Chapter 10 Lecture Outline

1. Chapter 10Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

2. Chapter 10 The Senses 2

3. 10.1 Introduction 3

4. Sensory receptors detect changes in the environment and stimulate neurons to send nerve impulses to the brain. • Sensory receptors fall into two categories: Somatic senses (widely distributed and structurally simple) and Special senses (complex specialized sensory organs) 4

5. 10.2 Receptors, Sensations, and Perception 5

6. All action potentials are the same, yet we experience different sensations because of different receptors. • Types of general receptors • Receptors sensitive to changes in chemical concentration are called chemoreceptors. • Painreceptorsdetect tissue damage. • Thermoreceptors respond to temperature differences. • Mechanoreceptors respond to changes in pressure or movement. • Photoreceptors in the eyes respond to light energy. 6

7. Sensations and Perception • A sensation is the awareness that occurs when the brain receives sensory impulses. • A perception occurs when the brain interprets the sensory input. • At the same time the sensation is being formed, the brain uses projection to send the sensation back to its point of origin so the person can pinpoint the area of stimulation. • The particular sensation depends on the region of the brain that receives the impulses. 7

8. Sensory Adaptation • The brain must prioritize all the incoming sensory impulses. • The brain can become less responsive to a maintained stimulus such as the feel of clothing on the skin, odors, sounds, etc. 8

9. 10.3 General Senses 9

10. Receptors associated with the skin, muscles, joints, and viscera make up the general (somatic) senses. • Touch and Pressure Senses • Free nerve endings of sensory nerve fibers in the epithelial tissues are associated with itching. • Tactile (Meissner's) corpuscles are flattened connective tissue sheaths surrounding two or more nerve fibers and are abundant in hairless areas that are very sensitive to light touch. 10

11. Touch and pressure senses, cont. • Lamellated (Pacinian) corpuscles are large structures of connective tissue and cells that resemble an onion. They function to detect deep pressure. 11

12. Fig 10.1 12

13. Temperature Senses • Temperature receptors include two groups of free nerve endings: warm receptors and cold receptors which both work best within a range of temperatures. • Both heat and cold receptors adapt quickly. • Temperatures near 45o C stimulate pain receptors; temperatures below 10o C also stimulate pain receptors and produce a freezing sensation. 13

14. Sense of Pain • Pain receptors consist of free nerve endings that are stimulated when tissues are damaged, and adapt little, if at all. • Found all over the body except in the nervous tissue of the brain. • Many stimuli affect pain receptors such as chemicals and oxygen deprivation. • How pain receptors are stimulated is poorly understood. 14

15. Sense of pain, cont. • Visceral pain receptors are the only receptors in the viscera that produce sensations. • Pain seems to come from mechanoreceptors, decreased blood flow (oxygen deprivation), or chemicals stimulating chemoreceptors. • Referred pain, when visceral pain is felt in another body area, occurs because of the common nerve pathways leading from skin and internal organs. 15

16. Fig 10.2 16

17. Fig 10.3 17

18. Pain Nerve Fibers • Fibers conducting pain impulses away from their source are either acute pain fibers or chronic pain fibers. • Acute pain fibers are myelinated fibers that carry impulses rapidly, are associated with sharp pain, and cease when the stimulus stops. • Chronic pain fibers are unmyelinated fibers that conduct impulses slowly, produce a dull, achy sensation, and continue sending impulses after the stimulus stops. 18

19. Pain nerve fibers, cont. • Pain impulses are processed in the gray matter of the dorsal horn of the spinal cord. • Pain impulses are conducted to the reticular formation, then to the thalamus, hypothalamus, and cerebral cortex. 19

20. Regulation of pain impulses • A person becomes aware of pain when impulses reach the thalamus, but the cerebral cortex judges the intensity and location of the pain, as well as emotional and motor responses. • Gray matter of the brain stem regulates the flow of pain impulses from the spinal cord and can trigger the release of enkephalins and serotonin, which inhibit the release of pain impulses in the posterior gray horns of the spinal cord. 20

21. Regulation of pain impulses, cont. • Endorphins released in the brain provide natural pain control. • These natural pain killers are opiates like morphine. 21

22. 10.4 Special Senses 22

23. The special senses are associated with fairly large and complex structures located in the head. • These include the senses of smell, taste, hearing, equilibrium, and sight. 23

24. 10.5 Sense of Smell 24

25. Olfactory Receptors • Smell (Olfactory) receptors and taste receptors are chemoreceptors and chemicals must dissolve in liquids to stimulate the receptors. • The senses of smell and taste operate together to aid in food selection. 25

26. Fig 10.4 26

27. Olfactory Organs • The olfactory organs contain the olfactory receptors plus epithelial supporting cells and are located in the upper nasal cavity. • The olfactory receptor cells are bipolar neurons with hair-like cilia covering the dendrites. The cilia project into the mucous membrane of the upper nasal cavity. • To be detected, chemicals that enter the nasal cavity must first be dissolved in the watery fluid surrounding the cilia. • Odorant molecules stimulate various sets of receptor proteins. 27

