Movements

What is movement?

Movement, or motion, is the state of changing something's position—that is, changing where something is. A flying bird or a walking person are moving, because they change where they are from one place to another.

No Movement, stationary & Flying Bird-Movement

What is Locomotion?

Locomotion is directional movement that enables someone or something to move from one location to another. The word derives from the Latin words locō (place) and mōtiō (to move).

Note: Locomotion is typically a voluntary movement.

Movement can be either voluntary or involuntary.

Different movements in different animals:

1.Ctenophora

Ctenophora (comb jellies) are invertebrate marine animals. For swimming around, they use little protrusions of the cells – cilia – and are also the largest animals to use cilia for swimming. The largest comb jellies can grow up to 1.5 metres in length. Although corals live as colonies attached to the seafloor, their larvae use cilia for swimming to the surface of the water in order to develop, after which they again descend to the bottom and form a colony.

2. Starfishes

Starfishes are echinoderms, as are sea urchins and sea cucumbers. These marine animals move along the seafloor by using little limbs that protrude from the body. Movement takes place when the starfish pumps water into the limbs by turns, creating a wavelike motion in the limbs.

Figure shows movement in starfish

3. Snails are molluscs.

They move around by crawling along the ground, on plants or the seafloor. The underside of their body generates wave-like movements that carry them forward on the ground. Some sea snails can also swim. For this purpose they have evolved small specialized wings that they wave in order to move in water.

4. The diversity of arthropods is immense, both in their ways of life and in appearance. Most crustaceans live in water, where they use legs for swimming and walking. Crustaceans that move on land – such as woodlouses – also use legs for walking. But among insects, we find all kinds of ways of moving around: flying, swimming, crawling, burrowing, as well as simply walking and running. As adults, the majority of insects can fly, and they have wings. Beetles have foldable hindwings that are hidden under forewings while at rest. Many insect larvae are capable of burrowing in the soil or decaying matter. Mole crickets spend most of their lives digging tunnels in the soil, but females fly to seek for a mate. Butterfly caterpillars have prolegs with a very good grip, which they use to move on leaves and branches. Insects that swim in water use legs for swimming, such as water beetles and backswimmers, or the energy of water ejected from the body, such as dragonfly nymphs.

In vertebrates we can see that among the larger groups of animals there is a dominant way of moving around: fishes swim, birds fly and mammals move on land. However, there are exceptions even in these groups. For example, the fish called mudskipper can use its fins to move on dry land and is capable of breathing through its skin; the sailfish can travel short distances by gliding above the water; and some fishes, such as moray eels, dig themselves into the seafloor.

Moving in water:

1. Grey Seals feed on fish. Their main diet consists of herring, European whitefish and sprat, but they also feed on carp, eelpouts, flatfishes and salmon. A Grey Seal eats about 7 kg of fish every day. Grey Seals weigh up to 300 kg and are 1.5-2.5 metres in length. The head of the Grey Seal has a longer snout than the Ringed Seal, who is smaller and also lives in the Baltic Sea.

2. Freshwater mammals, such as otters and beavers have webbing between their toes, and swimming is also assisted by the tail. The European Beaver (see drawing), our largest rodent, eats vegetative food. It fells down trees and uses their branches and trunks to construct dams and lodges on the water. The European Otter is a predator who mostly feeds on fish and slugs.

3. Fishes have adapted to life in water. Fishes swim by moving their bodies and the tail area, with the work of the tail fin being especially important. Fins allow the fish to move, to keep balance and to turn. Fish keep their balance with pelvic and pectoral fins. The scale-covered, streamlined body is slimy, which helps them swim faster. For moving up and down, and for keeping to a particular depth, fish use a gas-filled swim bladder. By changing the volume of the bladder, fish can descend deeper or rise up, closer to the water’s surface. When descending from the surface to the depth of 10 metres, the volume of the swim bladder decreases by half. For detecting vibrations in water, fish also have the lateral line organ.

Types of Body Movement in Humans:

Flexion and Extension

Flexion and extension are movements that take place within the sagittal plane and involve anterior or posterior movements of the body or limbs. For the vertebral column, flexion (anterior flexion) is an anterior (forward) bending of the neck or body, while extension involves a posterior-directed motion, such as straightening from a flexed position or bending backward. Lateral flexion is the bending of the neck or body toward the right or left side. These movements of the vertebral column involve both the symphysis joint formed by each intervertebral disc, as well as the plane type of synovial joint formed between the inferior articular processes of one vertebra and the superior articular processes of the next lower vertebra.

