muscles exstend

Question 1

several things muscles can do

Answer 1

Irritability (Responsiveness) – This means the muscle can sense and respond to nerve signals from a motor unit. It’s like the muscle “feels” the signal and gets ready to act.

Contractility – This is the special power muscles have to forcefully contract (get shorter) when they are stimulated. No other tissue in the body can do this like muscle can.

Extensibility – Muscles can stretch or extend when needed. This is important when another muscle is contracting on the opposite side.

Elasticity – After being stretched, muscles can snap back to their original resting length. It’s like a rubber band returning to shape after being pulled.

Question 2

orgin and insertion

Answer 2

Every one of our 600-odd skeletal muscles is attached to bone, or to other connective tissue structures, at no fewer than two points. One of these points, the origin, is attached to the immovable or less movable bone (Figure 6.12). Think of the origin as the anchor, or leverage, point. Another point, the insertion, is attached to the movable bone. When the muscle contracts, the insertion moves toward the origin.

Question 3

orgin or insertion can be interchangeable

Answer 3

Some muscles have interchangeable origins and insertions, depending on the action being performed. For example, the rectus femoris muscle of the anterior thigh crosses both the hip and knee joints. Its most common action is to extend the knee, in which case the proximal pelvic attachment is the origin. However, when the knee bends (by other muscles), the rectus femoris can flex the hip, and then its distal attachment on the leg is considered the origin.

Question 4

prime mover and antagonist

Answer 4

The prime mover is the muscle that does the main action (like bending the arm).
The antagonist does the opposite movement, bringing the body back to the starting position.
The antagonist can become the prime mover — but only when doing a different action.

Bending your arm:

Prime mover = Biceps

Antagonist = Triceps (relaxes and stretches)

Straightening your arm:

Prime mover = Triceps

Antagonist = Biceps

Question 5

synergist

Answer 5

The synergist is a helper muscle. It either:

Does the same movement as the prime mover, or

Helps by stabilizing or preventing unwanted movement in other parts that the prime mover doesn’t want to move.

Question 6

fixator

Answer 6

A fixator is a special kind of synergist that stabilizes a bone, especially the origin of a prime mover.
This lets the prime mover pull strongly and accurately on the insertion without the whole body moving or wobbling.