Animal Eyes: Structure and Function

Animal Eyes

• Compound vs. Simple Eyes: Arthropods have compound eyes with many ommatidia (independent units), each with its own photoreceptor. Humans have simple eyes with a single lens focusing light onto the retina.

• Light Path Through the Human Eye: Light enters the eye and strikes photoreceptors (rods and cones) in the retina. The path: cornea → pupil → lens → retina

• Accommodation: The lens changes shape to focus on near or far objects. A rounder shape focuses on near objects, a flatter shape on distant items. The ciliary body controls this lens shape.

• Refraction: The bending of light rays by the cornea and lens to focus light on the retina.

• Photoreceptors: Rods and cones are specialized cells in the retina that detect light and turn it into electrical signals. Rods are for black and white vision, cones for color vision. Rods are more numerous than cones.

• Nerve Impulses: Nerve impulses from the photoreceptors travel to the brain through the optic nerve.

• Occipital Lobe: The brain's occipital lobe processes information from the eyes.

• Blind Spot: The optic nerve exits the retina at a point with no photoreceptors, creating a blind spot. Invertebrates avoid this issue.

Eye Parts

• Sclera: Protects and supports the eyeball.
• Cornea: Refracts light rays.
• Choroid: Absorbs stray light rays.
• Lens: Refracts and focuses light rays.
• Retina: Contains photoreceptors.
• Fovea Centralis: Sharpest vision.
• Iris: Controls pupil size.
• Pupil: Allows light into the eye.
• Aqueous and Vitreous Humors: Transmit and refract light; support the eyeball.
• Optic Nerve: Carries impulses to the brain.

Accommodation

• Lens Shape & Accommodation: The lens changes shape to focus on different distances.
• Ciliary Muscles: Control the curvature of the lens.
• Presbyopia: Loss of lens elasticity, common in older individuals.

Animal Ears

Invertebrate Ears

• Invertebrate Ear Design: Some arthropods have air pockets with a tympanum (eardrum) to detect sound waves. Sensory neurons attached to the tympanum receive vibrations.

Human Ears

• Human Ear Structure: The ear is divided into three sections (outer, middle, & inner) for hearing and balance.

• Outer Ear:

  • Pinna: Collects sound waves.
  • Auditory Canal: Filters sound.

• Middle Ear:

  • Tympanic Membrane: The eardrum that vibrates.
  • Ossicles: (malleus, incus, stapes) amplify sound vibrations
  • Auditory Tube: Equalizes air pressure.

• Inner Ear:

  • Semicircular Canals: Detect rotational equilibrium.
  • Vestibule: Detects gravitational equilibrium.
  • Cochlea: (spiral organ) detects sound.

Human Ear Physiology

• Hearing Process: Sound waves vibrate the tympanic membrane. These vibrations are amplified by the ossicles.
• Cochlea Pressure Waves: Pressure waves in the cochlea stimulate hair cells, the receptors for sound and balance.
• Nerve Impulses: Sensory impulses go via the cochlear nerve and vestibular nerve to the brain.

Explore the fascinating differences between compound and simple eyes, and how light is processed in the human eye. Learn about accommodation, refraction, and the roles of rods and cones in vision. This quiz delves into the anatomy and function of eyes in various animals, highlighting the specifics of human eyesight.