1. Anatomy and Physiology
Marieb’s Human
Anatomy and Physiology
Ninth Edition
Marieb w Hoehn
Chapter 15
Special Senses
Lecture 22
55 slides, 155 min. (1 -> 26, 80 min; 28 -> end, 75 min.)

2. Lecture Overview Introduction to the senses and sensation
Types of sensors
Anatomy of the ear
Physiology of hearing and equilibrium
Anatomy of the eye
Physiology of vision
First, a few questions…

3. Background into Receptors…
What kinds of ‘messages’ does the brain understand?
What types of things in the environment do we have to respond to?
How do these environmental stimuli get converted into something the brain can understand?
What is a sensation? A perception?
Since all the messages in the CNS (brain) are the ‘same’ (electrical nerve impulses), how does the brain know
Where the impulses are coming from?
How to interpret the stimuli?
Brain understands ONLY action potentials (nerve impulses). Brain won’t respond if we shine a light on it, yell at it, rub a pizza on it, etc.
Light, sound, taste, odors, pressure, temperature, touch. These are the environmental stimuli we must interpret and respond to.
Receptors convert (transduce) environmental stimuli: eyes, ears, olfactory receptors, taste buds, touch receptors, pain receptors
Difference between SENSATION = arrival of impulses, and PERCEPTION = awareness of sensations
Axons are organized into bundles with specific origin and destination. So touch, pressure, pain arrive at the sensory cortex, while visual, auditory, gustatory, and olfactory stimuli arrive at their own regions of the cortex. The link between peripheral receptors and cortical neurons is a LABELED LINE. Brain interprets sensations only upon the labeled line over which it arrives, e.g., anything traveling over labeled lines carrying visual stimuli will be interpreted as light coming into the eye (e.g., flashes of light that occur when rubbing eyes).
Sensory coding over labeled lines has three components: a) identity of the labeled line = type of stimulus, b) location in sensory cortex = location on body, and c) Strength, duration, and variation of stimulus – conveyed by frequency and pattern of action potentials.

4. Sensory Receptors Sensory Receptors
specialized cells or multicellular structures that collect information (transduce information into nerve impulses)
stimulate neurons to send impulses along sensory fibers to the brain (receptor vs. generator [action] potentials)
Chemoreceptors (general)
respond to changes in chemical concentrations
Pain receptors or nociceptors (general)
respond to stimuli likely to cause tissue damage
Thermoreceptors (general)
respond to changes in temperature
Sensory receptors txmit four kinds of info: 1) Modality (type of stimulus or sensation via labeled lines), 2) Location (which nerve fibers are firing), 3) Intensity (number and kind of fibers that are firing and time interval between potentials), 4) Duration (change in nerve fibers fire over time).
Mechanoreceptors (general, special)
respond to mechanical forces
Photoreceptors (special)
respond to light

5. Mechanoreceptors
Sense mechanical forces such as changes in pressure or movement of fluid
Two main groups
baroreceptors – sense changes in pressure (e.g., carotid artery, aorta, lungs, digestive & urinary systems)
proprioceptors – sense changes in muscles and tendons

6. Stretch Receptors - Proprioceptors
send information to CNS concerning lengths and tensions of muscles (and pressure, tension, and movement of joints)
2 main kinds of proprioceptors
muscle spindles
in skeletal muscles
initiate contraction (mediates the stretch reflex)
Golgi tendon organs
in tendons
inhibit contraction

7. Stretch Receptors - Proprioceptors
Muscle spindle – initiates contraction (stretch reflex)
Golgi tendon organ – inhibits contraction

8. Sensory Adaptation
reduction in sensitivity of sensory receptors from continuous stimulation (painless, constant)
stronger stimulus required to activate receptors
smell and touch receptors undergo sensory adaptation
pain receptors usually do not undergo sensory adaptation (at level of receptor)
impulses can be re-triggered if the intensity of the stimulus changes

