I



Chapter 10 The Muscular System

1 The structural and functional organization of muscles

1 The functions of muscles

1 Movement

Movement of body parts, but also the movement of body contents in respiration, circulation, digestion, defecation, urination and childbirth.

2 Stability

Resisting the pull of gravity to maintain body posture. Stabilization of joints.

3 Communication

Facial expression, other types of “body language”, writing, speech.

4 Control of body openings and passages

1 Sphincters acting as valves

Sphincters are ring-like smooth muscles that prevent outflow from hollow organs, for example the contents of the stomach are held in place by the pyloric sphincter.

5 Heat Production

As muscles contract they produces heat. Much of this heat is used to maintain a constant body temperature, but energy must be expended to cool the body if excessive heat is generated by muscles.

2 Connective tissues of a muscle

Connective tissue surrounds and protects muscular tissue. The connective tissue also adds mechanical strength to muscles.

1 Fascia

A sheet or broad band of fibrous connective tissue that supports and surrounds muscles (and other organs).

1 Superficial fascia (subcutaneous layer or hypodermis)

Separates muscles from skin.

2 Deep fascia

Holds muscles with similar functions together. Three layers of connective tissue extend from the deep fascia.

1 Epimysium

Surrounds the entire muscle.

2 Perimysium

Surrounds bundles of muscle fibers (muscle cells).

1 Fascicles

The term for bundles of muscle fibers. When we see "grain" in a cut of meat, we are seeing the fascicles.

3 Endomysium

Separate individual muscle fibers from one another.

2 Tendon

The three connective tissue layers described above extend from the muscle and are continuous with tendons. Tendons are the structural attachments of muscles to bones or other muscles. A tendon is a cord of connective tissue composed of parallel bundles of collagen fibers.

3 Aponeurosis

When the connective tissue elements of a muscle extend in a broad, flat sheet (not the cord shape of a tend), this is referred to as an aponeurosis.

3 General anatomy of skeletal muscles

1 Muscle attachment sites: origin and insertion

When a skeletal muscle contracts it pulls one bone towards another. The two bones usually do not move equally: one usually remains relatively stationary.

1 Origin

The attachment of a muscle's tendon to the stable bone is called the origin of the muscle.

2 Insertion

The attachment of the muscle's tendon to the mobile bone is called the insertion.

3 Belly

The fleshy portion of a muscle between the origin and insertion is called the belly.

2 Effects of fascicle arrangement

1 Fascicles

Recall that fascicles are bundles of muscle fibers that are parallel to one another. They form various patterns relative to the tendon in the specific muscle.

2 Fascicle arrangement

Fascicle arrangement effects the muscle's power and range of motion. A single muscle fiber will contract to about 70% of its relaxed length and the longer the muscle fibers in a muscle, the greater the range of motion it can produce. Fascicle arrangement often represent a compromise between power and range of motion. Pennate muscles have a great deal of power because the fascicles are distributed along the tendon, however, they have a shorter range of motion.

1 Parallel

Fascicles are parallel to the longitudinal axis of the muscle. The fascicles terminate at either end of the muscle in flat tendons.

2 Fusiform

The fascicles are nearly parallel to the longitudinal axis of the muscle and they terminate in flat tendons, but the diameter of the muscle at the ends is less than at the belly.

3 Circular (sphincters)

Fascicles are arranged in concentric circular arrangements to form sphincter muscles that enclose an orifice.

4 Convergent or triangular

The fascicles are spread over a broad area and converge at a thick, central tendon.

5 Pennate

Pennate muscles have short fascicles relative to the total muscle length. The tendon extends nearly the entire length of the muscle.

1 Unipennate

The fascicles are arranged on only one side of the tendon.

2 Bipennate

The fascicles are arranged on both sides of the central tendon.

3 Multipennate

Fascicles attach obliquely (at an angle) from many directions to several tendons.

4 Coordinated actions of muscle groups

A specific movement is often the result of the activity of several muscles acting as a group. Most muscles are arranged in opposing (antagonist) pairs at joints: there will be extensors and flexors paired together for example.

1 Actions

The actions of a muscle are the main movements that occur when the muscle contracts.

