The Muscles

Question 1

Three main types of muscle tissue:

Answer 1

• Skeletal
• Smooth or Visceral
• Cardiac
Skeletal muscle tissue makes up most of the muscles in body. Skeletal muscle or voluntary muscle is anchored by tendons to bone and is used to affect skeletal movement such as locomotion and in maintaining posture. This is the muscle tissue that makes up the muscles that you are going to learn later in this section. As massage therapists we have the greatest direct impact on skeletal muscles so our discussion of muscles will center on skeletal muscle.

Smooth muscle or involuntary muscle is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and even the skin (in which it controls erection of body hair). Unlike skeletal muscle, smooth muscle is not under conscious control.

The cardiac muscle is a type of involuntary striated muscle found in the walls of the heart. As it contracts, it propels blood into the heart and through the blood vessels of the circulatory system.

Question 2

Muscle Functions and Characteristics:

The primary functions of the muscles include [6]:

Answer 2

• Movement
• Heat production (by-product of contraction)
• Maintenance of position of the body (stabilizing joints) • Fluid transport (blood, lymph, water)
• Nutrient transport
• Involuntary processes (heartbeat, digestion)

Question 3

Muscle Functions and Characteristics:

The functional characteristics of muscles are [4]:

Answer 3

• Excitability (they can be coaxed into action by the nervous system)
• Contractibility (they can shorten)
• Extensibility (they can lengthen or stretch)
• Elasticity (they can return to their original length after either shortening or lengthening)

Question 4

Muscle Anatomy

Answer 4

The anatomy of muscles includes both gross anatomies, comprising all the muscles of an organism, and, on the other hand, microanatomy, which comprises the structures of a single muscle.

Question 5

Microanatomy of Muscles

Pt 1 of 3

Answer 5

Muscles are a soft tissue made up mostly of water and proteins. They have a high concentration of blood vessels and nerves. Muscle is mainly composed of muscle cells.

Question 6

Microanatomy of Muscles

pt 2 of 3

Answer 6

Look at the illustration of the structure of a skeletal muscle shown below. Locate these anatomical features of a muscle. Skeletal muscle is arranged in discrete muscles or muscle bellies, an example of which is the biceps brachii. It is connected by tendons to processes of the skeleton.

• The muscle itself is called the muscle belly and is surrounded by a fascial membrane called the epimysium. Epimysium is a layer of connective tissue which ensheaths the entire muscle.
• Perimysium is a sheath of connective tissue which groups individual muscle fibers (anywhere between 10 to 100 or more) into bundles or fascicles.
• The fascicles are made up of muscle spindle fibers or muscle cells, also sometimes called myofibers, which are wrapped in a fascial membrane called endomysium. The endomysium, literally meaning within the muscle, is a layer of connective tissue that ensheaths a muscle fiber and is composed mostly from reticular fibers. Muscle spindles are distributed throughout the muscles and provide sensory feedback information to the central nervous system.
• Within the cells are myofibrils; myofibrils contain sarcomeres, which are composed of actin and myosin.

Question 7

Microanatomy of Muscles

pt 3 of 3

Answer 7

As you can see, muscles have quite a bit of fascia throughout them. The fascial layers (epimysium, perimysium and endomysium) do not end when the muscle fibers end. They continue on to form the tendon for the muscle and attach to the bones. The place where the tendon fibers and the muscle fibers intersperse is called the musculotendinous junction. The musculotendinous junction is the place that an injury is most likely to happen in a muscle due to the change in tissue density and type

Muscles cells can also be divided into even smaller units called myofibrils. Inside the myofibrils are the proteins called filaments that actually produce muscle contraction. These filament proteins actually slide over each other to form an overlapping pattern. Each set of filaments inside a myofibril can only overlap a short distance, but the combination of thousands of these myofibrils shortening inside a muscle fiber creates the shortening of the muscle fiber. Muscle fibers can either contract or relax. Either all of the myofibrils are shortened due to overlapping filaments or they are not. This is called the all or nothing principle. Basically, this means that once the nervous system has stimulated a muscle fiber to contract all of the myofibrils inside that cell will contract, not just some of them. When the nervous system signals the muscle to relax all of the myofibrils in that muscle fiber relax.

Question 8

Classification of Voluntary Muscular Contractions:

Concentric contraction

Answer 8

Concentric contraction occurs while the muscle is going from a state of rest into a shortened position. An example of this would be your Biceps brachii muscle while you are raising a glass to your mouth to drink.

