1. Anatomy & Physiology I Chapter 11
The Senses
Anatomy & Physiology I
Chapter 11

2. The Senses Protect a person by detecting changes in the environment
Stimulus – an environmental change that initiates or stimulate a nerve impulse
Sensation – when a specialized area of the cerebral cortex interprets the nerve impulse and the stimulus then becomes something we experience
Environmental change >> stimulus >> threshold stimulus >> sensory receptors >> sensory neuron>> CNS >> interpretation>> sensation (what we experience or sense)
Threshold stimulus - minimum amount of stimulus required to generate a nerve impulse

3. Sensory Receptors – Types based on Structure
Free dendrite of a sensory neuron; Example, pain, temperature
End-organ - the modified dendrite ending of a sensory neuron enclosed in a capsule -Pacinian & Meissner corpuscles for pressure & touch receptors
Specialized cell associated with an afferent neuron (afferent/ascending/to the CNS); rods & cones in the eye

4. Sensory Receptors

5. Sensory Receptors – Types based on Stimulus
Chemoreceptors – detect chemicals in solution; taste & smell
Photoreceptors – respond to light; eye retina
Thermoreceptors – detect temperature change; skin
Mechanoreceptors – respond to movement, vibration, pressure, stretch; located in skin, joints (monitor body position), hearing & equilibrium in ear

6. Types of senses based on the distribution of their receptors
Special senses; sensory receptors localized in a special sense organ
Vision
Hearing
Equilibrium
Taste
Smell
General senses; sensory receptors widely distributed throughout the body
Pressure
Temperature
Pain
Touch
Position

7. The Eye - Protective Structures
Skull bones form walls of eye orbit; over half of posterior eye
Upper & lower eyelids; anterior eye
Eyelashes & eyebrows; anterior eye
Conjunctiva; lines inner surface of eyelids & covers the visible portion of the white of the eye (sclera); produces mucus & is highly vascular
Lacrimal glands; produce tears which lubricate & produce enzyme that protects against infection
Flow from superior lateral eye into inferior medial nasolacrimal duct

8. Lacrimal Gland & Conjunctiva

9. Coats of the Eyeball 3 tunics (coats)
Sclera – outermost tunic made of tough connective tissue; white of the eye because made of collagen & no blood vessels
Choroid – coat made of delicate connective tissue; extensive blood supply which are visualized during eye exam; prevents light from scattering throughout eye
Retina – actual receptor layer; contains rods & cones which generate visual nerve impulses

11. What are some structures that protect the eye?
What are the names of the tunics of the eyeball?

12. Pathway of Light Rays & Refraction
Refraction – bending of light rays as they pass from one substance to another substance of a different density
Allows light from a very large area to be focused on a very small area of the retina
Cornea
Aqueous humor
Lens
Vitreous body

13. Light Refraction in the Eye
Cornea – transparent, colorless continuation of sclera that covers the pupil; the window of the eye
Aqueous humor – watery fluid that fills the eye anterior to the lens; aids in refraction & maintains eye shape
Lens – clear circular structure with biconcave surface made of firm, elastic material; can change in thickness & focus near or far
Vitreous body – soft gel that fills entire space posterior to the lens; aids in refraction & maintains eye shape

14. Layers of the Retina
Pigmented layer – deepest layer just anterior to choroid
Rods & cones – receptors of the eye
Connecting neurons that carry impulses toward the optic
nerve

15. Rods Rods – highly sensitive to light
function in dim light but do not provide sharp image
Dark adaptation; the time it takes for rods to begin working in a darkened area
120 million each retina
Distributed towards the periphery of the retina
See shades of gray; no colors
Rhodopsin – visual purple pigment that is sensitive to light; requires vitamin A; lack of this pigment leads to night blindness

16. Cones Cones – sensitive to color Function only in bright light
6 million per retina
Localized in center of retina
fovea centralis, pit near the optic nerve; area of greatest visual acuity
surrounded by the macula lutea
Optic disk; point where the optic nerve arises in the retina; no rods or cones in this area; blind spot on the retina
Sees sharp images
Pigments sensitive to red, green, blue
Hereditary lack of pigment can lead to colorblindness in males

