The eye is the major organ used for vision in the human body. In conjunction with the brain, an individual can have a visual perception of the surroundings. Several features of the eye make it possible to perceive light and colors, thus making vision possible. These features include both internal and external features. The external features of the eye are the eyebrows, eyelids, conjunctiva, lacrimal apparatus, and the accessory muscles (Marieb & Smith, 2018). The external features ensure that the eye is protected from external forces and help in eye movements (Marieb & Smith, 2018).
The Retina is the posterior layer of the eye that contains photosensitive nerves (Heiting, 2017). These nerves send electrical impulses to the optic nerves then finally to the brain. The first interpretation of light to signals the brain can interpret happens in the retina.
The Retina contains three major neurons involved in visual interpretation. These are the photoreceptors, the bipolar cells, and the ganglion cells (Heiting, 2017). There are two types of photoreceptors: the rods and cones. The rods are photoreceptors specialized to perceive vision in dim light, while the cons are color receptors that allow high visual acquisition but only possible in highlight intensity (Marieb & Smith, 2018).
For this reason, the eye is unable to perceive color in moonlighting. While rods are located throughout the retina, the cons are centrally located at a region called the macula. Inside the macula, there is a small depression called the fovea that is responsible for high visual acuity. In this region, only cons are present (Heiting, 2017).
The body’s equilibrium and static movement are dependent on the Vestibule of the ear. The Vestibule contains two small membranous sacs called Saccule and Utricle (“Hearing and Equilibrium,” n.d.). These membranes contain a specialized mechanoreceptor that detects static equilibrium. Static equilibrium is a sense that is responsible for interpreting the position of the head thus permitting the central nervous system to maintain stability and posture (“Hearing and Equilibrium,” n.d.). The semicircular canals are responsible for detecting acceleration and movements of the body by use of tiny hair cells. The impulse is transmitted to the cranial nerve into the CNS thus allowing the body to maintain posture (“Hearing and Equilibrium,” n.d.).
- Hearing and Equilibrium | Anatomy and Physiology. (n.d.). Retrieved from https://courses.lumenlearning.com/nemcc-ap/chapter/special-senses-hearing-audition-and-balance/
- Heiting, G. (2017, October). How the Retina Works – Detailed Illustration. Retrieved from https://www.allaboutvision.com/resources/retina.htm
- Marieb, E. N., & Smith, L. A. (2018). Human anatomy & physiology laboratory manual, fetal pig version (12th ed.) Boston, MA: Pearson.