Transcriber’s Notes:
Underscores “_” before and after a word or phrase indicate _italics_
in the original text.
Equal signs “=” before and after a word or phrase indicate =bold=
in the original text.
Small capitals have been converted to SOLID capitals.
Illustrations have been moved so they do not break up paragraphs.
Typographical and punctuation errors have been silently corrected.
[Illustration: The human skeleton (Lewis).]
STRUCTURE AND FUNCTIONS
_of_
THE BODY
A HAND-BOOK OF ANATOMY AND PHYSIOLOGY FOR
NURSES AND OTHERS DESIRING A PRACTICAL KNOWLEDGE
OF THE SUBJECT
BY
ANNETTE FISKE, A. M.
GRADUATE OF THE WALTHAM TRAINING SCHOOL FOR NURSES
_ILLUSTRATED_
PHILADELPHIA AND LONDON
W. B. SAUNDERS COMPANY
1911
Copyright, 1911, by W. B. Saunders Company
PRINTED IN AMERICA
PRESS OF
W. B. SAUNDERS COMPANY
PHILADELPHIA
TO MY FATHER
and
TO DR. ALFRED WORCESTER
as those who have perhaps most helped me in
the formation and realization of my ideals
this book is affectionately dedicated
PREFACE.
Although there are already in existence many books on anatomy and
physiology for nurses, none with which I am acquainted has seemed to me
to provide in concise form just the knowledge needed by the nurse in
her profession. Most of them, moreover, separate the anatomy from the
physiology and all treat the different systems of tissues separately,
first the bones, then the muscles, and so on. These defects, as they
seem to me, I have attempted to correct not only by weaving the
physiology in with the anatomy, but by treating first the general
structures found throughout the body and then describing the structure
and function of each part in detail. Thus, the first chapter is devoted
to a description of the general structure of all the tissues, a
separate chapter being devoted, however, to the skin, its appendages,
and function, including the sense of touch. Then the head with its
bones, muscles, and organs of special sense is described, while the
brain is treated with the rest of the nervous system, thus forming the
connecting link between the head and the body. In the same way the
back, chest, abdomen, pelvis, and extremities are taken up in turn and
the bones, muscles, blood-vessels, nerves, and special organs of each,
together with their functions, described.
Although written more particularly for nurses I am in hopes that
this book may prove useful to any others who may desire to acquire a
practical knowledge of anatomy and physiology.
Besides the usual text-books, I am much indebted for material to notes
taken in lecture courses given by Dr. Fred R. Jouett and Dr. F. J.
Goodridge of Cambridge, Mass., at the Cambridge School of Nursing, and
by Dr. Vivian Daniel of Watertown at the Waltham Training School for
Nurses.
I wish particularly to express my gratitude and appreciation for the
kind and helpful criticism given me by Dr. Eugene A. Darling, Assistant
Professor of Physiology, Harvard College.
ANNETTE FISKE.
_May, 1911._
CONTENTS.
CHAPTER I.
PAGE
COMPOSITION AND GENERAL STRUCTURE OF THE BODY 11
Chemical Constitution of the Body, 11--The Cell, 12--The
Fundamental Tissues of the Body, 13--Epithelial
Tissue, 14--Connective Tissue, 15--Structure of Bone,
17--Bone Formation, 18--Chemical Composition of Bone,
18--Classification and Function of Bones, 19--Joints,
20--Muscle, 21--Action of the Muscles, 23--Physiology
of Muscle, 24--Cilia, 27--The Blood, 27--Arteries,
27--Veins, 28--Capillaries, 28--Lymphatic System,
29--Lymphatic Vessels, 31--Lymphatic Glands,
32--Lymph, 32--Glands, 35--Ductless Glands,
36--Nervous Tissue, 36.
CHAPTER II.
THE SKIN, ITS APPENDAGES AND ITS FUNCTION 39
The Skin, 39--Appendages of the Skin: Nails, 40--Hair,
40--Sebaceous Glands, 41--Sweat Glands, 42--Sweat,
42--Temperature Regulation, 43--Fever, 45--Sense of
Touch, 45--Touch Corpuscles, 46.
CHAPTER III.
THE CRANIUM AND FACE 48
The Cranial Bones, 48--Frontal Bone, 49--Parietal
Bones, 49--Occipital Bone, 50--Occipito-frontalis
Muscle, 51--Temporal Bones, 51--Sphenoid or Wedge
Bone, 52--Ethmoid Bone, 53--Turbinated Bones,
53--Ossification of Sutures, 53--Bones of the
Face, 53--Superior Maxillary Bones, 54--Antrum of
Highmore, 54--Malar or Cheek Bones, 54--Lachrymal
Bones, 54--Palate Bones, 54--Nasal Bones, 55--Vomer,
55--Inferior Turbinated Bones, 55--Inferior
Maxillary Bone or Lower Jaw, 55--Sublingual Gland,
56--Submaxillary Gland, 56.
CHAPTER IV.
THE ORGANS OF SPECIAL SENSE 57
The Nose, 57--The Sense of Smell, 58--The Mouth, 59--The
Hyoid Bone, 60--The Teeth, 60--The Sense of Taste,
61--Salivary Glands, 61--The Tonsils, 62--The Ear,
63--Eustachian Tubes, 63--Sensation of Hearing,
65--The Eye, 66--Lachrymal Gland, 68--Coats of the
Eye, 68--Light Rays and Sight, 70--Accommodation,
72--Color Perception, 73.
CHAPTER V.
THE NERVOUS SYSTEM 75
The Cerebrum, 75--The Cerebellum, 78--Pons Variolii,
78--Medulla Oblongata, 78--Spinal Cord,
79--Brain-centers, 81--Motor Tract, 82--Sensory
Tract, 82--Reflex Action, 83--Cranial Nerves,
83--Spinal Nerves, 84--Brachial Plexus, 85--Sacral
Plexus, 85--The Sympathetic System, 87--The
Sympathetic Nerves, 87.
CHAPTER VI.
THE BACK 88
The Spine, 88--The Vertebræ, 88--Muscles of the Neck,
92--Muscles of the Back, 93.
CHAPTER VII.
THE CHEST 96
The Sternum, 97--The Ribs, 97--Costal Cartilages,
98--Muscles of the Chest, 98--Diaphragm, 98--Mammary
Glands, 100.
