The Skeletal System

Parts of the skeletal system

Bones (skeleton)

Joints

Cartilages

Ligaments (bone to bone) (tendon=bone to muscle)

Divided into two divisions

Axial skeleton- skull, spinal column

Appendicular skeleton – limbs and girdle

Cartilage Tendons Ligaments

Tough Attaches bone to muscle

Attaches bone to bone

Flexible Sturdy Elastic

At end of bone Non elastic Stabilise

Cushions Size changes depending on muscle

Made of many fibres

Anchor Strong

Functions of Bones

Support of the body

Protection of soft organs

Movement due to attached skeletal muscles

Storage of minerals and fats

Blood cell formation

Bones of the Human Body

The skeleton has 206 bones

Two basic types of bone tissue

Compact bone

Homogeneous

Spongy bone

Small needle-like pieces of bone

Many open spaces

Classification of bones (Shapes)

1. Long- bones are longer than they are wide (arms, legs)

2. Short- usually square in shape, cube like (wrist, ankle)

3. Flat- flat , curved (skull, Sternum)

4. Irregular- odd shapes (vertebrae, pelvis)

Lets put the bones into the four categories

Long Bones Short Bones Flat Bones Irregular Bones

Femur Tarsals Patella Atlas

Humerus Carpals Cranium Axis

Tibia Pelvis (Llium) Cervical

Radius Scapula Thoracic

Ulna Sternum Lumbar

Fibula Ribs Sacrum

Phalanges Coccyx

Meta Tarsals

Meta Carpals

Clavicle

Types of Bone Cells

Osteocytes

Mature bone cells

Osteoblasts

Bone-forming cells

Osteoclasts

Bone-destroying cells

Break down bone matrix for remodeling and release of calcium

Bone remodeling is a process by both osteoblasts and osteoclasts

Changes in the Human Skeleton

In embryos, the skeleton is primarily hyaline cartilage

During development, much of this cartilage is replaced by bone

Cartilage remains in isolated areas

Bridge of the nose

Parts of ribs

Joints

Bone Fractures

A break in a bone

Types of bone fractures

Closed (simple) fracture – break that does not penetrate the skin

Open (compound) fracture – broken bone penetrates through the skin

Greenstick- frays, hard to repair, breaks like a green twig

Bone fractures are treated by reduction and immobilization

Realignment of the bone

Axial skeleton

• Axial skeleton supports and protects organs of head, neck and trunk

• skull (cranium and facial bones)

• Hyoid bone (anchors tongue and muscles associated with swallowing)

• vertebral column (vertebrae and disks)

• Bony thorax (ribs and sternum)

Appendicular skeleton

• Appendicular skeleton includes bones of limbs and Bones that anchor them to the axial skeleton

• Pectoral girdle (clavicle, scapula)

• Upper limbs (arms)

• Pelvic girdle (sacrum, coccyx)

• Lower limbs (legs)

• Articulation- where joints meet, connect, and are formed.

The Skull

• 8 sutured bones in cranium

• Facial bones: 13 sutured bones 1 mandible

Cranium

• Encases brain

• Attachments for muscles

• Sinuses

Bones of the Skull

Figure 5.11

Paranasal Sinuses

Hollow portions of bones surrounding

the nasal cavity

Figure 5.10

The Hyoid Bone

The only bone that

does not articulate

with another bone

Serves as a

moveable base for

the tongue, and

other muscle

attachments

The Vertebral Column

Vertebrae separated

by intervertebral discs

made of cartilage

The spine has a

normal S curvature

Each vertebrae is

given a name

according to its

location

Thoracic cageribsthoracic Vertebraesternumcostal cartilages

•True ribs are directly attached to the sternum(first seven pairs)•Three false ribs are joined to the 7th

rib•Two pairs of floating ribs

Internal Structure of Bone

• Bone consists of two different types of tissue—compact bone and spongy bone.

• Another type of tissue called marrow fills the spaces in bones

• There are two types of marrow—red and yellow.

Compact BoneCompact bone makes up theouter layer of all bones. Althoughit looks dense and solid, It is fullof holes for nerves and blood vessels.

Spongy BoneSpongy bone contains flatand needlelike structuresthat resist stress. Red bonemarrow may fill the openspaces in some bones.

Central CavityCentral cavities in long bones usually containyellow bone marrow (fat).

Outer MembraneAn outer membranecovers most of a long bone.The inner portion of a membrane contains cells that build up and breakdown bone.

What are the types and functions of bone cells?

