This chapter should help the student to:

• Name the sensory receptor classes and list the receptors in each.
  
• Describe the structure, function, and location(s) of each receptor type.
  
• Describe the process by which each receptor type transduces a stimulus into a neuronal potential.
  
• Locate and identify the receptors in a micrograph of an organ or tissue.
  
• Identify the components of receptors in a diagram or micrograph.
  
• Relate the microscopic structure of each receptor to its “adequate stimulus”.

1. In which receptor types are generator and receptor potentials formed (I.A.1.a–c)?

2. List the receptors that fall into the following categories (Table 24–1) and note the overlaps:

1. 
   

   Mechanoreceptors

   
   
2. 
   

   Chemoreceptors

   
   
3. 
   

   Thermoreceptors

   
   
4. 
   

   Photoreceptors

   
   
5. 
   

   Neuronal receptors (I.A.1.a)

   
   
6. 
   

   Epithelial receptor cells (I.A.1.b)

   
   
7. 
   

   Neuroepithelial receptors (I.A.1.c)

   
   
8. 
   

   Proprioceptors (III.A and B)

   
   
9. 
   

   Touch and pressure receptors

   
   
10. 
    

    Warmth receptors

    
    
11. 
    

    Pain receptors (nociceptors)

    
    
12. 
    

    Cutaneous (skin) receptors (II. A–G)

3. List the types of sensations detected by free (unencapsulated) nerve endings (II.A).

4. Compare Merkel, Meissner, Ruffini, and pacinian corpuscles (II.B, D, E, and F) in terms of:

1. 
   

   Nerve fiber number and arrangement

   
   
2. 
   

   Capsule presence and structure

   
   
3. 
   

   Adequate stimulus

   
   
4. 
   

   Location

5. To what do the terms “intrafusal” and “extrafusal” refer (III.A.1)?

6. Name the two types of intrafusal muscle fibers (III.A.1) and compare them in terms of diameter and length, distribution of nuclei, and type of sensory nerve ending.

7. Compare muscle spindles with Golgi tendon organs in terms of function and the fibers (other than nerve) inside the capsule (III.A.1 and B).

8. List the receptors found in joint capsules and describe their function (Table 24–1).

9. Which sense organ in the head (other than the eye) contributes important information for proprioception (sense of equilibrium and position in space; VI.D; Table 24–1)?

10. Name the three types of lingual papillae with taste buds and compare them in terms of taste bud distribution (IV.A).

11. Name the cell types in taste buds (Table 24–2) and compare their structure, function, and location.

12. In which part of the nasal cavity is the olfactory epithelium located (IV.B)?

13. Name three cell types in olfactory epithelium (IV.B) and compare their shape, nuclear position, apical surface specializations (where applicable), and function.

14. Compare taste buds (IV.A; Table 24–2) and olfactory epithelium (IV.B) in terms of:

1. 
   

   Basic function

   
   
2. 
   

   Receptor cell type (I.A.1.b and c)

   
   
3. 
   

   Receptor cell apical surface specializations

   
   
4. 
   

   Signal transmission (I.A.1.b and c)

15. List, in order, the major steps in the embryonic development of the eye (V.A).

16. Name the eye’s three compartments and describe their boundaries (V.C.3 and I; Fig. 24–2).

17. Name, from outermost to innermost, the globe’s three basic tunics (or layers) (V.A–D); list the major components of each from anterior to posterior.

18. List, from anterior to posterior, the cornea’s five layers and describe the composition of each (V.B.1). Which layer is thickest?

19. Describe the sclera (V.B.3) in terms of its predominant tissue type, its vascularity, and the proportion of the eye it covers.

20. Compare the sclera and cornea (V.B.1 and 3) in terms of transparency, blood supply, source of nourishment (V.B.2,3 and C.1), and amount of sensory innervation (V.B.1).

21. Beginning with its outer surface (attached to the sclera), name the choroid’s layers and compare them in terms of the number and size of their blood vessels (V.C.1).

22. Name the ringlike, triangular anterior thickening of the eye’s vascular layer (V.C.2).

23. What is the function of the ciliary muscles (V.C.2)?

24. How is the ciliary body attached to the lens (V.C.2)?

25. Describe the site of production, composition, and circulation of the aqueous humor (V.B.2 and C.2).

26. Name the two muscles of the iris (V.C.3.b) and compare them in terms of:

1. 
   

   Cell type

   
   
2. 
   

   Fiber orientation

   
   
3. 
   

   Innervation

   
   
4. 
   

   Effect of contraction on light entering the eye

27. Name, from outside to inside, the layers of the lens (V.J.1–3).

28. Select the condition of the following when the eye is focusing on a near object (V.C.2):

1. 
   

   Ciliary muscles (contracted or relaxed)

   
   
2. 
   

   Lens shape (rounded or flattened)

29. Name the two principal layers of the retina (V.D.1 and 2) and compare them in terms of:

1. 
   

   Embryonic origin (V.A)

   
   
2. 
   

