Olfactory sensory neuron
Mucus
Route of inhaled air containing odor molecules
Nasal conchae
Route of inhaled air
Olfactory epithelium
Olfactory tract Olfactory bulb
(a)
(b)
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Disorders of the Chemical Senses
• Anosmia—absence of the sense of smell • Due to injury, colds, allergies, or zinc deficiency
• Uncinate fits—distortion of smells or olfactory hallucinations • Often result from irritation of olfactory pathways • After brain surgery or head trauma; sometimes
precedes seizures in olfactory cortex (auras)
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The Eye and Vision
• Visual organ—the eye • 70% of all sensory receptors are in the eyes • 40% of the cerebral cortex is involved in
processing visual information • Anterior one-sixth of the eye’s surface is
visible
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Accessory Structures of the Eye
• Eyebrows—coarse hairs on the superciliary arches • Eyelids (palpebrae)—separated by the palpebral
fissure • Meet at the medial and lateral angles (canthi) • Lacrimal caruncle—reddish elevation at the medial
canthus • Tarsal plates—connective tissue within the eyelids • Tarsal glands—modified sebaceous glands
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Accessory Structures of the Eye
• Conjunctiva— transparent mucous membrane • Palpebral
conjunctiva • Bulbar conjunctiva • Conjunctival sac
Figure 16.4b
(b) Lateral view; some structures shown in sagittal section
Levator palpebrae superioris muscle
Orbicularis oculi muscle Eyebrow Tarsal plate Palpebral conjunctiva Tarsal glands Cornea
Palpebral fissure
Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle
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Accessory Structures of the Eye
• Lacrimal apparatus—keeps the surface of the eye moist • Lacrimal gland—
produces lacrimal fluid
• Lacrimal sac— fluid empties into nasal cavity
Figure 16.5
Lacrimal gland Excretory ducts of lacrimal glands
Lacrimal punctum Lacrimal canaliculus
Nasolacrimal duct
Inferior meatus of nasal cavity Nostril
Lacrimal sac
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Extrinsic Eye Muscles
• Six muscles that control movement of the eye • Originate in the walls of the orbit • Insert on outer surface of the eyeball • Annular ring or common tendinous ring— origin of the
four rectus muscles
• The six extrinsic eye muscles are: • Lateral rectus and medial rectus • Superior rectus and inferior rectus • Superior oblique (“down and out”) and inferior oblique (“up and
out”)
• Strabismus: misalignment of the eyes (“cross-eyes” or “squint-eyes”)
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Extrinsic Eye Muscles
Figure 16.6a, b
Inferior rectus muscle
Common tendinous ring
Inferior oblique muscle
Superior oblique muscle Trochlea Superior oblique tendon Superior rectus muscle
Lateral rectus muscle
(a) Lateral view of the right eye (b) Anterior view of the right eye
Trochlea Superior oblique
Inferior rectus Inferior
oblique
Lateral rectus
Superior rectus
Medial rectus
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Summary of Muscle Actions
(c) Summary of muscle actions and innervating cranial nerves
Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Superior oblique
Moves eye laterally Moves eye medially Elevates eye and turns it medially Depresses eye and turns it medially Elevates eye and turns it laterally Depresses eye and turns it laterally
VI (abducens) III (oculomotor) III (oculomotor) III (oculomotor) III (oculomotor) IV (trochlear)
Muscle Action Controlling cranial nerve
Figure 16.6c
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Anatomy of the Eyeball
• Components of the eye serve to... • Protect and support the photoreceptors • Gather, focus, and process light into precise images
• Basic parts: • Anterior pole—most anterior part of the eye • Posterior pole—most posterior part of the eye • Internal cavity—contains fluids (humors) • External walls—composed of three tunics from superficial to deep :
• 1. Fibrous layer (outer tunic) • 2. Vascular layer (middle tunic) • 3. Neural or inner layer (nervous tunic/inner tunic)
Copyright © 2011 Pearson Education, Inc. Figure 16.7a
Ora serrata
(a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball.
Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris
Anterior pole
Pupil
Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor)
Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera
Central artery and vein of the retina Optic disc (blind spot)
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1. The Fibrous Layer • Most external layer of the eyeball
• Composed of two regions of connective tissue • Sclera—posterior five-sixths of the tunic
• White, opaque region • Provides shape and an anchor for eye muscles
• Cornea—anterior one-sixth of the fibrous tunic • Clear collagen fiber sheets sandwiched
between thin epithelial layers • Avascular, but heals quickly • Richly supplied with nerve endings
• Limbus—junction between sclera and cornea • Scleral venous sinus—allows aqueous humor to
drain
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2. The Vascular Layer • The middle coat of the eyeball • Composed of choroid, ciliary body, and iris • Choroid—vascular, darkly pigmented membrane
• Forms posterior five-sixths of the vascular tunic • Brown color—from melanocytes • Prevents scattering of light rays within the eye • Choroid corresponds to the arachnoid and pia maters
• Ciliary body—thickened ring of tissue, which encircles the lens • Composed of ciliary muscle (smooth muscle) • Ciliary processes—posterior surface of the ciliary body • Ciliary zonule (suspensory ligament): extend from ciliary
processes and attached around entire circumference of the lens
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The Iris (third part of vascular layer)
• Iris • Visible colored part of the eye • Attached to the ciliary body • Composed of smooth muscle (2 muscles):
• Sphincter pupillae muscle (parasympathetic innervation /ACh)
• Dilator pupillae muscle (sympathetic innervation /NE) • Pupil—the round, central opening
• Pupillary light reflex • Protective response of pupil constriction when a bright
light is flashed in the eye
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3. The Inner Layer (Retina)
• Retina—the deepest tunic • Composed of two layers:
• Pigmented layer—single layer of melanocytes • Neural layer—sheet of nervous tissue
• Contains three main types of neurons • Photoreceptor cells • Bipolar cells • Ganglion cells
• Also present: 2 other neuron types: • Horizontal cells • Amacrine cells
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Microscopic Anatomy of the Retina
Figure 16.8b, c
Pigmented layer of retina Pathway of light
Pathway of signal output
(b) Cells of the neural layer of the retina
Amacrine cell Horizontal cell
Rod Photoreceptors
Cone
Bipolar cells Ganglion
cells
Choroid
Pigmented layer of retina
Axons of ganglion cells
Outer segments of rods and cones Nuclei of
ganglion cells
Nuclei of rods and cones
Nuclei of bipolar cells
(c) Photomicrograph of retina
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The Inner Layer (continued)
• Photoreceptor cells send signals to bipolar cells
• Bipolar cells send signals to ganglion cells to generate nerve impulses in ganglion cell axons
• Axons from ganglion cells run along internal surface of the retina
• Converge posteriorly to form the optic nerve
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Posterior Aspect of the Eyeball
Figure 16.8a
(a) Posterior aspect of the eyeball
Neural layer of retina
Pigmented layer of retina
Central artery and vein of retina Optic
nerve
Sclera Choroid
Optic disc
Pathway of light
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Photoreceptors
• Two main types • Rod cells—more sensitive to low levels of
light and to movement • Allow vision in dim light
• Cone cells—operate best in bright light • Enable high-acuity, color vision
• Considered neurons
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Photoreceptors
Figure 16.9
Process of bipolar cell
Outer fiber
Apical microvillus
Discs containing visual pigments
Melanin granules
Discs being phagocytized
Pigment cell nucleus
Inner fibers Rod cell body
Cone cell body
Synaptic terminals Rod cell body Nuclei
Mitochondria Connecting cilia
Basal lamina (border with choroid)
Ligh
t
Ligh
t
Ligh
t
Inn
er
se
gm
en
t
Ou
ter
se
gm
en
t
Pig
me
nte
d l
aye
r
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Photoreceptors
• Rods and cones have an inner and outer segment • Outer segments are receptor regions where
light absorbing pigments are present
• Light particles/energy modify the visual pigment and generate a nerve impulse
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Photoreceptors
• Photoreceptors • Vulnerable to damage by light or heat • Cannot regenerate if destroyed • Continuously renew and replace their outer
segments
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Regional Specializations of the Retina • Ora serrata retinae
• Neural layer ends at the posterior margin of the ciliary body
• Pigmented layer covers ciliary body and posterior surface of the iris
• Macula lutea— contains mostly cones • Fovea centralis— contains only cones
• Region of highest visual acuity • Optic disc— area of no receptors (where ganglion
cell axons exit the eye as C.N.II) and therefore a “blind spot”
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View of the Eye
Figure 16.7a
Ora serrata
(a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball.
Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris
Anterior pole
Pupil
Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor)
Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera
Central artery and vein of the retina Optic disc (blind spot)
Copyright © 2011 Pearson Education, Inc. Figure 16.10
Blood Supply of the Retina
• Retina receives blood from two sources • Outer third of the
retina—supplied by capillaries in the choroid
• Inner two-thirds of the retina— supplied by central artery and vein of the retina
Macula lutea
Central artery and vein emerging from the optic disc
Optic disc
Retina
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Internal Chambers and Fluids • The lens and ciliary zonules divide the eye • Posterior segment (cavity)
• Filled with vitreous humor • Clear, jelly-like substance • Transmits light • Supports the posterior surface of the lens • Helps maintain intraocular pressure
• Anterior segment • Divided into anterior and posterior chambers
• Anterior chamber—between the cornea and iris • Posterior chamber—between the iris and lens • Filled with aqueous humor
• Renewed continuously • Formed as a blood filtrate • Supplies nutrients to the lens and cornea
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Internal Chambers and Fluids
Figure 16.11
Aqueous humor is formed by filtration from the capillaries in the ciliary processes.
Sclera
Bulbar conjunctiva
Scleral venous sinus
Posterior chamber
Anterior chamber Anterior segment (contains aqueous humor)
Corneoscleral junction
Cornea
Cornea
Corneal epithelium
Corneal endothelium
Aqueous humor
Iris
Lens Lens epithelium
Lens
Posterior segment (contains vitreous humor)
Ciliary zonule (suspensory ligament)
Ciliary processes
Ciliary muscle
Ciliary body
Aqueous humor flows from the posterior chamber through the pupil into the anterior chamber. Some also flows through the vitreous humor (not shown). Aqueous humor is reabsorbed into the venous blood by the scleral venous sinus.
1
2
3
1
2
3
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Vision
The Lens
• A thick, transparent, biconvex disc • Held in place by its ciliary zonule
• Lens epithelium—covers anterior surface of the lens
• Lens fibers form the bulk of the lens • New lens fibers are continuously added • Lens enlarges throughout life
PLAY
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The Eye as an Optical Device
• Structures in the eye bend light rays • Light rays converge on the retina at a single focal point • Light bending structures (refractory media) are interfaces
between media: • The lens, cornea, and humors
• Accommodation—curvature of the lens is adjustable • Allows for focusing on nearby objects
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The Eye as an Optical Device
Figure 16.13
Lens
Inverted image
Ciliary zonule Ciliary muscle
Nearly parallel rays from distant object
(a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens.
Sympathetic activation
(b) Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge.
Divergent rays from close object Inverted
image
Parasympathetic activation
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The Eye as an Optical Device
Figure 16.14
Concave lens moves focal point further back.
Focal point
Eyeball too short Eyeball
too long
Uncorrected Focal point is in front of retina.
Corrected
Uncorrected Focal point is behind retina.
Corrected Convex lens moves focal point forward.
Myopic eye (nearsighted) Hyperopic eye (farsighted)
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Visual Pathways
• Most visual information travels to the cerebral cortex
• Responsible for conscious “seeing” • Other pathways travel to nuclei in the
midbrain and diencephalon
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Visual Pathways to the Cerebral Cortex • Pathway begins at the retina ...
• Light activates photoreceptors • Photoreceptors signal bipolar cells • Bipolar cells signal ganglion cells • Axons of ganglion cells exit eye as the optic
nerve (C.N. II) • After optic chiasm, where partial decussation occurs,
optic tracts send axons to ... • Lateral geniculate nucleus (LGN) of the thalamus,
where axons synapse with thalamic neurons • Thalamic neuron axons form optic radiation &
reach the primary visual cortex in occipital lobe
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Visual Pathways to the Brain and Visual Fields
Figure 16.15a
Pretectal nucleus
Right eye Left eye
Fixation point
Optic radiation
Optic tract Optic chiasma
Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber
Optic nerve
Lateral geniculate nucleus of thalamus Superior colliculus Occipital
lobe (primary visual cortex)
(a) The visual fields of the two eyes overlap considerably. Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma.
