Structure and function of the muscular system

• A&P
• Higher Education (non-degree)

ANATOMY AND PHYSIOLOGY FOR SPORTS MASSAGE 

THE STRUCTURE AND FUNCTION OF THE SKELETAL SYSTEM

ANATOMY AND PHYSIOLOGY FOR SPORTS MASSAGE

THE STRUCTURE AND FUNCTION OF THE MUSCULAR SYSTEM

What are you going to learn?

In this lesson you're going to learn to . . .

1

2

3

Describe characteristics of types of muscle tissue

Locate and describe action of the major anterior and posterior skeletal muscles

Identify and locate muscle attachment and insertion points. 

Describe the role of muscles during movement

4

6

5

Explain different types of muscle contraction

Explain the principle of muscle contraction

CHARACTERISTICS OF TYPES OF MUSCLE TISSUE  

In the muscular system, muscle tissue is categorised into three distinct types: 

1) Skeletal 2) Cardiac 3) Smooth. 

Each type of muscle tissue in the human body has a unique structure and a specific role. Skeletal muscle moves bones and other structures. Cardiac muscle contracts the heart to pump blood. The smooth muscle tissue that forms organs like the stomach and bladder changes shape to facilitate bodily functions. 

CHARACTERISTICS OF TYPES OF MUSCLE TISSUE  

Skeletal muscles attach to and move bones by contracting and relaxing in response to voluntary messages from the nervous system. Skeletal muscle tissue is composed of long cells called muscle fibers that have a striated appearance. 

Smooth muscle is found in the walls of hollow organs throughout the body. Smooth muscle contractions are involuntary movements triggered by impulses that travel through the autonomic nervous system. 

Cardiac muscle is found only in the myocardium of the heart, it contracts in response to signals from the cardiac conduction system to make the heart beat. 

Muscle fibers are organized into bundles supplied by blood vessels and innervated by motor neurons.

Smooth muscle tissue allows for contraction and relaxation with great elasticity. In the urinary bladder they allow those organs to expand and relax. In the digestive tract they facilitate swallowed food and nutrients. In artery walls they relax and contract to move blood through the body.

Cardiac muscle is made from cells called cardiocytes. Like skeletal muscle cells cardiocytes have a striated appearance, but their overall structure is shorter and thicker. 

Match up the descriptions to the muscle tissue types

Contract by shortening in length

Located in the walls of the myocardium

Striated in appearance 

Voluntary - under conscious control

Involuntary - under unconscious control

Contract with peristaltic (wave) action 

Located in skeletal muscles

 Located in the walls of  organs and digestive system

Involuntary - under unconscious control

Appear spindle-shaped 

MUSCLE ATTACHMENTS 

Learning the muscular system often involves memorising details about each muscle, like where a muscle attaches to bones and how a muscle helps move a joint. 

A skeletal muscle attaches to bone (or sometimes other muscles or tissues) at two or more places. 

Origin

If the place is a bone that remains immobile for an action, the attachment is called an origin. 

Insertion

If the place is on the bone that moves during the action, the attachment is called an insertion. 

MUSCLE ACTION 

The muscles surrounding synovial joints are responsible for moving the body in space. These muscle actions are often paired, like flexion and extension or abduction and adduction. Below the common terms are listed and defined. 

Flexion and Extension

Flexion: decreasing the angle between two bones (bending).

Extension: increasing the angle between two bones (straightening a bend).

Example: At the elbow joint

The triceps brachii muscle extend the elbow. The biceps brachii, brachialis, and brachioradialis flex the elbow.

Abduction and Adduction

Abduction: moving away from the body’s midline.

Adduction: moving toward the body’s midline.

Example: At the hip joint

The gluteus medius, gluteus minimus, tensor fasciae latae, and sartorius are muscles that abduct the hip. The pectineus, adductor longus, adductor brevis, adductor magnus, and gracilis adduct the hip.

Dorsiflexion and Plantarflexion

Dorsiflexion: bringing your foot upward toward your shin.

Plantar flexion: depressing your foot down. 

