1. Chapter 12 The Senses

2. 2 Introduction General senses Receptors are widely distributed throughout the body Skin, various organs and joints Touch, pain, temperature, pressure, ect. Special senses Specialized receptors confined to structures in the head Vision, Taste, Smell, Hearing

3. 3 Receptors, Sensation, and Perception Sensory receptors Specialized cells or multicellular structures that collect information from the environment Stimulate neurons to send impulses along sensory fibers to the brain Sensation A feeling that occurs when brain becomes aware of sensory impulse Perception A person’s view of the stimulus; the way the brain interprets the information

5. 5 Receptor Types Chemoreceptors Respond to changes in chemical concentrations (smell, taste, pH) Pain receptors (nociceptors) Respond to tissue damage Thermoreceptors Respond to changes in temperature Mechanoreceptors Respond to mechanical forces Stretch receptors, proprioceptors, baroreceptors Photoreceptors Respond to light

6. Projection Process in which the brain projects the sensation back to the apparent source It allows a person to pinpoint the region of stimulation Sensations and Perception

7. Ability to ignore unimportant stimuli Involves a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the cerebral cortex (central adaptation) Sensory impulses become less frequent and may cease Stronger stimulus is required to trigger impulses Sensory Adaptation

8. 8 12.3: General Senses Senses associated with skin, muscles, joints and viscera Three (3) groups: Exteroceptive senses (exteroceptors) Senses associated with body surface such as touch, pressure, temperature, and pain Visceroceptive senses (interoceptors) Senses associated with changes in the viscera such as blood pressure stretching blood vessels and ingestion of a meal Proprioceptive senses Senses associated with changes in muscles and tendons such as at joints

9. 9 Touch and Pressure Senses Free nerve endings Common in epithelial tissues Simplest receptors Sense itching Tactile (Meissner’s) corpuscles Abundant in hairless portions of skin and lips Detect fine touch; distinguish between two points on the skin Lamellated (Pacinian) corpuscles Common in deeper subcutaneous tissues, tendons and ligaments Detect heavy pressure and vibrations

10. 10 Touch and Pressure Receptors Epidermis Dermis (a) (b) (c) Section of skin Free nerve endings Epithelial cells Sensory nerve fiber Epithelial cells Tactile (Meissner’s) corpuscle (touch receptor) Sensory nerve fiber Lamellated (Pacinian) corpuscle (pressure receptor) Connective tissue cells Sensory nerve fiber Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b, c: © Ed Reschke

11. 11 Temperature Senses Warm receptors Sensitive to temperatures above 25 o C (77 o F) Unresponsive to temperature above 45 o C (113 o F) Cold receptors Sensitive to temperatures between 10 o C (50 o F) and 20 o C (68 o F) Pain receptors Respond to temperatures below 10 o C Respond to temperatures above 45 o C

12. 12 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 Adapt very little, if at all

13. 13 Visceral Pain Pain receptors are the only receptors in viscera whose stimulation produces sensations Pain receptors respond differently to stimulation Pain receptors are not well localized Pain receptors may feel as if coming from some other part of the body Known as referred pain…

14. 14 Referred Pain May occur due to sensory impulses from two regions following a common nerve pathway to brain Appendix Ureter Lung and diaphragm Heart Stomach Pancreas Colon Kidney Urinary bladder Liver and gallbladder Small intestine Ovary (female) Liver and gallbladder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

15. 15 Pain Nerve Pathways Acute pain fibers A-delta fibers Thin, myelinated Conduct impulses rapidly Associated with sharp pain Well localized Chronic pain fibers C fibers Thin, unmyelinated Conduct impulses more slowly Associated with dull, aching pain Difficult to pinpoint

16. 16 Regulation of Pain Impulses Thalamus Allows person to be aware of pain Cerebral cortex Judges intensity of pain Locates source of pain Produces emotional and motor responses to pain Pain inhibiting substances: Enkephalins Serotonin Endorphins

17. 17 Proprioception Mechanoreceptors Send information to spinal cord and CNS about body position and length, and tension of muscles Main kinds of proprioceptors: Pacinian corpuscles – in joints Muscle spindles – in skeletal muscles* Golgi tendon organs – in tendons* *considered to be stretch receptors

