The document provides information on the anatomy and structure of the human sense organs. It describes the five main sensory organs - skin, eyes, ears, nose, and tongue and their role in touch, sight, hearing, smell, and taste. It then provides more detailed information on the structure and layers of skin, eyes, ears and nose and how they detect and process sensory information which is transmitted to the brain.

1. ANATOMY OF
SENSE ORGANS
BY,
MRS.WINCY THIRUMURUGAN

2. Sensory organs or Special senses:
• The nervous system must receive and process information about the
world outside in order to react, communicate, and keep the body
healthy and safe.
• Skin, eye, ear, nose & tongue (taste buds) are called sensory organ or
special senses.
• Sensory organs have special receptors that allow us to smell, taste,
see, hear, touch and maintain equilibrium or balance.
• Information conveyed from these receptors to the central nervous
system is used to help maintain homeostasis(self-regulating process by
which biological systems help to maintain stability while adjusting to
conditions that are optimal for survival).

3. Skin

4. Skin:
• Skin is the largest organ of our body.
• It is related to the sense of touch. The sense of touch
is also referred to as tactioception.
• The skin contains general receptors which can detect
touch, pain, pressure & temperature.
• They are present throughout the skin.
• Skin receptors generate an impulse, and when
activated, is carried to the spinal cord and then to
the brain.

5. Structure of the skin:
• The skin is composed of 3 major layers of tissue:
1. Epidermis layer
2. Dermis layer
3. Subcutaneous layer.
• The epidermis, the outermost layer of skin, provides a waterproof
barrier and creates our skin tone.
• The dermis - the middle layer, under the epidermis, contains tough
connective tissue, hair follicles, and sweat glands.
• The subcutaneous tissue (hypodermis) - deeper/ innermost layer, it
is made of fat and connective tissue.

7. Epidermis:
• The epidermis is the thin, outer layer of the skin that is visible to the eye.
• Contains different types of cells: keratinocytes, melanocytes, Merkel cells and
Langerhans cells.
• The skin’s color is created by special cells called melanocytes, which produce
the pigment melanin. Melanocytes are located in the epidermis. These form a
pigment shield against UV radiation.
• It does not contain blood vessels
• The epidermis consists of 4 layers: Stratum germinativum, Stratum spinosum,
Stratum granulosum, Stratum corneum
• Main functions: protection, absorption of nutrients and homeostasis.

8. Dermis:
• The dermis is the middle layer of the skin that offers elasticity.
• It is composed of connective tissues and collagen fibers.
• is much thicker than the epidermis
• The dermis provides a site for the hair follicles, sweat glands, sebaceous
glands, blood vessels, lymph vessels, sensory receptors, nerve fibers, muscle
fibers & specialized cells (mast cells and fibroblasts).
• The main functions of the dermis are:
• Protection
• Cushioning the deeper structures from mechanical injury;
• Providing nourishment to the epidermis;
• Playing an important role in wound healing

9. Subcutaneous:
• The subcutaneous is the layer of tissue directly underneath the
dermis.
• It is also called hypodermis.
• This layer of tissue is composed of fat cells and connective tissue.
• It is the thickest layer of the integumentary system
• Its functions include:
• Structural support for the skin,
• Insulation - maintaining temperature
• The storage of energy

10. Accessory structures of the
skin
Include hair , nails, sweat glands, and
sebaceous glands.
These structures embryologically originate from
the epidermis and can extend down through
the dermis into the hypodermis.

11. • Hair: keratinous filament growing out of the
epidermis
• It is a keratinous filament growing out of the epidermis
• It is primarily made of dead, keratinized cells. Strands
of hair
• Originate in an epidermal penetration of the dermis
called the hair follicle
• The hair shaft is the part of the hair not anchored to
the follicle, and much of this is exposed at the skin’s
surface.
• The rest of the hair, which is anchored in the follicle
lies below the surface of the skin and is referred to as
the hair root.
• The hair root ends deep in the dermis at the hair
bulb, and includes a layer of mitotically active basal
cells called the hair matrix.
• The hair bulb surrounds the hair papilla, which is
made of connective tissue and
contains blood capillaries and nerve endings from
the dermis