Example: at the ankle joint

The tibialis anterior dorsiflexes the ankle joint. Whereas the gastrocnemius plantarflexes the ankle joint. 

Elevation and Depression

Elevation: moving a body part up.

Depression: moving a body part down.

Example: at the shoulder girdle

The upper traperzius, rhomboids and levator scapula are muscles that elevate the shoulder girdle. Whereas the lower traperzius and pectorial minor depress the shoulder girdle.

Eversion and Inversion

Inversion: turning the sole of the foot inward.

Eversion: turning the sole of the foot outward.

Example: at the ankle joint

The tibialis anterior and tibialis posterior are muscles that invert the ankle joint. Whereas the peroneus longus, peroneus brevis and peroneus tertius evert the ankle joint.

Protraction and Retraction

Pronation: rotating the forearm so the palm is facing backward or down.

Supination: rotating the forearm so the palm is facing forward or up.

Example: at the shoulder girdle

The mid / lower traperzius and rhomboids are muscles that retract the shoulder girdle. Whereas the pectorialis minor and serratus anterior protract the shoulder girdle.

Pronation and Supination

Pronation: rotating the forearm so the palm is facing backward or down.

Supination: rotating the forearm so the palm is facing forward or up.

Example: at the elbow joint

The pronator teres and pronator quadratus pronate the forearm. Whereas the biceps brachii and brachioradialis supinate the forearm. 

MUSCLES OF THE SHOULDER GIRDLE 

Rhomboids

Origin- C7-T5

Insertion- Medial border of the scapula

Primary action/s- Elevation and retraction of shoulder girdle. 

Trapezius

Origin- Base of cranium and cervical and thoracic vertebrae 

Insertion- Clavicle and scapula 

Primary action/s- Elevation, depression and retraction of shoulder girdle. 

Pectoralis Minor

Origin- 3rd, 4th, 5th ribs

Insertion- Coracoid process (anterior scapula)

Primary action/s- Depression and protraction of shoulder girdle.

Serratus Anterior

Origin- Upper 8/9 ribs

Insertion- Medial border of scapula

Primary action/s- IProtraction of shoulder girdle.

Levator Scapula

Origin- C1-C4

Insertion- Superior angle of scapula

Primary action/s- Elevation of shoulder girdle and lateral flexion of neck. 

MUSCLES OF THE SHOULDER JOINT

Latissimus Dorsi

Origin- T6-T12, L1-L5, iliac crest and lower 3 ribs. 

Insertion- Anterior surface of humerus

Primary action/s- Extension, adduction and medial rotation of shoulder.

Pectoralis Major

Origin- Clavicle, sternum and 1st to 6th ribs

Insertion- Anterior humerus

Primary action/s- Adduction, horizontal flexion and medial rotation shoulder joint.

Deltoids

Origin- Scapula and clavicle

Insertion- Lateral humerus

Primary action/s- Flexion and extension, horizontal flexion and extension, lateral and medial rotation, abduction of shoulder joint. 

Teres Major

Origin-Inferior angle of scapula

Insertion- Superior anterior humerus

Primary action/s- Extension, adduction and medial rotation of shoulder joint.

MUSCLES OF THE ROTATOR CUFF   

Supraspinatus

Origin- Superior surface of scapula

Insertion- Superior humerus

Primary action/s- Initiates abduction of shoulder joint.

Infraspinatus

Origin- Posterior surface of scapula

Insertion- Superior posterior humerus

Primary action/s- Adduction and lateral rotation of shoulder joint.

Subscapularis

Origin- Anterior surface of scapula

Insertion- Superior  anterior humerus

Primary action/s- Medial rotation of shoulder joint.

Teres Minor

Origin- Lateral border of scapula

Insertion- Superior posterior humerus

Primary action/s- Medial rotation of shoulder joint.

UPPER LIMB SKELETAL MUSCLES   

Wrist Extensors

Origin- Lateral humerus

Insertion- Back of hand

Primary action/s- Extension of wrist.

Coracobrachialis

Origin- Superior scapula

Insertion- Medial humerus 

Primary action/s- Flexion and adduction of humerus. 

