Requirements for Movement (DP IB Biology)
Revision Note
Role of The Skeleton in Movement
The effective movement of the human body requires both muscle and an incompressible skeleton
Bones and exoskeletons provide anchorage for muscles and act as levers
Vertebrates have internal bones, called an endoskeleton, to support their bodies from the inside with tissues surrounding the bone
Many organisms, such as arthropods, have external skeletons called exoskeletons which are found on the outside of the organism to protect the internal tissues
Arthropods that have exoskeletons include:
Crustaceans
Insects
Arachnids
Centipedes and millipedes
Molluscs
Exoskeletons are made of polysaccharides called chitin
Key features of both exo and endo skeletons is that they provide support for the body of the organism whilst also facilitating movement
Exoskeletons also provide protection for the body's soft tissues within
Muscles are anchored to the skeleton either on the inside (as with exoskeletons) or the outside (as with endoskeletons) and the presence of pivot points means that skeletons act as levers transferring the size and direction of force
Levers have a point of effort, a point of load and a pivot point called the fulcrum
These same three features are seen in skeletons
Levers and Skeleton Diagram
Muscles attach to bones at the joints creating a system of levers
Arthropod exoskeletons also use the mechanisms of leverage in the same way as animals use with endoskeletons
They utilise jointed legs and jointed body parts with muscles attached in antagonistic pairs
Synovial Joints
Synovial joints are the most common type of joint in the human body
They are characterised by a joint cavity filled with a lubricating synovial fluid which reduces friction
The fluid is produced by the synovial membrane, which surrounds the joint
Synovial joints are capable of a variety of different movements which depends on the structure within the joint including the joint type and the ligaments
The movements possible at the joint are
Flexion
Extension
Rotation
Abduction (the movement of a limb away from the body)
Adduction (the movement of a limb towards the body)
Examples of Different Joint Types and their Associated Movements Table
Joint | Movement |
---|---|
Knee (hinge) | Flexion and extension |
Elbow (hinge) | Flexion and extension |
Hip (ball and socket) | Flex, extend, rotate, sideways and backwards |
Shoulder | Abduction and adduction, flexion and extension |
The Human Hip Joint
The hip joint is a ball and socket synovial joint
Articulation is between the bones of the femur (the ball), and the pelvis, (the socket)
Cartilage covers both bones and provides as surface to prevent the bones rubbing against each other
Synovial fluid is enclosed within the ball and socket by a membrane, it's function is to provide lubrication for smooth movement
The whole joint is encircled by ligaments which hold the bones in place; ligaments are made of a tough connective tissue
Skeletal muscles are involved to allow the femur to move within the pelvis socket
The muscles are connected to each bone via tendons
Hip Ball and Socket Diagram
The structure of the hip synovial joint
Examiner Tips and Tricks
You are not required to name the muscles and ligaments involved in the hip joint, but you should be able to name the femur and pelvis.
Antagonistic Muscles
There are over 600 skeletal muscles in the human body
Muscles are effectors, stimulated by nerve impulses from motor neurones (specialised cells adapted to rapidly carry electrical charges called nerve impulses from sensory neurones to the muscles to bring about movement)
Lengths of strong connective tissue called tendons, connect muscles to bones
They are flexible but do not stretch when a muscle is contracting and pulling on a bone
Muscles are only capable of contracting or pulling, they cannot push
As a result of this limitation muscles generally operate in pairs
One muscle pulls in one direction at a joint and the other muscle pulls in the opposite direction
This is described as antagonistic muscle action
Internal and external intercostal muscles
An example of this can be seen in the intercostal muscles of the rib cage
Two sets of intercostal muscles to work antagonistically to facilitate breathing
External intercostal muscles, pull the rib cage up
Internal intercostal muscles pull the ribcage down
During inhalation
The external set of intercostal muscles contract to pull the ribs up and out:
This increases the volume of the chest cavity (thorax)
Leading to a decrease in air pressure inside the lungs relative to outside the body
Air is drawn in
During exhalation
The external set of intercostal muscles relax so the ribs drop down and in
This decreases the volume of the chest cavity (thorax)
Leading to an increase in air pressure inside the lungs relative to outside the body
Air is forced out
Note that the diaphragm also relaxes and contracts during ventilation, but this is not part of an antagonistic muscle pair
The movement of the rib cage in opposite directions is due to the orientation of the muscle fibres in the internal and external layers of the intercostal muscles
As the external intercostal muscles contract, their expansion of the rib cage results in the stretching of the internal intercostal muscles
The stretching results in stored potential energy within the titin protein of the sarcomere of the internal intercostal muscles
The same is true for the antagonistic action of this muscle pair
Intercostal muscles diagram
The intercostal muscles are an example of an antagonistic muscle pair
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