Note: There are several subpages for the the Introduction to Muscles, including Muscle Clinical View and Introduction to muscles review.

Learning Objectives

• To learn the characteristics of skeletal muscles and how they interact in our bodies.

• Understand the connective tissue associated with skeletal muscle.

Notes, Pictures & Videos

Muscles

• Muscles are organs, composed of muscle tissue, epithelial, connective and nervous tissues
• There are 2 types of muscle tissues:
  

• Smooth muscle (which is essential for propelling materials through our internal tubes i.e., peristalsis along the digestive tract)
• Cardiac Muscle (found only in walls of heart, essential for pumping blood.)
• Skeletal muscles, while they are easily observed by bulges they cause on the exterior of the body, are not the only place where muscles tissue is found.

Muscle Facts

• There are over 600 muscles in the human body. Some are small and delicate while others are large and sturdy.
• Muscles make up between 25 to 45 percent of your body weight.
• Muscles are made up of cells called muscle fibers.
• Lifting weights can make muscle fibers grow. weightlifters have the same amount of muscles as skinny people but the weightlifters have bigger muscles.
• There are over 30 muscles in the face that help with facial expressions.
• The largest muscle in the body is the gluteus maximus in your buttocks.
• The smallest muscle in the body is the stapedius, which is located in the middle ear.

4 Properties of muscle Tissue:
-Excitability: responsiveness. Muscles are very responsive to input from stimuli. When stimulated by the nervous system or by other stimuli in environment, it responds by initiating electrical changes that spark internal events that lead to muscle contraction.
-Contractability: Stimulation generates tension within cell (contraction) which can shorten the cell. Shortening results in a pull on skeletal bones or movement of specific body parts.
-Elasticity: When applied tension is removed, muscle cells recoil to its resting length. It is not the muscles ability to stretch, but its ability to return to its normal length.
-Extensibility: Muscle cell has to extend in length in response to contraction of opposing muscle cells. i.e., triceps brachii muscle on the back of your arm extends when the biceps brachii muscle on the front of arm contracts.

Skeletal Muscle Tissue:
- Is an organ and composed of 4 types of tissue: epithelial, connective, muscle, and nervous.
- Is striated and usually attaches to one or more bones.
- Vary widely in shape (elongated and flat to thick and triangular and even circular).
- A single muscle can be composed of thousands of cells, each cell is as long as the muscle itself.
- Small muscle cell in a muscle in the toe may have a length of 100 micrometers and a diameter of 100 micrometers (thickness of fine human hair).
- Because of their extraordinary length, often referred to as muscle fibers.
- Increase in muscle fiber size, which often follows regular exercise, is called hypertrophy.

Functions of skeletal muscle tissue:

• Bone movement
  • Bones move when muscles contract and pull on tendons by which muscles are attached to bones. The combination of muscles, bones, and joints can produce highly coordinated movements (running) or simple (underlining a word in book)

• Maintenance of Posture
  • Contraction of certain muscles stabilizes joints and maintains body's posture or position (holding head erect when sitting). Postural muscles contract continually when a person is awake so they don't collapse (because of this, back muscles need to be much stronger than stomach and many anterior muscles).

• Temperature regulation
  • As a result of the useful heat released when skeletal muscles convert chemical energy (from food) to physical energy when you run or shiver. With exercise, you feel warmer- heat produced from muscles. You shiver when you are cold because your muscles are contracting and relaxing in order to produce heat to keep your body warm.

• Storage and movement of materials
  • Circular muscle bands called "sphincters" contract at openings ("orifices") of gastrointestinal and urinary tracts. They can be opened (to facilitate movement of materials) or closed (to store material within the organ). Lips create the first sphincter along gastrointestinal tract.

• Support
  • Stabilize body walls and help prevent displacement of internal structures. Arranged in flat sheets or layers (i.e., along walls of the abdominal cavity and the floor of the pelvic cavity. The sheets protect the organs and support the weight within the abdominal cavity. *primary function of abdominal muscles is to hold abdominal organs in place.

