Skeletal System: Functions and Components

Skeletal System Function

• Supports the body
• Provides a solid framework
• Maintains the body's overall shape
• Cartilage provides flexible yet firm support in areas like the nose, external ear, thoracic cage, and trachea
• Ligaments are strong connective tissue bands
• Protects soft organs
• The skull and vertebrae protect the brain and spinal cord
• The rib cage protects thoracic cavity organs
• Attached skeletal muscles enable movement
• Stores minerals and fats, including calcium, phosphorus, and fat within the internal marrow cavity
• Facilitates blood cell formation (hematopoiesis) of red blood cells (RBC) and platelets

Parts of the Skeletal System

• Bones (skeleton)
• Joints
• Cartilages
• Ligaments

Subdivisions of the Skeleton

• Axial skeleton
• Appendicular skeleton

Long Bones

• Typically longer than they are wide
• Consist of a shaft with enlarged ends
• Mainly contain compact bone, with spongy bone at the ends
• All limb bones (except wrist, ankle, and kneecap bones) are considered long bones
• Examples are the femur and humerus

Flat Bones

• Thin, flattened, and usually curved
• Composed of two thin layers of compact bone with a spongy bone layer in between
• Examples include most skull bones, ribs, sternum, and scapula

Short Bones

• Generally cube-shaped
• Primarily contain spongy bone with a compact bone outer layer
• Sesamoid bones, like the patella, are a type of short bone that form within tendons
• Examples: carpals (wrist bones) and tarsals (ankle bones)

Irregular Bones

• Have irregular shapes
• Do not fit into other bone classification categories
• Examples: vertebrae, hip bones, and facial bones

Long Bone Anatomy

• Diaphysis (central shaft):
  • Makes up most of the bone's length
  • Composed of compact bone
• Epiphysis (ends):
  • Mostly composed of spongy bone enclosed by a thin layer of compact bone
• Articular cartilage:
  • Covers epiphyses' external surfaces where bones articulate
  • Made of thin hyaline cartilage
  • Decreases friction at joint surfaces
• Epiphyseal plate/Growth plate:
  • Flat hyaline cartilage plate seen in young, growing bone
  • Causes lengthwise growth of a long bone
  • Located between epiphysis and diaphysis
• Epiphyseal line:
  • Remnant of the epiphyseal plate, present in adult bones
  • Previously cartilage, transformed into bone

Periosteum

• Outside covering of the diaphysis
• Fibrous, dense connective tissue membrane
• Perforating (Sharpey's) fibers secure periosteum to underlying bone
• Contains blood vessels and nerves

Endosteum

• Lines the inner surface of the shaft/medullary cavity
• Made of connective tissue

Medullary cavity

• Cavity inside the shaft
• Contains marrow
• Children (infants until age 6 or 7) contains more red marrow
• Adults, red marrow is replaced by yellow marrow (fat)
• Red marrow are confined in bones of central axis, proximal epiphysis of limbs

Bone Tissue Types

• Compact bone: Dense, smooth, and homogeneous
• Cancellous/Spongy bone: Has small noodle-like pieces of bone with many open spaces

Microscopic Anatomy of Compact Bone

• Osteon (Haversian system):
  • A structural unit of bone containing a central canal and matrix rings
• Central (Haversian) canal:
  • Opening in the center of an osteon
  • Runs lengthwise through bone
  • Carries blood vessels, nerves, and loose connective tissue
• Lacunae:
  • Cavities/spaces in bone matrix that house osteocytes
• Lamellae:
  • Concentric circles of lacunae around the central (Haversian) canal
• Perforating (Volkmann's) canal:
  • Canal perpendicular to the central canal
  • Carries blood vessels and nerves
  • Radiates from the central canal to lacunae
  • Connects all bone cells to a nutrient supply
• Trabeculae:
  • Small, needlelike pieces of bone found in spongy bone
  • Open spaces are filled by marrow, blood vessels, and nerves