12. the hair bulb divide and push cells outward in the hair root and shaft as
the hair grows.
• The medulla forms the central core of the hair, which is surrounded by
the cortex, a layer of compressed, keratinized cells that is covered by an outer
layer of very hard, keratinized cells known as the cuticle.
• These layers are depicted in a longitudinal cross-section of the hair follicle
although not all hair has a medullary layer. Hair texture (straight, curly) is
determined by the shape and structure of the cortex, and to the extent that it
is present, the medulla.
• The shape and structure of these layers are, in turn, determined by the shape
of the hair follicle. Hair growth begins with the production of keratinocytes by
the basal cells of the hair bulb. As new cells are deposited at thehair bulb,
the hair shaft is pushed through the follicle toward the surface.
• Keratinization is completed as the cells are pushed to the skin surface to form
the shaft of hair that is externally visible. The external hair is completely dead
and composed entirely of keratin. For this reason, our hair does not
have sensation.
• Furthermore, you can cut your hair or shave without damaging

13. The Accessory
Organs of the Skin:

16. Eye

17. Eye:
• Visual sensory organ in our body. These are sensitive to light
images.
• The eyes vary in color depending upon the amount of melanin
present in our body.
• It helps in the sense of sight by detecting and focusing on the light
images.
Visible parts:
• Eyelid
• Pupil
• Sclera
• Iris
Internal parts:
• Cornea
• Lens
• Aqueous humour
• Ciliary muscle
• Retina
• Choroid
• Macula.
• Optic nerve
• Vitreous humour

18. • Eyelid: Your eyelid covers your eye to protect it from dust, grit, and perspiration that
could cause damage. It opens and closes both voluntarily and involuntarily, and
facilitates blinking to help keep the eye hydrated and well-lubricated.
• Sclera: The sclera is outermost layer of the eyeball. It is the white (and opaque) part of
the eyeball. Muscles responsible for moving the eyeball are attached to the eyeball at
the sclera.
• Cornea: clear front window of the eye, Light rays from the outside world first pass
through the cornea before reaching the lens. Together with the lens, the cornea is
responsible focusing light on the retina.
• Choroid: The choroid is the middle layer of the eyeball located between the sclera and
the retina. It provides nutrients and oxygen to the outer surface of the retina.
• Anterior Chamber: The space between the cornea and the lens is known as the anterior
chamber. It is filled with fluid called aqueous humour. The anterior chamber is also
known as anterior cavity

19. • Aqueous humour: The Aqueous humour is a transparent watery fluid that
circulates in the anterior chamber. It provides O2 & nutrients to the inner eye &
exerts fluid pressure that helps maintain the shape of the eye. It is produced by the
ciliary body.
• Posterior Chamber: The posterior chamber is a larger area than the anterior
chamber. It is located opposite to the anterior chamber at the back of the lens. It is
filled with a fluid called vitreous humour. It is also referred to as the Vitreous body
• The conjunctiva: The conjunctiva lines the lids & then bends back over the
surface of the eyeball, Conjunctiva lubricates the front surface of the eye. It also
protects the eyes from debris, dust and infection-causing microorganisms.
• Vitreous humour: The vitreous humour is a transparent jelly-like fluid that fills the
posterior chamber. It exerts fluid pressure that keeps the retina layers pressed
together to maintain the shape of the eye and to maintain sharp focus of images on
the retina.

20. • Iris: The choroid continues at the front of the eyeball to form the Iris. The iris is a
flat, thin, ring-shaped structure sticking in to the anterior chamber. This is the part
that identifies a person’s eye colour. The iris contains circular muscles which go
around the pupil and radial muscles that radiate toward the pupil. When the circular
muscles contract they make the pupil smaller, when the radial muscles contract,
they makes the pupil wider.
• Ciliary muscles: The cilliary muscles are located inside the ciliary body. These are
the muscles that continuously change the shape of the lens for near and distant
vision. See diagram anatomy of the eye above.
• Ciliary Body: The choroid continues at the front of the eyeball to form the ciliary
body. It produces the aqueous humour. The ciliary body also contains the ciliary
muscles that contract or relax to change the shape of the lens.
• Zonules: The zonule also known as suspensory ligaments is a ring of small fibres
that hold the lens suspended in place. It connects the lens to the ciliary body and
allows the lens to change shape.

21. • Lens: The lens is a biconvex transparent disc made of proteins called crystallines.
It is located directly behind the iris and focuses light on to the retina. In humans,
the lens changes shape for near and for distant vision.
• Pupil: The pupil is the hole at the center of the iris located in front of the lens.
Whenever more light needs to enter the eyeball, the muscles in the iris contract
like the diaphragm of a camera to increase or decrease the size of the pupil.
• Retina: The retina is the innermost layer lining the back of the eyeball. It is the
light sensitive part of the eye. The retina contains photo receptors that detect
light. These photo receptors are known as cones and rods. Cones enable us to
detect color while rods enable us to see in poor light. The retina contains nerve
cells that transmit signals from the retina to the brain.
Macula: small central area in retina that contains special light sensitive cells and
allows us to see fine details clearly

