Unit 4: The Skeleton

Human Skeleton Bone Number

206 bones

Two Skeleton Divisions

• Axial Skeleton

• Appendicular Skeleton

Axial Skeleton Bone Number

80 bones

Axial Skeleton

• Bones that lie around longitudinal axis of human body

• Skull bones, auditory ossicles, hyoid bone, ribs, sternum, and bones of vertebral column

Auditory Ossicles

Ear bones

Appendicular Skeleton Bone Number

126 bones

Appendicular Skeleton

• Bones of the upper and lower limbs

• Bones forming girdles

Extremities

Upper and lower limbs

Girdles

Bones that connect limbs to axial skeleton

Types of Bones

• Long bones

• Short bones

• Flat bones

• Irregular bones

• Sesamoid bones

• Sutural bones

Long Bones

Greater length than width and slightly curved for strength

Long Bones Examples

• Femur, tibia, fibula, humorous, ulna, radius, phalanges

Short Bones

Cube shaped

• Nearly equal in length and width

Short Bones Examples

Carpal, tarsal

Flat Bones

Typically thin, it is also often curved and serve as points of attachment for muscles, and protect internal organs

Flat Bones Examples

Cranial, sternum, ribs, scapulae

Irregular Bones

Does not have any easily characterized shape and therefore does not fit any other classification

Irregular Bones Examples

Vertebrae, hip bones, some facial bones

Sesamoid Bones

• Small, round bone that is shaped like a sesame seed

• Protect tendons from excessive wear and tear

Sesamoid Bones Examples

Patellae, foot, hand

Sutural Bones

Small bones located in sutures of cranial bones

Surface Markings

Structural features adapted for specific functions

Two Major Types of Surface Markings

• Hole

• Projections

Hole

Allow passage of blood vessels and nerves

Articulations

Form joints

Projections

• Outgrowths that form joints

• Serve as attachment points for ligaments and tendons

Skull Bone Numbers

22 bones

Skull Categories

• Cranial bones

• Facial bones

Cranial Bone Number

8 bones

Cranial Bones

Frontal bone, two parietal bones, two temporal bones, occipital bone, sphenoid bone, ethmoid bone

Facial Bones Number

14 bones

Facial Bones

Two nasal bones, two maxillae, two zygomatic bones, mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, vomer

Parietal Bones

Form sides and upper lateral side of skull

Temporal Bones

Form lateral side and floor of cranium

Frontal Bone

Forms forehead

Occipital Bone

Posterior skull and posterior base of cranial cavity

Sphenoid Bone

Lies at middle part of base of skull

Ethmoid Bone

• Supporting structure of nasal cavity

• Increased surface area in nasal cavity helps humidify inhaled air trapping particles

Sutures

• Immovable joint

• Holds most skull bones together

Paranasal Sinuses

• Cavities within cranial and facial bones near nasal cavity

• Secretions produced by mucous membranes which line the sinuses, drain into nasal

• Resonance to voice

Fontanels

• At birth, unossified tissue spaces link cranial bones

• Eventually replaced with bone to become sutures

Fontanels Reason

Provide flexibility to fetal skull as it passes through birth canal

Hyoid Bone

• Does not have contact with any other bone

• Base for tongue above, and is attached to larynx below and pharynx posteriorly

• Coordinated with movements of tongue, larynx, and pharynx during swallowing and speaking

Vertebral Column

• Spine or spinal column

• Curved to varying degree

Vertebral Column Functions

• Protect spinal cord

• Supports head, neck, and body

• Point of attachment for ribs, pelvic girdle, and muscles

Vertebral Curve

• Increase the column strength

• Helps maintain balance in upright position

• Absorbs shock during walking

Vertebrae Bone Numbers

Adult = 26

Vertebrae

• 7 cervical neck region

• 12 thoracic posterior to thoracic cavity

• 5 lumbar support lower back

• 1 sacrum five fused sacral vertebrae

• 1 coccyx four fused coccygeal vertebrae

Cervical Vertebrae Bones

7

Thoracic Vertebrae Bones

12

Lumbar Vertebrae Bones

5

Vertebrae Consist Of

• Body (weight bearing)

