Chapter 22 Special Senses - Nassau Community College - Special Senses.pdf · Special Senses Copyright 2009 John Wiley & Sons, Inc. Olfaction: Sense of Smell Olfactory epithelium-10–100

11/27/2012

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Copyright 2009 John Wiley & Sons, Inc.

Chapter 22

Special Senses


Olfaction: Sense of Smell� Olfactory epithelium- 10–100 million receptors

� Superior nasal cavity, inferior surface of the cribriform plate and extending along the superior nasal concha.

� Cell Types:

� Olfactory receptors respond to chemical stimulation (odorant) by initiating the olfactory response.� Olfactory Hairs (cilia) –end of receptors

� Supporting cells of the mucous membrane line the nose. � Physically support, nourish, and electrically insulate the

olfactory receptors, and help detoxify chemicals.

� Basal cells continually undergo cell division to produce new olfactory receptors

� Olfactory (Bowman’s) glands produce mucus.


Olfactory Receptors

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The Olfactory Pathway

� Olfactory (I) nerves- right and left -unmyelinated axons

� Terminate in the brain in paired masses of gray matter- olfactory

bulbs,

� Axons of olfactory bulb neurons extend posteriorly and form the olfactory tract.

� Olfactory sensations are the only sensations that reach the

cerebral cortex without first synapsing in the thalamus.

� Project to the primary olfactory area

� located at the inferior and medial surface of the temporal lobe

and frontal area

� Projects to the limbic system and hypothalamus


Olfactory Pathway


Gustation

Taste or gustation, is a chemical sense.

� Five primary tastes:

sour, sweet, bitter, salty, and umami.

� All other flavors, are combinations of the five primary tastes, plus accompanying olfactory

and tactile sensations

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Anatomy of Gustatory Receptors

� Taste buds- receptors for taste

� 10,000 taste buds on the young adult ‘s tongue, soft palate,

pharynx, and epiglottis. Declines with age.

� Consisting of three kinds of epithelial cells:

� supporting cells, gustatory receptor cells, and basal cells.

� Supporting cells contain microvilli

� Surround 50 gustatory receptor cells.

� 1 Gustatory hair, projects from each gustatory receptor cell to the external surface through the taste pore (opening in the taste bud).

� Basal cells produce supporting cells that develop into gustatory receptor cells

� Have a life span of about 10 days


Gustatory Receptors


Taste budsPapilla- elevations on the tongue.

Three types of papillae contain taste buds:

1. Circular vallate papillae- form an inverted V-shaped row at

the back of the tongue.

2. Fungiform papillae- mushroom-shaped elevations

scattered over the entire surface of the tongue, contain

about five taste buds each.

3. Foliate papillae- located in small trenches on the lateral

margins of the tongue, but most of their taste buds

degenerate in early childhood.

Filiform papillae- contain tactile receptors but no taste buds.

They increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity.

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The Gustatory Pathway� Tastant- chemicals dissolved in saliva that stimulate

gustatory hairs resulting in action potentials.

� Three cranial nerves contain axons of sensory neurons from taste buds .

� The facial (VII) nerve- anterior two-thirds of the tongue

� The glossopharyngeal (IX) nerve-posterior one-third of the tongue

� The vagus (X) nerve- throat and epiglottis.

� To Gustatory nucleus in the medulla oblongata to:

� Limbic system and hypothalamus

� Thalamus to Parietal lobe


Vision: Accessory Structures of the

Eye


Eyelids

� Palpebrae- eyelids

� protect the eyes from excessive light and foreign objects, and lubricate the eyeballs.

� The upper eyelid is more movable than the lower

� Contains the levator palpebrae superioris muscle.

� Palpebral fissure- space between the upper and lower eyelids that exposes the eyeball.

� The angles are the lateral commissure, and medial commissure.

� Lacrimal caruncle contains sebaceous (oil) glands and sudoriferous (sweat) glands.

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Eyelids

� Tarsal plate- thick fold of connective tissue that gives form and support to the eyelids.

� Tarsal or Meibomian glands- secrete fluid that helps keep the eyelids from adhering to each other.

