Skeletal & Muscular System

• The skeletal system is the body's internal framework of bones and a few cartilages.
• An adult human has 206 bones plus some cartilages.
• A baby is born with more bones; many fuse during growth to give 206 in the adult.
• Functions: support and shape, protection of soft organs, and movement with muscles.
• Bones store calcium as a mineral reserve.
• The bone marrow inside some bones makes blood cells.
• Osteology is the branch of science that studies bones.

The skeletal system is the body's internal framework of bones and a few cartilages.

An adult human has 206 bones plus some cartilages.

A baby is born with more bones; many fuse during growth to give 206 in the adult.

Functions: support and shape, protection of soft organs, and movement with muscles.

Bones store calcium as a mineral reserve.

The bone marrow inside some bones makes blood cells.

Osteology is the branch of science that studies bones.

• Connective tissue binds, supports, strengthens and protects other tissues.
• Its family includes bone, cartilage, blood and fat (adipose).
• Its cells are spread out inside a non-living matrix (ground substance).
• The hardness of the matrix decides how stiff the tissue is.
• In the embryo the skeleton is mostly cartilage, later replaced by bone.

Connective tissue binds, supports, strengthens and protects other tissues.

Its cells are spread out inside a non-living matrix (ground substance).

The hardness of the matrix decides how stiff the tissue is.

In the embryo the skeleton is mostly cartilage, later replaced by bone.

• Bone has a hard, non-pliable matrix rich in calcium salts and collagen.
• Cartilage has a soft, pliable matrix with chondroitin salts and little calcium.
• Cartilage can be bent; bone cannot – felt in nose tip and outer ear (pinna).
• Bone cells = osteocytes (in spaces called lacunae); cartilage cells = chondrocytes.
• Cartilage also lies between vertebrae and at the ends of limb bones.
• Matrix — Hard, non-pliable — Soft, pliable
• Main content — Calcium + collagen — Chondroitin salts
• Cells — Osteocytes — Chondrocytes
• Can bend? — No — Yes
• Found in — Limbs, skull — Nose tip, pinna

Bone has a hard, non-pliable matrix rich in calcium salts and collagen.

Cartilage has a soft, pliable matrix with chondroitin salts and little calcium.

Cartilage can be bent; bone cannot – felt in nose tip and outer ear (pinna).

Bone cells = osteocytes (in spaces called lacunae); cartilage cells = chondrocytes.

Cartilage also lies between vertebrae and at the ends of limb bones.

• The skeleton splits by location into axial and appendicular.
• Axial (from axis) = bones of the central midline: head and trunk.
• Appendicular (from appendage) = limb bones plus the two girdles.
• Axial = 80 bones; appendicular = 126 bones.
• Memory check: 80 + 126 = 206 total bones.
• Axial — 80 — Skull, backbone, ribs, sternum
• Appendicular — 126 — Limbs + pectoral & pelvic girdles
• Total — 206 — Whole skeleton

The skeleton splits by location into axial and appendicular.

Axial (from axis) = bones of the central midline: head and trunk.

Appendicular (from appendage) = limb bones plus the two girdles.

Axial = 80 bones; appendicular = 126 bones.

Memory check: 80 + 126 = 206 total bones.

• The skull has 22 bones = 8 cranial + 14 facial.
• The 8 cranial bones form the cranium that protects the brain.
• Joints between cranial bones are fixed (immovable) for safety.
• Of the face, only the lower jaw can move; the upper jaw is fixed.
• The U-shaped hyoid bone sits at the base of the mouth.
• Each middle ear has three ossicles – Malleus, Incus, Stapes.
• The stapes is the smallest bone in the body (about 3 mm).

The skull has 22 bones = 8 cranial + 14 facial.

The 8 cranial bones form the cranium that protects the brain.

Joints between cranial bones are fixed (immovable) for safety.

Of the face, only the lower jaw can move; the upper jaw is fixed.

The U-shaped hyoid bone sits at the base of the mouth.

Each middle ear has three ossicles – Malleus, Incus, Stapes.

• Built from 26 vertebrae stacked along the back (dorsal) side.
• Each vertebra has a neural canal through which the spinal cord passes.
• The first vertebra, the atlas, joins the skull and lets you nod.
• The atlas–skull joint allows nodding; the axis (pivot joint) allows head rotation.
• Almost all mammals, even the giraffe, have 7 cervical vertebrae.
• The column protects the spinal cord and supports the head.
• Cervical (neck) — 7
• Thoracic (chest) — 12
• Lumbar (lower back) — 5
• Sacral (fused) — 1
• Coccygeal (fused) — 1
• Total — 26

Built from 26 vertebrae stacked along the back (dorsal) side.

Each vertebra has a neural canal through which the spinal cord passes.

The first vertebra, the atlas, joins the skull and lets you nod.

The atlas–skull joint allows nodding; the axis (pivot joint) allows head rotation.

Almost all mammals, even the giraffe, have 7 cervical vertebrae.

