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Study Guide Special Senses
General Senses:
1. Touch and Pressure
2. Temperature
3. Pain
4. Proprioception – detection of changes in body
Special Senses:
5. Vision
6. Hearing = Audition
7. Vestibular System – Posture and movements
8. Smell = olfaction
9. Taste = gustation
10. Sensory Receptors and Stimuli
Sensory Receptors
11. Sensory receptors are either endings of an afferent neuron or a receptor cell that passes information to an
afferent neuron.
12. Stimulus is a change in environment detected by a sensory receptor.
Types of Receptors:
13. Mechanoreceptor – touch, pressure, stretch
14. Thermoreceptor – temperature
15. Photoreceptor – light
16. Chemoreceptors – binding of particular chemical
17. Nociceptors – pain is due to tissue damage or potential of tissue damage
Special Senses
18. Special senses include chemical senses – smell (nose) and taste (tongue); vision – eyes; hearing and
balance – ears.
19. Chemical Senses – Smell = Olfaction: Olfactory epithelium = sensory epithelium for detecting smell lies in
roof of nasal cavity. Nerve fibers of these sensory cells pass through pores in Cribriform plate of ethmoid
bone and synapse with neurons of olfactory bulbs below cerebral hemispheres. Olfactory tracts carry
information to in temporal lobe. Some fibers of olfactory tract carry the sensory input also to limbic
system for emotional interpretation.
20. Chemical Senses – Taste = gustatory sensation: Tongue is the main organ of Taste. Smelling vapors of food
is 80% taste. Temperature, texture and touch etc. completes the experience. About 10,000 taste buds are
present on tongue. Each taste bud has sensory and basal cells in it. Sensory Cells of taste buds get burnt
with hot foods and are replaced every 7-10 days. Vapors of food dissolve in water or mucous and stimulate
specific sensory cells by binding to specific receptor proteins.
21. H+ = stimulate sour tasting sensory cells.
22. Metal ions = Na+, stimulate salt tasting sensory cells.
23. Sweet = sugars and other organic compounds
24. Bitter = alkaloids and some others like aspirin
25. Umami = recently discovered by Japanese scientists = beef, taste of steak, tang of aging cheese, yummy
taste of some foods = by amino acids asparate and glutamate.
26. Water receptors are present in pharynx.
27. Taste maps of tongue are not true.
28. The Eye and Vision: The eye is formed of eyeball and placed in bony socket – Orbit and is padded with fat.
6 extrinsic muscles rotate eyeball and lacrimal gland is also present in orbit.
29. The lacrimal apparatus: lacrimal glands secrete tears that protect and provide nourishment to eye.
Lacrimal canaliculi drain excess fluid to lacrimal sac nasolacrimal duct middle nasal meatus
30. 6 eyeball muscles’ nerve supply: lateral rectus = Trochlear - 4th; superior oblique, superior rectus, inferior
rectus and inferior oblique = Oculomotor - 3rd; medial rectus = Abducens - 6th cranial nerve
31. Eyebrows – shade and protection of eye
32. Eyelids – protection and lubrication of eye by reflex blinking. 2 muscles orbicular oculi and levator
palpebrae lie in the eyelids. Modified skin glands – sebaceous and sweat, are also present.
33. Conjunctiva – is the internal lining of eyelids and covers the anterior side of eyeball. It secretes mucous to
aid in lubrication.
34. Structure – the eyeball is formed of 3 layers = tunics; fibrous – Sclera, vascular – Choroid or uvea and
sensory – Retina.
35. Outer layer = 2 parts.
36. Sclera – white and opaque, protective, maintains shape and muscle attachments.
37. Cornea – transparent anterior part allows light to enter and participates in image focusing.
38. Middle layer = 3 parts choroid, ciliary body and iris.
39. Choroid – dark brown, vascular – provides nutrients to all 3 layers, eliminates scattering of light.
40. Ciliary body – ring like, has muscles to change lens shape and secretes aqueous humor.
41. Iris – the colored part of eye seen from eye, has Pupil – an opening at the center, has muscles to regulate
pupil size. These days used to positively identify humans.