9. Temperature Sensors (Thermoreceptors)
Warm receptors
sensitive to temperatures above 25oC (77o F)
unresponsive to temperature above 45oC (113oF)
Cold receptors (3-4x more numerous than warm)
sensitive to temperature between 10oC (50oF) and 20oC (68oF)
unresponsive below 10oC (50oF)
Pain receptors are activated when a stimulus exceeds the capability (range) of a temperature receptor
respond to temperatures below 10oC
respond to temperatures above 45oC

10. Sense of Pain pain receptors are called nociceptors free nerve endings
Substance P or glutamate (inhib. by endorphins/enkephalins)
widely distributed
nervous tissue of brain lacks pain receptors (but meninges have nociceptors)
stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature
nociceptors do not adapt (at the level of the receptor)
Visceral Pain
usually only type of visceral receptors that exhibit sensation
stretch, chemical irritation, ischemia (usu w/nausea)
may exhibit referred pain
not well localized

11. Special Senses
sensory receptors are within large, complex sensory organs in the head
hearing and equilibrium in ears
sight in eyes
smell in olfactory organs
taste (gustation) in taste buds

12. External Ear auricle (pinna) external auditory meatus
collects sounds waves
external auditory meatus
lined with ceruminous glands
carries sound to tympanic membrane
terminates at tympanic membrane
tympanic membrane
vibrates in response to sound waves

13. The Middle Ear (Tympanic Cavity)
Typanic (attenuation) reflex: Elicited about 0.1 sec following loud noise; causes contraction of the tensor tympani m. and stapedius m. to dampen transmission of sound waves

14. Auditory Tube Eustachian, auditory, or pharyngotympanic tube
connects middle ear to throat
helps maintain equal pressure on both sides of tympanic membrane
usually closed by valve-like flaps in throat
When pressure in tympanic cavity is higher than in nasopharynx, tube opens automatically. But the converse is not true, and the tube must be forced open (swallowing, yawning, chewing).

15. Inner Ear 3 Parts of Labyrinth cochlea semicircular canals vestibule
functions in hearing
semicircular canals
function in equilibrium
vestibule
functions in equilibrium
utricle and saccule
Labyrinth

16. Cochlea Scala vestibuli upper compartment
Cochlea as it would look ‘unwound’
Tympano = in relation to, in connection with
Oval window = base of scala vestibuli (vestibular duct); round window = base of scala tympani (tympanic duct).
Scala vestibuli and s. tympani are filled with perilymph (like interstitial fluid ad CSF); cochlear duct (s. media) is filled with endolymph (unique comp., but similar to intracellular fluid)
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
part of bony labyrinth

17. 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 (stereocilia) of receptor cells to bend
nerve impulse generated

18. Physiology of Hearing Know pathway for exam
Figure from: Marieb, Human Anatomy & Physiology, Pearson, 2013
Know pathway for exam
Tympanic membrane  malleus  incus  stapes  oval window  scala vestibuli  scala tympani  round window

19. Auditory Nerve Pathways
Accessory Nerve (CN XI)
Figure from: Martini, Fundamentals of Anatomy & Physiology, Pearson Education, 2004
(pons)

20. Vestibule
Utricle
communicates with saccule and membranous portion of semicircular canals
Saccule
communicates with cochlear duct
Macula
contains hair cells of utricle (horizontal) and saccule (vertical)
Utricle and saccule provide sensations of: 1) gravity and 2) linear acceleration
These organs function in static equilibrium (head/body are still)

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

22. Semicircular Canals
three canals at right angles
ampulla (expansion)
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
Acceleration of fluid inside canals causes nerve impulse
These organs function in dynamic equilibrium (head/body are in motion)

23. Crista Ampullaris
Semicircular canals respond to rotational, nonlinear movements of the head

24. Pathways for Equilibrium Sensations
For vestibulo-ocular reflex
80 min to this point.
Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004 *