Bone (Osseous) Tissue

• Dense, supportive connective tissue

• Contains specialized cells

• Produces solid matrix of calcium salt deposits around collagen fibers

Characteristics of Bone Tissue

• Dense matrix, containing:

– deposits of calcium salts

– bone cells (osteocytes) within lacunae organized around blood vessels

• Canaliculi:

– form pathways for blood vessels

– exchange nutrients and wastes

Characteristics of Bone Tissue

• Periosteum:

– covers outer surfaces of bones

– consist of:

• outer fibrous layer

• inner cellular layer

Matrix Minerals

• Two-thirds of the bone matrix is calcium phosphate, Ca3(PO4)2:

– Reacts with calcium hydroxide, Ca(OH)2 to form crystals of hydroxyapatite, Ca10(PO4)6(OH)2

– which incorporates other calcium salts and ions

Ca3(PO4)2 + Ca(OH)2 Ca10(PO4)6(OH)2

Bone Cells

• Make up only 2% of bone mass:– osteocytes

– osteoblasts

– osteoprogenitor cells

– osteoclasts

Matrix Proteins

• One-third of the bone matrix is protein fibers (collagen)

Osteocytes

• Live in lacunae

• Are between layers (lamellae) of matrix

• Connect by cytoplasmic extensions through canaliculi in lamellae

• Do not divide

Functions

• To maintain protein and mineral content of matrix

• To help repair damaged bone

Osteoblasts & Osteoid

• Immature bone cells that secrete matrix compounds (osteogenesis)

• Matrix produced by osteoblasts, but not yet calcified to form bone

• Osteoblasts surrounded by bone become osteocytes

Osteoprogenitor Cells

• Mesenchymal stem cells that divide to produce osteoblasts

• Are located in the inner, cellular layer of periosteum (endosteum)

• Assist in fracture repair

Osteoclasts

• Secrete acids and protein-digesting enzymes

• Giant, multinucleate cells

• Dissolve bone matrix and release stored minerals (osteolysis)

• Are derived from stem cells that produce macrophages

What is the difference between compact bone and spongy bone?

Compact Bone

Osteon

• The basic unit of mature compact bone

• Osteocytes are arranged in concentric lamellae

• Around a central canal (Haversian canal) containing blood vessels

Perforating Canals

• Perpendicular to the central canal

• Carry blood vessels into bone and marrow

Circumferential Lamellae

• Lamellae wrapped around the long bone

• Binds osteons together

Spongy Bone

• Does not have osteons

• The matrix forms an open network of trabeculae

– Trabeculae have no blood vessels

Red Marrow

• The space between trabeculae is filled with red bone marrow:– has blood vessels

– forms red blood cells

– supplies nutrients to osteocytes

Yellow Marrow

• In some bones, spongy bone holds yellow bone marrow:– is yellow because it stores fat

Periosteum and Endosteum

• Compact bone is covered with membrane:

– periosteum on the outside

– endosteum on the inside

Periosteum

• Covers all bones:

– except parts enclosed in joint capsules

• It is made up of:

– an outer, fibrous layer

– and an inner, cellular layer

Perforating Fibers

• Collagen fibers of the periosteum:

– connect with:

• collagen fibers in bone

• fibers of joint capsules

• attached tendons

• ligaments

Functions of Periosteum

1. Isolate bone from surrounding tissues

2. Provide a route for circulatory and nervous supply

3. Participate in bone growth and repair

Endosteum

• An incomplete cellular layer:– lines the marrow cavity

– covers trabeculae of spongy bone

– lines central canals

• Contains:– osteoblasts

– osteoprogenitor cells

– osteoclasts

• Is active in bone growth and repair

What is the difference between intramembranous ossification

and endochondral ossification?

Bone Development

• Human bones grow until about age 25

• Osteogenesis:

bone formation

• Ossification:

the process of replacing other tissues with bone

• Calcification:

The process of depositing calcium salts

Occurs during bone ossification and in other tissues

Ossification

• The 2 main forms of ossification are:

– intramembranous ossification

– endochondral ossification

Intramembranous Ossification

• Also called dermal ossification:

– occurs in the dermis

– produces dermal bones such as the mandible and clavicle

Endochondral Ossification

• Ossifies bones that originate as hyaline cartilage

• Most bones originate as hyaline cartilage

How does bone form and grow?

Blood Supply of Mature Bones

• 3 major sets of blood vessels develop

Blood Vessels of Mature Bones

• Nutrient artery and vein:

– a single pair of large blood vessels

– enter the diaphysis through the nutrient foramen

– femur has more than 1 pair

• Metaphyseal vessels:

– supply the epiphysealcartilage

– where bone growth occurs

• Periosteal vessels provide blood to:

– superficial osteons

– secondary ossification centers

• The periosteum also contains:

– networks of

• lymphatic vessels

• sensory nerves

How does the skeletal system remodel and maintain homeostasis,

and what are the effects of nutrition, hormones, exercise, and

aging on bone?

