Sensory organs of the human body | MPO training 12

Sensory organs	Helps
Eyes:	For seeing light, color, and movement
Ears:	For hearing sounds and helping with balance
Nose:	For smelling different scents
Tongue:	For tasting flavors like sweet or sour
Skin:	For feeling touch, temperature, and pain

Together, these organs send signals to our brain, helping us understand and enjoy our surroundings.

Yes. Besides the five main senses, our body has other ways to sense things:

• Balance: Tiny parts in the inner ear let us know if we are upright or upside down.
• Body Awareness: Nerves in our muscles and joints tell the brain where our arms and legs are without looking.
• Temperature and Pain: Special nerves in our skin sense if something is hot, cold, or might hurt us.

These are not separate organs like eyes or ears, but they help us feel the world. When people talk about sensory organs of the human body, they usually mean the five main ones (eyes, ears, nose, tongue, and skin), but our body has even more ways to sense things around us.

The senses for which there are special end organs for the reception of specific types of stimuli are called special senses.

Sensory organs have special receptors that allow us to smell, taste, see, hear, and maintain equilibrium or balance.

The Information conveyed from these receptors to the central nervous system is used to help maintain homeostasis. (Homeostasis: Normal body balance)

The organs used for these functions are eye, ear, tongue and skin.

Special sense	Sensory organ	Receptor
Vision	Eye	Rods and cones
Hearing	Ear	Hair cell of organ of corti
Olfaction or smell	Nose	Bipolar cell of olfactory mucosa
Taste	Tongue	Taste buds
Equilibrium	Ear	Vestibular apparatus

• Eye-related (e.g., conjunctivitis, dry eye) – 35%
• Ear-related (e.g., ear infection, hearing loss) – 25%
• Skin-related (e.g., dermatitis) – 20%
• Nose-related (e.g., rhinitis, sinusitis) – 10%
• Tongue-related (e.g., taste disorder) – 10%

More than half the sensory receptors in the human body are located in the eyes, and a large part of the cerebral cortex is devoted to processing visual information.

Our eyes work like natural cameras, helping us see the world. Light enters through the front of the eye and reaches the back, where special cells sense it. These cells detect light and color and send signals to our brain. The brain then turns these signals into the pictures we see around us. Because of our eyes and brain, we can recognize faces, read, watch movies, and enjoy the beauty around us.

The accessory structures of the eye include the eyelids, eyelashes, eyebrows, the lacrimal (tearing) apparatus, and extrinsic eye muscles.

There are three layers/tunics in the eye:

1. Outer fibrous layer: It contains sclera and cornea
2. Middle vascular layer: It consists of Iris, ciliary body, choroid. Together these three are called Uveal tract.
3. Inner neural layer: Retina.

• Cornea
• Iris
• Pupil
• Lens
• Retina
• Macula
• Optic nerve
• Choroid and
• Vitreous

Iris: Colored part of the eye that helps regulate the amount of light that enters.

Pupil: Dark aperture in the iris that determines how much light is let into the eye.

Lens: Transparent structure inside the eye that focuses light rays onto the retina.

Retina: Nerve layer that lines the back of the eye, senses light, and creates electrical impulses that travel through the optic nerve to the brain.

Macula: Small central area in the retina that contains special light sensitive cells and allows us to see fine details clearly.

Optic nerve: Connects the eye to the brain and carries the electrical impulses formed by the retina to the visual cortex of the brain.

Vitreous: Clear, jelly-like substance that fills the middle of the eye.

Light waves from an object (such as a tree) enter the eye first through the cornea, which is the clear dome at the front of the eye.

It is like a window that allows light to enter the eye.

The light then progresses through the pupil, the circular opening in the center of the colored iris.

Fluctuations in the intensity of incoming light change the size of the eye's pupil.

As the light entering the eye becomes brighter, the pupil will constrict (get smaller), due to the pupillary light response.

As the entering light becomes dimmer, the pupil will dilate (get larger).

Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens (located immediately behind the iris and the pupil), to a nodal point (N) located immediately behind the back surface of the lens.

At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).

The light continues through the vitreous humor, (the clear gel that makes up about 80% of the eye's volume), and then, ideally, back to a clear focus on the retina, behind the vitreous.

The small central area of the retina is the macula, which provides the vision of any location in the retina.

In the retina, rods and cones initiate visual signals and relay them to bipolar cells, which transmit the signals to ganglion cells.

The retina registers the tiny photons of light interacting with it.

Within the layers of the retina, light impulses are changed into electrical signals.

Then they are sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior (back) of the brain.

Here, the electrical signals are interpreted or "seen" by the brain as a visual image.

Myopia (Nearsightedness) : Near-sightedness is a common eye condition in which faraway objects appear blurry.

Hyperopia (farsightedness) : Farsightedness means it's easy to see things that are far away, but your closeup vision (near vision) is blurry.

