The Muscular System

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Chapter 6

• The Muscular System

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The Muscular System

• Interactions of Skeletal Muscles in the Body
• Muscles usually work in groups, i.e. perform
  group actions
• Muscles are usually arranged in antagonistic
  pairs
• flexor-extensor
• abductor-adductor, etc.

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600 Skeletal Muscles5 Golden Rules of Muscle
Activity

• With a few exceptions, all muscles cross at least
  one joint
• The bulk of the muscle lies proximal to the join
  crossed
• All muscles have at least two attachments the
  origin and the insertion
• Muscles can only pull they never push
• During contraction, the muscle insertion moves
  toward the orgin

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How Skeletal Muscles Produce Movement

• Muscles exert force on tendons that pull on bones
• Muscles usually span a joint
• Muscle contraction changes the angle or position
  of one bone relative to another
• Skeletal muscle must be stimulated by a nerve
  impulse to contract

Brachialis flexes forearm
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How Skeletal Muscles Produce Movement
origin

• Origin the attachment of the muscle to the bone
  that remains stationary
• Insertion the attachment of the muscle to the
  bone that moves
• Belly the fleshy part of the muscle between the
  tendons of origin and/or insertion

belly
insertion
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Interactions of Skeletal Muscles in the Body

• Prime Mover (agonist) the principle muscle that
  causes a movement
• ex biceps brachii, flexion of forearm
• Antagonist the principle muscle that causes the
  opposite movement
• ex triceps brachii, extension of forearm

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Antagonists of the Forearm
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Antagonists of the Thigh
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Antagonists of the Foot
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Interactions of Skeletal Muscles in the Body

• Synergists muscles that assist the prime mover
• ex extensor carpi (wrist) muscles are synergists
  for the flexor digitorum muscles when you clench
  your fist
• Fixators synergists that stabilize the origin of
  a prime over
• ex several back muscles that stabilize scapula
  when the deltoid flexes the arm

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Functional Roles of Skeletal Muscles

• Group Actions most movements need several
  muscles working together
• While the prime movers (agonist and synergists)
  are contracting to provide the desired movement
• other muscles (antagonists) are relaxing being
  stretched out passively
• agonist and antagonist change roles depending on
  the action
• e.g., abduction versus adduction
• Synergists and Fixators become Agonists and
  Antagonists in different movements

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Naming Skeletal Muscles

• Location of the muscle
• Shape of the muscle
• Relative Size of the muscle
• Direction/Orientation of the muscle fibers/cells
• Number of Origins
• Location of the Attachments
• Action of the muscle

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Muscles Named by Location

• Epicranius (around cranium)
• Tibialis anterior (front of tibia)

tibialis anterior
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Naming Skeletal Muscles

• Shape
• deltoid (triangle)
• trapezius (trapezoid)
• serratus (saw-toothed)
• rhomboideus (rhomboid)
• orbicularis and sphincters (circular)

Rhomboideus major
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Muscles Named by Size
Psoas minor

• maximus (largest)
• minimis (smallest)
• longus (longest)
• brevis (short)
• major (large)
• minor (small)

Psoas major
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Muscles Named by Direction of Fibers

• Rectus (straight)-parallel to long axis
• Transverse
• Oblique

Rectus abdominis
External oblique
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Muscles Named for Number of Origins

• biceps (2)
• triceps (3)
• quadriceps (4)

Biceps brachii
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Muscles Named for Origin and Insertion

• Sternocleidomastoid originates from sternum and
  clavicle and inserts on mastoid process of
  temporal bone

insertion
origins
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Muscles Named for Action

• Flexor carpi radialis (extensor carpi radialis)
  flexes wrist
• Abductor pollicis brevis (adductor pollicis)
  flexes thumb
• Abductor magnus abducts thigh
• Extensor digitorum extends fingers

Adductor magnus
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Arrangement of Fascicles

• Parallel (strap-like), ex sartorius
• Fusiform (spindle shaped), ex biceps femoris

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Arrangement of Fascicles

• Pennate ("feather shaped"), ex extensor
  digitorum longus
• Bipennate, ex rectus femoris
• Multipennate, ex deltoid

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Arrangement of Fascicles

• Convergent, ex pectoralis major
• Circular (sphincters), ex orbicularis oris

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Arrangement of Fascicles

• Range of motion depends on length of muscle
  fibers (fascicles) long fibers large range of
  motion
• parallel and fusiform muscles
• Power depends on total number of muscle fibers
  many fibers great power
• convergent, pennate, bipennate, multipennate

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Lever Systems and Leverage

• Lever i.e. bones, a rigid rod that moves on some
  fixed point
• Fulcrum i.e. joint, a fixed point
• Resistance the force opposing movement
• Effort the force exerted to achieve action

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Levers

• A lever is acted upon at 2 different points by
• resistance or load
• the force that opposes movement
• the load or object (bone or tissue) to be moved
• effort
• the force exerted to achieve a movement
• the effort is provided by muscle(s)
• Motion is produced when the effort exceeds the
  resistance (isotonic contraction)

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Lever Systems and Leverage

• Leverage the mechanical advantage gained by a
  lever
• Power muscle tension (effort) farther from joint
  (fulcrum) produces stronger contraction (opposes
  greater resistance)
• Range of motion (ROM) muscle tension (effort)
  closer to joint (fulcrum) produces greater range
  of motion.

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Mechanical Advantage

• Load is near fulcrum, effort is far away
• Only a small effort is required to move an object
• Allows a heavy object to be moved with a small
  effort
• Example car jack

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Mechanical Disadvantage

• Load is far from the fulcrum, effort is near the
  fulcrum
• a large effort is required to move the object
• allows object to be moved rapidly, a speed
  lever
• throwing a baseball

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Lever Systems and Leverage

• First-class lever (EFR) Effort-Fulcrum-Resistance
  

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Leverage Systems and Leverage

• Second class lever (FRE) Fulcrum-Resistance-Effor
  t

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Leverage Systems and Leverage

• Third-class lever (FER) Fulcrum-Effort-Resistance
  

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Skeletal MusclesYou will need to know all of
these!