Special Senses

Senses General Senses include temperature, pain, touch, pressure, vibration, and proprioception. Special Senses include olfaction, gustation, equilibrium, vision, and hearing.

Types of Receptors Mechanoreceptors—stretching, touch, pressure in autonomic NS structures (barorecpetors) and body position (proprioceptors) Chemoreceptors--chemical—gustation, olfaction, and autonomic NS chemicals Nociceptors--pain Thermoreceptors--temperature Photoreceptors--light--70% of all receptors

Taste (Gustation) closely associated with smell Gustatory Organs (Taste Buds) located along the surface in elevations called Papillae (10,000 or more)

Taste Buds Respond to dissolved chemicals 6 types of taste sensations Sweet Sour Bitter Salty Umami Water

Smell (Olfaction) Detect to 50 or more specific scents Olfactory Organs in the upper wall of the Nasal Cavity Bipolar neurons -- Receptor Cells --Olfactory Hair Cells Mucous membranes trap particles

Smell (Olfaction) LowThreshold: amount needed for detection Adaptation: time for decrease in sensitivity First second or so about 50% gone FYI: Usually in one minute even strong scents are no longer smelled

Sight (Vision) most complex of Includes eye, and accessory structures over 70% of the sensory receptors in the body are photoreceptors for sight Includes eye, and accessory structures

Accessory structures of the eye Eyelid, eyebrow, eyelashes = protects Exocrine glands Conjunctiva=mucous membrane of the eyelid and eye Helps moisten and lubricate the eyeball

Accessory Structures of the Eye Lacrimal apparatus Produces tears to keep eye moist Drains through the nasal cavity

Accessory structures of the eye Extrinsic muscle of the eye 6 muscles that move eyes

Tunics (layers) of the Eye Fibrous Tunic = outermost layer Sclera--forms most of the fibrous tunic--the white of the eye Cornea-refracts light

Fibrous layer of the Eye (cont) Cornea--transparent coat of iris--slightly bulged by aqueous humor (anterior cavity) Most common transplant

Vascular Tunic Blood supply Choroid --thin posterior portion Ciliary Body-thick anterior portion, attaches to lens with ligaments Iris-colored portion

Pupil dilation and constriction Iris = made of circular and radial smooth muscles Pupil= hole in iris changes size according to light

Vascular Tunic (cont) Lens--changes shape for close-up or long range—lens accommodation Ligaments attached to ciliary body Viterous Humor (fluid, body) looks like clear jelly Holds retina in place

Nervous Tunic the inner layer of the eye Retina = thin fragile layer of neurons (few mm thick)

Rods and Cones--neurons in retina Rods = elongated dendrites--black and white and night vision Cones = dendrites with tapered ends color sensitive Sharpens vision

Outer Ear direct sound waves toward the eardrum Auricle = the outer portion Auditory Canal = extends into temporal bone Cerumen=ear wax-modified sweat glands-protection

Middle Ear air filled space Aka Tympanic Cavity Auditory Ossicles smallest bones in the body Malleus (hammer) Incus (anvil) Stapes (stirrup)

Middle Ear (cont) Eustachian Tube = Middle Ear to the Pharynx (throat) pressure equalization Tympanic Membrane (Eardrum vibrates

The Inner Ear hearing and equilibrium Cochlea (hearing) Vestibule (balance) Semicircular Canals (balance)

Cochlea FYI: resembles a snail shell contains the Organs of Corti for hearing

Cochlea (cont) Winding canals Contains perilymph and endolymph (fluids) FYI: surrounded by bony labyrinth FYI: Fluids aid in transmission of vibration

Hearing Organs--Organs of Corti Vibrate to endolymph motion Release neurotransmitters

Steps of Hearing 1. Sound waves into auditory canal 2. Eardrum vibrates 3. Ossicles vibrate and magnify sound

Steps of Hearing 4. Oval window vibrates causes fluids to vibrate

Steps of Hearing 5. fluids causes hair cells to vibrate 6. Vibration –neurotransmitter - auditory nerve - brain

Equilibrium (Balance) Aided by receptor cells in the Inner Ear Determined by body position and movement of head Uses sight & neurotransmitters sent by semicircular canals and vestibule

Semicircular canals three loops Ampulla at entrance of loops contain Cristae Hair cells in Cristae release neurotransmitters brain interprets & responds

Vestibule Vestibule: chamber between the cochlea & semicircular canals contains perilymph and endolymph (bony labyrinth)

Vestibule cont Maculae =contain hair-like cells, Otoliths on surface, move Otoliths respond to gravity

END OF NOTES

DISEASES AND DISORDERS OF THE SPECIAL SENSES

Presbyopia Lens looses ability to change shape Usually caused by age

Myopia (near sighted) Caused by eye shape being too long Causes light to focus in front of retina Corrected with glasses or contacts

Hyperopia (far-sighted) Caused by eye shape being shorter than normal Causes light to focus behind the retina Corrected with glasses or contacts

Cataracts Caused by clouding of the lens Can be replaced with artificial lens

Conjunctivitis Caused by an infection of the conjuctiva More commonly called “pink eye”

Conjunctivitis

Deafness Two types: Conductive: caused by blockages in the auditory canal Caused by middle ear infections Eardrum damage

Sensorineural deafness Damage to auditory nerves Cochlear malformation or damaged by infection Brain damage in temporal lobe

Glaucoma Aqueous humor build up puts pressure on the retina Can damage retina if not treated

Macular Degeneration Section of the retina called the macula (large concentration of blood vessels) is damaged causing tunnel vision until vision is gone

Middle Ear Infection Usually involves the eardrum being infection by bacteria or virus Bacterial treated with antibiotics Common in children

Strabismus Caused by weak eye muscles Can be surgically corrected or by patching the good eye to encourage other eye to work properly

Tinnitis Caused by improper discharge of electrical impulses of the Organs of Corti Hair cells

Vertigo Caused by otoliths improperly aligning with membranes Causes dizziness and nausea