� Conjunctiva- thin, protective mucous membrane composed of nonkeratinized stratified columnar epithelium with goblet cells that is supported by areolar connective tissue.

� Palpebral conjunctiva- lines the inner aspect of the eyelids

� Bulbar conjunctiva passes from the eyelids onto the surface of the eyeball.


Eyelashes and Eyebrows

� Eyelashes and eyebrows- help protect the eyeballs from foreign objects, perspiration, and direct rays of the sun.

� Sebaceous ciliary glands- at the base of the hair follicles of the eyelashes

� Release a lubricating fluid into the follicles.

� Infection of these glands, by bacteria cause a painful pus-filled swelling called a sty.


The Lacrimal Apparatus

� Lacrimal apparatus produces and drains lacrimal fluid or tears.

� Lacrimal ducts empty tears onto the surface of the conjunctiva of the upper lid

� Supplied by parasympathetic fibers of the facial (VII)

nerves.

� Tears pass medially over the anterior surface of the eyeball to enter the lacrimal puncta.

� Tears then pass into the lacrimal canals, which lead into the lacrimal sac and the nasolacrimal duct.

� This duct carries the lacrimal fluid into the nasal cavity just

inferior to the inferior nasal concha.

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Extrinsic Muscles

� Six muscles:

� Superior Rectus

� Inferior Rectus

� Lateral Rectus

� Medial Rectus

� Superior Oblique

� Inferior Oblique

� Innervated by Cranial Nerves III, IV, VI

� Periorbital fat- surrounds the orbit


Layers of the Eye Wall

� Fibrous Tunic

� Vascular Tunic

� Retina



Anatomy of the Eyeball

Fibrous Tunic - outer layer of the eye, strong dense collagenous

connective tissue layer.

� Sclera- forms the white part of the eye.

� Provides protection, maintains the shape of the eyeball and the site of muscle attachment for the extrinsic muscles of the eyes.

� Cornea- anterior surface of the outer tunic becomes transparent.

� Both the sclera and cornea consist of dense collagenous connective

tissue

� The sclera is opaque.

� The cornea is transparent and avascular and has regularly

spaced collagen fibers that are smaller than the wavelength of light.

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� Vascular Tunic- middle layer of the eyeball.

� It is composed of three parts: choroid, ciliary body,

and iris.

� Choroid- highly vascularized, provides nutrients to the

posterior surface of the retina.

� Contains melanocytes- melanin in the choroid absorbs stray

light rays, which prevents reflection and scattering of light

within the eyeball.



� Ciliary body- anterior portion of the vascular tunic, from the

choroid

� Consists of ciliary processes and ciliary muscle.

� Ciliary processes contain blood capillaries that secrete aqueous humor.

� Extending from the ciliary process are zonular fibers

(suspensory ligaments) that attach to the lens.

� Ciliary muscle are arranged longitudinal, oblique, and

circularly.

� Contraction or relaxation of the ciliary muscle changes

the tightness of the zonular fibers, which alters the

shape of the lens, adapting it for near or far vision.



� Iris- colored portion of the eyeball, and its opening is called

the pupil.

� Pupil consists of melanocytes and circular and radial

smooth muscle fibers.

� The two distinct fiber arrangements of the smooth muscle

form the:

� sphincter pupillae muscle- circularly oriented muscle

fibers at the pupillary boundary

� dilator pupillae muscle- attaches to the circumference of

the sphincter pupillae and projects like the spokes of a

wheel toward the base of the iris.

� A principal function of the iris is to regulate the amount of light

entering the eyeball through the pupil.

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� Optic disc- site where the optic (II) nerve exits the eyeball.

� Bundled together with the optic nerve are the central retinal

artery, a branch of the ophthalmic artery, and the central retinal vein.

� The retina consists of a pigmented layer and a neural layer.

� The pigmented layer is a sheet of melanin-containing epithelial cells.

� The melanin in the pigmented layer of the retina, helps to

absorb stray light rays.


Neural Sensory Layer of Retina� Neural (sensory) layer of the retina is a multilayered outgrowth of

the brain.

