Chapter 11 The Senses

Sense Organs, and the Eye Lesson 11.1 Sense Organs, and the Eye 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. Describe the structure of the eye and the functions of its components. Name and describe the major visual disorders.

General Sense Organs Often exist as individual cells or receptor units Widely distributed throughout the body Different from special sense organs—groupings of receptors within highly complex organs

Special Sense Organs Large and complex organs Localized grouping of specialized receptors

Classification of Sense Organs Classification by presence or absence of covering capsule Encapsulated Unencapsulated (“free” or “naked”)

Classification of Sense Organs Classification by type of stimuli required to activate receptors 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 a Stimulus into a Sensation All sense organs have common functional characteristics All are able to detect a particular stimulus A stimulus is converted into a nerve impulse A nerve impulse is perceived as a sensation in the CNS

General Sense Organs Distribution is widespread; single-cell receptors are common Skin receptors Free nerve endings (several types)—pain, discriminative touch, tickle, and temperature Tactile (Meissner) corpuscle—fine touch and vibration Bulbous (Ruffini) corpuscle—touch and pressure Lamellar (Pacini) corpuscle—pressure and vibration Bulboid (Krause) corpuscle—touch

General Sense Receptors

General Sense Organs Muscle receptors Deep receptors Golgi tendon receptor—proprioception Muscle spindle—proprioception Deep receptors Stretch (pressure) receptors in hollow organs Chemical receptors—detect pH, carbon dioxide, other chemicals Third-degree burns can completely destroy general sense receptors throughout affected area Temporary impairment of general sense receptors occurs when blood flow to them is slowed

External Eye Structures

The Eye Layers of eyeball Sclera—tough outer coat; “white” of eye; cornea is transparent part of sclera over iris Choroid—pigmented vascular layer prevents scattering of light Front part of this layer made of ciliary muscle and iris, the colored part of the eye The pupil is the hole in the center of the iris Retina—innermost layer of the eye; contains rods (monochrome receptors for night vision) and cones (color receptors for day vision)

Components of the Eye

The Eye and Vision Function of the iris. Contraction of iris muscle dilates or constricts pupil 14

The Eye & Eye Fluids Conjunctiva—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 Aqueous humor—in the anterior cavity in front of the lens Vitreous humor—in the posterior cavity behind the lens

Cells of the Retina

The Eye and Vision structures Fovea- a small depression in the macula near the center of the retina The site of acute image formation and color vision Optic disc- where the optic nerve muscles exit the eye 17

Retinal (Fundus) of the Left Eye

Shaken Baby Syndrome Courtesy Stephen Ludwig, MD. Children’s Hospital of Philadelphia. In Zitelli, Davis: Atlas of pediatric physical diagnosis, ed 6, Mosby, 2012, St Louis.

The Eye and Vision (cont.) Pathway of Light Rays and Refraction Transparent parts of the eye that refract light Cornea Aqueous humor Crystalline lens Vitreous body

Visual Pathway Innermost layer of retina contains rods and cones Impulse travels from the rods and cones through the bipolar and ganglionic layers of retina

Visual Pathway 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

Visual Pathway

Visual Disorders Refraction disorders Myopia (nearsightedness) is often caused by elongation of the eyeball Hyperopia (farsightedness) is often caused by a shortened eyeball Astigmatism is distortion caused by an irregularity of the cornea or lens Cataracts are cloudy spots in the eye's lens

Refraction

Refraction Disorders Conjunctivitis (inflammation of the conjunctiva) can interfere with refraction Trachoma—chronic chlamydial infection Acute bacterial conjunctivitis—highly contagious infection that produces a discharge of mucous pus Conjunctivitis can be caused by allergies Strabismus—improper alignment of eyes Eyes can converge (cross) or diverge If not corrected, can cause blindness

Visual Disorders Sty Cataract From Swartz MH: Textbook of physical diagnosis, ed 6, Philadelphia, 2010, Saunders. From Palay DA, Krachmer JH: Ophthalmology for the primary care physician, St Louis, 1997, Mosby.

Acute Bacterial Conjunctivitis From Newell FW: Ophthalmology: principles and concepts, ed 8, St Louis, 1996, Mosby.

Muscles of the Eye Adjust eye so the retina receives clear image Extrinsic muscles Outer surface of eyeball Voluntary Control convergence for three-dimensional vision

Extrinsic muscles of the eye 30

Strabismus Seidel H et al: Mosby’s guide to physical examination, ed 3, St Louis, 2002, Mosby.