Brachialis

Origin- Mid humerus 

Insertion- Superior ulna 

Primary action/s- Flexion of forearm. 

Brachioradialis

Origin- Distal humerus

Insertion- Distal radius

Primary action/s- Flexion and supination of forearm. 

Wrist Flexors

Origin- Medial humerus

Insertion- Palm of hand

Primary action/s- Flexion of wrist.

Triceps Brachii

Origin- Long head: superior scapula, Lateral head: lateral posterior humerus, Medial head: Posterior humerus

Insertion- Superior ulna (olecranion)

Primary action/s- Extension of shoulder and elbow joint. 

Bicep Brachii

Origin- Long head: superior scapula, Short head: anterior scapula

Insertion- Radius 

Primary action/s- Flexion of shoulder and elbow joint, supination of forearm. 

TRUNK SKELETAL MUSCLES   

External Obliques

Origin- Lower 8 ribs

Insertion- Iliac crest and linea alba

Primary action/s- Rotation and lateral flexion of spine. 

Internal Obliques

Origin- Iliac crest and lumbar fascia

Insertion- 8-10th ribs and linea alba

Primary action/s- Rotation and lateral flexion of spine. 

Rectus Abdominis

Origin- Pubic symphysis, pubic crest

Insertion- Xiphoid process and 5th-7th ribs

Primary action/s-  Flexion of spine. 

Quadratus Lumborum

Origin- Iliac crest

Insertion- 12th rib and L1-L4

Primary action/s- Lateral flexion of spine, bilaterially extends the spine. 

Erector Spinae

Origin- Along the length of the vertebral cloumn, ribs and pelvis

Insertion- Vertebral column and ribs

Primary action/s- Extension of the spine.

Transversus Abdominis

Origin- Iliac crest, lower 6 ribs and lumbar fascia

Insertion- Linea alba and pubis

Primary action/s- Drawing abdomen inwards.

MUSCLES OF THE PELVIC GIRDLE AND HIP

Gluteus Medius

Origin- Lateral and posterior ilium

Insertion- Posterior and lateral surface of upper femur

Primary action/s- Abduction and medial rotation of hip. 

Tensor Fascia Latae

Origin- Anterior iliac crest

Insertion- Lateral tibia via iliotibal band (ITB)

Primary action/s- Flexion and abduction of hip. Medial rotation as hip flexes. 

Iliopsoas

Origin- Lumbar spine and pelvis 

Insertion- Less trochnater of femur 

Primary action/s- Flexion of hip and spine. 

Gluteus Minimus

Origin- Lateral ilium

Insertion- Anterior surface of upper femur

Primary action/s- Abduction and medial rotation of hip. 

Piriformis

Origin- Anterior sacrum

Insertion- Upper surface of upper femur

Primary action/s- Abduction and medial rotation of hip. 

Gluteus Maximas

Origin- Iliac crest, sacrum and coccyx

Insertion- Upper posterior femur and ITB

Primary action/s- Extension and lateral rotation of the hip.

LOWER LIMB SKELETAL MUSCLES   

Adductor Longus

Origin- Anterior pubis

Insertion- Medial femur

Primary action/s- Adduction of hip.

Adductor Magnus

Origin- Anterior pubis

Insertion- Medial femur

Primary action/s- Adduction of hip.

Gracilis

Origin- Ischiopubic ramus 

Insertion- Medial tibia

Primary action/s- Adduction of hip and flexion of knee. 

Sartorius

Origin- Anterior Superior iliac spine (ASIS)

Insertion- Medial condyle of tibia

Primary action/s- Flexion, abduction and lateral rotation of hip. Flexion and medial rotation of knee. 

Pectineus

Origin- Anterior pubis 

Insertion- Upper femur

Primary action/s- Adduction and flexion of the hip. 

Adductor Brevis

Origin- Anterior pubis

Insertion- Medial femur

Primary action/s- Adduction of hip.

MUSCLES OF THE UPPER LEG

Vastus Medialis

Origin- Medial femur

Insertion- Tibial tuberosity via patella

Primary action/s- Extension of knee (especially last 20 degrees of movement)

Vastus Intermedius

Origin- Anterior femur

Insertion- Tibial tuberosity via patella

Primary action/s- Extension of knee.

