Sight

1.Sight

We get 90% of information about our surroundings by eyes. Here the information is processed creating all the images that you can see. The eyeball is a slightly bulging sphere. Only the iris, the pupil, and the cornea are actually visible. The rest of the eyeball is set inside the skull.



The eyeball is a fluid-filled sphere with a tough outer coating called the sclera. Sclera or sclerotic coat. The ´white´ of the eye. Tough, fibrous and opaque, with blood vessels. The front part of the sclera, the cornea, is clear to allow light to enter the eyeball. Protects front of eye and bends /refracts/ light onto lens.Behind the cornea is the iris with opening, the pupil, in the centre. Light entering the eye passes through the pupil and the lens strikes the retina at the back of the eyeball. The light-sensitive cells of the retina send nerve impulses along the optics nerve to the brain.

Conjuctiva:Thin mucous membrane. Lines eyelids and covers cornea.
Cornea:Transparent continuation of sclera. Protects front eye and bends- refracts light rays onto lens.
Aqueous humour:Watery liquid with sugars, salts and proteins. Fills space called Anterior cavity. Protects lens and nourishes front of eye. Constantly drains away and is replaced.
Iris:is the coloured part of the eye that surrounds the pupil. The colour /pigment/ of the iris is inherited from parents, but there are not two people with the iris of the same colour. The iris has a circular muscle within it – a sphincter. The monvement of sphincter controls the size of the pupil at the centre of the eye. By this the iris controls the amount of light entering the eye, protecting it from too much light and allowing you to see in dim light.
The lens is transparent and light passes through it to be focused on the back of the eye. To focus on objects, both near and far away, the lens must change its shape. Suspensory ligaments around it allow this by pulling on the rim of the lens.
Ciliary body:Muscular ring /smooth muscle/ round lens. Contracts too make lens smaller /in diameter/ and fatter /fibre of suspansory ligament relax /. Relaxes to make lens larger and thiner /fibres tighten/. Together with muscles of iris, known as intrinsic eye muscles.
The muscles which move the eyeball are attached to the sclera.
Extrinsic eye muscle:The three pairs of muscles joining the eyeball to the eye socket / orbit/. They contract to make the eyeball swivel around.
Rectus muscle
Viterous humour:Fluid similar to aqueous humour, but stiff and jelly-like. Fills space called posterior cavity. Keeps shape of eyeball protects nervous layer/retina/and helps refract light.
The retina:is the lining on the back of the eye. It has millions of cells, which respond to light by creating nerve impulses which travel to the brain. These cells are made up of two types: Cones, which respond to light of a particular colour /Trichromatic vision- blue , red , green /
rods, which work in dim light but do not detect differences in colour./pigment retinol/
The fovea , macula fovea allows us to see in fine detail. It is the area in the center of the retina. It looks like a crater, the centre of which is filled with cones.
The blind spot:is the point where the optic nerve from the brain connects with the retina. Blood vessels supplying the retina also leave the eye at the blind spot. There are no light- sensitive cells on this part of retina.
Choroid or choroid coat: Layer of tissue with blood vessels and dark pigment. Pigment absorbs light to stop reflection back out.

Disorders and diseases of eye

Hemianopsia: is a blindness or reduction in vision in one half of the visual field. Hemianopsias can be caused by conditions such as stroke, tumors and trauma. The cause of a hemianopsia must always be carefully investigate by the patient's physicians. Hemianopsias may vary from an absolute loss of all vision on one side to a relative loss where vision is reduced, but not completely missing.

Color vision: is pretty complicated. If you're not color-deficient or color-blind then it's hard to understand what color-blind people see. There are four kinds of color vision:

• Trichromat:Regular vision is Trichromatic - it uses all three colour pigments (red/green/blue).

• Anomalous Trichromat
People with Anomalous Trichromatic vision use all three color receptors but reception of one pigment is misaligned.
Protanomaly: reduced red sensitivity.
Deuteranomaly: reduced green sensitivity.
Tritanomaly: reduced blue sensitivity.

• Dichromat
People with Dichromatic vision use only 2 of the 3 visual pigments - red, green or blue is missing.
Protanopia: unable to receive red.
Deuteranopia: unable to receive green.
Tritanopia: unable to receive blue.

• Monochromat (Achromatopsia)People with Monochromatic vision can only see one color, so their vision contains no 'color'.
Typical Monochromatic /rod monochromat/ unable to combine colors. Fully grayscale.
Atypical Monochromati /cone monochromat/: very low color recognition.

