3.16 Anatomy Chapter 16

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susaneers
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3.16 Anatomy Chapter 16
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2010-10-21 01:42:12
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Special Senses
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The Chemical Senses: Taste and Smell, The Eye and Vision, The Ear: Hearing and Equilibrium
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  1. The Chemical Senses: Taste and Smell
    Overview of receptor type
    • Taste: gustation
    • Smell: olfaction

    • Receptors: classified as chemoreceptors
    • - respond to chemical substances
    • - food chemicals dissolved in saliva
    • - airborne chemicals that dissolve in fluids on the nasal membranes
  2. Taste (Gustation)
    Taste Buds
    Taste receptors occur in taste buds

    - found on surface of the tongue, posterior region of the palate, inner cheeks, posterior pharynx, and on the epiglottis

    • - Most occur in the epithelium of projections of the tongue called papillae.
    • - Two types of papillae: small fungiform papillae on the surface of the tongue (taste buds are on apical surface) and larger vallate papillae arranged in a V shape near the back of the tongue (taste buds are in side walls of papillae)

    Taste Bud

    • Collection of 50–100 epithelial cells

    • • Contain two major cell types
    • Gustatory epithelial cells ( taste cells)
    • Basal epithelial cells

    • Cells in tastebuds replaced every 7–10 days


    • Five basic qualities of taste: Sweet, sour, salty, bitter, and umami



    • All taste modalities can be elicited from all areas containing taste buds
  3. The Gustatory Pathway
    •Taste information reaches the cerebral cortex primarily through the facial (VII) (anterior 2/3) and glossopharyngeal (IX) nerves (posterior 1/3)



    •Some taste information through the vagus nerve (X) (epiglottis)


    • Sensory neurons synapse in the solitary nucleus of the medulla


    • • Impulses are transmitted to the thalamus and ultimately to the
    • gustatory area of the cerebral cortex in the insula
  4. Smell (Olfaction)
    • Olfactory receptors are part of the olfactory epithelium


    • • Olfactory epithelium is pseudostratified columnar and contains three main cell types
    • 1. Olfactory sensory neurons (bipolar neurons)

    2. Supporting epithelial cells (columnar)

    3. Basal epithelial cells




    Olfactory nerve transmits signal to mitral cells in the olfactory bulb then relay the information along the olfactory tract to 1. the limbic region (emotions) and 2. the piriform lobe of the cerebral cortex
  5. The Ear: Hearing and Equilibrium
    • The ear—receptor organ for hearing and equilibrium


    • • Composed of three main regions
    • 1. Outer ear—functions in hearing

    • 2. Middle ear—functions in hearing
    • 3. Internal ear—functions in both hearing and equilibrium
  6. The Outer Ear
    • Composed of:
    • • The auricle (pinna); helps direct sounds
    • External acoustic meatus: contains hairs, sebaceous glands, and ceruminous glands
    • Tympanic membrane: "ear drum"; forms the boundary between the external and middle ear
  7. 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 and the Round window

    Pharyngotympanic tube (auditory or eustachian tube); links the middle ear and pharynx










    • • Ear ossicles—smallest bones in the body
    • 1. Malleus—attaches to the eardrum

    • 2. Incus—between the malleus and stapes
    • 3. Stapes—vibrates against the oval window

    • Tensor tympani and stapedius: Two tiny skeletal muscles in the middle ear cavity
  8. The Inner Ear
    Internal ear—also called the labyrinth; lies within the petrous portion of the temporal bone


    • • Bony labyrinth—a cavity consisting of three parts:
    • 1. Semicircular canals

    • 2. Vestibule
    • 3. Cochlea
    • • Bony labyrinth is filled with perilymph; continuous with cerebrospinal fluid


    • • Membranous labyrinth: series of membrane-walled sacs and ducts; Fits within the bony labyrinth
    • - Consists of three main parts:

    • 1. Semicircular ducts
    • 2. Utricle and saccule
    • 3. Cochlear duct
    • • Membranous labyrinthis filled with a clear fluid—endolymph
  9. The Cochlea
    • • A spiraling chamber in the bony labyrinth
    • • Coils around a pillar of bone—the modiolus
    • • The cochlear nerve runs through the core of the modiolus




    • The cochlear duct (scala media)—contains receptors for hearing

    • • Lies between two chambers: the scala vestibuli (continuous with the oval window)and the scala tympani (ends at the round window)

    •The vestibular membrane—the roof of the cochlear duct

    •The basilar membrane—the floor of the cochlear duct







    • •The cochlear duct (scala media)—contains receptors for hearing
    • - Spiral organ (of Corti)—the receptor epithelium for hearing; contains columnar supporting cells and one row of inner and three rows of outer hair cells that are the receptor cells, the tips of which contain stereocilia and are embedded in a gel-lik tectorial membrane
  10. Sound Pathway Through Ear
    • 1. Sound waves vibrate the tympanic membrane.
    • 2. Auditory ossicles vibrate. Pressure is amplified.
    • 3. Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli
    • 4a. Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells
    • 4b. Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on the inner hair cells
  11. The Vestibule
    The central part of the bony labyrinth; lies medial to the middle ear, contain two egg shaped parts suspended in perilymph:

    • Utricle (continuous with the semicircular ducts): has horizontal orientation, signals to brain if head is tilted
    • Saccule (continuous with the cochlear duct): has vertical orientation, signals to brain if head is upright or untilted
    • - Two egg-shaped parts of the membranous labyrinth

    • - House the macula—contains receptor cells that synapse with the vestibular nerve







    • static equilibrium: sense of balance when the head is still
    • linear acceleration: speed and direction of head movements
  12. Semicircular Canals
    Semicircular duct—snakes through each semicircular canal

    • *House receptors for rotational acceleration of the head
    • Three semicircular canals:
    • 1. anterior: (vertical, hole faces the cochlea)
    • 2. posterior: (vertical, hole faces the back)
    • 3. lateral: (horizontal, hole faces down)
    • *Expansion at one end of each called an ampulla
    • Membranous ampulla—located within bony ampulla

    • • Houses a structure called a crista ampullaris
    • • Cristae contain receptor cells of rotational acceleration
  13. Disorders of Equilibrium and Hearing
    Motion Sickness: may arise from a mismatch of sensory inputs; also, the vestibular nuclei lie near the centers in the medulla that control vomiting

    Meniere's syndrome: the membranous labyrinth is apparently distorted by excessive amounts of endolymph; causes disbalance, nausea, vomiting, "howling" in ears, deafness

    • Deafness:
    • Conduction deafness: sound vibrations cannot be conducted to the internal ear; caused by earwax blocking the external acoustic meatus, a ruptured eardrum, otitis media, or otosclerosis

    Sensorineural deafness: damage to the hair cells or any part of the auditory pathway to the brain; results in a normal, gradual loss of hearing
  14. The Eye and Vision

    General Overview

    • • 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
  15. The Eye and Vision
    Accessories of the Eye
    Eyebrows—coarse hairs on the superciliary arches, shade eye from sunlight and prevent perspiration from entering the eyes


    • Eyelids (palpebrae)—separated by the palpebral fissure
    • - Meet at the medial and lateral angles (canthi)



    Lacrimal caruncle—reddish elevation at the medial canthus, glands here produce eye "sand"


    Tarsal plates—connective tissue within the eyelids, attachment site for the orbicularis oculi


    • Tarsal glands—sebaceous glands in the tarsal plates that release oil that lubricates the eye
    • **infection leads to chalazion


    Ciliary glands—sebaceous and sweat glands; ducts open up into hair follicles






    **infection leads to a sty

    • Conjunctiva: a transparent mucous membrane that covers the inner surfaces of the eyelids (palpebral conjunctiva) and folds back over the anterior surface of the eye (bulbar conjunctiva)
    • *conjunctival sac is where a contact lens would lie
    • **inflammation of conjunctiva = conjunctivitis; caused by bacteria or viruses = pinkeye

    **vitamin A is necessary for maintaining epithelia; deficiency prevents conjunctiva from secreting mucus, and eye becomes dry
  16. Lacrimal Apparatus
    Keeps the surface of the eye moist with lacrimal fluid (tears)

    lacrimal gland: superolateral to the eye; produces lacrimal fluid that enters the superior part of the conjunctival sac and travels to the medial angle

    lacrimal punctum: tiny openings at the medial angle, empties tears into the lacrimal canaliculus and drains into the lacrimal sac.

    Fluid enters the nasolacrimal duct and empties into the nasal cavity.

    **lacrimal fluid contains mucus, antibodies, and lysozymes (destroys bacteria)
  17. Extrinsic Eye Muscles
    Six extrinsic eye muscles originate from the walls of the orbit and insert onto the outer surface of the eyeball; controls movement and holds the eye in place

    Four muscles are rectus muscles (straight): Inferior, superior, lateral, medial rectus

    • Superior oblique muscle: loops through a trochlea superiorly (turns eye down and out; depresses and turns laterally)
    • Inferior oblique muscle: elevates the eye and turns it somewhat laterally (up and out)
  18. Anatomy of the Eyeball
    General Functions/ Overview
    Components of the eye


    • Protect and support the photoreceptors


    • Gather, focus, and process light into precise images


    • Anterior pole—most anterior part of the eye


    • Posterior pole—most posterior part of the eye


    • Lens divides the eye into anterior segment and posterior segment (aqueous and vitreous humor)


    • External walls—composed of three tunics
  19. Anatomy of the Eyeball
    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
    • Limbus—junction between sclera and cornea

    • Scleral venous sinus—allows aqueous humor to drain
  20. Anatomy of the Eyeball
    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— folds between muscle and zonule

    Ciliary zonule (suspensory ligament); attached around entire circumference of the lens





    • Iris--visible colored part of the eye (pigmented)
    • - attached to the ciliary body; composed of smooth muscle
    • *pupil: the round, central opening
  21. Anatomy of the Eyeball
    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
    • 1. Photoreceptor cells: rods and cones
    • 2. Bipolar cells
    • 3. Ganglion cells




    • Photoreceptor cells signal bipolar cells

    • • Bipolar cells signal ganglion cells to generate nerve impulses
    • • Axons from ganglion cells run along internal surface of the retina

    • Converge posteriorly to form the optic nerve

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