Bone Cells

• Osteoblasts, located in periosteum and endosteum, are "bone forming cells." Lead to formation of new bones called ossification or osteogenesis. Remodeling and repair of bone.
• Osteocytes are mature bone cells situated in bone matrix, also actively dividing but less active than the osteoblasts.
• Osteoclasts are large multinucleate bone cell which reabsorbs the broken down Ca "back" into the bloodstream

Bone Composition

• Composed of 35% organic and 65% inorganic materials.
  • Organic: Collagen and proteoglycan, responsible for major functional characteristics of bone. Inorganic: Ca phosphate crystal called HYDROXYAPATITE, makes up the major portion of bone.

Bone Markings

BONE MARKINGS:

• Sites of attachments for muscles, tendons, and ligaments.
• Passages for nerves and blood vessels.

Categories of Bone Markings

• Projections or processes grow out from bone Surface
• Depressions or cavities indentations

Axial Skeleton

• Forms the longitudinal axis of the body as a central core
• Composed of 80 bones, divided into the skull, vertebral column, and bony thorax

Skull

• Includes 8 cranial bones, 14 facial bones, 6 auditory ossicles, and the hyoid bone
• Two sets of bones form the skull:
  • Cranial bones enclose the brain
  • Facial bones hold eyes in anterior position and attach facial muscles to allow facial expression Bones are joined by sutures
• The mandible is the only bone attached by a freely movable joint

Axial Skeleton- Skull divisions

• 1 Frontal bone
• 2 Occipital bone
• 3 Ethmoid bone
• 4 Sphenoid bone
• 5,6 Parietal bones (pair)
• 7,8 Temporal bones (pair)

Bones of the face

• Maxillae (pair)
• Palatine bones (pair)
• Lacrimal bones (pair)
• Zygomatic bones (pair)
• Nasal bones (pair)
• Vomer bone
• Inferior nasal conchae (pair)
• Mandible

Auditory Ossicles

• Malleus, Incus, Stapes

Hyoid bone

• Closely related to mandible and temporal bones, it's the only bone that doesn't articulate with another bone, serves as a movable tongue base, and aids in swallowing and speaking

Paranasal sinuses

• Hollow portions of bones surrounding the nasal cavity Function to Lighten the skull and Amplify speech sounds

Vertebral Column (Spine)

• The vertebral column provides axial support and extends from the skull to the pelvis, includes 26 vertebral bones separated by intervertebral discs,7 are cervical vertebrae in the neck, 12 are thoracic vertebrae in the chest region,5 are lumbar vertebrae associated with the lower back, and the Sacrum (formed by fusion of 5 vertebrae) Coccyx (formed by fusion of 3-5 vertebrae)

Vertebral Parts

• Body (centrum), Disk-shaped, usually the largest part with flat surfaces directed superiorly and inferiorly. Forms the anterior wall of the vertebral foramen, intervertebral disks are located between the bodies.
• Vertebral arch Forms the lateral and posterior walls.
• Vertebral foramen, the hole in each vertebra where the spinal cord Passes.

Primary Curvatures

• Present from birth; form a C-shaped curvature in newborns, spinal curvatures of the thoracic and sacral regions

Secondary Curvatures

• Develop after birth and result in an S-shaped curvature in adults; spinal curvatures of the cervical and lumbar regions

Atlas (C1)

• 1st cervical vertebra and holds up the head with no body and no spinous process, but it has large superior facets, where it articulates with the occipital condyles on the base of the skull, allows the head to move in a "yes" motion and to tilt from side to side

Axis (C2)

• 2nd cervical vertebra, Considerable rotation occurs at the axis to produce a "no" motion of the head, has a highly modified process on the superior side of its small body called the dens, or odontoid process

Cervical Vertebrae

• Have very small bodies; most have bifid (split) spinous processes and a transverse foramen in each transverse process through which the vertebral arteries extend toward the head, only cervical vertebrae have transverse foramina, Dislocations and fractures are more common in this area than in other regions of the column (because of small and delicate bodies)

