Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5521_Библиотеки_им_академика_М_И_Перельмана.pdf
Chapter 3 / Body Systems
91
The sternum is the other integral portion of the bony
thorax. The sternum lies in the middle of the anterior rib
cage and is the attachment site for the true ribs via the costal cartilage. The sternum has three distinct portions: the
manubrium (man-OO-bree-um), the body, and the xiphoid
(ZAHY-foyd) process. The manubrium is the most superior
portion of the sternum and has the bony landmark called
the sternal (jugular) notch at its superior end. The body,
sometimes referred to as the breastbone, joins the manubrium at the sternal angle. The sternal notch can be seen
through the skin, but the sternal angle, which represents the
location of the aortic arch, must be palpated.
The xiphoid process is a spear-like projection at the
inferior edge of the body of the sternum. It is often used
as a starting landmark when locating hand placement for
chest compressions during CPR. The suggested placement
is approximately three finger widths superior to the xiphoid
process. Because it is sharp and can cause damage if fractured, compression or deep pressure at or near the xiphoid
process should be avoided.
Appendicular Skeleton
The appendicular skeleton, which appropriately includes
the bones of the appendages, or upper and lower extremities, contains 126 bones. This section contains all the
bones peripheral to the axial skeleton: the shoulder girdle, the upper extremities, the pelvic girdle, and the lower
extremities.
Shoulder Girdle
The shoulder girdle, sometimes called the pectoral girdle,
consists of the clavicle and the scapula (Fig. 3-28). The clavicle, also known as the collarbone, is a long bone that is frequently broken. The scapula, often called the shoulder blade,
is a flat bone with many bony landmarks that are commonly
used in healthcare. The spine on the posterior surface of
the scapula runs transversely and is easily palpated. Above
the scapular spine is the supraspinous fossa, which is a long
depression that runs the length of the spine. The large, flat
area of the scapula below the spine is an infraspinous fossa,
which is a slight depression. The acromion process at the
lateral end of the spine protrudes like a knob. It, too, can
be palpated easily as the bony point of the shoulder. Below
the acromion process, on the lateral side of the scapula is
the glenoid cavity, which cradles the head of the humerus
in a ball-and-socket joint, a shallow marking that cannot be
palpated. Medial to the glenoid cavity is the coracoid process
that points anteriorly, like a fingertip. The coracoid process
can be delicately palpated just inferior to the lateral clavicle.
Upper Extremities
The upper extremities include the bones of the arms, wrists,
and hands. There are a total of 30 bones in each upper
extremity: 3 arm bones, 8 wrist bones, and 19 hand bones
(Fig. 3-29).
The humerus is the “upper arm” bone. Anatomically
speaking, the upper arm is the arm, whereas the lower arm is
called the forearm. Healthcare professionals reference several
bony landmarks of the humerus. The head of the humerus
is the ball at the proximal end that fits into the glenoid cavity
of the scapula to form the shoulder joint. The greater and
lesser tubercles, located more laterally on the proximal end
of the humerus, provide muscle attachment sites. Between
the tubercles is the bicipital (bahy-SIP-ih-tuhl) groove, sometimes called the intertubercular groove, which is a major site
for muscle attachment. The deltoid tuberosity lies midway
down the humerus, on the lateral surface, and serves as the
attachment site for the deltoid muscle. On the distal end, the
medial and lateral epicondyles of the humerus stick out as
bumps, also for muscle attachment.
Coracoid
process
Clavicle
Acromion
Coracoid
process
Scapula
Acromion
Glenoid
cavity
Axillary
border
Infraspinous
fossa
BA
Figure 3-28. Shoulder girdle. (A) Anterior view. (B) Posterior view.
Clavicle
Supraspinous
fossa
Spine of
scapula
Vertebral
border
92 INTRODUCTION TO MASSAGE THERAPY
Head
Greater
tubercle
Bicipital groove
Lesser tubercle
Deltoid
tuberosity
Lateral
epicondyle
of humerus
Radius
Scaphoid
Carpals
Metacarpals
Figure 3-29. Bones of the wrist, arm, and shoulder girdle.
