KT

Ch. 8 The Appendicular Skeleton

Learning Objectives

  • Name the major bones associated with the appendicular skeleton.
  • Identify the bones and parts of bones that participate in articulations about the body.
  • Name, describe, and identify the important markings associated with each of the major bones of the body.
  • Describe how the structures of the axial and appendicular skeleton facilitate body movements.

Appendicular Skeleton

  • The bones of the appendicular skeleton are primarily involved in body movements.
  • These bones include those of the upper and lower limbs (including the girdles that attach them to the axial skeleton).

Appendicular Skeleton Components

  • Pectoral girdle: shoulder
    • Clavicle and scapulas
  • Pelvic girdles: hip
    • Coxal bones, sacrum, pubic symphysis
  • Limbs
    • Arms: humerus, radius, ulna, wrist and hand bones
    • Legs: femur, tibia, fibula, ankle and foot bones

Bone Surface Markings

  • Bones have characteristic surface markings which are structural features adapted for specific functions.
  • Two major types of surface markings:
    • Depressions and openings
      • Allow the passage of soft tissues
      • Form joints
    • Processes
      • Projections or outgrowths that form joints
      • Serve as attachment points for ligaments and tendons

Bone Surface Markings: Depressions and Openings

  • Sites allowing the passage of soft tissue (nerves, blood vessels, ligaments, tendons) or formation of joints.

Bone Surface Markings: Examples of Depressions and Openings

  • Fossa: (plural: fossae) Shallow depression
    • Example: Coronoid fossa of humerus
  • Sulcus: (plural: sulci) Furrow along bone surface that accommodates blood vessel, nerve, or tendon.
    • Example: Intertubercular sulcus of humerus

Bone Surface Markings: Processes

  • Projections or outgrowths on bone that form joints or attachment points for connective tissue, such as ligaments and tendons

Bone Surface Markings: Processes that form joints

  • Condyle: Large, round protuberance with a smooth articular surface at end of bone.
    • Example: Lateral condyle of femur.
  • Facet: Smooth, flat, slightly concave or convex articular surface.
    • Example: Superior articular facet of vertebra.
  • Head: Usually rounded articular projection supported on neck (constricted portion) of bone.
    • Example: Head of femur.

Bone Surface Markings: Processes that form attachment points for connective tissue

  • Crest: Prominent ridge or elongated projection.
    • Example: Iliac crest of hip bone.
  • Epicondyle: (epi- = above) Typically roughened projection above condyle.
    • Example: Medial epicondyle of femur.
  • Line: Long, narrow ridge or border (less prominent than crest).
    • Example: Linea aspera of femur.
  • Spinous process: Sharp, slender projection.
    • Example: Spinous process of vertebra.
  • Trochanter: Very large projection.
    • Example: Greater trochanter of femur.
  • Tubercle: Variably-sized rounded projection.
    • Example: Greater tubercle of humerus.
  • Tuberosity: Variably-sized projection that has a rough, bumpy surface.
    • Example: Ischial tuberosity of hip bone.

Pectoral (Shoulder) Girdle

  • The two pectoral (shoulder) girdles include a clavicle and a scapula

Pectoral (Shoulder) Girdle: Clavicle

  • The clavicle (collarbone) is S-shaped
    • Medial (sternal) end articulates with the manubrium of the sternum
    • Lateral (acromial) end articulates with the acromion of the scapula

Pectoral (Shoulder) Girdle: Scapula

  • The scapula is a flat bone that is located in the superior part of the posterior thorax between the second and seventh ribs
  • Its glenoid cavity is the attachment point for the humerus

Upper Limb: Humerus

  • The humerus, or arm bone
    • Articulates with the scapula proximally (its rounded head fits into the glenoid cavity)
    • Articulates with the radius and ulna distally (the trochlea articulates with the ulna and the capitulum with the radius)

Upper Limb Bones

  • Pectoral girdle
    • Clavicle (collar bone)
    • Scapula (shoulder blade)
  • Humerus (upper arm)
  • Ulna (forearm)
  • Radius (forearm)
  • Carpals (wrist) - 8
  • Metacarpals (hand) - 5
  • Phalanges (finger bones) - 14

Upper Limb: Ulna and Radius

  • The ulna and radius are the two bones of the forearm
    • The olecranon and coronoid process at the proximal end of the ulna form the trochlear notch which wraps around the trochlea of the humerus making up the elbow joint
    • The radius is located on the lateral (thumb) side of the forearm
      • The articulation of its head with the capitulum of the humerus and with the ulna allow the forearm to rotate

Upper Limb: Hand - Carpal Bones

  • The carpal bones are 8 small bones connected to each other by ligaments and they are arranged in two rows of four bones each
    • The proximal row (scaphoid, lunate, triquetrum, pisiform) articulates with the distal radius and ulna
    • The distal row (trapezium, trapezoid, capitate, hamate) articulates with the metacarpals

Upper Limb: Hand - Metacarpals

  • The five metacarpals make up the palm and back of the hand
    • Numbered I through V (or 1–5) starting with the thumb
    • Bases articulate with the distal carpals while their heads articulate with the proximal phalanges

Upper Limb: Hand - Phalanges

  • The phalanges are the bones of the digits
    • 14 total
    • The thumb contains 2 (proximal and distal) while the other 4 fingers contain 3 each (proximal, middle and distal)