42. Innermost layer = Retina = 2 parts.
43. Pigment layer = outer layer and absorbs light.
44. Neural layer = inner layer – formed of 3 layers of neurons – in front ganglion cells, their nerve fibers form
optic nerve; middle layer of Bipolar neurons; and outer layer of photoreceptors – the cone cells and rod
cells.
45. I made a flow chart below and light comes from the front side of retina – bottom in chart
1.
2.
Cone Cells
Stimulated by bright light
Located at the center of retina
1.
2.
Rod Cells
Stimulated by dim light
Located at the periphery of retina
3.
Give colored vision
3.
Give black and white vision
Focusing for distant and close vision:
46. Far objects (parallel rays) – Ciliary muscles relaxed suspensory ligaments tense  lens thin or flat
47. Near objects (divergent rays) – Ciliary muscles tense suspensory ligaments relaxed  lens thick or
rounded
48. Myopia – near object seen clearly; can’t see far objects; corrected with a Concave lens glasses.
49. Hyperopia – far objects seen clearly; can’t see near objects; corrected with a Convex lens glasses.
50. Suspensory ligament holds the lens in position in the eye. Ciliary muscles in ciliary body can stretch or
relax the suspensory ligament which in turn makes the lens thin or thick. By default eyes are focused on
far objects.
51. Vitreous humor a thick jelly like material fills the posterior cavity behind lens – suspensory ligament –
ciliary body. It helps to maintain retina pressed against the choroid. Some impurities called floaters are
present in vitreous humor.
52. Aqueous humor fills the anterior cavity in front of lens – suspensory ligament – ciliary body. Ciliary body
secretes it and then it passes through pupil to anterior chamber. It is drained by Canal of Schlem. If not
drained, the eye pressure can increase dramatically and make a person blind within hours – homeostatic
imbalance is Glaucoma.
53. The EAR – Hearing and Balance: Ear is formed of 3 main parts as shown in the flow chart below.
54. Outer ear = auricle or pinna, collects sound waves, auditory canal carries sound waves to tympanum. The
meatus has ear wax glands – cerumen glands to protect against fungal and bacterial growth.
55. Middle ear = tympanum + 3 ear ossicles + middle ear cavity with auditory tube + oval and round windows
to inner ear.
56. Middle ear cavity is a narrow high cavity inside temporal bone. On lateral side it has tympanum. On
medial side it has Oval and round windows that open into bony labyrinth.
57. Tympanum vibrates with sound waves and passes vibrations to malleus joined at medial side of
tympanum. Tensor tympanic muscle is joined to malleus and regulates the tension of tympanum.
58. 3 Ear Ossicles: Malleus passes the vibrations to incus and incus in turn to stapes (the smallest bone in
human body). Stapedius muscle is the smallest muscle in human body. Ear ossicles amplify the sound
signal.
59. Auditory tube joins middle cavity to nasopharynx and helps to maintain similar pressure on both sides of
tympanum.
60. Inner ear = bony labyrinth + membranous labyrinth
61. Bony labyrinth has 2 membrane covered openings oval and round windows that open into middle ear
cavity. Bony labyrinth has Vestibular duct and Tympanic duct parts that lie superior and inferior to
Cochlear duct. Bony labyrinth is filled with a fluid perilymph.
62. Membranous labyrinth – named so due to complex structure: is filled with a fluid Endolymph. Its parts and
their functions are listed in the following chart.
63. Vestibule = detects movements of head and passes information to cerebellum to control body position.
Angular = Acceleration in rotational motion is discovered by cristae present in ampullae of semicircular
canals. Pull of gravity and Straight motion are detected by maculae of utricle and saccule.