Trapezium
Trapezoid
Lunate
Triquetrium
Pisiform
Hamate
Capitate
Phalanges
Humerus
Medial
epicondyle
of humerus
Ulna
Carpals
The radius and ulna are the two bones that make up
the forearm. The radius is on the lateral side and the ulna is
more medial. An easily palpable landmark of the forearm is
the styloid process of the radius, located at the lateral, distal
end. This landmark is often used when locating the radial
pulse, which can be found just medial and slightly anterior to the styloid process of the radius. The ulna has some
major landmarks of its own. The olecranon (oh-LEK-rahnahn) process is a bony landmark of the ulna that is often
mistaken for part of the humerus. It is very easily identified
as the point of the elbow, sometimes feeling sharp, depending on the amount of subcutaneous fat in the area. The styloid process of the ulna is the bump located at the distal end,
next to the wrist, on the posterior (dorsal) surface. It is most
easily seen and palpated with the forearm in a prone position, palm down.
The wrist comprises eight carpal bones: capitate,
hamate, lunate, pisiform, scaphoid, trapezium, trapezoid,
and triquetral. The carpals are short bones that fit together
like puzzle pieces (see Fig. 3-29).
The hand is made up of five metacarpals and the phalanges (see Fig. 3-29). The metacarpals are numbered 1
through 5, with the thumb being the first and the “pinky”
being the fifth. The phalanges consist of 14 bones, with 2 in
the thumb and 3 in each of the others.
Pelvic Girdle
The pelvic girdle consists of three bones that are fused
together: the ilium (ILL-ee-um), the ischium (ISH-ee-um),
and the pubis (PYOO-bis) (Fig. 3-30). There are two major
bony landmarks on the pelvic girdle that cannot be palpated. One is the acetabulum, literally translated to “vinegar
bowl.” Created at the intersection of the three fused bones,
the acetabulum (ASS-sih-TAB-yoo-lum) is the cuplike socket
that cradles the head of the femur. Another important bony
landmark that cannot be palpated is the obturator foramen.
This is a large hole encircled by the ischium and pubis that
allows nerves and blood vessels to pass through.
The individual bones of the pelvis each have some identifiable, easily palpated landmarks. The posterior side of the
ilium has a transverse ridge called the iliac crest, just inferior
to the waist. The front of each hip has a prominent bump
called the anterior superior iliac spine, commonly known as
the “hip bone.” The ischia have the ischial tuberosities that
are sometimes called the “sit bones” because these protruding landmarks can be felt and may become uncomfortable
when one sits on a hard surface. The pubic bones are joined
anteriorly at the cartilaginous pubic symphysis. During the
late stages of pregnancy, the cartilage softens to allow the
pelvic girdle to expand for childbirth.
The male pelvis differs from the female pelvis in several
ways. From the superior view, looking down through the
pelvis, the opening within the female pelvis is circular, and
the male’s is shaped more like a heart. In the anterior view,
the female pelvis has a less significant pubic arch than the
male pelvis. The more pronounced arch in the male pelvis
narrows the entire structure compared with the female pelvis, which is wider and gives women wider hips. The sacrum
is fairly straight in the female and more curved in the male
(compare Figs. 3-30 and 3-31).
Lower Extremities
The lower extremities of the appendicular skeleton consist
of the thigh, knee, lower leg, ankle, and foot. There are a
total of 30 bones in each lower extremity (Fig. 3-32).
The femur, or thighbone, is the largest bone in the
body. Its major proximal landmarks include the head and
neck, which fit into the acetabulum to create the hip joint,
Chapter 3 / Body Systems
93
Figure 3-30. Pelvic girdle, male.
Sacrum
Sacrotuberous
ligament
Sacrospinous
ligament
Male pelvis
and the trochanters, which serve as sites for muscle attachment. The greater trochanter is the large, lateral protrusion
that is easily palpated. The lesser trochanter is the smaller
and more distal of the two, located medially, and is quite difficult to palpate. The lateral and medial epicondyles of the
femur are located at the distal end, near the knee, just above
the condyles that articulate with the tibia of the lower leg.
The patella (puh-TEL-luh), also called the “kneecap,” is a
sesamoid bone embedded in the tendon of the quadriceps
femoris muscle. The linea aspera (LIN-ee-uh ASS-per-uh) is
a protruding line found on the posterior shaft of the femur
that serves as a site for muscle attachment.
