What is Anatomical pulley? Example of Anatomical pulley

Before we start exploring anatomical pulley, What is Pulley? – a pulley is a simple mechanical machine and consists of a wheel that turns readily on the axle.-the wheel is usually grooved for a rope or a wire cable.


What is an Anatomical pulley? 


In the human body, the pulley is replaced by a bone, cartilage, or ligament and the cord is replaced by a muscle tendon.
  • the tendon is lubricated by synovial fluid and the surface of the tendon is covered by a thin visceral synovial membrane.
  • the tendon is lubricated in a manner so that it may easily slide over the pulley. 

Classification of the pulley 

There are mainly four classes of pulley in the human body, The first three of them are an example of the fixed pulley and the fourth one is an example of movable one.

Class 1 Anatomical Pulley

The pulley is attached to the fixed point, the fixed pulley is acting as the first order lever. this type of pulley is used to alter the direction of the force by which the resistance or the traction can be applied to the body parts.
An improved muscle action comes from the muscle-tendon passing over external support, the external support serving as the pulley.

Example:

In the knee complex, the presence of the patella improves the efficiency of the quadriceps muscle as the pulley will increase the angle of insertion of the patellar ligament into the tibial tuberosity.

The action of the muscle at the joint is altered because of the pulley.

What is an Anatomical pulley? Example of Anatomical pulley

Class 2 Anatomical Pulley

In this type of pulley, the pulley is responsible for the action of the muscle at the joint. so because of the pulley, the action of the muscle at the joint is altered.

Example:
  1. The lateral malleolus of the fibula acts as a pulley for the peroneus longus muscle. if it was not for the malleolus, this muscle instead of passing behind the lateral malleolus to be inserted in the base of the first metatarsal and to produce ankle plantar flexion and eversion, it would have produced ankle dorsiflexion and eversion because of its passage in front of the ankle joint. so here, the pulley is a bone(lateral malleolus acts as a pulley for peroneus longus muscle).
  2. The trochlea of the eye allows the superior oblique muscle of the eye when it passes over it to rotate the eye obliquely. Without this pulley, the muscle would have little effect on the eye. The pulley is cartilage.
  3. The flexor retinaculum of the hand act as a pulley for the flexor of the finger to prevent its bowstring. Without this action, these muscles will not be effective in moving these joints. The pulley is a ligament.

Class 3Anatomical Pulley

This type of pulley is also called the movable pulley, The muscle acts as a pulley the muscle is its own pulley.

Example:

The biceps muscle increase in size so because of that its angle of insertion will increase. the muscle underneath acts as a pulley for another muscle, which passes over it. e.g brachialis will raise the biceps giving it a better angle of insertion.

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