Touch

Our skin, which has about 5 million sensory cells overll, is the main organ of the sense of touch. While your other four senses (sight, hearing, smell, and taste) are located in specific parts of the body, your sense of touch is found all over. The skin is one of the bodies largest and most complex organs. His weighs is between 1.5 and 2.5 kilograms. Skin is made up of two layers:

• The epidermis is the outermost layer which provides waterproofing and serves as a barrier to infection. The top part of the epidermis is a layer of dead skin cells. These flake off and are replaced all the time. Also In the epidermis are the melanocyte a cell type that produces pigment (melanin). That color protects the lower layers of the skin from harmaful ray of the Sun.



• The dermis or the layer beneath the epidermis. It contains hair follicles, nerve endings, sweat glands, blood vessels. (see in the figure) ant the different touch receptors.

The skin is not equally thick al over your body. The soles of your feet are the thickest. And the eyelid has the thinnest skin on the entire body.

The dermis is filled with many tiny nerve endings which give you information about the things with which your body comes in contact. The most common receptors are heat, cold, pain, and pressure or touch receptors. Pain receptors (nociceptors) are probably the most important for your safety because they can protect you by warning your brain that your body is hurt. In the figure you can see the differnt types of receptors.

Some parts of your skin have more nerve endings that other parts, so some parts are more sensitive to touch than others are. Your fingertips, tongue, and lips have the most nerve endings. You do not only have sense of touch on the outside of your body, you also have touch sense in the inside of your body.

Finally, in this link you have play and learn activities about the senses.

Ear: Hearing and Balance

The senses of hearing and balance are located in your ears
Hearing is the sense of sound perception that results from the movement of tiny hair fibers in the inner ear. These hairs detect the motion of a membrane which vibrates in response to changes in air pressure. Audible sound is sensed by the ear.
Balance sense is the sense which allows an organism to sense body movement, direction, and acceleration, and to attain and maintain postural equilibrium and balance.
Ear structure:
Outer ear: Pinna and ear canal.
The outer ear collects sounds from the environment and funnels them through the auditory system.
The folds of cartilage surrounding the outer ear canal are called the pinna. Sound waves are gathered by the pinna, and funnelled into the ear canal. The sound waves are guided down your ear canal towards the eardrum. The eardrum or tympanic membrane resembles a flexible window that vibrates as sound waves bounce on it
Middle ear: Eardrum and the ear bones (hammer, anvil and stirrup).
The middle ear transmits sound from the outer ear to the inner ear.
This is a hollow, air-filled space also known as the tympanic cavity. It connects to the back of the throat and nose through the Eustachian tubes .
Eardrum vibrations continue into the middle ear. Vibrations travel across the air-filled middle ear cavity through the ear ossicles, a group of three tiny, delicate bones: Hammer, anvil and stirrup. They amplify the eardrum vibrations and transfer to another membrane called the oval window. The oval window separates the middle ear from the inner ear.
Inner ear: Semicircular canals the vestibule and the coclea
The inner ear is responsible for interpreting and transmitting sound sensations and balance sensations to the brain.
This is found in the temporal bone of the head.
The cochlea is responsible for hearing. It is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear through the oval window. As the fluid moves, thousands of mechanoreceptors called hair cells bend and produce nerve impulses towards the temporal lobe of the cerebral cortex.
A very strong movement of the fluid within the cochlea, caused by very loud noise, can kill hair cells. This is a common cause of partial hearing loss and is the reason why users of firearms or heavy machinery should wear earmuffs or earplugs. Destruction of the hair cells usually leads to permanent hearing loss because once destroyed, the hairs do not generally grow back.
The vestibule and 3 semicircular canals are responsible for balance. The canals are arranged at right angles to each other. If you change the position of your head, the fluid in the canals moves. In each canal there is hair cells that sense the strength and direction of the fluid’s movement and send electrical signals to the cerebellum.
When the sense of balance is interrupted it causes dizziness and nausea. Balance can be upset by an inner ear infection, a bad head cold or a sinus infection, or a number of other medical conditions. It can also be temporarily disturbed by rapid and repetitive movement, for example riding on a merry-go-round or spinning around in a circle.
This two videos are aboaut the ear and sound. I think they can help you with your learning.


This last one is about the sense of balance:

Sense Organs and Sensory Perception

Your senses are your body’s means of making sense of the information your nervous system receives from inside your body and from the outside world (stimuli). Your senses enable you to adapt to change in your environment and survive. The sensory division of the peripheral nervous system is organized into highly developed sense organs, which are groups of tissues that work together in responding to a specific kind of stimulus. The sense organs correspond to a defined region within the brain where the nerve signals are received and interpreted. Your sense organs include your eyes, ears, nose, mouth, and skin. Sensory neurons send nerve impulses from sensory receptors to the central nervous system. The brain then interprets the nerve impulses to form a response. A sensory receptor is a cell, or a group of cells that detect stimuli. Types of receptor :

Sensory receptors can be classified based on the type of stimuli to which they respond.

• Mechanoreceptors respond to mechanical stimuli such as tension (stretching) or pressure. They tranduce mechanical energy into nerve impulses.



• Thermoreceptors respond to changes in temperature (heat and cold); they tranduce heat energy into nerve impulses.



• Nociceptors respond to injurious or painful stimuli; they tranduce a variety of forms of energy into nerve impulses.



• Photoreceptors respond to electromagnetic radiation, typically wavelengths of visible light, they tranduce light energy into nerve impulses; in humans (and most vertebrates), these are the rods and cones of the eyes.



• Chemoreceptor responds to chemical stimuli; they tranduce the binding of specific hemicals into nerve impulses; includes exteroceptors for smell and taste and interoceptors sensitive to concentration changes of some molecules in the blood.

It is generally agreed that there are at least seven different senses in humans. These are sight, sound, taste, smell, touch, balance, and body awareness (the sense of knowing where the regions of your body are located at any one time).