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Muscles – Working Together to
Create Movement!
PSK 4U
Unit 4 Day 5
Muscles Pull!
 Muscles pull (by contracting and
relaxing) by working in opposing pairs
or groups.
 Muscles cannot push.
 Sometimes muscles attached directly to
bone, but more often they are joined to
bone by tendons.
How Muscles Attach to Bone
 Indirect Attachment – the epimysium (sheath of
connective tissue that surrounds the exterior of the
muscle fibre) extends past the muscle as a tendon and
then attaches to the periosteum of bone. This is most
common.
 Direct Attachment – the epimysium adheres to and
fuses with the periosteum.
 Bone markings present where tendons meet bones
 Tubercles, trochanters, and crests
Basic Muscular Principles
 Skeletal muscles contract only if stimulated to do so
 Skeletal muscles produce movements by pulling on
bones
 Bones serve as levers and joints serve as fulcrums on
these levers
 Muscles that move a body segment do not usually lie
over that part (e.g. bicep flexes elbow but is in upper
arm)
 Skeletal muscles almost always act in groups rather
than individually (prime movers/agonists, antagonists,
stabilizers/fixators, synergists)
Force of Muscle Contraction
 The force of contraction is affected by:
 The relative size of the muscle
 Larger muscles have larger and more muscle fibers
 Larger fibers can generate more force than smaller fibers
 More muscle fibers can generate more force than fewer fibers
 The number of muscle fibers contracting
 Greater numbers of motor units generate more force than smaller
numbers of motor units
 Degree of muscle stretch
 Muscles contract strongest when muscle fibers are 80-120% of
their normal resting length
Force of Muscle Contraction
Figure 9.20 (a)
Isometric and Isotonic Contractions
 Isometric muscle contraction
 Tension (force) does not exceed resistance (load)
 important in postural muscle function
 Isotonic muscle contraction
 Tension exceeds resistance
 tension while shortening = concentric
 tension while lengthening = eccentric
Agonist and Antagonist Pairs
 Agonist– muscle that contracts to produce
movement of the body part (prime mover)
 Synergists – assist in the action of the agonists but
are not primarily responsible for action; known as
guiding muscles they assist in refined movements
and rule out undesired motions
 Antagonist – muscle that opposes or
counteracts the agonist (movement).
 It lengthens when the agonist contracts shortens.
Examples of opposing muscles and muscle groups
AGONIST
(Prime Mover)
Elbow flexion
Shoulder abduction
Medial shoulder
rotation
Knee extension
Wrist flexion
Dorsi flexion
Trunk flexion
Hip flexion
ANTAGONIST
Examples of opposing muscles and muscle groups
AGONIST
(Prime Mover)
ANTAGONIST
Elbow flexion
Biceps brachii
Triceps brachii
Shoulder abduction
Deltoid
Latissimus Dorsi
Medial shoulder
rotation
Pectoralis major
Infraspinatus
Knee extension
Quadriceps
Hamstrings
Wrist flexion
Flexor carpi radialis
Extensor carpi radialis
Dorsi flexion
Tibialis anterior
Gastrocnemius
Trunk flexion
Rectus abdominis
Erector spinae group
Hip flexion
Iliopsoas
Gluteus maximus
Fixators/Stabilizer
 Muscles that are active isometrically (muscle does not
shorten or lengthen) in order to fixate an area when the
agonist contracts
 Fixators/ Stabilizers - increase tension to stabilize a
joint that is more proximal to allow function at a distal
joint
 Example: When performing a push-up, the serratus
anterior stabilizes the shoulder girdle during the
downward stage in order to prevent adduction
Origins and Insertions
 Origin – is least moveable part or the part of the
muscle that attaches closest to the midline. It is the
proximal attachment.
 Insertion – is the most moveable part or the part
of the muscle that attaches farther from the midline.
It is the distal attachment.
 The origin usually stays fixed and the insertion
moves closer to it
NAMING MUSCLES: Tips
 Most skeletal muscles have names that describe some
feature of the muscle.
 Often several criteria are combined into one name.
 Associating the muscle's characteristics with its name
will help you learn and remember them.
 The following are some terms relating to muscle
features that are used in naming muscles.
Size:
 vastus (huge)
 maximus (large)
 longus (long)
 minimus (small)
 brevis (short)
Shape:
 deltoid (triangular)
 rhomboid (like a rhombus
with equal and parallel sides)
 latissimus (wide)
 teres (round)
 trapezius (like a trapezoid, a
four-sided figure with two sides
parallel).
Direction of fibers:
 rectus
(straight)
 transverse
(across)
 oblique
(diagonally)
 orbicularis
(circular)
Location:







pectoralis (chest)
gluteus (buttock)
brachii (arm)
supra- (above)
infra- (below)
sub- (under or beneath)
lateralis (lateral).
Number of origins:
 biceps (two heads)
 triceps (three heads)
 quadriceps (four heads)
Triceps
Brachii
Origin
long head: infraglenoid tubercle of scapula
lateral head: upper half of the posterior surface of humerus
medial head: distal two thirds of the posterior surface of
humerus
Origin and insertion:
 sternocleidomastoid (origin on the sternum and
clavicle, insertion on the mastoid process)
 brachioradialis (origin on the brachium or arm,
insertion on the distal end of radius at the styloid
process)
Action:





abductor (to abduct a structure)
adductor (to adduct a structure)
flexor (to flex a structure)
extensor (to extend a structure)
levator (to lift/elevate a structure)
The name given to a muscle reveals the main kind
of functional movement that muscle permits.
ADDUCTOR MUSCLES
 squeeze limbs in
towards the
median line of
the body
 ie. – adductor longus,
adductor brevis,
adductor magnus
 attached along the
femur – squeeze
thighs together
ABDUCTOR MUSCLES
 ”push out” from the median line of body.
 ie- abductor digiti minimus manus, abductor
pollicis longus, abductor pollicis brevis
EXTENSOR MUSCLES
 extend the limbs and increase the angle between
two limbs.
 movement is usually directed backwards (with
exception of the knee joint)
 ie- extensor carpi radialis brevis, extensor carpi
radialis longus, extensor carpi ulnaris
 run from humerus along back of the forearm to
the metacarpal bones
FLEXOR MUSCLES
 withdraw the limbs and decrease the angle
between bones on two sides of a joint.
 ie- flexor
carpi radialis,
flexor carpi
ulnaris
 from humerus
along inside of
forearm to
metacarpal bones
– flex wrist
HOMEWORK
 Start working on Muscles Origin/Insertion
Chart
 Start colouring in muscles in chart on pages
94-113 in your workbooks!
 Wednesday – more memorizing!