Principles of Anatomy & Physiology, 13th Edition

Principles of Anatomy and Physiology Five Interesting Functions of the Human Body

• Most forms of color blindness, an inherited inability to distinguish between certain colors, result from the absence or deficiency of one of the types of cones. The most common type is red-green color blindness, in which red cones or green cones are missing. As a result, the person cannot distinguish between red and green. Prolonged vitamin A deficiency and the resulting below-normal amount of rhodopsin may cause night blindness or nyctalopia, an inability to see well at low light levels.
• Women often have a keener sense of smell than men do, especially at the time of ovulation. Smoking seriously impairs the sense of smell in the short term and may cause long-term damage to olfactory receptors. With aging the sense of smell deteriorates. Hyposmia, a reduced ability to smell, affects half of those over age 65 and 75% of those over age 80. Hyposmia also can be caused by neurological changes, such as a head injury, Alzheimer disease, or Parkinson disease; certain drugs, such as antihistamines, analgesics, or steroids; and the damaging effects of smoking.
• Damage to the cerebellum can result in a loss of ability to coordinate muscular movements, a condition called ataxia. Blindfolded people with ataxia cannot touch the tip of their nose with their finger because they cannot coordinate movement with their sense of where a body part is located. Another sign of ataxia is a changed speech pattern due to uncoordinated speech muscles. Cerebellar damage may also result in staggering or abnormal walking movements. People who consume too much alcohol show signs of ataxia because alcohol inhibits activity of the cerebellum. Such individuals have difficulty in passing sobriety tests. Ataxia can also occur as a result of degenerative diseases (multiple sclerosis and Parkinson disease), trauma, brain tumors, and genetic factors, and as a side effect of medication prescribed for bipolar disorder.
• After death, the cellular membranes become leaky. Calcium ions leak out of the sarcoplasmic reticulum into the sarcoplasm and allow myosin heads to bind to actin. ATP synthesis ceases shortly after breathing stops, however, so the cross-bridges cannot detach from actin. The resulting condition, in which muscles are in a state of rigidity (cannot contract or stretch), is called rigor mortis (rigidity of death). Rigor mortis begins 3-4 hours after death and lasts about 24 hours; then it disappears as proteolytics enzymes from lysosomes digest the cross-bridges.
• A dislocated mandible can occur in several ways. Anterior displacements are the most common and occur when the condylar processes of the mandible pass anterior to the articular tubercles. Common causes are extreme mouth opening, as in yawning or taking a large bite, dental procedures, or general anesthesia. Posterior displacement can be caused by a direct blow to the chin. Superior displacements can be caused by a direct blow to the chin. Superior displacements are typically caused by a direct blow to a partially opened mouth. Lateral dislocations are usually associated with mandibular fractures.