Module 3 Review Questions

What is the definition of a fixator?

A fixator is defined as a muscle (or other force) that can stop an unwanted action at the fixed attachment of the muscle that is working. Fixators are also known as stabilizers.

What does the term gravity neutral mean?

A gravity-neutral motion is one in which gravity neither resists the motion nor aids it. Gravity-neutral motions usually occur when a body part is being moved horizontally.

What is a lever? What is a lever arm?

A lever is a rigid bar that can move; a lever arm is defined as the distance from the axis of motion to the point of application of force upon a lever.

Describe the steps of the sliding filament mechanism.

A message is sent from the nervous system telling muscle fibers to contract. This message causes the sarcoplasmic reticulum to release stored calcium into the sarcoplasm. These calcium ions attach onto the actin filaments, exposing actin filament binding sites. Myosin heads attach onto these exposed binding sites of the actin filaments, creating cross-bridges between the myosin filament and the actin filaments. Each myosin cross-bridge then bends, creating a pulling force that pulls the actin filament in toward the center of the sarcomere. These cross-bridges then break, reattach onto the next binding sites of the actin filaments, and bend, further pulling the actin filaments in toward the center of the sarcomere. This process occurs over and over again as long as the message to contract is given to the muscle by the nervous system. Since the actin filaments are attached to the Z-lines of the sarcomere (the boundaries of the sarcomere), the Z-lines are pulled in toward the center of the sarcomere. When Z-lines are pulled in toward the center of the sarcomere, the sarcomere shortens

Define motor unit.

A motor unit is defined as "one motor neuron and all the muscle fibers that it controls.

What is the definition of a mover?

A mover is defined as a muscle (or other force) that can do the action in question

How can a muscle have a partial contraction?

A muscle can have a partial contraction if some (not all) of its motor units are ordered to contract.

Give an example of a resistance exercise.

Examples of resistance exercises include using weights, springs, rubber tubing, or large rubber bands to increase the resistance force against which the mover musculature must work.

What is the term given to a bundle of muscle fibers?

Fascicle (fasciculus)

What are the three possible scenarios that can occur when a muscle contracts and shortens?

One attachment may move, the other attachment may move, or both attachments may move.

What is the name given to the attachment of a muscle that moves and to the attachment of a muscle that doesn't move?

The muscle attachment that moves is called the mobile attachment; the muscle attachment that does not move is called the fixed attachment.

How does one determine the action(s) of a muscle that has its line of pull within an oblique plane?

The oblique plane motion must be broken up into its cardinal plane component actions.

What is a pennation angle?

The pennation angle is the angle of the muscle fiber relative to the central tendon of the muscle.

What is the definition of a neutralizer?

A neutralizer is a muscle (or other force) that can stop an unwanted action at the mobile attachment of the muscle that is working.

Do muscles pull or push when they contract?

When muscles contract, they pull.

What are the questions that must be asked and answered in Step 3 of the 5-Step Approach to Learning Muscles?

The questions are: (1) What joint does the muscle cross? (2) Where does the muscle cross the joint? And (3) How does the muscle cross the joint (i.e., in what direction are its fibers running?)

Can a multijoint muscle create movement at every one of the joints that it crosses?

yes

Define co-contraction.

A co-contraction is defined as a simultaneous contraction of a mover muscle and an antagonist muscle

Why might a person contract mover muscles for a joint action that brings a body part downward?

A concentric contraction is necessary whenever a body part is moving downward and we want the body part to move faster than gravity would move it.

How does a cambered pulley differ from a regular pulley?

A pulley on a cable machine is typically designed to be round.This is known as a regular pulley because it is the most common type found on a cable machine.If a pulley is not round, it is described as a cambered pulley.These pulleys have a different effect on than a regular pulley on the resistance that is felt by the client at different points during the exercise.

Describe and give an example of a reverse action.

A reverse action occurs when a muscle concentrically contracts and the attachment of the muscle that usually stays fixed does the moving, and the attachment of the muscle that usually moves, stays fixed. An example of a reverse action is when the brachialis concentrically contracts and flexes the elbow joint and the arm is moved toward the forearm instead of the forearm moving toward the arm (for example, when doing a pull-up). Another example of a reverse action is when the quadriceps femoris group concentrically contracts and extends the knee joint, and the thigh moves toward the leg instead of the leg moving toward the thigh (for example, when standing up from a seated position).