Abduction and Adduction

Abduction and adduction motions occur within the coronal plane and involve medial-lateral motions of the limbs, fingers, toes, or thumb. Abduction moves the limb laterally away from the midline of the body, while adduction is the opposing movement that brings the limb toward the body or across the midline. For example, abduction is raising the arm at the shoulder joint, moving it laterally away from the body, while adduction brings the arm down to the side of the body. Similarly, abduction and adduction at the wrist moves the hand away from or toward the midline of the body. Spreading the fingers or toes apart is also abduction, while bringing the fingers or toes together is adduction. For the thumb, abduction is the anterior movement that brings the thumb to a 90° perpendicular position, pointing straight out from the palm. Adduction moves the thumb back to the anatomical position, next to the index finger. Abduction and adduction movements are seen at condyloid, saddle, and ball-and-socket joint

Circumduction

Circumduction is the movement of a body region in a circular manner, in which one end of the body region being moved stays relatively stationary while the other end describes a circle. It involves the sequential combination of flexion, adduction, extension, and abduction at a joint. This type of motion is found at biaxial condyloid and saddle joints, and at multiaxial ball-and-sockets joints

Rotation

Rotation can occur within the vertebral column, at a pivot joint, or at a ball-and-socket joint. Rotation of the neck or body is the twisting movement produced by the summation of the small rotational movements available between adjacent vertebrae. At a pivot joint, one bone rotates in relation to another bone. This is a uniaxial joint, and thus rotation is the only motion allowed at a pivot joint. For example, at the atlantoaxial joint, the first cervical (C1) vertebra (atlas) rotates around the dens, the upward projection from the second cervical (C2) vertebra (axis). This allows the head to rotate from side to side as when shaking the head “no.” The proximal radioulnar joint is a pivot joint formed by the head of the radius and its articulation with the ulna. This joint allows for the radius to rotate along its length during pronation and supination movements of the forearm.

Excursion

Excursion is the side to side movement of the mandible. Lateral excursion moves the mandible away from the midline, toward either the right or left side. Medial excursion returns the mandible to its resting position at the midline.

Joints:

There are three types of joints in the body. Synovial joints are freely movable and allow for motion at the location where bones meet. They provide a wide range of motion and flexibility

Joints can be classified by either their structure or function. Structural classifications are based on how the bones at joints are connected. Fibrous, synovial, and cartilaginous are structural classifications of joints.

Classifications based on joint function consider how movable bones are at joint locations. These classifications include immovable (synarthrosis), slightly movable (amphiarthrosis), and freely movable (diarthrosis) joints.

Immovable (Fibrous) Joints

Immovable or fibrous joints are those that do not allow movement (or allow for only very slight movement) at joint locations. Bones at these joints have no joint cavity and are held together structurally by thick fibrous connective tissue, usually collagen. These joints are important for stability and protection. There are three types of immovable joints: sutures, syndesmosis, and gomphosis.

Slightly Movable (Cartilaginous) Joints

Slightly movable joints permit some movement but provide less stability than immovable joints. These joints can be structurally classified as cartilaginous joints, as bones are connected by cartilage at the joints. Cartilage is a tough, elastic connective tissue that helps to reduce friction between bones. Two types of cartilage may be found at cartilaginous joints: hyaline cartilage and fibrocartilage. Hyaline cartilage is very flexible and elastic, while fibrocartilage is stronger and less flexible.

Freely Movable (Synovial) Joints

Freely movable joints are classified structurally as synovial joints. Unlike fibrous and cartilaginous joints, synovial joints have a joint cavity (fluid-filled space) between connecting bones. Synovial joints allow for greater mobility but are less stable than fibrous and cartilaginous joints. Examples of synovial joints include joints in the wrist, elbow, knees, shoulders, and hip.

Skeleton System:

The skeletal system provides support and protection for the body’s internal organs and gives the muscles a point of attachment. Humans have an endoskeleton, where our bones lie underneath our skin and muscles. In other animals, such as insects, there is an exoskeleton on the outside of the body

In humans, the skeletal system consists of bones, joints and associated cartilages. An adult human has 206 bones in their body and variety of different joints.