The diabetic retinopathy: The effect of diabetes on the eye. Over time, diabetes affects the circulatory system of the retina. The earliest phase of the disease is known as background diabetic retinopathy. In this phase, the arteries in the retina become weakened and leak, forming small, dot-like hemorrhages. These leaking vessels often lead to swelling or edema in the retina and decreased vision.
The next stage is known as proliferative diabetic retinopathy. In this stage, circulation problems cause areas of the retina to become oxygen-deprived or ischemic. New, fragile, vessels develop as the circulatory system attempts to maintain adequate oxygen levels within the retina. This is called neovascularization. Unfortunately, these delicate vessels hemorrhage easily. Blood may leak into the retina and vitreous, causing spots or floaters, along with decreased vision.
In the later phases of the disease, continued abnormal vessel growth and scar tissue may cause serious problems such as retinal detachment and glaucoma.
The affect of diabetic retinopathy on vision varies widely, depending on the stage of the disease.
• Blurred vision (this is often linked to blood sugar levels
• Floaters and flashes
• Sudden loss of vision
Glaucoma can steal your vision gradually and without you noticing, yet glaucoma is a serious disease that can result in severe loss of sight. The best defense against glaucoma is regular eye examinations. Glaucoma most often strikes people over age 50, but it is recommended that during adult life everyone be tested at least every two years.
Amaurosis fugax-transient monocular blindness: is a short-lived episode of blindness in one eye (monocular). This symptom usually develops suddenly, and many individuals describe the event as "it was as if a shade or curtain came over my eye." It is caused by a blockage or low blood flow within the main blood vessel supplying the eye. Blockages are usually due to a blood clot or plaque (small piece of cholesterol) that breaks off from a larger artery and travels upward to the brain or eye, becoming lodged in the main artery supplying the eye. Low blood flow to the eye may also result from a critical narrowing of one of the main blood vessels supplying blood to the brain and eye. The monocular blindness of amaurosis fugax is generally brief, but in rare cases it may be prolonged or permanent.
A cataract is a clouding of the lens in the eye that affects vision. Most cataracts are related to aging. Cataracts are very common in older people. A cataract can occur in either or both eyes. It cannot spread from one eye to the other.
Hyperopia is the medical term for farsightedness. This occurs when an eye is too short for the cornea's curvature. Light rays entering the eye focus behind the retina, and as a result a blurred image is produced.
Myopia (Near-sightedness, short-sightedness): is the refractive condition where the farthest point of focus is located at a point near to the observer, and not at infinity. When one is nearsighted, distance vision is blurred at all times while near vision is often excellent within a certain range.



2.hearing
Most of the ear (the organ of hearinf) is encased in bone inside the skull and is hidden from view. The hearing is devided into three parts: the outer, the middle and the inner ear.
Outer ear:
The auricle-pinna is the external flap of the outer ear and is the visible part of the ear. It is made up of the cartilage and covered with skin. It is shaped so that it channels sounds into the ear passage.
Ear canal- the auditory canal is a narrow tunnel 2.5 cm long. It carries sounds from the auricle to the eardrum. The canal is lined with fine hairs that trap dust. There are sebaceous or ceruminous glands which release ear wax-cerumen, which further helps to protect ear from infection and keeps th eardeum soft and waterproof.
The eardrum- tympanic membrane is a piece of skin stretched across the inner end of the outer ear canal. It is about 1 cm in diameter. It is very sensitive to pain as a defense against damage. It vibrates, when sound waves travel along the ear canal. This causes the movement of bones of middle ear.

Middle ear: air filled
There are three bones called ossicles- hammer /malleus/
anvil /incus/
stirrup /stapes/
They work together to transmit sound vibrations from outer to inner ear. The middle ear is conncected with pharynx by Eustachian tube- auditory tube. Its function is to keep on both sides of eardrum the same.

Inner ear: fluid filled
The cochlea: is hearing organ of the inner ear. It sits deep within your skull, behind the eye. It is a fluid-filled /perilymph/ tube that is coiled like a shell of a snail. The fluid recieves sound vibrations. As it vibrates, it causes the movement of sensory hairs. They are arranged in “V“ shapes and are surrounded by fluid. When vibrations pass into the fluid, the hairs move to and fro, and send nerve impulses to the brain by the acoustic nerve. There is also the oval window- fenestra ovalis:Oval-shaped hole in the bone that separates the middle ear from the inner ear. A thin membrane stretches across it.
The organ of Corti which is placed in the cochlear duct contains special hair cells whose hairs project into the endolymph and touch a shelf-like tissue layer and the bases of the cells are attached to nerve fibres.

