This document discusses various somatic and special senses in humans. It describes the five special senses of smell, taste, vision, hearing and balance. It also discusses the general somatic senses of touch, pressure, heat and pain detected by receptors in the skin, muscles, and internal organs. For each sense, it outlines the key sensory structures, receptors, pathways and common disorders. It provides details on the anatomy and physiology of smell, taste, vision, hearing, balance and the skin's sensory functions.

1. SOMATIC SENSES
AND
SPECIAL SENSES

2. • Special senses – smell, taste, vision, hearing and
balance.
• This 5 senses associated with sensory input to the
CNS
• General (somesthetic, somatosensory) – widely
distributed in skin, muscles, tendons, joints and
vicera.
• They detect touch, pressure, stretch, heat, cold and
pain, blood pressure

3. Definition of Sensation
• Conscious or subconscious awareness of changes in
the external or internal environment.
• For sensation to occur, four condition must be
satisfied :

4. 1. A stimulus or change in environment must occur. A stimulus
that activates a sensory receptor may be in form of light,
heat, pressure, mechanical/chemical
2. A sensory receptor must convert the stimulus to an
electrical signal – produce nerve impulses
3. Nerve impulses conducted along neural pathway from
sensory receptor to the brain.
4. A region of the brain must receive and integrate the nerve
impulses into a sensation

5. Sensory
Receptors
Mechanoreceptors
Themoreceptors
Nociceptors
(Pain Receptor)
Photoreceptors
Chemoreceptors
Osmoreceptors

6. Tpyes of Sensory Receptors
1. Mechanoreceptors – mechanical pressure,
vibration, sensation of touch, hearing and
equilibrium, monitors stretching of blood vessels
and internal organs.
2. Themoreceptors – changes in temperature
3. Nociceptors (Pain Receptor) – pain, damage of
tissue

7. 4. Photoreceptors – detect light that strikes the retina
of eye
5. Chemoreceptors – detect chemicals in mouth, nose,
and body fluid, detect changes in levels of O2, CO2
6. Osmoreceptors – sense the osmotic pressure of
body fluid.

8. Sense of Smell

9. • The olfactory system is responsible for our sense of smell.
• Also known as olfaction, involves the detection and
identification of molecules in the air.
• Once detected by sensory organs, nerve signals are sent to
the brain where the signals are processed.
• Our sense of smell is closely linked our sense of taste as both
rely on the perception of molecules.
• It is our sense of smell that allows us to detect the flavours in
the foods we eat.
• Olfaction is one of our most powerful senses. Our sense of
smell can ignite memories as well as influence our mood and
behaviour

10. Olfactory System Structures

12. Structure Description
Nose Opening containing nasal passages that allows outside air to
flow into the nasal cavity. Also a component of the
respiratory system, it humidifies, filters, and warms the air
inside the nose.
Nasal cavity Cavity divided by the nasal septum into left and right
passages. It is lined with mucosa.
Olfactory epithelium Specialized type of epithelial tissue in nasal cavities that
contains olfactory nerve cells and receptor nerve cells.
These cells send impulses to the olfactory bulb
Cribriform plate A porous extension of the ethmoid bone, which separates
the nasal cavity from the brain. Olfactory nerve fibers
extend through the holes in the cribriform to reach the
olfactory bulbs

13. Structure Description
Olfactory nerve nerve (first cranial nerve) involved in olfaction. Olfactory
nerve fibers extend from the mucous membrane, through
the cribriform plate, to the olfactory bulbs.
Olfactory bulbs bulb-shaped structures in the forebrain where olfactory
nerves end and the olfactory tract begins
Olfactory tract band of nerve fibers that extend from each olfactory bulb to
the olfactory cortex of the brain.
Olfactory cortex area of the cerebral cortex that processes information about
odors and receives nerve signals from the olfactory bulbs.

14. Odor Pathways
• Orthonasal pathway - involves odours that are
sniffed in through the nose
• Odours that enter the nasal passages and are
detected by chemical receptors in the nose

15. • Retronasal pathway - pathway that connects the top of the
throat to the nasal cavity
• Pathway involves aromas that are contained within the foods
we eat. Odours are released that travel through the
retronasal pathway connecting the throat to the nasal cavity.
• Once in the nasal cavity, these chemicals are detected by
olfactory receptor cells in the nose.
• When retronasal pathway blocked, the aromas in foods can
not reach odour detecting cells in the nose.
• This often happens when a person has a cold or sinus
infection.

