Exercise 10 The Appendicular Skeleton Review Sheet

The appendicular skeleton, a crucial component of the human skeletal system, is responsible for our body's movements and interactions with the environment. It includes all the bones of the limbs and the girdles that attach them to the axial skeleton. A comprehensive review of this system is essential for students of anatomy, physiology, and related fields.

Introduction to the Appendicular Skeleton

The appendicular skeleton comprises 126 bones, allowing for a wide range of motion and dexterity. It is divided into the upper and lower limbs, each connected to the axial skeleton via girdles. The pectoral girdle connects the upper limbs, while the pelvic girdle connects the lower limbs. Understanding the structure and function of each bone in this system is vital for comprehending human movement and biomechanics.

Components of the Appendicular Skeleton

The appendicular skeleton is organized into the following main components:

• Pectoral Girdle: Clavicle and Scapula
• Upper Limb: Humerus, Radius, Ulna, Carpals, Metacarpals, and Phalanges
• Pelvic Girdle: Hip Bones (Ilium, Ischium, and Pubis)
• Lower Limb: Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, and Phalanges

Functions of the Appendicular Skeleton

The appendicular skeleton serves several critical functions, including:

• Movement: Provides the framework for muscles to attach and facilitate movement.
• Support: Supports the body's weight and maintains posture.
• Manipulation: Allows for precise manipulation of objects through the hands and fingers.
• Locomotion: Enables walking, running, and other forms of locomotion.
• Protection: Protects certain organs and tissues in the limbs.

The Pectoral Girdle: Connecting the Upper Limbs

The pectoral girdle, also known as the shoulder girdle, consists of two bones: the clavicle (collarbone) and the scapula (shoulder blade). These bones connect the upper limbs to the axial skeleton, providing flexibility and a wide range of motion for the arms.

Clavicle

The clavicle is a long, slender bone that acts as a strut between the sternum (breastbone) and the scapula. It is S-shaped and articulates with the manubrium of the sternum at the sternoclavicular joint and with the acromion of the scapula at the acromioclavicular joint.

Key Features of the Clavicle:

• Sternal End: Medial end that articulates with the sternum.
• Acromial End: Lateral end that articulates with the acromion of the scapula.
• Shaft: The main body of the clavicle, which is curved.

Functions of the Clavicle:

• Supports the Upper Limb: Holds the upper limb away from the thorax, allowing for greater mobility.
• Transmits Forces: Transmits forces from the upper limb to the axial skeleton.
• Protects Nerves and Blood Vessels: Protects the underlying subclavian artery and vein, as well as the brachial plexus.

Scapula

The scapula is a flat, triangular bone located on the posterior aspect of the thorax. It articulates with the clavicle at the acromioclavicular joint and with the humerus at the glenohumeral joint (shoulder joint).

Key Features of the Scapula:

• Spine: A prominent ridge on the posterior surface.
• Acromion: A lateral extension of the spine that articulates with the clavicle.
• Coracoid Process: A hook-like process that projects anteriorly.
• Glenoid Cavity: A shallow depression that articulates with the head of the humerus.
• Superior Border: The superior edge of the scapula.
• Medial Border: The medial edge of the scapula, also known as the vertebral border.
• Lateral Border: The lateral edge of the scapula, also known as the axillary border.
• Superior Angle: The angle formed by the superior and medial borders.
• Inferior Angle: The angle formed by the medial and lateral borders.
• Subscapular Fossa: A large, concave depression on the anterior surface.
• Supraspinous Fossa: A depression superior to the spine on the posterior surface.
• Infraspinous Fossa: A depression inferior to the spine on the posterior surface.

Functions of the Scapula:

• Provides Attachment Sites: Serves as an attachment point for numerous muscles that control shoulder and arm movement.
• Facilitates Shoulder Movement: Allows for a wide range of motion at the shoulder joint.
• Supports the Upper Limb: Helps to support the weight of the upper limb.

The Upper Limb: Bones of the Arm, Forearm, and Hand

The upper limb consists of 30 bones in each arm, including the humerus in the arm, the radius and ulna in the forearm, and the carpals, metacarpals, and phalanges in the hand.

Humerus

The humerus is the longest and largest bone of the upper limb. It articulates with the scapula at the glenohumeral joint (shoulder joint) and with the radius and ulna at the elbow joint.

