Ebook Cellular physiology and neurophysiology (2th edition): Part 1

Cellular Physiology
and Neurophysiology


Look for these other Mosby Physiology Monograph Series titles:

BLANKENSHIP: Neurophysiology (978-0-323001899-9)
CLOUTIER: Respiratory Physiology (978-0-323-03628-3)
HUDNALL: Hematologic Physiology and Pathophysiology (978-0-323-04311-3)
JOHNSON: Gastrointestinal Physiology, 7th edition (978-0-323-03391-6)
KOEPPEN & STANTON: Renal Physiology, 4th edition (978-0-323-03447-0)
LEVY & PAPPANO: Cardiovascular Physiology, 9th edition (978-0-323-03446-3)
PORTERFIELD & WHITE: Endocrine Physiology, 3rd edition (978-0-323-03666-5)


Cellular Physiology
and Neurophysiology
SECOND EDITION

Edited by

MORDECAI P. BLAUSTEIN, MD

Professor, Departments of Physiology and Medicine
Director, Maryland Center for Heart Hypertension and Kidney Disease
University of Maryland School of Medicine
Baltimore, Maryland

JOSEPH P. Y. KAO, PhD

Professor
Center for Biomedical Engineering and Technology
and
Department of Physiology
University of Maryland School of Medicine
Baltimore, Maryland

DONALD R. MATTESON, PhD
Associate Professor
Department of Physiology
University of Maryland School of Medicine
Baltimore, Maryland


1600 John F. Kennedy Blvd.
Ste 1800
Philadelphia, PA 19103-2899
CELLULAR PHYSIOLOGY AND NEUROPHYSIOLOGY
Copyright © 2012 by Mosby, an imprint of Elsevier Inc.
Copyright © 2004 by Mosby, Inc., an affiliate of Elsevier Inc.

ISBN: 978-0-3230-5709-7

Cartoon in Chapter 1 reproduced with the permission of The New Yorker.
All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying, recording, or any information storage and retrieval system,
without permission in writing from the publisher. Details on how to seek permission, further information about
the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance
Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.
This book and the individual contributions contained in it are protected under copyright by the Publisher

(other than as may be noted herein).

Notices
Knowledge and best practice in this field are constantly changing. As new research and experience broaden our
understanding, changes in research methods, professional practices, or medical treatment may become necessary.
Practitioners and researchers must always rely on their own experience and knowledge in evaluating and
using any information, methods, compounds, or experiments described herein. In using such information
or methods they should be mindful of their own safety and the safety of others, including parties for whom
they have a professional responsibility.
With respect to any drug or pharmaceutical products identified, readers are advised to check the most
current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be
administered, to verify the recommended dose or formula, the method and duration of administration, and
contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of
their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient,
and to take all appropriate safety precautions.
To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise,
or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.
Library of Congress Cataloging-in-Publication Data
Cellular physiology and neurophysiology / edited by Mordecai P. Blaustein, Joseph P.Y. Kao, and
Donald R. Matteson.—2nd ed.
   p. ; cm.—(Mosby physiology monograph series)
  Rev. ed. of: Cellular physiology / Mordecai P. Blaustein, Joseph P.Y. Kao, Donald R. Matteson. c2004.
  Includes bibliographical references and index.
  ISBN 978-0-323-05709-7 (pbk. : alk. paper)
  I. Blaustein, Mordecai P. II. Kao, Joseph P. Y. III. Matteson, Donald R. IV. Blaustein, Mordecai P. Cellular
physiology. V. Series: Mosby physiology monograph series.
  [DNLM: 1. Cell Physiological Phenomena. 2. Biological Transport—physiology. 3. Muscle Contraction—physiology.
4. Nervous System Physiological Processes. QU 375]
  571.6—dc23


2011036478
Acquisitions Editor: Bill Schmitt
Developmental Editor: Margaret Nelson
Publishing Services Manager: Peggy Fagen/Hemamalini Rajendrababu
Project Manager: Divya Krish
Designer: Steven Stave
Printed in United States
Last digit is the print number:  9  8  7  6  5  4  3  2  1


PREFACE

Knowledge of cellular and molecular physiology is
fundamental to understanding tissue and organ function as well as integrative systems physiology. Pathological mechanisms and the actions of therapeutic
agents can best be appreciated at the molecular and
cellular level. Moreover, a solid grasp of the scientific
basis of modern molecular medicine and functional
genomics clearly requires an education with this level
of sophistication.
The explicit objective of Cellular Physiology and
Neurophysiology is to help medical and graduate
students bridge the divide between basic biochemistry and molecular and cell biology on the one hand
and organ and systems physiology on the other. The
emphasis throughout is on the functional relevance
of the concepts to physiology. Our aim at every
stage is to provide an intuitive approach to quantitative thinking. The essential mathematical derivations are presented in boxes for those who wish to
verify the more intuitive descriptions presented in
the body of the text. Physical and chemical concepts
are introduced wherever necessary to assist students
with the learning process, to demonstrate the importance of the principles, and to validate their ties

to clinical medicine. Applications of many of the
fundamental concepts are illustrated with examples
from systems physiology, pharmacology, and pathophysiology. Because physiology is fundamentally a
science founded on actual measurement, we strive

