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Physiology of Neurons

Neurons receive, combine, transform, store, and send information Neurons have arguably the most complex job of any cell in the body. Consequently, they have an elaborate morphology and physiology. Each neuron is an intricate computing device. A single neuron may receive chemical input from tens of thousands of other neurons. It then combines these myriad signals into a much simpler set of electrical changes across its…

The Neuronal Microenvironment

Extracellular fluid in the brain provides a highly regulated environment for central nervous system neurons Everything that surrounds individual neurons can be considered part of the neuronal microenvironment. Technically, therefore, the neuronal microenvironment includes the extracellular fluid (ECF), capillaries, glial cells, and adjacent neurons. Although the term often is restricted to just the immediate ECF, the ECF cannot be meaningfully discussed in isolation because of its…

Organization of the Nervous System

The human brain is the most complex tissue in the body. It mediates behavior ranging from simple movements and sensory perception to learning, memory, and consciousness. It is the organ of the mind and accounts for the human capacity for invention, discovery, and language. Many of the brain's functions are poorly understood. In fact, the most prominent function of the human brain, its capacity to think,…

Cellular Physiology of Skeletal, Cardiac, and Smooth Muscle

The primary function of muscle is to generate force or movement in response to a physiological stimulus. The human body contains three fundamentally different types of muscle adapted to specialized functions. Skeletal muscle is responsible for the voluntary movement of bones that underlies locomotion and work production. Skeletal muscle also controls the breathing cycle of the lungs via contraction of the diaphragm and functions as a…

Synaptic Transmission and the Neuromuscular Junction

The ionic gradients that cells maintain across their membranes provide a form of stored electrochemical energy that cells can use for electrical signaling. The combination of a resting membrane potential of −60 to −90 mV and a diverse array of voltage-gated ion channels allows excitable cells to generate action potentials that propagate over long distances along the surface membrane of a single nerve axon or muscle fiber.…

Electrical Excitability and Action Potentials

Cellular communication in the nervous system is based on electrical and chemical signaling events that are mediated by ion channels. Certain types of cells, including neurons and myocytes, have a remarkable property called electrical excitability. In cells with this property, depolarization of the membrane above a certain threshold voltage triggers a spontaneous all-or-none response called an action potential. This action potential is a transient, regenerative electrical…

Electrophysiology of the Cell Membrane

Physics is concerned with the fundamental nature of matter and energy, whereas the goal of medical physiology is to understand the workings of living tissue. Despite their different perspectives, physics and physiology share common historical roots in the early investigations of charge and electricity. In the late 1700s, Luigi Galvani, a professor of anatomy in Bologna, Italy, used the leg muscles of a dissected frog to…

Transport of Solutes and Water

The cells of the human body live in a carefully regulated fluid environment. The fluid inside the cells, the intracellular fluid (ICF), occupies what is called the intracellular compartment, and the fluid outside the cells, the extracellular fluid (ECF), occupies the extracellular compartment. The barriers that separate these two compartments are the cell membranes. For life to be sustained, the body must rigorously maintain the volume…

Regulation of Gene Expression

In this chapter, we discuss general principles of gene structure and expression as well as mechanisms underlying the regulation of tissue-specific and inducible gene expression. We will see that proteins (transcription factors) control gene transcription by interacting with regulatory elements in DNA (e.g., promoters and enhancers). Because many transcription factors are effector molecules in signal-transduction pathways, these transcription factors can coordinately regulate gene expression in response…

Signal Transduction

Even single-cell organisms must respond to environmental challenges, which necessitated the development of signal-transduction mechanisms. The evolution of multicellular organisms required the evolution of cell-to-cell communication within the organism to coordinate between cells activities ranging from the induction of embryonic development to the integration of physiological responses. All cells receive and process information. External signals such as odorants, metabolites, ions, hormones, growth factors, and neurotransmitters can…

Functional Organization of the Cell

In the minds of many students, the discipline of physiology is linked inextricably to images from its past. This prejudice is not surprising because many experiments from physiology's proud history, such as those of Pavlov on his dogs, have transcended mere scientific renown and entered the realm of popular culture. Some might believe that the science of physiology devotes itself exclusively to the study of whole…

Foundations of Physiology

What is physiology? Physiology is the dynamic study of life. Physiology describes the “vital” functions of living organisms and their organs, cells, and molecules. For centuries, the discipline of physiology has been closely intertwined with medicine. Although physiology is not primarily concerned with structure—as is the case for anatomy, histology, and structural biology—structure and function are inextricably linked because the living structures perform the functions. For…

Appendix 5

Endothelium The endothelium is the single-cell-thick lining of all blood vessels that is in direct contact with the blood stream. In arteries and veins, the endothelium is the inner most surface of the vessel, overlying the deeper wall components, such as layers of smooth muscle (see eFig. A5.1 ). In the capillaries, endothelial cells and the basal lamina layer upon which they rest constitute the entire…

Appendix 4

Cell-cell communication It is no surprise that cells communicate with each other. Signaling is essential for coordinating the function and differentiation of nearby cells. Cells located close to one another communicate in three main ways: If the cells are connected by a gap junction, one cell can send a signal through the gap junction directly into the adjoining cell’s cytoplasm. If the cells are close enough…

Appendix 3

Signal transduction The cell membrane is a barrier to the free movement not only of matter (molecules, ions), but also to that of information . Just as living cells must maintain an internal environment chemically separate from but in regulated exchange with the extracellular milieu, so too they must be informationally distinct inside and yet manage a connection with events outside, communicating with the extracellular world…

Appendix 1

Cell membrane structure and transport functions The contents of cells are sealed off from the extracellular environment by a lipid barrier called the plasma membrane that protects the cell’s interior from the changing conditions of the extracellular environment and helps maintain the specific chemical milieu supporting intracellular metabolic processes. This appendix contains additional background information about the structure and function of the plasma membrane. Proteins embedded…

Endocrine physiology

Presentation: History and physical examination J.B is a 38 year old woman who presents to her primary care physician with a chief complaint of fatigue and weight gain. She was in her normal state of health until about 6 months ago. Since that time, she has been getting tired more easily and has lost over 12 pounds despite no significant change in her workout regime. In…

The male reproductive system

Introduction The male reproductive system has three principal functions: 1. The differentiation and maintenance of the primary and secondary sex characteristics under the influence of the hormone testosterone, made in the testes. 2. Spermatogenesis: The creation of the male gametes inside the testes. 3. The penile delivery of sperm from the testes into the female’s vagina in the act of procreation. This includes penile erection and…

Pregnancy and parturition

The organs of pregnancy The placenta serves as the point of exchange between the circulatory systems of the mother and fetus; it is also a hormone-producing organ ( Fig. 35.1 A). The fully developed placenta is a round oval organ 15 to 20 cm in diameter and 2 to 3 cm thick, embedded in the uterine wall. It connects to the developing fetus via the umbilical…