Skeletal System Function

Support

The first and most apparent function of the skeletal system is to provide a framework for the body. The presence of a firm bony skeleton allows the organism to have a distinctive shape adapted towards a particular lifestyle. For instance, in a fast-moving animal like the cheetah, the skeleton contains long, thin limb bones and an extremely flexible spine. The structure of the skeleton also allows it to absorb the impact of running at high speeds.

The bones of birds are hollow, light and create a streamlined body adapted for flight. Many animals even have sexual dimorphism in their skeletons. In humans, while this dimorphism is fairly limited, there are differences in the angle of the pelvic bones, to accommodate pregnancy.

Integration with the Muscular System

The skeletal system also provides an important form of attachments to the muscular system. Bones and exoskeletons are hard and do not bend or move when muscles are flexed. This means that the contraction of muscle cells will lead to the shortening of muscles, while the bone retains its shape. This basic structure allows muscles to move different parts of the body, using forces generated while pulling on the skeletal system.

Protection

The next obvious function of the skeletal system is the role it plays protecting the fragile internal organs. In humans, this is seen in the skull, which surrounds the brain completely. It is also exhibited by the ribcage, which surrounds the lungs and heart but still allows for expansion. Even invertebrates like snails and prawns often have hard exoskeletons to protect themselves from predators.

The rigid endoskeleton allows the body to rise up above the ground or stand upright, and bears the weight of the organism, and provides the scaffolding for movement. Muscles generate the force required to move bones at joints. Muscle fibers contain actin and myosin, two protein filaments that can slide past each other to change the length of the muscle. When a nerve impulse arrives at the neuromuscular junction, it signals the muscle to contract. The force generated by the contracting muscle either pulls two bones together or apart, based on the nature of the interaction between the muscle and joint.

Blood Cell Production

The central part of a bone contains the bone marrow, the primary site for blood cell production in adult humans. There are two types of bone marrow in adults. Around 50% is red bone marrow containing hematopoietic stem cells and supportive tissue. The rest is yellow bone marrow made of fat and its proportion increases with age.

Bone marrow will revert to a higher proportion of red marrow if the body suffers an injury and needs to create more red blood cells. The bone marrow composition also changes during pregnancy and lactation in mammals. Over the course of gestation, blood volume increases by about 1.5 liters, and even the concentration of red blood cells and white blood cells increase.

Production of other Cell Types

In addition to producing red blood cells, bone marrow within the skeletal system is the production site of a number of other cells. These include lymphocytes, which are immune cells that travel the lymphatic system. In addition to providing immune functions, the skeletal system is also responsible for hosting stem cells which can differentiate into muscle cells, cartilage-producing cells, and cells that create bone (osteoblasts).

Osteoblasts in bone also have an endocrine function, secreting a hormone called osteocalcin. It requires vitamin K to be synthesized and is an anabolic hormone. It mediates an increase in insulin levels and increases the sensitivity of the body to insulin. Osteocalcin contributes to an increase in bone mass and bone mineralization.

Storing Minerals

The bones of the skeletal system act as a storehouse for calcium ions, changing the quantum of mineralized deposits within bones to maintain plasma calcium ion concentration within a narrow range. Calcium ions can affect crucial sodium ion channels in the plasma membrane of every cell, thereby affecting overall homeostasis.

For this reason, changes to the concentration of calcium ions have particularly adverse effects on excitable cells in the nervous system, and in cardiac, skeletal and smooth muscle. Different interacting hormones maintain the balance of calcium ions in the plasma and bones, especially the parathyroid hormone secreted from the parathyroid glands in the neck.

Skeletal System Parts

The anatomy of the skeletal system is complex, and it includes hundreds of bones in the human body. The anatomy of the system varies widely between organisms, as evolution has selected for various adaptations in certain species which change the structure and function of their bones.

Bone

Bones serve a variety of functions, but the most important is supporting movement of the limbs and body. Two bones or cartilages are held together at a joint through tough connective tissues called ligaments. Muscles are securely attached to bones through flexible but inelastic connective tissue called tendons. Muscles, joints, tendons, and ligaments are part of the intricate machinery that allows the movement of different bones.

Joints

Functionally, joints can be divided into three classes based on the range of movement they allow in the associated bones. Immovable joints are formed when two bones are held together by fibrous connective tissue with no synovial fluid. These kinds of joints hold the bones of the cranium together.

