Download unit 4. bones and muscles

UNIT 4. BONES AND MUSCLES
1. Skeletal System
1. Functions of the Skeletal
System
The cervical vertebrae make up the neck.
You have 7 of these and the top one is
connected to the base of the skull. They let
you bend, tilt and turn your head.
The skeletal system has five main functions:
9 It provides shape and support
9 It enables you to move
9 It protects your internal organs
You have 12 thoracic vertebrae. The ribs
are attached to these. They don´t move
much, so that your heart and lungs won`t get
squashed.
9 It produces blood cells
9 It stores certain materials until your body
needs them
Your skeleton determines the shape of your body.
The backbone, vertebral column or spine, is the
center of the skeleton. It consists of 26 small bones
called vertebrae (singular vertebra) that provide
axial support to the thrunk. Your vertebrae are
flexible and able to bend. This fact allow you to bend
or twist. If your backbone were just one bone, you
would not be able to bend or twist. The backbone
also provides protection to the spinal cord, which
runs through its central cavity. The backbone has
five different sections (look at the picture).
You have 5 lumbar vertebrae. They allow
twisting and turning.
The sacrum is the triangular shaped bone
located near the base of the spine.
The coccyx. It does nothing now, but it used
to be a tail.
The intervertebral disks are soft tissues
(cartilage) that sit between each vertebrae and
act as cushions between vertebrae, and absorb
energy while the backbone flexes, extends, and
twists.
The atlas is the first vertebra. The skull
balances on it. The atlas sits on a peg on the
second vertebra, the axis. The atlas can rotate
on the peg, letting you turn your head.
Skull (cranium): it is the bony framework of the head. It protects the brain.
Axial skeleton: consists of
bones that forms the axis of the
body and support and protect
the organs of the head, neck
and thrunk.
Sternum (breastbone): it is a long and flat bone , located in the middle of
the chest. With the ribs, the sternum forms the rib cage that protects the
heart, lungs, and the major blood vessels from damage.
Ribs: they are thin, flat and curved bones that form a protective cage
around the organs in the upper body. They are 12 pairs. Floating ribs are
the last two ribs and are smaller.
Vertebral column: the central axis determining shape of your body. All
the bones of your body are in some way connected to your vertebral
column.
The arm: region between the shoulder and the
elbow. It consists of a single long bone: the
humerus.
HUMAN BODY SKELETON
Upper Extremities
The forearm: region between the elbow and the
wrist. It is formed by two bones: radius and ulna.
The hand: three regions: wrist (carpal bones),
palm (metacarpals bones) and fingers
(phalanges).
Appendicular skeleton: it is
composed of bones that hold
the appendages to the axial
skeleton.
The thigh: region between the hip and the knee. It
consists of a single long bone: the femur (longest
and strongest bone in the body).
Lower Extremities
The leg: region between the knee and the ankle. It
is formed by two bones: tibia and fibula.
The foot: tarsals (ankle), metatarsals and
phalanges.
The patella (the kneecap): triangular bone
between the femur and the tibia.
Appendicular skeleton:
Clavicle (collarbone): this bone connects the upper arm to the thrunk of the
body.
Scapula (shoulder blade): large, triangular, flat bone on the back side of
the rib cage. It serves as an attachment point for several muscles.
Pelvic girdle (hip girdle / pelvis): it consists of coxal bones and sacrum.
HUMAN BODY SKELETON
Coxal bones
HUMAN BODY SKELETON
Bones in the hand
Phalanges
Metacarpals
Carpals
Bones in the foot
Phalanges
Metatarsals
Tarsals
THE SKULL BONES
Cranial bones: they make up the protective frame around the brain.
9 Frontal: it forms the forehead and the upper orbit of the eye and the
forward parts of the cranium.
9 Parietal: there are two parietal bones which form the largest portion of the
top and sides of the cranium.
9 Temporal: like the parietal bones, there are two distinct temporal bones.
They form the lower, central sides of the skull around the external ear.
