Chapter 36 The Skeleton & Muscle

Support – Bones of the skeleton provide a rigid frame that holds the body upright. Protection – The skull protects the brain, the vertebrae protect the spinal cord. Movement – Bones provide a system of rigid levers against with muscles can pull. Shape – The shape of the body is determined to a large extent by the skeleton. Manufacture of blood components – Bone marrow makes red blood cells, white blood cells & platelets. Structure of the Human Skeleton Human skeleton has 213 bones Divided into: Axial Skeleton – consists of skull, spine, ribs & sternum Appendicular skeleton – composed of limbs (arms & legs), pectoral girdle (shoulder) and pelvic girdle (hip) Functions of the Skeleton

Parts of Axial Skeleton 1.Skull (cranium) consists of 20 bones fused together. 2.Spine Made up of 33 bones called vertebrae. Divided up into 5 regions. The top 24 vertebrae can move slightly and are held together by ligaments. In between the vertebrae are discs of cartilage. These discs act as shock absorbers.

Last 9 vertebrae are fused together No discs between them They are not capable of any movement. Rib Cage Consists of the sternum (breast bone) and 12 pairs of ribs. All the ribs are attached to the vertebrae of spinal cord.

The top 7 pairs of ribs called True Ribs are attached to the breastbone at the front of the body. The next three ribs (numbers 8,9,10) are attached to each other at the front of the body by cartilage. These are called false ribs. The bottom two ribs called floating ribs are only attached to the spine and do not attach to anything at the front of the body. Called floating ribs

Parts of Appendicular Skeleton

Limbs The arms & legs have a similar design pattern. Each limb ends in five digits (fingers or toes). They are called pentadactyl limbs.

Cartilage Cartilage consists of a firm but flexible fibrous protein called collagen. Cartilage does not have blood vessels or nerves. It relies on diffusion for transport. This is why cartilage is slower to heal than bone. Cartilage is found in the pinna of the ear, the nose, trachea and discs between the vertebrae. Cartilage also covers the end of bones.

Function of Cartilage Cartilage protects bones. a)acting as a shock absorber b)Allows friction free movement between bones.

Structure of long bones External Structure Enclosed by a membrane called the periosteum. The periosteum contains blood vessels and nerves. The long shaft of the bone is the Diaphysis and the head of the bone is called The epiphysis.

Internal Structure of Bone There are three types of bone 1.Compact bone 2.Spongy bone 3.Bone marrow

1.Compact Bone Made of bone cells (called osteoblasts) Embedded in a matrix composed of 70% inorganic (non living) salts such as calcium phosphate and 30% protein (called collagen). The bone cells and the protein are both organic (living) material. Bone cells are supplied with nutrients by blood vessels. Nerve fibres also run through the bone. Compact bone is normally found in the shaft (diaphysis) of a bone. Also found located as a layer around the ends of a bone.

Function of compact bone Compact bone (calcium salts) gives a bone strength. The protein in the compact bone gives the bone flexibility. Spongy Bone Spongy bone is like compact bone that contains numerous hollows. Spongy bone consists of a network of thin, bony bars separated by Different sized spaces. The spaces are filled with red bone marrow that produces blood cells. Spongy bone is found mostly in the ends of bones.

Function of Spongy Bone Gives strength and rigidity to the bones. Bone Marrow Soft fatty substance found in the medullary cavity and within spongy bone. Red bone marrow makes blood components e.g. red blood cells, white blood cells and platelets. In young people bone marrow is full of active red marrow. In adults active marrow is confined to the spongy bone. The medullary cavity of adult bones contains inactive yellow fat rich marrow.

Bone Growth Embryonic cartilage begins to be replaced by cartilage around the 8 th week development in the uterus. Bone forming cells called osteoblasts produce the protein collagen. A hard compound (mainly calcium phosphate) Forms around the collagen fibres. The osteoblasts become Trapped in this hard Compound & become Dormant bone cells.

Growth Plate The increase in length of a bone is due to a growth plate made of cartilage. The growth plate is found between the epiphysis and diaphysis of the bone. Cartilage is continually formed and turned into bone (ossified) in the growth plate. The growth plate ceases to function when a person becomes an adult.

The inactivation of the growth plate stops the adult growing taller. Bone Development Throughout life bone is being dissolved & replaced. The restructuring of bone involves bone material being removed from the interior of the medullary cavity and extra bone material being deposited on the outside of the bone.