Download The Skeletal System

1
For the week of 9thMay, 2011
 All the work is due on Friday,13th May, 2011
 For the diagrams, please refer your text book.
The Skeletal System
The human skeleton is composed of a type of connective tissue called
bone. Bones and other connective tissues, such as cartilage and ligaments,
form the skeletal system.
The Skeleton
Functions of the skeletonThe skeleton supports the body, protects internal organs, provides for
movement, stores mineral reserves, and provides a site for blood cell
formation.
1. Bones The bones that make up the skeletal system support and
shape the body.
 Bones protect the internal organs of the body.
 They provide a system of levers on which muscles act to
produce movement. Levers are rigid rods that can be
moved about a fixed point.
 Bones contain reserves of minerals, mainly calcium salts,
that are important to many body processes
 Bones are the site of blood cell formation. Blood cells are
produced in the soft marrow tissue that fills the internal
cavities in some bones.
 There are 206 bones in the adult human skeleton.
 Bones can be divided into axial skeleton ( it consists of
the skull, the vertebral column, and the rib cage) and
appendicular skeleton ( bones of arms and legs, along with
the bones of the pelvis and shoulder area)
Structure of BonesBones are solid network of living cells and protein fibres that are
surrounded by deposits of calcium salts. The bone is made up of the
following parts:
 Periosteum-The bone is surrounded by a tough layer of connective
tissue called the periosteum. Blood vessels that pass through the
periosteum carry oxygen and nutrients to the bone.
 Compact bone- Beneath the periosteum is a thick layer of compact
bone. This bone is dense but not very solid. Running through
2
compact bone is a network of tubes called Haversian canals that
contain blood vessels and nerves.
 Osteocytes- They are mature bone cells and are embedded in the
bone matrix. Two other kinds of bone cells – osteoclasts and
osteoblasts line the Haversian canals and the surface of the bony
and spongy bone. Osteoclasts breakdown the bone and osteobalsts
make the bone.
 Spongy bone- Spongy bone is a less dense tissue found inside the
outer layer of compact bone. It is found in the ends of long bones
and in the middle part of short, flat bones. It is a very strong bone.
The latticework structure of the spongy bone helps to add
strength to bone without adding mass.
 Bone marrow- Within bones are cavities that contain a soft tissue
called bone marrow. There are two types of bone marrow- yellow
and red. Yellow marrow is made up primarily of fat cells. Red
marrow produces red blood cells, some kind of white blood cells and
cell fragments called platelets.
DEVELOPMENT OF BONESThe skeleton of an embryo is composed almost entirely of a type of
connective tissue called cartilage. Unlike bone, cartilage does not contain
blood vessels. Cartilage cells rely on diffusion of nutrients from the tiny
blood vessels in surrounding tissues. Because cartilage is dense and
fibrous, it can support weight, despite its extreme flexibility.
Cartilage is replaced by bone during a process of bone formation called
ossification.
TYPES OF JOINTS
A place where one bone attaches to another bone is called a joint.
Depending on its type of movement, a joint is classified as immovable,
slightly movable, or freely movable.
 Immovable Joints- They allow no movement. The bones are
interlocked and held together by connective tissue or they are
fused. For example- the bones of the skull.
 Slightly Movable joints – They permit a small amount of restricted
movement. The bones are separated from each other. For exampleThe joints between the two bones of the lower legs and the joints
between the adjacent vertebrae.
 Freely Movable Joints – They permit movement in one or more
directions. They are grouped according to the shapes of the
surfaces of the adjacent bones. For example- ball-and-socket
joints permit movement in many directions; Hinge joints permit
3
back and forth motion, like the opening and closing of a door; Pivot
joints allow one to slide in two directions.
STRUCTURES OF JOINTS
The joint capsule consists of two layers. One layer forms strips of
tough connective tissue called ligaments which are attached to the
membranes that surround bones. Cells in the other layer of the
joint capsule produce a substance called synovial fluid. Synovial
fluid enables the surfaces of the joint to slide over each other
smoothly.
THE MUSCULAR SYSTEM
The main function of muscular system is movement.
Types of muscle tissue
There are three types of muscle tissue: skeletal, smooth, and cardiac.
Skeletal Muscles
Skeletal muscles are usually attached to bones. Skeletal muscles are
responsible for voluntary movements. They are controlled by the central
nervous system. Skeletal muscle cells are large, have many nuclei. And
vary in length from 1 mm to about 30 cms. Complete skeletal muscles
consist of muscle fibres, connective tissues, blood vessels and nerves.
Smooth Muscles
Smooth muscles are usually not under voluntary control. A smooth muscle
cell is spindle- shaped, has one nucleus, and is not striated. They are
found in the walls of hollow structures such as the stomach, blood vessels
and intestines. Most smooth muscle cells can function without nervous
stimulation. They are connected to one another by gap junctions that
allow electrical impulses to travel directly from one muscle cell to a
neighbouring muscle cell.
Cardiac Muscle
Cardiac muscles are found only in the heart. It is striated like skeletal
muscle, although its cells are smaller. It is like smooth muscle because it
is normally not under the direct control of the central nervous system
and cardiac cells are connected to their neighbours by gap junctions.
