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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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?