The Special Senses Chapter 15

Unit Objectives Classify Sense organs as special or general and explain the basic differences between the two groups. Discuss how a stimulus is converted into a sensation. Discuss the general sense organs and their functions. List the major senses. Describe the structure of the eye and the functions of its components. Discuss the anatomy of the ear and its sensory function in hearing and equilibrium. Discuss the chemical receptors and their functions.

Classification of Sense Organs General Sense Organs: Exist as individual cells or receptor units Widely distributed throughout the body Special Sense Organs Large & Complex Localized grouping of specialized receptors Presence or absence of covering Encapsulated Unencapsulated

General Sense Organs Free Nerve Endings Location: Skin, Epithelial & mucosa General Senses: Pain, crude touch, temperature, itch, tickle

General Sense Organs Encapsulated Nerve Endings Meissner’s Corpuscles Location: Skin, fingertips & lips General Senses: Fine touch and low-frequency vibration Ruffini’s Corpuscles Location: Skin & subcutaneous tissue of fingers Touch & Pressure Pacinian Corpuscles Around joints, in mammary glands & external genitals of both sexes General Senses: pressure & high frequency vibration

General Sense Organs Encapsulated Nerve Endings Cont Krause’s end-bulbs Location : Skin dermal; mucosa of lips, eyelids, & external genitals General Sense: Touch & cold Golgi Tendon Receptors Location: Near Junction of Tendons & Muscles General Sense: Muscle tension (proprioception: individual perception) Muscle spindles Skeletal muscles General Sense: Muscle length (proprioception)

Special Sense Organs Eye Specific Receptor: Rods & Cones Type of Receptor: Photoreceptor Sense: Vision Ear Specific Receptor: Organ of Corti & Cristae ampullares Type of Receptor: Mechanoreceptor Sense: Hearing & Balance

Special Sense Organs Nose Taste Buds Specific Receptor: Olfactory cells Type of Receptor: Chemoreceptor Sense: Smell Taste Buds Specific Receptor: Gustatory cells Sense: Taste

Type of Stimuli Defined Photoreceptors (light) Chemoreceptors (chemicals) Pain receptors (injury) Thermoreceptors (temperature change) Mechanoreceptors (movement or deforming of capsule) Proprioceptors (position of body parts or changes in muscle length or tension)

Converting Stimulus to Sensation All sense organs have 3 common functional characteristics: Can detect a particular stimulus Stimulus is converted into a nerve impulse Nerve impulses is perceived as a sensation

The Eye Layers of eyeball Sclera: tough outer coat; white of eye; cornea is the transparent part of sclera over iris Choroid: pigmented vascular layer prevents scattering of light; front part of this layer is made of ciliary muscle & iris, the colored part of the eye; the pupil is the hole in the center of the iris; contraction of iris muscle dilates or constricts pupil Retina: inner most layer of the eye; contains rods (receptors for night vision) & cones (reception for day & color vision)

The Eye Conjuctiva: mucous membrane covering the front surface of the sclera and lining the eyelid Lens: transparent body behind the pupil; focuses light rays on the retina

Suspensory ligaments 2 1 9 3 10 4 8 11 humor 5 6 humor Optic Disk 12 7

Eye Fluids Aqueous humor: in the anterior chamber in front of the lens Vitreous humor: in the posterior chamber behind the lens

Visual pathway Innermost layer of retina contains rods & cones Impulse travels from the rods and cones through the layers of the retina Nerve impulse leaves the eye through the optic nerve; the point of exit is free of receptors and is therefore called a blind spot Visual interpretation occurs in the visual cortex of the cerebrum

The Ear Functions in hearing, equilibrium, & balance Receptors for hearing & equilibrium: mechanoreceptors

Divisions of Ear External Auricle (pinna) External auditory canal Curves approx. 2.5 cm in length Contains ceruminous glands (produce a waxy substance) Ends at tympanic membrane

Divisions of Ear Middle Ear Ear ossicles: malleus, incus, & stapes Ends in the oval window Eustacian tube connects the middle ear to the throat Inflammation called otitis media

Divisions of Ear Inner Ear Bony labyrinth filled with perilymph Subdivided into the vestibule, semicircular canals, and cochlea Membranous labyrinth filled with endolymph Receptors for balance in the semi-circular canals: cristae ampullairs Specialized hair cells on the organ of Corti respond when bent by the movement of surrounding endolymph set in motion by sound waves

Semi-Circular Canals Vestibulocochlear nerve Vestibule Malleus Incus Tympanic Membrane Cochlea Oval Window Pinna External Auditory Meatus Eustachian Tube Stapes

Taste Receptors Chemoreceptors called taste buds Cranial nerves carry gustatory (respond to chemicals dissolved in saliva) impulses 4 primary taste sensations Sweet Sour Bitter Salty Gustatory & Olfactory senses work together

Smell Receptors Receptors for fibers of olfactory/cranial nerve lie in olfactory mucosa of nasal cavity Olfactory receptors are extremely sensitive but easily fatigued Odor-causing chemicals initiate a nervous signal that is interpreted as a specific odor by the brain