1 Prime mover (agonist)

Within opposing pairs, one muscle contracts to cause an action and the other stretches to yield to the effects of the first. The prime mover or agonist is the muscle that causes an action. For example, in flexing the forearm at the elbow, the biceps brachii is the prime mover.

2 Synergist

When a prime mover crosses several joints before it reaches the joint at which the prime action occurs, the intermediate joints must be stabilized. Muscles called synergists stabilize intermediate joints. For example, the biceps brachii crosses the shoulder and elbow joints and the prime action moves the forearm. The brachialis acts synergistically with the biceps brachii.

3 Antagonist

The antagonist stretches in response to the action of the prime mover. In flexing the elbow, the triceps brachii is the antagonist.

Note that the prime mover and antagonist designation can switch for different movements: in extending the forearm, the triceps brachii is the prime mover.

4 Fixator

Fixators are muscles that stabilize the origin of a prime mover. For example, the muscles that originate on the scapula would move that bone when contracting if the pectoralis minor, trapezius, subclavius, serratus anterior muscles didn't act as fixators.

5 Intrinsic and extrinsic muscles

Intrinsic muscles are found within the structure that they move, such as the muscles found within the hand. Extrinsic muscles are found outside of the structure that they move, for example the muscles in the forearm which move the fingers.

6 Muscle innervation

7 How muscles are named

2 Muscles of the head and neck

1 Muscles of facial expression

1 The scalp

|Muscle |Origin |Insertion |Action/Function |

|Frontalis |Galea aponeurotica |Subcutaneous tissue of eyebrows |Elevates eyebrows |

2 The orbital and nasal regions

|Muscle |Origin |Insertion |Action/Function |

|Orbicularis oculi |Wall of orbit |Subcutaneous tissue around eye |Closes eyes |

|Levator palpebrae superior |Sphenoid bone |Upper eyelid |Opens eyes |

|Corrugator supercilii |Upper ridge of orbit (temporal |Skin of eyebrow |Draws eyebrows medially and |

| |bone) | |downward (frown) |

|Nasalis |Maxilla |Bridge cartilage of nose |Widens nostrils |

3 The oral region

|Muscle |Origin |Insertion |Action/Function |

|Orbicularis oris |Muscle fibers surrounding mouth |Modiolus |Closes, protrudes lips, speech |

|Zygomaticus major |Zygomatic arch |Modiolus |Draws angle of mouth upward and |

| | | |laterally (smiling) |

|Risorius |Zygomatic arch of skull, fascia |Skin at corners of mouth |Draws angle of mouth laterally |

| |more superficially |(modiolus) |(grimacing) |

|Depressor anguli oris |Mandible |Skin at corners of mouth |Draws angle of mouth laterally |

| | |(modiolus) |and downward (sad expressions) |

4 The mental and buccal regions

|Muscle |Origin |Insertion |Action/Function |

|Buccinator |Maxilla and mandible |Orbicularis oris |Compresses cheeks against teeth |

| | | |and gums |

5 The cervical and mental region

|Muscle |Origin |Insertion |Action/Function |

|Platysma |Fascia over deltoid and |Mandible, muscles around mouth, |Draws lower lip downward |

| |pectoralis major |skin of lower face |(surprise), depresses mandible |

2 Muscles of chewing and swallowing

1 Extrinsic muscles of the tongue

|Muscle |Origin |Insertion |Action/Function |

|Genioglossus |Mandible |Tongue |Unilateral action draws tongue |

| | | |to one side; bilateral action |

| | | |depresses midline of tongue or |

| | | |protrudes tongue |

2 Muscles of chewing

|Muscle |Origin |Insertion |Action/Function |

|Temporalis |Termporal bone |Mandible |Elevates and retracts mandible |

|Masseter |Zygomatic arch |Mandible |Elevates mandible |

|Medial pterygoid |Sphenoid, palatine, and maxilla |Mandible |Elevates mandible, etc |

|Lateral pterygoid |Sphenoid |Mandible |Depresses mandible, etc |

3 Hyoid muscles - suprahyoid group

|Muscle |Origin |Insertion |Action/Function |

|Digastric |Mandible |Hyoid |Depresses mandible, elevates |

| | | |hyoid (yawning) |

3 Muscles acting on the head

1 Flexors of the head

|Muscle |Origin |Insertion |Action/Function |

|Sternocleidomastoid |Sternum and clavicle |Mastoid process of termporal |Flex cervical vertebrae; raise |

