Muscle Function and Anatomy

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Muscle Function and Anatomy
Chapter 2
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Muscle Architecture
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Muscle Architecture

• Sections
• Deepest section contains two proteins
• Myosin (thick)
• Actin (thin)
• Myosin is surrounded by actin

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Muscle Architecture

• Myofibrils
• Bundles of actin and myosin

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Muscle Architecture

• Muscle fiber
• Among others things, a muscle fiber contains many
  groups of myofibrils

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Muscle Architecture

• Fascicle
• A group of muscle fibers.

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The Whole Muscle
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The Whole Muscle
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Tendons

• Three membranes converge to form a tendon which
  connects the muscle to the bone

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Shape of Muscles and Fiber Arrangement
Strap

• Parallel muscles (range of motion
• Flat (rectus abdominus)
• Fusiform (biceps)
• Strap (sartorius)
• Radiate (trapezius)
• Sphincter
• Pennate (force)
• Unipennate (biceps femoris)
• Bipennate (rectus femoris)
• Multipennate (deltoid)

Sphinter
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Muscle Tissue Properties

• Irritability or Excitability
• to be stimulated
• Contractility
• to contract (shorten)
• Extensibility
• to be stretched
• Elasticity
• return to original position after being stretched

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Muscle Terminology

• Origin
• proximal attachment
• least moveable end
• closest to the midline of the body
• Insertion
• distal attachment
• most moveable end
• furthest from the midline of the body
• Action
• The movement at the joint when the muscle(s)
  contract

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Types of Muscle Contraction
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Types of Muscle Contraction

• Concentric contraction
• Length of muscle shortens
• Muscle force is greater than the resistance
• If lifting 50 pounds and the muscle generates
  more than 50 pounds the muscle with shorten and
  move the weight.
• Static or Isometric contraction
• No change in muscle length
• Muscle force is equal to the resistance
• Lifting 50 pounds and the muscle generates 50
  pounds of force
• Eccentric contraction
• Muscle lengthens
• Muscle force is less than the resistance
• Lowering 50 pounds and the muscle generates less
  than 50 pounds

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Concentric
Concentric
Lengthens
Lengthens
Eccentric
Eccentric
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Eccentric Contraction

• Used to control agonist and prevent over
  lengthening of the antagonist.
• Example triceps lowers dumbbell while biceps
  controls the triceps activity (action).
• Causes more damage than other types
• Greater repair required
• producing a stronger muscle
• Also, results in more muscle soreness.

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ROLE OF MUSCLES

• Agonist
• prime mover
• Antagonist
• action opposite to the agonist
• Stabilizers
• fixate or stabilize the joint
• Synergists
• assist or guiding

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Agonist and Antagonist
Agonist
Agonist
Antagonist
Antagonist
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TABLE 2.1 Type of Contraction Type of Contraction Type of Contraction
TABLE 2.1 Isometric Isotonic Isotonic
TABLE 2.1 Isometric Concentric Eccentric
Agonist muscle No change Shortening Lengthening
Antagonist No change Lengthening Shortening
Joint angle No change Decrease Increase
Direction of body part Against immovable object Against gravity or external force Consistent with gravity or external force
Motion Pressure but no motion Causes motion Causes motion
Description Static Dynamic shortening Dynamic lengthening
Muscle force v. Resistance F R F gt R F lt R
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Determination of Muscle Action

• Muscle location
• Origin and insertion
• What joint(s) it crosses
• Planes and their actions
• Most muscle can not perform opposite actions
  (e.g. flexion AND extension)
• Line of pull
• Muscles only pull on bones, they do not push
  bones!
• Insertion is pulled towards the origin

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Joint Actions

• What joint does the muscle cross?
• Where does the muscle cross the joint e.g.
  anterior, lateral, etc.
• If the insertion end of the muscle is pulled
  towards the origin end, what action would result
  at the joint?