S-Cool Revision Summary
S-Cool Revision Summary
Functions of the Skeleton:
The Skeleton is a framework of bones that is held together by ligaments and joints, and has the following four functions:
movement, protection, support and blood production.
Parts of the Skeleton:
There are two parts to the skeleton; the axial skeleton and the appendicular skeleton.
The axial skeleton consists of the skull, the rib cage and the vertebral column.
The appendicular skeleton is made up from the pelvic girdle and the shoulder girdle. Both these girdles are quite rigid but they are attached to legs and arms that are free to move.
There are four types of bone and each type is given a name dependant of its shape or size:
Long bones, for example, the Humerus.
Short bones, for example, the Phalanges.
Flat bones, for example, the Scapula.
Irregular bones, for example, vertebrae.
Classification of Joints:
There are three kinds of joint and their classification is dependant upon how the bones are joined together.
Fibrous joints, where fibrous tissue holds the bones together.
Cartilaginous joints, these joints are linked by cartilage there is some movement, but it is very slight.
Synovial joints allow for greater ranges of movement and the type of movement will depend upon the type of joint between the bones.
A ball and socket joint: found in the shoulder and hip allows the greatest range of movement.
A hinge joint: found at the elbow and knee where movement is limited to one plane just like a door hinge.
A condyloid joint: found at the wrist and ankle. Movement is in two planes but not as great as the ball and socket.
A pivot joint: found in the neck where part of the bone fits into another ring of bone as in the atlas and axis, allowing rotation of the head.
A saddle joint: found at the base of the thumb allows the thumb to be moved in two directions.
A gliding joint: found in the wrist and vertebral column.
Parts of the Lever
It is due to muscles acting upon a system of levers; the skeleton that movement of some part of the body occurs. There are three types of lever, but all levers have three parts:
The Fulcrum. Is the point of movement or pivot, generally at the centre of a joint.
A Load. The load is the body's weight or some external object.
An Effort. An effort is a muscular force to move the load.
Classification of Levers
There are three classes of lever and each is classified depending upon where in relation to each other the fulcrum, the load and the effort are.
First Order Levers:
The fulcrum is between the effort and the load.
Both effort and load are in the same direction.
An example of this is the head where the head pivots on the atlas (fulcrum).
The load is the weight of the head going down.
The effort is the muscles at the back of the neck pulling down.
Second Order Levers:
The fulcrum is at one end of the lever.
The load is in the middle of the lever.
The effort is at the opposite end of the lever to the fulcrum with the direction of effort opposite the load.
An example of this is stepping up onto your toes. The fulcrum is at the toes. The load is that of the body going through the middle of the foot and the effort is in the calf muscles pulling the body up onto the toes.
This is the most effective lever as a relatively small force can move a large weight.
Third Order Levers:
Like second order levers, the fulcrum and load are at opposite ends of the lever but the effort is off-centre of the lever towards the fulcrum. This is not as efficient as second order levers but small muscle movement creates long lever movement.
An example of this is a biceps curl. The load is in the hand, the fulcrum is at the elbow and the biceps make the effort.
Types of Muscle:
There are three main types of muscles in the body. Each type has a special purpose that is vital to the normal functioning of the body:
Smooth or Involuntary Muscle. Found in the bowel, the gut and internal organs. There is no direct control of this muscle, that is, it works automatically.
Cardiac or heart muscle is specialised muscle that contracts constantly and automatically. Some factors can affect the speed of the contractions such as exercise and the release of hormones such as adrenaline. Further details of the heart can be found in the Circulatory System.
Skeletal muscles are the ones that can easily be seen as a shape under the skin. Unlike smooth muscle or cardiac muscle, we can control skeletal muscles and because of this it is sometimes known as voluntary muscle.
Muscle Fibre Types:
There are two types of muscle fibre, slow and fast twitch.
They are physiologically different and the percentage of each in a muscle is determined genetically.
The amounts of fast twitch or slow twitch fires in the muscle will determine their suitability to certain sporting activities.
This is why there are people who are 'natural' endurance athletes; they have greater amounts of slow twitch fibre which contracts slowly with little force but do not tire easily.
Other people have greater amounts of fast twitch fibres and are 'naturally' good at sprinting and throwing. These fibres produce larger forces but tire quickly.
Contraction of Skeletal Muscles
Skeletal muscle contractions are stimulated by electrical signals transmitted along motor nerve fibres that have been sent from the central nervous system (see Nervous System).
Cross-bridges are formed between the myosin and actin molecules. The cross-bridges originate on the myosin molecule and attach themselves to the actin molecule. They then drag the actin molecule towards the origin of the muscle. It is the actin molecule that is active and moves the myosin molecules are fixed.
Muscle Contraction and Energy
Duration of the nervous stimulus will determine the duration of the muscle contraction.
The strength of the stimulus will determine the force that the muscle contraction exerts.
There is a limited quantity of ATP in the muscle and for muscle contraction to continue over a long period of time.
ATP has to be re-built from ADP + P. The re-building of ATP is known as muscle respiration.
Antagonistic Muscle Action
Muscles can only contract and pull. Therefore, joints have to have two or more muscles working opposite each other. This is known as antagonistic muscle action.
For this to occur, one end of the muscle must be fixed. This is known as the origin. When the muscle contracts, the other end of the muscle then moves towards the origin.
The end that moves is known as the insertion.
A good example of this is the upper arm where the triceps and biceps are on opposite sides of the humerus.
The origins of both the triceps and the biceps are at the top of the humerus near the shoulder joint.
As the bicep contracts the lower arm (radius and ulna) moves up towards the shoulder. The triceps relax to allow this movement to happen.
The bicep is the prime mover or agonist, while the tricep is the secondary mover or antagonist.
Muscles are attached to bones at either side of the joints by tendons.
Muscle Contraction for Movement:
There are three types of muscle contraction.
Isometric: muscle remains the same length.
Isokinetic: the speed of the contraction remains constant throughout the movement.
Isotonic contraction can be divided into two types:
Concentric: the muscle shortens as it contracts.
Eccentric: the muscle lengthens but is still under tension.
Types of Body Movement:
Due to the range of movements required in sport, it is useful to be able to describe them technically.
Flexion: bringing two parts of a limb together - bending at the joint.
Extension: moving two parts of a limb away from each other - straightening at the joint.
Abduction: moving limbs away from the centre of the body.
Adduction: Moving limbs towards the centre of the body.
Circumduction: the movement of a limb around a joint.
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