to use original published data to illuminate key
concepts.
The book is organized into five major sections, each
comprising two or more chapters. Each chapter begins
with a list of learning objectives and ends with a set of
study problems. Many of these problems are designed
to integrate concepts from multiple chapters or
sections; the answers are presented in Appendix E.
Throughout the book key concepts and new terms are
highlighted. A set of multiple-choice review questions
and answers is contained in Appendix F. A review
of basic mathematical techniques and a summary of
elementary circuit theory, which are useful for understanding the material in the text, are included in
Appendixes B and D respectively. For convenience
Appendix A contains a list of abbreviations symbols
and numerical constants.
We thank our many students and our teaching colleagues whose critical questions and insightful comments over the years have helped us refine and improve
the presentation of this fundamental and fascinating
material. Nothing pleases a teacher more than a student
whose expression indicates that the teacher’s explanation has clarified a difficult concept that just a few
moments earlier was completely obscure.
Mordecai P. Blaustein
Joseph P. Y. Kao
Donald R. Matteson

v


This page intentionally left blank


ACKNOWLEDGMENTS

We thank Professors Clara Franzini-Armstrong
and John E. Heuser for providing original electron
micrographs, and Jin Zhang for an original figure.
We are indebted to the following colleagues for their
very helpful comments and suggestions on preliminary versions of various sections of the book: Professors Mark Donowitz and Luis Reuss (Chapters 10

and 11); Professors Thomas W. Abrams, Bradley E.
Alger, Bruce K. Krueger, Scott M. Thompson, and
Daniel Weinreich (Section IV); Professors Martin F.
Schneider and David M. Warshaw (Section V); and
Professor Toby Chai (Chapter 16). We also thank the
New Yorker for permission to reproduce the cartoon
in Chapter 1.

vii


This page intentionally left blank


CONTENTS

SECTION I

Fundamental Physicochemical
Concepts
CHAPTER

1

INTRODUCTION: HOMEOSTASIS
AND CELLULAR PHYSIOLOGY. . . . . 1
Homeostasis Enables the Body to Survive
in Diverse Environments............................. 1
The Body Is an Ensemble of Functionally
and Spatially Distinct Compartments........ 2
The Biological Membranes That
Surround Cells and Subcellular
Organelles Are Lipid Bilayers.............. 2
Biomembranes Are Formed Primarily
from Phospholipids but May
Also Contain Cholesterol
and Sphingolipids................................ 3
Biomembranes Are Not Uniform
Structures............................................. 3
Transport Processes Are Essential to
Physiological Function................................ 4
Cellular Physiology Focuses
on Membrane-Mediated Processes
and on Muscle Function.............................. 4
Summary........................................................... 5
Key Words and Concepts................................. 5

CHAPTER

2

DIFFUSION
AND PERMEABILITY. . . . . . . . . . . . . . . . 7

Diffusion Is the Migration of Molecules
down a Concentration Gradient................. 7
Fick’s First Law of Diffusion Summarizes
our Intuitive Understanding of Diffusion......7
Essential Aspects of Diffusion Are Revealed
by Quantitative Examination of Random,
Microscopic Movements of Molecules....... 9
Random Movements Result in
Meandering.......................................... 9
The Root-Mean-Squared Displacement
Is a Good Measure of the Progress
of Diffusion........................................ 10
Square-Root-of-Time Dependence Makes
Diffusion Ineffective for Transporting
Molecules Over Large Distances........ 10
Diffusion Constrains Cell Biology and
Physiology.......................................... 11
Fick’s First Law Can Be Used to Describe
Diffusion across a Membrane Barrier...... 11
The Net Flux Through a Membrane
Is the Result of Balancing Influx
Against Efflux.................................... 14

The Permeability Determines How
Rapidly a Solute Can Be
Transported Through a Membrane... 14
Summary......................................................... 18
Key Words and Concepts............................... 18
Study Problems............................................... 18
ix


x

CONTENTS

CHAPTER

3

OSMOTIC PRESSURE
AND WATER MOVEMENT . . . . . . . 19

Osmosis Is the Transport of Solvent Driven
by a Difference in Solute Concentration
Across a Membrane That Is Impermeable
to Solute...................................................... 19
Water Transport during Osmosis Leads to
Changes in Volume.................................... 20
Osmotic Pressure Drives the Net
Transport of Water during Osmosis......... 20
Osmotic Pressure and Hydrostatic Pressure
Are Functionally Equivalent in Their

Ability to Drive Water Movement
Through a Membrane............................... 22
The Direction of Fluid Flow Through
the Capillary Wall Is Determined
by the Balance of Hydrostatic and
Osmotic Pressures as Described
by the Starling Equation.................... 23
Only Impermeant Solutes Can Have
Permanent Osmotic Effects....................... 27
Transient Changes in Cell Volume
Occur in Response to Changes in
the Extracellular Concentration
of Permeant Solutes........................... 27
Persistent Changes in Cell Volume
Occur in Response to Changes in
the Extracellular Concentration
of Impermeant Solutes....................... 29
The Amount of Impermeant Solute
Inside the Cell Determines the
Cell Volume........................................ 29
Summary......................................................... 31
Key Words and Concepts............................... 32
Study Problems............................................... 32

CHAPTER

4

ELECTRICAL CONSEQUENCES
OF IONIC GRADIENTS. . . . . . . . . . . . 33

Ions Are Typically Present at Different
Concentrations on Opposite Sides
of a Biomembrane..................................... 33
Selective Ionic Permeability Through
Membranes Has Electrical Consequences:
The Nernst Equation................................. 33
The Stable Resting Membrane Potential
in a Living Cell Is Established by
Balancing Multiple Ionic Fluxes............... 37
Cell Membranes Are Permeable to
Multiple Ions...................................... 37
The Resting Membrane Potential
Can Be Quantitatively Estimated
by Using the Goldman-HodgkinKatz Equation.................................... 39
A Permeant Ion Already in
Electrochemical Equilibrium Does
Not Need to Be Included in the
Goldman-Hodgkin-Katz Equation.... 41
The Nernst Equation May Be Viewed
as a Special Case of the GoldmanHodgkin-Katz Equation..................... 41
EK Is the “Floor” and the ENa Is the
“Ceiling” of Membrane Potential...... 42
The Difference Between the Membrane
Potential and the Equilibrium
Potential of an Ion Determines the
Direction of Ion Flow......................... 42
The Cell Can Change Its Membrane
Potential by Selectively Changing
Membrane Permeability to Certain Ions.....42

