Hearing

Hearing

Hearing or audition is the sense of sound perception. Hearing is all about vibration. Mechanoreceptors turn motion into electrical nerve pulses, which are located in the inner ear. Since sound is vibrations propagating through a medium such as air, the detection of these vibrations, that is the sense of the hearing, is a mechanical sense because these vibrations are mechanically conducted from the eardrum through a series of tiny bones to hair-like fibers in the inner ear, which detect mechanical motion of the fibers within a range of about 20 to 20,000 hertz, with substantial variation between individuals. Hearing at high frequencies declines with an increase in age. Inability to hear is called deafess. Sound can also be detected as vibrations conducted through the body by tactition. Lower frequencies than can be heard are detected this way.

The Sense of Taste

1. The tongue is the sensory  organ that gives us the sense of taste. It is sensitive to sweet, salty, sour, and bitter tastes.

2. The upper surface of the tongue is rough. This is because it is covered with taste buds.

3. Taste receptors can be found in the taste buds. They responds to various chemicals in food.
     Each type of taste receptor is sensitive to a certain types of taste.

4. a) The tongue has four types of taste receptor.
    b) These are sweet receptors, sour receptors, salty receptors, and bitter receptors.
    c) Each receptor is located in a particular area of the tongue. Thus, each area of the tongue is    
        able to detect a certain type of taste.

5. Chemicals in food dissolved in saliva. => The chemicals stimulate taste receptors in the taste  
    buds => Impulses form the taste receptors are sent along the nerves to the brain. => The brain
    identifies the taste.

Detection of Smell

1. Certain chemical particles present in the air circulate the smells in the air. For example, flowers, food, and perfumes release chemicals into the air.

2. When these chemical particles enter the nasal cavity, they dissolve the mucous lining that coats the smell receptors in the nasal cavity.

3. The dissolved chemicals particles stimulate the smell receptors

4. The smell receptors then send out nerve impulses to the brain. The brains identifies the smell.

5. Structural adaptations of the nose to detect smells:
    a) Smell receptors are located at the root of nasal cavity. This enables the receptors to have     
       maximum exposure to the air that enters the nasal cavity.
    b) The smells receptors are always covered in moist muscus which is secreted by the glands in
        the nasal cavity.

The Sense Of Smell

Structure of The Nose.

1. The nose is the sensory organs for smell.

2. The upper part of the nasal cavity of the nose has many sensory cells or receptors to detect    
    smell.

3. These smell receptors are sensitive to all kinds of the smells.

Sensitve of the skin.

1.  a) When the receptors are stimulated, they send out nerve impulses along the nerves to the              
         brain.
    b) The brain interpprets these impulses as the sensation of touch.
    c) It will then send suitable messages to the effectors as how to react.

2. The skin on different parts of the body has different part of the body has different degrees of  
    sensitivity.
    a) The fingertips, the lips, the tongue, the nose, and the neck are more sensitive to touch.

3. The sensitive of the skin depends on:
    a) the distance between the receptors
    b) the thickness of the epidermis

4. The skin on parts of the body which has thinner epidermis and more receptors is more sensitive  
    to touch.

5. a) Blind poeple use their sense of touch to identify object in their environment.
    b) They use their fingertips to read book in braille.



6. Doctors usually give injections to their patients on their forearms or buttocks because these areas are less sensitive to touch and pain.

Cross section of human skin.

Name	Funtion
Pain receptor	Lie very close to the skin surface to detect even a slight pain.
Heat receptor	Sensitive to heat and is able to detect the temperature when it is hotter than usual.
Touch receptor	Detect any light touches and identify the texture of an object.
Pressure receptor	Lie deep within the skin and detect any forceful pressure against the skin.
Cold receptor	Sensitive to cold and is able to detect the temperature when it is colder than usualy.

The Sense Of Touch

Structure of the human skin.

1. The skin helps regulate body temperature. It is also a sensory organ that detects touch.
2. The skin has five different types of receptors.
    These are:
    a) pain receptors
    b) touch receptors
    c) heat receptors
    d) cold receptors
    e) pressure receptors
3. The receptor in the skin are sensitive to the stimuli of pain, touch, heat, cold, and pressure.
4. a) The pain receptors are situated in the epidermis of the skin.
    b) The touch, heat, and cold receptors are situated in the dermis.
    c) The pressure receptors are found in the fatty layer.