Key Features of the Humerus:

• Head: The proximal end that articulates with the glenoid cavity of the scapula.
• Anatomical Neck: A groove that encircles the head.
• Surgical Neck: A common site for fractures, located distal to the tubercles.
• Greater Tubercle: A large prominence on the lateral aspect of the proximal end.
• Lesser Tubercle: A smaller prominence on the anterior aspect of the proximal end.
• Intertubercular Sulcus: A groove between the greater and lesser tubercles.
• Deltoid Tuberosity: A roughened area on the lateral surface of the shaft where the deltoid muscle attaches.
• Lateral Epicondyle: A bony projection on the lateral distal end.
• Medial Epicondyle: A bony projection on the medial distal end.
• Capitulum: A rounded projection on the lateral distal end that articulates with the radius.
• Trochlea: A spool-shaped projection on the medial distal end that articulates with the ulna.
• Coronoid Fossa: A depression on the anterior distal end that accommodates the coronoid process of the ulna during flexion.
• Olecranon Fossa: A depression on the posterior distal end that accommodates the olecranon process of the ulna during extension.

Functions of the Humerus:

• Provides Attachment Sites: Serves as an attachment point for muscles that control shoulder and elbow movement.
• Supports the Forearm: Connects the shoulder to the forearm.
• Facilitates Movement: Allows for a wide range of motion at the shoulder and elbow joints.

Radius

The radius is one of the two bones of the forearm, located on the lateral (thumb) side. It articulates with the humerus at the elbow joint and with the ulna at the proximal and distal radioulnar joints. It also articulates with the carpal bones at the wrist joint.

Key Features of the Radius:

• Head: The proximal end that articulates with the capitulum of the humerus and the radial notch of the ulna.
• Neck: A constricted region distal to the head.
• Radial Tuberosity: A prominence on the medial side of the proximal end where the biceps brachii muscle attaches.
• Shaft: The main body of the radius.
• Styloid Process: A pointed projection on the lateral distal end.
• Ulnar Notch: A depression on the medial distal end that articulates with the ulna.

Functions of the Radius:

• Supports the Forearm: Provides support and stability to the forearm.
• Facilitates Pronation and Supination: Allows for rotation of the forearm (pronation and supination).
• Articulates with the Wrist: Connects the forearm to the wrist.

Ulna

The ulna is the other bone of the forearm, located on the medial (pinky) side. It articulates with the humerus at the elbow joint and with the radius at the proximal and distal radioulnar joints. It does not directly articulate with the carpal bones.

Key Features of the Ulna:

• Olecranon: A large, curved projection at the proximal end that forms the point of the elbow.
• Coronoid Process: A beak-like projection on the anterior side of the proximal end.
• Trochlear Notch: A deep notch that articulates with the trochlea of the humerus.
• Radial Notch: A small depression on the lateral side of the coronoid process that articulates with the head of the radius.
• Shaft: The main body of the ulna.
• Styloid Process: A pointed projection on the posterior distal end.
• Head: The distal end of the ulna.

Functions of the Ulna:

• Supports the Forearm: Provides support and stability to the forearm.
• Forms the Elbow Joint: Primarily responsible for forming the elbow joint with the humerus.
• Facilitates Forearm Movement: Works with the radius to allow for pronation and supination.

Carpals

The carpals are the eight small bones that make up the wrist. They are arranged in two rows of four bones each.

The Carpal Bones (from lateral to medial in the proximal row):

• Scaphoid: Boat-shaped bone located near the thumb.
• Lunate: Moon-shaped bone located next to the scaphoid.
• Triquetrum: Three-cornered bone located next to the lunate.
• Pisiform: Pea-shaped bone located on the anterior surface of the triquetrum.

The Carpal Bones (from lateral to medial in the distal row):

• Trapezium: Four-sided bone located near the thumb.
• Trapezoid: Wedge-shaped bone located next to the trapezium.
• Capitate: Head-shaped bone located in the center of the wrist.
• Hamate: Hook-shaped bone located near the pinky finger.

Functions of the Carpals:

• Form the Wrist: Provide a flexible connection between the forearm and the hand.
• Facilitate Hand Movement: Allow for a wide range of motion at the wrist.
• Transmit Forces: Transmit forces from the hand to the forearm.

Metacarpals

The metacarpals are the five bones that form the palm of the hand. They are numbered I-V, starting with the thumb. Each metacarpal consists of a base (proximal end), a shaft (body), and a head (distal end).

Functions of the Metacarpals:

• Support the Palm: Provide support and structure to the palm of the hand.
• Articulate with the Phalanges: Connect the wrist to the fingers.
• Allow Hand Movement: Contribute to the overall movement and dexterity of the hand.

Phalanges

The phalanges are the bones that form the fingers and thumb. Each finger has three phalanges (proximal, middle, and distal), while the thumb has only two (proximal and distal).

Functions of the Phalanges:

• Form the Fingers and Thumb: Provide the bony framework for the fingers and thumb.
• Allow Finger Movement: Enable precise and coordinated movements of the fingers for grasping and manipulation.
• Provide Sensitivity: Work with the soft tissues to provide sensory feedback for touch and pressure.

The Pelvic Girdle: Connecting the Lower Limbs

The pelvic girdle consists of two hip bones (also known as coxal bones or innominate bones), which connect the lower limbs to the axial skeleton. Each hip bone is formed by the fusion of three bones: the ilium, ischium, and pubis.

