Vocabulary Sense Organs

• Cornea: Clear, protective covering on the outside of the eye that helps focus light.



• Hyperopia: Vision problem in which distant objects are clear but nearby objects look blurry; also called farsightedness.



• Iris: Colored structure at the front of the eye.



• Lens: Clear, curved structure in the eye that focuses light on the retina.



• Myopia: Vision problem in which nearby objects are clear but distant objects look blurry; also called nearsightedness.



• Pupil: Black opening in the iris that lets light enter the eye.



• Retina: Layer of light-sensing cells that covers the back of the eye.



• Vision: Ability to see light.



• Anvil: Second of three tiny bones that pass vibrations through the ear.



• Cochlea: Liquid-filled structure in the ear that senses vibrations and generates nerve impulses in response.



• Ear: Sense organ that detects sound.



• Ear canal: Tube-shaped opening in the ear that carries sound waves to the eardrum. Eardrum: Membrane in the ear that vibrates when sound waves hit it.



• Hammer: First of three tiny bones that pass vibrations through the ear.



• Hearing: Ability to sense sound.



• Oval window: Membrane in the ear that passes vibrations from the stirrup to the cochlea.



• Pinna: Outer part of the ear that gathers sound waves.



• Semicircular canals: Liquid-filled part of the ear that senses changes in position and generates nerve impulses in response.



• Smell: Ability to perceive odors.



• Stirrup: Last of three tiny bones that pass vibrations through the ear.



• Taste buds: Tiny bumps on the tongue that contain taste neurons.



• Touch: Sense of pain, pressure, or temperature.

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.

Taste and smell

Taste is one of the two main chemical senses, the other being smell. There are at least four types of taste receptors on the tongue. Taste stimuli from each receptor type send information to a different region of the brain. The four well-known receptors detect sweet, salt, sour, and bitter and they are located in different areas of the tongue (figure). The existence of a fifth receptor, for a sensation called umami, was confirmed in 2000. The umami receptor detects the amino acid glutamate, which causes a savory, “meaty” flavor in foods. The chemoreceptors of the mouth are the taste cells that are found in bundles called taste buds. The compounds bind to receptors in the taste cells and stimulate neurons in the taste buds. Then, these neurons start nerve impulse which alerts the brain.The tongue can also feel sensations that are not generally called tastes. These include: temperature (hot or cold), coolness (as in “minty” or “fresh”), spiciness or hotness (peppery), and fattiness (greasy). If you click here you will view an animation of how we taste. Smell is the other "chemical" sense. The chemoreceptors of smell are called olfactory receptors. About 40 million olfactory receptor neurons line the nasal passages. Different odor molecules bind to and excite specific olfactory receptors. The combination of excitatory signals from different receptors makes up what we identify as “smell.” The receptors stop sending stimuli very quickly. That is why we get used to smells very easily. Have you ever noticed that you cannot taste anything when your nose is stuffed up? That is because your senses of smell and taste are closely linked. Your olfactory receptors and taste receptors both contribute to the flavor of food. Your tongue can only tell among a few different types of taste, while your nose can distinguish among hundreds of smells, even if only in tiny amounts.

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:

Optical illusions

This post is for publishing some curiosities about vision:
Motion silences awereness of color changes from Jordan Suchow on Vimeo
Instructions: Keep your eyes fixed on the small white mark in the center. At first, the ring is stationary and it's easy to tell that the dots are changing. A few seconds later, the ring begins to rotate and the dots suddenly appear to stop changing.
For most people, when the dots start to rotate, they either completely stop changing colour, or they hardly change colour at all. However the reality is that the dots are still changing colour, just as they were before they started rotating. Even when you know that the dots are changing colour, it does not affect the way you see the illusion.
So when an image of an object moves across our retina, our ability to detect changes in that object is substantially diminished.
If you like it, this link has several examples.
This optical illusion has been created in three dimensions. It is a real object. However impossible things seem to happen! The wooden balls seem to roll uphill. It cannot be magnets - they do not work on wood! This wonderful illusion was created by Koukichi Sugihara from the Meiji Institute for Advanced Study of Mathematical Sciences in Japan.
However once the structure rotates, we can see that it is not constructed as we initially thought. We might have thought that the wooden balls were rolling uphill. Once we view it from the other side, we can see that in fact the balls are rolling downhill, and that the laws of physics are still being obeyed. Whew!
In this webpage there are other videos about brain illusions
I suppose you already know M.C. Escher and his amazing drawings. This tower is from Hungarian artist István Orosz. The tower is like a Möbius Strip.