Thoracic Vertebrae

• Have long, thin spinous processes directed inferiorly, and they have relatively long transverse processes, first 10 thoracic vertebrae have articular facets on their transverse processes, where they articulate with the tubercles of the ribs

Lumbar Vertebrae

• Have large, thick bodies and heavy, rectangular transverse and spinous processes, the fifth lumbar vertebra may become fused into the sacrum, The first sacral vertebra may fail to fuse with the rest of the sacrum, resulting in six lumbar vertebrae

Sacral Vertebrae

• Highly modified compared with the others. These 5 vertebrae are fused into a single bone called the sacrum.
• ALAE = wing-shaped superior surfaces of the lateral parts
• AURICULAR SURFACES = ear-shaped lateral surfaces which join the sacrum to the pelvic bones
• MEDIAN SACRAL CREST = first 4 spinous processes of the sacral vertebrae partially fuse along the dorsal surface of the sacrum
• SACRAL HIA TUS = unfused 5th vertebrae with no spinous process; often the site of anesthetic injections
• COCCYX – tailbone; the most inferior portion of the vertebral column and usually consists of 3 to 5 semifused vertebrae that form a triangle, with the apex directed inferiorly; easily broken when a person falls by sitting down hard on a solid surface

Axial Skeleton- Thoracic Cage

• The bony thorax, or thoracic cage, protects organs of the thoracic cavity Forms a semi-rigid chamber, which can increase and decrease in volume during respiration. Consists of three parts, 1.Sternum, 2.Ribs, True ribs (pairs 1-7) False ribs (pairs 8-12) • Floating ribs (pairs 11-12)

3. Thoracic vertebrae

Sterrnum

• The breastbone, described as sword-shaped and has 3 parts. a.)Manubrium is the “sword handle, the 1st rib and the clavicle articulate b.)Body or gladiolus (sword), is the "blade" c.)Niphoid process is the “sword tip"

Jugular notch/suprasternal notch

• anterior base of the neck
• Sternal angle point at which the manubrium joins the body of the sternum can be felt as a prominence on the anterior thorax

Ribs

• True ribs (pairs 1-7) articulate with the thoracic vertebrae and attach directly through their costal cartilages to the sternum, False ribs (pairs 8-12) articulate with the thoracic vertebrae but do not attach directly to the sternum, Vertebrochondral ribs (pairs 8,9,10) are joined by a common cartilage to the costal cartilage of the 7th rib. Floating ribs (pairs 11–12) or vertebral ribs, because they do not attach to the sternum

Appendicular Skeleton

Composed of 126 bones

• Pectoral girdle
• Pelvic girdle
• Limbs (appendages)upper limbs
• Lower limbs

Appendicular Division

• Clavicle, Cranium, Skull, Vertebra, Radius, Scapula

Clavicle

• " a long bone" with a slight sigmoid (S-shaped) curve. It is easily seen and felt in the living human (COLLAR BONE). Because the clavicle holds the upper limb away from the body, it facilitates the limb's mobility. The lateral end of the clavicle articulates with the acromion process, and *Medial end articulates with the manubrium of the sternum.

Scapula

• is a flat, triangular bone, the Acromion process can be felt at the tip of the shoulder, protectively covers the shoulder joint, forms the attachment site for the clavicle, and provides attachment points for some of the shoulder muscles, The scapular spine extends from the acromion process across the posterior posterior surface of the scapula and surface into a small supraspious fossa, the surface is superior to the spine and a larger infraspinous fossa interior to the spine

Scapula- Anterior

• Coracoid process shaped like a crow's beak provides attachments for some shoulder and arm muscles
• The Glenoid cavity, located in the superior lateral portion, articulates with the head of the humerus

Bony Pelvis

• The Polvic girdle (ring of bone) = two coxal bones, Sacrum
• Bony Polvis (basin) = Two coxal bones, sacrum, coccyx