25. External Anatomy of the Orbital Region
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

26. The Eye and Deep Orbital Region
Visual Accessory Organs
eyebrows
eyelids (palpebrae)
conjunctiva
lacrimal apparatus
extrinsic eye muscles
Lacrimal caruncle - sebaceous plus sweat gland produces whitish oily secrn (‘sand’ in eyes)
Limbus

27. Eyelids palpebrae = eyelids composed of four layers
skin
muscle
connective tissue
conjunctiva
orbicularis oculi – closes eye (CN VII)
levator palpebrae superioris – raises eyelid (CN III)
tarsal (Meibomian) glands – secrete oil onto eyelashes; keep lids from sticking together
conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball; keeps eye from drying out
Fornix
Tarsal plates are CT and serve as insertion points for orbicularis oculi and lev. palpebrae sup. muscles. Blink reflex occurs every 3-7 sec. to spread oil, mucus, and saline across surface of eye.
Eyelash roots are richly innervated and will cause blinking if disturbed
Tarsal (Meibomian) glands embedded in tarsal plates – modified sebaceous gl produce oily secrn to help keeps lids from sticking together. Ciliary gland are located between eyelashes (sebaceous and modified sweat gl).
Infection of a tarsal gl = chalazion; infection of smaller glands = sty.
Conjunctiva is a transparent mucus membrane containing blood vessels that produces a lubricating mucus that helps keep the eye from drying out.
Sagittal section of right eye
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

28. Some External Disorders of Eye
Sty (Infection of smaller glands (eyelashes)
Chalazion (Infection of tarsal glands)
Conjunctivitis (Inflammation of conjunctiva)

29. Lacrimal (Tear) 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
Lacrimal gland is visible through the conjunctiva when the upper lid is everted. Lacrimal puncta are visible as tiny red dots on the medial margin of each eyelid.
Tears: - supply oxygen and nutrients to cornea (avascular) - are antibacterial (contain antibodies and lysozyme) - lubricate and bathe the conjunctiva

30. Extraocular Eye Muscles
Superior rectus
rotates eye up and slightly medially
Inferior rectus
rotates eye down and slightly medially
Medial rectus
rotates eye medially
Four rectus muscles originate from a common tendinous ring, the annuar ring.
The trochlea is a fibrocartilagenous ring through which the superior oblique muscle runs.
Superior and inferior oblique muscles are needed since the superior and inferior rectus muscles approach the eye from a posteromedial direction and their action turns the eye medially. The obliques balance this medial pull and allow the eye to be directly elevated or depressed.
Extrinsic muscles of the eye have a high axon:muscle fiber ratio (8-12 muscle cells per motor unit; some as few as two or three).

31. Extrinsic Eye Muscles Lateral rectus rotates eye laterally
Superior oblique
rolls eye, rotates eye down and laterally
Inferior oblique
rolls eye, rotates eye up and laterally
Diplopia = double vision. Inability to coordinate both eyes to look at same object. Stabismus = crossed-eyes.
Which cranial nerves innervate each of the muscles in the diagram above?
LR6SO4AO3

32. Extraocular Eye Muscles & their CN
Which cranial nerves innervate each of the muscles in the diagram above?
LR6SO4AO3

33. Structure of the Eye - Overview
Figure from: Martini, Fundamentals of Anatomy & Physiology, Pearson Education, 2004
Three layers (tunics) of the eye: - Outer fibrous tunic - Sclera and cornea - Middle vascular tunic (uvea) – Iris, ciliary body, and choroid - Inner neural tunic - Retina

34. Outer (Fibrous) Tunic Cornea anterior portion transparent
light transmission
light refraction
well innervated
avascular
Sclera
posterior portion
opaque
protection
support
attachment site for extrinsic eye muscles
Cornea is covered by epithelial sheets on both surfaces; outside = str. Squamous epithelium that protects from abrasion and merges with the ocular conjunctiva (cells for renewal come from this layer), inside is a simple squamous epithelium that contains sodium pumps that maintain the clarity of the cornea by keeping water content low.
Cornea is well supplied with nerve endings (mostly pain fibers). Touching of cornea causes reflexive blinking (corneal reflex; afferent V, efferent VII). Cornea has great capacity for repair.
Transverse section, superior view