CHAPTER VIII.
THE HEART AND CIRCULATION 101
The Heart, 101--The Pericardium, 101--Cavities of the
Heart, 103--The Endocardium, 103--The Valves of
the Heart, 103--Circulation, 105--Circulation in
the Fetus, 106--Arteries, 107--Veins, 109--Portal
Circulation, 109--Pulmonary Circulation, 110--Nerves
of the Heart, 110--Heart Sounds, 111--The Heart
Beat, 111--Factors Affecting Circulation, 112--The
Pulse, 113--Blood Pressure, 114--Nerve Supply of the
Blood-vessels, 115--The Blood, 116--Composition
of the Blood, 116--Coagulability of the Blood,
117--Blood-corpuscles, 118.
CHAPTER IX.
THE LUNGS AND RESPIRATION 121
The Larynx, 121--The Trachea, 123--The Thyroid Gland,
124--The Thymus Gland, 124--The Bronchi, 125--The
Lungs, 125--The Pleura, 125--The Mediastinum,
126--Respiration, 127--Air, 129--Respiratory
Sounds, 129--Changes in Air in Lungs, 129--Effect
of Respiration on Blood, 130--Nervous Mechanism of
Respiration, 130--Variations in Respiration, 131.
CHAPTER X.
THE ABDOMEN AND THE ORGANS OF DIGESTION AND EXCRETION 132
The Abdominal Cavity, 132--Muscles of the Abdomen,
132--The Peritoneum, 134--Abdominal Regions,
134--Salivary Digestion, 136--The Pharynx, 139--The
Esophagus, 138--The Stomach, 138--Gastric Digestion,
139--Vomiting, 140--Intestinal Canal, 141--The Small
Intestine, 142--Intestinal Digestion, 143--Absorption
in Intestine, 144--The Large Intestine, 145--Food and
Metabolism, 147--The Liver, 149--The Gall-bladder,
152--The Pancreas, 153--The Spleen, 153--The
Suprarenal Capsules, 154--The Kidneys, 155--The
Urine, 156--The Ureters, 159--The Bladder and
Urethra, 159.
CHAPTER XI.
THE PELVIS AND THE GENITAL ORGANS 161
The Pelvis, 161--The Male Generative Organs, 164--The
Prostate Gland, 164--The Testes, 165--The Penis,
165--The Female Generative Organs, 165--The Ovaries,
165--The Fallopian Tubes, 166--The Uterus, 167--The
Vagina, 168--The External Genitalia in the Female,
169--The Vulva, 169--The Mons Veneris, 169--The Labia
Majora, 169--The Labia Minora, 170--The Clitoris,
170--The Meatus Urinarius, 170--The Hymen, 170--The
Fourchette, 170--The Perineal Body, 170--The
Perineum, 170.
CHAPTER XII.
THE UPPER EXTREMITIES 171
The Shoulder Girdle, 171--The Clavicle, 171--The Scapula,
173--Shoulder Muscles, 174--The Humerus, 175--Upper
Arm Muscles, 176--The Ulna, 177--The Radius,
178--The Wrist, 180--The Hand, 181--Meta-carpals,
181--Phalanges, 181--Muscles of the Forearm,
182--Muscles of the Hand, 184--Joints of the Upper
Extremity, 185--Blood Supply of the Upper Extremity,
185--Nerves of the Upper Extremity, 186.
CHAPTER XIII.
THE LOWER EXTREMITIES 187
The Femur, 187--Thigh Muscles, 189--The Patella,
192--Joints of the Lower Extremity, 192--The Tibia,
194--The Fibula, 194--The Ankle, 195--The Foot,
195--Metatarsals, 195--Phalanges, 195--Muscles of the
Leg, 196--The Blood Supply of the Lower Extremity,
198--Nerves of the Lower Extremity, 199.
INDEX 201
STRUCTURE AND FUNCTIONS OF THE BODY.
CHAPTER I.
COMPOSITION AND GENERAL STRUCTURE OF THE BODY.
Anatomy is the study of the physical structure and physiology the study
of the normal functions of the human body.
=Chemical Constitution of the Body.=--In the body only twenty elements
have been found. These include carbon, oxygen, hydrogen, nitrogen,
sulphur, phosphorus, calcium, magnesium, manganese, chlorin, potassium,
and fluorin. For the most part they appear in very complex and highly
unstable combinations, though oxygen and nitrogen may be said to exist
uncombined in the blood, alimentary canal, and lungs. Hydrogen also
occurs in simple form in the alimentary canal, but as the result of
fermentation, not as an element of the body.
Of the organic compounds some contain nitrogen and some do not. The
most important of the former are the proteins, which are found only in
living bodies and consist of carbon, hydrogen, oxygen, nitrogen, and
sulphur combined in very similar proportions. The important proteins in
the body are the serum albumen and fibrin found in the blood, myosin in
muscle, globulin in the red blood-corpuscles, and casein in the milk.
Similar to the proteins but capable of passing through membranes are
the peptones, the final result of protein digestion, from which the
albuminoids differ in that they contain no sulphur. Ferments containing
nitrogen exist in all the cells of the body, though more particularly
in those of the digestive organs, and the coloring matters, as the
bilirubin of the bile, are nitrogenous.
The organic substances that do not contain nitrogen are the
carbohydrates or starches, the hydrocarbons or fats, and the acids, of
which the most important is carbon dioxide, given off by the lungs.
The inorganic substances are water, which forms a large percentage of
all the tissues and from one-fourth to one-third of the whole body
weight, sodium chloride or common salt, which plays an important part
in keeping substances in solution, potassium and magnesium chloride,
and hydrochloric acid, found in the stomach.
=The Cell.=--Although the body is a very complex organism, the cell
is its unit or foundation. In fact, the body begins life as a single
protoplasmic cell, the ovum, which is frequently compared to the
amœba, a microscopic animal consisting of a single cell of protoplasm
or living substance--a substance not well understood as yet--but
possessing practically all the functions of the human body. For,
although it has no organs and is homogeneous in structure, the amœba
can move by throwing out a process, and can surround and absorb food,
which it builds up into new tissue, discarding the waste. The ovum,
however, differs from the amœba in that it has a transparent limiting
membrane and contains a darker spot, the nucleus. This in turn contains
another smaller spot, the nucleolus, while through the protoplasm,
which is semi-fluid, extends a fine network that seems to hold it in
place.