Vastus Lateralis

Origin- Lateral upper femur 

Insertion- Tibial tuberosity via patella

Primary action/s-  Extension of knee.

Rectus Femoris

Origin- Anterior inferior iliac spine (AIIS)

Insertion- Tibial tuberosity via patella 

Primary action/s- Flexion of hip and extension of knee

MUSCLES OF THE UPPER LEG

Biceps Femoris

Origin- Ischial tuberosity and posterior femur

Insertion- Head of fibula and lateral condyle of tibia

Primary action/s- Extension of hip and flexion of knee.

Semimembranosus

Origin- Ischial tuberosity 

Insertion-  Medial condyle of tibia

Primary action/s- Extension of hip and flexion of knee.

Semitendinosus

Origin- Ischial tuberosity

Insertion- Medial condyle of tibia

Primary action/s- Extension of hip and flexion of knee.

MUSCLES OF THE LOWER LEG

Plantaris

Origin- Lateral upper femur

Insertion- Calcaneus 

Primary action/s- Plantarflexion of ankle. 

Gastrocnemius

Origin- Posterior medial / Lateral upper femur

Insertion- Calcaneus

Primary action/s- Flexion of knee and Plantarflexion of ankle. 

Tibialis Anterior

Origin- Lateral tibia

Insertion- Plantar surface of foot

Primary action/s- Dorsiflexion and Inversion of ankle. 

Tibialis Posterior

Origin- Posterior surfaces of tibia and fibula

Insertion- Plantar surface of foot

Primary action/s- Plantarflexion and Inversion of ankle. 

Popliteus

Origin- Lateral upper femur 

Insertion- Posterior upper tibia

Primary action/s- Flexion and medial rotation of the knee

Soleus

Origin- Upper posterior tibia and fibula

Insertion- Calcaneus

Primary action/s- Plantarflexion of ankle. 

MUSCLES OF THE LOWER LEG  

Peroneus Brevis

Origin- Lower lateral surface of fibula

Insertion- Plantar surface of foot

Primary action/s- Plantarflexion and Eversion of ankle. 

Peroneus Longus

Origin- Upper lateral surface of fibula

 

Insertion- Plantar surface of foot

Primary action/s- Plantarflexion and Eversion of ankle. 

Peroneus Tertius

Origin- Lower anterior surface of fibula

Insertion- Dorsal surface of foot

Primary action/s- Dorsiflexion and Eversion of ankle. 

MUSCLES OF THE LOWER LEG  

Extensor Digitorum Longus

Origin- Lateral upper tibia and anterior fibula

Insertion- Dorsal surface of 4 outer toes

Primary action/s- Dorsiflexion and Eversion of ankle. Extension of the 4 outer toes. 

Extensor Hallucis Longus

Origin- Anterior surface of the fibula 

Insertion- Dorsal surface of 1st (big) toe

Primary action/s- Dorsiflexion and Inversion of ankle. Extension of the 1st (big) toe. 

Flexor Digitorum Longus

Origin- Posterior surface of the tibia

Insertion- Plantar surface of 4 outer toes

Primary action/s- Plantarflexion and Inversion of ankle. Flexion of the 4 outer toes. 

Flexor Hallucis Longus

Origin- Lower fibula

Insertion- Plantar surface of 1st (big) toe

Primary action/s- Plantarflexion and Inversion of ankle. Flexion of the 1st (big) toe. 

ROLE OF MUSCLES DURING MOVEMENT  

While many muscles may be involved in any given action, muscle function terminology allows you to quickly understand the various roles different muscles play in each movement.

Prime movers and antagonists are often paired up on opposite sides of a joint, with their prime mover/antagonist roles reversing as the movement changes direction.

Prime movers / agonist

The prime mover, sometimes called the agonist, is the muscle that provides the primary force driving the action. 

Antagonist

An antagonist muscle is in opposition to a prime mover in that it provides some resistance and/or reverses a given movement. 