Balancing:
The semicilcular canals, the vestibul, the saccule and the utricle in the inner ear control the balance. The canals contain fluid /endolymph/ that vibrates when you move. The ampula in the semicircular ducts and maculae in the saccule and the utricle detects movement and send nerve impulse to the brain.
The round window fenestra rotunda: the sound vibrations leave the inner ear through this window.

Disorders and diseases of ear

Cerumen impaction: One of commonest causes of sudden hearing loss. Treat by removing wax.

External otitis: inflammation and swelling of canal skin

Tumors of external canal: a mass of cells growing in external canal.
Vestibular Neuronitis: is a condition that causes a sudden onset of spinning vertigo associated with nausea. The vertigo can persist for days to weeks during which time the patient may feel better when lying completely still, but is never completely free of the sensation of spinning. The symptoms are usually worse during the initial few days, and gradually improve over the following days to weeks. There are usually no symptoms of hearing loss or ringing of the ears (tinnitus).
Otosclerosis: is a disease in which there is abnormal hardening of the bone of the ear. This hardening causes the third middle ear bone, known as the stapes, to become fixed. Fixation of the stapes prevents it from moving and thus, prevents the transmission of sound of the middle ear to the inner ear.
Tinnitus: The sensation of tinnitus may differ from patient to patient. Some common sensations include whistling, whooshing, roaring, static electricity, or chirping. Occasionally, patients may experience a pulsing or humming sound.
Hearing loss with associated anomalies:
• Prenatal infection, especially syphilis, rubella, CMV Prenatal drugs
• Birth trauma
• Developmental anomaly
Presbycusis: hearing loss of old age. It is not universal etiology not known. Central interpretation deficit complicates peripheral sensitivity loss. Amplification can help, but hearing aids must be carefully fitted Cochlear distortion and central processing may preclude us.
Meniere's disease or syndrome: fluctuating ( to change frequently in size, amount, quality, etc., especially from one extreme to another) hearing loss. Characteristically associated with lose of balance.
Oval or round window rupture: Sudden onset of hearing loss, usually fluctuating, often accompanied by vertigo (lose of balance). Definitive diagnosis can only be made by surgical exploration. Usually associated with sudden pressure change: flying,Valsalva, scuba diving, sneeze.
Idiopathic sudden sensorineural hearing loss: Sudden hearing loss with no apparent cause. Etiology obscure, could be viral, autoimmune, vascular,or allergic.
Acoustic nerve tumor: Uncommon tumor. Usually arises in vestibular nerve. Usually present with hearing loss. Progression of vestibular nerve involvement is so slow that it is not noticed by patient. Characteristic audiometric results with abnormal acoustic reflex, poor discrimination. X-rays or CT show flaring of IAC in large tumors. Small tumors are seen with air contrast CT.
Infections: Viral infection. Bacterial infection - labyrinthitis, meningitis.
Sensorineural hearing loss: - often associated with poor discrimination out of proportion to degree of pure tone sensitivity loss - this is due to distortion of sound by cochlea or nerve
3.Touch
Our skin weighs around 4kg and covers all our body, which is an area of about 2 square meters. Skin varies in thickness. the skin in the eyelids is thinner than that on the middle of the back.
Skin has three main parts:
• epidermis: an upper layer that forms the surface of the skin
• dermis a lower layer that contains hair roots, blood vessels, glands and nerve endings
• subcutaneous layer-superficial fascia It is fatty tissue which forms an insulting layer.
Skin sensations:
We are always aware of our surroundings, even if we shut our eyes and block our ears. This is because we can feel the world through our skin. Each square inch of skin contains up to 1,500 special nerve endings called receptors. These receptors detect diffrent feelings such as pain, touch, pressure, temperature and hair movement.
Sensory receptors give us information about the outside world and also about the condition and position of our bodies themselves. Each receptor is a specialised nerve ending, designed to relay specific information to the central nervous system. The receptor sends impulses along its nerve fibre when it is stimulated.

Epidermis: It is the thin outer layer of the skin that protects the underlying tissues and makes the body waterproof. It is cornified, horny skin which is constantly worn away. It is replaced by layers from underneath. It is made of epithelial tissue. It consists of more than one layer.There are air pores in it.

Dermis: The dermis is the inner, thicker layer of the skin. It is a flexible connective tissue that fixes the epidermis to the body. The dermis has a rich supply of sensory nerve endings to detect touch, pressure , pain , heat, and cold. The dermis is well supplied with blood and has oil and sweat glands. The hair follicles extend from the dermis through the epidermis and open the surface of the skin.
Sensory receptors are various corpuscles:
• Meissner´s corpuscles:It is able to detect pain and touch.
• Pacinian corpuscle: It is able to detect pressure and tension.
• Ruffini´s corpuscle: It detects heat.
• Krause´s corpuscle: It detects cold.
There are many emboded structures such as:
• sebaceous glands: It produces sebum /oil/ which waterproofs the hairs and epidermis.
• sweat glands or sudoriferous glands : It excrete sweat.
• hair follicles
• hair erector muscles
• hair plexuses or root hair

Subcutaneous layer or superficial fascia: The layer of fatty tissue below the dermis. Elastic fibres run through it to connect the dermis to the organs below. It is an insulating layer.