16. Smell Disorders
• Individuals have difficulty detecting or perceiving odours.
• Factors - smoking, aging, upper respiratory infection, head
injury, and exposure to chemicals or radiation.
• Anosmia is a condition defined by the inability to detect
odours.
• Hyposmia, the diminished sense of smell, is also linked to
the development of neurodegenerative diseases such as
Parkinson's and Alzheimer's disease.

17. Sense Of Taste

18. • Taste, or gustation, is a sense that
develops through the interaction of
dissolved molecules with taste buds.
• Five Primary Taste – Sweet, Sour,
Bitter, Salty, Umami.
• Umami – “meaty” or ”savory” taste

19. Structure Of Taste Buds
• Receptors of taste sensations located in the taste
buds.
• Nearly 10,000 taste bud on tongue
• Some are found on the root of the mouth, pharynx
(throat) and epiglottis cartilage lid over the voice box.
• Number of taste bud declines with age.

20. Structure Description
Papilae Taste bud found in elevations on the tongue, provide
rough texture
Vallate papillae Form an inverted V-shape row back of toungue
Fungiform Papilae Mushroom shaped, scattered entire surface of the
tongue
Filiform Papilae Entire surface of tongue, contain touch receptors but
no taste buds.

21. Structure Description
Tatse Bud • An oval body consisting of three types of epithelial cells
(supporting cells, gustatory receptor cells, basal cells)
• Supporting cell surround abaut 50 gustatory receptor cells.
• Basal cells are stem cells produce supporting cells.

23. Sense Of Sight (Vision)

24. • We perceive shapes, distance, movement, color,
heat and depth by our sense of sight.
• The organ for the sense of sight is the eye, about the
shape of a ping-pong ball.
• The eye alone cannot make sight possible. It works
with the brain and on the outside, needs light to be
present.

25. External and Accessory Structures
• Eyelids – protect the eye from excessive light,
lubrications (blinking)
• Eyelashes & Eyebrows – protect the eyeball from
foreign objects
• Lacrimal apparatus – group of glands, ducts, canals
and sacs that produce and drain lacrimal fluid (tears)
• Tears contain salts, some mucus, lysozyme (enzyme)

27. Layers of the Eyeball
Layers
of
Eyeball
Fibrous
Tunic
Vascular
Tunic
Retina

28. Fibrous Tunic
• Outer coat of eyeball
• Cornea – transparent fibrous coat that covers colored
iris.
• Cornea help focus light rays onto retina
• Sclere – the “white” of eye. Gives shape, makes rigid and
protect inner parts.
• Conjuntiva – An epithelial layer covers the sclera but not
the cornea.

29. Vascular Tunic
• Middle layer of eyeball.
• Choroid – Thin membrane that lines internal surface of
sclera.
• Contain many blood vessels that help nourish retina
• Contain melanocytes which produce pigment melanin.
• Melanin absorbs stray light rays which prevent reflection
and scattering of light, so image cast on retina by the
cornea and lens remain sharp and clear.

30. Vascular Tunic
• Ciliary body consist of ciliary proses and ciliary
muscle.
• Ciliary proses – secrete fluid called aqueous humor
• Ciliary muscle – smooth muscle that alters shape of
lens for viewing objects up close or at distance

31. Vascular Tunic
• Lens – a transparent structure that focus light rays onto
retina.
• Zonular fibers attach the lens to the ciliary muscle and
hold the lens in position.
• Iris (colored circle) – light enter the eyeball through the
hole in the centre (pupil)
• Regulates the amount of light passing through the lens.

33. Responses of the pupil to light of varying
brightness

34. Retina
• Consist of two layers ( Neural Layer & Pigmented
Layer)
Rods and Cones (Photoreceptors)
• The retina has two special types of nerve cells: The rods and the cones.
• Rods are super-sensitive in the dark, and help us see things in the dark.
• Cones are active in the light and help us see colour.
• Special cone cells are sensitive to three colours, red, blue and yellow.
• With these three colours, the cone nerve cells are able to render them
into millions of beautiful colours.

36. How Eye Works
• Light reflects off the object we are looking at.
• Light rays enter the eye through the cornea at the front of the eye.
• The light passes through a watery fluid (aqueous humor), and enters the pupil to reach the
lens.
• The lens can change in thickness to bend the light, which will focus it onto the retina at the
back of the eye.
• On the way to the retina, the light passes through a thick, clear fluid called a vitreous humor.
• The light then reaches the back of the eye and hits the retina.
• The retina translates the light into electrical impulses
which are then carried to the brain by the optic nerve.
• Finally, the visual cortex (or centre) of the brain
interprets these impulses as what we see.