Muscle Contraction
The muscle fibres in skeletal muscles are composed of smaller structures
called myofibrils which in turn are made up of filaments. The striations in
skeletal muscle cells are formed by thick filaments- myosin and thin
filaments made of protein actin. The filaments are arranged in units
called sacromeres, which are separated from each other by regions called
Z lines.
4
A muscle contracts when the thin filaments in the muscle fibre slide over
the thick filaments. This process is called the sliding filament model of
muscle contraction.
For a muscle to contract, the thick myosin filament must form a crossbridge with the thin actin filament. As the cross-bridge changes shape, it
pulls on the actin filament, which slides toward the centre of the
sacromere. The distance between the Z lines decreases. The crossbridge detaches from the actin filament. The cycle is repeated when the
myosin binds to another site on the actin filament.
When hundreds of thousands of myosin cross- bridges change shape in a
fraction of a second, the muscle fibre shortens with considerable force.
This energy is supplied by ATP.
Control of Muscle Contraction
Motor neuron and central nervous system are connected at neuromuscular
junction. Vesicles or pockets, in the axon terminals of the motor neuron
release a neurotransmitter called acetylcholine. Acetylcholine molecules
diffuse across the synapse, producing an impulse in the cell membrane of
the muscle fibre. The impulse causes the release of calcium ions (Ca2+)
within the fibre. The calcium ions affect regulatory proteins that allow
actin and myosin filaments to interact. From the time a nerve impulse
reaches a muscle cell, it is only a few milliseconds before these events
occur and the muscle cell contracts.
A muscle cell remains contracted until the release of acetylcholine stops
and an enzyme produced at the axon terminal destroys any remaining
acetylcholine. Then, the cell pumps calcium ions back into storage, the
cross-bridges stop forming, and the contraction ends.
Muscle and Bone interaction
Skeletal muscles are joined to bones by tough connective tissues called
tendons. Tendons are attached in such a way that they pull on the bones
and make them work like levers. The joint functions as a fulcrum- the
fixed point around which the levers move. The muscle provides the force
to move the lever.
Most skeletal muscles work in opposing pairs. When one muscle contracts ,
the other relaxes. For controlled movement, however, contraction of both
the muscles is required.
Regular exercise is important in maintaining muscular strength and
flexibility.
THE INTEGUMENTARY SYSTEM
The Skin-
5
The integumentary system serves as a barrier against infection and injury,
helps to regulate body temperature, removes waste products from the
body, and provides protection against ultra violet radiation from the sun.
The skin is made up of two main layers- the epidermis and the dermis.
Beneath the dermis is a subcutaneous layer of fat (the hypodermis) and
loose connective tissue that help insulate the body.
Epidermis- It is the outermost layer which also has two layers- the outer
epidermis is made up of dead cells and the inner epidermis is made up of
living cells. Cells in the inner layer undergo rapid cell division, producing
new cells that push older cells to the surface of the skin. As they move
upward , the older cell become flattened and their organelles
distintegrate. They also begin making keratin, a tough fibrous protein.
Later on these keratin producing cells die and form a waterproof coating.
The epidermis also has melanocytes which are the cells which produce
melanin. The main function of melanin is to protect the body from the
harmful ultra violet radiations.
Epidermis lack blood vessels.
Dermis- is the inner layer. It contains collagen fibres, blood vessels,
nerve endings, glands, sensory receptors, smooth muscles and hair
follicles. The dermis contains two major glands – sweat glands and
sebaceous glands which help in maintaining the homeostasis in the body.
Skin Cancer- An excessive exposure to the ultra violet radiation in
sunlight can produce skin cancer, an abnormal growth of cells in the skin.
Hair and NailsHair- hair has important functions. They are made up of keratin. The hair
on the head protects the scalp from ultraviolet light from the sun and
provides insulation from the cold.
Class work questions:
Page 936, Q1, Q2, Q3, Q4, Q5, Q6
Page 939, Reviewing Content: Q1-Q10
Home work questions:
Total points : 20
1. List the different functions of the skeletal system.
2. Describe the structure of a typical bone.
3. What is a joint? List the three types of joints.
4. How does compact bone differs from the spongy bone?
5. Why do you think the amount of cartilage decreases and the mount
of bone increases as a person develops?
6
6. List the three types of muscle tissue and explain the function of
each.
7. Explain how a muscle contracts.
8. Describe the importance of regular exercise.
9. If a muscle cell receives a second stimulus while it is contracting,
will it respond to the second stimulus? Explain.
10. Osteoporosis is a disease that usually occurs in older women. It
involves a los and weakening of bone tissue. Doctors recommend
that all women eat more calcium rich foods. How might this be
helpful in preventing osteoporosis?
Critical thinking Questions
Total Points : 15
1. Suppose you want to build a robotic arm that works the same
way the human elbow works. Describe or sketch three facts
about the elbow that you could use in your planning.
2. Assume you have a habit of leaning on your elbow while
reading. One day, you notice that you have developed a
painful swelling on your elbow. Formulate a hypothesis to
explain what might have caused it.
3. How does a skeletal disorder, such as arthritis, affect the
functioning of the body as a whole?
Project :
Total points:20
Although exercising can increase your strength and endurance,
over exercising can have some adverse effects on the body. Use
resources in the library or on the internet to find out what these
adverse effects are. Summarize your findings in a paragraph.
(It is compulsary to use at least two print resources)