The Cardiac Cycle The sequence of mechanical and electrical events that repeats with every heartbeat is called the cardiac cycle. The duration of the cardiac cycle is the reciprocal of the heart rate: For example, for a heart rate of…
Different cardiac cells serve different and very specialized functions, but all are electrically active. The heart's electrical signal normally originates in a group of cells high in the right atrium that depolarize spontaneously; it then spreads throughout the heart from…
The microcirculation serves both nutritional and non-nutritional roles The primary function of the cardiovascular system is to maintain a suitable environment for the tissues. The microcirculation is the “business end” of the system. The capillary is the principal site for…
Arterial Distribution and Venous Collection Systems Hemodynamics is the study of the physical laws of blood circulation. It therefore addresses the properties of both the “content” (i.e., blood) and the “container” (i.e., blood vessels). In Chapter 18 , we discussed…
Blood is a complex fluid consisting of plasma—extracellular fluid rich in proteins—and of formed elements—red blood cells (RBCs), white blood cells (WBCs), and platelets. Total blood volume is ~70 mL/kg body weight in the adult woman and ~80 mL/kg body weight in…
Elements of the Cardiovascular System The circulation is an evolutionary consequence of body size Isolated single cells and small organisms do not have a circulatory system. They can meet their metabolic needs by the simple processes of diffusion and convection…
Elements of Neural Circuits Neural circuits process sensory information, generate motor output, and create spontaneous activity A neuron never works alone. Even in the most primitive nervous systems, all neurons participate in synaptically interconnected networks called circuits. In some hydrozoans…
Sensory receptors convert environmental energy into neural signals Sensation is a cognitive process that requires the full powers of the central nervous system (CNS). Sensation begins with the sensory receptors that actually interface with the world, and these receptors use…
When we are awake, we are constantly aware of sensory input from our external environment, and we consciously plan how to react to it. When we are asleep, the nervous system has a variety of mechanisms to dissociate cortical function…
After meticulous study of spinal reflexes, Charles Sherrington N10-2 deduced that neurons somehow communicate information, one to the next, by a mechanism that is fundamentally different from the way that they conduct signals along their axons. Sherrington had merged his…