lesson-4-sensory (1)

Sensory System Overview

• The sensory system is integral for interaction with the environment.

• Major modalities include vision, audition (hearing), gustation (taste), and somatosensation (touch).

The Human Visual System

Anatomy of the Eye

• Pupil: Regulates the amount of light entering the eye.

• Lens: Focuses light onto the retina.

• Cornea: Outer layer providing protection and helping focus light.

• Iris: Controls the size of the pupil.

• Sclera: Tough outer covering of the eye.

• Choroid: Supplies blood to the eye and reduces light reflection.

• Retina: Contains photoreceptors (rods and cones) that convert light into electrical signals.

  • Fovea: Area of sharpest vision, densely packed with cones.

  • Blind Spot: No photoreceptors, where optic nerve exits the retina.

  • Retina Layers: Contains 7 layers critical for processing visual information.

Retina Structure and Function

• Ganglion Cell Layer: Contains neurons that transmit visual information to the brain through the optic nerve.

• Photoreceptors:

  • Rods: More sensitive to light, responsible for night vision.

  • Cones: Responsible for color vision and visual acuity, present in three types (RGB).

• Plexiform Layers: Where synaptic connections occur between different retinal cells, allowing for complex signal processing.

Phototransduction Process

• Rods: Function in low light; hyperpolarization occurs due to light, leading to reduced glutamate release.

  • Rhodopsin: Light-sensitive protein that initiates phototransduction by altering membrane potential.

• Cones: Take over in bright light; operate on similar principles as rods but adapted for color perception.

Ganglion Cells and Visual Processing

• ON and OFF Cells: Respond to light and darkness, contributing to contrast detection.

• M-type (Magnocellular): Large, fast, responsible for motion detection and low contrast.

• P-type (Parvocellular): Smaller, responsible for detailed, sustained signals for color and form.

Pathway through the Visual Cortex

• Optic Nerve: Conducts visual information to the brain.

• Lateral Geniculate Nucleus (LGN): Relay center in the thalamus for visual signals.

• Primary Visual Cortex (V1): Initial processing area for visual information; organized retinotopically.

  • Processes color, motion, and edges.

Auditory System

Ear Anatomy and Sound Processing

• Outer Ear: Auricle collects sound waves.

• Middle Ear: Contains ossicles (malleus, incus, stapes) that amplify sound vibrations.

• Inner Ear: Cochlea transforms vibration into neural signals.

  • Organ of Corti: Contains hair cells that convert fluid movement into electrical signals.

Auditory Pathways

• Signals travel via the auditory nerve to the brain, processed through nuclei and complexes (inferior colliculus, medial geniculate nucleus).

Gustation (Taste)

Taste Mechanisms

• Taste buds contain receptor cells responsive to chemicals.

• Types of Taste:

  • Sweet, Umami, Bitter, Sour, Salty.

• Each flavor is processed through specific cranial nerves (VII, IX, X).

Somatosensation (Touch)

Mechanoreceptors

• Types include Merkel Disks (touch), Meissner’s Corpuscles (light touch), and Pacinian Corpuscles (deep pressure).

• Afferent pathways transmit information about pressure, pain, and temperature to the brain.

Pain Pathways

• Nociceptors: Aδ fibers for sharp pain; C fibers for dull pain. Pain signal travels to the brain via spinothalamic pathway.

Sensory Integration

• Brain Processing: Multi-sensory integration occurs in association areas to create a cohesive understanding of our environment.

• Prefrontal Cortex: Involved in complex decision-making based on sensory data.