9 Occipital: it forms the back base of the skull. Many neck muscles attach
here.
9 Sphenoid: there are two sphenoid bones and they sit behind the eyes
and run back towards the temporal bones.
9 Ethmoid: it forms medial portions of the orbits and the roof of the nasal
cavity.
Facial bones: they make up the upper and lower jaw and other facial
structures.
9 Mandible: it is the lower jaw. It is the only moveable bone in the skull. It
articulates with the temporal.
9Maxilla: there are two maxillae bones. They are the upper jaw and form
part of the nose, orbits and the roof of the mouth.
9 Nasal: the nasal bones are a pair of small, slender bones that support the
bridge of the nose. They are fused at the top of the frontal bone and to the
maxillae at the area that completes the inside orbit of the eye.
9 Lacrimal: there are two small lacrimal bones that sit at the inside corner
of each eye.
9 Zygomatic: there are two zygomatic bones and they sit on either side of
the skull and comprise the higher area of the cheek.
A side view of the skull
The bones of the skull are not joined
firmly at birth. The sutures gradually
accumulate minerals and harden
(ossification), firmly joining the skull bones
together. In an infant, the spaces where
sutures intersect but don’t completely
touch are called fontanels / fontanelles
and they are covered by a fibrous
membrane. By the time the child reaches
2 years of age, these fontanels have been
gradually covered to bone.
2. The structure of bones
Cross-section of bone
In a human body, a living bone is made up of different
layers:
9 Periosteum: a thin membrane covering bone surface.
It’s like the skin of bones. This membrane is full of blood
vessels and nerves that supply the cells of the hard compact
bone.
9 Compact bone: it is very dense and rigid being packed
with calcium and other minerals. Inside the compact bone
there is small holes (bone cells) and canals. These canals
carry blood vessels (which supply the bone with nutrients
and oxygen) and nerves from the bone’s surface to the
living cells within the bone.
9 Spongy bone: just inside the compact bone is a layer of
spongy bone. It is also found at the ends of the bone. It has
many small spaces within it. Spongy bone is lightweight but
strong.
9 Bone marrow: The spaces in bone contain a soft
connective tissue called marrow. There are two types of
marrow: red and yellow. Red bone marrow produces the
body’s blood cells, which fight infection, carry oxygen or stop
bleeding. As a child, most of your bones contained red bone
marrow. As a teenager, only the ends of your femurs, skull,
hip bones and sternum contain red marrow. Your other
bones contain yellow marrow, that stores fat and serves as
an energy reserve.
Canals
Bone cells organized
around canals
Spongy bone
Compact bone
Periosteum
Blood vessels
Spongy bone
Compact bone
Yellow marrow
Red marrow
Blood vessels
Periosteum
3. How bones form
Bone is formed in a cartilage model. As a child, much of your skeleton was cartilage. Over time, most of the cartilage is replaced with bone. This
process of replacement is usually complete by the time you stop growing. Finally, your bones only have cartilage at the end part of them.
X-rays of the hands of a 1-year-old (A) and 3-year-old (B)
show that the cartilage in the wrist has not yet been
replaced by bone. In the X-ray of the 13-year-old’s hand
(C), the replacement of cartilage by bone is almost
complete.
4. Joints of the skeleton
Body movements are carried out by the
interaction of the muscular and skeletal
systems.
9 Muscles are connected to bones by
tendons.
9 Bones are connected to each other
by ligaments.
9 Cartilage forms cushions between
bones to stop them rubbing.
9 Where bones meet one another is
typically called a joint (the union of two
or more bones).
Ball-and-socket
joint: this type of
joint allows the
greatest range of
motion. In your
shoulder, the top
of the arm bone
fits into the deep,
bowl-like socket of
the scapula. The
joint allows you to
swing your arm
freely in a circle.
Your hips also
have this type of
joint.
Pivot joint: this type of
joint allows one bone to
rotate around another.
The pivot joint in the top
of your neck gives you
limited ability to turn
your head from side to
side.