The Donnan Effect Is an Osmotic
Threat to Living Cells................................ 43
Summary......................................................... 45
Key Words and Concepts............................... 46
Study Problems............................................... 46




CONTENTS

SECTION II

Ion Channels and Excitable
Membranes
CHAPTER

5

ION CHANNELS. . . . . . . . . . . . . . . . . . . . 47

Ion Channels Are Critical Determinants
of the Electrical Behavior of Membranes....47
Distinct Types of Ion Channels Have
Several Common Properties..................... 48
Ion Channels Increase the Permeability
of the Membrane to Ions.................... 48
Ion Channels Are Integral Membrane
Proteins That Form Gated Pores....... 49
Ion Channels Exhibit Ionic Selectivity... 49

Ion Channels Share Structural Similarities
and Can Be Grouped into Gene Families....50
Channel Structure Is Studied with
Biochemical and Molecular
Biological Techniques......................... 50
Structural Details of a K1 Channel
Are Revealed by X-Ray
Crystallography.................................. 51
Summary......................................................... 54
Key Words and Concepts............................... 54
Study Problems............................................... 54

CHAPTER

6

PASSIVE ELECTRICAL
PROPERTIES
OF MEMBRANES. . . . . . . . . . . . . . . . . . 55
The Time Course and Spread of Membrane
Potential Changes Are Predicted by the
Passive Electrical Properties of the
Membrane.................................................. 55
The Equivalent Circuit of a Membrane
Has a Resistor in Parallel with
a Capacitor......................................................56

xi

Membrane Conductance Is Established

by Open Ion Channels....................... 56
Capacitance Reflects the Ability of the
Membrane to Separate Charge.......... 56
Passive Membrane Properties Produce
Linear Current-Voltage Relationships...... 57
Membrane Capacitance Affects the Time
Course of Voltage Changes........................ 57
Ionic and Capacitive Currents Flow
When a Channel Opens..................... 57
The Exponential Time Course of the
Membrane Potential Can Be
Understood in Terms of the Passive
Properties of the Membrane............... 59
Membrane and Axoplasmic Resistances
Affect the Passive Spread of
Subthreshold Electrical Signals................. 60
The Decay of Subthreshold Potentials
with Distance Can Be Understood
in Terms of the Passive Properties
of the Membrane................................ 61
The Length Constant Is a Measure of
How Far Away from a Stimulus
Site a Membrane Potential Change
Will Be Detectable.............................. 63
Summary......................................................... 63
Key Words and Concepts............................... 64
Study Problems............................................... 64

CHAPTER

7

GENERATION AND
PROPAGATION OF
THE ACTION POTENTIAL. . . . . . . . . 67

The Action Potential Is a Rapid and
Transient Depolarization of the
Membrane Potential in Electrically
Excitable Cells.................................................67
Properties of Action Potentials
Can Be Studied with Intracellular
Microelectrodes.................................. 67


xii

CONTENTS

Ion Channel Function Is Studied with a
Voltage Clamp............................................ 69
Ionic Currents Are Measured at a
Constant Membrane Potential
with a Voltage Clamp........................ 69
Ionic Currents Are Dependent on
Voltage and Time............................... 71
Voltage-Gated Channels Exhibit
Voltage-Dependent Conductances..... 72
Individual Ion Channels Have Two
Conductance Levels................................... 74

Na1 Channels Inactivate during
Maintained Depolarization....................... 75
Action Potentials Are Generated by VoltageGated Na1 and K1 Channels.........................76
The Equivalent Circuit of a Patch of
Membrane Can Be Used to Describe
Action Potential Generation.............. 76
The Action Potential Is a Cyclical Process
of Channel Opening and Closing...........78
Both Na1 Channel Inactivation
and Open Voltage-Gated K1
Channels Contribute to the
Refractory Period............................... 79
Pharmacological Agents That Block
Na1 or K1 Channels, or Interfere
with Na1 Channel Inactivation,
Alter the Shape of the Action
Potential............................................. 79
Action Potential Propagation Occurs as a
Result of Local Circuit Currents............... 80
In Nonmyelinated Axons an Action
Potential Propagates as a Continuous
Wave of Excitation Away from the
Initiation Site..................................... 80
Conduction Velocity Is Influenced by
the Time Constant, by the Length
Constant, and by Na1 Current
Amplitude and Kinetics..................... 81
Myelination Increases Action
Potential Conduction Velocity........... 82

Summary......................................................... 84
Key Words and Concepts............................... 84
Study Problems............................................... 84

CHAPTER

8

ION CHANNEL DIVERSITY. . . . . . . 87

Various Types of Ion Channels Help to
Regulate Cellular Processes....................... 87
Voltage-Gated Ca21 Channels
Contribute to Electrical Activity and
Mediate Ca21 Entry into Cells.................. 87
Ca21 Currents Can Be Recorded
with a Voltage Clamp........................ 88
Ca21 Channel Blockers Are
Useful Therapeutic Agents................. 90
Many Members of the Transient Receptor
Potential Superfamily of Channels
Mediate Ca21 Entry................................... 91
Some Members of the TRPC Family
Are Receptor-Operated Channels...... 91
K1-Selective Channels Are the Most
Diverse Type of Channel........................... 92
Neuronal K1 Channel Diversity
Contributes to the Regulation of
Action Potential Firing Patterns........ 92
Rapidly Inactivating Voltage-Gated