17. Macula lutea (yellowish)
Fovea & Macula lutea
Fovea (dark pink) &
Macula lutea (yellowish)

18. Visual Impulses
Light stimulates rods & cones which stimulate neurons that eventually merge to form the optic nerve (CN II)
Some optic nerve fibers crosses at optic chiasma
Visual center in the occipital cortex of the cerebrum interprets

19. Eye Muscles – Extrinsic & Intrinsic Groups
6 voluntary on outer surface of eye
Controlled by CN III, IV, VI (oculomotor, trochlear, abucens)
Convergence – pulling the eyeballs in a coordinated fashion so there is one visual field

20. Eye Muscles – Extrinsic & Intrinsic Groups
Involuntary muscles within the eyeball
Controlled by CN III (oculomotor)
Iris; pigmented part of the eye composed of 2 sets of muscles that control pupil size
Circular muscle constricts in bright light
Radial muscle constricts in dim light
Ciliary muscle; holds the lens of the eye in place by suspensory ligaments
Accomodation – ciliary muscle constriction changes the shape of the lens to allow for near & far vision

22. Intrinsic Eye Muscle Actions

23. The light rays from a close object diverge (separate) more than do the light rays from a distant object >>the lens must become more rounded to bend the light rays more
When the ciliary muscle is relaxed, tension on the suspensory ligaments keeps the lens in a more flattened shape. For close vision, the ciliary muscle contracts
For close vision, the ciliary muscle contracts, which draws the ciliary ring forward and relaxes tension on the suspensory ligaments. The elastic lens then recoils and becomes thicker

24. Nerve Supply to Eye Two sensory nerves supply the eye:
CNII – optic nerve; carries visual impulses from retinal rods & cones to the thalamus (diencephalon) to the visual center in occipital lobe of cerebrum
CNV – trigeminal nerve, opthalmic branch; carries pain, touch & temperature impulses from the eye to the brain
There are no retinal rods and cones in the area of the optic nerve. Consequently, no image can form on the retina at this point, which is known as the blind spot or optic disk

25. Nerve Supply to the Eye
Three nerves carry motor impulses to the eyeball muscles:
CNIII – oculomotor; largest motor nerve to the eyeball; supplies voluntary & involuntary muscles to all but two eye muscles
CNIV – trochlear; supplies superior extrinsic eye muscle
CNVI – abducens; supplies lateral extrinsic eye muscles

26. Steps in Vision Light refracts (bends)
Muscles of the iris adjust the pupil
Ciliary muscle adjusts the lens (accomodation)
Extrinsic eye muscles produce convergence (coordinate to allow one visual field)
Light stimulates rods & cones
Optic nerve transmits impulses to thalamus
Thalamus transmits impulses to occipital lobe
Occipital lobe cortex interprets impulses

27. Errors of Refraction Hyperopia – farsightedness
Usually due to abnormally short eyeball (flat cornea)
Light focuses behind retina
The lens can thicken only to a given limit to accommodate for near vision
move an object away from the eye to see it clearly
Glasses with convex lenses that increase light refraction
Myopia – nearsightedness
Usually due to abnormally long eyeball
Light focuses in front of retina
Distant objects appear blurred and may appear clear only if brought near the eye
A concave lens corrects for myopia
Astigmatism – blurred vision
Cornea or lens curves irregularly, bending light incorrectly

28. A. Normal B. Myopia C. Hyperopia D. Astigmatism

29. Eye Disorders
Strabismus – deviation of the eye due to lack of coordination of eye muscles
In convergent strabismus, the eye deviates toward the nasal side
In divergent strabismus, the affected eye deviates laterally.
if not corrected brain will not develop to see properly
Amblyopia – loss of vision in a healthy eye because it cannot work properly with the other eye

30. Eye Disorders Conjuntivitis – inflammation of conjunctiva
Pinkeye – conjunctivitis caused by infection; is usually caused by cocci or bacilli
Inclusion conjunctivitis is an acute eye infection caused by Chlamydia (AKA Trachoma)
Corneal laceration – most common eye injury & if untreated can result in blindness
Cornea is avascular so it is possible to receive transplant without rejection
Enucleation – removes the eye due to traumatic injury
Cataract – opacity of the lens which can lead to blindness
Glaucoma – excess pressure in the eyeball due to aqueous humor not being reabsorbed into blood

