CHAPTER 1: THE WORLD THROUGH OUR SENSES
Sensory Organs and Their Functions Sensory Organs and Their Stimuli
Humans being had five main sensory organs, which are skin, nose, tongue, ears, and eyes.
Sense detects stimuli, that is changes in surroundings (around us).
Five senses: i. sight ii. hearing iii. touch iv. taste v. smell
Senses are part of the body called sensory organs.
Changes or object that can detect by our senses are called stimuli
The ability of the sensory organs to detect stimuli is called senses.
All the sensory organs are complete with sensory receptors, that is the nerve endings that can detect stimuli. Stimuli Sense Sensory organ Light(Brightness, color) Sight Eye Sound Hearing Ear Touch, heat, cold, pain, pressure Touch Skin Sweet, sour, bitter, salty Taste Tongue Smell or odors Smell Nose The World through our senses Light and sight Sound and hearing Stimuli and responses in plants Touch (skin) Smell (nose) Taste (tongue) Hearing (ear) Sight (eye) Properties of light Vision defects Optical illusions Stereoscopic and monocular Properties of sound Reflection and absorption limitations stereophonic.
Structure of the human nose.
a. The human nose has a cavity lined with epithelium tissue.
b. On the surface of the epithelium tissue are the sensory cells known as olfactory cells.
c. The surface of the nasal cavity is moist because of the mucus secreted by the cells of a gland.
d. The nasal cavity has a pair of external opening (nostrils) which have hair to filter dust from the air inhaled through the nose.
The nose detects smell in the following way. The inside of the nasal cavity produce mucus v The chemical vapor entering nose during breathing dissolves in mucus. The dissolve chemicals stimulate the smell receptor at the top of the nasal cavity. The smell receptor then produces impulse which is sent through the nerves to the brain. The brain interprets/evaluates the smell. When we have a cold or flu, a lot of mucus is produced. The smell receptors are surrounded by this thick layer of mucus and vary little of chemical vapor gets to the smell receptors. Therefore, the smell receptors do not get stimulated enough to effectively function as a sensory organ of smell. 6. The sensitivity of the nose towards stimuli is influenced by the following factors: PMR 05 i. The strength of the smell. A stronger smell will be detected by the nose easily compared with a weaker smell. The presence of mucus in the nose. A lot of mucus will reduce the sensitivity of the nose.
FUNCTIONS OF DIFFERENT PARTS OF THE HUMAN EAR
Part function OUTER EAR Pinna collects and directs sound waves into the ear canal. ear canal / auditory canal transmits sound waves to the eardrum. The eardrum vibrates and transmits sound waves to the ossicles. MIDDLE EAR Ossicles intensify the vibrations of the sound waves by 22 times before transmitting to the oval window. Eustachian tube balances the air pressure at both sides of the eardrum. Val window transmits sound vibrations from the middle ear to the inner ear.
Cochlea transforms sound vibrations into impulses. semicircular canals balance the body position. auditory nerves send messages to the brain which interprets the messages as sound. Limitations of hearing. We cannot hear all the sounds around us. Different people have different limitations of hearing. For example, old people generally cannot hear as well as young people. Our eardrum becomes less sensitive to sound as we grow older. To overcome the limitations of hearing, we use i. the stethoscope – enables the doctor to detect the soft heartbeats of patients. ii. hearing aids – collects sound signals before being sent to the middle ear. iii. amplifier – boosts weak sound signals.
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