   Location (inner or outer; V.D.1 and 2)

   
   
3. 
   

   Tissue type (V.D.1 and E)

   
   
4. 
   

   Photosensitivity (V.D.1 and 2)

   
   
5. 
   

   Phagocytic capacity (V.D.1)

   
   
6. 
   

   Melanin content (V.D.1)

   
   
7. 
   

   How far and in what form they extend anteriorly (V.D)

30. Name the three layers of retinal nerve cells that receive and relay visual signals to the brain (V.E.1–3) and answer the following questions:

1. 
   

   Which cells serve as true photoreceptors?

   
   
2. 
   

   In which order do the cells relay a signal?

   
   
3. 
   

   Which layer is crossed first by incoming light?

   
   
4. 
   

   Which cells contribute axons to the optic nerve?

   
   
5. 
   

   Which cells can generate an action potential?

31. Compare rods and cones (V.E.1; Table 24–3) in terms of:

1. 
   

   Shape

   
   
2. 
   

   Photoreceptor function

   
   
3. 
   

   Relative number and location

   
   
4. 
   

   Presence of outer and inner segments

   
   
5. 
   

   Independence of flattened vesicles from the plasma membrane

   
   
6. 
   

   Phagocytosis of flattened vesicles by pigmented epithelium

   
   
7. 
   

   Visual pigment type and distribution

   
   
8. 
   

   Visual acuity in bright and low light

   
   
9. 
   

   Sensitivity to shades of gray and color

   
   
10. 
    

    Association with monosynaptic bipolar cells

32. Name the neuroglia in the neural retina (V.E.4).

33. Beginning with the tear layer on the cornea, list the components (e.g., layers, fluids, compartments) through which light must pass to reach the outer segments of the rods and cones (V.L).

34. Beginning with the bleaching of the visual pigment by light, list the steps leading to the generation of an action potential by the ganglion cells (V.L).

35. Name the muscles that open and close the eyelids (palpebrae; V.K.2).

36. Name the three types of glands in the eyelids and compare them in terms of their secretions and the locations of their duct openings (V.K.2).

37. Describe the lacrimal gland (V.K.3) in terms of its location, classification, and glandular epithelium.

38. Trace the flow of tears over the eye and through the components of the lacrimal apparatus (V.K.3). Why do our noses “run” when we cry?

39. List the major structural components of the external ear (VI.A), the middle ear (VI.B), and the inner ear (VI.C) and name the major function of each component.

40. Name the regions of the bony labyrinth and the parts of the membranous labyrinth each contains (VI.C.2).

41. Compare the perilymph and the endolymph (VI.C.2 and E.2) in terms of location and site of production.

42. List the divisions of the vestibular part of the membranous labyrinth (VI.D.1 and 2) and name the sensory organ located in each.

43. Name the auditory part of the membranous labyrinth (VI.E) and the sensory organ it contains (VI.E).

44. Make a schematic drawing of the cochlea’s contents as they would appear if they were removed and uncoiled (Fig. 24–4) and show the location of the following:

1. 
   

   Oval window

   
   
2. 
   

   Scala vestibuli

   
   
3. 
   

   Helicotrema

   
   
4. 
   

   Scala tympani

   
   
5. 
   

   Round window

   
   
6. 
   

   Scala media (cochlear duct)

   
   
7. 
   

   Perilymph

   
   
8. 
   

   Endolymph

Hint: The drawing should resemble a narrow tube (cochlear duct) within a wider tube, with the scala vestibuli extending from the oval window to the helicotrema, and the scala tympani extending from the helicotrema to the round window.

45. In situ, the cochlear duct (scala media) is triangular (Fig. 24–5). Name the structure(s) forming its roof, lateral wall, and floor (VI.E.2).

46. Name the structures in the maculae (VI.D.1) and in the crista ampullaris (VI.D.2) that correspond to the following structures in the organ of Corti (V.E.2.b):

1. 
   

   Inner and outer hair cells

   
   
2. 
   

   Stereocilia

   
   
3. 
   

   Pillar cells

   
   
4. 
   

   Tectorial membrane

47. Compare the organ of Corti’s apex and base in terms of the sound frequency to which each responds best (VI.E.3).

48. Beginning with the act of lying down, describe (naming all vestibular apparatus structures that play a part) the sequence of events that send a signal to the brain that the head’s position has changed (VI.D.1).

49. Beginning with a sound entering the external ear, list the events (naming all related cavities, moving bones, membranes, and cells) that cause the bipolar spiral ganglion cells to generate an action potential (V.E.3).

I. General Features of the Sense Organs

Sense organs respond to stimuli by generating action potentials in a sensory (afferent) nerve cell process. Signals travel to the central nervous system (CNS) for integration, enabling reflex or conscious reactions to environmental changes. Sensory fibers typically carry signals for only one sensory modality (e.g., pain, touch, or temperature).

A. Classification

Receptors are classified by their relationship to the nervous system, their stimulus sensitivity, and the presence or absence of a capsule.