The _ovum_ is very small, about ¹/₁₂₅ inch in diameter, and after
fertilization grows by segmentation, the nucleus dividing in two and
the protoplasm grouping itself anew about the two nuclei. This division
continues, each cell dividing and forming two, or sometimes four,
new cells, all of which at first appear alike. By degrees, however,
differentiation takes place and different groups of cells assume
different characteristics. Thus the various tissues are gradually
developed, each with a structure and a function of its own, and are
distributed among the various organs, each organ consisting of several
tissues. During the process of growth and even after full growth of the
body is attained old cells are continually dying and being replaced by
new ones.
The typical cell is circular, but through being squeezed together
in the tissues or for some other reason the cells vary in shape in
different parts, being at times hexagonal, spindle-shaped, or columnar.
Yet, whatever their differences in shape or other characteristics, they
all live the same sort of life. All protoplasm absorbs oxygen when it
comes in contact with it and in the process of combining with it is in
part burned or oxidized, with the consequent setting free of heat and
other forms of energy and the formation of carbon dioxide. So long as
the body is alive, therefore, whether it is in a state of activity or
of rest, it is the seat of constant chemical change throughout all its
cells, and to these chemical changes are due all the forms of energy
manifested by the body. For energy is never destroyed, though it may
appear in a different form, and the elements of the human body are
so combined that their energy may be liberated and manifested in the
different functions the body exhibits.
=The fundamental tissues of the body= are the epithelial tissues, the
connective tissues, including the cartilaginous and bony tissues, and
the muscular and nervous tissues. Of these the epithelial tissues serve
as a protection to the surface of other tissues; the connective tissues
together form a framework for the support and general protection of the
other tissues; while energy is expended by muscular and nervous tissue,
the latter directing the former in its movements. All the tissues are
inter-dependent and the organs work together. Besides cells every
tissue contains a certain amount of lifeless matter, the intercellular
substance, which was at some time produced by the cells.
[Illustration: FIG. 1.--Epithelium: 1, pavement epithelium; 2, columnar
epithelium; 3, ciliated epithelium; 4, stratified epithelium.]
In =epithelial tissue= there is little intercellular substance, the
cells being close together and arranged generally as a skin or membrane
covering external or internal surfaces. When there are several layers
of cells, the deepest are columnar in shape and the others become
more and more flattened and scale-like as they approach the surface,
where they are gradually rubbed off and replaced by the growth of new
cells from below. This stratified epithelium, as it is called, is
found wherever a surface is exposed to friction, as in the skin and
in the mucous membrane of the mouth, pharynx, and esophagus, and in
that of the vagina and the neck of the uterus. In simple epithelium,
where there is only a single layer of cells, the cells may be pavement
or hexagonal, columnar, glandular, or ciliated, according to their
different functions. The flat pavement cells occur where a very smooth
surface is required, as in the heart, lungs, blood-vessels, serous
cavities, etc. None of these surfaces communicate directly with the
external surface of the body and the name endothelium is substituted
for epithelium. The columnar form of cell in the intestine facilitates
the passage of leucocytes between the cells. In glandular epithelium
the cells vary according to the gland in which they occur, their
protoplasm being filled with the material the gland secretes. Finally,
ciliated epithelium is composed of columnar cells with cilia or little
hair-like processes upon their free surface which serve to send
secreted fluids and other matters along the surfaces where they occur,
as in the air passages, parts of the generative organs, the ventricles
of the brain, and the central canal of the spinal cord.
=Connective tissue= has a great deal of intercellular substance. One
form, _areolar tissue_, is composed of a loose network of fine white
fibers with a few yellow elastic fibers interspersed and with cells
lying in the spaces between the fibers. It connects and surrounds the
different organs and parts, holding them together, yet allowing free
motion, and is one of the most extensively distributed of the tissues.
It is continuous throughout.
[Illustration: FIG. 2.--Section of bladder epithelium. (Hill.)]
Closely allied to the areolar is the _fibrous tissue_, in which the
white fibers lie close together and run for the most part in one
direction only. This is found in ligaments, joints and tendons, as also
in such fibrous protective membranes as the periosteum, dura mater, the
fasciæ of muscles, etc. Fibrous tissue is silvery white in appearance
and is very strong and tough, yet pliant. It is not extensile.
_Elastic tissue_, on the other hand, has a large predominance of
yellow elastic fibers and is very extensile and elastic, though not so
strong as the fibrous. It is found in the walls of the blood-vessels,
especially the arteries, in the walls of the air tubes, in the
ligaments of the spine, etc.
_Fatty or adipose tissue_ is formed by the deposit of fat in the cells
of the areolar tissue and is found in most parts where the areolar
tissue occurs, though it varies largely in amount in different parts.
It is found pretty generally under the skin, fills in inequalities
about various organs and about the joints, and exists in large
quantities in the marrow of the long bones. In moderate amounts it
gives grace to the form and constitutes an important reserve fund.
[Illustration: FIG. 3.--Adipose tissue (Leroy): _a_, Fibrous tissue;
_b_, fat cells; _c_, nucleus of fat cells; _d_, fatty acid crystals in
fat cells.]
_Cartilage_ consists of groups of nucleated cells in intercellular
substance. It is very firm, yet highly elastic, and serves in the
joints to break the force of concussion of the harder and less elastic
bones. Except when it occurs at the end of a bone, it is covered with
a membrane called the perichondrium, which carries its blood supply.
In the nose, ear, larynx and trachea it serves to give shape, to keep
the passages open, and to afford attachment for muscles. Most of the
skeleton of the fetus consists of cartilage, which later develops into
bone.
_Bone._--In bone the intercellular tissue is rendered hard by the
deposit of mineral salts, the resulting material being of great
strength and rigidity. The texture may be close and dense like ivory or
open and spongy, the difference lying merely in the fact that the one
has fewer spaces between the solid particles than the other. There is
usually a hard, compact layer on the exterior of the bone, as that is
where the greatest cross-strain comes, especially in the long bones,
while within is the cancellous or spongy tissue, which gives lightness
to the bone and is capable of withstanding enormous pressure, though it
can bear little cross-strain.
[Illustration: FIG. 4.--Cross-section of compact bone tissue. (After
Sharpey.)]
