Chapter 12 Somatic and Special Senses Sensory Receptors 12-2

Receptor Types Chemoreceptors Pain receptors Thermoreceptors Mechanoreceptors Photoreceptors 12-3

Sensory Impulses stimulation of receptor causes change in its membrane if receptor is part of a neuron, the membrane potential may generate an action potential peripheral nerves transmit impulses to CNS Sensation 12-4

Sensory Adaptation stronger stimulus required to activate receptors smell receptors undergo sensory adaptation 12-1

Somatic Senses senses associated with skin, muscles, joints, and viscera three groups exteroceptive senses – proprioceptive senses – senses associated with changes in muscles and tendons visceroceptive senses – 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 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 above unresponsive to temperature above Cold receptors sensitive to temperature between and Pain receptors respond to temperatures below oC respond to temperatures above oC 12-9

Sense of Pain free nerve endings widely distributed nervous tissue of brain lacks pain receptors Visceral Pain not well localized 12-10

Referred Pain 12-11

Pain Nerve Fibers Chronic pain fibers Acute pain fibers conduct impulses more slowly Acute pain fibers conduct impulses rapidly 12-12

Regulation of Pain Impulses Thalamus allows person to be aware of pain Pain Inhibiting Substances enkephalins serotonin endorphins Cerebral Cortex judges intensity of pain locates source or pain produces motor response to pain produces emotions to pain 12-13

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

Special Senses sensory receptors are within large, complex sensory organs in the head smell in taste in hearing and equilibrium in sight in 12-16

Smell Olfactory Receptors chemoreceptors Olfactory Organs contain olfactory receptors and supporting epithelial cells 12-17

Olfactory Receptors Sense of Smell.mov 12-18

Taste Taste Buds organs of taste Taste Receptors chemoreceptors taste cells – taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells 12-20

Taste Receptors Sense of Taiste.mov 12-21

Taste Sensations Four Primary Taste Sensations sweet – sour – salty – bitter – Spicy foods activate pain receptors 12-22

Hearing Ear – organ of hearing 3 Sections 12-24

External Ear auricle external auditory meatus tympanic membrane lined with ceruminous glands terminates with tympanic membrane tympanic membrane 12-25

Middle Ear tympanic cavity air-filled space in temporal bone auditory ossicles malleus, incus, and stapes oval window opening in wall of tympanic cavity 12-26

Auditory Tube eustachian tube usually closed by valve-like flaps in throat Sense of Hearing.mov 12-27

Inner Ear complex system of labyrinths osseous labyrinth bony canal in temporal bone 12-28

Inner Ear 3 Parts of Labyrinths cochlea semicircular canals vestibule 12-29

Equilibrium Dynamic Equilibrium Static Equilibrium semicircular canals vestibule 12-36

Macula responds to changes in head position bending of hairs results in generation of nerve impulse Sense of Equilibrium.mov Sense of Rotation.mov 12-38

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

Lacrimal Apparatus lacrimal gland lateral to eye canaliculi lacrimal sac collects from canaliculi nasolacrimal duct collects from lacrimal sac 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 down and laterally Inferior oblique rotates eye up 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 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

Ciliary Body forms internal ring around front of eye ciliary processes – radiating folds ciliary muscles – contract and relax to move lens 12-51

Iris composed of connective tissue and smooth muscle dim light stimulates radial muscles and pupil dilates 12-53

Aqueous Humor fluid in anterior cavity of eye secreted by epithelium on inner surface of the ciliary body provides nutrients maintains shape of anterior portion of eye leaves cavity through canal of Schlemm 12-54

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 fovea centralis – center of macula lutea; produces sharpest vision optic disc – blind spot; contains no visual receptors vitreous humor – thick gel that holds retina flat against choroid coat 12-55

Light Refraction Refraction bending of light occurs when light waves pass at an oblique angle into mediums of different densities 12-57

Types of Lenses Convex Concave 12-58

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 contain light sensitive pigment called rhodopsin produce colorless vision produce outlines of objects Cones short, blunt projections contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe 12-60

Stereoscopic Vision results from formation of two slightly different retinal images 12-63

Visual Pathway Sense of Sight.mov 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 convex lens corrects farsightedness 12-66