Question

What are the three types of skeletons found in animals? For one of them, describe how the muscles are arranged around the skeleton and how contractions of the muscles result in movement of the skeleton.

Short answer

The three types of skeletons found in animals are hydrostatic skeleton, exoskeleton, and endoskeleton. Focusing on the endoskeleton, muscles are attached to bones through tendons, creating a system of levers. Muscles are arranged in pairs and pivot around joints, allowing for controlled and precise movement. Muscle contraction results in movement by exerting a pull on the bones, causing them to move closer together around a joint. This is facilitated by antagonistic muscle pairs, where one muscle contracts while the other relaxes.

Step-by-step solution

Identify the three types of skeletons

The three types of skeletons found in animals are: 1. Hydrostatic skeleton 2. Exoskeleton 3. Endoskeleton

Choose one skeleton type for further explanation

Among the three types of skeletons, let's choose the endoskeleton for a detailed explanation.

Describe the arrangement of muscles around the endoskeleton

In animals with an endoskeleton, the muscles are attached to the bones, usually through tendons. The bones act as a supportive structure (or framework) for the body, while the muscles are responsible for producing movement. The muscles and bones work together to create a system of levers. Muscles are arranged in pairs with their ends connected to different bones. These bones pivot around joints, and muscles on one side of the joint contract while muscles on the other side relax, allowing for controlled and precise movement.

Explain how contractions of muscles result in movement of the endoskeleton

Muscle contraction brings about movement due to the pull that the muscle exerts on the bones it is attached to. When a muscle contracts, it shortens. Since the muscle is connected to two different bones, that contraction pulls the bones closer together, causing movement around the joint. Muscles work in pairs, with one contracting while the other relaxes. This is called an antagonistic pair arrangement. For example, when a person bends their arm, the biceps muscle contracts, pulling the forearm bone closer to the upper arm bone, while the triceps muscle on the other side of the joint relaxes to allow this movement. Overall, the contractions of muscles lead to the movement of the endoskeleton by pulling bones closer together and, when working in concert with other muscles, allowing for controlled and precise movement.

Key concepts

Hydrostatic Skeleton

A hydrostatic skeleton is a type of support structure found in many soft-bodied animals, such as earthworms, slugs, and jellyfish. Unlike rigid skeletons, a hydrostatic skeleton is composed of fluid-filled compartments which provide the support for muscle contraction.

The fluid within these compartments is incompressible, which means when muscles contract, the pressure within the skeleton increases. This change in pressure results in movement. The muscles are arranged in layers, with circular and longitudinal muscles working against the hydrostatic pressure to change the shape of the animal, enabling it to move. For instance, when the longitudinal muscles of an earthworm contract, the body becomes shorter and thicker, pushing it forward through the soil.

Exoskeleton

An exoskeleton is an external shell that provides support and protection to an organism's body. You can find exoskeletons in insects, crabs, and lobsters. It is made of materials like chitin or calcium carbonate.

Since it is a rigid structure, it limits growth, which is why many exoskeletal animals must shed or molt their exoskeleton to grow, a process known as ecdysis. Muscle tissues attach to the inner surface of the exoskeleton. When these muscles contract, they cause the exoskeleton to move at the joints, facilitating motion. For example, when a crab wants to scuttle sideways, it contracts specific muscle groups attached to its legs, coordinating the bending of its exoskeletal joints to achieve movement.

Endoskeleton

Endoskeleton refers to an internal skeleton that is found in vertebrates, including humans. It is primarily made up of bone and cartilage and serves as a frame to support the body, protect internal organs, and facilitate movement.

The muscles attach to bones via tendons, and they operate by coordinating their contractions to move the bones at pivot points called joints. This endoskeletal framework enables a wide range of motions and is also involved in the production of blood cells and the storage of minerals, making it a multitasking system essential for the organism’s well-being.

Muscle Contraction and Movement

Muscle contraction is the process that leads to the movement of portions of the skeleton, depending on the skeletal type. Muscles are comprised of fibers that shorten or contract under stimuli. When a signal from the nervous system reaches a muscle, the fibers slide past each other, shortening the muscle's length.

For muscles attached to the skeleton, this contraction results in the drawing together of bones, producing movement at the joint. The ability to control the intensity and duration of muscle contractions results in the coordination necessary for complex movements such as walking, grasping, and running.

Antagonistic Muscle Pairs

Antagonistic muscle pairs refer to sets of two muscles that work against each other to move bones at a joint. One muscle of the pair contracts to move the bone in one direction, while the other muscle relaxes to allow the movement, and vice versa.

A classic example is the biceps and triceps in the human arm. When the biceps contract, the arm bends at the elbow, while the triceps relax. When the triceps contract to straighten the arm, the biceps relax. This system is key for controlled motion and prevents injury by ensuring that not all muscles contract at once, which would lead to immobility and muscle strain.