=Structure of Bone.=--The hard substance in bone is always arranged
in lamellæ or bundles of bony fibers, which in cancellous tissue
meet to form a kind of lattice-work, while in the dense tissue they
are generally arranged in rings about the Haversian canals, channels
through which the blood-vessels pass through the bone longitudinally.
Between the lamellæ are spaces called _lacunæ_, in which lie branched
cells, the spaces being connected with each other and with the
Haversian canals by numerous tiny canals or canaliculi, by which
nutrient material finds its way from the Haversian canals to all parts
of the bone.
Within the bone is the medulla or _marrow_, which is of two varieties:
the yellow, which is largely fat and is found in the long bones of
adults, and the red, which is nearly three-fourths water and is found
in most of the other adult bones and in the bones of the fetus and of
the infant.
Lining the medullary and cancellous cavities is a delicate connective
tissue lining, the _endosteum_, which contains many bone-forming cells,
while on the outside of the bone, except at the articular ends, is the
_periosteum_ with its outer protective layer and its inner vascular
layer containing osteoblasts or bone-forming cells. The periosteum is
essential for the growth of new bone where the old bone has died, and
if the periosteum is removed from healthy bone the part beneath is
liable to die, as it is by the constant growth of the osteoblasts that
the bone grows and is renewed. In the repair of broken bones tissue is
formed between and around the broken ends.
=Bone Formation.=--Most of the skull and face bones begin as
membranes of connective tissue, that is, are formed in membrane.
Bones are also formed in cartilage, the bone formation in this case
beginning from centers of ossification, where the deposit of lime
salts in the intercellular substance begins, the salts coming to the
centers dissolved in the plasma. Such a center of growth in a bone
is called the epiphysis and is separated from the main part of the
bone or diaphysis by cartilage until full growth is attained, when
ossification becomes complete. So in surgery, in working on the bones
of children, part of the epiphysis should always be left for the sake
of future growth. The outer shell of compact tissue is deposited by the
periosteum.
=Chemical Composition of Bone.=--Chemically bone is composed of about
one-third organic or animal matter, largely gelatine, and two-thirds
inorganic matter, including various salts of calcium, magnesium, and
sodium. In young children the animal matter predominates and the bones
are soft and often bend instead of breaking, only the outside shell on
one side giving way, as in “green-stick” fracture. In rickets there is
a deficiency of lime salts, but the increased brittleness of the bones
in old age is due, not to increase of mineral matter, but to the less
spongy texture of old bones.
=Classification and Function of Bones.=--There are in the body some
two hundred bones, which may be classified as long, short, flat, and
irregular. Occasionally an irregular bone develops in a fontanelle, the
membranous opening at the juncture of the sutures of the skull. This
is known as a Wormian bone. It is not, however, included in the two
hundred, as are not the sesamoid bones or bones developed in tendons,
with the exception of the patella or knee-cap.
Long bones are developed in cartilage and consist of a shaft, two
extremities, and various processes. They are more or less curved to
give them strength and grace. They serve as supports and act as levers
for purposes of motion and the exercise of power. Since a hollow
cylinder is just as strong as a solid one of the same size, the weight
coming only on the outer shell, the great bones which are accountable
for weight and which need to be light themselves have hollow shafts,
composed chiefly of compact tissue with a central medullary canal. The
ends, however, are expanded in order to make better connection at the
joints and to afford broad surfaces for muscular attachment, cancellous
tissue being used in them for lightness and strength. The large spongy
ends also give elasticity and lessen jar, and by bringing the tendons
to the bone at a greater angle increase their effectiveness. Blood is
brought to the long bones not only by the vessels of the periosteum but
by the medullary artery, which penetrates the compact tissue by the
nutrient foramen and divides into an ascending and a descending branch.
Short bones are spongy throughout. They are used for strength and where
little motion is required.
Flat bones are composed of two thin layers of compact tissue with a
varying amount of cancellous tissue between, and are for protection and
muscular attachment. The cancellous material between the two layers or
tablets of the skull is called the diploë.
Eminences and depressions occur on bones and when they are not
articular are for the attachment of ligaments and muscles. If they are
articular, they help to form joints.
As a whole the bony framework serves to keep the soft parts in place,
to support and protect them, and to aid in locomotion. The bones of the
head and trunk support and protect organs; those of the arms are for
tact and prehension; those of the lower extremities are for support and
locomotion.
Normally bones have little sensibility, but when inflamed they are
extremely sensitive and painful.
=Joints.=--The bones are connected with and move upon one another by
means of joints. These joints are of three kinds: 1. Immovable, where
the adjacent margins of the bones are closely applied, with little
fibrous tissue between, as in the sutures of the head; 2. those with
limited motion, which are very strong, the parts being connected with
tough fibro-cartilage; and 3. freely movable. In this last group the
articulating surfaces are covered with cartilage, which again is
lined with a delicate synovial membrane which secretes a small amount
of lubricating fluid, the synovial fluid, to reduce friction. Their
surfaces are also sometimes deepened by the presence of inter-articular
fibro-cartilages. Bursæ or sacs of synovial membrane occur outside the
joints under tendons and ligaments to reduce friction.
The nature and extent of the motion of a joint is defined and the bones
are held together by strong bands of fibrous tissue or ligaments, these
ligaments being more fully developed in joints where there is great
freedom of motion or where there is great weight to be supported. In a
ball-and-socket joint, such as the hip, there is a ligament in the form
of a strong capsule which surrounds the joint on all sides and limits
its motion, while hinge joints, like the elbow, and pivot joints, such
as that formed by the atlas on the axis, have lateral ligaments that
allow of freer motion. In the shoulder-joint, which is the most freely
movable joint in the body, the capsular ligament is very lax.
In general the kinds of motion possible in joints may be said to be
flexion, extension, abduction, adduction, circumduction, and rotation.
When much violence is applied to a joint and no dislocation results, as
in a sprain, there is often much stretching and even laceration of the
ligaments.