K1 Channels Cause Delays
in Action Potential Generation.......... 93
Ca21-Activated K1 Channels
Are Opened by
Intracellular Ca21.............................. 95
ATP–Sensitive K1 Channels
Are Involved in Glucose-Induced
Insulin Secretion from Pancreatic
b-Cells................................................ 95
A Voltage-Gated K1 Channel Helps
to Repolarize the Cardiac
Action Potential................................. 97




CONTENTS

Ion Channel Activity Can Be Regulated
by Second-Messenger Pathways................ 97
b-Adrenergic Receptor Activation
Modulates L-Type Ca21 Channels
in Cardiac Muscle.............................. 99
Summary......................................................... 99
Key Words and Concepts............................. 100
Study Problems............................................. 100

SECTION III

Solute Transport

CHAPTER

9

ELECTROCHEMICAL POTENTIAL
ENERGY AND TRANSPORT
PROCESSES . . . . . . . . . . . . . . . . . . . . . . . . 103

Electrochemical Potential Energy Drives
All Transport Processes............................ 103
The Relationship Between Force and
Potential Energy Is Revealed by
Examining Gravity.......................... 103
A Gradient in Chemical Potential
Energy Gives Rise to a Chemical
Force That Drives the Movement
of Molecules...................................... 104
An Ion Can Have Both Electrical
and Chemical Potential Energy....... 104
The Nernst Equation Is a Simple
Manifestation of the
Electrochemical Potential................. 104
How to Use the Electrochemical
Potential to Analyze Transport
Processes........................................... 108
Summary....................................................... 111
Key Words and Concepts............................. 111
Study Problems............................................. 111

CHAPTER

xiii

10

PASSIVE SOLUTE
TRANSPORT. . . . . . . . . . . . . . . . . . . . . . . 113

Diffusion across Biological Membranes
Is Limited by Lipid Solubility................. 113
Channel, Carrier, and Pump Proteins
Mediate Transport across Biological
Membranes............................................... 114
Transport Through Channels Is
Relatively Fast.................................. 114
Channel Density Controls the
Membrane Permeability to
a Substance...................................... 115
The Rate of Transport Through Open
Channels Depends on the Net
Driving Force................................... 115
Transport of Substances Through
Some Channels Is Controlled by
“Gating” the Opening and
Closing of the Channels................... 115
Carriers Are Integral Membrane Proteins
That Open to Only One Side of the
Membrane at a Time............................... 115
Carriers Facilitate Transport Through
Membranes...................................... 116

Transport by Carriers Exhibits Kinetic
Properties Similar to Those of
Enzyme Catalysis............................. 116
Coupling the Transport of One Solute
to the “Downhill” Transport of Another
Solute Enables Carriers to Move
the Cotransported or Countertransported
Solute “Uphill” against an Electrochemical
Gradient.................................................... 119
Na1/H1 Exchange Is an
Example of Na1-Coupled
Countertransport............................. 119


xiv

CONTENTS

Na1 Is Cotransported with a
Variety of Solutes Such as Glucose
and Amino Acids..................................... 119
How Does the Electrochemical Gradient
for One Solute Affect the Gradient
for a Cotransported Solute?............. 121
Glucose Uptake Efficiency Can Be
Increased by a Change in the
Na1-Glucose Coupling Ratio........... 121
Net Transport of Some Solutes across
Epithelia Is Effected by Coupling Two
Transport Processes in Series.................. 122

Various Inherited Defects of Glucose
Transport Have Been Identified....... 122
1
Na Is Exchanged for Solutes Such
as Ca21 and H1 by Countertransport
Mechanisms.............................................. 123
Na1/Ca21 Exchange Is an Example
of Coupled Countertransport........... 124
Na1/Ca21 Exchange Is Influenced
by Changes in the Membrane
Potential............................................ 125
Na1/Ca21 Exchange Is Regulated
by Several Different Mechanisms.........125
Intracellular Ca21 Plays Many
Important Physiological Roles.......... 126
Multiple Transport Systems Can Be
Functionally Coupled.............................. 126
Tertiary Active Transport..................... 129
Summary....................................................... 130
Key Words and Concepts............................. 130
Study Problems............................................. 131

CHAPTER

11

ACTIVE TRANSPORT. . . . . . . . . . . . . 133
Primary Active Transport Converts
the Chemical Energy from ATP into
Electrochemical Potential Energy

Stored in Solute Gradients...................... 133

Three Broad Classes of ATPases
Are Involved in Active
Ion Transport................................... 133
The Plasma Membrane Na1 Pump
(Na1, K1-ATPase) Maintains the Low
Na1 and High K1 Concentrations
in the Cytosol........................................... 134
Nearly All Animal Cells Normally
Maintain a High Intracellular
K1 Concentration and a
Low Intracellular Na1
Concentration.................................. 134
The Na1 Pump Hydrolyzes ATP
While Transporting Na1
Out of the Cell and
K1 into the Cell................................ 134
The Na1 Pump Is “Electrogenic”......... 135
The Na1 Pump Is the Receptor
for Cardiotonic Steroids Such as
Ouabain and Digoxin...................... 135
Intracellular Ca21 Signaling Is
Universal and Is Closely Tied to
Ca21 Homeostasis.................................... 136
Ca21 Storage in the Sarcoplasmic/
Endoplasmic Reticulum Is
Mediated by a Ca21-ATPase............ 139
SERCA Has Three Isoforms................. 139
The Plasma Membrane of Most