| | |bone |sternum during respiration; |

| | | |laterally extend and rotate head|

2 Extensors of the neck

|Muscle |Origin |Insertion |Action/Function |

|Trapezius |Occipital bone and vertebrae |Clavicle and scapula |Elevates, adducts and depresses |

| | | |scapula; extends neck |

3 Muscles of the trunk

1 Muscles of respiration

|Muscle |Origin |Insertion |Action/Function |

|Diaphragm |Xyphoid process, costal |Central tendon |Contraction causes the diaphragm|

| |cartilages, ribs, vertebrae | |to flatten, increasing the |

| | | |volume of the thoracic cavity |

|External intercostals |Inferior border of rib above |Superior border of rib below |Contraction elevates ribs and |

| | | |expands thoracic cavity |

|Internal intercostals |Superior border of rib below |Interior border of rib above |Contraction decreases the volume|

| | | |of the thoracic cavity |

2 Muscles of the anterior abdominal wall

|Muscle |Origin |Insertion |Action/Function |

|External abdominal oblique |Ribs |Ilium |Flexes vertebral column, |

| | | |compresses abdomend |

|Rectus abdominus |pubis |Ribs and xyphoid process |Flexes vertebral column, |

| | | |compresses abdomen |

|Linea alba |Aponeurosis of the external oblique, interior oblique and transversus abdominis meets at a midline|

|(not a muscle) |to form the linea alba |

3 Muscles of the back

4 Muscles of the pelvic floor

4 Muscles acting on the shoulder and upper limb

1 Muscles acting on the scapula

1 Anterior group

|Muscle |Origin |Insertion |Action/Function |

|Serratus anterior |Ribs |Scapula |Draws scapula laterally and |

| | | |forward around chest wall, etc |

2 Posterior group

|Muscle |Origin |Insertion |Action/Function |

|Trapezius |Occipital bone and vertebrae |Clavicle and scapula |Elevates, adducts and depresses |

| | | |scapula; extends head |

2 Muscles acting on the humerus

1 Axial muscles

|Muscle |Origin |Insertion |Action/Function |

|Pectoralis major |Clavicle and sternum |Humerus |Adducts and medially rotates arm|

| | | |at shoulder joint; flexes arm |

|Latissimus dorsi |Vertebrae and ilium |Humerus |Extends, adducts and medially |

| | | |rotates arm at shoulder joint |

2 Scapular muscles

|Muscle |Origin |Insertion |Action/Function |

|Deltoid |Clavicle and scapula |Humerus |Abducts, flexes, and medially |

| | | |rotates arm at shoulder joint |

|Teres major |Scapula |Humerus |Extends and medially rotates |

| | | |humerus |

3 The rotator cuff

|Muscle |Origin |Insertion |Action/Function |

|Infraspinatus |Scapula |Humerus |Modulates action of deltoid |

|Teres minor |Scapula |Humerus |Modulates action of deltoid |

3 Muscles acting on the forearm

1 Muscles with bellies in the arm (brachium)

|Muscle |Origin |Insertion |Action/Function |

|Brachialis |Humerus |Ulna |Prime mover of elbow flexion |

|Biceps brachii |Scapula |Radius |Supination of forearm, flexes |

| | | |forearm at elbow; flexes arm at |

| | | |shoulder joint |

|Triceps brachii |Humerus |Ulna |Extends forearm at elbow; |

| | | |assists in adducting humerus |

2 Muscles with bellies in the forearm (antebrachium)

|Muscle |Origin |Insertion |Action/Function |

|Brachioradialis |Humerus |Radius |Flexes forearm at elbow |

|Pronator teres |Humerus and ulna |Radius |Pronates forearm |

4 Muscles acting on the wrist and hand

1 Anterior compartment, superficial layer

|Muscle |Origin |Insertion |Action/Function |

|Flexor carpi radialis |Humerus |Metacarpals |Flexes wrist |

|Flexor carpi ulnaris |Humerus |Metacarpals |Flexes wrist |

|Palmaris longus |Humerus |Palmar aponeurosis |Anchors skin and fascia of palm |

| | | |(may be absent) |

2 Anterior compartment, deep layer

|Muscle |Origin |Insertion |Action/Function |

|Flexor pollicis longus |Radius |Distal phalanx of thumb |Flexes phalanges of thumb |