Disorders and diseases of skin
Psoriasis: is an inflammatory skin disease characterized by an increased rate of skin cell turnover resulting in thick scales appearing on the skin. The affected skin becomes dry and unsightly. Itching is often experienced in our hot and humid climate.
Photosensitivity: Some people develop a rash because their skin is sensitive to sunlight. Patients may not associate their skin complaint with the light. It is not always the bright summer sun which is responsible; some people also react to winter daylight, and very sensitive subjects may even be affected by fluorescent lamps indoors.
Cutaneous Lupus Erythematosus (LE): is an autoimmune disease that most often affects young adult women. Cutaneous LE can be provoked by sunlight but it is actually more common in dark skinned than in fair skinned people. Sunscreens do not totally prevent it.In the most common form, discoid LE, unsightly red scaly patches develop which leave white scars. Discoid LE predominantly affects the cheeks and nose, but sometimes involves the upper back, V of neck, and backs of hands. Bald patches can develop if the hair follicles are involved. Discoid LE may affect the lips causing ulcers and scaling.
Systemic lupus erythematosus:, often just called lupus, is a chronic disease that can affect almost any part of the body. People with mild lupus may only have skin rashes and/or joint pain. In more severe lupus, important organs like the kidneys, heart, blood vessels, lungs, gastrointestinal tract, and brain can be involved. Any two people with lupus may have different symptoms. They may also have different lengths of time when the disease is active or in remission. While lupus cannot be cured, your health care provider can help you control symptoms and lead a relatively normal life.
Solar urticaria: Solar urticaria is a rare form of physical urticaria (hives) in which skin swells within minutes of exposure to ultraviolet radiation. The reaction lasts up to an hour and can be very disabling. Oral antihistamines are helpful but rarely prevent the reaction altogether.
Hyperhidrosis (excessive sweating): Sweating is a natural phaenomenon necessary for the regulation of an individual's body-temperature. The secretion of sweat is mediated by a portion of our vegetative nervous system (the Sympathetic Nervous System). In some people (approximately 1% of the population), this system is working at a very high activity level, far higher than needed to keep a constant temperature. This condition is referred to as hyperhidrosis.

Blistering diseases: are defined as skin disorders that primarily give rise to vesicles (i.e. 5 mm or less in diameter). Blisters are accumulation of fluid lying within or below the epidermis. Blistering diseases can be classified according to the site of cleavage.
Nummular Dermatitis: Chronic inflammation of the skin characterized by coin-shaped, vesicular, crusted, scaling, and usually pruritic lesions.The cause is unknown. Nummular dermatitis is most common in middle-aged patients and is often associated with dry skin, especially during the winter.
Chloracne: is an acne-like eruption of blackheads, cysts, and pustules associated with over-exposure to certain halogenic aromatic hydrocarbons, such as chlorinated dioxins and dibenzofurans. The lesions are most frequently found on the cheeks, behind the ears, in the armpits and groin region. The inflammatory processes lead to the formation of keratinous plugs in skin pores, forming yellowish cysts and dark pustules. The skin lesions occur mainly in the face, but in more severe cases they involve the shoulders and chest, the back, and the abdomen. In advanced cases, the lesions appear also on the arms, thighs, legs, hands and feet.
4.smelling
The sense of smell detects airborne molecules. Smells are detected when you breathe in through your nose. Olfactory or smell receptors are found at the top of the nasal cavity. These receptors detects smells and send nerve impulses to the brain enabling you to distinguish as many as 10,000 different odors. Smelling is improved by sniffing, which exposes receptor to more than normal.

Olfactory receptors:
Olfactory receptors detect odors. Thereare around 20 million receptors in your nose, each ending in a number of hair-like cilia, which actually pick up the odors. Once an odor has been detected, a nerve impulse is sent from the receptors to the brain, and you experience th sensation of smelling the odor.

Olfactory bulb:
Humans have two olfactory bulbs which lie on each side of the nose, just above the roof of the nasal cavity. They collect message from smell receptors in the lining of the nasal cavity. These messages, in the form of nerve impulses, then travel along two olfactory nerves to the brain. The brain processes the information to tell you what you are smelling.