The tibia and fibula are the bones of the lower leg.
The tibia is the larger and more medial of the two and is
the weight-bearing bone. It has an anterior ridge that runs
Sacroiliac joint
Iliac crest
Ilium
Anterior superior
iliac spine
Acetabulum
Coccyx
Ischium
Pubis
vertically, a tibial tuberosity on the anterior surface of the
proximal end, and the medial malleolus (inner ankle bone)
at the distal end. The tibia is part of the knee joint, along
with the femur and the patella. The fibula is the smaller,
more lateral bone of the lower leg that does not bear weight
and is not part of the knee joint. Its landmarks are located
on the lateral aspect of the lower leg. The head of the fibula is on the proximal end, and the lateral malleolus (outer
ankle bone) is located at the distal end.
The seven tarsals that make up the ankle joint are
the calcaneus (the largest of the seven, also known as the
“heel”), talus, navicular, medial cuneiform, intermediate
cuneiform, lateral cuneiform, and cuboid.
The structure of the foot is similar to that of the hand.
The foot has five metatarsals that form the instep and the
Figure 3-31. Pelvic girdle, female.
Sacrum
Sacrotuberous
ligament
Sacrospinous
ligament
Coccyx
Female pelvis
Pubic symphysis
Iliac crest
Ilium
Acetabulum
Pubis
Ischium
94 INTRODUCTION TO MASSAGE THERAPY
Greater
trochanter
Lesser
trochanter
Femur
Patella
Lateral
epicondyle
Lateral femoral
condyle
Head
Neck
Fibula
Lateral
malleolus
Calcaneus
Cuboid
Head of femur
Medial
epicondyle
Medial femoral
condyle
Medial tibial
condyle
Tibial tuberosity
Anterior ridge
Tibia
Medial
malleolus
Talus
Navicular
Cuneiforms
Metatarsals
Phalanges
Medial
epicondyle
Medial femoral
condyle
Medial tibial
condyle
Tibia
Medial
malleolus
Talus
Navicular
Medial
cuneiform
Head of
femur
Greater
trochanter
Neck of
femur
Lesser
trochanter
Linea
aspera
Femur
Popliteal
surface
Lateral
epicondyle
Lateral
femoral
condyle
Lateral
tibial
condyle
Head
Neck
Fibula
Lateral
malleolus
Calcaneus
Cuboid
Metatarsals
Phalanges
A
B
Figure 3-32. Bones of the lower extremity. (A) Anterior view. (B) Posterior view.
ball of the foot; the metatarsal behind the “big toe” is metatarsal 1, and behind the “baby toe” is metatarsal 5. The toes
are made up of 14 phalangeal bones.
hyaline cartilage. It is firm but elastic, providing flexibility
and support and allowing smooth, efficient movement at the
joints. Examples of hyaline cartilage include the temporary
cartilage in infants and children, the costal cartilages of the
Cartilage
Cartilage is essential for bone formation early in life, and
it provides cushion and support for various body structures. The three types of cartilage are elastic, hyaline, and
fibrocartilage.
Hyaline cartilage is the most abundant in the body. It is
translucent and pearly blue, and no nerves are found within
ribs, and articular cartilage. Figure 3-33 illustrates the location of articular cartilage.
Fibrocartilage, sometimes called white fibrocartilage,
has much collagen that provides strength and structure but
little flexibility. It is found in the intervertebral discs of the
spinal column and in the temporomandibular joint (TMJ).
Elastic cartilage, also referred to as yellow cartilage, is
more opaque and flexible than the other types. It consists of
Chapter 3 / Body Systems
Synovial
membrane
Junction of
membrane
with
cartilage
Articular
cartilage
Articular
cartilage
Patella
Medial
meniscus
95
heart in the thoracic cavity, and the vertebral column protects the spinal cord. The abdominal cavity has minimal protection from bones, and it is therefore the most vulnerable
cavity of the body.
Movement
The skeleton provides the necessary leverage that the tendons and muscles use to create movement. Tendons attach
bones to muscles, muscles contract to pull the bones, and
the joints allow the neighboring bones to move in relation
to each other.