• The sternum (breast bone) is a flat bone on the frontmiddle of the chest.
• There are 12 pairs of ribs – thin, flat, curved bones.
• Each rib is bicephalic (two-headed) at its back end.
• True ribs (1–7) join the sternum directly by hyaline cartilage.
• False ribs (8–10) join the 7th rib, not the sternum directly.
• Floating ribs (11–12) are not joined to the sternum in front.
• Thoracic vertebrae + ribs + sternum form the rib cage protecting heart and lungs.
• True — 1–7 — Sternum directly
• False — 8–10 — 7th rib by cartilage
• Floating — 11–12 — None

The sternum (breast bone) is a flat bone on the frontmiddle of the chest.

There are 12 pairs of ribs – thin, flat, curved bones.

True ribs (1–7) join the sternum directly by hyaline cartilage.

False ribs (8–10) join the 7th rib, not the sternum directly.

Floating ribs (11–12) are not joined to the sternum in front.

Thoracic vertebrae + ribs + sternum form the rib cage protecting heart and lungs.

• A girdle is a ring of bones connecting a limb to the axial skeleton.
• The pectoral girdle attaches the arms: clavicle + scapula.
• The scapula's glenoid cavity holds the humerus to form the shoulder joint.
• The pelvic girdle (hip) attaches the legs; made of two coxal bones.
• Each coxal bone is the fusion of ilium, ischium and pubis.
• Arm bones: humerus, radius, ulna; leg bones: femur, tibia, fibula.
• The femur (thigh bone) is the longest and strongest bone.
• Pectoral — Arms — Clavicle + scapula
• Pelvic — Legs — Two coxal bones

A girdle is a ring of bones connecting a limb to the axial skeleton.

The pectoral girdle attaches the arms: clavicle + scapula.

The scapula's glenoid cavity holds the humerus to form the shoulder joint.

The pelvic girdle (hip) attaches the legs; made of two coxal bones.

Each coxal bone is the fusion of ilium, ischium and pubis.

Arm bones: humerus, radius, ulna; leg bones: femur, tibia, fibula.

The femur (thigh bone) is the longest and strongest bone.

• A joint is where two or more bones meet.
• Fixed (immovable) joints hold cranial bones together – no movement.
• Slightly movable joints occur between vertebrae.
• Freely movable (synovial) joints allow large movement, e.g. knee, shoulder.
• The ball-and-socket joint (shoulder, hip) moves in all directions.
• The hinge joint (knee, elbow) moves in one plane like a door.
• The pivot joint at the neck (atlas–axis) lets the head turn side to side.
• Ball-and-socket — Shoulder, hip — All directions
• Hinge — Knee, elbow — One plane
• Pivot — Neck (atlas-axis) — Rotation
• Fixed — Skull — None

A joint is where two or more bones meet.

Fixed (immovable) joints hold cranial bones together – no movement.

The ball-and-socket joint (shoulder, hip) moves in all directions.

The hinge joint (knee, elbow) moves in one plane like a door.

The pivot joint at the neck (atlas–axis) lets the head turn side to side.

• Muscles are the engines that move the skeleton by contracting.
• Muscle cells are contractile – they can shorten and pull.
• Muscles work in antagonistic pairs (one contracts, the other relaxes).
• Muscles can only pull, not push, so pairs are needed.
• Tendons attach muscle to bone; ligaments join bone to bone.
• The body has over 600 muscles, making up much of body weight.

Muscles are the engines that move the skeleton by contracting.

Muscle cells are contractile – they can shorten and pull.

Muscles work in antagonistic pairs (one contracts, the other relaxes).

Muscles can only pull, not push, so pairs are needed.

Tendons attach muscle to bone; ligaments join bone to bone.

The body has over 600 muscles, making up much of body weight.

• Skeletal (striated) muscle is voluntary and attached to bones for movement.
• Smooth (unstriated) muscle is involuntary, in walls of stomach and intestines.
• Cardiac muscle is involuntary, found only in the heart, and never tires.
• Skeletal muscle has stripes (striations); smooth muscle does not.
• Cardiac muscle is striated but involuntary – a unique mix.
• Skeletal — Voluntary — Attached to bones
• Smooth — Involuntary — Stomach, intestines
• Cardiac — Involuntary — Heart only

Skeletal (striated) muscle is voluntary and attached to bones for movement.

Smooth (unstriated) muscle is involuntary, in walls of stomach and intestines.

Cardiac muscle is involuntary, found only in the heart, and never tires.

Skeletal muscle has stripes (striations); smooth muscle does not.

Cardiac muscle is striated but involuntary – a unique mix.

• Osteology is the study of bones.
• Arthritis is inflammation and pain of the joints.
• Osteoporosis is weakening of bones from calcium loss, common in old age.
• Rickets in children is soft, bent bones from vitamin D deficiency.
• Biological resurfacing is a surgical technique to treat cartilage/joint problems.
• A fracture is a break or crack in a bone.

Osteology is the study of bones.

Arthritis is inflammation and pain of the joints.

Osteoporosis is weakening of bones from calcium loss, common in old age.

Rickets in children is soft, bent bones from vitamin D deficiency.

Biological resurfacing is a surgical technique to treat cartilage/joint problems.

A fracture is a break or crack in a bone.