he sense organs — eyes, ears, tongue, skin, and nose — help to protect the body. The human sense organs contain receptors that relay information through sensory neurons to the appropriate places within the nervous system. Each sense organ contains different receptors. General receptors are found throughout the body because they are present in skin, visceral organs (visceral meaning in the abdominal cavity), muscles, and joints. Special receptors include chemoreceptors (chemical receptors) found in the mouth and nose, photoreceptors (light receptors) found in the eyes, and mechanoreceptors found in the ears.

1. Prof. Amol B Deore
MVPs Institute of Pharmaceutical Sciences,
Adgaon, Nashik (Maharashstra)

5. Eyelids
The eyelids are two movable folds of skeletal muscles
situated above and below the front of each eye. The free
edges of eyelids composed of short curved hairs called
eyelashes. Conjunctiva is a fine transparent membrane
which lines the eyelids and the front of eyeball. It
consists of columnar epithelium. It protects the cornea
and the front of the eyeball.
Eyelashes
Eyelashes along the border of each eyelid help keep
dust out of the eyes. Eyelids and eyelashes protect the
eye from foreign objects. Blinking of the eyelids
lubricates the surface of the eye by spreading tears that
are produced by the lacrimal gland.

6. Eyebrows
The eyebrows help shade the eye and keep
perspiration from getting into the eye and
causing an irritation to the eye.

7. The lacrimal apparatus
consists of an almond
shaped lacrimal glands
located in upper, outer
corner of the eyeball,
within the orbital
cavity.
The lacrimal glands
produce and drains the
lacrimal fluid i.e. tears.
The lacrimal ducts take
tears to the anterior of
the eyeball, and
blinking spreads the
tears and washes the
surface of the eye.

8.  Secretion of tears occurs constantly, but is
increased by the presence of irritating
chemicals (for example, onion vapours) or dust,
and in certain emotional situations (sad or
happy).
 Composition: Daily tears secretion is about 1
mL. Tears are composed of water, mucus,
sodium chloride (about 1%), mineral salts,
bactericidal enzyme lysozyme and gamma
globulin.
 Functions: the tears permit cleaning, lubrication
and moistening of the eyeball.

9. The wall of the eye is composed of three layers of tissue.
 The outer fibrous layer: sclera and cornea
 The middle layer: choroid, ciliary body and iris
 The inner nervous tissue layer: retina

10.  Sclera: The outermost layer of eyeball is the sclera.
It is white of the eye and made up of fibrous
connective tissue. We see it as the white of the eye
when looking in a mirror. The cornea is the
transparent part of this outermost layer that
permits light to enter the eye.
 Choroid: The middle layer is the choroid. It contains
blood vessels and dark blue pigment cells. It is
black in colour due to melanin pigment which
absorbs light rays and prevents reflection and
scattering of light within the eyeball.
 Retina: The innermost layer of the eye is the retina.
It is gray in colour and contains the photosensitive
cells: the rod and cone cells.

11. The lens is made of a biconvex, transparent and
flexible elastic protein and has no blood
capillary network. The lens is located behind
the pupil. The ciliary body is a circular muscle
that that hold the biconvex lens in place.
The ciliary body is connected to the lens by
suspensory ligaments. The lens bends (refracts)
light rays focusing from objects in front of eye.
The shape of the lens is changed by the ciliary
muscle, which permits the eye to focus light
from objects at varying distances for clear
vision.

12. For near objects: the refractive power to be increased
by contraction of ciliary muscle thereby increasing
convexity of lens (thickness)
For distant objects: the refractive power is reduced by
relaxation of ciliary muscle thereby making the lens

13. The iris is the circular and
coloured part (melanin) of the
eyeball. It is suspended
between the cornea and the
lens and is attached to the
ciliary body. What we call “eye
colour” is the colour of the iris
and is a genetic characteristic.
The iris consists of two
smooth muscles: circular
muscles and radial muscles.
The hole (opening) in the
center of the iris is called
pupil. The iris regulates the
intensity of light that enters

14. In a strong sunlight (bright light), the
parasympathetic stimulation leads to contraction of
circular iris muscles and pupil size decreases (pupil
constriction). Pupil constriction permits fewer light
rays.
In a dark room (dim light), the sympathetic
stimulation leads to contraction of radial iris
muscles and pupil size increases (pupil dilation).
Pupil dilation permits more light rays.