Cells Has an ATP–Driven
Ca21 Pump...................................... 140
The Roles of the Several Ca21
Transporters Differ in Different
Cell Types......................................... 140
Different Distributions of the
NCX and PMCA in the Plasma
Membrane Underlie Their Different
Functions.......................................... 140
Several Other Plasma Membrane
Transport ATPases Are Physiologically
Important................................................. 141
H1,K1-ATPase Mediates Gastric
Acid Secretion.................................. 141




CONTENTS

Two Cu21-Transporting ATPases Play
Essential Physiological Roles............ 142
ATP-Binding Cassette Transporters
Are a Superfamily of P-Type
ATPases............................................ 144
Net Transport across Epithelial Cells Depends
on the Coupling of Apical and Basolateral
Membrane Transport Systems....................145
Epithelia Are Continuous Sheets
of Cells.............................................. 145

Epithelia Exhibit Great Functional
Diversity........................................... 145
What Are the Sources of Na1
for Apical Membrane Na1Coupled Solute Transport?............... 147
Absorption of Cl2 Occurs by
Several Different Mechanisms......... 148
Substances Can Also Be Secreted by
Epithelia........................................... 149
Net Water Flow Is Coupled to
Net Solute Flow across
Epithelia........................................... 150
Summary....................................................... 153
Key Words and Concepts............................. 153
Study Problems............................................. 154

SECTION IV

Physiology of Synaptic
Transmission
CHAPTER

12

SYNAPTIC PHYSIOLOGY I . . . . . . 155

The Synapse Is a Junction Between
Cells That Is Specialized for Cell-Cell
Signaling........................................................155
Synaptic Transmission Can Be Either
Electrical or Chemical...................... 156

Electrical Synapses Are Designed for
Rapid Synchronous Transmission.... 156
Most Synapses Are Chemical Synapses....157

xv

Neurons Communicate with Other
Neurons and with Muscle by Releasing
Neurotransmitters.................................... 159
The Neuromuscular Junction Is a
Large Chemical Synapse.................. 160
Transmitter Release at Chemical
Synapses Occurs in Multiples
of a Unit Size................................... 162
Ca21 Ions Play an Essential Role
in Transmitter Release..................... 164
The Synaptic Vesicle Cycle Is a Precisely
Choreographed Process for Delivering
Neurotransmitter into the Synaptic
Cleft.......................................................... 166
The Synaptic Vesicle Is the Organelle
That Concentrates, Stores, and Delivers
Neurotransmitter at the Synapse........167
Neurotransmitter-Filled Synaptic Vesicles
Dock at the Active Zone and Become
“Primed” for Exocytosis................... 167
Binding of Ca21 Ions to Synaptotagmin
Triggers the Fusion and Exocytosis
of the Synaptic Vesicle..........................169
Retrieval of the Fused Synaptic Vesicle

Back into the Nerve Terminal
Can Occur Through ClathrinIndependent and ClathrinDependent Mechanisms................... 171
Short-Term Synaptic Plasticity Is a
Transient, Use-Dependent Change in
the Efficacy of Synaptic Transmission.... 174
Summary....................................................... 177
Key Words and Concepts............................. 178
Study Problems............................................. 179

CHAPTER

13

SYNAPTIC PHYSIOLOGY II. . . . . 181

Chemical Synapses Afford Specificity,
Variety, and Fine Tuning
of Neurotransmission.............................. 181
What Is a Neurotransmitter?............... 181


xvi

CONTENTS

Receptors Mediate the Actions of
Neurotransmitters in Postsynaptic Cells....184
Conventional Neurotransmitters
Activate Two Classes of Receptors:
Ionotropic Receptors and

Metabotropic Receptors.................... 184
Acetylcholine Receptors Can Be Ionotropic
or Metabotropic....................................... 186
Nicotinic Acetylcholine Receptors Are
Ionotropic......................................... 186
Muscarinic Acetylcholine Receptors Are
Metabotropic.................................... 186
Amino Acid Neurotransmitters Mediate
Many Excitatory and Inhibitory
Responses in the Brain............................ 187
Glutamate Is the Main Excitatory
Neurotransmitter in the Brain......... 187
g-Aminobutyric Acid and Glycine Are
the Main Inhibitory Neurotransmitters
in the Nervous System.........................188
Neurotransmitters That Bind to Ionotropic
Receptors Cause Membrane
Conductance Changes............................. 189
At Excitatory Synapses, the Reversal
Potential Is More Positive Than the
Action Potential Threshold.............. 190
NMDAR and AMPAR Are Channels
with Different Ion Selectivities
and Kinetics..................................... 191
Sustained Application of Agonist
Causes Desensitization of
Ionotropic Receptors......................... 192
At Inhibitory Synapses, the Reversal
Potential Is More Negative Than the
Action Potential Threshold.............. 193

Temporal and Spatial Summation of
Postsynaptic Potentials Determine the
Outcome of Synaptic Transmission......195
Synaptic Transmission Is Terminated
by Several Mechanisms.................... 196
Biogenic Amines, Purines, and Neuropeptides
Are Important Classes of Transmitters
with a Wide Spectrum of Actions........... 197

Epinephrine and Norepinephrine
Exert Central and Peripheral
Effects by Activating Two Classes
of Receptors..........................................197
Dopaminergic Transmission Is
Important for the Coordination
of Movement and for Cognition...... 198
Serotonergic Transmission
Is Important in Emotion
and Behavior.................................... 199
Histamine Serves Diverse Central
and Peripheral Functions................. 200
ATP Is Frequently Coreleased with
Other Neurotransmitters................. 200
Neuropeptide Transmitters Are
Structurally and Functionally
Diverse............................................. 201
Unconventional Neurotransmitters
Modulate Many Complex
Physiological Responses.......................... 202
Unconventional Neurotransmitters

