This chapter describes the mechanisms whereby the ear receives sound waves, discriminates their frequencies, and transmits auditory information into the central nervous system, where its meaning is deciphered. Tympanic Membrane and the Ossicular System Conduction of Sound From the Tympanic Membrane to the Cochlea Figure 53-1 shows the tympanic membrane (commonly called the eardrum ) and the ossicles , which conduct sound from the tympanic membrane…

Visual Pathways Figure 52-1 shows the principal visual pathways from the two retinas to the visual cortex . The visual nerve signals leave the retinas through the optic nerves . At the optic chiasm , the optic nerve fibers from the nasal halves of the retinas cross to the opposite sides, where they join the fibers from the opposite temporal retinas to form the optic tracts…

The retina is the light-sensitive portion of the eye that contains the following: (1) the cones , which are responsible for color vision; and (2) the rods , which can detect dim light and are mainly responsible for black and white vision and vision in the dark. When either rods or cones are excited, signals are transmitted first through successive layers of neurons in the retina…

Physical Principles of Optics Understanding the optical system of the eye requires familiarity with the basic principles of optics, including such factors as the physics of light refraction, focusing, and depth of focus. A brief review of these physical principles is presented in this chapter, followed by discussion of the optics of the eye. Refraction of Light Refractive Index of a Transparent Substance Light rays travel…

Many ailments of the body cause pain. Furthermore, the ability to diagnose different diseases depends to a great extent on a physician’s knowledge of the different qualities of pain. For these reasons, the first part of this chapter is devoted mainly to pain and to the physiological bases of some associated clinical phenomena. Pain occurs whenever tissues are being damaged and causes the individual to react…

The somatic senses are the nervous mechanisms that collect sensory information from all over the body. These senses are in contradistinction to the special senses , which mean specifically vision, hearing, smell, taste, and equilibrium. Classification of Somatic Senses The somatic senses can be classified into three physiological types: (1) the mechanoreceptive somatic senses , which include both tactile and position sensations that are stimulated by…

Our perceptions of signals within our bodies and of the world around us are mediated by a complex system of sensory receptors that detect such stimuli as touch, sound, light, pain, cold, and warmth. In this chapter, we discuss the basic mechanisms whereby these receptors change sensory stimuli into nerve signals that are then conveyed to and processed in the central nervous system. Types of Sensory…

The nervous system is unique in the vast complexity of thought processes and control actions that it can perform. Each minute it receives literally millions of bits of information from the different sensory nerves and sensory organs and then integrates all these to determine responses to be made by the body. Before beginning this discussion of the nervous system, the reader should review Chapter 5, Chapter…

When people descend beneath the sea, the pressure around them increases progressively as they go to greater depths. To keep the lungs from collapsing, air must be supplied at very high pressure to keep them inflated. This maneuver exposes the blood in the lungs to extremely high alveolar gas pressures, a condition called hyperbarism . Beyond certain limits, these high pressures cause major alterations in body…

As humans have ascended to higher and higher altitudes in aviation, mountain climbing, and space exploration, it has become progressively more important to understand the effects of altitude and low gas pressures on the human body. This chapter deals with these problems and acceleratory forces, weightlessness, and other challenges to body homeostasis that occur at high altitudes and in space flight. Effects of Low Oxygen Pressure…

Diagnosis and treatment of most respiratory disorders depend heavily on understanding the basic physiological principles of respiration and gas exchange. Some respiratory diseases result from inadequate ventilation. Others are caused by abnormalities of diffusion through the pulmonary membrane or abnormal blood transport of gases between the lungs and tissues. Therapy is often entirely different for these diseases, so it is not satisfactory simply to make a…

The nervous system normally adjusts the rate of alveolar ventilation to meet the demands of the body almost exactly so that the oxygen partial pressure (P o 2 ) and carbon dioxide partial pressure (P co 2 ) in the arterial blood are hardly altered, even during heavy exercise and most other types of respiratory stress. This chapter describes the function of this neurogenic system for…

Once oxygen (O 2 ) has diffused from the alveoli into the pulmonary blood, it is transported to the tissue capillaries almost entirely in combination with hemoglobin. The presence of hemoglobin in the red blood cells allows the blood to transport 30 to 100 times as much O 2 as could be transported in the form of dissolved O 2 in the water of the blood.…

After the alveoli are ventilated with fresh air, the next step in respiration is diffusion of oxygen (O 2 ) from the alveoli into the pulmonary blood and diffusion of carbon dioxide (CO 2 ) in the opposite direction, out of the blood into the alveoli. The process of diffusion is simply the random motion of molecules in all directions through the respiratory membrane and adjacent…

The lung has two circulations, a high-pressure, low-flow circulation and a low-pressure, high-flow circulation . The high-pressure, low-flow circulation supplies systemic arterial blood to the trachea, bronchial tree (including the terminal bronchioles), supporting tissues of the lung, and outer coats (adventitia) of the pulmonary arteries and veins. The bronchial arteries , which are branches of the thoracic aorta, supply most of this systemic arterial blood at…

The main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide. The four major components of respiration are the following: (1) pulmonary ventilation , which means the inflow and outflow of air between the atmosphere and the lung alveoli; (2) diffusion of oxygen (O 2 ) and carbon dioxide (CO 2 ) between the alveoli and the blood ; (3) transport…

Hemostasis Events The term hemostasis means prevention of blood loss. Whenever a vessel is severed or ruptured, hemostasis is achieved by several mechanisms: (1) vascular constriction; (2) formation of a platelet plug; (3) formation of a blood clot as a result of blood coagulation; and (4) eventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently. Vascular Constriction Immediately…

Antigenicity Causes Immune Reactions of Blood When blood transfusions from one person to another were first attempted, immediate or delayed agglutination and hemolysis of the red blood cells (RBCs) often occurred, resulting in typical transfusion reactions that frequently led to death. Soon it was discovered that the blood types of different people have different antigenic and immune properties so that antibodies in the plasma of one…

The human body has the ability to resist almost all types of organisms or toxins that tend to damage the tissues and organs. This capability is called immunity . Much of the immunity is acquired immunity that does not develop until after the body is first attacked by a bacterium, virus, or toxin; often, weeks or months are required for the immunity to develop. An additional…

Our bodies are exposed continually to bacteria, viruses, fungi, and parasites, all of which occur normally and to varying degrees in the skin, mouth, respiratory passageways, intestinal tract, lining membranes of the eyes, and even the urinary tract. Many of these infectious agents are capable of causing serious abnormal physiological function or even death if they invade deeper tissues. We are also exposed intermittently to other…