Lab 11: Sensory Organs

Overview

• Final lab of the semester focusing on sensory organs as part two of the nervous system exploration.
• Topics: cranial nerves, skull formation, brain structures, and sensory organs.
• Includes an eyeball dissection.

Key Concepts for Sensory Organs

• Sensory organs have three main components:
  • Sensate molecule or force they respond to
  • A receptor (peripheral nerve)
  • Cortex of the brain for processing
• Reception types include photo reception, mechano reception, etc.
• Trace signal pathways from the sensory organ to the brain.

Olfaction (Sense of Smell)

• Type: Chemoreception
• Major structures: Thalamus (sensory integration center), Olfactory nerve, Olfactory bulb, Cribriform plate (part of ethmoid bone)
• Signal pathway: Olfactory nerve -> Thalamus -> Caudate nucleus and Globus polytus -> Temporal lobe

Gustation (Sense of Taste)

• Closely related to olfaction, but requires molecules to be dissolved in fluid (saliva).
• Major structures: Circumvallate papillae (bitterness), Fungiform papillae (umami, sweet, salty), Foliate papillae (sour)
• Signal pathway: Taste buds -> Facial, Glossopharyngeal, Vagus nerves -> Brain stem -> Gustatory cortex

Auditory System

• Type: Mechanoreceptor (dependent on physical force)
• Related to vestibular system (orientation in 3D space)
• Major structures:
  • Tympanic membrane (eardrum)
  • Ossicles (Incus, Malleus, Stapes): smallest bones, evolved from gill bones
  • Cochlea: site of hair cells, responsible for sound
  • Vestibule: responsible for 3D orientation
  • Semicircular ducts/canals: orientation on X, Y, Z axes
• Signal pathway: Cochlea/Vestibule -> Cochlear/Vestibular nerves -> Brain stem -> Temporal lobe

Vision

• Type: Photoreception
• Photoreceptive proteins: Rhodopsins
• Major structures:
  • Optic nerve, Trochlear nerve, Abducens
  • Eye components: Cornea, Iris, Pupil, Ciliary bodies, Lens, Retina
  • Humors: Aqueous (anterior, water-like), Vitreous (posterior, glass-like)
  • Rods and Cones: Resolve light density and color
  • Retina: Photoreceptors located here
  • Optic disc: Site near optic nerve attachment
• Signal pathway: Rods/Cones -> Optic nerve -> Optic chiasm -> Thalamus -> Superior caliculus -> Primary visual cortex in occipital lobe

Eye Dissection

• Focus on identifying parts and understanding their functions:
  • Cornea, Lens, Iris, Pupil, Aqueous and Vitreous humor
  • Retina and Optic disc
  • Optic nerve location and identification

Conclusion

• Thank you for your hard work throughout the semester.
• Final exam preparation materials are available online.
• Wishing good luck for future courses.