Human Skeletal System Overview

Vertebrae

• Vertebral body is the main weight-bearing component of the vertebrae
• Vertebral arch forms the lateral and posterior walls of the vertebral canal
• Vertebral arch also serves as the point of attachment for muscles and ligaments, as well as site of articulation with adjacent vertebrae
• Contains the spinal cord, blood vessels and connective tissue
• Thoracic vertebrae - large costal elements form articulation

Vertebral Column

• Vertebrae increase in size from C2 to L5

Human Skull

• Consists of 22 bones: 8 cranial and 14 facial (+6 inner ear ossicles)
• Bones are joined immovably, except the mandible
• Divided into: forehead - frontal, roof - parietal, side - temporal, back - occipital

Appendicular Skeleton

• Consists of the bones of the pectoral and pelvic girdles and the upper and lower limbs
• Upper limb: 64 bones; pectoral girdle: scapulae and clavicles (4); arms and forearms (6); wrist and hands (54)
• Lower limb: 62 bones; pelvic girdle (2), thigh and lower leg (8); ankle and feet (52)

Pectoral (Shoulder) Girdle

• Anchors limbs to the axial skeleton
• Consists of 2 clavicles and 2 scapulae
• Not typically weight bearing, stability is sacrificed for mobility
• Most mobile joint in the body, hence not very stable and can easily dislocate the shoulder

Synovial Joints

• Most mobile joint in the body - why? - The head of the humerus rests in the glenoid cavity of the scapula, which is shallow and the joint capsule is loose.
• Provides great manoeuvrability but can be easily dislocated

General Structure of Synovial Joints

• Joint Cavity: contains synovial fluid
• Articular Cartilage: reduces friction between joints
• Synovial Fluid: egg white consistency, lubricates joints, preventing damage

Types of Synovial Joints

• Pivot: allows rotation, round bony process fits into bony ligamentous socket
• Hinge: Permits flexion and extension only, e.g., elbow
• Saddle: concave and convex joint surfaces
• Plane: permits gliding or sliding movements
• Condyloid: permits flexion, extension, abduction, adduction, and circumduction, e.g., wrist
• Ball & Socket: allows for movement in several axes, rounded head, e.g., hip

Osteoporosis

• Bone mineral density is reduced
• Bone loss is greater than bone growth
• Bones progressively weaken and fracture with minor stress
• Most common bones affected: neck of femur, wrist, forearm, hip and vertebrae
• No obvious symptoms until fractures
• Higher risk groups: elderly, women over 50, family history, petit and thin, previous fracture, Caucasian and Asian women, certain diseases, and lifestyle factors

Muscle

• Specialised for generating force and motion
• Represents ~50% body mass in adult humans
• Divided into three types: skeletal, cardiac and smooth muscle
• Many similarities but also differ considerably from one another

Muscle Functions

• Body Movement: skeletal muscle contraction
• Body Posture: continual adjustment of skeletal muscles
• Support and Protection: skeletal muscles surrounding joints and within the abdominal wall
• Sphincter Control: skeletal and smooth muscle e.g., cardiac sphincter in stomach, bladder, and anus
• Movement of food along GI tract: smooth muscle generates peristalsis
• Regulation of Blood: Cardiac muscle pumps blood

Muscle Histology

• Skeletal Muscle Cell:
  • Cell membrane - sarcolemma
  • Cytoplasm - sarcoplasm
  • Full of myofibrils
  • Myofibrils - actin/myosin
  • Many mitochondria
  • Extensive endoplasmic reticulum - sarcoplasmic reticulum

Muscle Fibre Anatomy

• Muscle Fibre: Contains myofilaments
• Myofilaments: contractile units called sarcomeres
• Sarcomere: Striations caused by overlapping actin and myosin (myofilaments)

Muscle Cell Function: Contraction

• Actin and Myosin make up - 90% muscle protein
• Actin: Actin subunits polymerise into long filamentous or “F actin” and two intertwined actin filaments
• Myosin: Rod-like tail attached to two globular heads, tail - intertwines helices. Globular heads link thick and thin filaments in contraction.

Sarcomere Contraction

• Sliding Filament Theory
• Actin filaments slide past myosin filaments, shortening the sarcomere

Sarcomere Components

• A band: dark band containing myosin filaments
• I band: light band containing actin filaments
• H zone: central region of A band containing only myosin filaments
• M line: middle of sarcomere
• Z disc: attachment point for actin filaments.

Muscular System

• Muscles can be classified into three functional groups:
  • Agonist: the prime mover - responsible for the primary movement
  • Antagonist: may stretch or be relaxed - works opposite to the agonist
  • Synergist: may add extra force or prevent undesirable effects - assists the agonist
  • Fixator: maintains body structure, e.g., stabilising a joint

This quiz covers key aspects of the human skeletal system, including the vertebrae, vertebral column, human skull, and appendicular skeleton. You'll learn about the structure and function of bones, as well as their arrangement in various parts of the body. Test your knowledge of human anatomy with this engaging quiz!