37. Normal and Abnormal Refraction In The Eyeball
• In the normal (emmetropic) eye, light rays from an object
bent sufficiently by the cornea and lens to focus on the
fovea centralis.
• In the nearsighted (myopic) eye, the image is focused in
front of the retina.
• Correction for myopia by usage of concave lens that
diverges entering light rays so that they have to travel
further through eyeball

38. Normal and Abnormal Refraction In The Eyeball
• In the farsighted (hyeropic) eye, the image is focused
behind the retina.
• Correction can be made by convex lens that causes
entering light rays to converge.

40. Common Eye Related Disorders
• Colour blindness: This occurs when cone cells are
absent or do not work correctly. Someone who is
colourblind finds it difficult to distinguish between
certain colors.
• Cataracts: Clouding of the lens causes cataracts. They
lead to blurred vision and, if untreated, blindness.
• Glaucoma: Pressure builds up inside the eye and can
eventually damage the optic nerve. It can eventually
lead to loss of sight.

41. Sense Of Hearing

42. • The ear is the organ of both hearing and equilibrium.
• Hearing is the transduction of sound waves into a
neural signal that relies on the structures of the ear.
• The ear is subdivided into 3 major parts: the external
ear, middle ear, and internal ear.

43. Structure of An Ear

44. External or outer ear
• Pinna or auricle. This is the outside part of the ear.
• External auditory canal or tube. This is the tube that
connects the outer ear to the inside or middle ear
• Tympanic membrane (eardrum). The tympanic
membrane divides the external ear from the middle ear

45. Middle ear (tympanic cavity)
• Ossicles. Three small bones that are connected and
transmit the sound waves to the inner ear. The bones
are called:
*Malleus
*Incus
*Stapes

46. • Eustachian tube. A canal that links the middle ear
with the back of the nose. The eustachian tube helps
to equalize the pressure in the middle ear. Equalized
pressure is needed for the proper transfer of sound
waves. The eustachian tube is lined with mucous, just
like the inside of the nose and throat.

47. Inner ear
• Cochlea – This contains the nerves for hearing.
• Vestibule – This contains receptors for balance.
• Semicircular canals – This contains receptors for
balance.

48. How do we Hear
• Hearing starts with the outer ear.
• The sound waves, or vibrations, travel down the external auditory
canal and strike the eardrum (tympanic membrane).
• The eardrum vibrates. The vibrations are then passed to 3 tiny bones
in the middle ear called the ossicles.
• The ossicles amplify the sound.
• They send the sound waves to the inner ear and into the fluid-filled
hearing organ (cochlea).
• Once the sound waves reach the inner ear, they are converted into
electrical impulses.
• The auditory nerve sends these impulses to the brain. The brain then
translates these electrical impulses as sound.

49. Physiology Of Equilibrium
• Static Equilibrium – Tells brain the basic position of head.
*up,down,left,right,forward,back
• Uses receptor called the Macuale.
On top of Macuale lies the otolithic membrane
When head moves – otoliths Move
Movement of otoliths places pressure on macuale,
sending message through vestibular nerve to brain.

51. • Dynamic Equilibrium – Tells brain the more detailed position and
movement of head
*Rotation, Angles
• Uses the Semicircular Canals of Cochlea
*Contain channels called Crista Ampullari
*Crista Ampullari contains receptor cell, endolymph fluid and
capula cap
*When head turns, fluids pushes against capula cap, stimulating
receptors and send impulse to brain.

53. Sensorineural Deafness
• Damage of receptor cell, cochlea, Vestibular Nerve
• Can be hereditary, damage from loud noise, disease

54. Conduction Deafness
• Something blocks Tympanic Membrane
• Sound Waves cannot reach Ear Drum & Inner Year
• Causes – ear wax, Ruptured Ear Drum,
• Usually temporary, can be solved by surgery.

55. SKIN

56. Touch
• Meissner’s corpuscles
• React to light touch
• Located mostly at palms,soles,lips,eyelids,
Pressure
• Paccinian corpuscles
• Detect pressure & vibration deep inside skin
Pain
• Skin receptors register pain
• Most numerous in skin

57. Temperature
• Skin receptors register temperature
• Cold receptors – stimulate when skin is 77°F @ 25°C
• Hot receptors - stimulate when skin is 86°F @ 30°C
• Beyond 113°F@ 45°C, pain receptors take over to avoid damage to skin
• Thermoreceptors – found all over the body, but cold receptors has
higher density. This is because our environment is colder than body
temperature
• Most found in ear and nose and face