15. The retina is the innermost layer of the eyeball which
detects light and colours. Retina is composed of two
types of photosensitive cells: the rods and cones.
Rods
Rod cells (around 120 million) are situated toward the
periphery, or edge, of the retina. Rod cells detect
black & white colours in dim light (low intensity light).
They are not sensitive to other colours. Rod cells
consist of a photosensitive pigment Rhodopsin
(Scotopsin + Retinal). Retinal is a derivative of
Vitamin A synthesized from carotenoids.

17. Cones
Cone cells (around 6-7 million) are found in the
center of the retina called the macula lutea and a
small depression called fovea centralis. There are
three kinds of cones; each is sensitive to a different
colour: red, green, or blue. These three types of
cones allow us to distinguish between different
colours. Cone cells consist of a photosensitive
pigment Iodopsin (Photopsin+Retinal) which permit
light absorption.

18. The rod and cone cells synapse with the
bipolar cells of the retina. The bipolar neurons
synapse with ganglionic cells whose axons form the
optic nerve. Eventually the fibers of the optic nerve
reach the thalamus of the brain and synapse at its
posterior portion and enter to the visual cortex of
the occipital lobe of the cerebrum for
interpretation.
The yellowish spot in the center of the retina
is called the macula lutea. In its center is a
depression called the fovea centralis. This region
produces the sharpest vision, like when we look
directly at an object. Medial to the fovea centralis is
the optic disk. It is here that nerve fibers leave the
eye as the optic nerve. Because the optic disk has
no receptor cells, it is called the blind spot.

19. The eyeball is divided into two compartments.
Anterior chamber: In front of the lens is the anterior chamber that is filled with
a watery fluid called the aqueous humor. The aqueous humor is produced by
the ciliary body. It is constantly being formed, drained, and replaced in the
anterior cavity.
Posterior chamber: The posterior chamber of the eyeball is filled with jelly like
fluid called the vitreous humor.
Both fluids are essential to hold the retina and lens in place. They maintain the
normal shape of the eyeball and help refract light rays; that is, the fluids bend light
rays to bring them to focus on the retina. These fluids also help for nourishment of
the eyeball and maintaining the intraocular pressure.

20.  For the vision, light rays must be focused on
the retina and the resulting nerve impulses
must be transmitted to the visual areas of the
cerebral cortex in the brain. Refraction is the
bending of a light ray as it passes through
one medium and into another medium.
 The refraction of light within the eye takes
place in the following pathway of structures:
the cornea, aqueous humor, pupil, lens, and
vitreous humor. The lens is the only
adjustable part of the refraction system.

21.  When light rays strike the retina, they stimulate
chemical reactions in the rods and cones. In
rods, on colour absorption the photosensitive
pigment Rhodopsin breaks down to form
scotopsin and trans-retinal.
 In cone cell, on colour absorption the
photosensitive pigment Iodopsin is breaks down
to form photopsin and trans-retinal. This
chemical reaction generates nerve impulse.
 The nerve impulses are transmitted to bipolar
cells then to the ganglion cells. These ganglionic
neurons entered at the optic disc and become
the optic nerve. The images focused on retina
are upside down (inverted).

22.  The optic nerves from both eyes come together
at the optic chiasma in the brain. Here, the
fibers of optic nerve cross to each other. This
crossing permits each visual area to receive
impulses from both eyes, which is important for
binocular vision. The impulses are further
transmitted to visual areas of cerebrum. The
visual areas integrate them, to make a single
image that has depth and three dimensions.
This is called binocular vision. The visual areas
also right the image, because the image on the
retina is upside down.

25.  1) Conjunctivitis: Inflammation of conjunctiva
membrane is referred as conjunctivitis, may be
caused by allergies or by certain bacteria or
viruses, and makes the eyes red, itchy, and
watery.
 2) Hypermetropia (far-sightedness): In
hypermetropia, the patient can see far distant
objects well but fails to see near vision. The far-
sighted eye focuses light from near objects
“behind” the retina due to the flattening of the
lens. This condition can be corrected by convex
eye glasses or lenses.

26.  3) Myopia (near-sightedness): In myopia, the
patient can see near objects well but fail to see
distant (far objects). The near-sighted eye can
see only if the object is brought to 20 feet away.
The near-sighted eye focuses images from
distant objects in front of the retina, because
the eyeball is too long or the lens too thick.
Correction requires a concave lens to spread out
light rays before they strike the eye.