Fixator / Stabilisers

Stabilisers act to keep bones immobile when needed. Your back muscles, for example, are stabilizers when they are keeping your posture sturdy.

Synergists.

One or more synergists are often involved in an action. Synergists are muscles that assist the prime mover in its role.

Match up the muscle actions to the movement 

Knee flexion

Hip flexion

Knee extension 

Shoulder abduction

Press up - upward phase

Hip extension

Elbow flexion 

Glute Bridge - upward phase

Agonist- Bicep 

femoris 

Antagonist- Rectus femoris  

Antagonist- Bicep femoris  

Agonist- Rectus femoris 

Agonist- Iliopsoas 

Antagonist- Gluteus maximus

Agonist- Gluteus maximus 

Antagonist- Iliopsoas

Agonist- Deltoids 

Antagonist- 

Latissimus dorsi

Agonist- Biceps brachii

Antagonist- Triceps brachii

Antagonist- 

Rhomboids

Agonist- Pectoralis major

Agonist- Gluteus maximus 

Antagonist- Iliopsoas

The synergist muscle during hip extension?

1. Rectus femoris
2. Bicep femoris
3. Tibialis anterior
4. Adductor longus

The stabiliser muscle during a squat?

1. Rectus femoris
2. Supraspinatus
3. Erector spinae
4. Latissimus dorsi

The synergist muscle during a press up?

1. Pectoralis major
2. Infraspinatus
3. Transverse abdominis
4. Triceps brachii

The stabiliser muscle of the shoulder joint?

1. Teres minor
2. Gluteus maximus
3. Transverse abdominis
4. Tensor fascia latae

TYPES OF MUSCLE CONTRACTION 

There are three types of muscle contraction. 

1) Concentric contraction - The muscle shortens whilst it contracts 

2) Eccentric contraction - The muscle shortens whilst it contracts and usual involves the control or deceleration of movement. 

3) Isometric contraction -  Where there is no change in the length of the contracting muscle.  

TYPES OF MUSCLE CONTRACTION 

An example of muscle contraction types can be provided with a press up exercise. 

Once in an initial start position (bottom left) this provides an isometric contraction as muscles are neither shortening or lengtening.  An eccentric contraction is then provided when lowering towards the ground in the bottom position. Followed by a concentric contraction when pushing up from the ground returning to the start position. 

Match the description to the type of muscle contraction

Isometric

Concentric 

Eccentric 

Press up- downward phase

Biceps- elbow extension 

Biceps- elbow flexion

Deltoid- shoulder abduction 

Press up- bottom position 

Pull up - lowering phase

Iliopsoas- hip flexion 

Hamstrings - knee flexion

Quadricieps - knee extension

Triceps- elbow flexion

Hamstrings - knee extension

Pull up - upward phase

Abdominals - Plank 

Squat- Bottom position

Gripping a dumbbell

STRUCTURE OF SKELETAL MUSCLE 

1.

Muscles are bound together by different fascia made of dense irregular connective tissue. This is composed mainly of collagen fibres that run in many different directions. 

2.

The fascia of the muscle eventually converge to become the tendon which will attach to the bone. The tendon is made of dense regular connective tissue. The collagen fibres in the tendon run in one direction to create a strong connection for the muscle in the direction of pull. 

5.

A bundle of fibres is referred to as the fascicle

4.

Many fibres are bundled together and wrapped in the perimysium. Around the fascicles. 

3.

The outer covering of the muscle is called the epimysium.

6.

A sheath of endomysium surrounds each muscle fibre cell. The endomysium is continuous with the muscle fibre's membrane, or sarcolemma

8.

Myofibrils are divided along their length into repeating units called sarcomeres.

7.

Muscle fibres (cells) are the approximate width of a human hair and often run the full length of a muscle. They are composed of smaller elements known as myofibrils. 

9.

Sarcomeres are packed with two different types of protein filaments (myofilaments); thin actin and thick myosin. The myosin and actin filaments are strictly arranged inside the sarcomere to overlap each other. 