22. • Fovea: The fovea is a small depression in the retina near the optic disc. The fovea
has a high concentration of cones. It is the part of the retina where visual acuity is
greatest.
• Optic nerve: The optic nerve is located at the back of the eyeball. It contains the
axons of retina ganglion cell (nerve cells of the retina) and it transmits impulses
from the retina to the brain.
• Optic disc: Impulses are transmitted to the brain from the back of the eyeball at the
optic disc also called the blind spot. It is called the blind spot because it contains no
photoreceptors, hence any light that falls on it will not be detected.
• Central Artery and Vein: The central artery and vein runs through the center of the
optic nerve. The central artery supplies the retina while the central vein drains the
retina.
• Tear Duct: This is a small tube that runs from the eye to the nasal cavity. Tear
drains from the eyes in to the nose through the tear duct. This is why a teary eye is
usually accompanied by a runny nose.

23. • Eye muscles: Muscles of the eye are very strong and efficient, they
work together to move the eyeball in many different directions. The
main muscles of the eye are Lateral rectus, Medial rectus, Superior
rectus and inferior rectus.
• Medial rectus muscle: There are six extra ocular movement muscles in
your eye (medial rectus, lateral rectus, superior oblique, superior rectus,
inferior rectus, and the inferior oblique) and the medical rectus is the
largest of them. It moves the pupil closer to the midline of your body
(towards your nose) and makes sure that the eye is aligned correctly.
• Lateral rectus muscle: This is the muscle which is responsible for
lateral or sideways movement of the eye, particularly movements away
from the midline.

26. EAR

27. Ear:
• Ears are the auditory sense organs of our body.
They help us to perceive sounds.
• Apart from hearing, this sense is also important
for balancing our body or equilibrium.
Anatomy of ear:
• The ear is divided into 3 main regions:
1. The external ear, which collects sound
waves and channels them inward
2. The middle ear, which conveys sound
vibrations to the oval window
3. The internal ear, which houses the
receptors for hearing and equilibrium.

29. External ear:
•The external ear consist of auricle (or pinna), the external acoustic
meatus & the tympanic membrane
• The auricle is a paired structure found on either side of the head. It
functions to capture and direct sound waves towards the external
acoustic meatus
•The external acoustic meatus does not have a straight path, and
instead travels in an S-shaped curve
•The tympanic membrane is also called the eardrum. It separates
the outer ear from the middle ear. When sound waves reach the
tympanic membrane they cause it to vibrate.

31. • Middle ear or tympanic cavity is a small, narrow,
irregular, laterally compressed chamber, situated within the
temporal bone.
• It is also known as tympanum. It is separated from external
auditory meatus by tympanic membrane.
• Middle ear consists of auditory bones, auditory muscles &
Eustachian tube.
• Auditory ossicles (bones): Malleus, Incus & Stapes.
• Auditory muscles: There are two muscles which serve a
protective function in the middle ear; the tensor tympani
and stapedius
• Eustachian tube: (pharyngotympanic tube) connects the
middle ear cavity with the nasopharynx

32. Internal ear:
• It consists the sense organs of hearing
and equilibrium. Sense organ for
hearing is the cochlea and the sense
organ for equilibrium is the vestibular
apparatus.
• Inner ear is the deepest part of your
ear.
• The inner ear has two special jobs. It
changes sound waves to electrical
signals (nerve impulses). This allows the
brain to hear and understand sounds.
• The inner ear is also important for
balance.

33. NOSE

34. Nose:
• The nose is an olfactory organ. Our olfactory system helps us to perceive
different smells.
• This sense of organ also aids our sense of taste with the help of sensory
receptors. The sense of smell is also known as olfaction.
• During a cold, the body produces mucus which blocks the sense of smell, this is
the reason why the food which we eat tastes bland.
• In the olfactory (smelling) portion of the nose, most of the lining is mucous
membrane. A small segment of the lining contains the nerve cells that are the
actual sensory organs.
• Fibres, called dendrites, which project from the nerve cells into the nasal cavity,
are covered only by a thin layer of moisture.
• The moisture dissolves microscopic particles that the air has carried into the nose
from odour-emitting substances, and the particles dissolved in the fluid stimulate
the olfactory nerve cells chemically.

