Special Senses Overview and Anatomy

Special Senses Overview

• Special senses include vision, hearing, taste, smell, and balance.
• Other senses are called general senses.
• Special senses have specialized sensory organs.
• These organs are eyes, ears, nose, tongue, and vestibular apparatus.

Vision

• Eyes are composed of an optical component focusing the visual image on receptor cells.
• A neural component transforms the image into graded and action potentials.
• Eyes have 120 million rod cells and 6 million cone cells.
• Rods are sensitive to dim light, while cones function in bright light for color and detail.
• Information from rod and cone cells is sent to the brain via the optic nerve (CN II).

Anatomy of the Human Eye

• Includes various parts like:
  • Muscles
  • Vitreous humor
  • Retina
  • Sclera
  • Cornea
  • Lens
  • Iris
  • Pupil
  • Aqueous humor
  • Optic nerve
  • Choroid and pigment epithelium

Hearing

• Hearing depends on sound physics, external/middle/inner ear function, nerve pathways, and brain processing.
• Sound energy travels through mediums (air, liquid, solid) causing vibrations.
• Vibrations of eardrum transmit to tiny bones (malleus, incus, stapes) in the middle ear amplifying the vibrations.
• Stapes vibrations push the oval window, sending vibrations to the organ of Corti in the inner ear.
• Hair cells in Corti convert vibrations into electrical signals traveling to the brain via sensory nerves.

Balance (Equilibrioception)

• Eustachian tube equalizes air pressure in the middle ear with atmospheric pressure, contributing to balance.
• The vestibular apparatus in the inner ear regulates equilibrium and balance through receptors.
• Information about hearing and balance is carried to the brain via the vestibulocochlear nerve (CN VIII).

Chemical Senses

• Chemicals binding to chemoreceptors in the nose and mouth detect taste and smell.
• Chemoreceptors, in particular the receptor cells, are activated when chemicals bind to their respective receptors.
• The signals triggered from chemoreceptors are relayed to the brain via converged axons.
• Taste receptors (tongue) include those for sweet, sour, salty, bitter, and umami.
• Olfactory receptors in the nasal cavity detect odor molecules, live ~2 months, and are constantly replaced via stem cells.

Types of Taste Receptors

• Different types of chemicals activate different taste receptors (sweet, sour, salty, bitter, umami).
• Umami is detected by glutamate and similar amino acids, giving a savory or flavorful sensation.

Signalling of Taste Receptors

• Distinct signal transduction mechanisms determine taste sensations.
• Examples:
  • Salt taste uses Na+
  • Sour taste uses H+
  • Sweet taste uses glucose
  • Bitter flavor can come from alkaloids
  • Umami receptors are activated by glutamate.

Olfactory Receptors

• Olfactory receptor neurons are in the olfactory epithelium of the nasal cavity.
• These receptor neurons live for about 2 months and are constantly replaced.
• Cilia in these neurons contain receptor proteins that bind odor molecules.
• Axons of receptor neurons form the olfactory nerve (CN I).

Explore the fascinating world of special senses including vision and hearing. This quiz covers the anatomy of the human eye and how sensory organs are specialized for their functions. Perfect for understanding the mechanisms behind sight and sound.