1. Inquiry into Life Twelfth Edition
Lecture PowerPoint to accompany
Inquiry into Life Twelfth Edition
Sylvia S. Mader
Chapter 18
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 18.1 Sensory Receptors and Sensations
Specialized to detect specific stimuli
Interoreceptors - detect stimuli inside body
Includes receptors for blood pressure, blood volume, and pH of the blood.
Directly involved in homeostasis, regulated by negative feedback
Exteroreceptors - detect stimuli outside body
Includes receptors for taste, smell, vision, hearing, and equilibrium.
They function to inform the CNS about environmental conditions

3. 18.1 Sensory Receptors and Sensations
Types of Sensory Receptors
Chemoreceptors
Taste, smell, blood pH
Photoreceptors
Vision (light)
Mechanoreceptors
Hearing, gravity, motion, body position
Thermoreceptors
Temperature
Located in the hypothalamus and skin

4. 18.1 Sensory Receptors and Sensations
Detection
Sensation

5. 18.1 Sensory Receptors and Sensations
How Sensation Occurs
Sensory Transduction
Energy from a chemical or physical stimulus is converted into an electrical signal (nerve impulse)
The stronger the stimulus, the more frequent the action potentials
The sensation that results depends on the part of the part of the brain receiving the nerve impulses

6. 18.1 Sensory Receptors and Sensations
How Sensation Occurs
Integration: the summing up of environmental signals by sensory receptors
Sensory Adaptation: a decrease in response to a stimulus (not being consciously aware of a stimulus)

7. 18.2 Somatic Senses Three Types of Somatic Sensory Receptors
Proprioceptors
Cutaneous Receptors
Pain Receptors

8. 18.2 Somatic Senses Three Types of Somatic Sensory Receptors
Proprioceptors
Mechanoreceptors involved in reflex action
Help maintain muscle tone
Muscle spindles increase the degree of muscle contraction
Golgi tendon organs decrease the degree of muscle contraction
The result is proper muscle length and tension (tone)

9. Muscle Spindle

10. 18.2 Somatic Senses Three Types of Somatic Sensory Receptors
Cutaneous Receptors
In the dermis of the skin
Fine touch receptors
Meissner corpuscles and Krause end bulbs - fingertips, lips, palms, penis, clitoris
Merkel disks - junction of epidermis and dermis
Root hair plexus - free nerve endings at base of follicles
Allows sensation when hair is touched
Pressure receptors
Pacinian corpuscles - onion-shaped, deep in dermis
Ruffini endings - encapsulated receptors with complex nerve networks
Temperature receptors - free nerve endings

11. Cutaneous Receptors in the Human Skin

12. 18.2 Somatic Senses Three Types of Somatic Sensory Receptors
Pain Receptors
Free nerve endings
Damaged tissues release chemicals that stimulate pain receptors
Alert us to possible danger
Referred Pain
In some areas stimulation of internal pain receptors is also perceived as pain from the skin
Most likely explanation- impulses from internal pain receptors also synapse in cord with neurons receiving pain impulses from skin
Ex: pain originating in heart is also referred to left arm and shoulder

13. 18.3 Senses of Taste and Smell
Sense of Taste
Taste buds contain chemoreceptors and are located in the tongue, hard palate, pharynx, epiglottis
There are different receptors for salty, sour, bitter, and sweet tastes
Taste bud structure
Each has a pore surrounded by supporting cells and taste cells
Taste cells have microvilli with receptors
How the brain receives taste information
Chemicals bind to receptors on microvilli-impulses generated
Gustatory (taste) cortex surveys incoming pattern of impulses
“Weighted average” is the perceived taste

14. Taste Buds in Humans

15. 18.3 Senses of Taste and Smell
Sense of Smell
80-90% of what we perceive as taste is actually smell
Olfactory Cells
Chemoreceptors (modified neurons) located high in nasal cavity
Olfactory cells have a tuft of olfactory cilia with receptors for odor molecules
How the Brain Receives Odor Information
Nerve fibers lead to olfactory bulb, an extension of the brain,
A single odor is composed of many different molecules which activates a characteristic combination of receptor proteins
Odor’s “signature” is interpreted by brain

16. Olfactory Cell Location and Anatomy

17. 18.4 Sense of Vision

18. Anatomy of the Human Eye

19. Anatomy and Physiology of the Eye

20. 18.4 Sense of Vision Anatomy and Physiology of the Eye
Function of the Lens
Focuses light rays onto the retina
Image is inverted and upside down on the retina
If eyeball is too long or too short corrective lenses are needed to bring image into focus on the retina
Visual accommodation
For viewing close objects
Lens rounds up to bring the image into focus on the lens
Lens shape is controlled by the ciliary muscle
Elasticity of the lens may decrease with age

21. Focusing the Human Eye

22. 18.4 Sense of Vision

23. 18.4 Sense of Vision Visual Pathway to the Brain
Function of Photoreceptors (Rods and Cones)
Rods
Very sensitive to light, important for night vision
Visual pigment is rhodopsin
Also provide us with peripheral vision and the perception of motion
Cones
Activated by bright light
Allow for color perception

