1. Dr. Steve W. Altstiel Bahrain High School
Special Senses
Dr. Steve W. Altstiel
Bahrain High School

2. Special Senses Taste - mostly on tongue… related to sense of smell.
Papillae of tongue – bumps.
Taste buds, pores – found on papillae – bulb-like structures sunken into the epithelium.
Receptors (gustatory) cells
Taste “hairs” – found on the end of taste cells (microvilli) – this is the part that is in contact with the chemicals and the solution in the mouth.
Nerve fibers (CN VII, IX) – in contact with taste buds.
Nerve pathways – VII or IX will go to brain stem  cerebral cortex (taste area).
Taste sensations – 4 basic taste sensations: 1) sweet; 2) salty; 3) sour; and 4) bitter.

3. Smell has far reaching effects with memory… also very adaptive.
Smell (olfactory)
Olfactory area – upper part of nasal cavity… out of the way where most air moves.
Olfactory receptor cells (axons – CN I) – chemoreceptor cells – mucous layer aids in moistening chemicals to be able to smell. Bipolar neurons.
Olfactory bulb  olfactory tract  cerebral cortex
Smell has far reaching effects with memory… also very adaptive.

4. Hearing and Equilibrium
External ear
Auricle (pinna) – outer part that is seen – helps collect sound waves.
External auditory canal – lined with skin, hair, and glands (produces a wax called cerumen.
Tympanic membrane (eardrum) – separates external ear from the internal ear – vibrates when sound waves hit it.
Middle ear
Tympanic cavity – air-filled chamber.
Auditory (eustachian) tube – connects the tympanic cavity with the pharynx.
Auditory ossicles – 3 bones in the tympanic cavity

5. Middle Ear Cont… Auditory ossicles (3):
Malleus – attached to eardrum.
Incus – attached to the malleus and stapes.
Stapes – attached to the oval window which opens to the inner ear.
Muscles – dampen the sound waves, especially loud sounds – aid to reduce damage to CN V, VII
Otitis media – middle ear infection.

6. Inner Ear (neural part)
Bony (osseous) labyrinth – series of elaborate canals hollowed out of the temporal bone. Located just behind the eye socket. 3 subdivisions:
Cochlea, vestibule, and semicircular canals.
Membranous labyrinth – found in the bony labyrinth – similarly shaped series of membranous ducts within the bony labyrinth.
Cochlear duct, utricle and saccule, semicircular ducts.
Endolymph – fluid in the membranous labyrinth (thicker than perilymph).

8. Inner Ear cont… Cochlear Division – hearing.
Cochlea – snail-shaped part of the bony labyrinth. Contains: Scala vestibuli, scala tympani.
Cochlear duct – separates scala vestibuli and scala tympani.
Vestibular membranes, basilar membrane
Organ of Corti – sensory receptor structure located on the basal membrane.
Hair cells – receptors
Tectorial (gel-like) membrane – overlies the hair cells – ends of the hair cells are embedded in the membrane.
Cochlear fibers for CN VII – come in contact with hair cells.

9. Inner Ear cont…
Passage of sound waves
Auditory nerve pathways – hairs on the hair cells bend due to sound waves – causes nerve impulse.
Lesion – if in inner ear or CN VIII, will have diminished hearing or deafness in that ear…difficulty localizing sound if the lesion is in the brain.
Vestibular division – equilibrium – divided into two functional arms:

10. Inner Ear cont… Vestibular division
Static equilibrium – position of head
Dynamic equilibrium – deals with movement of the head, along with acceleration and deceleration – found in the semicircular canals.
Vestibular nerve pathways – some kind of motion causes fluid to move causing hairs to bend, which gives a verve impulse through CN VIII  brainstem  1. cerebelum; 2. spinal cord; 3. cerebral cortex; 4. reticular formation; and 5. eye muscles.
Lesion – vertigo (spinning sensation).

11. Vision Accessory Organs
Orbit – eye socket – cone-shaped region that the eyeball fits in. Contains muscles, optic nerves, blood vessels, fat all around the orbit.
Eyelids (palpebrae) – upper and lower – protects eyes from dust, intense light, impact, etc. Ptosis – drooping eyelid. Eyelashes – keep dust and perspiration out of the eyes.
Conjunctiva – thin mucous membrane with lots of blood vessels. Lines inner part of eyelid.
Lacrimal Apparatus – makes and drains tears.
Lacrimal gland – secretes tears. CN VII
Ducts – open onto surface of eyes – tears help wash away debris and has bacterial components helpful to the eye.

12. Vision Cont.. Diplopia – double vision.
Extrinsic Muscles – have origin on bone of orbit.
Superior rectus III – moves eye up.
Inferior rectus III – moves eye down.
Medial rectus III – moves eye inward toward nose.
Lateral rectus VI – moves eye outward.
Superior oblique IV – moves eye diagonally.
Inferior oblique III – moves eye diagonally.
Diplopia – double vision.
Strabismus – lateral or medial.

13. Eyeball Outer (fibrous) tunic
Sclera – tough outer part – make posterior 5/6 of eyeball – the white of your eye – function: protection, muscle attachment.
Cornea – bulge in front – makes up anterior 1/6 – transparent – contains nerves, but no blood vessels – function: bends light waves to aid in focusing.
Ciliary body – more forward – continuation of the choroid – projects into the eyeball.

14. Ciliary Body cont… Ciliary processes – bumps or folds.
Suspensory ligaments – strings that attach to lens.
Lens – biconvex disc – bends light waves and helps focus – can become cloudy (cataracts) – can be removed and replaced.
With age, the lens gets stiffer not able to ball up.
Ciliary muscles (CN III) – during contraction, relaxes tension on the lens.
Accommodation – rounding up of lens causing near vision.
Epithelial Cells – produce Aqueous Humor – a fluid found in front of the lens – continuously being produced and drained into the venous system.
Glaucoma – increased pressure due to too much aqueous humor.

15. Retina – sensory portion made up of many layers of cells.
Iris – colored part of the eye due to pigment associated with it.
Pupil – hole found inside of iris – allows light to pass through.
Smooth muscle
SNS – dilates pupil – used to see at distances and low light.
PSNS – constricts pupil - for near vision and bright light.
Inner (nervous) Tunic
Retina – sensory portion made up of many layers of cells.
Pigment epithelium – outermost layer next to choroid – helps to trap light.
Photoreceptors – receive light – convert light to neuron impulse.
Rods – function more in dim light and black and white vision – also peripheral vision.
Cones – color, bright light
Bipolar neurons
Ganglion cells – axons from the optic nerve CN II

16. More on Vision Macula lutea – spot (yellow)
Fovea centralis – depression – sharpens vision occurs here – no cones – no blood vessels.
Optic disc – where optic nerve fibers exit – no rods or cones – known as “Blind Spot”.
Viterous body (humor) – gel-like substance behind the lens – gives shape to eyeball.
Passage of light – cornea  aqueous humor  pupil  lens  vitreous body  ganglion cells  bipolar cells  photoreceptor cells.

17. More on Vision
Visual Nerve Pathways – visual fields  retina  optic nerve  optic chiasma  optic tract  thalamus  optic radiations (fiber tracts within the cerebrum)  primary visual area.
Lesion
Anopsia – blindness
Hemianopsia – can see out of one side of the eye but not the other.