Muscle … Types, Action, Function and Mechanical Levers Flashcards
Skeletal Muscle Types
- Always attached to bones
- Movement of the body and all of its joints
- aids fluid and blood movement within the body
- Muscle contraction produces force (torque) that causes joint movement (venous return/lymph movement)
- 600 skletal muscles; 40-50% of body weight
Characteristics of muscle
- Aggregate muscle action - mms work in groups to achieve a given joint motion
- Different shapes/fiber arrangements - affect mms ability to exert force
- Cross section diameter - affects mms ability to exert force; greater cross section diameter = greater force
- Muscles ability to shorten - longer mms can shorten through a greater range and are more effective in moving joints through large ROM
types of muscle fibers
- Parallel - fibers parallel to length of mms, produce greater ROM (sartorius)
- Fusiform - spindle shaped - fibers parallel with large cross section diameter, produce greater ROM (biceps brachii)
- Pennate - feather like - shorter fiberts, arranged obliquely, arrangement increases cross sectional area increasing its power
a. Unipennate - extensor digitorum
b. Bipennate - Rectus femoris
c. Multipennate - Deltoid - Convergent - Broad origin, pointed insertion, direction of pull varied (Pectoralis Major)
- Circular - concentric fibers, sphincter (orbicularis oris)
Muscle Action … definitions
Strength: The maximal force a mms can generate for a single maximal effort, the amount of tension a muscle produces
Power: work done over a given period of time (work/time), a muscle contracting in a very brief amount of time
Torque: Muscle force causing rotary movement of a body around an axis, a turning or twisting
Contraction:
tension developed in a muscle as a result of a stimulus (chemical, electrical, mechanical)
Purpose:
Cause, control or prevent joint movement
a. to initiate or accelerate movement of a body segment
b. to slow down or decelerate movement of a body segment
c. to prevent movement of a body segment by external forces
Isometric
a. Tension developed within a muscle without joint motion; static contractions
b. Used to stabilize joints
Isotonic
a. Muscle contraction without appreciable change in the force of contraction; maintains tension under constant load
b. Tension is developed within a muscle for either initiating movement or controlling movement; dynamic contractions
Concentric
a. Shortening contraction; coming to the center (bicep curls); mms develops enough tension to overcome the resistance being applied to it
Eccentric
a. Lengthening contraction; away from center (decelerate body segment); controlled joint motion, more force than concentric and isometric movements
Line of Pull
The direction of movement produced by the contracting mms
chronic forward head posture…
Angle of Pull
The angle b/t the line of pull of the mms and the bone on which it inserts, changes with every degree of joint motion
30 degrees - rotational and stabilizing force near equal (radius/ulna)
45 degrees, rotational and stabilizing forces are equal
90 degrees - 100% rotational
120 degrees - Dislocating component
Reverse Action of Concentric Muscle Contraction
When a muscle contracts it pulls both ends toward the center of the muscle. less stabilized bone usually moves toward the more stabilized one
o Biceps curls - open chain
o Chin up - closed chain
Range of Motion
Depends on length of muscle fibers
Long = large ROM; parallel and fusiform muscles
Power
Depends on total number of mms fibers
Many = great power; convergent, unipennate, bipennate, multipennate
Properties of Muscle Force Production and Movement
- Irritability or excitement
- Contractility
- Extensibility
- Elasticity
muscle function (4)
- Irritability (excitability)
- Contractility
- Extensibility
- Elasticity
Irritability (excitability)
property of muscle being sensitive or responsive to chemical, electrical or mechanical stimuli
Contractility
ability of muscle to contract and develop tension (internal force) against resistance when stimulated
Extensibility
ability of muscle to be passively stretched beyond its normal resting length
Elasticity
- ability of muscle to return to its original length following stretching
Muscle roles (4)
- Prime mover (agonist)
- antagonist
- Synergist
- Stabilizer (fixator)
Agonist
mms that assume the major responsibility for producing a specific movement
Antagonist
Mms that oppose or reverse the movement of the prime mover.
a. When a prime mover is active, the antagonist mms is relaxed allowing movement of the joint
Synergist
-a muscle which performs or assists the same joint motion as the agonist
Two mms’s are synergists if their contraction causes movement in the same direction
i. TFL and Glut med
Stabilizer
Synergists that act to control motion of the prime mover
a. Immobilize the origin of the prime mover so that the prime mover can act more efficiently
deltoid, pec minor etc
Lever defenitions
Lever - a rigid bar that moves on a fixed point - bones of skeleton
Fulcrum - a fixed point of leverage - joints
Effort - the force applied to move a resistance tension (torque) of the mms
Load - the resistance to be moved - bone, tissue mass and objects to be moved
Functions of levers
- force into torque; the work of contracting mms to rotate bone
- torque produced throughout the body by a system of bone levers
- The forces involved are produced by mms, gravity and external physical contacts
- A lever allows a mms to move a heavier load or to move a load farther or faster than it otherwise could
- A small difference in the site of a muscles insertion can translate into large differences in the amount of force that must be generated to move a given load
Mechanical Advantage (Power lever)
a. Load is close to fulcrum
b. Effort is applied far from the fulcrum
c. A small effort applied over a rellatively long distance can be used to move a large load over a small distance
d. Lifting a car with a jack
Mechanical Disadvantage (Speed lever) -
a. Load is far from the fulcrum
b. Effort is applied near the fulcrum
c. The force exerted must be greater than the load moved
d. Shovling gravel
First Class Levers -
a. The fulcrum lies b/t the EFFORT and the LOAD (resistance)
b. Effort is applied at one end of the lever and the load lies on the other end with the fulcrum b/t
c. Atlanto-occipital joint lies b/t the posterior cervical mms and the weight of the forehead and face
Second Class Levers -
a. The load (resistance) lies b/t the FULCRUM and the EFFORT
b. Great STRENGTH, less speed and ROM
c. Effort is applied at one end, fulcrum at the other end, load in between
plantar flexion
Third Class Levers - Most Common Type in the body
a. Effort is applied at a point b/t the LOAD and the FULCRUM
b. Great SPEED and mechanical disadvantage
c. Allow rapid movement with little shortening of the mms, produce fast large movements with little effort
d. Biceps
