Chapter Somatic and Special Senses

Chapter 12 Somatic and Special Senses Sensory Receptors specialized cells or multicellular structures that collect information stimulate neurons to send impulses along sensory fibers to the brain 12-2

Receptor Types Chemoreceptors respond to changes in chemical concentrations Nociceptors (Pain receptors) respond to tissue damage Thermoreceptors respond to changes in temperature Mechanoreceptors respond to mechanical forces Photoreceptors respond to light 12-3

Sensation and Adaptation Sensation feeling that occurs when brain interprets sensory impulse Sensory Adaptation adjustment of sensory receptors from continuous stimulation stronger stimulus required to activate receptors smell and temperature receptors undergo sensory adaptation 12-1

Somatic Senses senses associated with skin, muscles, joints, and viscera three groups exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain proprioceptive senses – senses associated with changes in muscles and tendons visceroceptive senses – senses associated with changes in viscera 12-6

Touch and Pressure Senses Free nerve endings common in epithelial tissues detect touch and pressure Meissner’s corpuscles abundant in hairless portions of skin detect light touch detect motion on skin detect texture Pacinian corpuscles common in deeper subcutaneous tissues, tendons, and ligaments detect heavy pressure 12-7

Touch and Pressure Senses 12-8

Temperature Senses Warm receptors sensitive to temperatures between 25 o C (77 o F) and 45 o C (113 o F) Cold receptors sensitive to temperature between 10 o C (50 o F) and 20 o C (68 o F) In between – brain interprets impulses from both Pain receptors respond to temperatures below 10 o C (50 F) respond to temperatures above 45 o C (113 F) 12-9

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 do not adapt Visceral Pain may exhibit referred pain not well localized 12-10

Referred Pain may occur due to sensory impulses from two regions following a common nerve pathway to brain 12-11

Stretch Receptors proprioceptors send information to CNS concerning lengths and tensions of muscles involved in many reflexes 2 main kinds of stretch receptors muscle spindles – in skeletal muscles Golgi tendon organs – in tendons 12-14

Stretch Receptors 12-15

Special Senses sensory receptors are within large, complex sensory organs in the head smell in olfactory organs taste in taste buds hearing and equilibrium in ears (hair cells) sight in eyes (rods and cones) 12-16

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 small patch of tissue (12 million cells) on the roof of nasal cavity smells start as a gas, but must be dissolved in watery fluid that surrounds the cilia of the receptors (each receptor has 10-12) to be detected 12-17

Olfactory Receptors 12-18

Olfactory Nerve Pathways Once olfactory receptors are stimulated, nerve impulses travel through olfactory nerves to olfactory bulbs to olfactory tracts to limbic system (for emotions) and olfactory cortex (for interpretation) 12-19

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 12-20

Taste Receptors 12-21

Taste Sensations Five Primary Taste Sensations sweet – stimulated by carbohydrates most plentiful near tip sour – stimulated by acids most plentiful at margins salty – stimulated by salts most plentiful at tip and upper front bitter – stimulated by many organic compound most plentiful at back may be protective – spit out umami – stimulated by amino acids (meat, cheese) Spicy foods activate pain receptors 12-22

What does food REALLY Taste like? Taste is affected by: Smell Temperature Texture Psychological impacts such as color 12-22

Taste Nerve Pathways Sensory impulses from taste receptors travel along cranial nerves to medulla oblongata to thalamus to gustatory cortex (for interpretation) 12-23

Hearing Ear – organ of hearing 3 Sections External Middle Inner 12-24

External Ear auricle collects sounds waves external auditory meatus lined with ceruminous glands carries sound to tympanic membrane terminates with tympanic membrane tympanic membrane vibrates in response to sound waves 12-25

Middle Ear tympanic cavity air-filled space in temporal bone auditory ossicles (bones) vibrate in response to tympanic membrane malleus, incus, and stapes oval window opening in wall of tympanic cavity (cochlea) stapes vibrates against it to move fluids in inner ear 12-26

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 12-27

Inner Ear complex system of labyrinths osseous (bony) labyrinth bony canal in temporal bone filled with perilymph membranous labyrinth tube within osseous labyrinth filled with endolymph 12-28

Inner Ear 3 Parts of Labyrinths cochlea functions in hearing semicircular canals functions in equilibrium vestibule functions in equilibrium 12-29

Cochlea Scala vestibuli upper compartment Scala tympani lower compartment Cochlear duct ** portion of membranous labyrinth in cochlea contains Organ of Corti 12-30

