The document summarizes how each of the 5 human senses (smell, taste, hearing, sight, touch) works. Each sense consists of specialized sensory organs and cells that detect stimuli and transmit signals to the brain. For smell, odor molecules bind to receptors in the nose. For taste, receptors on the tongue detect sweet, salty, bitter, sour, and umami flavors. Hearing involves sound waves vibrating the eardrum and bones to stimulate hair cells in the cochlea. Sight relies on light stimulating photoreceptor cells in the retina to form images. Touch is mediated by mechanoreceptors, thermoreceptors and other receptors in the skin that detect pressure, temperature and pain.

2. Each of the 5 senses consists of organs with
specialized cellular structures that have
receptors for specific stimuli. These cells have
links to the nervous system and thus to the
brain. Sensing is done atprimitive levels in the
cells and integrated into sensations in the
nervous system. Sight is probably the most
developed sense in humans, followed closely
by hearing.

3. Our sense of smell works…
Our sense of smell is part of our
chemosensory system, or the
chemical senses. Specialized sensory
cells, called olfactory sensory
neurons, are found in a small patch
of tissue high inside the nose. These
cells connect directly to the brain.
Each olfactory neuron expresses one
odor receptor.

4. Smells reach the olfactory sensory
neurons by way of two pathways.
The first pathway is through your
nostrils. 95% of our nasal cavity is
used just to filter air before it gets
your lungs.
The second pathway is through a
channel that connects the roof of
the throat region to the nose.

5. The olfactory epithelium is a layer
of olfactory receptor cells. When
odor molecules hit the back of our
nose, it stucks in a layer of mucus
covering the olfactory epithelium,
as they dissolved, they bind to the
olfactory receptor cells, which fire
and send signals through the
olfactory track, up to our brain

6. Our brain has 40,000,000 olfactory receptor neurons, so an odor can trigger many neurons
and all those combinations let us detect an smell. Plus our olfactory neurons are always
fresh, they`re the only neuron in our body that get`s replace regularly (4-8 WEEKS)

7. Our sense of taste works…
Our tongue contains five types of taste receptors that
register sweetness, saltiness, bitterness, sourness and
umami (savory or meaty taste). Chemicals interact
with receptors to generate signals which are sent to
the brain. Processed signals give us certain ideas
about the kind of food we are dealing with and
allows us to take certain decisions and modify our
behavior
accordingly.

8. Thereceptors for taste, called taste buds,
aresituated chiefly in the tongue, but they
are also located in the roof of the mouth
and nearthe pharynx. At the base ofeach
taste bud there is a nervethat sends the
sensations to the brain. The sense of taste
functions in coordination with the sense of
smell.

9. Sweetness,usuallyregardedas apleasurablesensation,
is producedbythepresence ofsugarsandafew other
substances
Sournessis thetastethatdetectsacidity.The sournessof
substancesis ratedrelativeto dilutehydrochloricacid,
which hasasournessindex of1
Saltinessis atasteproducedprimarilybythe presenceof
sodiumions.
Bitternessis themostsensitive ofthe tastes,andmany
perceive it asunpleasant,sharp,ordisagreeable,butitis
sometimesdesirable andintentionallyaddedvia various
bitteringagents
Umami is an appetitive taste and is described as a
savory or meaty taste. It can be tasted in cheese and
soy sauce, and while also found in many other
fermented and aged foods, this taste is also present in
tomatoes,grains,andbeans.

10. Our sense of hearing works…
Ears play a significant role in human
as well as animal life. It is one of the
very important sense organs for
human andanimal system. It’s a
complex energytransfer and
exchangesystem that translates the
sound waves into mechanical energy,
then into fluid energyand finally into
electrical energy.

11. The auricle and ear canal channel sound waves toward the eardrum. The eardrum vibrates in
response to the sounds, setting in motion the bones of the middle ear (ossicles). As the third
bone moves in and out of the oval window, the vibrations make waves in fluid of the cochlea -
not unlike dropping pebbles in a still lake. The membrane inside the cochlea moves as a reply to
these vibrations, stimulating the hair-like nerve endings. The nerve endings send the impulse to
the brain for understanding.

12. Our sense of sight works…
The organs of sight or vision are the eyes. These, along with the optic nerves and the brain
allow us to see. Light enters the eye, first passing through the transparent front part of the eye
called the cornea. The cornea refracts, or bends, the light waves to focus on the pupil. The
light then passes through the pupil, which is an opening in the middle of the colored part of
the eye, or iris. The iris can open the pupil wider when there is not much light, or make it
smaller when the light is strong.

13. Once through the pupil, the light passes through the lens, which further refracts and inverts the
light, and can be changed in shape by muscles in the eye, finally projecting a focused, upside-
down image onthe retina.
Theretina, at the back ofyour eye, contains millions of photoreceptor cells which respond to
light. These cells contain protein molecules called opsins. We havetwo types of opsins - rods
and cones.
Opsins each can absorb a particle of light, called a photon, and transmit a signal to the cell.
Rods detect colors in shades of grey, and can sense movementand shape.

14. Cones mainly distinguish color. You have three types which detect different wavelengths of light
- red, blue or green.Signals from many cones can produce all the colors we see.They only work
in bright light, so in dim light colors areharder to see.Once the cells receivethe signal from the
opsins, it is transmitted to the optic nerve,which is connected to the retina at the back ofyour
eye. (There are no photoreceptors where the optic nervejoins the retina, and this is why you
have what is known as a "blind spot" in your eye.) The optic nervesends the signal to your brain,
which interprets the image, and turns it back the right way up.

15. Our sense of touch works…
Our skin acts as the protective barrier between
our internal body systems and the outside
world. Its ability to perceive touch sensations
gives our brains a wealth of information about
the environment around us, such as
temperature, pain, and pressure. Our sense of
touch is controlled by a huge network of nerve
endings and touch receptors in the skin known
as the somatosensory system. Within the
somatosensory system, there are four main
types of receptors: mechanoreceptors,
thermoreceptors, pain receptors, and
proprioceptors.

16. When your hand touches an object, the mechanoreceptors in the skin are activated, and they
start a chain ofevents by signaling tothe nearest neuron that they touched something. This
neuron then transmits this message to the next neuron which gets passed on to the spinal
corduntil the message is sent to the brain. Nowthe brain can process what your hand
touched and send messages backto your hand via this same pathway to let the hand knowif
the brain wants more information about the object it is touching orif the hand should stop
touching it.