Ilium

The ilium is the largest and most superior part of the hip bone. It forms the superior portion of the acetabulum (the socket for the head of the femur) and articulates with the sacrum at the sacroiliac joint.

Key Features of the Ilium:

• Iliac Crest: The superior border of the ilium.
• Anterior Superior Iliac Spine (ASIS): A prominent projection at the anterior end of the iliac crest.
• Anterior Inferior Iliac Spine (AIIS): A projection inferior to the ASIS.
• Posterior Superior Iliac Spine (PSIS): A projection at the posterior end of the iliac crest.
• Posterior Inferior Iliac Spine (PIIS): A projection inferior to the PSIS.
• Iliac Fossa: A large, concave depression on the medial surface of the ilium.
• Greater Sciatic Notch: A large notch on the posterior border of the ilium.
• Arcuate Line: A ridge on the medial surface that forms part of the pelvic brim.

Functions of the Ilium:

• Supports the Upper Body: Transmits weight from the axial skeleton to the lower limbs.
• Provides Muscle Attachment Sites: Serves as an attachment point for muscles of the hip, thigh, and abdomen.
• Forms Part of the Pelvic Cavity: Contributes to the bony structure that protects the pelvic organs.

Ischium

The ischium is the posteroinferior part of the hip bone. It forms the lower portion of the acetabulum and bears the body's weight when sitting.

Key Features of the Ischium:

• Ischial Tuberosity: A large, roughened projection that supports the body's weight when sitting.
• Ischial Spine: A pointed projection superior to the ischial tuberosity.
• Lesser Sciatic Notch: A notch inferior to the ischial spine.
• Ramus of the Ischium: A branch of the ischium that joins with the inferior pubic ramus.

Functions of the Ischium:

• Supports Body Weight: Bears the body's weight when sitting.
• Provides Muscle Attachment Sites: Serves as an attachment point for muscles of the hip and thigh.
• Forms Part of the Pelvic Cavity: Contributes to the bony structure that protects the pelvic organs.

Pubis

The pubis is the anteromedial part of the hip bone. It forms the anterior portion of the acetabulum and articulates with the other pubis at the pubic symphysis.

Key Features of the Pubis:

• Superior Pubic Ramus: A branch of the pubis that joins with the ilium.
• Inferior Pubic Ramus: A branch of the pubis that joins with the ischium.
• Pubic Crest: A thickened ridge on the superior border of the pubis.
• Pubic Tubercle: A projection at the lateral end of the pubic crest.
• Obturator Foramen: A large opening in the hip bone formed by the ischium and pubis.

Functions of the Pubis:

• Provides Muscle Attachment Sites: Serves as an attachment point for muscles of the hip and thigh.
• Supports the Pelvic Organs: Contributes to the bony structure that protects the pelvic organs.
• Articulates at the Pubic Symphysis: Forms a joint with the other pubis, providing stability to the pelvic girdle.

The Lower Limb: Bones of the Thigh, Leg, and Foot

The lower limb consists of 30 bones in each leg, including the femur in the thigh, the patella (kneecap), the tibia and fibula in the leg, and the tarsals, metatarsals, and phalanges in the foot.

Femur

The femur is the longest and strongest bone in the body. It articulates with the hip bone at the hip joint and with the tibia and patella at the knee joint.

Key Features of the Femur:

• Head: The proximal end that articulates with the acetabulum of the hip bone.
• Neck: A constricted region distal to the head.
• Greater Trochanter: A large prominence on the lateral side of the proximal end.
• Lesser Trochanter: A smaller prominence on the medial side of the proximal end.
• Intertrochanteric Line: A ridge on the anterior side connecting the trochanters.
• Intertrochanteric Crest: A ridge on the posterior side connecting the trochanters.
• Shaft: The main body of the femur.
• Linea Aspera: A prominent ridge on the posterior surface of the shaft.
• Lateral Epicondyle: A bony projection on the lateral distal end.
• Medial Epicondyle: A bony projection on the medial distal end.
• Lateral Condyle: A rounded projection on the lateral distal end that articulates with the tibia.
• Medial Condyle: A rounded projection on the medial distal end that articulates with the tibia.
• Intercondylar Fossa: A depression between the condyles on the posterior distal end.
• Patellar Surface: A smooth surface on the anterior distal end that articulates with the patella.

Functions of the Femur:

• Supports Body Weight: Transmits weight from the hip to the lower leg.
• Provides Muscle Attachment Sites: Serves as an attachment point for muscles of the hip and thigh.
• Facilitates Movement: Allows for a wide range of motion at the hip and knee joints.

Patella

The patella, also known as the kneecap, is a small, triangular bone located anterior to the knee joint. It is embedded within the tendon of the quadriceps femoris muscle.