Supra- chiasmatic nucleus
Left eye only Righ
t eye
onl
y
Both eyes
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Visual Pathways to Other Parts of the Brain
• Some axons from the optic tracts ... • Branch to midbrain & synapse in the ... • Superior colliculi • Pretectal nuclei
• Other branches from the optic tracts • Project to the suprachiasmatic nucleus
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Disorders of the Eye and Vision
• Age-related macular degeneration (AMD) • Involves the buildup of visual pigments in the retina
• Retinopathy of prematurity • Blood vessels grow within the eyes of premature
infants • Vessels have weak walls—causes hemorrhaging and
blindness • Trachoma—contagious infection of the conjunctiva • Presbyopia: “old eye”– loss of lens plasticity with
age
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Embryonic Development of the Eye
• Eyes develop as outpocketings of the brain • By week 4, optic vesicles protrude from the
diencephalon
Figure 16.16b, c
(b) Week 4, late. Optic vesicles invaginate to form the optic cups. The overlying surface ectoderm thickens to form the lens placode.
Optic stalk
Optic cup
Invaginating lens placode
Ectoderm
Optic fissure
(c) Week 5. Lens placode invaginates and forms the lens vesicle.
Optic cup Lens
vesicle
Optic stalk
Optic fissure
Retina
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Embryonic Development of the Eye
• Ectoderm thickens and forms a lens placodes • By week 5, a lens vesicle forms • Internal layer of the optic cup becomes • Neural retina
• External layer becomes • Pigmented retina
• Optic fissure—pathway for blood vessels
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Embryonic Development of the Eye
Figure 16.16d, e
(d) Week 6. The neural and pigmented layers of the retina differentiate from the optic cup. Central artery reaches the interior of the eye. Mesenchyme derived from neural crest invades.
Lens vesicle
Developing neural layer of the retina Developing pigmented
layer of the retina
Mesenchyme invades
Surface ectoderm
Central artery
(e) Week 7. Mesenchyme surrounds and invades the optic cup to form the fibrous and vascular layers and the vitreous humor. Lens vesicle forms the lens. Surface ectoderm forms the corneal epithelium and the conjunctiva.
Iris
Fused eyelids
Corneal epithelium
Cornea (fibrous part) Lens Deteriorating internal blood vessels
Vitreous humor
Sclera and choroid
Central artery
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The Ear: Hearing and Equilibrium
• The ear—receptor organ for hearing and equilibrium
• Composed of three main regions: • Outer ear—functions in hearing • Middle ear—functions in hearing • Internal ear—functions in both hearing and
equilibrium
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Structure of the Ear
Figure 16.17a
External acoustic meatus
Auricle (pinna)
(a) The three regions of the ear
Helix
Lobule
Pharyngotympanic (auditory) tube
Tympanic membrane
External ear Middle ear
Internal ear (labyrinth)
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The Outer (External) Ear
• Composed of • The auricle (pinna)
• Helps direct sounds • External acoustic meatus • Lined with skin • Contains hairs, sebaceous glands,
and ceruminous glands • Tympanic membrane • Forms the boundary between the
external and middle ear
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The Middle Ear
• Composed of • The tympanic cavity
• A small, air-filled space • Located within the petrous portion of the
temporal bone • Medial wall is penetrated by
• Oval window • Round window
• Pharyngotympanic tube (auditory or Eustachian tube) • Links the middle ear and pharynx
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Structures of the Middle Ear
Figure 16.17b
Pharyngotympanic (auditory) tube
Auditory ossicles
Entrance to mastoid antrum in the epitympanic recess
Tympanic membrane
Semicircular canals
Cochlea
Cochlear nerve
Vestibular nerve
Oval window (deep to stapes)
Round window
Incus (anvil)
Malleus (hammer)
Stapes (stirrup)
(b) Middle and internal ear
Vestibule
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Pharyngotym- panic tube
Tensor tympani muscle
Tympanic membrane (medial view)
Stapes
Malleus
View
Superior
Anterior
Lateral
Incus Epitympanic recess
Stapedius muscle
Figure 16.18
The Middle Ear • Ear ossicles—smallest
bones in the body • Malleus—attaches to
the eardrum • Incus—between the
malleus and stapes • Stapes—vibrates
against the oval window • Tensor tympani (C.N V)
and stapedius (C.N. VII) • Two tiny skeletal
muscles in the middle ear cavity
