Support and Movement in Humans and Animals, revision notes

Overview

Animals need support to hold their shape and a system to move. This chapter covers the types of skeleton, the human musculoskeletal system, how antagonistic muscles move a joint, and related health issues.

The biceps-and-triceps example of antagonistic muscles is a classic exam question.

Beyond the human arm, content standard 14.3 expects you to relate a skeleton and its muscles to how an animal actually moves through its own habitat. A fish bends a flexible vertebral column into travelling waves by contracting muscle blocks called myotomes along each side of its body, using its tail fin for main thrust and other fins for steering and balance in water.

A bird instead combines a light, largely fused skeleton with hollow bones and a keeled sternum, a bone that anchors the powerful flight muscles pulling the wings downward for lift and upward for recovery. Comparing locomotion across water, air and land is a favourite way examiners test structure-function understanding rather than memorised facts.

Health issues form the final content standard, 14.4, and are usually tested through short structured questions that ask for a cause, an effect and a preventive measure. Osteoporosis develops when the rate of bone breakdown outpaces the rate of bone rebuilding, so density falls; it is linked to low calcium or vitamin D intake, hormonal changes and ageing, and it raises the risk of fracture from even a minor fall.

Arthritis is inflammation of a joint, most often affecting the cartilage that cushions bone ends or the synovial membrane that lines the joint capsule, producing pain, swelling, stiffness and reduced movement. Weight-bearing exercise and a balanced diet help protect against both conditions.

Types of skeleton (14.1)

A skeleton gives an animal support, holds its shape and provides a framework against which muscles can work to produce movement. Three types are studied.

A hydrostatic skeleton, as in the earthworm, uses the pressure of fluid held in body compartments; muscles squeeze against this fluid to change the body shape and move. An exoskeleton, as in insects and crabs, is a hard outer casing that also protects the soft body inside.

An endoskeleton, as in humans and other vertebrates, is an internal framework of bone and cartilage that supports the body from within and gives muscles a firm attachment.

A key idea for this standard is why an exoskeleton limits growth. Because it is a rigid outer shell, it cannot expand as the animal inside grows, so an insect or crustacean must periodically moult, shedding the old exoskeleton and hardening a larger new one before the body can increase further in size.

An endoskeleton grows steadily with the animal, so no moulting is needed.

The human musculoskeletal system (14.2)

The human musculoskeletal system combines bones for support, joints for movement and muscles to produce force. A skeletal muscle is joined to a bone at each end by a tough band called a tendon, while a ligament joins one bone to another and holds a joint together.

A useful way to keep these apart is that a tendon connects muscle to bone, and a ligament connects bone to bone.

Bone itself is a hard, living tissue reinforced with calcium and phosphate salts, giving the skeleton the rigidity needed to support the body and protect organs such as the brain and heart. A long bone such as the femur has a tough outer covering called the periosteum, which carries blood vessels and nerves; beneath it lies dense compact bone for strength, surrounding a central marrow cavity that makes blood cells and stores fat, with spongy bone at each rounded end.

Cartilage is a softer, more flexible connective tissue that cushions joint surfaces and forms flexible parts such as the outer ear and the nose tip.

Joints and antagonistic muscles (14.2)

Joints allow the skeleton to bend. A hinge joint, as at the elbow and knee, allows movement in one plane, while a ball-and-socket joint, as at the shoulder and hip, allows movement in all directions.

Muscles move these joints, but a muscle can only pull by contracting; it cannot push. This is why skeletal muscles are arranged in antagonistic pairs, where one muscle pulls a bone one way and a second muscle pulls it back.

The classic example is the arm at the elbow. To bend the arm, the biceps contracts and pulls the forearm up while the triceps relaxes; to straighten it, the triceps contracts and pulls the forearm down while the biceps relaxes.

The same principle works at the knee, where the quadriceps at the front of the thigh straightens the leg while the hamstrings relax, and the hamstrings bend the leg while the quadriceps relaxes.

Movement and locomotion across habitats (14.3)

Locomotion is the movement of the whole body from place to place, and the way an animal does it matches its habitat. A fish bends its flexible vertebral column into travelling side-to-side waves by contracting blocks of muscle called myotomes arranged along both sides of the body, pushing against the dense medium of water; the tail fin gives most of the forward thrust while the other fins steer, balance and brake.

A streamlined body reduces drag.

A bird is built for the light demands of flight. Its bones are largely hollow and fused, cutting the number of separate joints and the overall mass that must be lifted, and a keeled sternum, a ridge of bone on the chest, gives a large surface for attaching the powerful flight muscles that pull the wings down for lift and thrust.

A land mammal instead swings jointed limbs against solid ground. Comparing locomotion across water, air and land is a common way examiners test structure-and-function reasoning rather than memorised facts.

Bone compared with cartilage (14.2)

Bone and cartilage are both parts of the human skeleton, but they suit different jobs. Bone is hard and mineralised, built for support, movement and protection of organs, and it cannot bend without breaking.

Cartilage is softer and more flexible, so it cushions the ends of bones where they meet at a joint, lets surfaces slide smoothly, and forms the flexible outer ear, nose tip and parts of the airway. Knowing which tissue does which job is a common short-answer target.

