1

Sensory Physiology

2

Nervous System - 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

Sensory Receptor Types

Figure 10-1: Sensory receptors

5

Pathways From Sensation to Perception (Example of an Apple)

6

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

7

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

8

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

9

Touch and Pressure Senses

Free nerve endings• common in epithelial tissues• simplest receptors• sense itching•Ex ( nociciptor)

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

10

Touch and Pressure Receptors

11

Touch (pressure)

Figure 10-11: Touch-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 (nociceptor) • respond to temperatures below 10oC• respond to temperatures above 45oC

13

Summary of Receptors of the General Senses

14

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

15

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

16

Olfactor: Sense of Smell

Figure 10-14a, b: ANATOMY SUMMARY: Olfaction

17

Olfactory Receptors

18

Olfactor: Sense of Smell

Figure 10-14c: ANATOMY SUMMARY: Olfaction

19

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)

20Figure 10-4: Sensory pathways

21

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

22

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

23

Taste Receptors

24

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

25

Taste Nerve Pathways

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

26Figure 10-4: Sensory pathways

27

Taste: Chemoreceptors

28

Taste: Chemoreceptors

• Salt --- Na passive • Acids– H block k channels • Sweet – Gs anhydrate cyclase – protein kinase(A) –

Phosphorylation of k channels so it will close• Bitter – Gb – phospholipasec – release of ca from ER • Depolarization –activate neurotransmitter vesicle to

diffues to membrane and release neurotransmitter

29

The Ear: Hearing and Equilibrium

• The ear – receptor organ for hearing and equilibrium

• Composed of three main regions– Outer ear – functions in hearing– Middle ear – functions in hearing– Inner ear – functions in both hearing and

equilibrium

30

The Outer (External) Ear• Composed of:

– The auricle (pinna)• Helps direct sounds

– External acoustic meatus• Lined with skin

– Contains hairs, sebaceous glands, and ceruminous glands

– Tympanic membrane• Forms the boundary between the external and

middle ear

31

The Outer (External) Ear

Figure 16.17a

32

The Middle Ear

• The tympanic cavity – A small, air-filled space

– Located within the petrous portion of the temporal bone

• Medial wall is penetrated by:– Oval window

– Round window

• Pharyngotympanic tube (auditory or eustachian tube) – Links the middle ear and pharynx

33

Structures of the Middle Ear

Figure 16.17b

34Figure 16.19

The Middle Ear

• Ear ossicles – smallest bones in the body– Malleus – attaches to

the eardrum – Incus – between the

malleus and stapes– Stapes – vibrates

against the oval window

35

The Inner (Internal) Ear

• Inner ear – also called the labyrinth• Lies within the petrous portion of the

temporal bone• Bony labyrinth – a cavity consisting of three

parts– Semicircular canals– Vestibule– Cochlea

36

The Inner (Internal) Ear

• Membranous labyrinth – Series of membrane-walled sacs and ducts– Fit within the bony labyrinth– Consists of three main parts

• Semicircular ducts

• Utricle and saccule

• Cochlear duct

37

The Inner (Internal) Ear

• Membranous labyrinth (continued)– Filled with a clear fluid – endolymph

• Confined to the membranous labyrinth

– Bony labyrinth is filled with perilymph • Continuous with cerebrospinal fluid

38

The Membranous Labyrinth

Figure 16.20

39

The Inner (Internal) Ear

Figure 16.17b

40

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

41

The Cochlea

Figure 16.23a–c

42

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

43

Hearing: Mechanoreceptors

Figure 10-19: Sound transmission through the ear

44

Hearing: Hair Cell Transduction

Figure 10-20: The cochlea

45

Hearing: Hair Cell Transduction

Figure 10-21: Signal transduction in hair cells

46

47

Summary of the Generation of Sensory Impulses from the Ear

48

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

49

Vestibule

• Utricle• communicates with saccule and membranous portion of semicircular canals

• Saccule• communicates with cochlear duct

• Mucula• hair cells of utricle and saccule

50

Macula

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

51

Anatomy and Function of the Maculae

Figure 16.21a

52

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

53

Crista Ampullaris

54

Vestibular System & Balance

55

Rotation & Gravity

56

Auditory Pathway from the Organ of Corti

Figure 16.25

57

Sight

Visual Accessory Organs• eyelids• lacrimal apparatus• extrinsic eye muscles

58

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

59

Extrinsic Eye Muscles

Superior rectus• rotates eye up and medially

Inferior rectus• rotates eye down and medially

Medial rectus• rotates eye medially

60

Extrinsic Eye Muscles

Lateral rectus• rotates eye laterally

Superior oblique• rotates eye down and laterally

Inferior oblique• rotates eye up and laterally

61

Structure of the Eye

• hollow• spherical• wall has 3 layers

• outer fibrous tunic• middle vascular tunic• inner nervous tunic

62

Outer Tunic

Cornea• anterior portion• transparent• light transmission• light refraction

Sclera• posterior portion• opaque• protection

63

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

64

Anterior Portion of Eye

• filled with aqueous humor

65

Lens

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

66

Ciliary Body

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

67

Accommodation• changing of lens shape to view objects

68

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

69

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

70

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

71

Posterior Cavity

• contains vitreous humor – thick gel that holds retina flat against choroid coat

72

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

73

Layers of the Eye

74

Light Refraction

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

75

Types of Lenses

Convex lenses cause light waves to converge

Concave lenses cause light waves to diverge

76

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

77

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

78

Rods and Cones

79

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

80

Rod Cells

81

Visual Nerve Pathway

82