chapter 10
DESCRIPTION
Chapter 10. The Muscular System J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D. 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 - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 10
The Muscular System
J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
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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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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 Brachialis
flexes forearm
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How Skeletal Muscles Produce Movement
• 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
origin
insertion
belly
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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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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 togetherWhile the prime mover (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
Know the muscle names as described in Lab Guide 6!
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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 by Shape
• Deltoid (triangle)
• Trapezius (trapezoid, 2 parallel sides)
• Serratus (saw-toothed)
• Rhomboideus (rhomboid, 4 parallel sides)
• Orbicularis and sphincters (circular)
Rhomboideusmajor
Trapezius
Deltoid
Serratus anterior
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Muscles Named by Size
• Maximus (largest)• Minimis (smallest)
• Longus (longest)• Brevis (short)
• Major (large)• Minor (small)
Psoas major
Psoas minor
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Muscles Named by Direction of Fibers• Rectus
(straight)-parallel to long axis
• Transverse
• Oblique
Rectusabdominis
External oblique
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• Biceps (2)
• Triceps (3)
• Quadriceps (4)
Muscles Named for Number of Origins
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
origins
insertion
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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
Adductormagnus
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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 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-Effort
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Leverage Systems and Leverage• Third-class lever: (FER) Fulcrum-Effort-Resistance
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Skeletal Muscles
Know the muscles, their origins and insertions as described in your Lab Guide 6.
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Additional Information
• You do not need to memorize the details of the different leverage system types for Exam 3.
• Slides with some examples of the naming of muscles can be found in the PowerPoint presentation for Lab 6.
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End Chapter 10