senses output: motor...

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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


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)


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


Peripheral Sensory Receptors

•  Sensory receptors also classified according to •  Location •  Type of stimulus detected •  Structure


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


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


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


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


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


Tactile Corpuscles

Table 14.1 (2 of 4)

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Lamellar Corpuscles and Bulbous Corpuscles


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


Proprioceptors


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


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)


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


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


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


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


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


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


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


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


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)


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)


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



•  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



•  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


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”)


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


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)


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


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


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


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


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


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


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


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

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Pig

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aye

r


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


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”


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


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


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


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



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



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)


Visual Pathways

•  Most visual information travels to the cerebral cortex

•  Responsible for conscious “seeing” •  Other pathways travel to nuclei in the

midbrain and diencephalon


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


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


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


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



•  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



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


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)


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


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


Structures of the Middle Ear

Figure 16.17b


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


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


The Internal Ear

Figure 16.17b


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


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


The Internal Ear

Table 16.1


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


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


The Cochlea

Figure 16.20b, c

(b)


Tectorial membrane

Vestibular membrane



Basilar membrane


Stria vascularis

Spiral ganglion


(c)

Tectorial membrane Inner hair cell

Outer hair cells

Hairs (stereocilia) Afferent nerve fibers

Basilar membrane

Fibers of cochlear nerve

Supporting cells


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


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)


Tectorial membrane Vestibular membrane



Basilar membrane


Stria vascularis

Spiral ganglion


(c)

Tectorial membrane

Inner hair cell

Outer hair cells

Hairs (stereocilia) Afferent

nerve fibers

Basilar membrane

Fibers of cochlear nerve

Supporting cells


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


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

15


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


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


The Maculae in the Internal Ear

Figure 16.22b (b)

Head upright Head tilted

Hair cell

Otoliths Otolithic membrane

Force of gravity


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



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



•  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

16


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)

Copyright © 2011 Pearson Education, Inc. Figure 16.23c

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.


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


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)


Bipolar cell

Spiral ganglion of cochlear nerve

Vestibulocochlear nerve

Medulla

Midbrain

Cochlear nuclei

Vibrations

Vibrations


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


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

17


The Special Senses Throughout Life

•  Smell and taste •  Sharp in newborns

•  In the fourth decade of life •  Ability to taste and smell declines



•  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



•  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



•  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

senses output: motor...

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