35. Aqueous Humor fluid in anterior cavity of eye
secreted by epithelium on inner surface of the ciliary processes
provides nutrients
maintains shape of anterior portion of eye
leaves cavity through canal of Schlemm (scleral venous sinus)
Nomral intraocular pressure is about 16 mm Hg, maintained by constant production and drainage of aqueous humor. Aq humor supplies nutrients and oxygen to the lens and cornea and to some cells of the retina, and carries away metabolic wastes.
Pressure build up in the eye compresses the retina and optic nerve (glaucoma). Late signs include halos around light and blurred vision.
Normally about 1-2 ul / min of aqueous humor is secreted, the same amount being drained via the scleral venous sinus

36. Lens Loss of lens transparency = cataracts transparent, avascular
biconvex
lies behind iris
largely composed of lens fibers
enclosed by thin elastic capsule
held in place by suspensory ligaments of ciliary body
focuses visual image on retina
(Crystallins)
Loss of lens transparency = cataracts

37. SEM of Lens
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

38. Cataracts

39. Accommodation changing of lens shape to view objects nearby
Far vision (emmetropia) (20 ft. or greater)
The far point of vision is the distance beyond which no change in lens shape is needed for focusing. This is about 20 ft. for the normal (emmetropic) eye.
Closer than 20 ft, the lens must round up (accommodate) in order to focus light acutely on the retina (and the pupils constrict and the eyeballs converge). This close vision reflex appears to be triggered by blurring of the retinal image. Pupils constrict to prevent the most divergent light rays from entering the eye since they would pass through the edges of the lens and not be focused properly. Convergence occurs in order to keep the object’s light rays falling on the foveae.
Myopia = nearsightedness, i.e., NEAR vision is UN impaired. Hyperopia = farsightedness, i.e., far vision is unimpaired.
Presbyopia is the loss of the ability to accommodate with age
Near vision

40. Middle (Vascular) Tunic = Uvea
1. Iris
anterior portion
pigmented CT
controls light intensity
2. Ciliary body
anterior portion
pigmented
holds lens
muscles reshape lens for focusing
aqueous humor
Blood vessels of uvea provide nutrition to all eye tunics.
Iris is most anterior portion of the uvea. Made up of two smooth muscle layers, one circular and one radial. Most babies irises are slate gray or blue because their iris pigment is not yet developed.
3. Choroid coat
provides blood supply
pigments absorb extra light
This layer contains the intrinsic muscles of the eye - Regulate the amount of light entering the eye - Regulate the shape of the lens

41. Iris How would viewing near objects affect pupil size?
composed of connective tissue and smooth muscle
pupil is hole in iris
dim light stimulates (sympathetic) radial muscles and pupil dilates
bright light stimulates (parasympathetic, CN III) circular muscles and pupil constricts
mydriasis
Cycloplegia = paralysis of the ciliary smooth muscles
miosis
How would viewing near objects affect pupil size?

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

43. Inner (Neural) 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 surrounds fovea
fovea centralis – center of macula lutea; produces sharpest vision; only cones
optic disc – blind spot; contains no visual receptors
vitreous humor – thick gel that holds retina flat against choroid coat
Visual axis
Retina has an inner neural layer and an outer pigmented layer (single layer thick, covers ciliary body and posterior face of the iris). The pigmented cells also function as phagocytes and store vitamin A needed for photoreceptors. Anterior neural layer extends to posterior margin of the ciliary body (junction is called the ora serrata rentinae). The two layers are closely approximated but are not fused.
Neural retina receives blood from: 1) Outer third from vessels in the choroid, 2) Inner two-thirds by central artery and central vein of retina that enter and leave via through the center of the optic nerve. Retinal detachment allows vitreous humor to seep in between the retinal layers and deprives the outer neural retinal layer of blood supply from the choroid.
Transverse section, superior view

44. Optic Disc (Blind Spot)
Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004
Fovea centralis is about 0.4 mm in diameter (about the size of the head of a pin).