Gross anatomy of skeletal muscle:
1. Composed of layers of skeletal muscle fibers, blood vessels and nerves, and connective tissue sheets that surround muscle fibers and connect muscle to bone.
2. Skeletal Muscle compositions:
skeletal muscle has several layers of organization. We are only focusing on macroscopic gross anatomy.
3. Connective tissue components:

-Three concentric layers of connective tissue, composed of collagen and elastic fibers, encircle each individual muscle fiber, groups of muscle fibers, and entire muscle itself. These layers provide protection, sites for distribution of blood vessels and nerves, and a means of attachment to skeleton.

• a. "endomysium" (within muscle) is innermost connective tissue layer that surrounds each muscle cell (fiber). Is a delicate, areolar tissue layer that surrounds each muscle fiber. It has reticular fibers to bind together neighboring fibers and support capillaries near these fibers.

• b. "perimysium" (around muscle) surrounds bundles of muscle fibers called "fascicles". Dense, irregular connective tissue that surrounds whole skeleton.

• c. "epimysium" (upon muscle) is a layer of dense irregular connective tissue that surrounds whole skeletal muscle.

These connective tissue layers are en-sheathed by "deep facia" (band); an expansive sheet of dense irregular connective tissue that separates individual muscles, binds together muscles with similar functions, forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels, and to fill spaces between muscles.

• a. Deep fascia is deep or internal to a layer called "superficial facia" (subcutaneous layer or hypodermis) Composed of loose connective tissue and fat (adipose tissue) that separates muscle from skin.

-Entire steak is equivalent to at least one skeletal muscle:

*The fat and connective tissue encircling the steak is the epimysium
*Within the steak itself, a whitish marbled texture is perimysium, which encircles bundles of muscle fibers (fascicles)
*You won't be able to distinguish individual muscle fibers or the endomysium in the steak because they are too small.
4. Muscle attachments:
a. at the ends of a muscle the connective tissue layers merge to form a fibrous, cord like "tendon", which typically attaches to bone. Sometimes the tendon forms a thin, flattened sheet, termed aponeurosis (greek: from sinew).



Examples of Naming Skeletal Muscles:

MUSCLE ACTION
a. b.' c. .d.

a.ADDUCTOR b.FLEXOR EXTENSOR c.PRONATOR d.LEVATOR (LIFTER)

Actions of Skeletal Muscles
-Skeletal muscles work together to produce body movement.
-Muscles are grouped together according to their primary actions and are classified into three different groups.
1. Agonist- If a muscle contracts to produce a particular movement it is considered an "agonist" or "prime mover".
2. Antagonist- When a muscle action opposes that of an agonist it is an "antagonist".
3. Synergist- Muscles that assist in performing actions of an agonist/prime mover are synergist muscles. They do not produce actions on their own.


SPECIFIC BODY REGIONS

a b C.

a. PECTORALIS b. INTERCOSTAL c. BRACHII



MUSCLE ATTACHMENTS


a. b.

a. ZYGOMATICUS b. STERNOCLEIDOMASTOID


ORIENTATION OF MUSCLE FIBERS
a. b. c.

a. RECTUS (STRAIGHT) b. TRANSVERSE (ACROSS) c. OBLIQUE

Skeletal Muscle Fiber Organization:
Fascicles are bundles of muscle fibers that lie parallel to each other within every muscle.

Circular Functions of a sphincter closes a passageway or opening Contracts an o close off on opening Arranged concentrically around an opening
Convergent Muscle fibers that are widespread but converge on a common attachment site Triangular muscle Direction of pull of muscle can be changed Does not pull as hard as equal-sized parallel muscle
Parallel Fascicles are parallel to the long axis of muscle. Body of the muscle increases in diameter with contraction. High endurance, not very strong
Pennate Muscle fibers and tendons that look like a large feather Muscles with one or more tendons Fasciles are oblique Pulls harder then parallel muscles of equal size Unipennate muscles are muscles that are on same side of tendon Bipennate muscles are when muscles are on both sides of the muscle Multipennate muscles are tendon branches within the muscle

Blood Vessels and Nerves
Blood vessels and nerve fibers extends through the epimysium and perimysium. The blood vessels delivers nutrients and oxygen to muscles for the production of ATP. They also remove waste products produced by muscle fibers.
Skeletal muscles are classified as voluntary muscles because they are controlled by the "somatic (voluntary) nervous system" and we can voluntarily move our skeletal muscles. The neurons (nerve fibers)that stimulate muscle contraction are called "motor neurons" ( also referred to as "efferent neurons" because they travel away from the center of activity which is the central nervous system) and they are said to innervate muscle fibers within the muscle.