3 Posterior compartment, superficial layer

|Muscle |Origin |Insertion |Action/Function |

|Extensor digitorum |humerus |Phalanges |Extends wrist |

|Extensor carpi radialis longus |humerus |Metacarpals |Extends wrist |

|Extensor carpi ulnaris |Humerus and ulna |Metacarpal of thumb |Extends wrist |

4 Posterior compartment, deep layer

|Muscle |Origin |Insertion |Action/Function |

|Abductor pollicis longus |Radius and ulna |Metacarpal of thumb |Abducts thumb |

|Extensor pollicis longus |Ulna |Distal phalanx of thumb |Extends distal phalanx of thumb |

5 Intrinsic muscles of the hand

5 Muscles acting on the hip and lower limb

1 Muscles acting on the hip and femur

1 Anterior muscles of the hip

|Muscle |Origin |Insertion |Action/Function |

|Iliacus |Iliac crest and sacrum |Femur |Flexes thigh at hip, flexes |

| | | |trunk at hip |

|Psoas |Lumbar vertebrae |Femur |Flexes thigh at hip, flexes |

| | | |trunk at hip |

2 Lateral and posterior muscles of the hip

|Muscle |Origin |Insertion |Action/Function |

|Gluteus maximus |Ilium, sacrum, coccyx |Iliotibial fascia and femur |Extends thigh at hip and abducts|

| | | |thigh |

3 Lateral rotators

4 Medial (adductor) compartment of the thigh

|Muscle |Origin |Insertion |Action/Function |

|Adductor magnus |Pubis and ischium |Femur |Adducts and medially rotates |

| | | |thigh |

|Gracilis |Pubis and ischium |Tibia |Flexes and medially rotates |

| | | |tibia at knee |

|Pectineus |Pubis |Femur |Flexes and adducts thigh |

2 Muscles acting on the knee and leg

1 Anterior (extensor) compartment of the thigh

|Muscle |Origin |Insertion |Action/Function |

|Quadriceps femoris |The four heads of the quadriceps femoris are described below |

|Rectus femoris |Ilium and acetabulum |Patella and tibia |All four extend leg at knee |

| | | |joint |

|Vastus lateralis |Femur |Patella and tibia | |

|Vastus medialis |Femur |Patella and tibia | |

|Vastus intermedius |Femur |Patella and tibia | |

|Sartorius |Ilium |Tibia |Flexes leg at knee; flexes |

| | | |abducts, and laterally rotates |

| | | |thigh at hip |

2 Posterior (flexor) compartment of the thigh

|Muscle |Origin |Insertion |Action/Function |

|Biceps femoris |Ischium and femur |Fibula |Flexes leg at knee; extends |

| | | |thigh at hip |

|Semimembranosus |Ischium |Tibia and femur |Flexes knee |

|Semitendinosus |Ischium |Tibia |Flexes knee |

3 Posterior compartment of the leg

|Muscle |Origin |Insertion |Action/Function |

|Popliteus |Femur |Tibia |Rotates tibia medially, etc |

3 Muscles acting on the foot

1 Anterior compartment of the leg

|Muscle |Origin |Insertion |Action/Function |

|Extensor digitorum longus |Tibia and fibula |Middle and distal phalanges |Extends toes, dorsiflexes foot |

2 Posterior compartment of the leg, superficial group

|Muscle |Origin |Insertion |Action/Function |

|Gastrocnemius |Femur |Calcaneous (tarsal) |Plantar flexes foot at ankle; |

| | | |flexes leg at knee |

|Soleus |Fibula and tibia |Calcaneous |Plantar flexes foot at ankle |

3 Posterior compartment of the leg, deep group

4 Lateral (fibular) compartment of the leg

|Muscle |Origin |Insertion |Action/Function |

|Fibularis (peroneus) longus |Fibula |cuneiform and metatarsal of big |Maintains concavity of sole, |

| | |toe |everts and plantar flexes foot |

4 Intrinsic muscles of the foot

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