Sight

Sight or vision describes the ability of the brain and eye to detect certain wavelengths of electromagnetic radiation (light), and interpret the image as "sight." Different receptors are responsible for the perception of color (the frequency of photons of light) and perception of brightness (number of photons of light). Photoreceptors are found in the retina. Just in case you don't remember or you don't know the external parts of the eye you can see in this link
Eye structure The eye has a structure to be able to focus light onto the retina. In the drawing above you can study the different parts of the eye. Each eye is in the socket of the skull. They have a spherical structure (eye ball) with a three-layered wall. This layers are:

• Sclera: It is the outermost white layer that is tough and opaque. The anterior part is transparent and is called cornea. It is covered by a thin transparent membrane called the conjunctiva The sclera provides protection and gives shape to the eye. It provides surface for the attachment of eye muscles.The anterior transparent cornea allows the light to pass through the lens. The bulging shape of the cornea also refracts the light that results in the light focussing properly on the retina.



• Choroid: It is darkly pigmented and highly vascular. In its front is the iris, a circular, muscular diaphram with a hole in the centre. The hole is called pupil. The iris give colour to the eyes. The muscles in the iris contract and expand to increase and decrease the size of the pupil, respectively.



• Retina It is the innermost layer of the eye wall. It is also pigmented layer. It has the photoreceptor cells.There are two forms of photosensitive cells: Rod cells are highly sensitive to light which allows them to respond in dim light and dark conditions, but, they cannot detect color. Cone cells respond to different wavelengths of bright light (different colors). They do not respond well in poor light conditions. Humans have three different types of cone cells. Depending on the distribution of rods and cones, there are two spots on the retina. They are the blind spot and the yellow spot. The blind spot is the point on the retina where the optic nerve leaves the eye. At this region, there are no rods or cones and therefore, no image is formed on this spot. (you can discover your blind spot in this link). Yellow spot (Macula lutea or fovea) . It is the point where most light rays are focussed. It contains only cone cells and is, thus, most sensitive in bright light. The image formed at this point is the sharpest.



• Lens. It is a biconvex, circular, transparent object located just behind the pupil. It serves to focus the light on the retina. It is an elastic structure and its shape can be varied to adjust to objects at varying distances. The adjustment is made with the help of muscles. The lens is held in place with the help of ligament called the suspensory ligament. The chamber between the lens and the cornea is filled with aqueous humour. The posterior, larger chamber between the lens and retina is filled with a semi-solid substance called the vitreous humour.

This video is a good explanation of eye structure

and if you prefer something more real, this is a good option: cow's eye disection

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).

Nervous system vocabulary

axon : A long, membrane-bound extension of the cell body that passes the nerve impulse onto the next cell.
brain stem : Part of the brain involved with unconscious (autonomic) functions such as breathing, heartbeat, and temperature regulation
cell body : Part of a neuron that contains the nucleus and other organelles.
cerebellum : The part of the brain that is involved in coordination and control of body movement.
cerebral cortex :The highly-folded outer layer of the cerebrum; controls higher functions, such as consciousness, reasoning, emotions, and language.
cerebrum : The part of the brain that generally controls conscious functions such as problem-solving and speech.
central nervous system (CNS) : Made up of the brain and spinal cord; .
dendrites : Extend from the cell body and receive a nerve impulse from another cell.
interneurons : Neurons that connect sensory and motor neurons in neural pathways that go through the CNS; also called association or relay neurons.
motor neuron : Neuron that carries nerve impulses from the central nervous system to internal organs, glands, or muscles.
myelin sheath : An electrically insulating layer; covers the axon; speeds up the transmission of a nerve impulse along the axon.
nerve : An enclosed, cable-like bundle of axons.
nerve impulse : Electrical signal that is transmitted by neurons.
nervous system : Body system that controls all the other systems of the body.
neuron : The structural unit of the nervous system. This cell transmits electrical signals.
neurotransmitter : Chemical messages which are released at the synapse and pass the “message” onto the next neuron or other type of cell.
peripheral nervous system (PNS) : All the nerves of the body that lie outside the central nervous system.
sensory neurons : Neurons that carry signals from tissues and organs to the central nervous system; sometimes called afferent neurons.
spinal cord : A thin, tubular bundle of nervous tissue that extends from the medulla oblongata (brain stem) and continues to the lower back
synapse : A specialized junction at which the axon of one neuron comunicate with dendrite of another neuron.