Head: Special Senses. Taste Smell Vision Hearing/Balance

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Gwendoline Arline Simpson
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1 Head: Special Senses Taste Smell Vision Hearing/Balance

bud contains several cell types in microvilli that project through pore and

2 TASTE: how does it work? Taste buds on tongue on fungiform papillae ( mushroom-like projections) Each bud contains several cell types in microvilli that project through pore and chemically sense food Gustatory receptor cells communicate with cranial nerve axon endings to transmit sensation to brain M&M, Fig. 16.1

3 Five taste sensations Sweet front middle Sour middle sides Salty front side/tip Bitter back umami posterior pharynx M&M, Fig. 16.1

4 Cranial Nerves of Taste Anterior 2/3 tongue: VII (Facial) Posterior 1/3 tongue: IX Glossopharyngeal) Pharynx: X (Vagus( Vagus) M&M, Fig. 16.2

5 Smell: How does it work? Olfactory epithelium in nasal cavity with special olfactory receptor cells Receptor cells have endings that respond to unique proteins Every odor has particular signature that triggers a certain combination of cells Axons of receptor cells carry message back to brain Basal cells continually replace receptor cells they are only neurons that are continuously replaced throughout life.

6 Olfactory epithelium just under cribiform plate (of ethmoid bone) in superior nasal epithelium at midline midline M&M, Fig. 16.3

7 Vision 1. Movement of eye extrinsic extrinsic eye muscles and location in orbit 2. Support of eye lids, brows, lashes, tears, conjunctiva 3. Lens and focusing structures structures of eyeball and eye as optical device 4. Retina and photoreceptors

8 Movement of eye Eye movement simulator ( es/version1/eyesim.htm)

9 Extrinsic eye muscles Muscle Superior oblique Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Movement Depresses eye, turns laterally Turns laterally Turns medially Elevates Depresses eye Elevates eye, turns laterally Nerve IV (Trochlear( Trochlear) VI (Abducens( Abducens) III (Oculomotor III Oculomotor) (Oculomotor III Oculomotor) (Oculomotor III Oculomotor) (Oculomotor)

10 M&M, fig. 16.4

11 Support/Maintenance of Eye Eyebrows: shade, shield for perspiration Eyelids (palpebrae( palpebrae): skin-covered folds with tarsal plates connective tissue inside Levator palpebrae superioris muscle opens eye (superior portion is smooth muscle why?) Canthus (plural canthi): corner of eye Lacrimal caruncle makes eye sand at medial corner Epicanthal folds in many Asian people cover caruncle Tarsal glands make oil to slow drying Eyelash ciliary gland at hair follicle infection infection is sty

Support of Eye-- --conjunctiva Mucous membrane that coats inner surface of eyelid (palpebral part) and then folds back onto surface of eye (ocular part) Thin layer of connective tissue covered with

12 Support of Eye-- --conjunctiva Mucous membrane that coats inner surface of eyelid (palpebral part) and then folds back onto surface of eye (ocular part) Thin layer of connective tissue covered with stratified columnar epithelium Very thin and transparent, showing blood vessels underneath (blood-shot eyes) Goblet cells in epithelium secrete mucous to keep eyes moist Vitamin A necessary for all epithelial secretions lack leads to conjunctiva drying up scaly

13 Support of eye-- --tears M&M, fig Lacrimal glands superficial/lateral in orbit, produce tears Lacrimal duct (nasolacrimal duct) medial corner of eye carries tears to nasal cavity (frequently closed in newborns opens by 1 yr usually) Tears contain mucous, antibodies, lysozyme (anti-

Eye as lens/optical device M&M, fig. 16.