31. Conjunctivitis & Cataract

32. Glaucoma

33. Disorders related to retina
Diabetic retinopathy – retina damaged by vascular hemorrhages & overgrowth
Retinal detachment – retina separates from underlying layer as the result of trauma or fluid accumulation between tunics of eye
Macular degeneration – macula lutea deteriorates & distorts visual field

34. Diabetic Retinopathy

35. Detached Retina

36. Macular Degeneration

37. The Ear - Structure Outer ear – external ear to the tympanic membrane
Middle ear – contains 3 bones (ossicles) of ear & eustachian tube
Inner ear – contains sensory receptors for hearing & equilibrium

38. Outer Ear Pinna – aka auricle; the external ear
External auditory canal – aka external auditory meatus
Contains ceruminous glands
Tympanic membrane – aka eardrum
Vibrates as sound waves enter the ear

39. Middle Ear - Ossicles
Small cavity containing 3 ossicles (bones) that amplify sound waves received by tympanic membrane
Malleus (hammer) – attached to tympanic membrane by handle & head attaches to incus
Incus (anvil) – connects to malleus & stapes
Stapes (stirrup) – connects to oval window, the membrane of inner ear

40. The middle ear- ossicles

41. Middle Ear – Eustachian Tube
Eustachian tube – connects middle ear to pharynx
Allows pressure to equalize on the 2 sides of tympanic membrane

42. Inner Ear aka Bony Labyrinth
3 separate divisions of sensory receptors
Vestibule, semicircular canals & cochlea
Perilymph – fluid of inner ear
Membranous labyrinth – within bony labyrinth & filled with endolymph

43. Inner Ear aka Bony Labyrinth
Vestibule – 2 bony chambers that contain equilibrium receptors
Semicircular canals – 2 bony tubes that contain equilibrium receptors

44. Inner Ear aka Bony Labyrinth
Cochlea – bony coil that contains hearing receptors
Round window – membrane through which sound waves leave the inner ear

46. Hearing Organ of Corti – sensory organ of hearing
Consists of ciliated receptor cells
Located inside membranous cochlea aka cochlear duct
Wave against the roof of the cochlear duct (tectorial membrane)
Stimulates cochlear nerve (auditory branch of vestibulocochlear nerve CN VIII)
Sound waves leave inner ear through round window

47. Steps of Hearing Sound waves vibrate tympanic membrane
Amplified by ossicles in middle ear
Reach the oval window & create waves in the inner ear fluids
Vibrating the chochlear duct
Causing cilia or organ of Corti to wave against the tectorial membrane
Cochlear nerve stimulated (branch of CNVIII)
The temporal lobe of cerebrum interprets stimuli

48. Hearing
Organ of Corti differentiates both pitch (tone) & intensity (loudness)
Higher pitched tones near the base
Lower pitched tones near the top
Loud sounds stimulate more cells & produce more vibrations, sending more impulses to the brain

49. Equilibrium - Balance
Sensory receptors are ciliated cells located in vestibule & semicircular canals
Shifting in position of cilia within the thick fluid that surrounds them generates a nerve impulse
Send impulses to vestibular branch of CN VIII (vestibulocochlear)

50. Equilibrium - Balance
Static equilibrium- Sensing the position of head or body when moving in a straight line
Due to vestibule receptors known as macula
Fluid surrounding maculae contains crystals called otoliths which drag the fluid & increase pull of gravity
Detail of Macula

51. Equilibrium
Dynamic equilibrium – function during spinning or moving in different directions
Semicircular canal receptors known as cristae

52. Ear Disorders Otitis media – inflammation of the middle ear
Children susceptible because short eustachian tube
Otitis externia – inflammation of external auditory canal - aka swimmer’s ear

53. Hearing Loss
Conductive hearing loss – interference with sound waves passing through ear
Foreign body obstruction
Tympanic membrane damage
Otosclerosis – hereditary malfunction of stapes
Sensorineural hearing loss – cochlea, CNVIII or temporal lobe of brain improperly transmit or interpret neural stimuli
Prolonged exposure to loud noises
Certain drugs or toxins
Cochlear implant can stimulate cochlear nerve directly, bypassing receptor cells
Presbycusis – age related hearing loss due to atrophy of sensory receptors an CNVIII fibers