The Eye and Vision (cont.) Nerve Supply to the Eye Sensory Optic nerve (CN II) Ophthalmic branch of trigeminal nerve (CN V) Motor Oculomotor nerve (CN III) Trochlear (CN IV) Abducens (CN VI)

Disorders of the Retina Retinal detachment can be a complication of aging, eye tumors, or head trauma Diabetic retinopathy—damage to retina from hemorrhages and growth of abnormal vessels associated with diabetes mellitus Glaucoma—increased intraocular pressure decreases blood flow in retina and thus causes retinal degeneration Age-related macular degeneration (AMD) —progressive degeneration of the central part of the retina

Retinal detachment 34

Retinal disorders. 35

Disorders of the Retina Nyctalopia (night blindness) or the inability to see in dim light is caused by retinal degeneration or lack of vitamin A Color blindness—most forms inherited Red-green color blindness is an X-linked genetic condition involving the inability to perceive certain colors It is caused by an abnormality in the cones’ photopigments

Color Vision Screening Figures From Ishihara’s tests for colour deficiency, Tokyo, Japan, 1973, Kanehara Trading Co, Copyright Isshinkai Foundation.

Disorders of the Visual Pathway Scotoma is the loss of only the central visual field when only certain nerve pathways are damaged Cerebrovascular accidents (CVAs) can damage visual processing centers; example is acquired cortical color blindness

The Ear, and Taste and Smell Receptors Lesson 11.2 The Ear, and Taste and Smell Receptors Discuss the anatomy of the ear and its sensory function in hearing and equilibrium. Name and describe the major forms of hearing impairment. Discuss the chemical receptors and their functions.

The Ear Sense organ of hearing and also of equilibrium and balance Divisions of the ear: External ear Middle ear Inner (internal) ear

External Ear Auricle (pinna)—appendage on side of head External acoustic canal Curving tube 2.5 cm (1 inch) in length Contains ceruminous glands Ends at the tympanic membrane

Examining the Ear

Middle Ear Epithelium-lined cavity that houses the ear ossicles—malleus, incus, and stapes Ends in the oval window The auditory (eustachian) tube connects the middle ear to the throat Inflammation called otitis media

Acute Otitis Media

The Ear

Inner Ear Bony labyrinth filled with perilymph Subdivided into the vestibule, semicircular canals, and cochlea Membranous labyrinth filled with endolymph The receptors for balance in the semicircular canals are called cristae ampullaris Sensory hair cells on the organ of Corti (spiral organ) respond when bent by the movement of surrounding endolymph set in motion by sound waves

The Inner Ear

Effect of Sound Waves on Cochlear Structures

Effect of Sound Waves on Cochlear Structures 49

Equilibrium Ciliated equilibrium sensory receptors (mechanoreceptors) are located in vestibule and semicircular canals. Types of receptors Maculae Cristae Nerve supply via vestibular nerve

The Ear Action of the vestibular equilibrium receptors (maculae). 51

The Ear Action of the equilibrium receptors (cristae) in the semicircular canals. 52

Hearing Disorders Conduction impairments Can be caused by blockage of the external or middle ear (for example, by cerumen and tumors) Otosclerosis—inherited bone disorder involving irregularity of the stapes; it first appears as tinnitus (ringing) then progresses to hearing loss Otitis—ear inflammation caused by infection; can produce swelling and fluids that block sound conduction

Nerve Impairment Equilibrium Disorders Presbycusis—progressive nerve deafness associated with aging Progressive nerve deafness can also result from chronic exposure to loud noise Equilibrium Disorders Often characterized by vertigo, disorientation, falling, dizziness, or lightheadedness Some are caused by infection or inflammation of inner ear Ménière disease—chronic inner ear disorder characterized by tinnitus, nerve deafness, and vertigo

The Taste Receptors Receptors are chemoreceptors called taste buds Cranial nerves VII and IX carry gustatory impulses Only four kinds of taste sensations Sweet Sour Bitter Salty Gustatory and olfactory senses work together

The Tongue

The Smell Receptors Receptors for fibers of olfactory (cranial nerve I) 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

Olfactory Structures

Integration of Senses Senses are all perceived by the brain All incoming signals are integrated with other sensory signals and even memories to produce our perceptions Severe nasal congestion can interfere with stimulation of olfactory receptors, preventing foods from having full flavor Advancing age often brings a structural degeneration that results in reduced function