11.1 Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems

anatomy & physiology

how does the skeleton move?

* tension is created by the contraction of fibers in the skeletal muscle.
* the tension is transferred to the tendons.

what is forearm flexion?

bending the elbow

what is insertion?

* the moveable end of a muscle that attaches to the bone that is being pulled.

what is the origin?

* stabilized bone that the end of the muscle is attached to.

what is a prime mover/agonist?

* the principle muscle that is involved in an action.

what is a synergist/fixator?

* stabilizes the bone that is the attachment for the prime movers origin.

what is an antagonist?

* an antagonist is a muscle with the opposite action of a prime mover.
* plays 2 important roles in muscle function:
* they maintain body or limb position.
* the control rapid movement.

to extend the knee, a group of four muscles called the quadriceps femoris in the anterior compartment of the thigh are activated (and would be called the ____ of knee extension). However, to flex the knee joint__,__ an ____ set of muscles called the hamstrings is activated.

1. angonist
2. antagonist

**these terms would be reversed for the opposing action*\*

If you consider the first action as the knee bending, the hamstrings would be called the ____ and the quadriceps femoris would then be called the ____

1. agonist
2. antagonist

if the biceps brachii (anterior compartment of arm) is the agonist and the triceps brachii (posterior compartment of arm) is the antagonist, what is the movement?

biceps brachii flexes the forearm and the triceps brachii extends the forearm.

if the hamstrings (posterior compartment of thigh) are the agonist and the quadriceps (anterior compartment of thigh) are the antagonist, what is the movement?

hamstrings extend the leg and the quadriceps extend the leg.

true or false: are there skeletal muscles that do not pull against the skeleton for movements?

true.

* there are muscles that produce facial expressions.

true or false: are there skeletal muscles in toungue and external urinary and anal sphincters?

true.

what is a fascicle?

* a group of muscle fibers in a whole muscle covered by the perimysium

in what ways can skeletal muscles be classified based on the pattern of the fascicle arrangement?

parallel, circular, convergent and pennate.

how are fascicles arranged in parallel muscles?

* the fascicles are arranged in the same direction of the long axis of the muscle.
* majority of the skeletal muscle in the body have this fascicle arrangement.
* some parallel muscles are flat sheets that make broad attachment, others are rotund (plump) with tendons at one or both ends.

what is fusiform?

* when a parallel muscle has a central large belly that is spindle-shaped (meaning it tapers when it extends to the origin and insertion).

what are circular muscles also called?

sphincters

what occurs to circular muscles when they relax and contract?

* when relaxed, the muscle fibers increase the size of the opening.
* when contracted, the opening shrinks to the point of closure.

when you contract the circular muscle around your mouth, what happens?

* the oral opening shrinks, like you are puckering for a kiss.

what does orb refer to?

* circular

what does oris refer to?

* oral (oral cavity or mouth)

what does oculi refer to?

* eye

what is a convergent?

* when a muscle has a wide spread expansion and the fascicle all come to a single attachment point.

what could the attachment point for a convergent muscle be?

* tendon, aponeurosis, or raphe (slim tendon)

what is an example of a convergent muscle and why?

* large chest muscle (pectoralis major).
* this muscle converges on the greater tubercle of the humerus through a tendon.

what is a pennate muscle?

* a muscle that blends into a tendon that runs through the central region of the muscle for the entire length.

true or false: the muscle fibers in a pennate muscle can only pull straight?

false.

* the muscle fibers can only pull at an angle.

what are the three types of pennate muscles?

* unipennate, bipennate, and multipennate.

what is a unipennate muscle?

* where the fascicles of the muscle are located on one side of the tendon.

example: extensor digitorum of forearm.

what is a bipennate muscle?

* where the fascicles are on both sides of the tendons.

what is a multipennate muscle?

* where the muscle fibers wrap around the tendon and sometimes for individual fascicles.

what is abduct?

* to move away from the midline of the body.

what does the connection of the muscle to the bone determine?

* range of motion, speed, and force.