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The Special Senses CHAPTER 15. Unit Objectives  Classify Sense organs as special or general and explain the basic differences between the two groups.

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Presentation on theme: "The Special Senses CHAPTER 15. Unit Objectives  Classify Sense organs as special or general and explain the basic differences between the two groups."— Presentation transcript:

1 The Special Senses CHAPTER 15

2 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.

3 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

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

5 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

6 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)

7 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

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

9 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)

10 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

11 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 )

12 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

13 humor Suspensory ligaments Optic Disk

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

15 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

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

17 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

18 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

19 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

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

21 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

22 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


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