SPECIAL SENSES CHAPTER 8 NOTES

External Eye Eyelids Eyelashes Meibomian glands Ciliary glands Conjunctiva Lacrimal apparatus Six extrinsic eye muscles (fig 8.2)

Internal Eye Eyeball Sclera Cornea Choroid Ciliary body Iris Pupil Retina Rods Cones (fovea centralis) Lens Optic nerve Optic disc (fig 8.5 activity!)

Homeostatic Imbalances “watery” eyes Conjunctivitis Night blindness Colorblindness Cataracts Glaucoma

Light

Visual Fields & Visual Pathway

Ear Mechanoreceptors Outer ear Pinna Ceruminous glands Tympanic membrane Middle Ear Oval window Round window Auditory tube Ossicles (malleus, incus, stapes) Inner Ear Osseous labyrinth Cochlea, Vestibule, Semicircular canals Perilymph

Hearing Inside the cochlea is organ of Corti which has hearing receptors (hair cells). Sound waves create vibrations on eardrum, ossicles and oval window. This sets cochlear fluid in motion. Receptor cells on basilar membrane stimulated with their hairs are bent by tectorial membrane. High-pitched sounds disturb receptor cells close to oval window Low-pitched sounds stimulate specific hair cells further in the cochlea One stimulated, hair cells transmit impulses on cochlear nerve – to vestibulocochlear nerve – to the temporal lobe FYI: When same sounds keep stimulating ears, we adapt and “stop” hearing them.

Frequency animation Animation

Equilibrium Vestibular apparatus (static and dynamic equilibrium) Static: In vestibule are receptors – maculae. Maculae report on position of head with respect to gravity with body is NOT moving. Maculae are embedded in otolithic membrane (gel with otoliths - tiny stones) When head rolls, otoliths roll in response to gravity, which pulls gel, which slides over hair cells, bending them. Hair cells send info down the vestibular nerve (part of the vestibulocochlear nerve) reporting on position of head. Dynamic: Angular or rotatory movements of head Semicircular canals are oriented in 3 planes In each canal is region called crista ampullaris (tuft of hair cells covered with gelatinous cap called cupula) When head moves in arclike direction, endolymph moves in OPPOSITE direction, pushing cupula in opposite direction of movement. Transmits messages up vestibular nerve. When motion stops, pushes cupula back, stopping firing.

Deafness/ Equilibrium Deficits Conduction Results when something interferes with the conduction Hearing aids help Sensorineural deafness Degeneration or damage to receptor cells, cochlear nerve, or to neurons of auditory cortex. FROM LISTENING TO LOUD MUSIC!!!! Hearing aids not very helpful Meniere’s syndrome Progressive deafness Vertigo

Chemical Senses Chemoreceptors (both smell and taste) Olfactory receptors Olfactory receptor cells – neurons equipped with olfactory hairs When receptor cells are stimulated by chemicals, transmit impulses along olfactory filaments (make up olfactory nerve) Olfactory pathways closely tied into limbic system (smells – related closely to memories) “Adapt” to continuous smell and stop sending message Anosmias – problem with smell/taste. Usually due to head damage, nasal cavity inflammation, or aging. Olfactory auras (olfactory hallucinations) – experienced by some epileptics before they have seizures (brain is mimicking smell)

Chemical Senses Taste Buds and Sense of Taste Taste buds – widely scattered in oral cavity. 10,000, most on tongue. Papillae – small projections on tongue. House taste buds. Gustatory cells – specific cells found in the taste buds that respond to chemicals dissolved in saliva Gustatory hairs – microvilli that protrude through the taste pore, depolarize and impulses are transmitted to brain 3 cranial nerves (facial, glossopharyngeal and vagus) transmit taste information to brain. Taste sensations: Sweet receptors – respond to sugars, saccharine, some amino acids (-OH) Sour receptors – respond to acidity (H+) Bitter receptors – respond to alkaloids Salty receptors – respond to metal ions Need for taste preferences: When you crave sweets, body needs carbs. Bitter tastes are often poison When you crave sour, need vitamin C

Congenital eye problems: Strabismus Maternal rubella can result in congenital blindness or cataracts Conjunctivitis can result from maternal gonorrhea ALL states require newborn babies’ eyes to be treated with silver nitrate or antibiotics Development: Eyeballs continue to enlarge until 8-9 years old Babies can’t cry with tears until about 2 weeks old By 5 months, baby can focus on close objects (20/200) By 5 years, full color is developed, depth perception is present (20/30)