Describe the big picture function of a muscle contraction.

A skeletal muscle attaches onto two bones, thereby crossing the joint that is located between the two bones. When a muscle contracts, it attempts to shorten toward its center, thereby creating a pulling force upon its bony attachments. If this pulling force is sufficiently strong, one or both of the bones to which the muscle is attached will be pulled toward the center of the muscle. Since bones are located within body parts, movement of a bone results in movement of a body part.

What is the difference between active tension and passive tension of a muscle?

Active tension of a muscle is generated by the sliding filament mechanism, that is, its contraction. Passive tension is created by the elastic nature of the fascia of the muscle.

What is the definition of an antagonist?

An antagonist is defined as a muscle (or other force) that can do the opposite action of the action in question.

Give an example of a closed kinetic chain exercise and an open chain kinetic exercise. Explain how and why they are different.

An example of a closed kinetic chain exercise is a push-up, an example of an open kinetic chain exercise is a barbell chest press. These exercises work similar muscle groups but are different because of the way they are performed. A push-up requires that the distal attachment is fixed and the body must overcome the resistance applied to it in order to move. A barbell chest press does not fixate the distal attachment, allowing it to move freely, as long as it can overpower the resistance being applied to it.

Give an example of a postural muscle and a mobility muscle and describe a primary function of each muscle.

An example of a postural muscle is the semispinalis of the transversospinalis group, which functions primarily as a stabilizer and extender of the trunk, neck, and head. An example of a mobility muscle is longissimus of the erector spinae group, which functions primarily as an extender of the trunk, neck, and head and plays a relatively smaller role in stabilization.

What is the name given to a shortening contraction of a muscle?

Concentric contraction

What type of contraction occurs when a muscle contracts and shortens?

Concentric contraction

What type of muscle contraction is necessary for a person in anatomic position to rotate the neck to the right at the spinal joints?

Concentric contraction.

What type of muscle contraction is necessary for a person to flex the arm at the shoulder joint from anatomic position?

Concentric contraction.

What are the three types of muscle contractions?

Concentric, eccentric, and isometric

What type of contraction occurs when a muscle contracts and lengthens?

Eccentric contraction.

What type of muscle contraction is necessary for a person to slowly adduct his/her arm from a position of 90 degrees of abduction (at the shoulder joint) to anatomic position?

Eccentric contraction.

What is the most common scenario in which a muscle eccentrically contracts?

Eccentric contractions usually occur when the force of the eccentric contraction is needed to slow down a movement caused by gravity or some other external force.

What is the name given to the muscular fascia that surrounds an entire muscle?

Epimysium.

Name two types of longitudinal muscle fiber architecture and three types of pennate muscle fiber architecture.

Examples of longitudinal muscle fiber architecture are: fusiform (also known as spindle), strap, rectangular, rhomboidal, and triangular (also known as fan-shaped muscles). Spiral and sphincter muscles may also be considered to be longitudinal muscles. Examples of pennate muscle fiber architecture are: unipennate, bipennate, and multipennate.

What is the most common external force that can be a mover or an antagonist?

Gravity.

Give an example of an internal force and an external force.

Internal forces are forces generated within the body; these occur when muscles contract. External forces are generated outside the body; the most common example is gravity, and other examples are the wind, a wave, another person pushing or pulling upon us, or using springs or rubber tubing or bands for extra resistance when doing exercises.

What type of contraction occurs when a muscle contracts and stays the same length?

Isometric contraction.

What type of muscle contraction is necessary for a person (otherwise in anatomic position) to hold his/her left thigh in 30 degrees of abduction at the hip joint?

Isometric contraction.

Which type of muscle contraction fixes (i.e., stabilizes) a body part in position?

Isometric contraction.

Which type of muscle contraction stops movement from occurring?

Isometric contraction.

What is the term used to describe the fact that a muscle's contraction is weakened when it is lengthened beyond resting length?

Lengthened active insufficiency.

What is the definition of leverage?

Leverage is defined as the mechanical advantage that a force can have when moving an object.

What is the difference between postural stabilization muscles and mobility muscles?