Pelvic Girdle

  • Function:
    • Support the weight of the upper body against the force of gravity
    • Protects organs inside the pelvic cavity
    • Serves as the site of attachment of lower limbs
  • Made up of two coxal bones, sacrum and the coccyx
  • Attach to sacral region of the vertebral column at the back
  • Curve forward to meet the pubic symphysis

Pelvic Girdle Composition

  • The pelvic girdle is made up of two hip bones that articulate with the sacrum posteriorly
    • Each hip bone is actually made up of three individual bones: ilium, ischium, pubis
  • The two bones articulate anteriorly at the pubic bones (pubic symphysis)
    • There is a disc of fibrocartilage between the two bones

Pelvic (Hip) Girdle: Acetabulum

  • The head of the femur articulates with the acetabulum of the hip bone as a ball and socket joint
  • The acetabulum is composed of parts of all three of the bones that make up the hip bone.

Pelvic Girdle: Pelvic Brim

  • The pelvis is divided into a superior and an inferior portion by the pelvic brim which is where the abdomen meets the pelvic cavity

Pelvic Girdle: False and True Pelvis

  • The area of the bony pelvis superior to the pelvic brim is known as the false (greater) pelvis
  • The area of the bony pelvis inferior to the pelvic brim is known as the true (lesser) pelvis

Pelvic Girdle: Female vs. Male Pelvis

  • The true pelvis is wide and shallow in the female, and the pelvic inlet, also known as the superior pelvic aperture is wide, oval and rounded.
  • While in the male it is heart shaped, and narrow. A male pelvis has a v-shaped pubic arch that is approximately < 90^\circ
  • The bones of the female pelvis are structured to meet the requirements of pregnancy and childbirth

Identification of a male skeleton: Male Skull

  • Larger and heavier
  • Forehead shorter
  • Face less round
  • Jaw larger

Identification of a male skeleton: Male pelvic cavity

  • Narrower and longer
  • Less roomy and more funnel shaped

Identification of a male skeleton: Male sacrum

  • Narrower
  • Sacral promontory projects forward
  • Sacral curvature is less sharp posteriorly

Identification of a male skeleton: Male coccyx

  • Less movable

Lower Limb: Femur

  • The femur is the longest, heaviest, and strongest bone in the body
  • The proximal end (head) inserts into the acetabulum of the hip bone
  • The distal end articulates with the tibia and patella

Lower Limb: Patella

  • The patella is a triangular bone that develops in the quadriceps tendon
  • Its posterior surface articulates with the femur

Lower Limb: Tibia and Fibula

  • The lower leg consists of the tibia and the fibula
  • The tibia’s proximal end articulates with the femur
  • The tibia’s distal end articulates with the talus bone of the ankle
  • The tibial tuberosity on the anterior surface is the point of attachment for the patellar ligament

Lower Limb: Foot - Tarsus

  • The tarsus consists of 7 bones which form the posterior aspect of the foot.
  • The tarsus contains 7 tarsal bones:
    • talus,
    • calcaneus,
    • navicular,
    • 3 cuneiforms [medial, intermediate and lateral]
    • cuboid

Lower Limb: Foot - Metatarsus

  • The metatarsus is made up of 5 metatarsal bones
    • Just like the metacarpals, they are numbered I through V (1–5) starting with the big toe
  • They make up the sole and dorsal surface of the foot
  • The proximal ends articulate with the 3 cuneiform bones and the cuboid
  • The distal ends articulate with the proximal phalanges

Lower Limb: Foot - Phalanges

  • The phalanges are arranged exactly like those of the hand
    • The big toe has a proximal and distal phalanx and the other toes have a proximal, middle and distal phalanx

Lower Limb: Foot - Arches

  • The foot has two arches that are supported by ligaments and tendons
  • The purpose of the arches is to allow the foot to support the weight of the body, provide leverage while walking, and distribute the body’s weight over the foot
  • The two arches are:
    • longitudinal arch which is made up of a medial and a lateral portion and
    • transverse arch

Development of the Skeletal System

  • Most skeletal tissue arises from the middle primary germ layer in embryos known as the mesoderm although most of the skull arises from the outer layer called the ectoderm
  • Skull bones develop in 2 ways:
    • The cartilaginous neurocranium (hyaline cartilage) undergoes endochondral ossification
    • The membranous neurocranium undergoes intramembranous ossification

Development of the Skeletal System: Viscerocranium

  • The bones of the face form from the viscerocranium
  • This is divided into 2 parts:
    • The cartilaginous viscerocranium comes from cartilage of the pharyngeal arches and this forms the ear bones and hyoid bone
    • The membranous viscerocranium comes from mesenchyme of the first pharyngeal arch, undergoes intramembranous ossification, and forms the facial bones

Development of the Skeletal System: Limb Girdles and Limbs

  • The skeleton of the limb girdles and limbs is derived from mesoderm
  • Between week 4 and week 8 after fertilization, there is an extensive amount of growth and development in the formation of the upper and lower limbs

The Skeletal System and Homeostasis

  • The skeletal system plays an important role in the homeostasis of every system in the body
  • Both directly and indirectly, the skeletal system ensures the proper functioning of these systems