Storage
Bones serve as storage sites for several different minerals as
well as fat. Magnesium, phosphorus, sodium, and calcium
are minerals stored in the bones. Much of the body’s calcium is stored as calcium salts in the extracellular matrix of
bones. Calcium is constantly being used as a necessary component for nerve conduction, muscle contraction, and blood
clotting. The interior cavities of long bones store fat in the
form of yellow marrow. The fat serves as a thermal insulator and a source of energy.
Figure 3-33. Knee joint showing articular cartilage.
many elastin fibers within the collagen, giving strength to
flexible structures. For example, the external ear is made up
of elastic cartilage, as is the larynx.
Functions of the Skeletal
System
The skeleton provides the basic support and general shape
of the human body. Many of the bones serve as levers that
are pulled by the muscles to create movement, and because
muscles are the focus of the scope of practice for massage,
the bones are a very important part of anatomy education.
They also provide protection for organs, act as storage sites
for calcium salts, and manufacture blood cells. Bone formation, growth, and repair are processes that are responsible
for converting cartilage to bone, lengthening long bones,
and remodeling bones in response to the levels of calcium in
the blood and mechanical stresses on the bones.
Support
The calcium salts in the extracellular matrix of bones makes
them especially hard. Their hardness provides a strong internal framework for our bodies that can hold us up and firmly
anchor muscles and organs.
Protection
The hardness of bone also helps protect internal organs and
structures. For example, the ribs protect the lungs and the
Hematopoiesis
Blood cell formation, or hematopoiesis (HEM-ah-toh-pohEE-sis), is another function of the skeleton. The interior
cavities of some flat bones contain red marrow, which is a
site of RBC formation. RBCs are essential for life because
they carry the oxygen required for everything from cellular
respiration to healing. The blood cells and components of
blood are discussed in the section covering the cardiovascular system.
Bone Formation, Growth, and
Remodeling
Continuous regeneration and adjustments occur within the
bones to ensure that the skeleton can support and protect
our bodies adequately. This is an ongoing and dynamic process that begins prior to birth and continues throughout
life as our bodies are subjected to gravity and other physical stressors. The process of bone formation converts cartilage to bone. Once all of the bones have ossified, they
grow larger as we grow older. Bones undergo remodeling
to maintain the proper levels of calcium in the blood and to
change the shape of the bone in response to physical stressors. Hormones that regulate and encourage growth influence the continuous process of creating new bone. Without
calcium and vitamin D, growth will not occur.
Bone Formation
Ossification, the process by which cartilage is turned into
hardened bone, begins with osteoblast cells in the fetus.
When the fetus is only 2 or 3 months old, the osteoblasts
96 INTRODUCTION TO MASSAGE THERAPY
become active, manufacturing the matrix that surrounds
them. The matrix is rich in collagen, a fibrous white protein
that provides strength and resilience. After it is deposited,
the matrix accumulates calcium and other minerals that
contribute to the hardening of the bone tissue. Once hardened, osteoblast cells are called osteocytes, or mature bone
cells. Most of the hyaline cartilage has been transformed
into bone by the time babies are born.
Bone Growth
A small amount of hyaline cartilage remains in bones during childhood, in the epiphyseal (ee-PIH-fih-SEE-uhl) plates,
or growth zones, of long bones. Located toward the knobby end of a long bone, the epiphyseal plates are where long
bones grow longer. The hyaline cartilage acts as a model
for bone growth. The epiphyseal plate first grows wider,
and then bony matrix is deposited on the side closer to the
center of the bone. By following the hyaline model, bones
maintain their shape and proportion through the normal
growth process. Lengthening continues through the late
teenage years, and when it stops, the epiphyseal plates
solidify and become inactive. They can then be identified
on an x-ray film at the junction between the shaft (long
part) of the bone and its knobby ends as thin lines called
epiphyseal lines.
Bone Remodeling
Long bones increase in diameter as well but use the process of bone remodeling instead of the hyaline model. Bone
remodeling is a process of moving bone material from one
place to another for maintaining normal calcium levels in
the blood, for bone growth, and for strengthening bone in
response to physical stressors.
When there is not enough calcium in the blood, osteoclast cells in the bony matrix are activated by hormones to
destroy bone tissue, a process called resorption. Bone breakdown releases calcium into the blood to maintain homeostasis. Conversely, if there is too much calcium in the blood,
the body will deposit calcium salts into the bony matrix.