=Muscle.=--The flesh, which forms a large proportion of the weight of
the body, consists of muscular tissue. Of this two kinds are found:
1. The striated or striped muscle of animal life, which is under the
control of the will and so is known as voluntary muscle, and 2. the
unstriped or smooth muscle of organic life over which we have no
control, that is, the involuntary muscle. Each fiber of striped muscle
has an elastic, membranous sheath, the sarcolemma, and consists of
rod-shaped cells with a nucleus along the edge, set end to end and
having crosswise striations. In unstriated muscle the fibers, which
have no sarcolemma, consist of oval or spindle-shaped cells, with
a nucleus much smaller than that of striped muscle and situated in
the middle. In both kinds of muscle the fibers are bound together
with connective tissue and blood-vessels into fasciculi or bundles,
and many bundles go to make up a muscle. The muscle in turn has a
connective tissue envelope or sheath, the fascia. These fasciæ are
found throughout the body, the superficial ones being just beneath
the skin, while the deep ones not only form sheaths for the various
muscles but form partitions between them and serve to strengthen their
attachments. The striped muscles are those of motion, while the
unstriped occur in the hollow organs, surrounding the cavity and in
some cases lessening its capacity by their contraction.
An intermediate form of muscle known as cardiac muscle occurs in the
heart. Here the fibers have striations but the nucleus is generally in
the middle of the cell and the fibers branch and run together.
[Illustration]
[Illustration: FIG. 5.--Voluntary muscle (Leroy). _A_, Three voluntary
fibers in long sections: _a_, three voluntary muscle fibers; _b_,
nuclei of same; _c_, fibrous tissue between the fibers (endomysium);
_d_, fibers separated into sarcostyles. _B_, Fiber (diagrammatic): _a_,
dark band; _b_, light band; _c_, median line of Hensen; _d_, membrane
of Krause; _e_, sarcolemma; _f_, nucleus. _C_: _a_, Light band; _b_,
dark band; _c_, contracting elements; _d_, row of dots composing the
membrane of Krause; _e_, slight narrowing of contracting element aiding
in production of median line of Hensen.]
In life muscle appears more or less translucent and is contractile and
alkaline, but in death it loses its translucency and becomes rigid,
at the same time giving off in decomposition much carbon dioxide, so
that its reaction is acid. This phenomenon of the muscles becoming
rigid in death is called rigor mortis and occurs generally a few hours
after death, though it may come at once or be considerably delayed.
It may last anywhere from a few moments to several days but generally
lasts from twenty-four to thirty-six hours. It is probably due to the
formation in the muscle of myosin, a substance which probably comes
from myosinogen in the living muscle and which is closely akin to
the fibrin of blood. Probably the myosin or what precedes it causes
clotting of the muscle just as fibrin or what precedes it causes
clotting of the blood.
[Illustration: FIG. 6.--Three voluntary muscle fibers from an injected
muscle, showing network of blood capillaries. (Hill.)]
The muscles vary in shape in different parts of the body, being long
and slender in the limbs and broad and flat in the trunk. They are
attached chiefly to bones but also to cartilages, ligaments, and skin,
either by means of tendons, which are cords or bands of white inelastic
fibrous tissue, or by means of aponeuroses, membranous expansions of
the same nature. Most voluntary muscles consist of a belly and two ends
or tendons. The origin is the fixed point from which it acts while the
movable point upon which it acts is known as its insertion.
=Action of the Muscles.=--When attached to bones, muscles are
distributed in three ways: 1. When it is necessary to produce much
motion rapidly, a short muscle is used. 2. When a part needs to be
moved far and much contraction on the part of the muscle is, therefore,
needed, the muscle is very long, as in the case of the sartorius
muscle, which shortens half its length. 3. Finally, where less distance
has to be covered but greater power is required, tendons are used, as
in this case the contraction is powerful but does not carry the part
far.
In performing the mechanical work of the body the muscles are aided by
the fact that the bones, to which they are largely attached, are set
together loosely and form a set of levers, on which the muscles act
to perform certain definite acts. All three classes of levers occur:
1. where the fulcrum is between the weight and the power, as in the
case of the head, which is balanced by the muscles of the neck on the
vertebræ; 2. where the weight is between the fulcrum and the power, as
when a person raises himself upon his toes; and 3. where the power is
between the fulcrum and the weight, as when the biceps is used to raise
a weight held in the hand. The erect position of the body is difficult
to maintain because the center of gravity is high up, and it is by the
contraction of many muscles in the legs, thighs, back, abdomen, and
neck that the body is balanced upright upon the feet.
=Physiology of Muscle.=--_Irritability_ or sensitiveness to stimulation
and _contractility_ or the power to contract are the two most important
functions of muscle. Contraction occurs in response to nervous energy
brought by the nerves, a nerve filament going to each muscle fiber,
into which it plunges, its substance being lost and its sheath
becoming continuous with that of the muscle fiber. Any irritant,
as heat, electricity, etc., when applied to the nerve, causes the
muscle to contract. Moreover, muscle has an irritability of its own
and can contract independently of the nervous system. In contracting
it shortens and thickens, bringing the two ends closer together, and
becomes firm and rigid. The amount of contraction depends upon the
strength of the stimulus and the irritability of the muscle. The
minimal stimulus is the least stimulus that will cause a contraction
and the maximal is one that will cause the greatest contraction. The
work done depends in like manner upon the strength of the stimulus.
During contraction certain sounds are given off called muscle sounds,
which can be heard with the stethoscope but have no special
significance.
The muscles which have the greatest power of rapid contraction are
generally attached to levers. Indeed, striated muscle is characterized
by the rapidity and strength with which it works, though its rhythmic
motion is slight. Smooth muscle, on the other hand, is characterized
by its great force, considerable rhythm, considerable tone, and slight
rapidity, that is, its contraction is slower and lasts longer than that
of striated muscle. Cardiac muscle is characterized by great rhythm and
force, fair rapidity, and slight tonicity, tonicity being the amount of
tone or readiness to work. For even in sleep muscle is always in tone,
that is, ready to do its work. It is this that makes the difference in
appearance between a living and a dead person and enables one to spring
to his feet at night if he hears a noise, a thing he could not do if
his muscles were wholly relaxed. Thus, rapidity is the great function
of striated, tonicity of smooth, and rhythm of cardiac muscle. In
paralysis the muscles droop and lose their tone. Muscles are frequently
the seat of rheumatic disorders.
When set free, potential energy accomplishes work. In muscle there is
a good deal of potential energy, which is set free as heat and as work
accomplished. Even when the muscles are at rest, chemical changes are
going on and heat is being produced, though more heat is produced when
they are functioning. If the body depended upon its gross motions for
all its heat it would grow cold while a person rested. The respiratory
organs, however, and the heart are always working and chemical changes
are constantly taking place.