45. Layers of Retina
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
Some ganglion cells absorb light directly for circadian rhythms and control of pupillary diameter.

46. 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 object
view off-center at night
Cones
short, blunt projections
contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe (photopsins)
provide vision in bright light
produce sharp images
produce color vision
About 130 million rods and about 6.5 million cones – and only about 1.2 million nerve fibers in the optic nerve.
Dark adaptation by the rods takes approximately 30 minutes. This adaptation can be destroyed by white light in just milliseconds

47. Rods and Cones Storage site of vitamin A
Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004
Discs are continually replaced; old used discs are shed and phagocytized by pigmented epithelium.
Rods participate in converging pathways (as many as 100 rods may converge on a single ganglion cell); cones have a one-to-one relationship with bipolar and ganglion cells.
Rhodopsin maximally absorbs in green range in rods. Cones also use retinal and opsin, but the cone opsins differ both from the opsin of the rods and from one another. Blue cones absorp maximally at around 420 nm, green cones at about 530 nm, and red cones at or close to 560 nm.
Nyctalopia = night blindness.
Retinal is chemically related to vitamin A and is made from it.

48. Mechanism of Light Transduction
Ganglion cells generate about action potentials per second even in dark.
Phosphodiesterase (PDE) in the retina is a form of the enzyme that Viagra inhibits. Could this cause visual problems?
Figure from: Marieb, Human Anatomy & Physiology, Pearson Education, 2004

49. Rods and Cones – Neural Connections
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Rods have a high degree of spatial summation since about 600 rods impinge upon 1 biplolar cell, and many bipolar cells impinge upon a single ganglion cell. This allows an additive effect of rod stimulation so a weak intensity stimulus can be detected. Tradeoff is that rods cannot resolve finely detailed images.
(in fovea centralis)
Many rods synapse with a single bipolar cell giving poor resolution (acuity). In fovea, 1 cone synapses with one bipolar cell. Therefore, the resolution (acuity) is better using cones and they produce sharp vision.

50. Image Information
Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004

51. Stereoscopic Vision
Because the pupils and fovea are 6-7 cm apart, each eye receives a slightly different image.
This allows the slightly different pictures to be integrated by the brain resulting in stereoscopic vision and depth perception.

52. Visual Pathway
The right side of the brain receives input from the left half of the visual field
The left side of the brain receives input from the right half of the visual field
Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004
Hemidecussation – half the fibers of the optic nerve cross over to the other side of the brain.

53. And Finally…

54. Touch and Pressure Senses
Class of mechanoreceptor

55. Referred Pain
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

56. Spinal Gating of Pain Signals
Descending Analgesic Fibers (What is an ‘analgesic’, anyway?)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

57. Smell (Olfaction)
Adaptation occurs here
Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Most people can distinguish 2000 to 4000 odors; some up to 10,000 odors. Women generally more sensitive and measurably more sensitive to some odors at time of ovulation. We can detect odors as dilute as a few parts per trillion.
Olfactory cells have a life span of only about 60 days (their exposure to the external environment is unique in the nervous system). However, they are replaceable and the basal cells continually divide and replace the olfactory cells.

58. Taste (Gustation)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
CN X
CN IX
CN VII
About 4,000 taste buds, mostly on tongue (lingual papillae) but some on cheeks, soft palate, pharynx, and epiglottis.

59. 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 (ringing in the ears)
Age-related visual problems include
dry eyes
floaters (crystals in vitreous humor)
loss of elasticity of lens – difficult accommodation
glaucoma
cataracts
macular degeneration