What are the two primary characteristics used to define a muscle?
Muscles are defined by their location and action.
What is the origin of a muscle?
The origin is the stationary, or fixed, end of the muscle
What is the insertion of a muscle?
The insertion is the moveable end of the muscle.
In the action of elbow flexion (like curling a weight), what is the origin and insertion of the biceps brachii muscle?
The origin of the biceps brachii is on the scapula (fixed) , and the insertion is on the radius (moveable)
What is an agonist or prime mover?
An agonist is a muscle that causes a movement , and it is also called the prime mover.
What is an antagonist?
An antagonist is a muscle that opposes the action of the agonist.
During elbow flexion, which muscle acts as the agonist/prime mover, and which acts as the antagonist?
The biceps brachii is the agonist , and the triceps brachii is the antagonist.
Are the terms agonist and antagonist fixed?
No, they are relative terms. If the action were elbow extension, the triceps would be the agonist, and the biceps would be the antagonist
What is a synergist?
A synergist is a muscle that supports the action of the agonist. They help to stabilize the movements of the agonist.
Name the synergist muscles for elbow flexion.
The brachioradialis and brachialis muscles are synergists for elbow flexion
What is a fixator?
A fixator is a muscle that holds a bone in place during movement
Which muscle acts as a fixator during elbow flexion?
The deltoid muscle of the shoulder acts as a fixator by stabilizing the humerus bone.
How do muscles, bones, and joints function together?
They work together to form a network of levers to allow for body movement
Define a lever, a fulcrum, the load, and the force in the context of the human body.
A lever is a rigid structure that pivots on a fixed point (the bones).
A fulcrum is the fixed pivot point (the joints or axis) .
The load is the weight or resistance
The force is the muscle action applied to overcome the load
What is the most common form of lever in the human body?
Class III levers are the most common form of lever in the body
Describe the arrangement of a Class III lever and give an example
The applied force is between the fulcrum and the load
Example: Lifting a weight with the hand, where the elbow is the fulcrum, the arm muscles apply the force (between the elbow and hand), and the weight in the hand is the load.
What is the mechanical advantage/disadvantage of a Class III lever?
It provides a large movement distance but has reduced force because the force is applied close to the fulcrum.
Describe the arrangement of a Class II lever and give an example.
The load is between the fulcrum and the applied force.
Example: Standing on tip toes. The toe joints are the fulcrum, the body weight is the load (in the middle), and the gastrocnemius calf muscle applies the force
What is the mechanical advantage/disadvantage of a Class II lever?
This arrangement requires less force to move the load , but the distance of movement is limited.
Describe the arrangement of a Class I lever and give an example
The fulcrum is between the load and the applied force.
Example: Lifting the head. The head weight is the load, the trapezius muscle is the applied force, and the joint between the occipital condyles and the atlas vertebra is the fulcrum (in the middle)
What two factors determine the action of a muscle?
Shape and fiber direction.
What are the characteristics of a Parallel muscle?
Fibers run parallel to one another along the length of the muscle. They are the most common type. Example: Sartorius
What is a Parallel Fusiform muscle?
A parallel muscle that bulges at the center (belly) and tapers at the ends (spindle shaped). Example: Biceps brachii.
What are the characteristics of Circular muscles?
They are made of concentric rings of muscle. Contraction closes the opening.
Example: Orbicularis oris (mouth).
