Transcript Muscular System A

Muscular System
Part A
Prepared by Vince Austin and W. Rose.
Figures from Marieb & Hoehn, 7th and 8th eds.
Portions copyright Pearson Education
Interactions of Skeletal Muscles
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Skeletal muscles work together or in opposition
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Muscles only pull (never push)
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As muscles shorten, the insertion generally moves
toward the origin
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Whatever a muscle (or group of muscles) does,
another muscle (or group) “undoes”
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Classification: Functional Groups
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Prime movers – provide the major force for
producing a specific movement
Antagonists – oppose or reverse a particular
movement
Synergists
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Add force to a movement
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Reduce undesirable or unnecessary movement
Fixators – synergists that immobilize a bone or
muscle’s origin
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Naming Skeletal Muscles
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By location: associated bone or body region
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By shape: e.g., deltoid muscle (deltoid = triangle)
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By relative size – e.g., maximus, minimus, longus
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By fiber direction: e.g., rectus (fibers run straight),
transversus, oblique
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By number of origins (heads): e.g., biceps, triceps
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By site of attachment: point of origin or insertion
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By action: e.g., flexor, extensor
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Fascicle Arrangment Varies
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Parallel – fascicles run parallel to muscle long axis (e.g.,
sartorius)
Fusiform – spindle-shaped muscles (e.g., biceps brachii)
Pennate (feather-like) – short fascicles attach obliquely to
central tendon running lengthwise (e.g., rectus femoris)
Convergent – fascicles converge from a broad origin to a single
tendon insertion (e.g., pectoralis major)
Circular – fascicles are arranged in concentric rings (e.g.,
orbicularis oris)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Arrangement of Fascicles
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 10.1
Lever Systems
Lever: rigid bar that rotates about a …
Fulcrum: fixed point or hinge point
Effort: force applied to lever
Load: resistance to the effort, usually at a
different point along the lever
A & P equivalents:
– lever = bone (one or more)
– fulcrum = joint
– effort = force applied by muscle
– load = “external” force which the effort acts against
Muscles: Name, Origin, Insertion, Action
• Name and description of the muscle – be alert to
information given in the name
• Origin and insertion – there is always a joint (or
two – biarticular muscles) between the origin and
insertion
• Action – best learned by acting out a muscle’s
movement on one’s own body
Muscle force and torques
For a muscle to carry a load without giving way, the torque on
the joint from the muscle must be equal and opposite to the
torque on the joint from the load.
Torque is twisting force, i.e. force that causes angular motion.
Torque = Force x Distance*
where Distance is from the point where force is applied to the
“axis” or center of rotation
* I am making the assumption that the force is at right angles to “axis of pull”.
Lever Systems
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Figure 10.2a
Lever Systems
Figure 10.2b
In figure above: shovel=lever, right hand=fulcrum,
load=weight of dirt, effort=upward force applied by
left hand
Muscle force and torques
Joint Torque due to muscle =
(Muscle force) x (Distance from joint to muscle insertion)
Joint Torque due to load =
(Load force) x (Distance from joint to load).
Muscle force and torques
Example:
Load =100 N. Distance from joint to load = 20 cm.
Distance from joint to muscle insertion = 4 cm.
What force must the muscle provide, to support the load?
Answer: Using the equation above, we see that
(Muscle force) x 4 cm
=
100 N x 20 cm.
Therefore: Muscle force = 2000 N-cm / 4 cm = 500 N. The
muscle force must be bigger than the load. This is not
uncommon.
* I am making the assumption that the forces are at right angles to the limb axis.
Major Skeletal Muscles: Anterior View

The 40 superficial
muscles here are
divided into 10
regional areas of the
body
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 10.4b
Major Skeletal Muscles: Posterior View

The 27 superficial
muscles here are
divided into seven
regional areas of the
body
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 10.5b