� Three distinct layers of retinal neurons—

� photoreceptor layer, bipolar cell layer, and ganglion cell layer.

� Separated by two zones, outer and inner synaptic layers.

� Light passes through the ganglion and bipolar cell layers and both

synaptic layers before it reaches the photoreceptor layer.

� Two other types of cells in the bipolar cell layer of the retina are

called horizontal cells and amacrine cells.

� Two types of photoreceptors: rods and cones.

� Rods allow us to see in dim light.

� Bright lights stimulate the cones, which produce color vision.


Macula Lutea

� Macula lutea- in the exact center of the posterior portion of the retina, at the visual axis of the eye.

� Fovea centralis- small depression in the center of the macula lutea, contains only cones.

� Area of highest visual acuity or resolution (sharpness of vision).

� The optic disc is also called the blind spot.

� Cranial nerve II enters

� Contains no rods or cones

� Cannot see an image that strikes the blind spot

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Lens� Within the cells of the

lens, proteins called crystallins, arranged like the layers of an

onion, make up the refractive media of the lens.

� Surrounded by a connective tissue capsule

� Cataracts- cloudy lens due to changes in proteins




Interior of the Eye

� Interior of the eye- two fluid-filled cavities, separated by the lens,

permits light to pass through the eye from the cornea to the retina.

� Anterior cavity- between the cornea and lens

� Contains a clear watery fluid- aqueous humor.

� Consists of two chambers.

� Anterior chamber- between the cornea and the iris

� Posterior chamber- behind the iris and in front of the zonular fibers and lens.

� Aqueous humor continually filters out of blood capillaries in the

ciliary processes of the ciliary body, enters the posterior chamber.

Flows forward between the iris and the lens, through the pupil, and into the anterior chamber.

� Aqueous humor drains into the scleral venous sinus (canal of

Schlemm) and then into the blood.

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Interior of the Eye� Vitreous chamber- Posterior cavity between the lens

and retina

� Vitreous body- jelly-like substance

� Maintains the shape of the eyeball

� Outer layers form the Zonulafr fiber- support the lens

� Hold the retina against the choroid

� Intraorbital Pressure- from aqueous humor and vitreous body

� 16 mmHg

� Glaucoma- increased aqueous humor production



The Visual Pathway

Processing of Visual Input in the Retina

� In the retina, input from several cells converge on a smaller number of postsynaptic neurons or diverge to a larger

number.

� Convergence predominates: 1 million ganglion cells receive input from about 126 million photoreceptor cells.

� Chemicals (neurotransmitters) released by rods and cones

induce changes in both bipolar cells and horizontal cells

that lead to the generation of nerve impulses.

� Amacrine cells synapse with and transmit signals to

ganglion cells, which then initiate nerve impulses.


Pathway in the Brain

� Optic chiasm- crossing point of the optic nerve axons.

� Become part of the optic tract, enter the brain.

� Terminate in the lateral geniculate nucleus of the thalamus.

� Synapse with neurons form optic radiations, which project to the primary visual areas in the occipital lobesof the cerebral cortex.

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Visual Pathway in the Brain


Hearing and Equilibrium

� Anatomy of the Ear:

� The ear is divided into three main regions:

� External ear- collects sound waves and channels

them inward;

� Middle ear- conveys sound vibrations to the oval

window; and

� Internal ear- houses the receptors for hearing and

equilibrium


The External Ear

� Auricle (pinna) made of elastic cartilage

� Helix and lobe

� External auditory canal- in the temporal bone

� Contains ceruminous glands and hair

� Tympanic membrane- semitransparent membrane between the external auditory canal and middle ear.

� Fibrocartilage ring attached to the temporal bone and across a three layered window

� Umbo- apex of the tympanic membrane

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Anatomy of the Ear


The Middle EarSmall, air-filled cavity in the temporal bone that is lined by epithelium

� Auditory ossicles- connected to one another by synovial joints and

attached by ligaments.

� Three ossicles: malleus, incus, and stapes

� Head of the malleus articulates with the incus.

