Muscular System Part A Prepared by Vince Austin and W. Rose. Figures from Marieb & Hoehn, 7 th and 8 th eds. Portions copyright Pearson Education

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Interactions of Skeletal Muscles  Skeletal muscles work together or in opposition  Muscles only pull (never push)  As muscles shorten, the insertion generally moves toward the origin  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  Prime movers – provide the major force for producing a specific movement  Antagonists – oppose or reverse a particular movement  Synergists  Add force to a movement  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  By location: associated bone or body region  By shape: e.g., deltoid muscle (deltoid = triangle)  By relative size – e.g., maximus, minimus, longus  By fiber direction: e.g., rectus (fibers run straight), transversus, oblique  By number of origins (heads): e.g., biceps, triceps  By site of attachment: point of origin or insertion  By action: e.g., flexor, extensor

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Fascicle Arrangment Varies  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 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

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 Muscles: Name, Origin, Insertion, Action

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”.

Copyright © 2010 Pearson Education, Inc. Lever Systems Figure 10.2a

In figure above: shovel=lever, right hand=fulcrum, load=weight of dirt, effort=upward force applied by left hand Lever Systems Figure 10.2b

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.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Major Skeletal Muscles: Anterior View  The 40 superficial muscles here are divided into 10 regional areas of the body Figure 10.4b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Major Skeletal Muscles: Posterior View  The 27 superficial muscles here are divided into seven regional areas of the body Figure 10.5b