Muscle Function and Anatomy
Chapter 2
Muscle Architecture
Muscle Architecture
 Sections
 Deepest section
contains two proteins
 Myosin
(thick)
 Actin (thin)
 Myosin is surrounded
by actin
Muscle Architecture
 Myofibrils
 Bundles of actin
and myosin
Muscle Architecture
 Muscle fiber
 Among others things, a muscle fiber contains
many groups of myofibrils
Muscle Architecture
 Fascicle
 A group of muscle fibers.
The Whole
Muscle
The Whole Muscle
Tendons
 Three membranes converge to form a tendon
which connects the muscle to the bone
Shape of Muscles and
Fiber Arrangement

Parallel muscles (range
of motion
1.
2.
3.
4.
5.

Strap
Flat (rectus abdominus)
Fusiform (biceps)
Strap (sartorius)
Radiate (trapezius)
Sphincter
Pennate (force)
1. Unipennate (biceps femoris)
2. Bipennate (rectus femoris)
3. Multipennate (deltoid)
Sphinter
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
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
Types of Muscle Contraction
QuickTime™ and a
Video decompressor
are needed to see this picture.
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
Concentric
Concentric
Lengthens
Eccentric
Lengthens
Eccentric
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.
ROLE OF MUSCLES
 Agonist
 prime
mover
 Antagonist
 action
opposite to the agonist
 Stabilizers
 fixate
or stabilize the joint
 Synergists
 assist
or guiding
Agonist and Antagonist
Agonist
Agonist
Antagonist
Antagonist
TABLE 2.1
Type of Contraction
Isotonic
Isometric
Concentric
Eccentric
Agonist muscle
No change
Shortening
Lengthening
Antagonist
No change
Lengthening
Shortening
Joint angle
No change
Decrease
Increase
Direction of body part
Against immovable
object
Against gravity or
external force
Consistent with gravity or
external force
Motion
Pressure but no motion
Causes motion
Causes motion
Description
Static
Dynamic shortening
Dynamic lengthening
Muscle force v.
Resistance
F=R
F>R
F<R
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
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?