Chapter 11 Flashcards
Muscular system
The voluntarily controlled muscles of your body.
Origin
The attachment of a muscle’s tendon to the stationary bone.
Insertion
The attachment of the muscle’s other tendons to the moveable bone.
The origin is usually ______ and the
insertion ______; the ______ is usually pulled toward the ______.
Proximal; distal; insertion; origin
Belly actions
The fleshy portion of muscle between tendons.
Reverse muscle action (RMA)
The capability of certain muscles to reverse actions during specific movements of the body; therefore, the positions of the origin and insertion of a specific muscle are switched.
Lever
A rigid structure that can move around a fixed point.
A lever is acted on at two different points by two different forces which are ______ and ______.
Effort; load
Effort
Causes movement; force exerted by muscular contractions.
Load
AKA resistance; opposes movement; the weight of the body part that is moved or some resistance that the moving body part is trying to overcome (Eg. Such as the weight of a book you might be picking up).
_______ occurs when the ______ applied to the bone at the ______ exceeds that ______.
Motion; effort; insertion; load
Fulcrum
A fixed point.
Mechanic advantage
When the load is closer to the fulcrum and the effort is farther from the fulcrum, only a relatively small effort is required to move a large load over a small distance (Eg. Compare chewing something hard (the load) with your front teeth to chewing it with the teeth in the back of your mouth. It is much easier to crush the hard food item with the back teeth because they are closer to the fulcrum (the jaw or temporomandibular joint) than are the front teeth).
Mechanical disadvantage
When the load is farther from the fulcrum and the effort is applied closer to the fulcrum, a relatively large effort is required to move a small load (but a greater speed) (Eg. Compare chewing something hard (the load) with your front teeth to chewing it with the teeth in the back of your mouth. It is much easier to crush the hard food item with the back teeth because they are closer to the fulcrum (the jaw or temporomandibular joint) than are the front teeth).
First-class levers
The fulcrum is between the effort and the load. Scissors and seesaws are examples of first-class levers. A first-class lever can produce either a mechanical advantage or a mechanical disadvantage depending on whether the effort of the load is closer to the fulcrum - Eg. Think of an adult and a child on a seesaw - if the effort (child) is farther from the fulcrum than the load (adult), a heavy load can be moved, but not very far or fast. If the effort is closer to the fulcrum than the load, only a lighter load can be moved, but it moves far and fast. There are few first-class levers in the body. One example is the lever formed by the head resting on the vertebral column. When the head is raised, the contraction of the posterior neck muscles provides the effort, the joint between the atlas and the occipital bone (atlanto-occipital joint) forms the fulcrum, and the weight of the anterior portion of the skull is the load.
Second-class levers
The load is between the fulcrum and the effort. These kind of levers operate like a wheel barrow. They always produce a mechanical advantage because the load is always closer to the fulcrum than the effort. This arrangement sacrifices speed and range of motion for force; this type of lever produces the most force. This class of lever is uncommon in the human body. An example is standing up on your toes. The fulcrum is the ball of the foot. The load is the weight of the body. The effort is the contraction of the muscles of the calf, which raise the heel off the ground.
Third-class levers
The effort is between the fulcrum and the load. These kinds of levers operate like a pair of forceps and are the most common levers in the body. Third-class levers always produce a mechanical disadvantage because the effort is always closer to the fulcrum than the load. In the body, this arrangement favours speed and range of motion over force. The elbow joint, the biceps brachii muscle, and the bones of the arm and forearm are one example of a third-class lever. As we have seen, in flexing the forearm at the elbow, the elbow joint is the fulcrum, the contraction of the biceps brachii muscle provides the effort and the weight of the hand and forearm is the load.
Fascicles
Bundles of skeletal muscle fibers (cells) within a muscle. Within a fascicle, all muscle fibers are parallel to one another. The fascicles, however, may form one of five patterns with respect to the tendons.
What are the five patterns of fascicles?
- Parallel
- Fusiform (spindle-shaped, narrow towards the ends and wide in the middle)
- Circular
- Triangular
- Pennate (shaped like a feather)
Parallel
Fascicles parallel to longitudinal axis of muscle; terminate at either end in flat tendons.
Fusiform
Fascicles nearly parallel to longitudinal axis of muscle; terminate in flat tendons; muscle tapers towards tendon, where diameter is less than at belly.
Circular
Fascicles in concentric circular arrangements form sphincter muscles that enclose an orifice (opening).
Triangular
Fascicles spread over broad area converge at thick central tendon; gives muscle a triangular appearance.
Pennate
Short fascicles in relation to total muscle length; tendon extends nearly entire length of muscle; includes unipennate, bipennate, and multipennate.