� Incus articulates with the stapes

� Footplate of the stapes fits into the oval window (fenestra

vestibuli).

� Below the oval window is the round window (fenestra cochlea).

� Below the round window is a secondary tympanic membrane


The Middle Ear� Tensor tympani muscle limits

movement and increases tension on the eardrum.

� Stapedius muscle dampens

large vibrations of the stapes

due to loud noises, to protects the oval window.

� Auditory tube

(pharyngotympanic tube),

commonly known as the eustachian tube connects the

middle ear with the

nasopharynx.

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Internal Ear (Labyrinth)

Structurally two main divisions:

� The outer bony labyrinth that encloses an inner membranous labyrinth.

� Bony labyrinth- lined with periosteum and contains perilymph.

� Membranous labyrinth- contains endolymph

The three main areas:

(1) the semicircular canals

(2) the vestibule,

(3) the cochlea, receptors for hearing.


Internal Ear


The Cochlea

Cochlea- bony spiral canal divided into three channels:

� Cochlear duct or scala media- filled with

endolymph.

� Scala vestibuli ends at the oval window.

� Scala tympani ends at the round window.

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Organ of Corti

� Vestibular membrane separates the cochlear

duct from the scala vestibuli

� Basilar membrane separates the cochlear

duct from the scala tympani.

� Basilar membrane contains the Organ of Corti

(Spiral Organ)

� Contains receptors for hearing; hair cells and

supporting cells.


Mechanism of Hearing

� Auricle directs sound to the tympanic membrane which vibrates against the malleus, incus, and stapes which vibrates against the membrane that covers the oval window.

� Vibrations initiate fluid pressure waves in the perilymphof the scala vestibuli; transmitted to the scala tympani and to the round window.

� Pressure waves in the endolymph of the cochlear duct cause the basilar membrane to vibrate and the hair cells move against the tectorial membrane; bending of the stereocilia results in nerve impulses being generated in cochlear nerve fibers (CN VIII).

Mechanism of Hearing

� Transmission proceeds to the medulla

and to either:

� Inferior colliculus of the midbrain

� Superior olivary nucleus in the pons followed by the Inferior colliculus

� Both ascend to the thalamus and then the

auditory center in the temporal lobe


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Mechanism of Equilibrium

The receptor organs for equilibrium of the vestibular

apparatus includes the saccule, utricle, and

semicircular ducts.

Two types of equilibrium:

� Static equilibrium- maintenance of the position of the

body relative to the force of gravity.

� Dynamic equilibrium- maintenance of body position in

response to sudden movements.


Saccule and Utricle

Otolithic Organs: Saccule and Utricle

� Walls of both contain maculae- receptors for static equilibrium and

contribute to dynamic equilibrium

� Maculae consist of two kinds of cells:

� Hair cells- the sensory receptors

� Have one stereocilia of graded height, plus one kinocilium,

anchored to the basal body and extending beyond the longest

stereocilium.

� Supporting cells- columnar cells

� Secrete otolithiuc membrane- glycoprotein layer over the hair cells

� Otoliths- calcium carbonate crystals embedded in the membrane


Maculae of the Right Ear

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Semicircular ducts

� Three semicircular ducts function in dynamic equilibrium.

� Lie at right angles to one another in three planes.

� Permits detection of rotational acceleration or deceleration in the ampulla at the crista.

� The crista contains hair cells and supporting cells covered by gelatinous material called the culopa.

� Bending of the hair bundles produces responses that lead to nerve impulses. that pass along the ampullary nerve.


Semicircular Ducts

Equilibrium Pathway

� Nerve impusles pass along the ampullary nerve to the Vestibulocochlear nerve (CN VIII) to the

medulla and pons, and then to the cortex

� CN III, IV, VI, and XI coordinate information

� Cerebellum- maintains static and dynamic equilibrium


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Equilibrium Pathway

Documents

Chapter 22 Special Senses - Nassau Community College - Special Senses.pdf · Special Senses Copyright 2009 John Wiley & Sons, Inc. Olfaction: Sense of Smell Olfactory epithelium-10–100