18. 18 Stretch Receptors (a) Muscle spindle Skeletal muscle fiber Golgi tendon organ Tendon (b) Sensory nerve fiber Sensory nerve endings Sensory nerve fiber Connective tissue sheath Intrafusal fiber Skeletal muscle fiber Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18

19. 19 Visceral Senses Receptors in internal organs Convey information that includes the sense of fullness after eating a meal as well as the discomfort of intestinal gas and the pain that signals a heart attack

20. Summary of Receptors of the General Senses End of Section 1, chapter 12

21. 21 section 2, chapter 12 Smell, Taste, and Hearing Sensory receptors are within large, complex sensory organs in the head Smell in olfactory organs Taste in taste buds Hearing and equilibrium in ears Sight in eyes

22. 22 Sense of Smell Olfactory receptors Bipolar Chemoreceptors Respond to chemicals (called odorants) dissolved in liquids Olfactory organs Olfactory epithelium - contain olfactory receptors and supporting epithelial cells Cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

23. Olfactory Receptors Figure 12.5 Olfactory receptors. (a) columnar epithelial cells support olfactory receptor cells, which have cilia at their distal ends. The olfactory receptors pass through olfactory foramina in the cribriform plate and synapse with the olfactory bulb in the brain. (b) Olfactory epithelium cover the upper nasal cavity and superior nasal conchae.

24. 24 Olfactory Nerve Pathways Once olfactory receptors are stimulated, nerve impulses travel through Olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) & olfactory cortex (for interpretation) The limbic system, which is involved with emotions and memory is strongly effected by smell.

25. 25 Olfactory Stimulation Olfactory code Hypothesis Odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins Olfactory organs located high in the nasal cavity above the usual pathway of inhaled air Olfactory receptors undergo sensory adaptation rapidly Sense of smell drops by 50% within a second after stimulation

26. 26 Sense of 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

27. 27 Taste Receptors Papillae (a) (b) Connective tissue Sensory nerve fibers Epithelium of tongue Supporting cell Taste pore Taste hair Taste cell Taste buds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28. 28 Taste Sensations Four primary taste sensations Sweet – stimulated by carbohydrates Sour – stimulated by acids Salty – stimulated by salts Bitter – stimulated by many organic compounds Spicy foods activate pain receptors

29. 29 Taste Nerve Pathways Sensory impulses from taste receptors travel along: Cranial nerves to… Medulla oblongata to… Thalamus to… Gustatory cortex (for interpretation)

30. 30 Sense of Hearing Ear Organ of hearing Three (3) sections: External ear Middle ear Inner ear

31. 31 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane

32. 32 Middle Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane Tympanic cavity Air-filled space in temporal bone Auditory ossicles Vibrate in response to tympanic membrane Malleus, incus and stapes Hammer, anvil and stirrup Oval window Opening in wall of tympanic cavity Stapes vibrates against it to move fluids in inner ear

33. 33 Auditory Tube Also known as the 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane

34. Inner Ear Complex system of labyrinths Osseous labyrinth Bony canal in temporal bone Filled with perilymph Membranous labyrinth Tube within osseous labyrinth Filled with endolymph Cochlear nerve Maculae Utricle (a) Cochlea Saccule Ampullae Endolymph Perilymph Membranous labyrinth Bony labyrinth Vestibular nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph VestibuleOval window Round window Semicircular canals Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 34

35. Inner Ear Three (3) parts of labyrinths: Cochlea Functions in hearing Semicircular canals Functions in equilibrium Vestibule Functions in equilibrium Cochlear nerve Maculae Utricle (a) Cochlea Saccule Ampullae Endolymph Perilymph Membranous labyrinth Bony labyrinth Vestibular nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph VestibuleOval window Round window Semicircular canals Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 35

36. 36 Cochlea Scala vestibuli Upper compartment Leads from oval window to apex of spiral Part of bony labyrinth Scala tympani Lower compartment Extends from apex of the cochlea to round window Part of bony labyrinth Stapes vibrating in oval window Scala vestibuli filled with perilymph Vestibular membrane Basilar membrane Scala tympani filled with perilymph Round window Helicotrema Membranous labyrinth Cochlear duct filled with endolymph Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

37. 37 Cochlea Cochlear duct Portion of membranous labyrinth in cochlea Vestibular membrane Separates cochlear duct from scala vestibuli Basilar membrane Separates cochlear duct from scala tympani Spiral organ (organ of Corti) Basilar membrane (a) Scala vestibuli (contains perilymph) Vestibular membrane Cochlear duct (contains endolymph) Scala tympani (contains perilymph) Branch of cochlear nerve Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

