Myology. Myology is the science that studies muscles from their different types of classifications in conjunction with their related elements.


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  • 1 Objectives
  • 2 muscles
  • 3 Brief histological account
  • 4 Functional properties of muscles
  • 5 Types of musculature
  • 6 Skeletal muscle
  • 7 General functions
  • 8 Portions of Skeletal Muscles
  • 9 Muscle contraction
  • 10 Dialectical-materialistic relationship between location, form and function.
  • 11 Classification of muscles according to their function
  • 12 About the innervation of the muscles
  • 13 Vascularization of skeletal striated muscle
  • 14 Muscle tone
  • 15 Muscles that act on the upper limb
    • 1 Pectoralis major
    • 2 Deltoids
    • 3 Brachial Triceps
    • 4 Brachial Biceps
  • 16 Muscles that act on the lower limb
  • 17 Examples of muscles that move the neck and head
  • 18 Muscles that Move the Jaw
  • 19 Trunk muscles
  • 20 Source


  • Anatomically identify each muscleor muscle group, according to its topographic location.
  • Locate the origin and insertion of the fundamental muscles, explaining their action (agonist or antagonist) according to the movement (bone segment they displace), taking into account their innervation.
  • Link the correct mastery of the origin, insertion and innervation of muscleswith the successful application of the different procedures.


A muscle is an organ made up mainly of muscle tissue mixed with connective tissue , made up of contractile spindle cells that shorten and lengthen their length in response to a nervous stimulus .

The muscles have developed the property of contraction, a process in which muscle proteins , calcium and ATP participate; during heat it occurs, this being one of the mechanisms of thermogenesis in the body . The muscles given their function have an exquisite vascularization and innervation.

Brief histological count

In muscle tissue the cells are elongated, so called muscle fibers. This shape is adapted to the function they perform, thus achieving greater efficiency in their contractions.

The structural elements of this fabric adopt a special terminology. For example:

  • The sarcolemma is the cell membrane.
  • The sarcoplasm is the cytoplasm.
  • The muscle fibers are grouped into bundles or bundlesand these meet with other increasingly larger bundles to form the muscle.
  • The connective tissuethat surrounds each muscle fiber is called the endomysium; the one that surrounds the fascicles is called perimysium and the one that surrounds the muscle as a whole is called epimysium.

Functional properties of muscles

The functional properties of the muscles are:

  • Excitability: It is the property of reaching a state of excitement in response to certain stimuli. The excitability can be direct when the stimulus occurs directly on the muscle, and indirect when the stimulus comes from the nerve that reaches it.
  • Extensibility: It is the ability of the muscles to relax, that is, to stretch when they experience violent tension.
  • Elasticity: It is the ability to regain its initial shape by ceasing the action of the force that has caused its deformation.
  • Contractility: It is the fundamental property of muscle, which occurs as a result of excitation.

Types of musculature

  • Smooth muscle
  • Heart muscle
  • Skeletal striated muscle

Skeletal muscle

These muscles are soft fleshy organs, brownish red in color, which have the property of contracting, causing the mechanical work of the body and therefore, act on its movement and balance. There are approximately 400 muscles in the human body.

General functions

These muscles perform the function of animal mechanics causing body movements and maintaining balance or posture. Furthermore, they produce caloric energy. The skeletal muscles in the human are numerous, there are approximately 400, most of them are inserted in the bones, but some do it in other structures.

Skeletal muscle portions

In general, the fundamental portions of the skeletal muscles are the belly and the extremities.

  • Muscular belly: It is the fleshy part that actively contracts.
  • Muscle ends.
    • Origin head
    • Insertion glue

Muscle contraction

Muscle contraction is the ability of the muscle to shorten by decreasing its length, or to develop tension in this regard. That is, they are the changes in shape and tension that occur in the muscle. When a muscle becomes active, three phenomena can occur:

  • That the active muscle shortens, bringing its ends closer, this is known as isotonic contraction; example, the action of the biceps brachii muscle when you. lift a heavy object with your upper limb.
  • That the muscle is activated but its length remains constant, this is known as isometric contraction; example the action of the biceps brachii when you. supports a heavy load with both arms.
  • That the muscle is activated but its ends move away, elongating the muscle, this is known as eccentric contraction; .example, the action of the biceps brachii when you. it places a heavy load on a table, straining with the upper limbs.