Mobility muscles tend to be larger, longer, more superficial muscles and are important primarily for their ability to contract concentrically and create large joint movements. Postural stabilization muscles tend to be smaller, deeper muscles that are located close to joints; they are important primarily for their ability to contract isometrically and hold the posture of joints fixed while mobility muscles do their actions

What is the name given to a muscle that concentrically contracts?

Mover

What is a synonym for the term muscle cell?

Muscle fiber.

What are myofibrils?

Myofibrils are organelles of a muscle fiber located within the muscle fiber's cytoplasm (sarcoplasm). They are longitudinally oriented and run the entire length of the muscle fiber.

Regarding nervous system control of muscle contraction, what is the role of neurotransmitters?

Neurotransmitters travel from the lower motor neuron through the synaptic cleft to the membrane (motor endplate) of the muscle fiber. As their name implies, neurotransmitters transmit the neural message from the lower motor neuron that tells the muscle cell to contract.

Do antagonist muscles always contract when a joint action occurs?

No. Antagonist muscles always lengthen when the joint action occurs, but they do not always contract. They can eccentrically contract and lengthen, or they can relax and lengthen.

Do mover muscles always contract when a joint action occurs?

No. Mover muscles always shorten when the joint action occurs, but they do not always contract. They can concentrically contract and shorten, or they can relax and shorten

Other than the reverse action(s), how many actions will a muscle have if it has one line of pull and that line of pull is oriented within a cardinal plane?

One action

Describe the difference between red slow-twitch fibers and white fast-twitch fibers

Red slow-twitch muscle fibers are red because of a good blood supply and are slow to contract as their name implies; they are usually small. White fast-twitch muscle fibers are white because of a relative lack of blood supply and they contract quickly as their name implies; they are usually large. Red slow-twitch fibers are better adapted for endurance aerobic activities; white fast-twitch fibers are better adapted for activities that require short bursts of energy at maximal effort.

Which type of muscle fibers predominates in postural stabilization muscles?

Red slow-twitch muscle fibers.

What is the name given to the force that a concentrically contracting muscle must work against?

Resistance force (antagonist).

Describe the structure of a sarcomere.

Sarcomeres are bounded on both sides by Z-lines. Within each sarcomere are protein filaments known as actin and myosin; actin filaments are thin and myosin filaments are thick. These filaments are arranged in an orderly fashion. Actin filaments are attached to the Z-lines at both ends of a sarcomere. Myosin filaments are not attached to the Z-lines; rather they are located in the center of the sarcomere. Myosin filaments have globular projections known as heads, which stick out toward the actin filaments.

What are the 5 steps of the 5-Step Approach to Learning Muscles?

Step 1: Look at the name of the muscle to see if it gives you any "free information." Step 2: Learn the general location of the muscle well enough to be able to visualize the muscle on your body. Step 3: Use this general knowledge of the muscle's location (from step 2) to figure out the actions of the muscle. Step 4: Go back and learn (memorize, if necessary) the specific attachments of the muscle. Step 5: Now look at the relationship of this muscle to other muscles (and other soft tissue structures) of the body.

In order, what are the four sources of energy for the sliding filament mechanism within a muscle cell?

Stored ATP; regeneration of ATP from stored creatine phosphate; regeneration of ATP from anaerobic breakdown of glucose (glycolysis); and regeneration of ATP from aerobic breakdown of glucose (Krebs cycle).

What is the difference between a tendon and an aponeurosis?

Tendons and aponeuroses differ based upon their shape. A tendon is round and cord-like; an aponeurosis is broad and flat.

What type of force is a tensile force?

Tensile forces are pulling forces.

What is the A-band of skeletal muscle tissue?

The A-band is a striation of muscle tissue. It is dark and is defined by the presence of myosin. Since myosin is in the center of a sarcomere, the A-band is located in the center of the sarcomere. Within the A-band, there is a region where only myosin is located and a region wherein both myosin and actin are located.

What is the Henneman size principle?

The Henneman size principle describes the order in which motor units are recruited to contract. If a muscle needs a weak contraction, a smaller motor unit is recruited to contract. If the muscle then needs a stronger contraction, the muscle recruits a larger motor unit in addition to the smaller one that is already contracting.

