ch 12. part 4

Olfaction

• Mentioned as a sense: relates to smell but not detailed in the transcript.

Hearing

• Cochlea: Main organ for hearing.

  • Spiral Organ (Organ of Corti): Contains hair cells (inner and outer).

Static and Dynamic Equilibrium

• Static Equilibrium: Relates to the position of the head when stationary.

  • Controlled in the vestibule of the ear.

  • Involves utricle and saccule, which contain macula.

  • Macula: Patch of hair and supporting cells.

  • Hair cells detect movement due to gravity affecting the gelatinous layer with crystals (otoliths).

  • Movements generate nerve impulses sent via the vestibular branch of the vestibulocochlear nerve (Cranial Nerve VIII).

• Dynamic Equilibrium: Relates to head movement.

  • Controlled in the semicircular canals which are at right angles to each other.

  • Contains ampullae, which house sensory organs for detecting motion via hair cells embedded in a gelatinous mass called the cupula.

  • Movements (rotations) bend the cupula, stimulating hair cells and generating nerve impulses.

Eye Structure and Function

Objectives for Learning

• Distinguish between static and dynamic equilibrium.

• Understand the roles of accessory organs in vision.

• Describe the parts of the eye and how light is refracted through it.

General Overview

• Eye: Main organ of sight with several accessory structures contributing to vision.

Accessory Organs

• Eyelids: Protect the eye; composed of skin, muscle, connective tissue, and conjunctiva. Muscles include:

  • Orbicularis Oculi: Closes eyelid.

  • Levator Palpebrae Superioris: Opens eyelid.

• Eyebrows & eyelashes: Provide additional protection.

• Lacrimal Apparatus: Secretes tears, which contain protective lysozymes.

Eye Muscles

• Extraocular Muscles: Six muscles control eye movement (medial, lateral, superior, inferior, and oblique muscles).

Parts of the Eye

• Outer Fibrous Tunic:

  • Cornea: Transparent and refractive surface of the eye.

  • Sclera: Protective outer white fibrous coat.

• Middle Vascular Tunic (Choroid): Contains pigments, protects the inner structures, provides blood supply. Includes:

  • Ciliary Body: Holds and adjusts the lens for focusing light.

  • Iris: Controls light entry through the pupil.

• Inner Layer (Retina): Contains light-sensitive photoreceptors (rods and cones).

Lens Function

• Accommodation: Lens changes shape to focus light on the retina.

  • Becomes more convex for near objects.

  • Flattens for distant objects.

Equilibrium in the Ear

• Static Equilibrium involves the vestibule, which includes utricle, saccule, and macula.

• Dynamic Equilibrium involves semicircular canals with ampullae housing sensory receptors for movement detection.

Key Terms and Concepts

• Cochlea: For sound perception.

• Utricle and Saccule: Static equilibrium.

• Semicircular Canals: Dynamic equilibrium.

• Macula and Hair Cells: Critical components in equilibrium detection.

• Conjunctivitis: Inflammation of the conjunctiva, can be allergic or bacterial (pink eye).

• Meibomian glands: Produce oil to lubricate the eye, can become blocked.

Conclusion

• Importance of maintaining eye hygiene, distinguishing parts of the ear related to hearing and balance, understanding function of the vestibular system (static and dynamic).

• Encouragement to engage in further detailed study as this topic continues to expand beyond introductory concepts.