Bony pelvis- Coxal bones

• Coxal bones (ossa coxae) composed of three fused bones composed of three fused boness 1 Lilum , 2 Lichium, 3 Pubin

The Female’s Peris

• The inlet is larger and more circular and also Shallows
• Sacrum is the shorter less curved
• Punic Angle is greater and the Pubic Arch is more rounded

Greater and lesser tubercules

• Where sites of muscle attachment The Surgical Neck
• is a common fracture site that often requires surgical repair

Distal End Articulation – lateral

Capitulum – lateral portion of the articular surfaces

• and Trochlea - medial portion that resembles a pulley, articulates with the ulna Lateral and medial epicondyles - proximal to the capitulum and the trochlea; points of attachment for the muscles of the forearm

Radius (Bone of the Forearm)

• Head/articulates with capitulum, lateral tuberosity is the point at which an anterior muscle attaches Humerus (Bone of the Upper arm)
• Forms the arm, only single bone in upper arm, proximal/ distal and articulations

Carpal and Hand Bones

8 carpals

• arranged in two transverse rows Metacarpals
• 5 per hand (palm bones) Phalanges
• 14 phalanges per hand In fingers 3 bones are present and in thumb there are just 2

Patella

Kneecap, quadracepts bones, a smooth articulate surface over the anterior

Lower Leg and Bones

shinbone (Tibia) and Thin Fibula There are 7 bones in the tarsals Talus is the heeel portion of the largest Metatarsals there are 5 and bones in the foot are 7

Bone structures

Collagen, rigig but can spring back, is like reinforcement.

Joints function and Definition

Are articulations, where two or more bones meet, and may or may not be mobile. Classified according to what joins it.

joints

• Hold bones together securely
• Allow for mobility

Functional class -Synarthroses

Immovable joints

-Amhiathroses

Slightly movable joints

Diathroses

Freely movable joints

Structues

Fibrous, cartilaginous, and Synovial joints

Synovial joints

Are Freely moveable joints and Hyaline. contain smooth surface and synovial membrade

Fibrous Joints

• Stronger and bones are united and exhibit little to no movement
• Types Sutures syndesomeses and Gumphoses

Cartilages

Absorbs compresses shock

• 2 bones Connected of hyaline or Fibro cartilage

Features of synovial joints

Articulating cartilage; meets smoothly Ligaments for connection; holding Juice joint contains cavity and synovial.

synovial joints

Freely moveable, lubricator by the fluid thin layers. Has 4 distinguished features A- Artilage helps where bones meet B- Joint capsules, helps hold bones together C- Joint cavity, Fluidy with Synovial D Reinforcing ligaments, strong point

Synovial tendon

• Are sacs of synovial membrane that prevent inflammitory

tendon sheath

• elongated and wrapped around

types of synovial joints:

uniaxial joints, pivot/ hinge, flex bi axial joints (inter carpal hands), carpal joints multiaxial joints and shoulders joints with hylane cartilage

Joint movement

-Flexion

decreasing the joint angle

-Extension

increasing the joint angle

-Hyper extension

joint beyond its normal range

Dosiflextion

ankle towards superior of flexion

Plantar

ankly to move inferiour

Inversion

move foot inwards

Eversion

to move foot outward

Abducton

move away from line

AddictIon

Toward, horizontal

Retraction.

move part posteriorly

Protractaction

move Anteriorly

Tendons and Lingaments

Ligament

Strong but Elastic/ Connect bones Fibers not parallel/ Lie fibrolalsts Modified yellow tissue

Tendons

Connect/ is Muscles bones Tough Inelastic and almost Parallel fibers Mod white tissue. Fibrolbalsts rows

Bone formation

• ossification creates bne in bone
• Osteoblast of the synthesis of organic matter w collagen
• Fecal inside membrane bones created cartilage bone created inside

Intramembraneous ossification

Outside begin to produce bones Forming Tabule Bone result Remodel trabecular

Endochondral ossification -

Bones at the base of skull bones process At the base of the skull is a hyaline process Enlarge matrix gets replaced