Are Secreted in Nonquantal
Fashion.................................................202
Many Effects of Nitric Oxide and Carbon
Monoxide Are Mediated Locally
by Soluble Guanylyl Cyclase............ 202
Endocannabinoids Can Mediate
Retrograde Neurotransmission........ 202
Long-Term Synaptic Potentiation and
Depression Are Persistent Changes in
the Efficacy of Synaptic Transmission
Induced by Neural Activity..................... 203
Long-Term Potentiation Is a LongLasting Increase in the Efficacy
of Transmission at Excitatory
Synapses........................................... 203
Long-Term Depression Is a LongLasting Decrease in the Efficacy of
Transmission at Excitatory
Synapses........................................... 205
Summary....................................................... 206
Key Words and Concepts............................. 207
Study Problems............................................. 208




CONTENTS

SECTION V

Molecular Motors
and Muscle Contraction

CHAPTER

14

MOLECULAR MOTORS
AND THE MECHANISM
OF MUSCLE CONTRACTION. . . . 211

Molecular Motors Produce Movement
by Converting Chemical Energy into
Kinetic Energy.......................................... 211
The Three Types of Molecular Motors
Are Myosin, Kinesin, and Dynein... 211
Single Skeletal Muscle Fibers Are
Composed of Many Myofibrils............... 212
The Sarcomere Is the Basic Unit of
Contraction in Skeletal Muscle............... 212
Sarcomeres Consist of Interdigitating
Thin and Thick Filaments............... 212
Thick Filaments Are Composed
Mostly of Myosin............................. 214
Thin Filaments in Skeletal Muscle Are
Composed of Four Major Proteins:
Actin, Tropomyosin, Troponin, and
Nebulin............................................ 214
Muscle Contraction Results from Thick and
Thin Filaments Sliding Past Each Other
(The “Sliding Filament” Mechanism)..... 215
The Cross-Bridge Cycle Powers Muscle
Contraction.............................................. 216

In Skeletal and Cardiac Muscles, Ca21
Activates Contraction by Binding to
the Regulatory Protein Troponin C........ 218
The Structure and Function of Cardiac
Muscle and Smooth Muscle Are
Distinctly Different from Those
of Skeletal Muscle.................................... 220
Cardiac Muscle Is Striated................... 220
Cardiac Muscle Cells Require a
Continuous Supply of Energy.......... 220

xvii

To Enable the Heart to Act as a Pump,
Myocytes Comprising Each Chamber
Must Contract Synchronously......... 220
Smooth Muscles Are Not Striated........ 220
In Smooth Muscle, Elevation of
Intracellular Ca21 Activates
Contraction by Promoting the
Phosphorylation of the Myosin
Regulatory Light Chain................... 223
Summary....................................................... 226
Key Words and Concepts............................. 227
Study Problems............................................. 227

CHAPTER

15

EXCITATION-CONTRACTION
COUPLING IN MUSCLE . . . . . . . . . 229

Skeletal Muscle Contraction Is
Initiated by a Depolarization of
the Surface Membrane............................ 229
Skeletal Muscle Has a High Resting
Cl2 Permeability.............................. 230
A Single Action Potential Causes a
Brief Contraction Called a Twitch......230
How Does Depolarization Increase
Intracellular Ca21 in
Skeletal Muscle?............................... 230
Direct Mechanical Interaction Between
Sarcolemmal and Sarcoplasmic
Reticulum Membrane Proteins
Mediates Excitation-Contraction
Coupling in Skeletal Muscle.................... 231
In Skeletal Muscle, Depolarization of the
T-Tubule Membrane Is Required for
Excitation-Contraction Coupling.......231
In Skeletal Muscle, Extracellular
Ca21 Is Not Required
for Contraction................................ 232
In Skeletal Muscle, the Sarcoplasmic
Reticulum Stores All the Ca21
Needed for Contraction.................... 232


xviii

CONTENTS

The Triad Is the Structure That Mediates
Excitation-Contraction Coupling
in Skeletal Muscle............................ 233
In Skeletal Muscle, ExcitationContraction Coupling Is
Mechanical....................................... 235
Skeletal Muscle Relaxes When Ca21
Is Returned to the Sarcoplasmic
Reticulum by SERCA....................... 235
Ca21-Induced Ca21 Release Is Central
to Excitation-Contraction Coupling
in Cardiac Muscle.................................... 237
In Cardiac Muscle, Communication
Between the Sarcoplasmic Reticulum
and Sarcolemma Occurs at
Dyads and Peripheral Couplings..... 237
Cardiac Excitation-Contraction
Coupling Requires Extracellular
Ca21 and Ca21 Entry Through
L-Type Ca21 Channels
(Dihydropyridine Receptors)........... 238
Ca21 That Enters the Cell during
the Cardiac Action Potential Must
Be Removed to Maintain a
Steady State...................................... 240
Cardiac Contraction Can Be Regulated
by Altering Intracellular Ca21.............240
Smooth Muscle Excitation-Contraction

Coupling Is Fundamentally Different from
That in Skeletal and Cardiac Muscles..... 241
Smooth Muscles Are Highly Diverse.... 241
The Density of Innervation Varies
Greatly among Different Types of
Smooth Muscles............................... 241
Some Smooth Muscles Are Normally
Activated by Depolarization............ 242
Some Smooth Muscles Can Be Activated
without Depolarization by
Pharmacomechanical Coupling....... 243
Ca21 Signaling, Ca21 Sensitivity,
and Ca21 Balance in Smooth
Muscle May Be Altered Under
Physiological and Pathophysiological
Conditions............................................245