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The Internal Ear
• Internal ear—also called the labyrinth • Lies within the petrous portion of the
temporal bone • Bony labyrinth—a cavity consisting of three
parts • Semicircular canals • Vestibule • Cochlea
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The Internal Ear
Figure 16.17b
Pharyngotympanic (auditory) tube
Auditory ossicles
Entrance to mastoid antrum in the epitympanic recess
Tympanic membrane
Semicircular canals
Cochlea
Cochlear nerve
Vestibular nerve
Oval window (deep to stapes)
Round window
Incus (anvil)
Malleus (hammer)
Stapes (stirrup)
(b) Middle and internal ear
Vestibule
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The Internal Ear • Membranous labyrinth
• Series of membrane-walled sacs and ducts • Fit within the bony labyrinth • Consists of three main parts
• Semicircular ducts • Utricle and saccule • Cochlear duct
• Filled with a clear fluid—endolymph • Confined to the membranous labyrinth
• Bony labyrinth is filled with perilymph • Continuous with cerebrospinal fluid
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The Internal Ear
Table 16.1
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The Internal Ear
Figure 16.19
Anterior
Semicircular ducts in semicircular canals
Posterior Lateral
Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule
Stapes in oval window
Temporal bone Facial nerve
Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ (of Corti) Cochlear duct in cochlea Round window
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The Cochlea • A spiraling chamber in the bony labyrinth
• Coils around a pillar of bone—the modiolus • Spiral lamina—a spiral of bone in the modiolus • The cochlear nerve runs through the core of the modiolus
• Has three areas/ chambers: scala media, scala vestibuli. And scala tympani
• The cochlear duct (scala media)—contains the receptors for hearing • Lies between two chambers
• The scala vestibuli • The scala tympani
• The vestibular membrane—the roof of the cochlear duct • The basilar membrane—the floor of the cochlear duct
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The Cochlea
Figure 16.20a, b
(a) Helicotrema
Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII)
Cochlear duct (scala media)
Spiral ganglion Osseous spiral lamina Vestibular membrane
(b)
Cochlear duct (scala media; contains endolymph)
Tectorial membrane Vestibular membrane
Scala vestibuli (contains perilymph)
Scala tympani (contains perilymph)
Basilar membrane
Spiral organ (of Corti)
Stria vascularis
Spiral ganglion
Osseous spiral lamina
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The Cochlea
Figure 16.20b, c
(b)
Cochlear duct (scala media; contains endolymph)
Tectorial membrane
Vestibular membrane
Scala vestibuli (contains perilymph)
Scala tympani (contains perilymph)
Basilar membrane
Spiral organ (of Corti)
Stria vascularis
Spiral ganglion
Osseous spiral lamina
(c)
Tectorial membrane Inner hair cell
Outer hair cells
Hairs (stereocilia) Afferent nerve fibers
Basilar membrane
Fibers of cochlear nerve
Supporting cells
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The Cochlea
• The cochlear duct (scala media) (continued) • The Spiral organ (of Corti)— is the receptor epithelium for
hearing • Consists of:
• Supporting cells • Inner and outer hair cells (receptor cells) • Inner hair cells are the receptors that transmit
vibrations of the basilar membrane • Outer hair cells actively tune the cochlea and
amplify the signal
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The Anatomy of the Cochlea
Figure 16.20a–c
(a) Helicotrema
Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII)
Cochlear duct (scala media)
Spiral ganglion Osseous spiral lamina Vestibular membrane
(b)
Cochlear duct (scala media; contains endolymph)
Tectorial membrane Vestibular membrane
Scala vestibuli (contains perilymph)
Scala tympani (contains perilymph)
Basilar membrane
Spiral organ (of Corti)
Stria vascularis
Spiral ganglion
Osseous spiral lamina
(c)
Tectorial membrane
Inner hair cell
Outer hair cells
Hairs (stereocilia) Afferent
nerve fibers
Basilar membrane
Fibers of cochlear nerve
Supporting cells
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The Role of the Cochlea in Hearing
Figure 16.21
Sound waves vibrate the tympanic membrane.
Malleus Incus Auditory ossicles
Stapes
Oval window
Scala vestibuli Helicotrema
Cochlear nerve
Scala tympani Cochlear duct Basilar membrane
Round window Tympanic
membrane
Auditory ossicles vibrate. Pressure is amplified. Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells.