54. Loud Noise Damage to Ear

55. Taste - Gustation Tongue receptors aka taste buds
Taste buds are stimulated only if the substance to be tasted is in solution or dissolves in the fluids of the mouth
Sweet – tip of the tongue
Salty – middle of tongue
Sour – middle sides of tongue
Bitter – posterior tongue
Transmitted along CN VII & IX (facial & glossopharyngeal) to frontal cortex; no special center in cortex
Other tastes include water, alkaline, metallic
Tastes can be combined with smells

56. Smell - Olfaction
Important for protection, taste, triggering memory, sexual behavior
Receptors located in superior nasal cavity
Conduct impulses along olfactory nerve (CNI) to olfactory center in temporal lobe of cerebral cortex

57. General Senses Located throughout body Touch Pressure Temperature
Position
Pain

58. General Senses
Touch –
The touch receptors, tactile (TAK-til) corpuscles, are found mostly in the dermis of the skin and around hair follicles
Meissner corpuscles in skin, also near hair follicles; # of corpuscles determines sensitivity to touch
Lips, tip of tongue, fingertips very sensitive
Back, back of hand less sensitive
Pressure – Pacinian corpuscles in skin, also near joints
sensory end-organs
Can respond even when a person is under anesthesia

59. General Senses Temperature – free nerve endings; dendrite branches
Widely distributed in skin
Separate branches for heat & cold
Stimulus travels to hypothalamus (diencephalon)
Position – proprioceptors - receptors located in joints, muscles, tendons
Kinesthesia – sense of body movement – where the body is in time & space
Inform brain about muscle contraction/tendon tension
Muscle tone, posture, coordination, complicated skills
Stimulus travels to cerebellum

61. Temperature & Proprioceptors

62. General Senses
Pain – free nerve endings; widely distributed in skin, muscles, joints, and scattered sparsely in viscera & blood vessels
Nocioceptors – nerve endings that transmit pain signals
Sharp – acute, fast Adelta fibers
Dull – slow, chronic C fibers

63. Pain
The 5th vital sign
An unpleasant sensory & emotional experience associated with actual or potential tissue damage or described in terms of such damage
Pain is always subjective
Pain is whatever the experiencing person says it is, existing whenever he or she says it does

64. Neuroanatomy of Pain
Nocioception – how noxious stimuli are perceived as pain
3 phases of nocioception
Transduction – a noxious stimulus occurs peripherally and travels to the spinal cord
Transmission – pain impulse moves from the level of the spinal cord to the brain
Perception – conscious awareness of a painful sensation
Modulation – pain is inhibited
The brain sends signals to slow down or impede the pain impulse

65. Sources of Pain Visceral pain – from organs
Deep somatic pain – from structures like vessels, bones, muscles, joints
Cutaneous pain – from skin
Referred pain – pain felt at a particular site but originates at a different location innervated by the same spinal nerve
Neuropathic pain – an abnormal neurological processing of pain signals
the most difficult to assess & treat
Pain often perceived long after the site of injury heals

66. Referred Pain

67. Different Pain Scales

68. Neonatal Pain Scoring

69. Pain Relief Analgesics – drugs that relieve pain
Nonnarcotic analgesics – act locally to reduce inflammation i.e. NSAIDs
Narcotics – act on CNS to alter the perception of pain
Anesthetics – drugs that block pain
Endorphins – chemicals released from the brain to modulate pain; massage can activate endorphins
Heat – reduces chronic pain as long as there is no inflammation
Cold – acts as an anesthetic; reduces inflammation; when in doubt, ice
Relaxation or distraction techniques

71. Sensory Adaptation
Sensory receptors exposed to continuous stimulus adjust so sensation becomes less acute; warmth, cold & light pressure adapt rapidly
Pain receptors do not adapt; C fiber (slow pain) receptors become more sensitive if exposed to continuous stimulation

72. Chronic Pain

73. Chronic Pain