38. 38 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 Spiral organ (organ of Corti) Hair cells Basilar membrane (a) (b) Scala vestibuli (contains perilymph) Cochlear duct (contains endolymph) Scala tympani (contains perilymph) Branch of cochlear nerve Tectorial membrane Basilar membrane Supporting cells Nerve fibers Branch of cochlear nerve Vestibular membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

39. 39 Organ of Corti Cochlear duct Scala tympaniHair cells (a) (b) Basilar membrane Tectorial membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited

40. 40 Auditory Nerve Pathways Midbrain Pons Thalamus Auditory cortex (temporal lobe) Medial geniculate body of thalamus Superior olivary nucleus Medulla oblongata Vestibulocochlear nerve Cochlear nuclei Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

41. 41 Summary of the Generation of Sensory Impulses from the Ear

42. 42 Sense of Equilibrium Static equilibrium Vestibule Senses position of head when body is not moving Dynamic Equilibrium Semicircular canals Senses rotation and movement of head and body

43. 43 Vestibule Utricle Communicates with saccule and membranous portion of semicircular canals Saccule Communicates with cochlear duct Macula Hair cells of utricle and saccule Saccule Utricle Cochlea Maculae Ampullae of semicircular canals Vestibulocochlear nerve Cochlear duct Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vestibule

44. Macula Responds to changes in head position Bending of hairs results in generation of nerve impulse Hair cells Sensory nerve fiber Supporting cells Otoliths (a) Head upright(b) Head bent forward Macula of utricle Hairs of hair cells bend Gelatinous material sags Gravitational force Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 44

45. 45 Semicircular Canals Three (3) canals at right angles Ampulla Swelling of membranous labyrinth that communicates with the vestibule Crista ampullaris Sensory organ of ampulla Hair cells and supporting cells Rapid turns of head or body stimulate hair cells Saccule Utricle Cochlea Maculae Ampullae of semicircular canals Vestibulocochlear nerve Cochlear duct Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vestibule

46. 46 Crista Ampullaris Hair cell Supporting cells Sensory nerve fibers Hairs Cupula Crista ampullaris (a) Head in still position (b) Head rotating Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (c) Crista ampullaris Semicircular canal Endolymph Ampulla Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. End of section 2, chapter 12

47. section 3, chapter 12 vision ivyanatomy.com

48. 48 Sense of Sight Visual accessory organs Eyelids Lacrimal apparatus Extrinsic eye muscles

49. Eyelid Palpebra Composed of four (4) layers: Skin Muscle Connective tissue Conjunctiva Orbicularis oculi – closes eyelid Levator palpebrae superioris – opens eyelid Tarsal glands – secrete oil onto eyelashes Conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball Eyelash Cornea Conjunctiva Eyelid Tendon of levator palpebrae superioris Superior rectus Orbicularis oculi Inferior rectus Tarsal glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 49

50. Lacrimal Apparatus Lacrimal gland Lateral to eye Secretes tears Canaliculi Collect tears Lacrimal sac Collects from canaliculi Nasolacrimal duct Collects from lacrimal sac Empties tears into nasal cavity Lacrimal gland Lacrimal sac Superior and inferior canaliculi Nasolacrimal duct Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 50

51. Extrinsic Eye Muscles Inferior rectusInferior oblique Medial rectus Superior rectus Superior oblique Lateral rectus (cut) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Superior rectus Rotates eye up and medially Inferior rectus Rotates eye down and medially Medial rectus Rotates eye medially 51

52. Extrinsic Eye Muscles Inferior rectusInferior oblique Medial rectus Superior rectus Superior oblique Lateral rectus (cut) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lateral rectus Rotates eye laterally Superior oblique Rotates eye down and laterally Inferior oblique Rotates eye up and laterally 52

53. Structure of the Eye The eye has three distinct layers “tunics” 1.Fibrous tunic 2.Vascular tunic 3.Nervous tunic

54. Outer Tunic Sclera Posterior portion Opaque Protection Cornea Anterior 1/6 th of eye “window of the eye” Transparent Light transmission

55. Middle Tunic Iris “rainbow” Anterior portion Pigmented Controls light intensity Ciliary body Anterior portion Pigmented Suspensory ligaments holds lens Ciliary muscles moves lens for focusing Choroid coat Provides blood supply Pigments absorb extra light