Dialectical-materialistic relationship between location, form and function.

  • Flat muscles, such as the diaphragm, are located in the chest and abdomen, forming muscle walls. It allows to increase or decrease the capacity of the box or tuning fork that makes up (rib cage).
  • The long muscles, for example the biceps, are located in the extremities and allow a wide range of motion.
  • Short muscles, such as the masseter, chewing muscle, interspinous; they are located in the head and in the vertebral column; determining short movements, but of great power.

Classification of muscles according to their function

  • Agonists: They are those whose action directly produces a certain movement, for example the biceps brachii during flexion of the arm.
  • Antagonists: They are those who perform the opposite movement of the agonist muscles, for example, the triceps in the previous case.
  • Synergists: They are those that facilitate and cooperate to make the action of the agonist muscles efficient without performing the function of these examples, the muscles that stabilize the scapula in the previous case.

There are muscle groups that oppose the action of gravity, these are the so-called antigravity or postural muscles and that are responsible, in the case of men, for maintaining the upright position. They are constantly required during the biped season, and are resistant to exhaustion. These muscles are located: on the back of the leg , avoiding flexion of the ankle ; on the front of the thigh avoiding knee flexion and on the back of the trunk , avoiding trunk flexion.

About the innervation of the muscles

The muscles have sensory receptors that provide information about pain and proprioceptive receptors informing the nervous system on the degree of tension that develops muscle contraction and range of motion made, giving the position information in space.

In addition, muscles have motor innervation, which is the relationship between a motor nerve and muscle. A muscle receives several motor nerve fibers; the unit between a motor nerve fiber and the number of muscle fibers it supplies is known as a motor unit. This relationship can range from one nerve fiber innervating to ten muscle fibers. This means that the motor unit ratio is quite low, the muscle performs quite fine and delicate movements.

One nerve fiber can innervate two hundred muscle fibers, which means that the ratio of the motor unit is quite high, the muscles develop grosser, but powerful movements.

The innervation for striated or skeletal muscles comes through mixed somatic, motor, and sensory nerves. These nerves approach the muscle through its deep face, where this innervation is less vulnerable.

Vascularization of skeletal striated muscle

Muscle blood flow: Although striated muscles make up almost 40% of body mass, their total blood flow under resting conditions is only 1L / min. approximately. However, during intense exercise this flow can increase to 20L / min. Therefore, the muscular blood flow undergoes extreme changes and is almost entirely related to the increased need of the muscles for nutrients during activity, especially oxygen. In fact, blood flow is related almost entirely directly to the use of oxygen by the muscles, which is one of the main factors that regulate blood flow .

Muscular tone

A muscle has a high number of motor units, these contract alternately, determining in the muscle a constant state of semi-contraction known as muscle tone.

The motor unit responds to the law of all or nothing, that is, a stimulus triggers or not the contraction of muscle fibers, depending on its magnitude. A muscle moves all the joints it passes over. Thus, there are short, single- joint muscles that move only one joint , and long, polyarticular muscles that move several joints.

In general terms, the innervation of a joint is given by the same nerves that innervate the muscles that act on that joint.

Muscles that act on the upper limb

Pectoralis major

Flat fan-shaped muscle, located in the anterior chest area behind the mammary gland , extends from the internal end of the clavicle , the anterior aspect of the sternum and the first six rib cartilages. It is directed outward, inserting itself into the proximal end of the humerus ; forms the anterior wall of the armpit . Action, produces adduction and internal rotation of the arm , bringing it forward and medial.


Muscle of more or less triangular shape, covers the scapulo-humeral joint , extends from the external third of the clavicle and the spine of the shoulder blade and the acromion ; it is directed downward to insert into the upper end of the humerus . Due to its shape it has three different functions, the middle portion of the muscle produces abduction; the ventral portion, internal rotation and adduction and the posterior portion, external rotation and adduction.