Astigmatism : Astigmatism is a common vision problem caused by an error in the shape of the cornea. With astigmatism, the lens of the eye or the cornea, which is the front surface of the eye, has an irregular curve. This can change the way light passes, or refracts, to your retina. This causes blurry, fuzzy, or distorted vision.

Presbyopia : Presbyopia is an eye condition in which your eye slowly loses the ability to focus quickly on objects that are close.

Cataract :  A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil.

Glaucoma : Glaucoma is an eye disease that can damage your optic nerve. The optic nerve supplies visual information to your brain from your eyes. Glaucoma is usually the result of abnormally high pressure inside your eye.

Corneal Ulcer : A corneal ulcer is an open sore that forms on the cornea

Night blindness : Night blindness is also called "nyctalopia." It's a type of vision impairment. People with night blindness experience poor vision at night or in dimly lit environments.

Strabismus : Crossed eyes is also called strabismus, a condition in which your eyes don't line up. If you have this condition, your eyes look in different directions. And each eye will focus on a different object.

Blepharitis : Inflammation of the eyelids.

Conjunctivitis (Pink eye) : Inflammation or irritation of the conjunctiva. It may be due to viral, bacterial or allergic inflammation.

Dry eye : A common condition that occurs when the eyes do not produce enough tears to keep the eye moist and comfortable.

Keratitis : Inflammation of the cornea.

The ear can transduce sound vibrations with small amplitudes into electrical signals 1000 times faster than photoreceptors can respond to light.

Our ears pick up sound waves and send them to the brain so we can hear. Sound enters the ear and vibrates a drum-like part (the eardrum). These vibrations travel through tiny parts in the ear and reach the inner ear, where special cells turn them into signals. The brain receives these signals and understands them as sounds like music, voices, or a car horn.

Besides receptors for sound waves, the ear also contains receptors for equilibrium.

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.

1. Auricle or pinna 
2. External auditory meatus.

1. Auditory ossicles 

• Malleus
• Incus
• Stapes

2. Auditory muscles

3. Eustachian tube

Internal ear or labyrinth is a membranous structure, enclosed by a bony labyrinth in the petrous part of the temporal bone.

It consists of the sense organs of hearing and equilibrium. Sense organ for hearing is the cochlea and the sense organ for equilibrium is the vestibular apparatus.

The nose is a sensory organ that helps us to smell and also plays an important role in breathing and filtering air.

Our nose has a special job: detecting different scents in the air. Inside the nose are tiny cells that pick up scent particles from things we sniff. These cells send a message to the brain, which figures out the scent. This lets us enjoy nice smells (like flowers or baking bread) and notice warnings (like smoke from a fire or spoiled food).

• External Nose – The visible part outside the face.
• Nasal Cavity – The hollow space inside the nose.
• Nasal Septum – The divider that separates the left and right sides.
• Turbinates – Curved bones that help in filtering and warming air.
• Olfactory Region – The area responsible for smelling.

Function	Description
Smelling (Olfaction)	Detects smell using the olfactory nerve.
Breathing	Takes air in and out, helps respiration.
Air Filtration	Filters dust and germs using mucus and cilia.
Humidification	Adds moisture to the air.
Voice Resonance	Helps in clear and proper voice production.

• Smell is detected by olfactory receptors.
• Signal goes to the olfactory bulb.
• Then it travels to the brain (olfactory cortex) to identify the smell.

Disease	Explanation
Rhinitis	Inflammation of the nasal lining (can be allergic or due to infection).
Sinusitis	Infection or inflammation of the sinus cavities.
Nasal Polyps	Soft, painless growth inside the nose.
Anosmia	Loss of smell (can happen due to infection, trauma, or drug effect).
DNS (Deviated Nasal Septum)	The nasal divider is not in the center; can cause breathing problems.

The tongue is a muscular sensory organ inside the mouth. It plays a vital role in tasting, speaking, swallowing, and chewing.

Our tongue is covered with many tiny bumps called taste buds. These taste buds sense flavors like sweet, sour, salty, and bitter. When you eat something, molecules from the food touch the taste buds on your tongue and send signals to your brain. The brain figures out the flavor, so you know if something is candy-sweet or lemony-sour. The tongue also helps us chew food and speak clearly.