• Vertebral arch (surrounds spinal cord)

• Seven processes (Points of attachment for muscles)

Vertebrae Conditions

• Scoliosis

• Kyphosis

• Lordosis

Intervertebral Discs

Found b/w bodies adjacent vertebrae

Intervertebral Discs Function

• Form strong joints

• Permit various movements of vertebral column

• Absorb vertical shock

Thoracic Cage

• Sternum

• Ribs

• Costal cartilages

• Thoracic vertebrae

Thorax Functions

• Enclose and protect organs in thoracic and abdominal cavities

• Provide support for bones of upper limbs

• Role in breathing

The Appendicular Skeleton

• Primary function is movement

• Includes bones of upper and lower limbs

• Girdles attach limbs to axial skeleton

Upper Limb

Each upper limb has 32 bones

Upper Limb Regions

• Pectoral (shoulder) girdle

• Free part

Pectoral Girdle Bone Number

2 bones

Pectoral Girdle Bones

• Clavicle

• Scapula

Clavicle

Collarbone

Scapula

Shoulder blade

Free Part Bone Numbers

30 bones

Free Part Bones

• Humerus

• Radius and ulna

• Carpals

• Metacarpals

• Phalanges

Humerus

• Longest and largest bone of free part of upper limb

• Distal end articulates at elbow with radius and ulna

Forearm

• Ulna

• Radius

Ulna

Longer of two forearm bones

Radius

Right down to thumb

Hand

• Carpus consists of 8 small bones (carpals)

• 2 rows of carpal bones

Carpus

Wrist

Rows of Carpal Bones

• Proximal row

• Distal row

• Scaphoid

Scaphoid

Most commonly fractured

Lower Limb Regions

• A single pelvic girdle (2 bones)

• The free part (30 bones)

Hip Bone

• Coxal or pelvic bone

• Formed from ilium, pubis, ischium

Foot

Tarsals, metatarsals, phalanges

Fibrous Joints

• Fibrous tissue

• No joint cavity b/w bones

• Mostly immovable

Most Common Fibrous Joints

Suture joints

Syndesmosis Joints

Distal ends of tibia and fibula

Gomphosis Joints

Tooth fits into socket via ligament

Cartilaginous Joints

• Bones are joined by cartilage tissue

• No joint cavity b/w bones

Synchondrosis

Diaphysis and epiphysis region in long bone in children

Symphysis

Two anterior pelvic bones join to form pubic symphysis

Synovial Joints

• Bones separated by fluid-containing cavity

• Most joints in body are synovial

• Elbow and knee

Synarthrosis

• Immovable joint

• Held together by dense fibrous connective tissue

• Suture joints in skull

Amphiarthrosis

• Slightly movable joint

• Separated by cartilage

• Pubic symphysis and vertebrae

Diarthrosis

Synovial Joint

• Articular cartilage

• Joint capsule

• Synovial membrane

• Synovial fluid

Articular Cartilage

Surface end of joining bones covered in smooth articular cartilage (hyaline)

Joint Capsule

• Made of fibrous connective tissue

• Encloses joint in strong sleeve-like covering

Synovial Membrane

• Inner surfaces of joint cavity lined with membrane

• Secretes synovial fluid into joint cavity

Synovial Fluid

Lubricant helps to ease friction

Pivot

Rotation of radius

Hinge

Elbow

Condyloid

Knuckles

Knuckles

Metacarpophalangeal joint

Saddle

Carpometacarpal joint of thumb

Plane

Wrist and ankle bones

Ball and Socket

Shoulder and hip joints

Flexion

• Bending of joint

• Decreases angle b/w bones