Remodeling

• The adult skeleton:

– maintains itself

– replaces mineral reserves

• Remodeling:

– Recycles and renews bone matrix

– involves osteocytes, osteoblasts, and osteoclasts

KEY CONCEPTS

• Bone continually remodels, recycles, and replaces

• Turnover rate varies

• If deposition is greater than removal, bones get stronger

• If removal is faster than replacement, bones get weaker

Bone Degeneration

• Bone degenerates quickly

• Up to 1/3 of bone mass can be lost in a few weeks of inactivity

KEY CONCEPTS

• What you don’t use, you lose

• Stresses applied to bones during physical activity are essential to maintain bone strength and mass

Effects of Hormones and Nutrition on Bone

• Minerals: A dietary source of calcium and phosphate salts plus small amounts of magnesium, fluoride, iron, and manganese

• Calcitriol: The hormone calcitriol, is made in the kidneys and helps absorb calcium and phosphorus from digestive tract its synthesis requires vitamin D3 (cholecalciferol)

• Vitamins:

• Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation

• Vitamin A stimulates osteoblast activity

• Vitamins K and B12 help synthesize bone proteins

Other Hormones

• Growth hormone and thyroxine stimulate bone growth

• Estrogens and androgens stimulate osteoblasts

• Calcitonin and parathyroid hormone regulate calcium and phosphate levels

Hormones for Bone Growth and Maintenance

Chemical Composition of Bone

Calcium Regulation

• Calcium ions in body fluids:

– must be closely regulated

• Homeostasis is maintained:

– by calcitonin and parathyroid hormone

– which control storage, absorption, and excretion

Calcitonin and Parathyroid Hormone Control

• Bones:

– where calcium is stored

• Digestive tract:

– where calcium is absorbed

• Kidneys:

– where calcium is excreted

Parathyroid Hormone (PTH)

Parathyroid Hormone (PTH)

• Produced by parathyroid glands in neck

• Increases calcium ion levels by:

– stimulating osteoclasts

– increasing intestinal absorption of calcium

– decreases calcium excretion at kidneys

Calcitonin

Calcitonin

• Secreted by C cells (parafollicular cells) in thyroid

• Decreases calcium ion levels by:

– inhibiting osteoclast activity

– increasing calcium excretion at kidneys

Joints

A joint, or articulation, is the place where two bones come together.

• Fibrous- Immovable: connect bones, no movement. (skull and pelvis).

• Cartilaginous- slightly movable, bones are attached by cartilage, a little movement (spine or ribs).

• Synovial- freely movable, much more movement than cartilaginous joints. Cavities between bones are filled with synovial fluid. This fluid helps lubricate and protect the bones.

The Synovial Joint

Types of Synovial Joints Based

on Shape

Types of Synovial Joints Based

on Shape

Ball-and-Socket JointA ball-and-socket joint allows movementin all directions. Your shoulders and hipsare ball-and-socket joints.

Hinge JointHinge joints allow bending and straightening movements.Your knees and elbows are hinge joints.

Gliding JointGliding joints allowmovement in many directions as the bones slide along each other. Your wrists and ankles contain gliding joints.

Pivot JointA pivot joint connects yourhead to the first vertebra inyour backbone. It allows youto turn your head from side to side.

General Structure of Synovial Joints

1. Articular cartilage Hyaline

Spongy cushions absorb compression

Protects ends of bones from being crushed

2. Joint (synovial) cavity Potential space

Small amount of synovial fluid

3. Articular (or joint) capsule Two layered

Outer*: fibrous capsule of dense irregular connective tissue continuous with periosteum

Inner*: synovial membrane of loose connective tissue (makes synovial fluid)

Lines all internal joint surfaces not covered by cartilage*

*

**

4. Synovial fluid Filtrate of blood

Contains special glycoproteins

Nourishes cartilage and functions as slippery lubricant

“Weeping” lubricatioin

5. Reinforcing ligaments (some joints) Capsular (most) – thickened parts

of capsule

Extracapsular

Intracapsular

6. Nerves

Detect pain

Monitor stretch (one of the ways of sensing posture and body movements)

7. Blood vessels

Rich blood supply

Extensive capillary beds in synovial membrane (produce the blood filtrate)

Types of Joints

Hinge- A hinge joint allows extension and

retraction of an appendage. (Elbow, Knee)

Ball and Socket- A ball and socket joint

allows for radial movement in almost

any direction. They are found in the hips

and shoulders. (Hip, Shoulder)

Gliding- In a gliding or plane joint bones

slide past each other. Mid-carpal and mid-

tarsal joints are gliding joints. (Hands,

Feet)

Saddle- This type of joint occurs when the

touching surfaces of two bones have both

concave and convex regions with the shapes

of the two bones complementing one other

and allowing a wide range of movement.