64. Cochlea is responsible for hearing. Cochlea has 3 ducts – vestibular, cochlear, and tympanic ducts.
65. Hearing is detected by spiral organ of Corti present in basilar membrane of cochlear duct of Cochlea. Each
cell of Organ of Corti gets depolarized by a narrow range of sound frequency. High frequency sounds
stimulate cells closer to oval window. Low frequency sounds stimulate sensory cells closer to end of
cochlear duct.
66. Vestibular nerve collect information about balance from vestibule and Cochlear nerve collect information
about hearing from Cochlea and make VESTIBULOCOCHLEAR (8th) cranial nerve. Vestibulocochlear nerve
passes through Internal Acoustic Meatus and synapses with ganglia in pons.
Recap 1 General and Chemical Senses
1. Nerve fibers from olfactory neurons pass through ----- foramina in ------- plate in roof of nasal cavity.
2. Bipolar neurons are present in ----- and ----- sensory epithelia.
3. Vapors must ------------ before can stimulate olfactory cells.
4. --------- stimulate sour tasting = gustatory cells.
5. ----------stimulate salt tasting gustatory cells.
6. Facial nerve collects sensory information about taste from --- of tongue and glossopharyngeal nerve
collects sensory input from ---- of tongue.
7. ---- ----- are wide spread tactile receptors in finger tips, lips, dermal papillae, nipples and genitals.
8. ----- ----- collect information about deep pressure, vibrations and tickle.
9. ----- receptors are distributed in mucous membranes.
10. Muscle spindles and tendon organs are responsible for -------, sensory input inside the body.
Recap 2 Eyes
1. Tears are produced by -------------- glands.
2. ----------is the internal lining of eyelids, the mucous membrane covering anterior side of the eyeball.
3. Light passes through ---------, ------------- humor, ---------- in iris, --------------, -------------humor and reaches
retina.
4. Inside retina light 1st passes through ---------- cells, ---------------neurons and ------------or ----------- cells.
5. Muscles in ----------regulate the amount of light entering the eye through pupil.
6. Eyes focus on far objects when ciliary muscles are -----------, suspensory ligament is -------- and lens is
thin.
7. Eyes focus on near objects when ciliary muscles are -----------, suspensory ligament is -------- and lens is
thick.
8. -------------is anterior transparent part of eyeball and is continuous with sclera.
9. Anterior cavity is filled with ------------- humor and posterior cavity is filled with ----------humor.
10. ----------- are activated by dim light and give black and white images; ------------- are stimulated by bright
light and give colored images.
11. --------------- --------- secretes aqueous humor and ------- --- -------------- delivers it back to venous blood.
12. ------------ --------- is ring like body and has muscles to change thickness of lens to focus eyes.
13. Maximum refraction (bending of light rays) to focus images in eye is done by ---------------------.
14. Blindness caused due to clouding of lens = opacity of lens is ------------------.
15. Blindness caused due to very high aqueous pressure (due to blockage of Canal of Schlem) is -------.
16. Inability to see clearly far objects is --------------; and inability to see clearly near objects is ----------Recap 3 Ear
1. -------------- is the organ of hearing and balance.
2. 3 small bones ----, ------, and ------ are present in middle ear.
3. Stapes passes sound energy to --------- window.
4. --------------- is responsible for equilibrium; and ------------- for hearing.
5. Sensory hair cells of Organ of Corti lie on -------- membrane and are stimulated by --------------.
6. Cochlear duct is filled with fluid ------and vestibular duct and tympanic duct are filled with --------.
7. Hair cells get depolarized when their hair hit and bend against ---------------------- membrane.
8. 1 ---------- is present in each utricle and saccule (vesicular sacs); detects ------ and ------ .
9. 1 ---------- is present in each ampulla of 3 semi-circular canal and detects ------ ----- .
10. ------- nerve carries information for equilibrium and -------------- nerve for hearing.
11. ----- carries equal pressure on both sides of tympanic membrane.