35. External
nose
The external part of the nose consists of a root (superiorly), apex (inferiorly), dorsum, nares
(nostrils) and the separating nasal septum.
Bony component: nasal, maxillae and frontal bones
Cartilaginous component: alar cartilages (major, minor), lateral processes, septal cartilage
Nasal cavity Bones: nasal, maxilla, sphenod, vomer, palatine, lacrimal, ethmoid
(mnemonic: Nerdy Medical Students are often Very PaLE)
Apertures: nares, nasal conchae (superior, middle, inferior)
Channels: inferior nasal meatus, middle nasal meatus, superior nasal meatus,
sphenoethmoidal recess
Regions: vestibule, respiratory region, olfactory region
Blood
supply
External carotid artery and its branches: sphenopalatine, greater palatine, superior labial and
lateral nasal arteries
Internal carotid artery and its branches: anterior and posterior ethmoidal arteries
Nerve
supply
Olfactory nerve: olfaction
Trigeminal nerve: general sensation
Facial nerve: serous glands secretion (parasympathetic)
T1 level of spinal cord: regulation of mucosal blood flow (sympathetic)

36. • Nose:
• The external nasal anatomy is quite simple. It is a pyramidal
structure, with its root located superiorly and apex sitting
inferiorly. The root is continuous with the anterior surface of the
head and the part between the root and the apex is called
the dorsum of the nose. Inferior to the apex are the
two nares (nostrils), which are the openings to the nasal cavity.
The nares are separated by the nasal septum and are laterally
bounded by the ala nasi (wings of the nostrils).
• The external nose is comprised of both bony and cartilaginous
components. The bony part shapes the nose root, formed by
the nasal, maxillae and frontal bones. The cartilaginous part is
located inferiorly and is comprised of several alar, two lateral,
and one septal cartilage:

39. • Nasal cavity
• The internal part of the nose is the nasal cavity. The two nasal cavities sit
within the external nose and the adjacent skull. The cavities open
anteriorly to the face through the two nares. Posteriorly the cavities
communicate with the nasopharynx by two apertures called choanae.
• Besides the anterior and posterior apertures, each nasal cavity has a roof,
floor, and lateral and medial walls.
• There are 12 cranial bones in total that contribute to the nasal cavity
structure, which include
the paired nasal, maxilla, palatine and lacrimal bones, as well as
the unpaired ethmoid, sphenoid, frontal and vomer bones.
• Among all of them, the ethmoid bone is the most important element, for
two reasons: first, it makes the greatest portion of the nasal skeletal
framework by forming the roof and walls of the nasal cavities; and
second, it contains ethmoidal cells which, as a group, are one of the four

40. • Three bony shelves called the inferior, middle and superior nasal
conchae are attached to the lateral walls and by projecting into the
cavities, they divide both nasal cavities into four air channels:
• Inferior nasal meatus; between the floor and inferior concha
• Middle nasal meatus; between the inferior and middle concha
• Superior nasal meatus; between the middle and superior concha
• Spheno ethmoidal recess; between the superior concha & the nasal
cavity roof
• Common nasal meatus: between the conchae and nasal septum
• Three regions
• The nasal cavity is divided into three regions, aligned as if a three floor
building. The vestibule is located just inside the anterior external opening
of the nose (1st floor) and it contains hair follicles. The largest region is
the respiratory region, which is lined with respiratory epithelium (2nd
floor). Finally, there is the olfactory region, a small area located inside the

42. • Human beings can smell thousands of various odors and fragrances.

43. • Para nasal sinuses
• The two nasal cavities communicate with four bony recesses called the paranasal
sinuses. They are named according to the bones they are placed within, as
the: sphenoidal, maxillary, and frontal sinuses, and the ethmoidal cells. All of the
sinuses are covered by respiratory mucosa and innervated by the trigeminal nerve
(CN V).

44. • Clinical aspects
• Epistaxis
• Epistaxis, which is the clinical term for a nosebleed, is usually
caused by: trauma, sinus infection, rhinitis, hypertension, hematologic
disorders, neoplasms
• Rhinitis
• Rhinitis is another clinical term and its simple name is a stuffy
nose. An inflammation causes nasal congestion, sneezing,
rhinorrhea or a runny nose and nasal itching.
• Deviated septum
• A deviated septum means that the bony midline of the nasal
cavity is off centre, either due to a trauma or birth defects and this
results in partial or total occlusion of one side of the cavity. The
treatment is surgical and a septoplasty is usually performed.

45. TONGUE

46. Tongue:
• The tongue helps in perceiving various tastes and flavours.
• The taste buds are present between the papillae on the tongue. These help in
sensing different tastes. The senses of smell and taste tend to work together.
• If one could not smell something, they could not taste it either. The sense
of taste is also known as gustaoception.