Bone remodeling maintains the general shape of the
bones through their course of growth. To increase the width
of long bones and to increase the overall size of bones other
than long bones, growth follows the remodeling process.
The process starts in the cavity at the center of the bone
with resorption at the cavity wall. A rest period follows, and
then bony matrix is deposited on the outside of the bone.
The process creates a thicker, wider bone.
The rate of bone formation exceeds that of bone
resorption during childhood and adolescence, allowing
bones to become larger and denser. In young and middle
adulthood, however, the rates tend to be fairly balanced. As
a person enters old age, osteoclastic (breakdown) activity
tends to exceed osteoblastic (creative) activity, resulting in
weaker bones.
Effects of Massage on the
Skeletal System
Even though massage is not intentionally used as treatment
for the bones and joint structures, they do benefit. Massage
enhances circulation of blood and lymph, thus increasing
nutrient delivery to, and waste removal from, body tissues
including the bones. The result is healthier bones and better healing of fractures and other bone injuries. Massage
increases the number of red and white blood cells in the
blood, which increases the body’s ability to deliver oxygen
to cells and fight germs. The bones house the red marrow,
which is the site for RBC production, and higher numbers of
blood cells benefit all of the tissues and organs of the body.
The joints of the body can also benefit from massage.
Regular movement of some joints can increase the production of the fluid that lubricates the joints. Also, if joint pain
is caused by excessive muscle tension or tissue adhesions
near the joint, massage therapy may be able to relieve those
conditions, thus relieving the joint pain.
Muscular System
Muscles make up almost half of an average person’s body
weight. Muscle tissue, like nervous tissue, does not reproduce as rapidly and regularly as other body tissues. Muscle
cells can get larger or smaller, and can die, but muscle tissue
is not constantly replenished. Because muscle cells have an
elongated shape, they are often referred to as muscle fibers.
Types of Muscle Tissue
Classified by structure, function, and location, there are
three types of muscle tissues: cardiac, smooth, and skeletal.
These different types of muscle tissues all share the following features:
• Contractility—the elongated muscle fibers contract
better than a square or round cell, thus creating
tension
• Excitability—the fibers are capable of a forceful
response to a nervous impulse
• Extensibility—muscles can be stretched beyond their
normal resting length
• Elasticity—after being stretched or contracted, muscles can return to their original length
Cardiac Muscle
Cardiac muscles are only found in the walls of the heart and are
responsible for pushing blood into the blood vessels. The muscle cells are striated, each cell has only one nucleus, they have
Chapter 3 / Body Systems
Intercalated discs
Nucleus
Figure 3-34. Cardiac muscle cells. (Reprinted with permission
from Cohen BJ, Wood DL. Memmler’s Structure and Function
of the Human Body. 9th ed. Philadelphia: Lippincott Williams &
Wilkins, 2009.)
a branching structure, and they contract involuntarily. Between
cardiac muscle cells are intercalated discs. They are unique to
cardiac muscle tissue and allow the electrical impulses that stimulate contraction to be conducted along the network of fibers,
creating contractions that are strong and rhythmic (Fig. 3-34).
These cardiac muscle contractions forcibly pump blood out of
the heart with a rush that can be felt, referred to as the pulse.
Smooth Muscle
Smooth muscles are found in the walls of hollow organs,
such as the stomach and intestines. They have no striations,
each cell has only one nucleus, and they contract involuntarily (Fig. 3-35). Smooth muscle contracts as nerve impulses
move from one fiber to the next, creating sequential, strong,
slow contractions. Primarily arranged in sheetlike layers in
which one runs along the length and the other encircles the
tube like a belt, the layers take turns alternating contraction and relaxation. These coordinated contractions result
in a wavelike movement called peristalsis that squeezes the
97
organ to move substances through the system, such as food
through the digestive tract. (Fig. 3-13 illustrates the layering
of smooth muscle.)
Skeletal Muscle
Skeletal muscles attach to the skeleton in most cases. Made
up of masses of muscle fibers wrapped in connective tissue organized in bundles, the muscle cells are long and
thin (Fig. 3-36). Some are almost a foot long. They are striated and each muscle fiber has more than one nucleus. The
more bundles of fibers there are, the thicker that particular
muscle is. The contraction of an entire skeletal muscle can
be fast and forceful. Contraction is controlled voluntarily,
meaning that we can consciously make skeletal muscles
contract. There are, however, nervous system reflexes that
create involuntary skeletal muscle contractions, usually in
response to a potentially dangerous situation. When you
touch a burning hot surface, reflexes will contract a series
of muscles to pull your arm away before you think about it.
