Skeletal System

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					             Skeletal System
The skeletal system consists of 206
 bones as well as connective tissues
What two connective tissues belong to
 the skeletal system?
Ligaments and cartilage

At birth humans have 270 bones but
 many bones fuse together during
Skull and spinal cord

The skeletal system has two main
The axial skeleton –
The appendicular skeleton -

Skeletal system functions
1. support
2. storage
3. produces blood cells
4. protection
Bone structure
Spongy bone and compact bone
Compact bone contains Haversion canals
 which contain blood vessels

Why would there need to be blood
 vessels in bones?
Osteocytes (bone cells) – need

Central cavity contains yellow marrow
 which stores fat

Spongy bones contains red marrow in
 certain parts
Red marrow is where red blood cells and
 white blood cells are manufactured

Development of Bones
The second month of development bone
 starts to form where before the embryo
 had only a cartilage skeleton. The
 process of cartilage turning into bone is
 called ossification.

Growth takes place at both ends of the
-these regions are called the epiphyseal

An epiphyseal plate is a layer of
 cartilage that contains cells that undergo

Divisions of these cells cause the
 cartilage to grow and the bones to
 lengthen as the bone cells ossify.
 Growth stops when these cells stop
 dividing. Although bones continue to
 grow in width throughout life growth in
 length stops at 25 if not sooner.
The point where bones meet is a joint
 movable and immovable
Where are immovable joints?

Four major types of joints:
1. Hinge – elbow, knee, and ankle
2. Pivot – neck
3. Ball-and-socket – hip and shoulder
4. Gliding – carpal and tarsal bones

Cartilage and a special lubricant called
 synovial fluid keep joints moving

Ligaments join together bones at a joint

A stretch or tear of a ligament is called a

Arthritis – when joints become swollen or
Rheumatoid arthritis in which cartilage
becomes inflamed and enlarged.
Eventually it is replaced by bone, which
fuses and prevents movement.

Osteoarthritis is when cartilage wears
 away and bones rub together.

Osteoporosis as one gets older one may
 lose bone density
           The Muscle System

The body has more than 600 muscles
 (35-45% of body weight)

Functions of Muscle System
1. Movement – main function
2. Protection of internal organs
3. Sitting and standing

Muscle types
1. Skeletal muscles –
   move bones attached directly to bones
 or attached indirectly to bone by a
2. Smooth muscles -
   digestive, respiratory, and circulatory
 system organs, involuntary

3. Cardiac muscle –
   found only in the heart, involuntary
Muscle movement
Muscles can only contract and relax

When a skeletal muscle contracts, it
 creates a pulling (not a pushing) action
 that results in movement, so for this
 reason, muscles act in pairs.

Flexor – muscle that bends the joint
Extensor – muscle that straightens the

Most muscles are attached to 2 bones
Insertion – the point at which the muscle
 is attached to the moving bone
Origin – serves as an anchor
Between these two points is the joint
Bicep                  Tricep
Origin – shoulder      Origin – humerus
Insertion – radius     Insertion – ulna
When the bicep         When the tricep
 contracts, the         contracts, the
 forearm is drawn       arm straightens
 toward the shoulder

How muscles contract
1. A nerve impulse transmitted to the
 muscle cell by a nerve.
2. The nerve releases Calcium into the
3. Calcium attaches to molecules called
 actin (protein)
4. ATP bins to myosin (protein)
   What does ATP do?
5. Using the energy from the ATP the
 myosin pulls on the actin which causes
 the muscle to contract.
6. When the message from the brain
 ends the Calcium leaves and the muscle

With aerobic exercise, chest muscles can
 be strengthened so that more air enters
 the body.
Why would this help?
Resistance exercise such as weight lifting
 increase muscle size and strength but it
 does not increase the amount of oxygen
 that enters the body

Anabolic steroids increase the size and
 strength of your muscles, synthetic
 chemicals (that resemble testosterone)
 trick your muscles into growing larger.
 They also cause many irreversible side
 effects including cancer, heart disease,
 and altered sexual development.
Muscle Problems
Shin splints – inflammation of the tendons
 on the inside front of the lower leg,
 muscle strain, overuse, compartment

Muscle Cramps – occurs when a muscle
 cannot relax

Muscular dystrophy – muscle tissue
 degenerates and is replaced by fatty

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