Organ of Corti group of hearing receptor cells (hair cells) on upper surface of basilar membrane different frequencies of vibration move different parts of basilar membrane particular sound frequencies cause hairs of receptor cells to bend nerve impulse generated 12-32

Organ of Corti 12-33

Auditory Nerve Pathways 12-34

Summary of the Generation of Sensory Impulses from the Ear 12-35

Equilibrium Static Equilibrium vestibule sense position of head when body is not moving Dynamic Equilibrium semicircular canals sense rotation and movement of head and body 12-36

Vestibule Macula **(sensory organ) hair cells of utricle and saccule sense static balance 12-37

Macula responds to changes in head position bending of hairs results in generation of nerve impulse 12-38

Semicircular Canals three canals at right angles ampulla swelling of membranous labyrinth crista ampullaris (in ampulla) sensory organ of dynamic balance hair cells and supporting cells rapid turns of head or body stimulate hair cells 12-39

Crista Ampullaris 12-40

Sight Visual Accessory Organs eyelids lacrimal apparatus extrinsic eye muscles 12-41

Eyelid palpebra (eyelid) composed of four layers skin muscle connective tissue conjunctiva orbicularis oculi - closes levator palpebrae superioris – opens tarsal glands – secrete oil onto eyelashes conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball 12-42

Lacrimal Apparatus lacrimal gland lateral to eye secretes tears canaliculi (superior, inferior) collect tears lacrimal sac collects from canaliculi nasolacrimal duct collects from lacrimal sac empties tears into nasal cavity 12-43

Extrinsic Eye Muscles Superior rectus rotates eye up and medially Inferior rectus rotates eye down and medially Medial rectus rotates eye medially 12-44

Extrinsic Eye Muscles Lateral rectus rotates eye laterally Superior oblique rotates eye up and laterally Inferior oblique rotates eye down and laterally 12-45

Structure of the Eye hollow spherical wall has 3 layers (outer) fibrous tunic (middle) vascular tunic (inner) nervous tunic 12-46

Outer Tunic Cornea anterior portion transparent light transmission light refraction Sclera posterior portion opaque protection 12-47

Middle Tunic Iris anterior portion pigmented controls light intensity Ciliary body (muscle) anterior portion pigmented holds lens moves lens for focusing Choroid coat provides blood supply pigments absorb extra light 12-48

Anterior Portion of Eye filled with aqueous humor 12-49

Lens transparent biconvex lies behind iris largely composed of lens fibers elastic held in place by suspensory ligaments of ciliary body 12-50

Accommodation changing of lens shape to view objects 12-52

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 12-53

Inner Tunic retina contains visual receptors continuous with optic nerve ends just behind margin of the ciliary body composed of several layers macula lutea – yellowish spot in retina, center, 1 mm fovea centralis – center of macula lutea; produces sharpest vision, where lens tries to focus light** optic disc – blind spot; contains no visual receptors vitreous humor – thick gel that holds retina flat against choroid coat 12-55

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 12-59

Visual Receptors Rods long, thin projections contain light sensitive pigment called rhodopsin hundred times more sensitive to light than cones provide vision in dim light produce colorless vision produce outlines of objects Cones short, blunt projections contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe provide vision in bright light produce sharp images produce color vision 12-60

Rods and Cones 12-61

Visual Pigments Rhodopsin light-sensitive pigment in rods decomposes in presence of light triggers a complex series of reactions that initiate nerve impulses impulses travel along optic nerve Pigments on Cones each set contains different light- sensitive pigment each set is sensitive to different wavelengths color perceived depends on which sets of cones are stimulated erythrolabe – responds to red chlorolabe – responds to green cyanolabe – responds to blue 12-62

Stereoscopic Vision provides perception of distance and depth results from formation of two slightly different retinal images 12-63

Visual Pathway 12-64

Life-Span Changes Age related hearing loss due to damage of hair cells in organ of Corti degeneration of nerve pathways to the brain tinnitus Age-related visual problems include dry eyes floaters (crystals in vitreous humor) loss of elasticity of lens glaucoma cataracts macular degeneration 12-65

Clinical Application Refraction Disorders concave lens corrects nearsightedness (myopia) when eye is too long or lens focuses light in front of retina convex lens corrects farsightedness (presbyopia or hyperopia) when eye is too short or lens focuses light behind retina 12-66