In Western massage and bodywork, the best massage
therapists are, in essence, muscle specialists. Just knowing
the names of the muscles is not sufficient for a professional
massage therapist. You should also know the attachment
points of muscles, the actions of the muscles, how skeletal
muscles work on a microscopic level, as well as how they
work to create movement of the skeleton. Because skeletal
muscles are the most relevant to massage therapy, they are
the focus of this text (Fig. 3-37).
Structures of Skeletal Muscle
The structural aspect of skeletal muscle can be studied from
a microscopic, cellular level as well as an overall view of
a whole muscle. The basic muscle cell, or muscle fiber, is
made up of several different components that influence the
overall look of a whole muscle.
Nucleus
Figure 3-35. Smooth muscle cells. (Reprinted with permission
from Cohen BJ, Wood DL. Memmler’s Structure and Function
of the Human Body. 9th ed. Philadelphia: Lippincott Williams &
Wilkins, 2009.)
Nucleus
Figure 3-36. Skeletal muscle cells. (Reprinted with permission
from Cohen BJ, Wood DL. Memmler’s Structure and Function
of the Human Body. 9th ed. Philadelphia: Lippincott Williams &
Wilkins, 2000.)
98 INTRODUCTION TO MASSAGE THERAPY
Orbicularis oculi
Masseter
Sternocleidomastoid
Deltoid
Pectoralis
major
Serratus
anterior
Biceps
brachii
External
obliques
Brachioradialis
Flexor carpi
Extensor
carpi
Adductors
of thigh
Rectus
femoris
Peroneus
longus
Temporalis
Orbicularis oris
Trapezius
Intercostals
Internal oblique
Rectus abdominis
Abdominal
aponeurosis
Sartorius
Vas tus
lateralis
Vas tus
medialis
Gastrocnemius
Tibialis
anterior
Soleus
A
Figure 3-37. Skeletal muscle system. (A) Anterior.
Chapter 3 / Body Systems
99
Sternocleidomastoid
Trapezius
Teres minor
Teres major
Latissimus
dorsi
Thoracolumbar
fascia
Gluteus
maximus
Iliotibial
band
Hamstring group:
Biceps femoris
Semitendinosus
Semimembranosus
Gastrocnemius
Deltoid
Triceps brachii
Achilles tendon
B
Figure 3-37. (continued ) (B) Posterior.
Peroneus longus
100 INTRODUCTION TO MASSAGE THERAPY
Splenius capitis
Sternocleidomastoid
Platysma
Trapezius
Biceps brachii
Brachialis
Triceps brachii
Serratus anterior
Rectus abdominus
External oblique
Tensor fascia latae
Rectus femoris
Vastus lateralis
Iliotibial band
Deltoid
Teres major
Latissimus dorsi
Thoracolumbar
fascia
Gluteus medius
Gluteus maximus
Biceps femoris
Tibialis anterior
Extensor digitorum
longus
C
Figure 3-37. (continued ) (C) Side view.
Microscopic Structures of a Skeletal
Muscle Cell
The microscopic anatomy and physiology of skeletal muscle
cells illustrates how they create movement. Muscle cells consist of a bundle of myofibrils, also called fibrils, encased in a
plasma membrane called the sarcolemma (SAHR-koh-LEMmuh). The myofibrils are made of thick myofilaments called
myosin (MAHY-oh-sin) and thin myofilaments called actin.
Because bunches of dark myosin filaments alternate with
Gastrocnemius
Peroneus longus
Soleus
bunches of light actin filaments, the muscle fibers appear to
have shaded bands, or stripes, which is why they are called
striated muscle tissue. Multiple chains of these bands, called
sarcomeres (SAHR-koh-meerz), are the contractile units of
the muscle fiber.
Sliding Filament Theory
Although it has not been proven, the sliding filament mechanism is a widely accepted theory of how muscle contraction occurs. This theory suggests that the actin and myosin