Download Skeleton and muscles

Skeleton and muscles
Support and movement
• The skeleton is mainly used to support the body, but does a lot of
other things as well
• Including movement, protection, and making blood
• The muscles are used for movement including both voluntary in
involuntary movement
• Skeleton and muscles work together and so are usually grouped into
one system called the skeletomusculatory system
Dry bones
• There are 4 basic bone categories in humans
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Irregular bones (pelvis or coccyx)
Flat bones (skull, scapula, ribs)
Short bones (carpals, metacarpals, vertebrae)
Long bones (femur, tibia, humorous)
• All bones are made of cells called osteocytes
• An adult human has 206 bones
• A human baby has about 300 bones
• Where do the 94 extra bones go?
Case of the disappearing bones
• Bones are not necessarily perfectly solid
• In adults, the ends of many bones (particularly in joints) are made of
cartilage
• Cartilage: dense connective tissue that cushions the bones and reduces
friction.
• This makes it easier to move and helps protect the bones
• When cartilage is lost from the bones it causes a condition called arthritis
• A baby has more bones made of cartilage than osteocytes
• Over time, the cartilage “bones” will be replaced with osteocytes and
will eventually fuse together
• Why would a baby have bones made of cartilage?
To protect and support
• Bones help protect our organs and support our bodies
so we can stand upright
• Babies bodies cannot stand upright yet and so
support becomes less important than protection
• Babies fall a lot and cannot protect themselves from
danger
• Cartilage is dense enough to protect the baby’s organs, but
flexible enough to not break when the baby falls – babies
“bounce”
• Babies also grow very quickly while bones grow slowly.
Cartilage can grow at the same speed as a baby or child
• Humans complete bone development around 25
Parts of a bone
• Bones in humans are NOT solid
• They have 4 layers
• Outer covering: thin layer of blood vessels that carry nutrients and waste to
and from the bone cells as well as nerves.
• Why nerves on bones?
• Compact bone: thick hard layer that provides most of the support
• Spongy bone: Soft bone layer with lots of holes that allows some flexibility
and makes the bones lighter.
• Why do bones need to be flexible and light?
• Marrow: hollow area at the center filled with a reddish jelly that makes red
and white blood cells and platelets. Mostly found in the long bones (arms and
legs)
Movement
• Since bones are rigid, movement can only happen at a break in the
skeleton at the joints
• Joint: area where bones meet
• Some are fixed joints (unable to move like the skull)
• Some are movable
• There are 4 types of movable joints
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Ball and socket: allows movement in any direction (hips, shoulders)
Hinge: move back and forth and specific direction (knee, elbow, knuckle)
Pivot: rolls or rotates (top of neck)
Gliding: slides in several directions (wrist, ankle)
The leg bone is CONNECTED to the…
• Even at joints, bones are still
connected to each other
• Bones at movable joints are held
together with dense bands of
connective tissue called ligaments
• Ligaments are able to bend and stretch
some to allow movement but still hold
the bones together
• If a ligament is stretched too far, it is
called a sprain
• Bones at fixed joints are fused
together in what is called a suture
Muscles move me
• There are over 600 different muscles
in the human body
• All do some form of movement
• This movement can be voluntary
• You think about it and decide to do it
• This movement can be involuntary
• It happens without you being aware of it
Three types
• There are 3 basic types of muscles
• Skeletal: attached to skeleton and skin on the face to allow voluntary
movement and some involuntary (reflexes)
• Long muscle cells are bundled into fibers which are bundled into muscles
• Looks striped (striated)
• Smooth: lines digestive tract and blood vessels to help move materials
through your body through involuntary motion
• Made of small muscle cells connected directly to each other
• Cardiac: found only in the heart to strongly constrict to pump blood
involuntary throughout the body
• Striated but not in fiber bundles
• Your fingers and toes have no muscles, so how do they move?
Muscle-bone connection
• Skeletal muscles must be attached to bones to allow movement
• They are attached using tendons
• Tendons are dense connective tissues that are pulled by the muscles and in
turn pull the bones
• They allow movement in your fingers and toes where there are no muscles
• Why are there no muscles in your fingers or toes?
I like to move it, move it, move it
• Muscles can only pull so they must work in pairs
• For every muscle that pulls in one direction, there is another muscle
that pulls in the opposite direction
• A muscle the bends a joint is the flexor
• On the opposite side is a muscle that pulls the joint straight, the
extensor
Express yourself
• While most skeletal muscles are attached to
bones, some are attached to skin as well
• Mostly on the face (42 facial muscles)
• This allows us to move the skin on our faces so we
can have expressions
• Humans have about 21 distinct expressions and
hundreds of variations