48. • Taste buds:
• Sensory organs involved in sense of taste
• Taste buds are microscopic sensory organs containing
chemosensory cells which synapse with afferent fibers of
gustatory nerves. The number of taste buds in the oral cavity
and uppermost gastrointestinal tract is subject to a high
degree of interindividual variation (500-5000) while the
number of cells in one taste bud can be up to 150.
• Due to the abrasive environment of the oral cavity, gustatory
cells are highly regenerative with their average turnover being
8-12 days, however, some of them remain much longer.

50. Structure of Taste Bud Taste Areas of tongue

51. •There are four types of cells found in taste buds:
1. Type I (glial-like) gustatory epithelial cells: Supporting cells. Long spindle-
shaped cells extend from the taste pore to the basal lamina. Their apical ends
may be involved in salt taste transduction, however this is still debated.
2. Type II (receptor) gustatory epithelial cells: express G protein receptors for
bitter, sweet and umami taste. They secrete adenosine triphosphate (ATP) and
acetylcholine (ACh) neurotransmitters.
3. Type III (presynaptic) gustatory epithelial cells: Receptors for sour taste. They
secrete serotonin, gamma-aminobutyric acid (GABA) and
norepinephrine/noradrenaline neurotransmitters.
4. Type IV gustatory epithelial/basal cells: Placed on the basal lamina of the
epithelium. Thought to be undifferentiated or immature precursors to type I-III
gustatory epithelial cells.

52. • Gustatory cells are collectively organized into barrel-shaped epithelial
structures that look like flower buds.
• At the top of each taste bud is an opening known as a taste pore: a
fluid-filled funnel in which finger-like extensions (microvilli) of the
gustatory cells called gustatory/taste hairs are located.
• Each of the sensory gustatory epithelial cells is in contact with
terminals of nearby gustatory nerves (branches of the facial,
glossopharyngeal, or vagus nerves).
• Taste buds are largely located in the lingual papillae (except for the
filiform variety) but they can also be found in the uppermost parts of
the gastrointestinal tract i.e. soft palate, epiglottis, oropharynx and
upper esophagus.

54. • There are five gustatory sensations: sweet, salty, sour, bitter, and umami.
• Salty taste is the detection of high concentrations of Na+/sodium ions in the saliva which
directly diffuse into the gustatory sensory epithelial cells causing them to depolarize and
release neurotransmitters.
• Sour tastes occur via a similar means to that of salty (i.e. direct diffusion of ions), however
this time in response to high H+/hydrogen ion concentrations (i.e. acids). As the
concentrations increase, sour-detecting gustatory cells will depolarise.
• Sweet, bitter and umami tastes are transduced via specific G-protein coupled receptors
rather than direct diffusion of ions as seen with salt/sour tastes. Sweet taste involves the
detection of sugars (e.g. glucose and other monosaccharides). Bitter taste is detection of
long-chain organic compounds known as alkaloids which contain basic (as in pH) nitrogen
ions. Umami taste is action of receptors by certain amino acids e.g. glutamine, and therefore
may be loosely considered as the ‘taste of proteins’.
• ‘Hot and spicy’ flavors, even if often referred to as taste, are actually pain/temperature
sensations caused by the substance called ‘capsaicin’ in food. This compound binds to
thermoreceptors whose primary function is to detect hot foods/liquid in order to prevent
burning of the lingual/oral mucosa. Such sensations are transmitted afferent nerve fibers of
the trigeminal nerve.

55. • CLINICAL APPLICATIONS:
• Taste dysfunction is often a symptom of viral or bacterial
infections in the upper respiratory and oral parts.
• Ageusia is a rare condition with total loss of taste usually
related to the lack of proper gustatory nerve supply.
• Hypogeusia is a condition characterized by a decreased
sense of taste due to chemotherapy, Bell's Palsy or other
neuronal dysfunction, as well as drug use.
• Hypergeusia is usually very rare and refers to increased
taste sensitivity. It can be associated with a lesion of the
posterior cranial fossa.

56. NERVE SUPPLY TO THE TONGUE
• Facial nerve (chorda tympani, greater petrosal nerve),
glossopharyngeal nerve, vagus nerve
• Facial nerve (CN VII): the chorda tympani (via the lingual nerve)
innervates taste buds in the anterior two-thirds of the tongue
• Glossopharyngeal nerve (CN IX): This nerve, predominantly
innervates the posterior one-third of the tongue (containing the
circumvallate papillae), palatoglossal arch of the soft palate, and
oropharynx.
• Vagus nerve (CN X): Through its internal laryngeal branch, this
nerve provides innervation for the epiglottic region and pharyngeal
part of the tongue.

57. Thank you