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 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 special senses 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 = protect Exocrine glands Conjunctiva=mucous membrane of the eyelid and eye Helps moisten and lubricate the eyeball

Accessory Structures of the Eye Lacrimal apparatus (lacrimal glands, lacrimal canals, nasolacrimal duct) Produces tears to keep eye moist Fights infection (enzymes) Drains through the nasal cavity

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

Structure of the Eye The wall consists of three layers of tissue or tunics Fibrous Tunic - outer layer Vascular Tunic - middle layer Nervous Tunic - inner layer

Fibrous Tunic Outermost layer Sclera forms most of the fibrous tunic the white of the eye

Fibrous layer of the Eye (continued) Cornea- anterior transparent portion of the eye Refracts light Bulges outward due to aqueous humor (anterior cavity) Most common transplant

Vascular Tunic Blood supply Choroid-thin posterior portion Thin dark brown membrane 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 Viterous Humor (fluid body) 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) Contains photoreceptors (rods and cones) and neurons Optic Nerve Transmits images to occipital lobe

Rods and Cones--neurons in retina Elongated dendrites Black and white and night vision Cones Dendrites with tapered ends Color sensitive Sharpens vision

Other Structures of the Nervous Tunic Optic Disc - blind spot where the optic nerve exits the retina Fovea Centralis - an area of the retina containing many cone cells the area of sharpest vision

Visual Pathway

Hearing Dependent upon special organs within the ear The ears are also associated with maintaining equilibrium and balance Three Regions of the Ear Outer Ear Middle Ear Inner Ear

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 Amplify sound wave and pass it to the oval window 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 Transmits movement to the “oval window” Opens to the cochlea Causes fluid to stimulate receptors for hearing

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

Cochlea Resembles a snail shell Contains the Organs of Corti for hearing Contains perilymph and endolymph (fluids) Receptor cells that move in response to endolymph motion 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 enter auditory canal 2. Eardrum vibrates 3. Ossicles vibrate and magnify sound 4. Oval window vibrates causes fluids to vibrate 5. Fluids movement 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 at right angles 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

DISEASES AND DISORDERS OF THE SPECIAL SENSES

Presbyopia Lens looses ability to change shape Results in farsightedness 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”

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

Glaucoma Aqueous humor build up puts pressure on the retina resulting in atrophy of optic nerve Can damage retina if not treated Eye drops Surgical incision

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

Deafness 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

Middle Ear Infection (Otitis Media) Usually involves the eardrum being infected by bacteria or virus Bacterial treated with antibiotics Common in children

Tinnitis Ringing in the ears 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

DISEASES AND DISORDERS OF THE SPECIAL SENSES

Presbyopia Lens loses 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

Astigmatisim Caused by corneal malformation Creates a distorted image on the retina

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

Cataract

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

Conjunctivitis

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

Macular Degeneration Occurs in section of the retina called the macula damaged causing a dark area that progresses over time

Macular Degeneration

Strabismus Caused by weak eye muscles Sometimes referred to as crossed eyes Can be surgically corrected or by patching the good eye to encourage other eye to work properly

Deafness Two types: Conductive: caused by blockages in the auditory canal Can be blocked with ear wax Can be caused by middle ear infections or Eardrum damage

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

Cochlear Implants

Middle Ear Infection Usually involves the eardrum being infected by bacteria or virus Bacterial treated with antibiotics Common in children Called Otis Media

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

Vertigo Caused by otoliths improperly aligning with membranes May also be caused by middle ear infection moving into inner ear Causes dizziness and nausea

THE END!