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1 PowerPoint Lecture Outlines to accompany
Hole’s Human Anatomy and Physiology Eleventh Edition Shier w Butler w Lewis Chapter 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Chapter 12 Nervous System III - Senses
General Senses receptors that are widely distributed throughout the body skin, various organs and joints Special Senses specialized receptors confied to structures in the head eyes and ears

3 Senses 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

4 Pathways From Sensation to Perception (Example of an Apple)

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

6 Sensory Impulses stimulation of receptor causes local change in its receptor potential a graded electrical current is generated that reflects intensity of stimulation if receptor is part of a neuron, the membrane potential may generate an action potential if receptor is not part of a neuron, the receptor potential must be transferred to a neuron to trigger an action potential peripheral nerves transmit impulses to CNS where they are analyzed and interpreted in the brain

7 Sensations Projection
process in which the brain projects the sensation back to the apparent source it allows a person to pinpoint the region of stimulation

8 Sensory Adaptation ability to ignore unimportant stimuli
involves a decreased response to a particular stimulus from the receptors (peripheral adaptations) 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

9 General Senses senses associated with skin, muscles, joints, and viscera three groups exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain visceroceptive senses – senses associated with changes in viscera; blood pressure stretching blood vessels, ingesting a meal proprioceptive senses – senses associated with changes in muscles and tendons

10 Touch and Pressure Senses
Free nerve endings common in epithelial tissues simplest receptors sense itching Meissner’s corpuscles abundant in hairless portions of skin; lips detect fine touch; distinguish between two points on the skin Pacinian corpuscles common in deeper subcutaneous tissues, tendons, and ligaments detect heavy pressure and vibrations

11 Touch and Pressure Receptors

12 Temperature Senses Warm receptors
sensitive to temperatures above 25oC (77o F) unresponsive to temperature above 45oC (113oF) Cold receptors sensitive to temperature between 10oC (50oF) and 20oC (68oF) Pain receptors respond to temperatures below 10oC respond to temperatures above 45oC

13 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

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

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

16 Pain Nerve Pathways Chronic pain fibers Acute pain fibers C fibers
thin, unmyelinated conduct impulses more slowly associated with dull, aching pain difficult to pinpoint Acute pain fibers A-delta fibers thin, myelinated conduct impulses rapidly associated with sharp pain well localized

17 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 of pain produces emotional and motor responses to pain

18 Proprioceptors mechanoreceptors
send information to spinal cord and CNS about body position and length and tension of muscles Main kinds of proprioreceptors Pacinian corpuscles – in joints muscle spindles – in skeletal muscles* Golgi tendon organs – in tendons* *stretch receptors

19 Stretch Receptors

20 Summary of Receptors of the General Senses

21 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 sight in eyes

22 Sense of 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

23 Olfactory Receptors

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

25 Olfactory Stimulation
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 Olfactory Code hypothesis odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins

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 Taste Receptors

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

30 Hearing Ear – organ of hearing Three Sections External Middle Inner

31 External Ear auricle external auditory meatus tympanic membrane
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

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

33 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

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

35 Inner Ear Three Parts of Labyrinths cochlea semicircular canals
functions in hearing semicircular canals functions in equilibrium vestibule

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

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

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

39 Organ of Corti

40 Auditory Nerve Pathways

41 Summary of the Generation of Sensory Impulses from the Ear

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

43 Vestibule Utricle communicates with saccule and membranous portion of semicircular canals Saccule communicates with cochlear duct Mucula hair cells of utricle and saccule

44 Macula responds to changes in head position
bending of hairs results in generation of nerve impulse

45 Semicircular Canals three 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

46 Crista Ampullaris

47 Sight Visual Accessory Organs eyelids lacrimal apparatus
extrinsic eye muscles

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

49 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

50 Extrinsic Eye Muscles Superior rectus rotates eye up and medially
Inferior rectus rotates eye down and medially Medial rectus rotates eye medially

51 Extrinsic Eye Muscles Lateral rectus rotates eye laterally
Superior oblique rotates eye down and laterally Inferior oblique rotates eye up and laterally

52 Structure of the Eye hollow spherical wall has 3 layers
outer fibrous tunic middle vascular tunic inner nervous tunic

53 Outer Tunic Cornea anterior portion transparent light transmission
light refraction Sclera posterior portion opaque protection

54 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

55 Anterior Portion of Eye
filled with aqueous humor

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

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

58 Accommodation changing of lens shape to view objects

59 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

60 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

61 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

62 Posterior Cavity contains vitreous humor – thick gel that holds retina flat against choroid coat

63 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

64 Layers of the Eye

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

66 Types of Lenses Convex lenses cause light waves to converge
Concave lenses cause light waves to diverge

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

68 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

69 Rods and Cones

70 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

71 Rod Cells

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

73 Visual Nerve Pathway

74 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

75 Clinical Application Refraction Disorders
concave lens corrects nearsightedness convex lens corrects farsightedness


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