56. Anterior Portion of Eye Filled with aqueous humor

57. Lens The lens is an elastic, biconvex, and transparent structure largely composed of epithelial cells, called lens fibers. The lens lies behind the iris and is held in place by suspensory ligaments of ciliary body

58. 58 Accommodation Changing of lens shape to view objects (a) Lens thick Lens thin (b) Ciliary muscle fibers contracted Suspensory ligaments relaxed Ciliary muscle fibers relaxed Suspensory ligaments taut Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

59. 59 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 Sclera Iris Lens Aqueous humor Cornea Vitreous humor Ciliary process Ciliary muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Posterior chamber Ciliary body Scleral venous sinus (canal of Schlemm) Anterior chamber

60. Ciliary Body Forms internal ring around the front of the eye Ciliary processes – radiating folds Ciliary muscles – contract and relax to move lens Figure 12.28 Lens and ciliary body viewed from behind.

61. 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

62. Inner Tunic Retina Contains visual receptors Continuous with optic nerve Fovea centralis – center of macula lutea; produces sharpest vision Macula lutea – yellowish spot in retina Optic disc – blind spot; contains no visual receptors Vitreous humor – thick gel that holds retina flat against choroid coat

63. 63 Posterior Cavity Contains vitreous humor – thick gel that holds retina flat against choroid coat Ciliary body Retina Choroid coat Sclera Fovea centralis Optic nerve Lens Iris Pupil Cornea Lateral rectus Medial rectus Optic disc Posterior cavity Vitreous humor Posterior chamber Anterior chamber Aqueous humor Suspensory ligaments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anterior cavity

64. 64 Layers of the Eye

65. 65 Light Refraction Refraction Bending of light Occurs when light waves pass at an oblique angle into mediums of different densities Light wave Perpendicular line Air Glass Refracted light wave Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

66. 66 Types of Lenses Convex lenses cause light waves to converge Concave lenses cause light waves to diverge Air Glass (a)(b) Diverging light waves Convex surface Light wave Converging light waves Concave surface Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

67. 67 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 Light waves Object Cornea Image Retina Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

68. Major Groups of Retinal Neurons Receptor cells, bipolar cells, and ganglion cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve Horizontal cells and amacrine cells – modify impulses Figure 12. Notice that photoreceptors (rods and cones) are the posterior most cells in this circuit. Light waves stimulate the photoreceptors, which send impulses forward to horizontal cells and ganglion cells before leaving the eye through the optic disc.

69. Rods Long, thin projections Contain light sensitive pigment called rhodopsin Hundred times more sensitive to light than cones Provide vision in dim light Produce outlines of objects Cones Short, blunt projections Provide vision in bright light Produce sharp images Produce color vision Pigments include: Erythrolabe – responds to red Chlorolabe – responds to green Cyanolabe – responds to blue Visual Receptors Color perceived depends on which sets of cones are stimulated

70. Figure 12.38 Rods and cones. (a) Several rods converge onto a single sensory nerve fiber to the brain (b) separate sensory nerve fibers transmits impulses from the cones to the brain. (c) Scanning electron micrograph of rods and cones.

71. 71 12.6 Clinical Application Refraction Disorders Concave lens corrects nearsightedness Convex lens corrects farsightedness Light waves Cornea Lens Retina (a) Eye too long (myopia) (b) Normal eye (c) Eye too short (hyperopia) Point of focus Point of focus Point of focus Light waves Concave lens Convex lens (a) (b) Uncorrected point of focus Corrected point of focus Uncorrected point of focus Corrected point of focus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

72. 72 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

73. 73 Stereoscopic Vision Provides perception of distance and depth Results from formation of two slightly different retinal images Light waves Right eyeLeft eye Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

74. Visual Nerve Pathways Axons from ganglion cells in retina leave the eyes to form the optic nerves. Some of the fibers decussate at the optic chiasm. Fibers from the nasal (medial) half of retina cross over Fibers from temporal half (lateral) of retina do not cross over Most fibers of the optic tract continue to the lateral geniculate nucleus of the thalamus, which relays impulses towards the visual cortex.

75. Figure 12.41 The visual pathway includes the optic nerve, optic chiasma, optic tract, and optic radiations. End of Chapter 12