Question 9

Classification of Voluntary Muscular Contractions:

Eccentric contraction

Answer 9

Eccentric contraction occurs as the shortened muscle returns to a lengthened state under control (some fibers remain in contraction until the muscle returns to rest to prevent abrupt motion that could damage tissue). An example of this would be when you are lowering the glass back to the table. If your Biceps brachii muscle just completely relaxed back to resting you would probably spill the contents of the glass as it comes flying back down. So your Biceps brachii muscle stays in a contracted state while lengthening so that you have control over how fast the muscle lengthens.

Question 10

Classification of Voluntary Muscular Contractions:

Isometric contraction

Answer 10

Isometric contraction occurs when muscles contract and does not produce movement of bones. Isometric contraction occurs when a muscle contracts but does not bring its bony attachments closer together as in carrying a box. Again your Biceps brachii must maintain its contraction to bear the weight of the load placed on it, but it is not actually moving any bones.

Question 11

Classification of Voluntary Muscular Contractions:

Answer 11

Isotonic contraction occurs when muscles contract to produce movement of bones. Isotonic contractions can be either concentric or eccentric, although these two typically happen one after the other.

Question 12

Gross Anatomy of Muscles

Answer 12

The gross anatomy of a muscle is the most important indicator of its role in the body. The action a muscle generates is determined by the origin and insertion locations. The muscle’s action is defined as the movement created when actively shortened or when its bony attachments are brought closer together.

Both origin and insertion are important for understanding the physiological function of the muscle. Some muscles have greater than two attachments and multiple actions, which can blur the distinction between the origin and insertion.

Question 13

Gross Anatomy of Muscles:

The origin of a muscle

Answer 13

The origin of a muscle (a fixed anchor) is the point at which it attaches to a bone (usually) or another muscle. The structure that the origin is attached to is not moved by the contraction of the muscle.

Question 14

Gross Anatomy of Muscles:

The insertion of a muscle

Answer 14

The insertion of a muscle (a moving attachment) is the opposite end of the muscle. This definition means that there is a functional aspect to the definition of a muscle’s origin and insertion.

Question 15

Muscle can be divided into ____ functional categories or groups according to their actions.

Answer 15

three:

• Agonist
• Antagonist
• Synergist

Question 16

Agonist

Answer 16

Agonist is a classification used to describe a muscle that causes specific movement or possibly several movements to occur through the process of its own contraction. Agonists are also referred to, interchangeably, as “prime movers” since they are the muscles being considered that are primarily responsible for generating a specific movement. For an agonist to be effective, as a mover in the skeletal system, it must actually cross one or more structure(s) that can move. This is typically where the muscle crosses a joint by way of a connecting tendon. As the myofibrils of a muscle are excited into action and then contract, they will create tension and pull through the tendon and pulling the lever arm of bone on the opposite side of the joint closer to the muscles origin. For example, both Iliopsoas and Rectus femoris flex the hip, but Iliopsoas is the prime mover because it is actually stronger in hip flexion than Rectus femoris.

Question 17

Antagonist

Answer 17

Antagonist is a classification used to describe a muscle that acts in opposition to the specific movement generated by the agonist and is responsible for returning a limb to its initial position. Antagonistic muscles are found in pairs called antagonistic pairs. These consist of an extensor muscle, which “opens” the joint (i.e. increasing the angle between the two bones), and a flexor muscle, which does the opposite to an extensor muscle. Antagonistic pairs are needed in the body, because muscles can only exert a pulling force and can not push themselves back into their original positions. An example of this kind of muscle pairing is like the biceps and triceps. When the biceps are contracting, the triceps are relaxed, and are able to be stretched back to its original position. This is the opposite when the triceps are contracting.

Question 18

Synergist

Answer 18

Synergist is a kind of muscle which performs, or assists in performing, the same set of joint motion as the agonists or “prime movers”. Synergists are muscles that act on movable joints. Synergists are sometimes referred to as “neutralizers” because they help cancel out, or neutralize, extra motion from the agonists to make sure that the force generated works within the desired plane of motion. An example would be Iliopsoas and Tensor fascia latae. The Tensor fascia latae is a synergist to Iliopsoas in hip flexion. They both perform hip flexion.

Question 19

Individual Muscles

Answer 19

The names of the muscles are packed with information about the muscle. Muscles are often named for their location (serratus ventralis), their muscle shape (triceps, trapezius), their action (adductor), or their attachment site (brachiocephalicus).

For example, we can learn several things about this muscle: superficial digital flexor

• Superficial = location of the muscle is on the surface • Digital = attachment is on the digits
• Flexor = the action is flexion of the digits

Before you begin studying the musculature, please read the following study guidelines designed to help you learn the material in the most effective and efficient manner.