24. Photoreceptors in the Eye

25. 18.4 Sense of Vision Visual Pathway to the Brain
Function of the Retina
Three Layers of Cells
Layer closest to choroid contains rods and cones
Middle layer composed of bipolar cells
Inner layer composed of ganglion cells
Sensory fibers become the optic nerve
Rod and cone cells synapse with bipolar cells which synapse with ganglion cells
Integration occurs as signals pass to bipolar and ganglion cells
Considerable processing occurs in the retina before ganglion cells generate impulses
Impulses from the ganglion cells travel in the optic nerve to the visual cortex where further integration occurs

26. Structure and Function of the Retina

27. 18.4 Sense of Vision Visual Pathway to the Brain
From the Retina to the Visual Cortex
Optic nerves from each eye travel to the optic chiasma
Some of the axons cross over at the optic chiasma
Fibers from the right half of each retina join together to form the right optic tract
Fibers from the left half of each retina join together to form the left optic tract
Optic tracts travel around the hypothalamus and most fibers synapse with nuclei in the thalamus
Axons from the thalamic nuclei form optic radiations that carry impulses to the visual area
Right and left visual areas must communicate for us to see entire visual field

28. Optic Chiasma

29. 18.5 Sense of Hearing The Ear Has Two Sensory Functions
Hearing and Balance
Mechanoreceptors (hair cells) located in the inner ear associated with both functions

30. Anatomy of the Human Ear

31. 18.5 Sense of Hearing Auditory Pathway to the Brain
Sound waves enter the auditory canal
Tympanic membrane (ear drum) begins to vibrate
Vibrations are amplified across the middle ear bones
The stapes is attached to the oval window
Oval window vibrates and transmits vibrations to fluid inside the cochlea

32. Mechanoreceptors for Hearing

33. 18.5 Sense of Hearing Auditory Pathway to the Brain Continued . . .
Stapes causes the oval window to vibrate
Vibrations move from the vestibular canal to the tympanic canal across the basilar membrane
Basilar membrane moves up and down and the stereocilia of the hair cells bend
This generates nerve impulses in the cochlear nerve
The nerve impulses travel to the brain
The auditory cortex interprets them as sound

34. 18.6 Sense of Equilibrium Rotational Equilibrium Pathway
Three semicircular canals arranged so that one is in each plane of motion
Each semicircular canal has an enlarged base called an ampulla
Each ampulla contains hair cells with stereocilia embedded in a cupula
As fluid within a canal flows and bends a cupula, the stereocilia are bent and this changes the pattern of impulses carried in the vestibular nerve to cerebellum and cerebrum
Brain uses this information to make postural corrections

35. 18.6 Sense of Equilibrium Gravitational Equilibrium Pathway
Depends on utricle and saccule
Utricle is sensitive to horizontal movements of the head
Saccule is sensitive to vertical movements of the head
Both contain hair cells with stereocilia embedded in an otolithic membrane
Large central cilium called the kinetocilium
Calcium carbonate granules (otoliths) rest on otolithic membrane
When head or body moves in horizontal or vertical plane the otoliths are displaced and the otolithic membrane sags

36. Mechanoreceptors for Equilibrium

37. 18.7 Disorders that Affect the Senses
Disorders of Taste and Smell
Sense of smell begins to decline after age 60
Some people are born without a sense of smell
Other factors that contribute to a decrease in the ability to taste and/or smell include:
Upper respiratory infections
Allergies
Exposure to certain drugs or chemicals (including tobacco smoke)
Brain trauma

38. 18.7 Disorders that Affect the Senses
Disorders of the Eye
Color Blindness
Complete colorblindness is rare
Most common types involve deficiency in one type of cone
Red-green colorblindness
Most common type
X-linked recessive trait
5-8% of the male population

39. Testing for Colorblindness

40. 18.7 Disorders that Affect the Senses
Distance Vision
Nearsighted
Can see close objects better than distant ones
Eyeball is elongated so image is brought to point focus in front of the retina
Corrected by concave lenses which diverge light rays so point focus is farther back
Farsighted
Can see distant objects better than close ones
Eyeball is shortened so image is brought to point focus behind the lens
Corrected by convex lenses to increase bending of light rays so point focus is farther forward

41. Corrective Abnormalities of the Eye and Possible Corrective Lenses

42. 18.7 Disorders that Affect the Senses
Common Causes of Blindness
Retinal Disorders
Capillaries to the retina may become damaged
Macular Degeneration
Cones are destroyed
Detached retina
Glaucoma
Fluid builds up in the eye destroying nerve fibers associated with peripheral vision
Cataracts
Cloudy spots on the lens
Exposure to UV light, diabetes, heavy alcohol consumption,and smoking are all risk factors

43. 18.7 Disorders that Affect the Senses
Disorders of Hearing and Equilibrium
Hearing Loss
Mobility of the middle ear bones decreases with age
The ability to hear high-pitched sounds is affected first.
Sudden Deafness
Usually occurs in only one ear
Causes include infections, trauma, and side effects of some drugs
Sometimes resolves itself
Deafness at Birth
Genetic and/or environmental causes (pathogens)

44. 18.7 Disorders that Affect the Senses
Disorders of Hearing and Equilibrium
Vertigo (dizziness)
Can be caused by problems in the brain or inner ear
Meniere’s Disease
Caused by an increased fluid volume in the inner ear
Hearing loss and vertigo are both characteristics of this condition