28. Olfactory Nerve Pathways • When olfactory receptors are stimulated, their fibers synapse with neurons in the olfactory bulbs lying on either side of the crista galli of the ethmoid bone. • Sensory impulses are first analyzed in the olfactory bulbs, then travel along olfactory tracts to the limbic system, and lastly to the olfactory cortex within the temporal and frontal lobes. 28

29. Olfactory Stimulation • Each odor stimulates a set of specific protein receptors in cell membranes. • This causes an influx of sodium ions and then depolarization. If threshold is reached, an action potential is generated. • The brain interprets different receptor combinations as an olfactory code. • Olfactory receptors adapt quickly but selectively. 29

30. 10.6 Sense of Taste 30

31. Taste buds are the organs of taste and are located within papillae of the tongue and are scattered throughout the mouth and pharynx. 31

32. Fig 10.5 32

33. Taste Receptors • Taste cells (gustatory cells) are modified epithelial cells that function as receptors. • Taste cells contain the taste hairs that are the portions sensitive to taste. These hairs protrude from openings called taste pores. • Chemicals must be dissolved in water (saliva) in order to be tasted. • The sense of taste involves specific membrane protein receptors that bind with specific chemicals in food. 33

34. Taste Sensations • There are five types of taste cells: sweet, sour, salty, bitter, and umami. (others that may be recognized are alkaline and metallic) • Specific taste receptors are concentrated in different areas of the tongue. • Sweet receptors are plentiful near the tip of the tongue. • Sour receptors occur along the lateral edges of the tongue. • Salt receptors are widespread over the tongue. 34

35. Taste receptors, cont. • Bitter receptors are at the back of the tongue. • Umami receptors responds to certain amino acid derivatives such as monosodium glutamate (MSG) and are widespread. • Taste buds are responsive to one taste sensation with distinct receptors. • Flavors result from combinations of the primary sensations. • Taste receptors rapidly undergo adaptation. 35

36. Taste Nerve Pathways • Taste impulses travel on the facial, glossopharyngeal, and vagus nerves to the medulla oblongata and then to the gustatory cortex in the parietal lobe of the cerebrum. 36

37. 10.7 Sense of Hearing 37

38. The ear has external, middle, and inner sections and provides the senses of hearing and equilibrium. • Outer (External) Ear • The external ear consists of the auriclewhich collects the sound which then travels down the external acoustic meatus. • The meatus ends at the tympanic membrane or eardrum that vibrates with the sound waves. 38

39. Fig 10.6 39

40. Middle Ear • The middle ear (tympanic cavity) is an air-filled space housing the auditoryossicles. • Three auditory ossicles are the malleus, incus, and stapes. • The tympanic membrane vibrates the malleus, which vibrates the incus, then the stapes. • The stapes vibrates the fluid inside the oval window of the inner ear. • Auditory ossicles both transmit and amplify sound waves. 40

41. Fig 10.7 41

42. Auditory Tube • The auditory(eustachian) tube connects the middle ear to the nasopharynx to help maintain equal air pressure on both sides of the eardrum. • Mucous membrane infections of the throat can travel up the auditory tube to the middle ear and cause middle ear infections. 42

43. Inner Ear The inner ear is made up of a membranous labyrinthinside an osseous labyrinth within the temporal bone. Between the two labyrinths is a fluid called perilymph. Endolymph is inside the membranous labyrinth. The cochlea houses the organ of hearing while the semicircularcanals function in equilibrium. 43

44. Fig 10.8 44

45. Inner ear, cont. • Within the cochlea, the oval window leads to the upper compartment, called the scala vestibuli. • A lower compartment, the scala tympani, leads to the round window. • The cochlear duct lies between these two compartments and is separated from the scala vestibuli by the vestibular membrane, and from the scala tympani by the basilar membrane. 45

46. Fig 10.9a 46

47. Inner ear, cont • The spiral organ (organ of Corti), with its receptors called hair cells, lies on the basilar membrane. • Hair cells possess hairs that extend into the endolymph of the cochlear duct. • Above the hair cells lies the tectorial membrane, which touches the tips of the hair cells. 47

48. Fig 10.9b 48

49. Inner ear, cont. • Vibrations in the fluid of the inner ear cause the hair cells in different parts of the spiral organ to bend resulting in an influx of calcium ions. • This causes the release of a neurotransmitter from vesicles which stimulate the ends of nearby sensory neurons. • Louder sounds cause more action potentials. 49

50. Auditory nerve pathways Nerve fibers carry impulses to the auditory cortices of the temporal lobes where they are interpreted. Some fibers do cross over. Hearing loss can be either conductive or sensorineural. 50