28.  4) Presbyopia: The term presbyopia means “old
eye” and is a vision condition characterised by
inability of eye to focus on closed objects. It is
associated with aging and loss of elasticity of
the lens. Hence lens is unable to recoil and
thicken for near vision, and glasses for reading
are often necessary.
 5) Astigmatism: astigmatism is an error of
refraction, caused by an irregular curvature of
the cornea or lens that scatters light rays and
blurs the image on the retina. Correction
requires a lens ground specifically for the
curvature of the individual eye.

29.  6) Glaucoma: Glaucoma defined as a group of
disorders characterised by damage the optic nerve
and cause loss of vision due to increase in intraocular
pressure. Increased pressure in the anterior cavity is
transmitted to the lens, the vitreous humor, and the
retina and optic nerve. As pressure on the retina
increases, halos may be seen around bright lights,
and peripheral vision is lost. Other risk factors
include high blood pressure and diabetes.

30.  7) Night blindness: Night blindness is the
inability of the patient to see in dim light
(darkness). Night blindness is due to disorder of
rod cells in the retina that are responsible for
vision in dim light. Its causes include: vitamin A
deficiency, glaucoma, cataract and near-
sightedness. Night blindness affects the ability to
drive in night.
 8) Cataract: A cataract is a clouding (opacity) of
the lens of the eyeball leading to a decrease in
vision. Cataracts are most commonly due to
aging and develop slowly. Symptoms may
include: faded colours, blurred vision, halos
around light and trouble with bright lights and at
night.

35.  The outer ear consists of the auricle and the
ear canal. The auricle (or pinna) is made up of
elastic cartilage. This auricle connected with
ear canal known as the external auditory
canal. The auricle allows sound waves to
enter the ear canal, which then directs those
waves to the delicate eardrum (or tympanic
membrane). The ear canal is lined with hairs
and ceruminous glands that produce earwax
(or cerumen). The hairs and earwax protect
the eardrum from foreign matters.

36.  The middle ear is the air-filled cavity that
contains the three auditory ossicles: malleus,
the incus, and the stapes. These bones
transmit the sound vibrations from the
eardrum to the oval window. The middle ear
also consists of the auditory tube. This
auditory tube opens into the pharynx and
permits air pressure to be equalized between
the middle ear and the outside air, thus
ensuring that hearing is not distorted.

37.  The inner ear is made of the cochlea, the
vestibule and the semicircular canals. The
cochlea involved hearing whereas
semicircular canals involved in body posture,
balance and equilibrium.

38. Auditory ossicles are the
three small bones of
middle ear that extend
from tympanic membrane
to the oval window. These
bones transmit the sound
vibrations from the
eardrum to the oval
window. They are
connected to each other
by synovial joints. They
are named according to
their shapes.

39.  The malleus: the malleus is hammer shaped
bone. The handle is in contact with the
tympanic membrane and the head forms a
synovial joint with the incus.
 The incus: the incus is anvil shaped bone. Its
body articulates with malleus and its other
end articulates with stapes.
 The stapes: the stapes is stirrup shaped
bone. Its head articulates with the incus and
its base attached to oval window.

41. A cross section of cochlea contains three compartments:
 Scala vestibuli
 Cochlear duct
 Scala tympani
The scala vestibule originates from the oval window and
consists of perilymph fluid. The scala tympani ends at
the round window and consists of perilymph fluid. These
two compartments are continuous to each other. The
cochlear duct is composed of membranous canals filled
with endolymph fluid. The cochlear duct is consists of
basilar membrane and hair cells with auditory receptors.
These hair cells respond to sound vibrations and
generate nerve impulses. The nerve impulses are
transmitted by vestibuloochlear nerve to the auditory
area of cerebrum

44. The process of hearing involves the
transmission of vibrations and the generation
of nerve impulses. When sound waves enter the
ear canal, vibrations are transmitted by the
following sequence of structures.

