1103 10 Sensory Systems A

Sensory Systems

Overview of Sensory Systems

  • The sensory systems are organized to detect various stimuli via specialized receptors.

  • Five main categories of sense receptors:

    1. Mechanoreceptors: respond to pressure, stretch, sound.

    2. Photoreceptors: detect light.

    3. Chemoreceptors: respond to chemicals (taste/smell).

    4. Thermoreceptors: detect temperature changes.

    5. Nociceptors: pain receptors detecting harmful stimuli.

Cutaneous Sensors and Proprioceptors

  • Cutaneous Sensors:

    • Detects sensations like touch, pain, temperature.

    • Specialized cells including free nerve endings, Merkel cells, Meissner's corpuscles, and Pacinian corpuscles.

  • Proprioceptors:

    • Provide information about body position and muscle stretch.

    • Includes muscle spindles and Golgi tendon organs.

Olfactory System

  • Structure: Olfactory receptors in the olfactory epithelium respond to odorant molecules.

  • Function: Process of detecting and transmitting smell from olfactory bulb to cerebral cortex.

Gustatory System

  • Structure: Taste buds located on tongue papillae detect chemical stimuli in food.

  • Function: Transmit taste information via cranial nerves VII, IX, and X to the brain for processing.

Sensory Reception and Transmission

  • Sensation: Activation of sensory receptors leading to perception.

  • Transduction: Converting stimulus energy into membrane potentials in sensory cells.

  • Perception: Central processing to create meaning from sensory information.

Types of Sensory Receptors

  • Different classifications for sensory receptors exist:

    • Based on Cell Type: Specialized neurons or sensory cells.

    • Based on Position:

      • Exteroceptors: Detect external stimuli (e.g., touch, vision).

      • Interoceptors: Detect internal conditions (e.g., blood pressure).

      • Proprioceptors: Inform on muscle and joint positioning.

Classification by Function

  • Mechanoreceptors: Respond to pressure and motion.

  • Photoreceptors: Detect light.

  • Chemoreceptors: Respond to chemical stimuli (taste/smell).

  • Thermoreceptors: Detect changes in temperature.

  • Nociceptors: Signal pain from harmful stimuli.

The Eye and Vision

Anatomy of the Eye

  • Composed of three layers:

    • Fibrous Tunic: Cornea and sclera.

    • Vascular Tunic: Choroid, ciliary body, iris.

    • Retina: Contains photoreceptors (rods and cones).

  • Components:

    • Conjunctiva: Outer protection.

    • Lens: Refractive structure for focusing light.

    • Macula Lutea/Fovea: Area for high-acuity vision.

Image Formation

  • Refraction: Light bending occurs in the cornea and lens (75% and 25% respectively).

  • Accommodation: Lens changes shape to focus on objects at different distances.

  • Pupil Constriction: Limits light entry to prevent blurred images during accommodation.

Photoreceptors in Retina

  • Rods: Sensitive to dim light, peripheral vision; responsible for non-color vision.

  • Cones: Function in bright light for color vision (three types: red, green, blue).

  • Pathway of Signal Output: Light hits photoreceptors, stimulating bipolar and ganglion neurons through optic nerve to the visual cortex.

Visual Pathway

  • Image Processing: Images from the left field project to the right side of the brain and vice versa after crossing over at the optic chiasma.