BSC 2346 Module 09 Lab Worksheet: Special Senses and Eyeball Dissection

BSC 2346 Module 09 Lab Worksheet: Special Senses and Eyeball Dissection.Introduction This week’s lab will focus on the special senses of vision, hearing, balance, smell and taste. Objectives Objectives for this week’s lab include: 1) Identify the anatomical components of the special senses, 2) Identify the anatomical structures of the eye through dissection, and 3) Analyze the function of the special senses. Overview The special senses consist of vision, taste, smell, hearing and equilibrium. Compared to the general senses (touch sensation, pain, temperature, pressure) that are widespread throughout the body, the special senses are localized to the head region of the body and contain highly complex nerve receptors. Nearly 70% of our sensory receptors are found in the eye and just about half of our cerebral cortex is dedicate to visual processing. Technically, there are three layers to the eye: Fibrous layer (outer layer which includes the sclera), vascular layer (middle layer that includes the choroid and iris) and the inner layer (which includes the retina). The major components of the eye include the: Cornea, iris, pupil, vitreous humor and the retina. The retina contains two types of photoreceptor cells: Rods, which are responsible for dimly light/black & white vision and cones, which are responsible for color vision. In a very simplistic sense, incoming light is refracted (bent) by the cornea, lens and vitreous humor to be focused on a specific spot of the retina. The photoreceptor cells of the retina will convert light energy into an electrical impulse that is transmitted to the occipital lobe via the optic nerve. The eye can have imbalances with the refraction of the light on the retina, producing vision that is labeled ‘near-sightedness’ or ‘far-sightedness’ and leading to the need for corrective eyewear. Both the sense of taste and smell are classified as a chemical sense because they contain chemoreceptors, which are receptors that bind molecules to initiate their sense perception. For the sense of taste, mastication of food releases molecules that bind to sensory nerves found within our tastes buds. A human has roughly 10,000 taste buds that are housed within these tiny projections called papillae. Once the taste cell (gustatory epithelial cell) binds a molecule, it initiates an action potential that is sent to various locations of the cerebrum creating the sense of taste. The sense of smell utilizes the same method. Odor molecules, known as odorants, enter the nose and bind to the olfactory cells, which are connected to the olfactory bulb. Upon binding an odorant, the olfactory cells will generate an action potential that is projected to various regions in the cerebrum and stimulates our sense of smell. The sense of hearing and equilibrium is housed within the inner ear. The cochlea, vestibule, and semicircular canals are the major structures involved. The cochlea is a small, spiral shaped boney chamber that houses the spiral organ, which ultimately allows for the sense of hearing. The spiral organ contains hair cells that move in accordance to air vibrations sensed by the tympanic membrane and generate an action potential that is sent to the temporal lobe for the sense of hearing. The vestibule contains the saccule and utricle while the semicircular canals contain the ampullas. These structures contain sensory hair cells that move in accordance to the movement of head creating the sense of acceleration, de-acceleration, head position and rotational movements of the head. Materials 1. Models of the eye and ear 2. Tuning fork 3. Starbursts™ candy 4. Eyeball specimen 5. Dissection tray and kit