48. •The auricle passes the sound waves into
external auditory canal
• Sound waves strikes on tympanic membrane, due to
which it starts vibrating back and forth. Membrane
vibrates slowly in response to low frequency sound
and rapidly in response to high frequency sounds
• The malleus starts to vibrate. The vibrations
conducted from malleus to the incus and then to the
stapes

49. • As stapes vibrates, it pushes the oval window in and
out
• Oval window pushes perilymph of scala vestibuli
• Pressure waves are transmitted from scala vestibuli
to scala tympani and eventually to the round
window

50. • Vestibular membrane starts vibrating. As a result, the
pressure of endolymph inside the cochlear duct
increases and decreases
• Pressure waves transmitted from vestibular
membrane to basilar membrane
• Hair cells start vibrating to generate nerve impulses

51. • Nerve impulses are transmitted by
vestibulocochlear nerve to the brain
• Nerve impulses are transmitted to
the auditory area of cerebrum
• Sense of hearing
High-intensity sound waves cause greater vibration of basilar
membrane, which leads to a higher frequency of nerve impulses
conducted to brain.

52.  1) Motion sickness: Motion sickness is characterized
by cold sweating, hyperventilation, nausea, and
vomiting when the person is exposed to repetitive
motion that is unexpected or unfamiliar, or that
cannot be controlled.
 2) Deafness: Deafness is the inability to hear
properly. Deafness may be caused by punctured
eardrum, deterioration of the hair cells in the cochlea,
auditory cranial nerve damaged, and damage to the
auditory areas in the cerebrum.
 3) Otitis media: Otitis media or middle ear infection
is quite common in young children. It can result in a
temporary loss of hearing due to fluid buildup near
the tympanic membrane. Symptoms include fever and
irritability, and on examination, a red eardrum.

53. SKIN

58.  The epidermis is made of stratified squamous
epithelial tissue and is thickest on the palms
and soles. There are no capillaries present
between them. The epidermis may be further
subdivided into four or five sublayers.

59. The stratum corneum consists on average of 25 to 30 layers of
flattened dead keratinocytes. Keratinocytes produce the protein
keratin is a tough, fibrous protein that helps protect the skin and
underlying tissues from heat, microbes, and chemicals. These
cells are continuously shed and replaced by cells from the
deeper strata. The interior of the cells contains mostly keratin.
These cells are also covered and surrounded with lipids to
prevent any passage of fluids through this layer. This layer acts
as a physical barrier to light and heat waves, microorganisms
(e.g., like bacteria, fungi, protozoa, and viruses), and most
chemicals.

60.  The stratum lucidum is present only in the
thick skin of areas such as the fingertips,
palms, and soles. It consists of three to five
layers of flattened clear, dead keratinocytes
that contain large amounts of keratin and
thickened plasma membranes.

61. 3) Stratum granulosum
The stratum granulosum consists of two or
three layers of flattened cells.
4) Stratum spinosum
The stratum spinosum consists of 8 to 10
layers of polyhedron shaped cells.

62. It is the deepest layer of the epidermis is
composed of a single row of keratinocytes. Some
cells in this layer are stem cells that undergo cell
division to continually produce new keratinocytes.
It also contains melanocytes, which are responsible
for producing skin color. They produce a pigment
called melanin; which is responsible for variations
in skin pigmentation. Melanocytes are activated to
produce melanin by exposure to sunlight. We
darken when we expose ourselves to the sun. All
races get darker after exposure to the sun over a
period of time. We call this getting a suntan.

63. The second, deeper part of the skin, the dermis, is
composed of a strong connective tissue containing
collagen and elastic fibers. The few cells present in
the dermis include predominantly fibroblasts, with
some macrophages, and a few adipocytes near its
boundary with the subcutaneous layer. Blood
vessels, nerves, glands, and hair follicles are
embedded in the dermal layer. Based on its tissue
structure, the dermis can be divided into a
superficial papillary region and a deeper reticular
region.

64. Papillary region
Reticular region

65.  The papillary region consists of connective
tissue containing thin collagen and fine
elastic fibers. Dermis contain tactile receptors
called Meissner corpuscles (touch receptors).
Different sensory receptors give rise to
sensations of warmth, coolness, pain,
tickling, and itching.
 The reticular region, which is attached to the
subcutaneous layer, it consists of few adipose
cells, hair follicles, nerves, sebaceous (oil)
glands, and sweat glands occupy the spaces
between fibers.

