Sensory receptor can be disthinguised based on the detected signal characteristic, namely chemoreceptor, which detects chemical stimulation, nociceptor (pain receptor) which detects pain felling, photoreceptor which detects light, mechanoreceptor which detects stimulation of motion, touch, and pressure, and thermoreceptor which detects temperature change.
We recognize that there are five sense in ours body, which are touch sense (skin), taste sense (tongue), smell sense (nose), hearing and balance sense (ears), and vision sense (eyes).
Skin comprise of five receptors, namely receptor of touch (Meissner nerve and Merkel disc), pressure (Paccini nerve), pain (nerve without membrane), heat (Ruffini nerve or Mazzoni golgy), and cold (Krause nerve).
Sensory nerves on skin are scattered unevenly and can be found in difference depth. Head and cold stimulations are received by different receptor, so that we can differentiate between hot and cold. A strong pain stimulation affecting the skin generates pain receptor to react. Pain sensation is a protection to our body because pain is a signal of wound on our body
The food mixed with saliva will go into taste papillae through the pores. It will stimulate nerve terminal with hair-like structure. Then, the message is carried to brain and nerve base, and finally it is interpreted as taste.
Smell Sense (Nose)
Smell sense is composed of olfactory epithelial tissue and olfactory receptor cells which are located on the upper part of nose cavity. The sensation that we call taste is basically smell. When we chew onion or apple, the vapor or gas goes into the open nose. The gas will affect smell nerve end, so that we can differentiate the taste of union and apple.
Smell is produced by chemical stimulation in the form of gas. Gas goes into nose cavity, diffuses into mucus layers and binds with receptor in dendrite. The gas will stimulate olfactory cell, so that the impulses from olfactory nerves move toward the brain. The impulse will be interoreted as smell.
Smell nerves will not give any responsive to aroma stimulation continuously received in a long period of time. The nerves become active when it receives different aroma stimulation. The brain can also memorize certain aroma because olfactory pumpkin is directly connected to emotional and memory center in the brain.
Ears are the hearing sense as well as balance sense.
Ear is divided into outer ear, middle ear, and inner ear. Inner ear consisit of hearing basic organ and fluid (perilymph and endolymph fluid).
Outer ear comprises of ear lobe (auricle) and auditory canal. The function is help directing the sound entering auditory canal.
Middle ear begins from ear drum (tympanic membrane) to oval window. In this chamber there are three fused bones called ossicle. Ossicle functions as a generator to transmit the vibrate produced by bone (malleus), Incus, and stapes bone. In the inner part of tympanic membrane there is Eustachius tube that connects the middle ear with mouth cavity. Inner ear is composed of two main parts, cochlea (snail shell) and semi-circular canal. Cochlea is divided into three parts, namely vestibule at the beginning part of which there is oval window membrane, coclear duct, and tympanic scale. Middle pipe contains endolymph fluid.
Vestibelea and tympani contain perlymph fluid. Both pipes connect to each other at the top of cochlea.
Between the middle pipe and tympani there is basilar membrane. In the membrane there are cells that form the real auditory organ, the organ of corti. At the end of this organ there are hair cells. The cell connects to nerve fibers toward the brain. In cochlea, in vestibular pipe exactly, there are two small cavity sacks, saccule and utricle. Semi-circular canal is the balace organ. It consists of three ducts having semi-circular shape. There are a lot of receptors within it and also fluid which looks similar with cochlea fluid.
When sound wave reaches ears, it will pass through the outer ear, go down to auditory canal, and get into tympanic membrane. Sound wave vibrates the tympanic membrane, hammer bone, stapes, and finally goes into oval window. As a result, it vibrates the cochlea fluid and stimulates hearing nerve. Afterward, the nerve beginning sends impulse to cerebrum and interprete it. The result is we can hear certain sound.
The Balance process is conducted by semi-circular canal. It detects rotation balance (rotating motion of head) and gravitation balance (straight head motion).
Rotation balance involves three semi-circular canals. At the base of the three canals there is a structure called ampulla. Within the ampulla, there is hair cell planted in gelatin called cupule. When the fluid in the canal flows, cupule moves along with the flow direction and generates nerve impulse. The impulse then travels through vestibular nerve toward the brain.
Gravitation balance depends utricle and saccule which contain earstone. Utricle is very sensitive to tilting motion. The earstone motion will press the tip of nerve balance and impulse will be transmitted to balance center in the brain.
Eye is vision sense. The front of the eye is protected by transparent membrane (conjunctive ), which protects the cornea. The membrane is often flowed by tears. Tear is produced by lacrimal gland which serves the function to keep the eye ball moist, to clean the eye ball from dirt, and to kill bacteria since it contains antobacteria enzyme.
Eye lies in eye cavity and has oval round shape. Eye ball and eye cavity are connected by six muscle which can generate eye movement to various direction.
Eye is composed of three layers, namely scelera, choroid, and retina.
Sclerea is the outer layers of the eye ball in the form of tough white tissues. It maintains the shape of the eye globe. Scelera contains cornea which is transparent and composed of collagen fibers.
Choroid is a thin, dark tissue which lies between scelera and retina (intermediate layer), and contains a large amount of pigment and blood vessel. Between the anterior of choroid and posterior of the cornea there is iris which consists of circular muscle and contains pigment. Iris pigment determines human eye color. Iris is also important to control the amount of light entering the eyes by regulating the pupil size (a sphere located in the center of iris). When receiving strong light intensity, the pupil size will constrict. Conversely, when receiving weak light intensity, the pupil will dilate.
At the back of iris there lies eye lens which is a transparent and biconvex structure suspended in place by ciliary muscle of suspensory ligament. When the muscle contracts, the lens shape changes so that we can see an object in focus. The eye lens change is called accommodation.
Lens divides the eye into two part. The anterior portion of the lens (between lens and cornea) contains aqueous humor fluid. The posterior portion of the lens contains vitreous humor fluid which is transparent and has function to maintain the eye ball shape.
Retina is the innermost layer containing photoreceptor and nerve cells which are sensitive to light. Retina has the thickness of less than 1 milimeters. It is composed of several cell layers, which are receptor cell, ganglion cell, and nerve fibers. In the center of retina there is light focus site called yellow spot (macula lutea).
Inside the retina there are two kinds of photoreceptor, cone cell and rod cell. The receptor cell is not found in the area between optical nerve and retina, which is called blind spot.
We can see an object if there is a light reflected from the object. Light reflection is received by the eyes, through cornea, aqueous humor, pupil, lens, vitreous humor and finally retina. The light stimulates photoreceptor toward optical nerve. The eye lens will focus the light, so that it fall in the center of yellow spot called fovea. The light that fall on retina but not exactly on the fovea will caused the object cannot be clearly seen because the cone cell is mostly found in fovea.
The cone cell is responsible for the color sight, and it is more sensitive to bright light than the rod cells. At night, there is not enough strong light to stimulate cone cell, however it is strong enough to stimulate rod cell. Nevertheless, rod cell cannot differentiate colors so that we can see much color in less intense light.
Inside the fovea, there is no rod cell, but there is much rod cell outside the fovea. That is why, in dark room or a room without enough light, we will see the objects around us more easily by using the corner of our eyes.
1. Write down the pathway sound until it can be heard?
2. What do you know about iris, lens, and yellow spot?
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