Brachial triceps

Long muscle located in the posterior region of the arm , it has three origins, one below the glenoid cavity of the shoulder blade (long portion) and two origins on the posterior aspect of the humerus (vast internal and external); the three portions are united in a single tendon that are inserted into the olecranon ; It produces extension of the forearm and also collaborates in the movements of extension and adduction of the shoulder .

Brachial biceps

Muscle located in the anterior region of the arm, has two origins in the shoulder blade, one from the coracoid process (short portion) and the other from the end of the bone over the glenoid cavity (long portion). It is directed downward forming a single tendon that is inserted into the bicipital tuberosity of the radius. Action flexes and produces supination of the forearm, and also collaborates in the movement of flexion of the shoulder.

Muscles that act on the lower limb

  • Iliac psoas: Located in the posterior abdominal wall, it has two origins; the psoas is inserted into the anterior body and the transverse process of the lumbar vertebrae and the iliac is inserted into the internal iliac fossa, the two portions in front of the hip joint converge to go and insert into the lesser trochanter of the femur . Action, raise the hip and laterally tilt the lumbar spine .
  • Quadriceps femoris: Long muscle located in the anterior region of the thigh, it has four origins: the anterior rectum at the anterior border of the coxal bone; the vast internal and external from the internal and external edges of the rough line of the femur respectively; the vast intermediate or femoral from the anterior aspect of the femoral shaft.

They are inserted into the patella and continue with the patellar tendon until they are fixed in the anterior tubercle of the tibia. Action, elevates the hip joint and extends the knee joint.

  • Buttocks: Three gluteal muscles are recognized: major, medium and minor.

They originate from the external iliac fossa and from the posterior aspect of the sacrum and coccyx, cross the posterior aspect of the hip joint and insert into the greater trochanter, extending the gluteus maximus slightly towards the rough line of the femur . Action, the gluteus maximus is the extensor and external rotator of the hip joint; The minor and medial glutes are abductors and rotators internal to the hip joint.

Examples of muscles that move the neck and head

  • Sternocleidomastoid muscle: Muscle located in the lateral region of the neck, partially covering the carotid artery (carotid pulse) and the jugular vein to internal. It extends from the mastoid process and the adjacent occipital area to the shaft of the sternum and the medial end of the clavicle . Simultaneous contraction of both muscles strongly flexes the head and neck, unilateral contraction produces inclination to the same side and rotation of the head and neck to the opposite side.

Muscles that move the jaw

  • Masseter muscle: Rectangular short muscle that extends from the zygomatic arch to the external aspect of the mandibular branch, its contraction produces mouth closure.
  • Diastric muscle: Ribbon-shaped muscle that has two muscle segments or bellies joined by an intermediate tendon. It extends from the temporal bone to the midline of the lower border of the jaw. The intermediate tendon is in relation to the hyoid. The contraction of the anterior belly produces mouth opening.

Trunk muscles

  • Intercostal muscles: They are flat muscles, which close the spaces of the thoracic cage, arranged between adjacent ribs. The external intercostal muscles occupy the intercostal spaces from the costotransverse joint to the costochondral joint, that is, they cover the posterior three-fourths of the intercostal space. Its fibers run obliquely ventrally and caudal from the inferior border of the overlying rib to the superior border of the rib underlying the intercostal space. The internal intercostal muscles occupy the three fourths anterior to the intercostal space, from the sternal border to the costal angle. Its fibers are directed downwards and laterally, crossing at a right angle to the external intercostals.diaphragm.
  • Latissimus dorsi muscle: Covers the posterior lateral region of the chest. It originates from the spinous processes of the last thoracic vertebrae, and from the lumbar vertebrae, the sacrum in the last four ribs. Its fibers are obliquely directed up and out to insert at the upper end of the shaft of the humerus. When taking the chest as a fixed point, this muscle produces an adduction and an internal rotation of the arm. When you take the humerus as a fixed point, you can lift the trunk, as in the climbing action.
  • Trapezius muscle: Flat muscle that covers the posterior region of the chest and the posterior region of the neck. Its fibers originate in the occipital, in the ligament of the nape, and the spinous processes of the first thoracic vertebrae. The fibers are directed towards side and inserted into the acromion of the scapula and the lateral end of the clavicle. This muscle extends the head and raises the stump of the shoulder.


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