Gliding joint: this type of joint
allows one bone to slide over
another. Wrist and ankles
have gliding joints.
Hinge joint: this type of
joint allows extensive
forward and backward
motion but not side to
side. Knee and elbow
have hinge joint
Movable joints
2. Muscular System
1. Muscle action
Muscles make up about 35 – 40% of
the human body weight. There are
about 600 muscles in your body.
Muscles in your body can be divided
into two general groups:
9 Voluntary muscles: they allow us
to walk, to smile, to play football.
They allow keep your body stable
when we are sitting and standing. Our
brain sends messages to the muscle
when we conciously decide that we
want the muscle to contract.
9 Involuntary
muscles:
their
contraction is not under our conscious
control. These muscles are normally
found in the walls of our internal
organs. They are responsible for
activities such as breathing and
digesting food.
2. Types of muscles
There are three types of muscle tissue in your body:
9 Skeletal muscle: they are attached to the bones of your skeleton (by tendons) for voluntary movement. This kind
of muscle is commonly called striated muscle because the skeletal muscle cells appear banded or striated. It
contains alternating light and dark bands (striations). These striations are caused by the overlapping of the
contractile proteins: actin and myosin. This kind of muscle has two important characteristics: they react very quickly
and they tire very quickly too.
9 Smooth muscle: This kind of muscle is found in the walls of internal organs like the stomach or blood vessels.
Their contraction is not under conscious control so it is an involuntary muscle. They are not striated muscles. Unlike
skeletal muscles, they react more slowly and tire more slowly too.
9 Cardiac muscle: this kind of muscle is only found in the heart. Like skeletal muscle cells, cardiac muscle cells
contain striations. It is an involuntary muscle. However, unlike skeletal muscles, cardiac muscle does not get tired. It
can contract repeatdly. It maintains a consistent heart rate.
MAJOR MUSCLES IN YOUR BODY
Sternocleidomastoid: long muscle in the neck that rotates the neck and
flex the head.
Deltoids (shoulder muscles): they move the upper arm.
Trapezius: a flat, triangular muscle that covers the back of the neck
shoulders and thorax. It elevates and rotates scapula.
Pectoral: flexes and adducts arm across chest, pulls shoulders forward.
Biceps (brachii): flexes forearm at the elbow.
Triceps (brachii): it adducts the arm.
Rectus abdominis: a large muscle in the front of the abdomen that
assists in the regular breathing movement and supports the muscles of
the spine while lifting and keeping abdominal organs such as the
intestines in place.
Sartorius: it flexes hip and knee.
Rectus femoris: it extends knee and flexes hip.
Gluteus maximus: powerful extensor of hip.
Femoral biceps: it flexes the knee and rotates the leg laterally.
Gastrocnemius (calf): the muscle in the back part of the leg that forms
the greater part of the calf. It is responsible for the plantar flexion of the
foot.
MUSCLES OF THE FACE AND HEAD
Temporalis: it acts to raise the mandible and close the
jaws.
Occipital frontal: it raises the eyebrows.
Compressor nasi: it constrics the nostrils.
Levator labii superioris: it elevates the upper lip.
3. Muscles at work
Like other skeletal muscles, the muscles in
your arm do their work by contracting, or
becoming shorter and thicker. Muscle cells
contract when they receives messages from
the nervous system.
Because muscle cells can only contract,
not extend, skeletal muscles must work in
pairs. While one muscle contracts, the
other muscle in the pair returns to its
original length.
Figure shows the muscle action involved in
moving the lower arm. First, the biceps muscle
on the front of the upper arm contracts to
bend the elbow, lifting the forearm and hand.
As the biceps contracts, the triceps on the
back of the upper arm returns to its original
length. Then to straighten the elbow, the
triceps muscle contracts. As the triceps
contracts to extend the arm, the biceps returns
to its original length. Another example of
muscles that work in pairs are those in your
thigh that bend and straighten the knee joint.