Sensory Systems and Perception

Sensory Systems Overview

Section 9.1a: Definitions

  • Sensation: The ability to perceive stimuli; how your body detects changes in the environment.
      - Involves sensory receptors being stimulated to detect changes.
  • Perception: The conscious awareness of those stimuli; how the brain interprets sensory information.
      - Involves the understanding and processing of sensations.
  • General Senses: Found all over the body.
      - Include:
        - Touch
        - Pressure
        - Pain
        - Temperature
        - Vibration
        - Itch
        - Proprioception (awareness of body position)
      - Types:
        - Somatic: Relating to the body and environment.
        - Visceral: Relating to internal organs.
  • Special Senses: Located in special organs.
      - Include:
        - Smell (olfaction)
        - Taste (gustation)
        - Sight (vision)
        - Hearing (audition)
        - Balance (equilibrium)

Section 9.2a: Types of Sensory Receptors

  • Mechanoreceptors: Respond to mechanical changes such as touch, pressure, or stretch.
  • Chemoreceptors: Respond to chemical stimuli; involved in smell and taste.
  • Photoreceptors: Respond to light; involved in vision.
  • Thermoreceptors: Respond to changes in temperature.
  • Nociceptors: Respond to pain or tissue damage.

Section 9.3: Pain Perception

  • Referred Pain: An unpleasant sensory and emotional experience where pain is perceived in a different location than where it originates.
      - Types of Pain:
        - Sharp Localized Pain:
          - Characterized by fast signals; easy to pinpoint.
        - Diffuse Aching Pain:
          - Characterized by slow signals; hard to locate.
        - Superficial Pain:
          - Well-localized, occurs in the skin.
        - Visceral Pain:
          - Not localized, originating from internal organs.
      - Example: Heart attack may present as pain in the left shoulder or arm due to nerve connections to the spinal cord.

Section 9.4: Special Senses Overview

  • Smell (Olfaction): Chemical sense responsible for detecting airborne chemicals.
  • Taste (Gustation): Chemical sense that detects dissolved food molecules.
  • Sight (Vision): Sensory perception of light.
  • Hearing (Audition): Perception of sound waves.
  • Balance (Equilibrium): Sense of spatial orientation and balance.

Section 9.5a: Olfactory System

  • Olfactory Neurons: Bipolar neurons located in the nasal cavity responsible for the sense of smell.
      - Airborne molecules (odorants) bind to the receptors on these neurons, triggering action potentials.
      - Even a small number of odorants can trigger action potentials that travel through the olfactory nerve to the brain.
  • Adaptation to Smell:
      - The process whereby sensitivity to an odor decreases over time due to prolonged exposure.
      - After odorants bind, receptors temporarily become less responsive, contributing to the fading perception of the smell even when it is present.

Section 9.6a: Taste Perception

  • Taste Buds: Oval structures located on papillae of the tongue.
      - Contain supporting cells and about 40 taste cells inside.
      - Function: Taste cells have tiny taste hairs that reach into a taste pore, binding to dissolved food molecules to trigger action potentials to the brain.
  • Types of Taste:
      - Five basic tastes: Sweet, Sour, Salty, Bitter, Umami (savory).
      - Note: Taste perception is affected when you have a cold due to reduced smell.

Section 9.7a: Accessory Structures of the Eye

  • Eyebrows: Prevent sweat from entering the eyes and provide shade from sunlight.
  • Eyelids & Eyelashes: Protect eyes from debris; eyelids use blinking to spread tears to keep the eyes moist.
  • Conjunctiva: Thin membrane that lubricates the eye.
  • Lacrimal Apparatus: Produces tears for cleaning, moistening, and fighting infection.
  • Extrinsic Eye Muscles: Move the eyeball in different directions.

Section 9.7b: Tunics of the Eye

  1. Fibrous Tunic:
       - Sclera: Tough, white layer that protects the eye and maintains its shape.
       - Cornea: Clear front part of the eye that allows light to enter and bends the light.
  2. Vascular Tunic:
       - Choroid: Contains blood vessels; absorbs light and prevents reflection.
       - Ciliary Body: Controls lens shape for focusing (accommodation).
       - Iris: The colored part of the eye; controls pupil size and the amount of light entering the eye.
  3. Nervous Tunic:
       - Retina: Contains a pigmented layer that absorbs light and a sensory layer that contains rods and cones essential for vision.

Section 9.8a: Phototransduction in Vision

  • Rods vs. Cones:
      - Rods: Very sensitive to light; function in dim light; responsible for black and white vision.
      - Cones: Require bright light; responsible for color vision (red, green, blue) and sharp detail.
  • Chambers & Fluids of the Eye:
      - Anterior Chamber: Between cornea and iris; contains aqueous humor.
      - Posterior Chamber: Between iris and lens; contains aqueous humor.
      - Vitreous Chamber: Behind lens; contains vitreous humor; jelly-like substance.

Section 9.9: Focus and Processing of Visual Information

  • How Images are Focused:
      1. Light enters through the cornea, which bends the light.
      2. Light passes through the aqueous humor, lens, and vitreous humor.
      3. The lens changes shape (accommodation) to focus light.
  • Retinal Image: The image is focused on the retina and is inverted.

Steps of Seeing

  1. Light enters the eye and is refracted.
  2. Light hits rods and cones in the retina.
  3. Photoreceptors convert light into nerve signals.
  4. Signals pass to bipolar cells, then to ganglion cells.
  5. Ganglion cell axons form the optic nerve.
  6. Signals travel through the optic chiasm, thalamus, and optic radiations.
  7. Finally, signals reach the visual cortex in the occipital lobe.
  8. The brain interprets the image, resulting in what you actually see.

Section 9.8b: Ear Structures

  • Outer Ear Structures:
      - Auricle: Collects and directs sound waves.
      - External Auditory Canal: Carries sound to the eardrum.
      - Tympanic Membrane (Eardrum): Vibrates when sound hits; protects from debris.
  • Middle Ear Structures:
      - Ossicles: Malleus, Incus, Stapes; amplify sound vibrations by 220 times.
      - Oval Window & Round Window: Transfer vibrations to the inner ear.
      - Auditory (Eustachian) Tube: Equalizes pressure between the middle ear and environment.
  • Inner Ear Structures:
      - Cochlea: Responsible for hearing; converts sound signals into nerve impulses.
      - Vestibule: Part of balance; contains structures for static equilibrium.
      - Semicircular Canals: Detect head movements for dynamic equilibrium.

Section 9.9: Sound Detection in the Cochlea

  • Cochlear Structure:
      - Contains three chambers: Scala Vestibuli, Scala Tympani, and Cochlear Duct (which houses the Organ of Corti with hair cells).
  • How Hearing Works:
      1. Sound causes the eardrum to vibrate.
      2. Ossicles amplify the sound; stapes hits the oval window.
      3. Fluid (perilymph) moves within the cochlea.
      4. Basilar membrane vibrates, bending hair cells against the tectorial membrane.
      5. Bending of hair cells generates nerve signals sent to the brain.
  • Key Details:
      - High-pitched sounds detected near the oval window; low-pitched sounds near the tip of the cochlea.
      - Louder sounds create stronger vibrations.

Balance Mechanisms

  • Vestibule (Static Equilibrium):
      - Structures: Utricles, Saccules, Maculae, Otoliths.
      - Function: Detect head position in relation to gravity; otoliths shift and bend hair cells, sending signals.
  • Semicircular Canals (Dynamic Equilibrium):
      - Structures: Ampulla, Crista, Ampullaris, Cupula.
      - Function: Detect head movement and rotation; fluid movement bends hair cells to inform direction and speed of movement.