Chapter 12Somatic and Special Senses

Receptor Types

Chemoreceptors• respond to changes in chemical concentrations

Pain receptors• respond to tissue damage

Thermoreceptors• respond to changes in temperature

Mechanoreceptors• respond to mechanical forces

Photoreceptors• respond to light

Sensory Adaptation

• adjustment of sensory receptors from continuous stimulation• stronger stimulus required to activate receptors• smell receptors undergo sensory adaptation

Touch and Pressure Senses

Free nerve endings• common in epithelial tissues• detect touch and pressure

Touch and Pressure Senses

Meissner’s corpuscles

• abundant in hairless portions of skin

• detect light touch

Touch and Pressure Senses

Pacinian corpuscles

• common in deeper subcutaneous tissues, tendons, and ligaments• detect heavy pressure

Temperature Senses

Warm receptors• sensitive to temperatures above 25oC (77o F)• unresponsive to temperature above 45oC (113oF)

Cold receptors• sensitive to temperature between 10oC (50oF) and 20oC (68oF)

Pain receptors• respond to temperatures below 10oC• respond to temperatures above 45oC

Sense of Pain

• free nerve endings • widely distributed • nervous tissue of brain lacks pain receptors• stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature

•Phantom Pain

Referred Pain

• may occur due to sensory impulses from two regions following a common nerve pathway to brain

Special Senses

• smell in olfactory organs•# 1

• taste in taste buds•# 7,9 &10

• hearing and equilibrium in ears•# 8

• sight in eyes•# 2 (vision)•# 3,4 & 6 (movement)

Olfactory Receptors

Smell

Olfactory Receptors• chemoreceptors• respond to chemicals dissolved in liquids

Olfactory Organs• contain olfactory receptors and supporting epithelial cells• cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

Taste

Taste Buds• organs of taste• located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx

Taste Receptors• chemoreceptors• taste cells – modified epithelial cells that function as receptors• taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells

Taste Receptors

Cranial nerves 7, 9 & 10

Taste Sensations

Four Primary Taste Sensations• sweet – stimulated by carbohydrates• sour – stimulated by acids• salty – stimulated by salts• bitter – stimulated by many organic compound

Spicy foods activate pain receptors

Hearing

Ear – organ of hearing

3 Sections• External• Middle• Inner

External Ear

• pinna• collects sounds waves

• outer ear canal• aka ear canal• carries sound to tympanic membrane

• eardrum • aka ear tympanic membrane• vibrates in response to sound waves

Middle Ear

• auditory ossicles• vibrate in response to tympanic membrane• malleus, incus, and stapes• aka hammer, anvil & stirrup

• oval window • stapes (stirrup) vibrates against it to move fluids in inner ear

Auditory Tube

• eustachian tube • connects middle ear to throat• helps maintain equal pressure on both sides of tympanic membrane• usually closed by valve-like flaps in throat

Inner Ear

• complex system of labyrinths• osseous labyrinth

• bony canal in temporal bone• filled with perilymph

• membranous labyrinth• tube within osseous labyrinth• filled with endolymph

Inner Ear

Parts of Inner Ear• cochlea

• functions in hearing• snail-shaped• Have hearing receptor cells (hair cells) that bend with different frequencies to generate a nerve impulse

• semicircular canals• functions in equilibrium• fluid-filled

Semicircular Canals

• balance •three canals at right angles• rapid turns of head or body stimulate hair cells

Sight

Visual Accessory Organs• eyelids• lacrimal apparatus• extrinsic eye muscles

Eyelid

• composed of four layers• skin• muscle • connective tissue• conjunctiva

• orbicularis oculi - closes• levator palpebrae superioris – opens• tarsal glands – secrete oil onto eyelashes; so lids don’t stick• conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball

Lacrimal Apparatus

• lacrimal gland• lateral to eye• secretes tears

• canaliculi• collect tears

• lacrimal sac• collects from canaliculi

• nasolacrimal duct• collects from lacrimal sac• empties tears into nasal cavity

Extrinsic Eye Muscles

Superior rectus• rotates eye up and medially

Inferior rectus• rotates eye down and medially

Medial rectus• rotates eye medially

Extrinsic Eye Muscles

Lateral rectus• rotates eye laterally• *Abducens Nerve VI

Superior oblique• rotates eye down and laterally• * Trochlear Nerve IV

Inferior oblique• rotates eye up and laterally

Outer Eye

Cornea• anterior portion• transparent• light transmission• light refraction

Sclera• posterior portion• white of eye• protection

Middle Tunic

Ciliary body• holds lens• moves lens for focusing

Choroid coat• provides blood supply• pigments absorb extra light

Lens

• transparent• biconvex• lies behind iris• elastic!!!• held in place by suspensory ligaments

Accommodation• changing of lens shape to view objects

Iris

• composed of connective tissue and smooth muscle• pupil is hole in iris• dim light stimulates radial muscles and pupil dilates• bright light stimulates circular muscles and pupil constricts

Anterior Portion of Eye

• filled with aqueous humor• maintains shape of anterior portion of eye

Inner Eye

• retina•contains photoreceptors•continuous with optic nerve•rods provide vision in dim light•cones provide color vision

• optic disc – blind spot; contains no visual receptors; index card trick

• vitreous humor – thick gel that holds retina flat against the back of the eye; gives eye round shape

Layers of Retina

Focusing On Retina• as light enters eye, it is refracted by

• convex surface of cornea• convex surface of lens

• image focused on retina is upside down and reversed from left to right

Clinical Application

Refraction Disorders

Visual Pathway

Snellen Chart

• What does 20/40 or 20/100 mean?

Astigmatism

Due to irregular shaped cornea

Or

Irregular curvature of the lens

Colorblindness

• Sex-linked trait; usually in males

• Varying degrees of colorblindness

• Tests

Corneal transplants

• Cornea disease is the leading cause of blindness

• Restore sight with a transplant

• Central 2/3 of the cornea are replaced

• Heals well; usually not rejected