Ordinarily a muscle has some object in contracting, such as the raising
of a load, and it contracts voluntarily more or less according to
the weight of the load. The amount of work done is calculated in
foot-pounds or gram-meters, that is, the energy required to raise one
pound one foot or one gram one meter. As a rule the muscles with the
longest fibers, as the biceps, do the most work and those with a large
number of fibers do more than those with less. It has been calculated
that whereas an engine gives back one-twelfth of the energy of the coal
consumed, muscle liberates one-fourth of the energy brought to it in
the form of food. During activity the glycogen or sugar in the muscle
is used up and the muscle becomes more acid, owing to the lactic acid
that is formed. The carbon is taken in and carbon dioxide given off.
Nitrogen puts the muscle in condition to do its work but is not so
much used up in the work as is the carbohydrate material. So it is the
non-nitrogenous matter that does the work and any increase in urea, the
end-product of protein metabolism, is mere wear and tear.
Sudden heat or cold causes muscular contraction and moderate heat
favors both muscular and nervous irritability. Moderate cold, however,
lessens the force of contraction and below zero muscle very largely
loses its irritability without necessarily becoming rigid.
While well supplied with blood, muscle will contract without fatigue,
but if the blood supply is shut off, it soon loses its irritability
and becomes rigid. The more a muscle is used in moderation the more it
develops, but after it has done a certain amount of work it becomes
exhausted, losing its irritability or power to respond to stimuli
and later becoming rigid. Such fatigue is due to the production of
certain poisonous waste products which have a paralyzing effect on the
nerves and which are ordinarily gradually carried away in the blood,
but which sometimes, if produced to excess, accumulate too fast for
the blood wholly to remove them. Usually the nerve becomes exhausted
first and the muscle substance later. So long as it is connected with
the nervous system a muscle will respond to stimuli, but when the
nerve becomes tired, degeneration is more rapid. In fact, the degree
of exhaustion is determined by several factors, as by relation to the
central nervous system, variations in temperature, blood supply, and
functional activity, the process being more rapid in warm than in cold
blooded animals.
=Cilia.=--A few motions are accomplished by tissue that is not
muscular, as in the case of the cilia attached to the cells of the
respiratory tract, which lie flat on the free surface and then lash
forward, serving in the air cells to keep the air in motion and in the
tubes to send secretions from below upward and outward and to keep out
foreign bodies. Cilia are also found in the female genital tract, where
they aid the passage of the ovum from the ovary to the womb. They act
together, though apparently not governed by the nervous system. As in
the white corpuscles of the blood, whose motion also is not muscular,
the changes that take place in ciliated epithelium are probably about
the same as those in muscular tissue, that is, contractile.
=The Blood.=--To most of the tissues just described nourishment is
brought in the blood, which circulates through the body in a system
of hollow tubes, the arteries and veins, whence it is distributed
through the agency of the lymphatic system. There are no blood-vessels,
however, in the epidermis, epithelium, nails, hair, teeth, nor in the
cornea of the eye. The vessels that carry the blood from the heart
are called arteries, those that return it veins. The former begin as
large vessels and gradually decrease in size; the latter begin as small
vessels and form larger and larger trunks as they approach the heart.
The _arteries_ have three coats: 1. a thin, serous coat, the internal
or intima; 2. a middle or muscular coat, and 3. an external coat of
connective tissue. The middle coat is the thickest and is the one that
prevents the walls from collapsing when cut across. Except in the
cranium, each artery is enclosed in a sheath with its vein or veins,
the venæ comites. Usually the arteries occupy protected situations and
are straight in their course. Where a vessel has to accommodate itself
to the movements of a part, however, it may be curved, as in the case
of the facial artery which is curled on itself to allow for movements
of the jaw. They anastomose or communicate freely with one another,
thus promoting equality of distribution and pressure and making good
circulation possible even after the obliteration of a large vessel.
The _veins_ have three coats like the arteries, but they are not so
thick and the muscular coat is not so highly developed, so that the
walls collapse when cut and have no elasticity. There are constrictions
on the surface of many of the veins due to the presence of valves.
These valves are formed of semilunar folds of the lining membrane
and are arranged in pairs. They serve to prevent the blood, whose
circulation in the veins is sluggish, from flowing back.
There are two sets of veins, the superficial and the deep, which
communicate with each other. In fact, all the veins, large and small,
anastomose very freely, especially in the skull and neck, where
obstruction would result in serious trouble, throughout the spinal
cord, and in the abdomen and pelvis. The deep veins accompany the
arteries in their sheath, while the superficial ones have thicker walls
and run between the layers of the superficial fascia under the skin,
terminating in the deep veins. In the skull the venous channels take
the form of sinuses, formed by a separating of the layers of the dura
mater, with an endothelial lining that is continuous with that of the
veins.
The _capillaries_ are intermediate between the arteries and the veins,
the final division of the arteries and the first source of the veins.
They are tiny vessels with but a single coat, continuous with the
innermost coat of both arteries and veins and consisting practically of
one layer of cells with a small amount of connective tissue between.
They spread in a great network throughout the tissues, forming plexuses
and being especially abundant where the blood is needed for other
purposes than local nutrition, as in the secreting glands. Their
diameter is so small that the red corpuscles have to pass in single
file and may even then be squeezed out of shape. As they have no
muscular tissue in their walls, they have no power of contracting.
Their walls, however, like those of the smaller arteries and veins, are
porous and by virtue of this quality they play an important part in the
economy, since in them the exchange takes place between the tissues and
the blood.
The arteries in general carry freshly oxidized blood and the veins
blood from which the oxygen has been largely used up and which contains
waste material. In the pulmonary system, however, the case is reversed,
the pulmonary arteries conveying venous blood, as it is called, from
the heart to the lungs to be oxidized and the veins returning the blood
after it has received its new supply of oxygen.
The pumping of the blood through the arteries is assisted by the
contractions of the muscular coat, while the elastic tissue, of which
it contains a certain amount, gives elasticity to the walls and enables
them to stretch and so to accommodate the larger blood supply forced
into them at each beat by the heart. The walls of the veins have not
the power of contracting and the blood is pushed through more by
gravity and the action of the arteries than by any action of their own.