What determines the action(s) of a muscle?

The action of a muscle is determined by the line of pull of the muscle relative to the joint that it crosses.

What advantage does a muscle gain by having greater leverage?

The advantage of increased leverage is that it allows a muscle to move a weight, that is, otherwise too heavy to move; in other words, a muscle can expend less effort to move a heavier object.

Define and give an example of the all-or-none response law.

The all-or-none response law states that a muscle fiber either contracts all the way , or it doesn't contract at all. The all-or-none response law applies to sarcomeres, myofibrils, muscle fibers, and motor units. It does not apply to an entire muscle (i.e., a muscle can have a partial contraction).

What disadvantage does a muscle have if it has greater leverage?

The disadvantage of greater leverage of a muscle is that the muscle must contract a greater distance to move the bone a certain distance.

What factors determine the extrinsic strength of a muscular contraction?

The extrinsic strength of a muscle takes into account all the factors outside of the muscle itself. These factors include such things as the leverage that the muscle has upon its attachments as well as the angle of the muscle's pull relative to the joint where the movement is occurring.

What factor determines the intrinsic strength of a muscular contraction?

The intrinsic strength of a muscle is determined by the sliding filament mechanism (active tension) and the elastic recoil property of the tissues of the muscle (passive tension).

Describe the concept of muscle memory.

The term muscle memory describes that fact that there is a stored memory of the pattern of muscle contractions in our bodies. This stored pattern of muscle memory is located in the nervous system, not within the muscles themselves.

What do the three length-tension relationship curves describe?

The three length-tension relationship curves describe the tension (pulling force) that a muscle can generate at a given length. One length-tension relationship curve can be drawn for active tension; another can be drawn for passive tension; and another can be drawn for total tension (active tension and passive tension)

What are the two major tissue types found in a skeletal muscle?

The two major types of tissue found in a skeletal muscle are skeletal muscle tissue and fibrous fascia connective tissue

What is the relationship between joint mobility and joint stability?

There is an antagonistic relationship between joint mobility and joint stability: the more mobile a joint is, the less stable it is; the more stable a joint is, the less mobile it is. While joints exist to allow movement, they must also be sufficiently stable to remain healthy. Each joint of the body must find its balance between mobility and stability.

What is the importance of core stabilization, and what effect does it have on our health?

This concept of core stabilization is crucial to the functioning and health of the body for two reasons: (1) creates stronger and more efficient movements; (2) important for the health of the spine.

What is the role of troponin molecules?

Troponin molecules are part of the actin filament, and they have the ability to move tropomyosin out of the way so that the binding sites of actin are exposed to the myosin heads. This allows muscle contraction to occur.

Explain why variable resistance is often chosen during physical therapy and why a client might benefit from incorporating this style of training in conjunction with constant resistance.

Variable resistance techniques are often used in physical therapy because injuries are often aggravated more in certain ranges of motion during joint movement, therefore being able to manipulate the load on a muscle or joint during an exercise can tailor that exercise so that the client is challenged in an optimal way. Certain exercises can be designed so that the client is working harder when he or she is in the strongest range of motion, which could potentially speed up the recovery of the injured area. These exercises are often performed in conjunction with constant resistance exercise, depending on the exact protocol of the rehabilitation program.

What defines a muscle contraction?

What defines a muscle as contracting is the fact that myosin cross-bridges are grabbing actin filaments, attempting to bend and pull the actin filaments toward the center of the sarcomere. This creates the tension or pulling force toward the center of the sarcomere that defines contraction. Extrapolating this idea to an entire muscle, it can be stated that it is the tension or pulling force of the muscle toward its center that defines a muscle as contracting (not whether the muscle is actually shortening).

When a joint action occurs, what happens to the length of an antagonist?

When a joint action occurs, the antagonist muscles of that joint action lengthen.

When a joint action occurs, what happens to the length of a mover?

When a joint action occurs, the mover muscles of that joint action shorten

When a muscle contracts, does it always succeed in shortening?

When a muscle contracts, it does not always succeed in shortening.

Why is the strength of a muscular contraction weakened when it is shortened beyond resting length?

When a muscle is shortened beyond resting length, it becomes weaker because fewer actin-myosin bonds can form.