-Muscle fibers will waste away (atrophy) if they are not used periodically stimulated to contract by motor neurons.
-Each motor neurons has a long extension called an axon, which transfer nerve impulses to muscle fibers.
-Sensory neurons, also called afferent neurons because they travel towards the central nervous system, and send impulses to the brain and spinal cord about the activity of muscles.
Muscles move the bones often just like how a lever works.

MUSCLE SHAPE AND SIZE

a. b. c. d. e.

a. DELTOID (TRIANGLE) b. TRAPEZIUS c. LONGUS d. BREVIS(SHORT) e. TERES (LONG&ROUND)

f.

f. MAXIMUS (LARGE) MINIMUS (SMALL) MEDIUS (MEDIUM)

MUSCLE HEADS / TENDONS OF ORIGIN

a. b.



a. BICEPS (2 HEADS) TRICEPS (3 HEADS) b. QUADRICEPS (4 HEADS)

Aging

• Increasing inactivity (especially after the mid-30s) causes a slow but progressive loss of skeletal muscle mass. This is either replaced by adipose tissue or fibrous connective tissue.
• Atrophy- the muscle fibers decrease in size because of a decreased amount of contractile filaments within the muscle cell.
• Tolerance for exercise is diminished so with age, a person tends to fatigue more easily. This is also due to decreased cardiovascular performance.
  
• Elasticity of muscles is lost because of increased amounts of connective tissue (fibrosis).
  
• Exercise is always a good idea. It helps combat the effects of aging with muscles as well as other body organs and systems.
  

I found this website to be very helpful in studying the muscles. Study and find the all of the muscles here!

Glossary

Muscle fibers: any of the elongated cells characteristic of muscle
Endomysium: areolar connective tissue layer surrounding a muscle fiber.
Perimysium: fibrous sheath enveloping each of the fascicles of skeletal muscle fibers.
Epimysium: fibrous connective tissue envelope surrounding a skeletal muscle.
Deep facia: a firm fascia that ensheaths and binds together muscles and other internal structures
Superficial facia: the thin layer of loose fatty connective tissue underlying the skin and binding to the parts underneath
Tendon: cord of dense regular connective tissue that connects muscle to bone
Aponeurosis: fibrous sheet or flat, expanded tendon
Origin: the less moveable of the two points of attachment of a muscle.
Insertion: the usually distal and more movable attachment of a muscle

Connections to other body systems

Review Questions

1. Excitability of the muscle cell is:

a. the ability of the muscle to contract.
b. the muscle cell will recoil to its resting length when the applied tension is removed.
c. to respond to electrical stimuli
d. muscle cell is capable of extending in length in response to contraction of opposing muscle cell.

2. Skeletal muscle cells are often referred to as muscle fibers because:
a. they are very strong
b. they are made of collagen
c. they are cord-like
d. they are very long

3. The Perimysium
a. surrounds bundles of muscle fibers
b. is the innermost connective tissue layer that surrounds each individual cell
c. is a layer of dense irregular connective tissue that surrounds whole skeletal muscle.
d. none of the above

4. From the clinical view, tendonitis:
a. is a disease of the tendon
b. must be treated with surgery
c. symptoms can be relieved with anti-inflammatory drugs, icing
d. symptoms will go away with regular use

5. In a skeletal muscle fiber, a trad is composed of?
a. myosin, actin, and myofibers
b. one A band, one h zone, and one I band
c. one transverse tubule and two terminal cisternae
d. myofilements, myofibils, and sarcomeres

6. During the contraction of a muscle fiber, myofibrils
a. lengthen
b. remain unchanged
c. increase in diameter
d. shorten

7. Muscles are attached to bone by
a. ligaments
b. subcutaneous
c. protein fibers
d. tendons

8. What bone connects to biceps brachii?
a. Humerous
b. radius
c. spinous process
d. the biceps brachii doesn't connect to a bone.