The walls of all the vessels are nourished by tiny blood-vessels in
the outer coat, known as _vasa vasorum_, and the nerves that regulate
the action of the arteries are the vasomotor nerves from the vasomotor
center in the medulla. Sufficient impulse goes from this center to the
blood-vessels all the time to keep them somewhat contracted, in a state
of tone, that is, which is increased or diminished as the blood supply
is to be diminished or increased.
=Lymphatic System.=--The lymphatic system also extends throughout
the body and consists of a system of channels, spaces, and glands
very closely related to the circulatory system and containing a fluid
called lymph. There are three principal parts to the system: 1. the
lymph spaces, which are open spaces, with no definite walls, in the
connective tissue framework of the body, more frequent near arteries
and veins and especially so among the capillaries; 2. the lymph
capillaries or small vessels which connect the lymph spaces; and 3. the
lymphatic vessels, of which there is a deep and a superficial set, the
latter accompanying the superficial veins on the surface of the body,
the former accompanying the deep blood-vessels.
[Illustration: FIG. 7.--Diagram showing the course of the main trunks
of the absorbent system: the lymphatics of lower extremities (D) meet
the lacteals of the intestines (LAC) at the receptaculum chyli (R.C.),
where the thoracic duct begins. The superficial vessels are shown in
the diagram on the right arm and leg (S), and the deeper ones on the
left arm (D). The glands are here and there shown in groups. The small
right duct opens into the veins on the right side. The thoracic duct
opens into the union of the great veins of the left side of the neck
(T). (Yeo.)]
The _lymph spaces_ are generally small, though there are some large
serous cavities, such as the abdomen, that may be considered as
extended lymph spaces.
[Illustration: FIG. 8.--Diagram of a lymphatic gland, showing afferent
(_a. l._) and efferent (_e. l._) lymphatic vessels; cortical substance
(_C_); medullary substance (_M_); fibrous coat (_c_); sending trabeculæ
(_tr_) into the substance of the gland, where they branch, and in the
medullary part form a reticulum; the trabeculæ are surrounded by the
lymph path or sinus (_l. s._), which separates them from the adenoid
tissue (_l. h._). (Sharpey.)]
The _lymphatic vessels_ have delicate, transparent walls, with three
coats like the arteries, though much thinner, and anastomose even
more freely than the veins. They have a beaded appearance due to
the presence of numerous valves, which form constrictions on their
surface. The right lymphatic duct, which is only about an inch long,
drains all the lymphatics of the right half of the upper part of the
trunk, the head, and the neck approximately, while the thoracic duct
drains those of the rest of the body. The latter, which is the largest
vessel of the system, begins opposite the second lumbar vertebra
with a bulb-like reservoir for the lymph or chyle, the receptaculum
chyli, and extends up along the spinal column for a distance of
about eighteen inches to the seventh cervical vertebra, where, with
the right lymphatic duct, it empties into the left subclavian vein
at its junction with the internal jugular, thus establishing direct
communication between the lymph spaces and the venous system. The
orifices of both vessels are guarded by semilunar valves to prevent
regurgitation of the blood.
[Illustration: FIG. 9.--Central (superficial) lymphatic glands of the
axilla. (After Leaf.)]
The _lymphatic glands_ are small oval glandular bodies and occur here
and there along the course of the lymphatics. Before entering one of
them the vessel breaks up into several afferent vessels which form
a plexus within and then emerge again as several efferent vessels
which soon unite to form one trunk. These glands occur chiefly in the
mesentery, along the great vessels, and in the mediastinum, axilla,
neck, elbow, groin, and popliteal space.
The _lymph_ varies in character with the locality, being a little
thicker and more opalescent in the lacteals, as the lymphatics of the
small intestine are called, especially during digestion, when fat is
present. Here it is called chyle. Otherwise it is generally a clear,
transparent and slightly opalescent fluid, which, owing to the presence
of fibrin, clots when drawn from the body and allowed to stand. In
fact, it resembles blood plasma very closely in composition and, as it
also contains a certain number of corpuscles or leucocytes that just
correspond to the white corpuscles of the blood, it is practically
blood without the red corpuscles. These leucocytes have considerable
power of amœboid movement and are thought by some to play an important
part in the absorption of food.
Owing to intracapillary pressure, the lymph transudes into the
lymph spaces and bathes the tissues, being carried away again by
the lymphatics. The amount of transudation is determined by the
blood pressure--the greater the pressure, the greater the amount of
transudation--and is increased by some organic action of the cells in
the walls of the vessels. In the process of transudation a certain
amount of solid matter goes through the wall of the vessel and it is
probable that certain protein elements can be carried thus from the
blood-vessels to the lymphatics, though they do not pass through the
capillary wall as readily as other substances. Some lymph is also
probably formed by the action of the tissues themselves, though the
process is not understood.
All muscular movements, active or passive, including the respiratory
movements, tend to drive the lymph on its way by pressure, the valves
of the vessels keeping it from flowing back. Moreover, its flow is
from the capillaries to the veins or from a region of high pressure to
one of less pressure. There is probably also some contraction in the
walls of the vessels themselves, and the continual formation of lymph
helps to drive it along. If an obstruction to the circulation occurs,
however, back-pressure results and causes too great transudation. In
that event a limb becomes swollen, pale, and generally cool. It pits
on pressure, the pressure driving the lymph out and there being no
circulation to bring it back. This condition is called œdema and occurs
in liver, kidney, and heart troubles, being generally first observed at
the ankles. In ascites, hydrothorax, hydrocephalus, and pericardial and
pleural effusions the fluid corresponds to lymph in its composition and
the large amount is due to excessive formation of the fluid, which is
normally present in small quantities.
Lymph gives the tissues substances from the blood that they need and
carries off those they do not, whether waste or substances of use to
other tissues. Because they thus absorb certain materials not needed
by the tissues and convey them to the circulation, the lymphatics have
also been called absorbents. Indeed, lymph may be spoken of as the
middleman between the blood and the tissues.
Another function of the lymph is to lubricate. Thus, the synovial fluid
of the joints is lymph and the pleuræ and the pericardium contain lymph
or serum to reduce the friction between the adjoining surfaces as much
as possible. The brain and spinal cord do not quite fill the cavities
of the cranium and the spinal column but float on a cushion of lymph,
the cerebro-spinal fluid. When the brain, which is subject to increase
and diminution in size, increases in size, it drives the lymph out, and
when it diminishes, the lymph returns.