Key Features of the Patella:

• Anterior Surface: The rough, convex surface on the front of the patella.
• Posterior Surface: The smooth surface that articulates with the femur.
• Base: The superior border of the patella.
• Apex: The inferior point of the patella.

Functions of the Patella:

• Protects the Knee Joint: Shields the knee joint from injury.
• Increases Leverage: Improves the leverage of the quadriceps femoris muscle.
• Reduces Friction: Reduces friction between the quadriceps tendon and the femur.

Tibia

The tibia, also known as the shinbone, is the larger and more medial of the two bones of the leg. It articulates with the femur and patella at the knee joint and with the fibula at the proximal and distal tibiofibular joints. It also articulates with the talus (a tarsal bone) at the ankle joint.

Key Features of the Tibia:

• Medial Condyle: A rounded projection on the medial proximal end that articulates with the medial condyle of the femur.
• Lateral Condyle: A rounded projection on the lateral proximal end that articulates with the lateral condyle of the femur.
• Tibial Tuberosity: A prominence on the anterior proximal end where the patellar ligament attaches.
• Anterior Border: A sharp ridge on the anterior surface of the shaft.
• Medial Malleolus: A bony projection on the medial distal end that forms the medial side of the ankle.
• Fibular Notch: A depression on the lateral distal end that articulates with the fibula.

Functions of the Tibia:

• Supports Body Weight: Transmits weight from the femur to the foot.
• Provides Muscle Attachment Sites: Serves as an attachment point for muscles of the leg and foot.
• Forms the Knee and Ankle Joints: Contributes to the structure and function of the knee and ankle joints.

Fibula

The fibula is the smaller and more lateral of the two bones of the leg. It articulates with the tibia at the proximal and distal tibiofibular joints. It does not participate in the knee joint but forms the lateral part of the ankle joint.

Key Features of the Fibula:

• Head: The proximal end that articulates with the lateral condyle of the tibia.
• Neck: A constricted region distal to the head.
• Shaft: The main body of the fibula.
• Lateral Malleolus: A bony projection on the lateral distal end that forms the lateral side of the ankle.

Functions of the Fibula:

• Provides Muscle Attachment Sites: Serves as an attachment point for muscles of the leg and foot.
• Stabilizes the Ankle Joint: Helps to stabilize the ankle joint.
• Does Not Bear Significant Weight: Primarily involved in muscle attachment rather than weight-bearing.

Tarsals

The tarsals are the seven bones that make up the ankle and posterior part of the foot.

The Tarsal Bones (from proximal to distal and medial to lateral):

• Talus: Articulates with the tibia and fibula to form the ankle joint.
• Calcaneus: The largest tarsal bone, forming the heel.
• Navicular: Located on the medial side of the foot, between the talus and the cuneiforms.
• Medial Cuneiform: The most medial of the three cuneiform bones.
• Intermediate Cuneiform: Located between the medial and lateral cuneiforms.
• Lateral Cuneiform: The most lateral of the three cuneiform bones.
• Cuboid: Located on the lateral side of the foot, distal to the calcaneus.

Functions of the Tarsals:

• Form the Ankle and Heel: Provide support and flexibility to the ankle and heel.
• Transmit Body Weight: Transmit weight from the leg to the foot.
• Facilitate Foot Movement: Allow for a range of motion at the ankle and foot.

Metatarsals

The metatarsals are the five bones that form the anterior part of the foot. They are numbered I-V, starting with the big toe. Each metatarsal consists of a base (proximal end), a shaft (body), and a head (distal end).

Functions of the Metatarsals:

• Support the Foot: Provide support and structure to the foot.
• Articulate with the Phalanges: Connect the ankle to the toes.
• Allow Foot Movement: Contribute to the overall movement and flexibility of the foot.

Phalanges

The phalanges are the bones that form the toes. Each toe has three phalanges (proximal, middle, and distal), while the big toe has only two (proximal and distal).

Functions of the Phalanges:

• Form the Toes: Provide the bony framework for the toes.
• Allow Toe Movement: Enable precise and coordinated movements of the toes for balance and propulsion.
• Provide Sensitivity: Work with the soft tissues to provide sensory feedback for touch and pressure.

Clinical Significance

Understanding the appendicular skeleton is crucial for diagnosing and treating various clinical conditions, including fractures, dislocations, arthritis, and congenital abnormalities. Knowledge of the specific features and functions of each bone helps healthcare professionals provide appropriate care and rehabilitation.

Conclusion

The appendicular skeleton is a complex and essential part of the human skeletal system, providing the framework for movement, support, and manipulation. A thorough understanding of its components and functions is vital for anyone studying or working in the fields of anatomy, physiology, and medicine. Reviewing the appendicular skeleton regularly ensures a solid foundation for further learning and clinical practice.