Partially movable joints are also called cartilaginous joints and are present in the spine and ribs. The third type of joints are called synovial joints and have a fluid-filled synovial cavity that allows the interfacing bones the largest range of movement. Based on the structure of the synovial joints, they can be classified into 6 types, including the hinge joints of the fingers and the ball and socket joints of the hips and shoulders.

Cellular Composition

Each bone is made of complex sets of cells, tissues and a specialized extracellular matrix. The two main cell types are called osteoblasts and osteoclasts with mostly opposing functions. While osteoblasts are involved in the formation of bone, osteoclasts are associated with a reduction in bone mass. The extracellular matrix of the bone consists of collagen and other organic fibers as well as the inorganic component containing calcium salts such as hydroxyapatite. In the interior of bones, a soft tissue called the bone marrow plays an important role in immunity and hematopoiesis. The bone is also richly supplied with nerves and blood vessels.

Skeletal System Structure

In general, the skeletal system is structured to provide support against gravity and protect an animal’s internal organs. While this article mainly discusses the human skeletal system, most animals have some sort of skeleton. Some animals, like sponges, can have an extremely simplified skeleton made of calcium deposits within the animal. Others, like the turtle, have drastically modified their skeletal system to provide extra protection.

While this article mostly discusses an endoskeleton, many animals use an exoskeleton for the same purposes. Instead of bones being on the inside, the bones, protective plates, or chitinous skeleton actually surrounds the muscles. While this may seem completely different, the structure of the system is still very similar. The only difference is that muscles and tendons connect to the inside of the system, rather than to the surface of bones.

The structure of the skeletal system reflects an animal’s evolution, as well as the needs it has to survive. For example, humans have a tailbone. This is an evolutionary relic, from the time when our ancestors had tails and were swinging from the trees. As we became bipedal, we lost the need for a tail, and it was reduced to a single, nonfunctional bone. Likewise, all animals are constantly adapting and changing their skeletal system through evolutionary time.

Muscles-

Human muscle system, the muscles of the human body that work the skeletal system, that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle—like the muscles of all vertebrates—is often divided into striated muscle (or skeletal muscle), smooth muscle, and cardiac muscle. Smooth muscle is under involuntary control and is found in the walls of blood vessels and of structures such as the urinary bladder, the intestines, and the stomach. Cardiac muscle makes up the mass of the heart and is responsible for the rhythmic contractions of that vital pumping organ; it too is under involuntary control. With very few exceptions, the arrangement of smooth muscle and cardiac muscle in humans is identical to the arrangement found in other vertebrate animals.

Skeletal muscles are our voluntary muscles, meaning that we can control them at will. We use them to govern movement and posture and regulate body temperature.

Smooth muscle

Smooth muscle is involuntary muscle tissue controlled by the autonomic nervous system. It lines organs such as the stomach and bladder as well as our blood vessels. 

Smooth muscle contracts much more slowly than skeletal and cardiac muscle. Its purpose is to move substances through an organ or vessel, and it does so by contracting in waves, which is known as peristalsis (and occurs, for example, in the intestines).

Cardiac muscle

Cardiac muscle is found only in the heart. Another involuntary muscle controlled by the autonomic nervous system, it stimulates itself using electrical impulses to contract and pump blood around our bodies.

This is made possible by specialised junctions called ‘intercalated discs’, which lie between the heart muscle cells (cardiomyocytes), defining their borders. These discs help conduct impulses from one cell to another rapidly, allowing them to synchronise their contractions.

Like skeletal muscle, cardiac muscle tissue is striated. In between its fibres are intermittent spaces, which contain connective tissue and many capillaries to ensure a constant supply of oxygen.

The thickness of cardiac muscle differs across the heart. For example, the left ventricle has to pump blood all over the body, and is therefore characteristically thick. The wall of the right ventricle is thinner, as it only has to pump oxygen-depleted blood the short distance from the heart to the lungs. 

Summary

Type of muscle	Where found?	Voluntary or involuntary?	Striated?
Skeletal	Over joints, throughout body	Voluntary	Yes
Smooth	Blood vessels, intestines, stomach, uterus, bladder, lungs	Involuntary	No
Cardiac	Heart	Involuntary	Yes