The lymph glands serve as a protection to adjacent parts and when it
leaves the gland the lymph is purer and richer in leucocytes than
when it entered. In fact, they filter harmful matter from the lymph
and apparently also form white corpuscles. Normally they can with
difficulty be felt, but in disease, if the leucocytes are unable to
destroy or carry off the poison, the lymph carries it along to the
glands, which swell and become tender. If the infection is not severe
the swelling goes down and the tenderness passes after a short time,
but if it is severe, there may be suppuration and abscess formation
and the gland even perhaps be destroyed, giving its life for the
health of the part. Thus a wound in the foot, if infected, may cause
irritation and enlargement of the glands at the knee and in the groin.
The lymphatic glands are frequently the seat of tubercular infection,
especially in the neck, and are enlarged in scarlet fever, tonsillitis,
and diphtheria. In syphilis there is general glandular enlargement, and
the glands in the groin become enlarged in all diseases of the genital
organs. In malignant growths, such as cancer, the extension of the
disease is often along the lines of the lymphatics.
=Glands.=--Of glands in general a word might now be spoken. They are of
two kinds, excreting and secreting, and, when simple, are formed by the
folding in of a free surface, as in the case of the salivary, gastric,
and sebaceous glands, the cells at the gland becoming so modified as to
be able to perform the function of excreting or secreting. In racemose
glands the gland is broken up into many pockets. Excreting glands take
from an organ or from a part substances which have outlived their
usefulness and are to be cast out of the body, while the secreting
glands form from the blood substances that did not exist in it before,
but which are of use to the body, as the ptyalin of the saliva. A
strict line cannot, however, be drawn between the two kinds of glands,
most glands partaking more or less of both functions, though the
sebaceous and sweat glands are probably purely excreting glands and
the salivary glands are almost purely secreting. The glands, moreover,
are more or less interchangeable in their functions, that is, they
have vicarious function, and one gland can take up and do for another
what that other is for some reason unable to do. In jaundice, where
there is stoppage of the bile duct, the kidneys help out the liver by
excreting the bile. If one kidney is removed the other does work for
both, and the glands of the skin may help out the kidneys or _vice
versa_. Hemorrhage from the lungs sometimes occurs in suppression of
the menses.
In a general way the _function of glands_ is chemical. They filter out
by osmosis, selecting the useful parts for secretion and the useless
for excretion. In the chemical action that goes on considerable energy
is given off, as is shown by the amount of pressure in the glands and
by the fact that their temperature is higher than that of the blood.
They all work in a reflex manner, being under the control of the
central nervous system. Thus, what is eaten affects the nerve terminals
in the mouth, the sensation passes to the nervous system, and an
impulse is carried by the motor nerves to the salivary glands.
Most of the glands have ducts to convey away their secretion to other
parts of the body or to send excretions out of the body, but there are
also _ductless glands_, which, though they seem to have some important
function in the process of metabolism, are not well understood. Most
of them seem to manufacture some substance that is absorbed by the
tissues and that plays an important part in the bodily metabolism,
though nothing is secreted by them externally. They are said to have
an internal secretion, whereas the glands with ducts have an external
secretion. The liver has both forms of secretion, the bile which is
sent out and the glycogen that is stored. The ductless glands are the
thymus and thyroid glands, the suprarenal capsules, and the pituitary
body in the brain.
=Nervous Tissue.=--Presiding over all the organs, muscles, and
blood-vessels, as the source of all action and all sensation, are the
nerves. Nervous tissue is of two kinds: 1. the gray or vesicular, which
originates impulses and receives impressions, and 2. the white or
fibrous, which conveys impressions. The gray matter consists of large
granular cells of protoplasm containing nuclei, which give off many
branches or dendrites. From the under surface there usually comes one
main branch, the axis-cylinder process. These processes sometimes give
off branches and sometimes not, but they form the nerve fibers and
carry impulses away from the nerve cells. The cells of the processes
are elongated in shape, have a nucleus, and are placed end to end, with
a definite constriction between them.
Each axis-cylinder process is surrounded by a sheath called the
medullary sheath, while each nerve fiber consists of a central
axis-cylinder process surrounded by the white substance of Schwann
and enclosed in a sheath. A bundle of these fibers invested in a
fibro-areolar membrane called the neurilemma constitutes a nerve, and
of these the white matter is formed. The blood supply is brought by
minute vessels, the _vasa nervorum_.
[Illustration: FIG. 10.--Longitudinal nerve fiber (diagrammatic): _a_,
Axis-cylinder; _b_, medullary sheath; _c_, neurilemma; _d_, nucleus;
_e_, node of Ranvier. (Leroy.)]
The nerves of the cerebro-spinal system preside over animal life and
have to do with voluntary acts, while those from the sympathetic
system regulate organic life and are quite independent of the will.
Both sensory and motor nerves extend all over the body, accompanying
the arteries in a general way. The sensory nerves end on the surface
in plexuses, in end bulbs situated in the papillæ of the skin, or
in tactile corpuscles, these last occurring more especially where
there is no hair. The motor nerves end peripherally in plexuses or
by end plates. The central terminations of the motor nerves and the
terminations of sensory nerves in special organs, except where they end
in a cell, are not well understood.
Like muscles, nerves are probably never at rest, for through them the
muscles get their tone. When a nerve acts, no heat is produced and
there is no change in the nerve afterward, as there is in muscle.
Probably nerve impulse is the transmission of physical rather than
chemical changes along the fiber, the atoms of the nerve being set
in vibration and the vibrations being transmitted along its length.
Stimulation is produced by physical injury, by chemical influence, by
electricity, by heat, and the message is always referred to the nerve
termination. Thus, if the nerve at the elbow, over the “crazy bone,” is
touched, a tingling is felt in the fingers rather than at the point of
pressure. A person who has had an arm or leg amputated will frequently
speak of his fingers or toes on that side being cold, or complain of
pain in them, because the scar below the point of amputation tightens
around the nerves and pinches them.
It is through the nerves that people get in touch with the outer world
and that they judge of size, weight, etc. All careful adjustment of the
muscles is under the control of the nervous system.