(Thumb)

Joints (Types of Movements at Synovial Joints)

Gliding Simple movement back-and-forth and from side-to-side There is no significant alteration of the angle between the bones Limited in range Intercarpal joints

Angular Movements Increase or a decrease in the angle between articulating bones Angular movements include

FlexionExtensionLateral flexionHyperextensionAbductionAdductionCircumduction

• Flexion– Decrease in the angle between articulating bones– Bending the trunk forward

• Extension– Increase in the angle between articulating bones– Flexion and extension are opposite movements

• Lateral flexion– Movement of the trunk sideways to the right or left at the waist

• Hyperextension– Continuation of extension beyond the normal extension– Bending the trunk backward

• Abduction– Movement of a bone away from the midline– Moving the humerus laterally at the shoulder joint

• Adduction– Movement of a bone toward the midline– Movement that returns body parts to normal position from abduction

• Circumduction– Movement of a body part in a circle– Moving the humerus in a circle at the shoulder joint

• Rotation– A bone revolves around its own longitudinal axis– Turning the head from side to side as when you shake your head “no”

• Special Movements– Elevation– Depression– Protraction– Retraction– Inversion– Eversion– Dorsiflexion– Plantar flexion– Supination– Pronation– Opposition

• Elevation– Upward movement of a part of the body– Closing the mouth– Its opposing movement is depression

• Depression– Downward movement of a part of the body– Opening the mouth

• Protraction– Movement of a part of the body anteriorly– Thrusting the mandible outward– Its opposing movement is retraction

• Retraction– Movement of a protracted part of the body back to normal

Inversion Movement of the foot medially Its opposing movement is eversion

Eversion Movement of the sole laterally

Dorsiflexion Bending of the foot at the ankle in an upward direction Its opposing movement is plantar flexion

Plantar flexion Bending of the foot at the ankle in a downward direction

Supination Movement of the forearm so that the palm is turned upward Its opposing movement is pronation

Pronation Movement of the forearm so that the palm is turned downward

Opposition Movement of the thumb in which the thumb moves across the palm to touch

the tips of the fingers on the same hand

Muscle Structure

• Each muscle fibre has its own motor nerve ending; the neuromuscular junction is where the motor neuron terminates on the muscle fibre

• The axon terminal is the enlarged tip of the motor neuron; it contains sacs of the neurotransmitter acetylcholine (ACh).

• The membrane of the muscle fibre is the sarcolemma, which contains receptor sites for acetylcholine, and an in-activator called cholinesterase.

• Within the muscle fibre are thousands of individual contracting units called sarcomeres, which are arranged end to end in cylinders called myofibrils

• The Z lines are the end boundaries of a sarcomere.

• Filaments of the protein myosin are in the centre of the sarcomere, and filaments of the protein actin are at the ends, attached to the Z lines. Myosin filaments are anchored to the Z lines by the protein titin.

• Myosin and actin are the contractile proteins of a muscle fibre. Their interactions produce muscle contraction.

• the myosin and actin filaments partially interdigitate and thus cause the myofibrils to have alternate light and dark bands

• The light bands contain only actin filaments and are called I bands because they are isotropic to polarized light.

• The dark bands contain myosin filaments, as well as the ends of the actin filaments where they overlap the myosin, and are called A bands because they are anisotropic to polarized light.

• Also present are two inhibitory proteins, Troponinand Tropomyosin, which are part of the actin filaments and prevent the sliding of actin and myosin when the muscle fibre is relaxed.

• Surrounding the sarcomeres is the sarcoplasmireticulum, the endoplasmic reticulum of muscle cells.

• The sarcoplasmic reticulum is a reservoir for calcium ions (Ca2), which are essential for the contraction process.

• All of these parts of a muscle fibre are involved in the contraction process.

• Contraction begins when a nerve impulse arrives at the axon terminal and stimulates the release of acetylcholine.

• Acetylcholine generates electrical changes (the movement of ions) at the sarcolemma of the muscle fibre.

• These electrical changes initiate a sequence of events within the muscle fibre that is called the sliding filament mechanism of muscle contraction.

The Sliding Filament Theory/Physiology of Muscle Contraction

• Nerve impulse causes depolarization of a muscle fibre, and this electrical change enables the myosin filaments to pull the actin filaments toward the centre of the sarcomere, making the sarcomere shorter.

• All of the sarcomeres shorten and the muscle fibre contracts.