Muscles Working Together to Create Movement!

PSK 4U

Unit 4 Day 5

Muscles – Working Together to

Create Movement!

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)

ANTAGONIST

Elbow flexion

Shoulder abduction

Medial shoulder

rotation

Knee extension

Wrist flexion

Dorsi flexion

Trunk flexion

Hip flexion

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!