Health issues of the musculoskeletal system (14.4)

Osteoporosis develops when the rate of bone breakdown outpaces the rate of bone rebuilding, so bone density falls and bones fracture easily, even from a minor fall; it is linked to low calcium or vitamin D intake, hormonal changes and ageing. Arthritis is inflammation of a joint, usually affecting the cartilage that cushions bone ends or the synovial membrane lining the joint, and it causes pain, swelling, stiffness and reduced movement.

The two are different conditions: osteoporosis weakens bone, while arthritis inflames a joint.

Injuries are also examined. A dislocation is a bone forced out of its normal position at a joint, often tearing the surrounding ligaments, while a sprain is the milder overstretching or partial tearing of a ligament with the bone still in place.

Caring for the system through regular weight-bearing exercise, adequate calcium and vitamin D, and correct posture helps protect against bone loss and joint damage.

Key concepts to master

• Types of skeleton, Hydrostatic skeleton (e.g. earthworm), exoskeleton (e.g. insects) and endoskeleton (e.g. humans) each support and allow movement.
• Musculoskeletal system, Bones give support, joints allow movement, and muscles attached by tendons produce the force.
• Joints, A hinge joint (elbow, knee) allows movement in one plane; a ball-and-socket joint (shoulder, hip) allows movement in many directions.
• Antagonistic muscles, Muscles work in pairs: when the biceps contracts to bend the arm, the triceps relaxes, and the reverse straightens it.
• Movement and locomotion, Muscle contraction pulls on bones across a joint to produce movement; locomotion is movement of the whole body.
• Health issues, Arthritis (joint inflammation) and osteoporosis (weak bones) affect the musculoskeletal system.
• Locomotion in water, A fish bends its flexible vertebral column into side-to-side waves by contracting myotome muscle blocks arranged along both sides of the body, pushing against the denser medium of water. The tail fin provides most of the forward thrust, while the dorsal, pelvic and pectoral fins give stability, steering and braking as the fish swims.
• Locomotion in air, A bird's skeleton is light because many bones are hollow and fused, reducing the number of separate joints and the overall mass that must be lifted. A keeled sternum, a ridge of bone on the chest, anchors large flight muscles that pull the wings down to generate lift and thrust, then relax as smaller muscles raise the wings again.
• Bone versus cartilage, Bone is a hard, living tissue reinforced with calcium and phosphate salts, giving the skeleton the rigidity needed for support, movement and protection of organs such as the brain and heart. Cartilage is softer, more flexible connective tissue that cushions joint surfaces, allows smooth movement and forms flexible parts such as the outer ear, the nose tip and parts of the airway.
• Skeletal muscle attachment, A skeletal muscle is joined to a bone by a tendon at each end, so contraction pulls the two bones of a joint closer together. Because a tendon cannot push, every movement in one direction needs a second muscle, or muscle group, to pull the joint back the other way once the first muscle relaxes.
• Caring for the musculoskeletal system, Regular weight-bearing activity such as walking or jogging stimulates bone to stay dense, while an adequate daily intake of calcium and vitamin D supplies the minerals bone needs and helps the body absorb them. Correct posture when sitting, standing or lifting, together with avoiding repetitive strain, reduces the long-term risk of joint damage and bone loss.
• Antagonistic muscles at the knee, At the knee, the quadriceps on the front of the thigh and the hamstrings at the back form another antagonistic pair: the quadriceps contracts to straighten the leg while the hamstrings relax, and the hamstrings contract to bend the leg while the quadriceps relaxes, the same principle as the biceps and triceps at the elbow.
• Why an exoskeleton limits growth, Because an exoskeleton is a rigid outer casing, it cannot expand as the animal inside grows. An insect or crustacean must therefore periodically shed its old exoskeleton in a process called moulting, or ecdysis, and quickly harden a new, larger one underneath before the body can increase further in size.
• Dislocation and sprain, A dislocation occurs when a bone is forced out of its normal position at a joint, often tearing the surrounding ligaments and requiring the bone to be manipulated back into place. A sprain is a milder injury in which a ligament is overstretched or partially torn, causing pain and swelling but without the bone leaving the joint.
• Structure of a long bone, A long bone such as the femur has a tough outer covering called the periosteum, which carries blood vessels and nerves and allows the bone to grow in width; beneath it lies dense compact bone for strength, surrounding a central marrow cavity that produces blood cells and stores fat, with spongy bone at each rounded end.

Quick recall checklist

1. Can you define and explain Types of skeleton?
2. Can you define and explain Musculoskeletal system?
3. Can you define and explain Joints?
4. Can you define and explain Antagonistic muscles?
5. Can you define and explain Movement and locomotion?
6. Can you define and explain Health issues?
7. Can you define and explain Locomotion in water?
8. Can you define and explain Locomotion in air?
9. Can you define and explain Bone versus cartilage?
10. Can you define and explain Skeletal muscle attachment?
11. Can you define and explain Caring for the musculoskeletal system?
12. Can you define and explain Antagonistic muscles at the knee?
13. Can you define and explain Why an exoskeleton limits growth?
14. Can you define and explain Dislocation and sprain?
15. Can you define and explain Structure of a long bone?

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Source:SRC-DSKP-EN