Olfactory nerve:
The olfactory nerve conveys smells, in the form of nerve impulses, from the node to the brain. Humans have two olfactory nerves, each taking signals from one of the two olfactory bulbs. These bulbs lie above the nasal cavity and collect signals from receptor endings inside the nose.

Snezzing:
Snezzing is caused by an irritation of olfactory receptors in the nose. To clear it, you breathe in a lot of air which is forced from your lungs and out of your nose, taking the irritant with it. When you sneeze, up to 5,000 moisture droplets burst into the air at great speed, trveling as far as 3.5m.

Disorders and diseases of smell
People who experience smell disorders experience either a loss in their ability to smell or changes in the way they perceive odors. As for loss of the sense of smell, some people have hyposmia, which is when their ability to detect odor is reduced. Other people can't detect odor at all, which is called anosmia. As for changes in the perception of odors, some people notice that familiar odors become distorted. Or, an odor that usually smells pleasant instead smells foul. Still other people may perceive a smell that isn't present at all.
Sinusitis: simply means inflammation of the sinuses. Each sinus has an opening into the nose for the free exchange of air and mucus, and each is joined with the nasal passages by a continuous mucous membrane lining. Therefore, anything that causes a swelling in the nose – an infection or an allergic reaction — also can affect the sinuses. Air trapped within an obstructed sinus, along with pus or other secretions, may cause pressure on the sinus wall. The result is the sometimes intense pain of a sinus attack. Similarly, when air is prevented from entering a paranasal sinus by a swollen membrane at the opening, a vacuum can be created that also causes pain.
Chronic Sinusitis refers to inflammation of the sinuses that continues for at least 3 weeks, but often continues for months or even years. Allergies are frequently associated with chronic sinusitis. Patients with asthma have a particularly high frequency of chronic sinusitis. Inhalation of airborne allergens (substances that provoke an allergic reaction), such as dust, mold, and pollen, often set off allergic reactions (allergic rhinitis) that, in turn, may contribute to sinusitis.
Nasal polyps: Nasal polyps occur in around 1 in 200 people. Polyps are soft, jelly-like overgrowths of the lining of the sinuses. They look like grapes on the end of a stalk. The result is often a blocked nose. They usually only cause symptoms when they grow through the tunnel that connect the sinuses to the nose. Large polyps can block the nose and increase the risk of sinusitis. More importantly, they can block the tunnels connecting the nose to the sinus cavities. Like water in a stagnant pond, and increase the risk of sinus infection (sinusitis). They are rarely cancerous.
5.Tasting

Taste is the ability to respond to dissolved molecules and ions. You taste with the surface of your tongue as it comes into contact with food. The tongue is covered by small bumps, called papillae, which carry the tastebuds. The front of tongue is sensitive to sweet tastes , the sides to salty and sour tastes, and the back of the tongue to bitter tastes.

Tastebud:
Tastebuds detect different flavours. There are 10,000 tastebuds in your tongue. They all look the same, but there are four kinds of them. They respond to either sweet, salty, sour or bitter tastes. When the taste receptor cells inthe tastebuds are stimulated by a flavour, impulses are sent along nerve fibres to the brain, and food can be tasted.

Papillae:
Papillae are small bumps that cover the surface of the tongue. The tastebuds are embedded un the sides of the papillae. There are lots of diffferent sizes of papillae carrying various types of tastebuds. Papillae of a similar type are arranged in groups all over the surface of the tongue.



Disorders and diseases of taste
The most common true taste complaint is phantom taste perceptions. Additionally, testing may demonstrate a reduced ability to taste sweet, sour, bitter, salty, and umami, which is called hypogeusia. Some people can detect no tastes, called ageusia. True taste loss is rare; perceived loss usually reflects a smell loss, which is often confused with a taste loss.
In other disorders of the chemical senses, the system may misread and or distort an odor, a taste, or a flavor. Or a person may detect a foul taste from a substance that is normally pleasant tasting.
Some people are born with a poor sense of smell or taste. Upper respiratory infections are blamed for some losses, and injury to the head can also cause smell or taste problems.
Loss of smell and taste may result from polyps in the nasal or sinus cavities, hormonal disturbances, or dental problems. They can also be caused by prolonged exposure to certain chemicals such as insecticides and by some medicines.
Tobacco smoking is the most concentrated form of pollution that most people will ever be exposed to. It impairs the ability to identify odors and diminishes the sense of taste. Quitting smoking improves the smell function.
Radiation therapy patients with cancers of the head and neck later complain of lost smell and taste. These senses can also be lost in the course of some diseases of the nervous system.