the senses

Lesson 3 - Sense Organs

The Five Senses

  • Taste

  • Smell

  • Touch

  • Hearing

  • Sight

Types of Receptors

  • Chemical Receptors

  • Light Receptors

  • Sensory receptors are specialized neurons found in sense organs.

  • Sensory receptors detect stimuli and transform them into nerve impulses transmitted to the Central Nervous System (CNS).

  • The CNS interprets these impulses to form a response.

The Sense of Smell

  • Chemicals in the environment stimulate smell.

  • Smell and taste combine to create food flavor perceptions.

Smelling Process

  1. Chemicals enter the nose.

  2. Olfactory nerve receptors get stimulated.

  3. Information is sent to the olfactory bulb.

  4. The olfactory bulb transmits messages to the brain for processing.

The Sense of Taste

  • Taste buds on the tongue act as chemical receptors.

  • They identify tastes: sweet, sour, salty, bitter.

Tasting Process

  1. Chemicals in food enter the mouth.

  2. Taste receptors detect these chemicals.

  3. Information is sent to the brain for processing.

The Sense of Touch

  • The skin is the organ of touch.

  • Contains sensory receptors for pain, pressure, and temperature.

Types of Sensory Receptors

  • Temperature Receptors: Detect temperature changes.

  • Pressure Receptors:

    • Light touch, found in fingertips.

    • Heavy pressure, found in the soles of the feet.

  • Pain Receptors: Free nerve endings found in all tissues except the brain.

  • The distribution of receptors varies by body area.

The Sense of Sight

  • Key Components:

    • Cornea: Transparent layer for light entry and focusing.

    • Pupil: Opening controlled by the iris for light regulation.

    • Lens: Inverts and projects images onto the retina.

    • Retina: Contains rods and cones; rods detect low light, cones detect color.

    • Vitreous Humor: Gel-like substance between lens and retina.

  • Light travels through the eye, and signals are processed by the brain.

Hearing and Balance

  • Cochlea: Snail-shaped structure in the inner ear, contains fluid and hair cells.

  • Hearing Process:

    1. Sound waves enter the ear canal, vibrating the eardrum.

    2. Vibrations through middle ear bones (malleus, incus, stapes).

    3. Stapes vibrates the oval window, transmitting sound to the cochlea.

    4. Hair cells in the cochlea generate nerve impulses sent to the brain.

The Role of Ears in Balance

  • Semicircular Canals:

    • Three canals at right angles filled with fluid and hair cells.

    • Fluid movement bends hair cells, sending signals to the brain for balance and body position interpretation.