Put in order the structure of a skeletal muscle 

Tendon

Bone 

Muscle Fibre

Deep fascia 

Epimysium

Perimysium

Endomysium 

Fascicle 

Myofilament

Myofibril

STRUCTURE OF SKELETAL MUSCLE 

2.

Actin filaments look like two pearl necklaces, wound around each other.

1.

Sarcomeres are packed with two different types of protein filaments (myofilaments); thin actin and thick myosin.

3.

Myosin filaments are composed of collections of strands, each of which looks like a double-headed golf club. The myosin filaments form together, making the heads of the clubs protrude out of the surface of the filament.

4.

It is these myosin heads that make contact with the actin during muscle contraction. The myosin and actin filaments are strictly arranged inside the sarcomere to overlap each other. 

SLIDING FILAMENT THEORY

Terminology 

Sarcomere

The functional unit of the myofibril

Actin

A thin contractile protein filament containing 'active' or'binding' sites

Myosin

A thick contractile protein filament, with protrusions known as myosin heads

Tropomyosin

An actin-binding protein which regulates muscle contraction

Troponin

A complex of proteins, attached tropomyosin

Sacroplasmic reticulum

A type of endoplasmic reticulum found in muscle fibres, whose function is to store and telease calcium ions 

ATP (adenosine triphosphate)

A chemical compound stored/produced in the body which breaks down to release energy for actions such as muscle contraction 

Sliding filament theory

The process used by muscles to contract

 

A nervous impulse arrives at the neuromuscular junction, which causes the release of calcium (Ca+) from the sarcoplasmic reticulum. 

Calcium binds to troponin >tropomyosin which then allows myosin filaments to bind to the actin (cross-bridge).

The breakdown of ATP releases energy which enables the myosin to pull the actin filaments inwards, shortening the muscle. This occurs along the entire length of every myofibril in the muscle cell.

Myosin then detaches from the actin (cross-bridge is broken)

This process can last for as long as there are adequate ATP and Ca+ stores

Once the impulse stops the Ca+ is pumped back to the sarcoplasmic reticulum and the actin returns to its resting position causing the muscle to lengthen and relax.

 

Fill in the missing blanks

When stimulated by a nerve message, the      myosin             heads attach to the actin molecules, forming what is known as a cross-bridge, they then pivot and bend, pulling the            actin           filaments over the myosin filament towards the centre of the sarcomere. The myosin heads then        detach           from the actin, relax back to their original       positions        and prepare to attach to the actin again, further down the molecule. The myosin walks along the actin,      progressively pulling each filament towards the middle of the      sarcomere     . In this way, the muscle                shortens without any change in the overall length of the myosin or actin filaments. At any one instant some of the myosin heads are  attached             to actin generating          force, whereas others are detached ready to bind again. This is called a contraction cycle and referred to as the 'sliding                  filament theory' 

Sacromere

actin

Myosin

detach

progressively

positions

muscle

attached

generating

sliding

Fill in the missing blanks

Calcium                is very important to the process of muscle contraction. It assists in connecting the myosin head to the actin                     by revealing a binding site on the actin filament. Once the binding site is revealed, the myosin                 can form a cross-bridge       attachment. A single adenosine           triphosphate (ATP) molecule is used up every time a myosin head pivots and pulls on an actin filament               . For the contraction cycle to occur, muscles               need a continual supply of calcium and energy in the form of ATP. Fortunately, muscle cells carry their own store                     of calcium, and this is                                  being replenished from blood, which in turn will replace its reservoir from the bone (if dietary intake is inadequate). ATP needs to be                                 in the muscle by the energy systems. 

adenosine

cross-bridge

Calcium

actin

fliament

myosin

muscles

re-synthesised

store

continuously 

What you have learnt

Following this lesson you should now be able to . . .

1

2

3

Describe characteristics of types of muscle tissue

Locate and describe action of the major anterior and posterior skeletal muscles

Identify and locate muscle attachment and insertion points. 

Describe the role of muscles during movement

4

6

5

Explain different types of muscle contraction

Explain the principle of muscle contraction

Well done! Great job, you have now completed this lesson. 

Next up...The structure and function of the nervous system.