1. Anterior 2/3 – Front portion; responsible for most taste sensation.

2. Posterior 1/3 – Back part; contains lymphoid tissue (part of tonsils).

3. Papillae – Small bumps on the tongue surface that contain taste buds:

• Fungiform
• Filiform
• Circumvallate
• Foliate

4. Muscles of Tongue – Help in movement during speaking, eating, etc.

5. Lingual Frenulum – A fold of tissue under the tongue that holds it in place.

1. Taste buds detect the taste.

2. Signals are sent through cranial nerves:

• Facial Nerve (VII) – Anterior 2/3
• Glossopharyngeal Nerve (IX) – Posterior 1/3
• Vagus Nerve (X) – Base of tongue

3. Brain processes taste in the gustatory cortex.

Condition	Description
Glossitis	Inflammation of the tongue (due to infection or deficiency).
Geographic Tongue	Map-like appearance, usually harmless.
Oral Thrush	Fungal infection (white coating on tongue).
Taste Loss (Ageusia)	Can happen due to illness, drug reaction, or nerve damage.
Tongue-tie (Ankyloglossia)	Short frenulum limiting tongue movement.

Skin is the largest sensory organ of the human body. It not only covers and protects the body but also helps us feel touch, temperature, pressure, and pain.

Our skin is the largest sensory organ in our body, full of nerve endings. These nerves help us feel touch, temperature, and even pain. When something touches your skin (like a soft blanket or a hot stove), the nerve endings send signals to your brain. The brain then tells you what you’re feeling – like hot or cold, soft or rough. This lets you enjoy gentle touches (like a warm hug) and stay safe (by sensing if something is too hot).

The skin has three main layers:

• Outermost layer.
• Contains keratin (protects against bacteria).
• Contains melanocytes (controls skin color).
• No blood vessels.

• Contains blood vessels, nerve endings, sweat glands, hair follicles, and touch receptors.
• Responsible for sensation and temperature regulation.

• Contains fat cells (adipose tissue).
• Acts as cushion and insulation.

Condition	Explanation
Dermatitis	Inflammation of skin (e.g., eczema, allergic reaction)
Psoriasis	Autoimmune skin condition with red, scaly patches
Fungal Infection	Ringworm, athlete’s foot, etc.
Acne	Inflammation of hair follicles and oil glands
Urticaria (Hives)	Itchy, allergic skin reaction

To know more about skin and skin disease, first you have to know about the integumentary system.

Equilibrium

Dynamic Equilibrium

We can protect the sensory organs of the human body by taking good care of them in our daily lives.

• Eyes: Wear sunglasses on sunny days, and get regular eye check-ups.
• Ears: Turn down loud music and use earplugs in noisy places.
• Nose and Tongue: Don’t sniff or taste harmful chemicals, and keep your mouth and nose clean.
• Skin: Use sunscreen and wear gloves to protect your skin from sun and injury.

These steps help keep our eyes, ears, nose, tongue, and skin working well so we can keep sensing the world.

All the sensory organs of the human body send signals to our brain to help us understand our surroundings. For example, our eyes send images of what we see, and our ears send information about what we hear. The brain mixes these signals together to create our full experience.

For instance, when you eat, your nose and tongue team up – your nose smells the food and your tongue tastes it, and together they tell the brain exactly what flavor you are enjoying. This teamwork helps you fully enjoy events like watching and listening to a movie or smelling and tasting a delicious meal.

The human sense of hearing is attributed to the auditory system, which uses the ear to collect, amplify, and transduce sound waves into electrical impulses that allow the brain to perceive and localize sounds.

The ear can be divided into the outer ear, middle ear, and inner ear, each of which has a specific function in the process of hearing.

The outer ear is responsible for the collection and amplification of sound. The air filled middle ear transforms sound waves into vibrations, protecting the inner ear from damage. The fluid-filled inner ear transduces sound vibrations into neural signals that are sent to the brain for processing.

The cochlea is the major sensory organ of hearing within the inner ear. Hair cells within the cochlea perform the transduction of sound waves.

Humans are capable of estimating a sound's origin through a process called sound localization, which relies on timing and intensity differences in sound waves collected by each of our two ears.

Sensory organs help you stay aware of your surroundings. They protect you from danger and help you enjoy life through sound, sight, smell, taste, and touch.

The eye captures light and sends signals to the brain so you can see. It is a complex organ that helps you recognize color, shape, and distance.

The ear helps you hear sounds and also controls balance. It sends sound signals to the brain through tiny vibrations.

The nose detects smells. It also helps in breathing and filtering the air. Smell signals go directly to the brain.

The tongue helps you taste different flavors like sweet, sour, salty, bitter, and umami. It also helps in talking and swallowing.

The skin is the largest sensory organ. It helps you feel temperature, pressure, pain, and touch through nerve endings.

You can protect your senses by avoiding loud noise, using sunglasses, eating healthy foods, and avoiding harmful chemicals. Regular check-ups are also helpful.

In conclusion, understanding the sensory organs of the human body is important for anyone learning medical basics. This article showed you how our eyes, ears, nose, tongue, and skin help us sense our world. You now see why knowing these organs matters in health and MPO training.

Remember, this basic knowledge helps you talk confidently about medical topics. Keep it in mind as you become an MPO. It lays a strong foundation for your future career in medical communication. Value this knowledge as a stepping stone to success in your healthcare communication career.