14 Eye as lens/optical device M&M, fig Light path: Cornea Anterior segment Pupil Lens Posterior segment Neural layer of retina Pigmented retina

15 Eye as optical device-- --structures Sclera (fibrous tunic): is tough connective tissue ball that forms outside of eyeball like box/case of camera Corresponds to dura mater of brain Cornea: anterior transparent part of sclera (scratched cornea is typical sports injury); begins focusing light Choroid Internal to sclera/cornea Highly vascularized Darkly pigmented (for light absorption inside box) Ciliary body: thick ring of tissue that encircles and holds lens Iris: colored part of eye between lens and cornea, attached at base to ciliary body Pupil: opening in middle of iris Retina: sensory layer that responds to light and transmits visual signal to brain

16 M&M, fig. 16.4

Detail: Aperture and focus APERTURE Pupil changes shape due to intrinsic autonomic muscles Sympathetic: Dilator pupillae (radial fibers) M&M, fig. 16.

17 Detail: Aperture and focus APERTURE Pupil changes shape due to intrinsic autonomic muscles Sympathetic: Dilator pupillae (radial fibers) M&M, fig Parasympathetic: (animation of lens sphinchter pupillae FOCUS Ciliary muscles in ciliary body pull on lens to focus far away Elasticity of lens brings back to close focus Thus, with age, less elasticity, no close focus far-sighted

18 Detail: eye color Posterior part of iris always brown in color People with brown/black eyes with pigment throughout iris People with blue eyes rest of iris clear, brown pigment at back appears blue after passing through iris/cornea

19 Details: Retina and photoreceptors Retina is outgrowth of brain Neurons have specialized receptors at end with photo pigment proteins (rhodopsins( rhodopsins) Rod cells function in dim light, not color-tuned Cone cells have three types: blue, red, green In color blindness, gene for one type of rhodopsin is deficient, usually red or green Photoreceptors sit on pigmented layer of choroid. Pigment from melanocytes-- --melanoma possible in retina!! Axons of photoreceptors pass on top or superficial to photoreceptor region Axons congregate and leave retina at optic disc (blind spot) Fovea centralis is in direct line with lens, where light is focused most directly, and has intense cone cell population (low light night vision best from side of eye) Blood vessels superficial to photoreceptors (retina is good sight to check for small vessel disease in diabetes)

20 Retina and photoreceptors M&M, fig

21 Ear/Hearing M&M, fig Outer Ear: auricle is elastic cartilage attached to dermis, gathers sound Middle ear: ear ossicles transmit and modulate sound Inner ear: cochlea, ampullae and semicircular canals sense sound and equilibrium

Middle Ear External auditory canal ends at tympanic membrane which vibrates against malleus on other side Inside middle ear chamber malleus incus stapes which vibrates

22 Middle Ear External auditory canal ends at tympanic membrane which vibrates against malleus on other side Inside middle ear chamber malleus incus stapes which vibrates on oval window of inner ear Muscles that inhibit vibration when sound is too loud Tensor tympani m. (inserts on malleus) Stapedius m. (inserts on stapes) M&M, fig

Inner Ear/Labyrinth Static equilibrium, linear motion 3-D D motion, angular acceleration Sound vibrations M&M, fig. 16.

23 Inner Ear/Labyrinth Static equilibrium, linear motion 3-D D motion, angular acceleration Sound vibrations M&M, fig Utricle, saccule are egg-shaped sacs in center (vestibule) of labyrinth Auditory Nerve (Acoustic) VIII receives stimulus from all to brain 3 semicircular canals for X,Y,Z planes Vestibular n. equilibrium Cochlear n. hearing

Cochlea-- --how it works Which is more incredible? Retina or spiral organ? M&M, fig. 16.

24 Cochlea-- --how it works Which is more incredible? Retina or spiral organ? M&M, fig Spiral organ is receptor epithelium for hear Range of volume and tone that are perceive astonishing Basilar membrane running down middle Thicker at start, vibrates with lower sounds Thinner at end, vibrates at higher sound (in figure shown uncoiled in life is spiral in

The Senses. Chapter 10 7/8/11. Introduction

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