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25 Cards in this Set
- Front
- Back
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Big picture of how muscles function |
- the nervous system directs a muscle to contract - the muscle attempts to contract- whether it is successful in shortening towards the center is determined by the strength of the pulling force of the muscle compared to the force necessary to move one or both body parts to which the muscle is attached. - the force necessary to move a body part is usually the force necessary to move the weight of the body part. |
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What is a concentric contraction? |
- the type of contraction wherein a muscle contracts and shortens. - the bending force of the myosin xbridge pulls the actin to the center, zlines are drawn to the center and the sarcomere shortens. - the message for contraction is given to every sarcomere of the muscle fiber, so if one sarcomere succeeds in shortening, every sarcomere will succeed in shortening and the entire muscle will shorten. |
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What is the term used to identify the concentrically contracting muscle that generates the force that moves a body part to create the joint action that is occurring? |
- It is the mover - the mover creates that movement
Note: the joint action that is occurring is usually termed the "action in question" |
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What is the force that opposes the action of the mover? |
- Resistance force - the antagonist: the force of the antagonist is opposite to the action that is occurring
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What is an eccentric contraction? |
- occurs when a muscle contracts and lengthens
- if the force of the muscle's contraction is less than the resistance to muscle's contraction (if the force of the antagonist is greater than the force of the muscle), the muscle will lengthen instead of shorten. - the resistance force (the weight of the body part) creates the action that is occurring and is now termed the mover and the muscle that is eccentrically lengthening is now called the agonist |
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What is an isometric contraction? |
- wherein the muscle contracts and stays the same length - when the force of the muscle's contraction is exactly equal to the resistance force, then the muscle will neither shorten or lengthen - in this case there is no movement of a body part at the joint; therefore no joint action occurs - b/c no joint action occurs the muscle that is isometrically contracting is neither a mover nor an antagonist |
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Review of the muscle structure |
- a muscle is an organ that attaches from one bone to another (via its tendons), thereby crossing the joint that is located between the 2 bones - a muscle is composed of thousands of muscle fibers that generally run longitudinally w/in the muscle - ea. muscle fiber is composed of many myofibrils that run longitudinally w/in the muscle fiber -ea. myofibril is composed of thousands of sarcomeres laid end to end; ea. sarcomere is made up of actin & myosin - the myosin is found at the center of the sarcomere -actin is located on both sides of the myosin filament and are attached to the z-line (which are the boundaries of the sarcomere)
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Define a motor unit |
one motor neuron and all the muscle fibers that it controls. |
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Sliding Filament Mechanism Review |
- explains how actin and myosin filaments slide along ea/ other - when a contraction is desired, the CNS sends a message vfor contraction to the muscle to be contracted. - when the message enters the interior of the muscle fiber it causes the release of calcium that is stored in the sarcoplasmic reticulum - the calcium binds to the actin, which causes a structural change in the actin so that its binding (active) sites are exposed. - when actin's active sites are exposed, myosin heads attach to them creating a cross-bridge - the cross bridges bend and pull the actin filament to the center of the sarcomere -the formation of cross-bridges between actin & myosin and the fulling force that they exert defines a muscle contraction |
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What defines a muscle contraction? |
- the fact that myosin xbridges are grabbing actin filaments attempting to bend and pull the actin filaments toward the center of the sarcomere. - the tension or pulling force of the muscle toward its center. |
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What is tension? |
- a pulling force; tensile forces are pulling force - muscles pull they do not push - muscles create tensile forces in the body. |
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What is tone? |
-describes a muscle contracting (when it is generating tension) - concentric contraction muscles shorten w/tone - eccentric contraction muscles lengthen w/ tone - isometric contraction muscle stays the same length w/ tone
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When do concentric contractions occur? |
- Scenario 1: against gravity (vertically upward); muscle in the body must generate force to create upward movement- it must generate MORE upward force on the body part thatn the downward force that gravity is exerting. - Scenario 2. gravity neutral (horizontal); gravity neither resists the motion nor aids it (b/c/ the body part is not being lifted up or down); gravity-neutral movments are usually rotation movements. - Scenario 3. W/ gravity (vertically downward) |
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muscle contractions & gravity |
- downward movement of a body part does not require contraction of a muscle; gravity pulls it down -if we want to move the body part FASTER than gravity is moving it requires concentric contraction - i.e. swing a golf club to hit a ball. gravity would bring arm/club down but not with enuf force to move the ball. |
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lengthening contractions |
- just because a muscle is lengthening doesn't mean that it is eccentrically contracting. - A muscle can lengthen when it is relaxed (i.e. when a person stretches) - a muscle can also lengthen while it is contracting (i.e when myosin filament heads are grabbing actin filaments) - if a muscle is lengthening then its attachements are moving away from each other. Instead of myosin heads pulling actin towards the center, the resistance force and myosin heads are stretched in the opposite direction. Actin filaments are pulled away from the center of the sarcomere so the sarcomere lengthens. |
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What is an external resistance force? |
- a force that is generated outside of the body - the movement of a body part created by this external force is slowed down by an eccentric contraction of a muscle b/c it has an action that is opposite to the action of the external force. |
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What is the relationship of a muscle that is eccentrically contracting to the joint action that is occurring? |
-b/c a muscle that is eccentrically contracting creates a force that is opposite to the joint action that is occurring, an eccentrically contracting muscle always acts as an antagonist
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What is another name for an eccentric contraction? |
- negative contraction b/c an eccentric contraction opposes (i.e. negates) the force that is creating the action that is occurring. |
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(Page 444) 3 scenarios where gravity is the only resistance force to movement:
Scenario 1: Slowing Gravity's Vertical Downward Motion |
Scenario 1: Slowing Gravity's Vertical Downward Motion - gravity creates a downward mvment of a body part; the eccentrically contracting muscle creates an upward force that is opposite the downward force of gravity which slows gravity and thus the body part. - it is necessary to slow the movement caused by gravity to avoid the body part from crashing into whatever surface stops it |
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(Pg 444) 3 scenarios where gravity is the only resistance force to movement:
Scenario 2: Slowing Momentum of a Horizontal Motion |
- eccentric contractions also occur to slow movement of a body part when it is moving horizontally
- horizontal movement is gravity neutral (gravity neither adds or resists the movement) |
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3 scenarios where gravity is the only resistance force to movement:
Scenario 3: Slowing Momentum of a Vertical Upward Motion
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- eccentric contractions also occur to slow a body part when it is moving upward (against gravity)
- in a case where a body part is moving upward quickly b/c of a previous muscular contraction, the muscle that initiated the movement were to relax, gravity would eventually slow down the upward movement. |
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What are same length contractions? (pg 446) |
- Isometric Contractions - a contraction where a muscle contracts and stays the same length - there must be an opposing force (of resistance) that is acting on the body part that keeps the body part from moving and therefore stops the muscle from being able to shorten. (could be gravity or some internal force)
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What is a fixator force? |
- two equally strong forces acting on a body part which holds it still - can also be called a stabilizer force
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What are 2 scenarios for ISOMETRIC Contractions |
Scenario 1: against gravity (holding a body part up)
Scenario 2: against any force other than gravity (holding a body part in position) |
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Muscle contractions |
- concentric contraction creates movement - eccentric contractions modifies movement - isometric contraction stops movement |