Summary....................................................... 246
Key Words and Concepts............................. 247
Study Problems............................................. 247

CHAPTER

16

MECHANICS OF MUSCLE
CONTRACTION. . . . . . . . . . . . . . . . . . . . 249

The Total Force Generated by a Skeletal
Muscle Can Be Varied.............................. 249

Whole Muscle Force Can Be Increased
by Recruiting Motor Units............... 249
A Single Action Potential Produces a
Twitch Contraction.......................... 249
Repetitive Stimulation Produces Fused
Contractions..................................... 251
Skeletal Muscle Mechanics Is Characterized
by Two Fundamental Relationships........ 252
The Sliding Filament Mechanism
Underlies the Length-Tension
Curve................................................ 253
In Isotonic Contractions, Shortening
Velocity Decreases as Force
Increases........................................... 255
There Are Three Types of Skeletal Muscle
Motor Units.............................................. 255
The Force Generated by Cardiac Muscle
Is Regulated by Mechanisms That
Control Intracellular Ca21...................... 257
Cardiac Muscle Generates LongDuration Contractions..................... 257
Total Force Developed by Cardiac
Muscle Is Determined by
Intracellular Ca21............................ 257
Mechanical Properties of Cardiac and
Skeletal Muscle Are Similar but
Quantitatively Different.......................... 259
Cardiac and Skeletal Muscles Have
Similar Length-Tension
Relationships.................................... 259

CONTENTS

The Contractile Force of the Intact
Heart Is a Function of Initial
(End-Diastolic) Volume................... 259
Shortening Velocity Is Slower in Cardiac
Than in Skeletal Muscle................... 260
Dynamics of Smooth Muscle Contraction
Differ Markedly from Those of Skeletal
and Cardiac Muscle................................. 260
Three Key Relationships Characterize
Smooth Muscle Function................. 260
The Length-Tension Relationship in
Smooth Muscles Is Consistent with
the Sliding Filament Mechanism
of Contraction.................................. 260
The Velocity of Shortening Is Much
Lower in Smooth Muscle Than in
Skeletal Muscle................................. 261
Single Actin-Myosin Molecular
Interactions Reveal How Smooth
and Skeletal Muscles Generate the
Same Amount of Stress Despite Very
Different Shortening Velocities........ 261
Velocity of Smooth Muscle Shortening
and the Amount of Stress Generated
Depend on the Extent of Myosin

Light Chain Phosphorylation.......... 263
The Kinetic Properties of the CrossBridge Cycle Depend on the Myosin
Isoforms Expressed in the Myocytes......263
The Relationships among Intracellular
Ca21, Myosin Light Chain
Phosphorylation, and Force
in Smooth Muscles Is Complex.............. 264
Tonic Smooth Muscles Can Maintain
Tension with Little Consumption
of ATP.............................................. 264
Perspective: Smooth Muscles Are
Functionally Diverse........................ 265
Summary....................................................... 267
Key Words and Concepts............................. 268
Study Problems............................................. 268

xix

EPILOGUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
APPENDIXES
APPENDIX A
ABBREVIATIONS, SYMBOLS,
AND NUMERICAL CONSTANTS. . . . . . . . . . . 273

Abbreviations................................................ 273
Symbols......................................................... 274
Numerical Constants................................... 274
APPENDIX B
A MATHEMATICAL REFRESHER . . . . . . . . . . 275

Exponents..................................................... 275
Definition of Exponentiation............... 275
Multiplication of Exponentials............. 275
Meaning of the Number 0 as
Exponent.......................................... 275
Negative Numbers as Exponents.......... 275
Division of Exponentials...................... 276
Exponentials of Exponentials............... 276
Fractions as Exponents......................... 276
Logarithms.................................................... 276
Definition of the Logarithm................. 276
Logarithm of a Product........................ 277
Logarithm of an Exponential............... 277
Changing the Base of a Logarithm....... 277
Solving Quadratic Equations....................... 277
Differentiation and Derivatives................... 278
The Slope of a Graph and the
Derivative......................................... 278
Derivative of a Constant Number........ 279
Differentiating the Sum or
Difference of Functions.................... 279
Differentiating Composite Functions:
The Chain Rule................................ 280
Derivative of the Natural Logarithm
Function........................................... 281
Integration: The Antiderivative
and the Definite Integral......................... 281


xx

CONTENTS

Indefinite Integral (Also Known
as the Antiderivative)...................... 281
Definite Integral................................... 282
Differential Equations.................................. 283
First-order Equations with
Separable Variables.......................... 283
Exponential Decay............................... 283
First-order Linear Differential
Equations......................................... 284

Definitions of Electrical Parameters............ 291
Electrical Potential and Potential
Difference.............................................291
Current................................................. 291
Resistance and Conductance................ 291
Capacitance.......................................... 292
Current Flow in Simple Circuits................. 292
A Battery and Resistor in Parallel........ 292
A Resistor and Capacitor in Parallel.... 294

APPENDIX C
ROOT-MEAN-SQUARED DISPLACEMENT
OF DIFFUSING MOLECULES. . . . . . . . . . . . . . 287

APPENDIX E
ANSWERS TO STUDY PROBLEMS . . . . . . . . 299

APPENDIX D
SUMMARY OF ELEMENTARY
CIRCUIT THEORY . . . . . . . . . . . . . . . . . . . . . . . . 291

Cell Membranes Are Modeled
with Electrical Circuits............................ 291

APPENDIX F
REVIEW EXAMINATION . . . . . . . . . . . . . . . . . . 311

Answers to Review Examination................. 323


Cellular Physiology
and Neurophysiology



Section I

1

Fundamental Physicochemical
Concepts
INTRODUCTION: HOMEOSTASIS
AND CELLULAR PHYSIOLOGY

O BJECTIVES
1. Understand the need to maintain the constancy of the
internal environment of the body and the concept of

homeostasis.
2. Understand the hierarchical view of the body as an
ensemble of distinct compartments.