1
2 3
4a
4b 1
2 3
4a
4b
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The Vestibule
• The central part of the bony labyrinth • Lies medial to the middle ear • Utricle and saccule —suspended in perilymph • Two egg-shaped parts of the membranous
labyrinth • House the macula—a patch of sensory
epithelium
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The Vestibule
• Macula—contains receptor cells • Monitor the position of the head when the
head is still • Contains columnar supporting cells • Receptor cells here are also called hair cells • Synapse with the vestibular nerve • Tips of hair cells are embedded in
otolithic membrane • Membrane contains crystals of
calcium carbonate called otoliths
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The Maculae in the Internal Ear
Figure 16.22a
Macula of saccule
Otoliths Hair bundle
Kinocilium
Stereocilia Otolithic membrane
Vestibular nerve fibers
Hair cells Supporting cells
(a)
Macula of utricle
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The Maculae in the Internal Ear
Figure 16.22b (b)
Head upright Head tilted
Hair cell
Otoliths Otolithic membrane
Force of gravity
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The Semicircular Canals
• Lie posterior and lateral to the vestibule • Anterior and posterior semicircular canals • Lie in the vertical plane at right angles
• Lateral semicircular canal • Lies in the horizontal plane
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The Semicircular Canals
Figure 16.19
Anterior
Semicircular ducts in semicircular canals
Posterior Lateral
Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule
Stapes in oval window
Temporal bone Facial nerve
Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ (of Corti) Cochlear duct in cochlea Round window
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The Semicircular Canals
• Semicircular duct—snakes through each semicircular canal
• Membranous ampulla—located within bony ampulla • Houses a structure called a crista ampullaris • Cristae contain receptor cells of rotational
acceleration • Epithelium contains supporting cells and
receptor hair cells
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Structure and Function of the Crista Ampullaris
Figure 16.23a, b
Fibers of vestibular nerve
Hair bundle (kinocilium plus stereocilia)
Hair cell
Supporting cell
Membranous labyrinth
Crista ampullaris
Crista ampullaris
Endolymph
Cupula
(a) Anatomy of a crista ampullaris in a semicircular canal
(b) Scanning electron micrograph of a crista ampullaris (45X)
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Structure and Function of the Crista Ampullaris
Fibers of vestibular
nerve
At rest, the cupula stands upright.
Section of ampulla, filled with endolymph
(c) Movement of the cupula during rotational acceleration and deceleration
Cupula Flow of endolymph
During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind because of inertia). Endolymph flow bends the cupula and excites the hair cells.
As rotational movement slows, endolymph keeps moving in the direction of the rotation, bending the cupula in the opposite direction from acceleration and inhibiting the hair cells.
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Equilibrium and Auditory Pathways
• The equilibrium pathway • Transmits information on the position and
movement of the head • Most information goes to lower brain centers
(reflex centers) • Cortical input to posterior insula
• The ascending auditory pathway • Transmits information from cochlear receptors
to the cerebral cortex • To the Superior temporal gyrus
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Auditory Pathway from the Organ of Corti
Figure 16.24
Medial geniculate nucleus of thalamus
Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (pons- medulla junction)
Spiral organ (of Corti)
Bipolar cell
Spiral ganglion of cochlear nerve
Vestibulocochlear nerve
Medulla
Midbrain
Cochlear nuclei
Vibrations
Vibrations
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Disorders of Equilibrium and Hearing
• Motion sickness—carsickness, seasickness • Popular theory for a cause—a mismatch of
sensory inputs • Meniere’s syndrome—equilibrium is greatly
disturbed • Excessive amounts of endolymph in the
membranous labyrinth
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Disorders of Equilibrium and Hearing
• Deafness • Conduction deafness • Sound vibrations cannot be conducted to
the inner ear • Ruptured tympanic membrane, otitis
media, otosclerosis • Sensorineural deafness • Results from damage to any part of the
auditory pathway
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The Special Senses Throughout Life
• Smell and taste • Sharp in newborns
• In the fourth decade of life • Ability to taste and smell declines
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The Special Senses Throughout Life
• Photoreceptors—fully formed by 25 weeks • All newborns are hyperopic • By 3 months—image can be focused on the
retina • By 6 months—depth perception is present
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The Special Senses Throughout Life
• With increased age • The lens loses its clarity • The dilator muscles of the iris become
inefficient • Visual acuity is dramatically lower in people
over 70
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The Special Senses Throughout Life
• In the newborn • Responses to sounds are reflexive • Low-pitched and middle-pitched sounds can
be heard • In the elderly • Hair cells are gradually lost • Ability to hear high-pitched sounds fades • Presbycusis—gradual loss of hearing with
age