SENSE ORGANS power point presentation 123

sense organs

1. The Sensory Organs

2. Our “senses” continually provide us with information
about our surroundings.
Sense organs are complex organs like the eye or
specialized receptors in areas such as the nasal
mucosa or tongue.

3. Conversion of a stimulus to a sensation:
•Stimuli (light, sound, temperature, etc. are changed into an
electrical signal or nerve impulse.
•The signal is then transmitted over a ? neuron to the ?
•The signal is interpreted and we become consciously aware
of a sensation.

4. Your senses are means of detecting and interpreting stimuli
of you external environment.
These are the sense of taste, sight, hearing, touch and smell.
A sensory organ is a specialised organ that allows for the
reception of a stimulus, the formation of an impulse and it’s
transmission to the brain for interpretation.
The main sense organs are your eyes, ears, olfactory organs
in your nose, taste buds on your tongue and your skin.

5. Contains receptors for vision and a refracting system
that focuses light rays on the receptors in the retina.
The eye sits in the orbit formed by the maxilla,
zygomatic, frontal, sphenoid and ethmoid bones.
Extrinsic muscles attach the surface of the eyeball to
bones.

10. Eyelids – contain skeletal muscle that allow us to
close them and totally cover the exterior eyeball.
Eyelashes – help to keep dust out of our eyes.
Tears
Cranial Nerves
•Optic – vision
•Oculomotor , abducens and trochlear – eye movement
The eye contains 3 layers

11. Structure of the eyeball
•Sclera – tough fibrous tissue.
Front surface is the “white” of our eyes and the cornea. The cornea is
transparent, receives no blood supply and is nourished by the aqueous humor.
Sclera is covered by the conjunctiva in the front of the eyeball.
•Choroid - contains a dark pigment to prevent scattering of light that
enters the eyeball. Also contains blood vessels and 2 involuntary
muscles.
Iris –
Ciliary body (muscle) –
•Lens – composed of transparent, elastic protein; no blood supply,
nourished by the aqueous humor.
•Retina – contains microscopic receptor cells called rods and cones.
Rods –
Cones –
Fovea –

12. Layer of the eye
•Retina
Ganglionic neurons carry impulses generated by
the rods and cones until they converge at the optic
disc. From the optic disc they form the optic
nerve and pass through the wall of the eyeball to
the occipital nerve.
Optic disc – also know as the “blind spot”, no rods
or cones; exit to the optic nerve.
Occipital lobe of the cerebrum – visual
interpretation.

14. Structure - fluids of the eyeball – 2 types:
Aqueous humor – watery fluid in front of the lens
(anterior cavity) nourishes the lens and cornea.
○Continually formed by the capillaries in the
ciliary body, flow through the pupil and is
reabsorbed in the canal of Schlemm.
○If drainage is blocked, the internal pressure in the
eye increases and may damage the eye and lead
to blindness = glaucoma.

15. Structure - fluids of the eyeball – 2 types:
•Vitreous humor – jelly-like fluid behind the lens
(posterior cavity). Literally holds the retina in
place and gives structure to the eyeball.

16. Focusing Problems
•Presbyopia – “old sightedness” or “short arm
syndrome”. Ciliary bodies lose their elasticity and
can no longer change the shape of the lens to bring
near objects into focus.
•Myopia – nearsightedness, image focuses in front
of the retina rather than on it, eyeball is elongated.
Corrected by glasses, contacts or radial keratotomy
(Lasix).

17. Focusing Problems
•Hyperopia – “farsightedness”, image focuses
behind the retina, produces a fuzzy image.
Corrected by lenses.
•Astigmatism – refraction error – fuzzy image,
irregular curvature of the cornea or lens, requires
special lenses to correct (Toric lenses) or contacts.

19. Light enters the eye, the amount of which is
controlled by the iris and is bent (refracted) slightly
by the cornea.
It is then focused by the lens (controlled by the ciliary
muscles) onto the retina.
On the retina, rods and cones convert the light into a
nerve impulse, carrying the image to the brain.
The brain interprets the images from both our eyes
forming a composite image.

22. Short Sight (Myopia)
A short sighted person can view close objects clearly
but distant objects are out of focus.
Light rays are focussed short of the retina.
Cause: eyeball is too long or the focussing elements
of the eye are too strong.
Correction: use a concave (divergent) lens to widen
the angle over which the light rays have to be
refracted.

24. Long Sight (Hyperopia)
Condition: can view distant objects clearly but close
objects are out of focus,
The focal point is long of the retina i.e. is behind
retina.
Cause: eyeball is too short or the focussing elements
of the eye are too weak.
Correction: use a convex (convergent) lens to reduce
the angle over which the light rays have to be
refracted.

26. The ear has two major functions:
Hearing: detection of vibrations, their frequency
(pitch) and amplitude (loudness).
Balance: detection of direction of motion, acceleration
and head position related to gravity.
It is divided into three sections, the outer ear, middle
ear and inner ear.

