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

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.

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.

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

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.

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).

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.

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:

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).

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.

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.

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.

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.

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

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.

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.