66.  The combination of collagen and elastic
fibers in the reticular region provides the skin
with strength, extensibility (ability to stretch),
and elasticity (ability to return to original
shape after stretching)

68.  Sebaceous glands (oil glands) are connected
to hair follicles with few exceptions. The
secreting portion of a sebaceous gland lies in
the dermis and usually opens into the neck of
a hair follicle.
 Locations: Sebaceous glands are present in
the skin of the breasts, face, neck, and
superior chest the lips, glans penis, labia
minora, and glands of the eyelids. Sebaceous
glands are absent in the palms and soles.

69.  Functions: Sebaceous glands secrete an oily
substance called sebum (a mixture of
triglycerides, cholesterol, proteins, and
inorganic salts). Sebum covers the surface of
hairs and helps keep them from drying and
becoming hard. Sebum also prevents
excessive evaporation of water from the skin,
keeps the skin soft and pliable, and inhibits
the growth of some (but not all) bacteria.

70.  Sweat glands release sweat onto the skin
surface through pores. Sweat glands are
divided into two main types, eccrine and
apocrine, based on their structure, location,
and type of secretion.
 Eccrine sweat glands
 Apocrine sweat glands

71. A. Eccrine sweat glands:
They are distributed in the skin of the forehead,
palms, and soles. The sweat produced by eccrine
sweat glands (about 600 mL per day) consists of
water, minerals, urea, uric acid, ammonia, amino
acids, glucose, and lactic acid. The main function
of eccrine sweat glands is to help regulate body
temperature through evaporation. Eccrine sweat
glands also release sweat in response to an
emotional stress such as fear or embarrassment.
This type of sweating is referred to as emotional
sweating or a cold sweat.

72.  Apocrine sweat glands: They are found
mainly in the skin of the underarm (armpit),
around the nipples of the breasts, and
bearded regions of the face in adult males.
Apocrine sweat is slightly viscous and
appears milky or yellowish in color.

73.  Normal body temperature is maintained at
approximately 98.6°F (37°C). Temperature
regulation is critical to our survival because
changes in temperature affect the functioning of
enzymes. The presence of enzymes is critical for
normal chemical reactions to occur in our cells.
When people get high fevers they can die
because the heat of a fever destroys the enzymes
by breaking up their chemical structure. Without
enzymes, chemical reactions cannot occur and
our cellular machinery breaks down and death
results. The skin contributes to thermoregulation
in two ways:

74.  In response to high environmental
temperature, autonomic nervous system
initiates vasodilation (dilation of blood
vessels) in the dermis to increase blood flow
to the dermis of skin, which increases the
amount of heat loss from the body. The heat
is then lost by convection, conduction, and
evaporation. When we sweat, the water in
sweat evaporates, which requires energy and
thus carries away heat to reduce body
temperature.

75.  In response to low environmental
temperature, production of sweat from
eccrine sweat glands is decreased, which
helps conserve heat. Also, vasoconstriction
(constriction blood vessels) in the dermis of
the skin decreases blood flow through the
skin and reduces heat loss from the body.

76.  Sensation: Sensory receptors in the skin produce
the sensations of external environment for
temperature, pressure, pain, and touch. These
receptor sites allow us to react to external stimuli
and to interpret what is occurring in the outside
world.
 Protection: The skin acts an elastic, resistant
covering. It prevents passage of harmful physical
and chemical agents. The melanin produced by
the melanocytes protects us from the damaging
ultraviolet rays of sunlight. The lipid content of
the skin inhibits the excessive loss of water and
electrolytes through the skin.

77.  Thermoregulation: Normal body temperature
is maintained at approximately 98.6°F (37°C).
In response to high environmental
temperature evaporation of sweat from skin
helps to lower elevated body temperature. In
response to low environmental temperature,
sweating is decreased to conserve heat.
 Excretion: The skin produces two secretions:
sebum and sweat. Sweating helps in excretion
of toxins. Sebum is secreted by the
sebaceous glands. Sebum helps for
moisturizing of skin. Sebum has both
antifungal and antibacterial properties.

78.  Synthesis of vitamin D: The skin is involved in
the production of vitamin D. Exposure to the
ultraviolet rays of the sun stimulates our skin
to produce a precursor molecule of vitamin D
to form calcitriol (vitamin D). Calcitriol helps
for absorption of calcium. Calcium is
necessary for muscle contraction and bone
development.
 Immunity: Skin kills most bacteria and other
microorganisms that make contact with our
skin.

79.  THANKING YOU