Support Systems in Animals: The Human Musculoskeletal System
Exploring the types of skeletons, human skeletal structure, joints, muscles, and common diseases
Animals need support so that they can keep their shape and move. Learners should know the types of skeletons, the main parts of the human skeleton, how joints work, and how muscles and bones work together during movement.
1. Types of Skeletons
Animals utilize three primary types of support systems, each adapted to their environment and evolutionary needs:
Hydrostatic Skeleton
This type consists of a fluid-filled cavity surrounded by muscles. Animals rely on the pressure of the fluid to maintain their shape and facilitate movement.
Exoskeleton
An exoskeleton is a hard external shell, often composed of chitin. These structures must be shed through a process known as molting or ecdysis to allow for growth.
Endoskeleton
An endoskeleton is an internal support structure made of bone or cartilage. Provides a framework for the body and protects vital organs.
Quick Check: Skeleton Types
2. The Human Skeleton
The human endoskeleton is composed of 206 bones and is categorized into two main parts: the axial skeleton and the appendicular skeleton.
Axial Skeleton
Appendicular Skeleton
Axial Skeleton Labels
Appendicular Skeleton Labels
Axial Skeleton
This central axis includes the skull (comprising the cranium and facial bones), the vertebral column (which consists of 33 vertebrae), and the rib cage (made up of the sternum and 12 pairs of ribs).
- Skull: Protects the brain
- Vertebral column: Supports body and protects spinal cord
- Rib cage: Protects heart and lungs
Appendicular Skeleton
This part includes the limbs and their attachments, specifically the pectoral girdle (shoulders) and pelvic girdle (hips). Together, these components facilitate movement and support the body's structure.
- Pectoral girdle: Connects arms to axial skeleton
- Pelvic girdle: Connects legs to axial skeleton
- Limbs: Enable movement and manipulation
3. Musculoskeletal Tissues and Joints
Ligaments
Connect bone to bone, providing stability to joints.
Tendons
Connect muscle to bone, facilitating movement.
Cartilage
Flexible tissue found at joints, reducing friction and absorbing shock.
Types of Joints
Fixed/Immovable Joints
Such as the sutures in the skull, which do not allow movement.
Partly Movable Joints
Found between vertebrae, allowing limited movement.
Freely Movable (Synovial) Joints
Allow for a wide range of motion. Several types exist:
Joint Types Memory Match
4. Human Locomotion and Muscles
Antagonistic Muscle Pairs Simulator
Biceps Brachii
Triceps Brachii
Muscle Structure: Voluntary skeletal muscles are composed of myofibrils, which contain protein filaments called actin and myosin. These filaments slide past each other to cause muscle contraction.
Antagonistic Pairs
Muscles work in pairs to facilitate movement. For example, when the biceps contract, the triceps relax, and vice versa. This coordinated action allows for smooth and controlled movements.
5. Diseases of the Skeleton
Rickets
This condition results in weak, soft bones in children, primarily due to a deficiency in Vitamin D, which is crucial for calcium absorption.
Osteoporosis
A condition characterized by the loss of bone density, leading to brittle bones that are more susceptible to fractures.
Arthritis
This disease involves inflammation of the joints, resulting in pain and a decrease in the range of motion.
Bone Health Risk Calculator
Calcium intake (mg/day): 800 mg
Sunlight exposure (min/day): 20 min
Age: 30 years
Exam Practice
Multiple choice questions to check your understanding
Skeleton & Bones
1. How many bones are in the adult human skeleton?
Joints & Movement
2. What type of joint is the elbow?
Muscles
3. What protein filaments slide past each other during muscle contraction?
Diseases
4. Which disease is caused by Vitamin D deficiency?
Quick Check Questions
1. What is the difference between ligaments and tendons?
Show Answer
Ligaments connect bone to bone and provide joint stability. Tendons connect muscle to bone and facilitate movement.
2. Name the two main divisions of the human skeleton.
Show Answer
Axial skeleton (skull, vertebral column, rib cage) and Appendicular skeleton (limbs and girdles).
3. What is molting and which skeleton type requires it?
Show Answer
Molting (ecdysis) is the shedding of the exoskeleton to allow for growth. It occurs in animals with exoskeletons like insects and crabs.
4. How do antagonistic muscle pairs work?
Show Answer
One muscle contracts while the other relaxes. For example, when biceps contract (flexing elbow), triceps relax, and vice versa.
5. What are the three types of joints based on movement?
Show Answer
Fixed/immovable (skull sutures), partly movable (between vertebrae), and freely movable/synovial (elbow, hip).
Did You Know?
The human skeleton completely renews itself every 10 years! Babies are born with about 300 bones, but some fuse together as they grow, resulting in 206 bones in adults. The smallest bone is the stapes in the ear (just 3mm long), and the largest is the femur (thigh bone).
Key Terms
Quick Recap
- Three skeleton types: hydrostatic (fluid-filled), exoskeleton (external), endoskeleton (internal)
- Human skeleton: 206 bones divided into axial and appendicular skeleton
- Ligaments connect bone to bone; tendons connect muscle to bone
- Joints: fixed, partly movable, and freely movable (synovial)
- Muscles work in antagonistic pairs (biceps/triceps)
- Common diseases: rickets (Vitamin D deficiency), osteoporosis (bone density loss), arthritis (joint inflammation)