4. Understand why the protein-mediated transport processes that regulate the flow of water and solutes
across biomembranes are essential to all physiological
functions.

3. Understand the composition and structure of the lipid
bilayer membranes that encompass cells and organelles.

HOMEOSTASIS ENABLES THE
BODY TO SURVIVE IN DIVERSE
ENVIRONMENTS
Humans are independent, free-living animals who can
move about and survive in vastly diverse physical
environments. Thus we find humans inhabiting
habitats ranging from the frozen tundra of Siberia and
the mountains of Nepal* to the jungles of the Amazon
and the deserts of the Middle East. Nevertheless, the
elemental constituents of the body are cells, whose
survival and function are possible only within a narrow
range of physical and chemical conditions, such as
temperature, oxygen concentration, osmolarity, and pH.

* The adaptability of humans can be surprising: humans can survive
on Mount Everest, which, at 29,028 feet above sea level, is at the
cruising altitude of jet airplanes. At the summit the temperature is
approximately 240° Celsius (same as 240° Fahrenheit), the thin
atmosphere supplies only approximately one third of the oxygen at

sea level, and the relative humidity is zero.

Therefore the whole body can survive under
diverse external conditions only by maintaining the
conditions around its constituent cells within narrow
limits. In this sense the body has an internal environment, which is maintained constant to ensure survival
and proper biological functioning of the body’s cellular
constituents. The process whereby the body maintains
constancy of this internal environment is referred to as
homeostasis.† When homeostatic mechanisms are
severely impaired, as in a patient in an intensive care

†
The concept of the internal environment was first advanced by the
19th-century pioneer of physiology, Claude Bernard, who discussed
it in his book, Introduction à l’étude de la médecine expérimentale in
1865. Bernard’s often-quoted dictum is: “The constancy of the internal environment is the prerequisite for a free life.” (“La fixeté du
milieu intérieur est la condition de la vie libre.” from Leçons sur les
phénomènes de la vie communs aux animaux et aux végétaux, 1878.)
The term “homeostasis” was introduced by Walter B. Cannon in his
physiology text, The Wisdom of the Body (1932).

1


2

CELLULAR PHYSIOLOGY

unit, artificial life support systems become necessary

for maintaining the internal environment.
Achieving homeostasis requires various component physiological systems in the body to function
coordinately. The musculoskeletal system enables
the body to be motile and to acquire food and water.
The gastrointestinal system extracts nutrients
(sources of both chemical energy, such as sugars,
and essential minerals, such as sodium, potassium,
and calcium) from food. The respiratory (pulmonary) system absorbs oxygen, which is required in
oxidative metabolic processes that “burn” food to
release energy. The circulatory system transports
nutrients and oxygen to cells while carrying metabolic waste away from cells. Metabolic waste products are eliminated from the body by the renal and
respiratory systems. The complex operations of all
the component systems of the body are coordinated
and regulated through biochemical signals released
by the endocrine system and disseminated by the
circulation, as well as through electrical signals
generated by the nervous system.

THE BODY IS AN ENSEMBLE OF
FUNCTIONALLY AND SPATIALLY
DISTINCT COMPARTMENTS
The organization of the body may be viewed hierarchically (Figure 1-1). The various systems of the body
not only constitute functionally distinct entities, but
also comprise spatially and structurally distinct compartments. Thus the lungs, the kidneys, the various
endocrine glands, the blood, and so on are distinct
compartments within the body. Each compartment
has its own local environment that is maintained
homeostatically to permit optimal performance of
different physiological functions.
Compartmentation is an organizing principle that

applies not just to macroscopic structures in the body,
but to the constituent cells as well. Each cell is a compartment distinct from the extracellular environment
and separated from that environment by a membrane
(the plasma membrane). The intracellular space of
each cell is further divided into subcellular compartments (cytosol, mitochondria, endoplasmic reticulum,
etc.). Each of these subcellular compartments is encompassed within its own membrane, and each has a
different microscopic internal environment to allow

Body

Physiological
Systems

Organs

Tissues

Cells

Organelles

Microscopic Structures
(Membranes, cytoskeleton)

Biomolecules
(Lipids, proteins,
polysaccharides)
FIGURE 1-1 n Hierarchical view of the organization of the

body. (Modified from Eckert R, Randall D: Animal physiology,

ed 2, San Francisco, 1983, WH Freeman.)

different cellular functions to be carried out optimally
(e.g., protein synthesis in the cytosol and oxidative
metabolism in the mitochondria).

The Biological Membranes That Surround
Cells and Subcellular Organelles Are Lipid
Bilayers
As noted previously, cells and subcellular compartments are separated from the surrounding environment by biomembranes. Certain specific membrane
proteins are inserted into these lipid bilayer membranes. Many of these proteins are transmembrane
proteins that mediate the transport of various solutes
or water across the bilayers. Ion channels and ion
pumps are examples of such transport proteins. Other
transmembrane proteins have signaling functions and
transmit information from one side of the membrane
to the other. Receptors for neurotransmitters, peptide