27. External ear –
External Auditory canal – a curving tube about one
inch long; extends into the temporal bone and end at
the tympanic membrane (eardrum).

28. Middle ear – tiny epithelium lined cavity which is
hollowed out of the temporal bone.
•Tympanic membrane – separates the external and
middle ear and vibrates when sound waves strike it.
•3 tiny bones called ossicles (bones) transmit sound
waves.

29. Middle Ear
•Bones
Malleus –
Incus –
Stapes –

30. Middle Ear
•Oval Window separates the middle ear from the
inner ear.
•Eustachian tube – connects the throat with the
middle ear; allows air to enter and leave the middle
ear which equalizes pressure. Why do throat and
ear infections occur together?

32. Middle Ear - Hearing Sequence
•Sound waves cause the eardrum to vibrate, and this
movement is transmitted and amplified by the ear
ossicles.
•Movement of the stapes against the oval window
causes movement of fluid in the inner ear which
generates electrical impulses.

34. Inner Ear – contains mechanoreceptors that are
activated by vibration and generate nerve impulses
that result in hearing and equilibrium. The 3 spaces
are called the bony labyrinth and contain fluids called
perilymph and endolymph.
•Vestibule – membranous sacs (utricle and saccule)
adjacent to the oval window and between the
semicircular canals. Contains receptors for
equilibrium.

35. Inner Ear
•Cochlea – snail shell; contains the Organ of Corti
which holds the receptors for hearing (hair cells).
As the hairs bend (vibration) they generate an
electrical impulse.
•Semicircular Canals – contain the crista ampularis
which is a specialized receptor that generates a
nerve impulse when you move your head.
Receptors for equilibrium.

39. The skin is the outer layer of vertebrate animals. Its major
functions are protection, temperature regulation and to act as a
sense organ.
Two major layers of the skin: epidermis and dermis.
Epidermis
 
The epidermis is the outer renewable layer of the skin.
Malpighian Layer: This is the base layer, which is constantly
producing new cells by mitosis. The new cells are pushed
towards the surface. The dark pigment melanin is produced
here.
Granular Layer: The protein keratin accumulates in the cells
giving them a granular appearance. The cells finally die.
Cornified Layer: This is the surface layer of dead keratinised
cells, which is constantly being eroded.

41. Protection
Prevents excessive loss of water (the cornified layer of the
epidermis is waterproof).
Prevents the entry of pathogens.
‘Sebum oil’ keeps the skin intact preventing it from
‘cracking’.
Sebum from the sebaceous glands contain anti-microbial
chemicals.
Melanin gives protection against the damaging UV rays of
sunlight.
The dermis and adipose tissue protect against mechanical
injury.

42. Sense Organ
The skin contains receptors for touch, pressure, pain,
temperature rise and temperature decrease. The skin
supplies information about a variety of external
environment conditions.
Vitamin D Production
Made when ultraviolet light penetrates the skin converting
a chemical in the blood to vitamin D. As a result vitamin
D is often called the ‘sunshine vitamin’.
Excretion
The skin has about 2.5 million sweat glands.
Sweat is a dilute solution of water, sodium chloride, urea,
ammonia, uric acid and lactic acid.

43. Energy Storage
There is a layer of fat storage adipose tissue below
the dermis of the skin.
Fat is also a poor conductor of heat and so the skin
acts as a heat insulator.
This fat layer also acts as a shock absorber protecting
against mechanical damage.
The Skin is a Homeostatic Organ!

44. The olfactory region is high up in the nasal cavity
about 5 cm
2
in area with about 20,000 receptors.
Stimulatory chemicals must be volatile and soluble in
water.
There are 50 primary smell qualities but in
combination they can produce over 3,000 different
odours.
Prolonged exposure to a particular chemical causes
fatigue of that sensation.

45. Olfactory receptors – chemical receptors responsible
for the sense of smell are located in the upper part of
the nasal cavity.
Olfactory receptors are stimulated by chemicals
dissolved in the watery mucus that lines the nasal
cavity. We detect about 10,000 different scents.
Olfactory receptors are easily fatigued – many odors
are not noticeable after a time.

48. There are four primary taste qualities: bitter, sour,
salty, sweet.
Most tastes are combinations of these.
The taste receptors are collected in groups of about
ten in the taste buds.
Taste buds are present on the tongue’s edges and
upper surface.
Taste buds are also present on the soft palate and on
the back of the pharynx.
Certain regions of the tongue are more sensate to a
particular primary tastes than others.

49. Taste buds – chemical receptors that generate nervous
impulses resulting in the sense of taste. There are
about 10,000 microscopic taste buds located on the
papillae of the tongue.
Gustatory cells –

50. Taste Sensations
•Sweet, sour, bitter, salty, and Umami (=savory).
•Other flavors results from a combination of taste
bud stimulations and olfactory receptor stimulation.
i.e. our taste sensations include odors as well.