Much of this chapter in your text deals with how muscles function at the cellular level. We will NOT discuss that in this class because the cellular activity of muscle is normally covered in the Human Physiology (Biol 2420) class.

Muscles convert chemical energy into physical energy to help bones to move, hollow tubes to contract, or to pump blood.

Muscles are considered organs because they are composed many different types of tissue (muscle, epithelial, nervous, connective, etc.)

Skeletal muscles are those muscles attached to bones and are easily seen on the body’s exterior. However, other types of muscle (smooth muscle and cardiac muscle) are found deeper in the body.

Open heart surgery

Lung

Heart

Smooth muscle is essential for propelling materials through our internal tubes

Cardiac muscle, found only in the walls of the heart, pumps blood

All muscles are excitable, contractile, elastic and extensible. This means when nerves stimulate the biceps brachii, it contracts, and the opposing triceps brachii relaxes and extends.

A muscle cell on the anterior side of the arm may extend up to 35 centimeters and have a diameter of about 100 micrometers (about the same thickness of a fine human hair). Because of their potentially extraordinary length, skeletal muscle cells are often referred to as muscle fibers.

Make this addition to your notes!

Skeletal muscle functions to pull on bones to use them as lever systems, maintain posture, generate heat for temperature control, promote storage and movement of materials in the body, and to support and stabilize body walls.

(Muscle cell)

Contents of muscle cell

In general, a skeletal muscle is composed of layers of skeletal muscle fibers (muscle cells), blood vessels, nerves, and connective tissue sheaths that surround the muscle fibers and connect muscle to bone.

Bone

Note the epimysium, which is dense irregular connective tissue that surrounds the whole muscle.

(Muscle cell)

(Muscle cell)

Contents of muscle cell

The perimysium surrounds bundles of muscle cells (fasicles)

The endomysium is the innermost connective tissue layer and surrounds each individual muscle cell (muscle fiber).

Fascia can be either superficial or deep. It is continuous with the epimysium

Superficial and deep fascia of chest wall.

(Subcutaneous layer or hypodermis)

Steak

WHAT IS THE NAME OF THE CONNECTIVE TISSUE LAYER THAT IS THE INNERMOST AND SURROUNDS EACH INDIVIDUAL MUSCLE FIBER (MUSCLE CELL)?

A EPIMYSIUM

B ENDOMYSIUM

C DEEP FASCIA

D PERIMYSIUM

E MYELIN SHEATH

At the ends of a muscle the connective tissue layers merge to form a fibrous, cordlike tendon, which typically attaches to bone.

External oblique aponeurosis

Read clinical view in text about tendonitis.

The origin is usually the more proximal stationary attachment while the insertion is typically distal and is the moveable attachment.

There is extensive blood and nerve supply to the skeletal muscles

Motor neurons are also called efferent neurons because they travel away from the center of activity, which is the central nervous system. They innervate muscle fibers within the muscle.

Muscle fibers will atrophy if they are not periodically stimulated to contract. We learned earlier, that if the muscles or nerves are damaged, pulling stress on the periosteum will diminish and bone density will also decrease.

Sensory neurons are also called afferent neurons because they travel towards the central nervous system. They send impulses to the brain and spinal cord about the activity of the muscles.

WHICH OF THE FOLLOWING IS A CORRECT STATEMENT?

A AFFERENT NEURONS CONDUCT IMPULSES TO THE SPINAL CORD

B MOTOR NEURONS ARE EFFERENT NEURONS

C RHABDOMYOLYSIS IS TREATED WITH BAKING SODA

D HYPNIC JERKS ARE ASSOCIATED WITH DECREASED BRAIN FUNCTION

E ALL OF THE ABOVE

Circular muscles have their fibers concentrically arranged around an opening or recess.

Pectoralis major

Convergent muscles have widespread muscle fibers that converge on a common attachment site.

Parallel muscles have fascicules (bundles of muscle fibers) that run parallel to its long axis. Examples are the rectus abdominis and the biceps brachii.

Pennate muscles are so named because their tendons and muscle fibers resemble a large feather.

A lever is an elongated, rigid object that rotates around a fixed point called the fulcrum

Effort arm

Resistance arm

Bones are the levers, the joint is the pivot or fulcrum (F), the muscle provides the effort (E), and the resistance (R) is what is being moved. Please note that the effort (E) is truly located where the tendon attaches to the bone (lever)!

Effort (E)

• F (fulcrum) is in the middle in #1

• R (resistance) is in the middle in #2

• E (effort) is in the middle in #3

• Remember “FRE#1 #2 #3

Atlantooccipital joint is a first class lever system

Rising onto the ball of the foot (distal ends of metatarsals) by contacting the calf muscles is an example of a second-class lever system.

Flexion of the elbow is an example of a third-class lever system. Remember, the effort (E) is where the tendon attaches to the bone (lever)!

WHICH OF THE FOLLOWING IS CORRECT ABOUT THE PROCESS OF EXTENDING YOUR TIBIOFEMORAL JOINT?

A IT IS A FIRST CLASS LEVER SYSTEM

B IT INCORPORATES A MULTIAXIAL JOINT

C IT IS A THIRD CLASS LEVER SYSTEM

D IT UTILIZES A CONDYLOID JOINT

E IT IS A SECOND CLASS LEVER SYSTEM

In this instance, the triceps brachi is the agonist (prime mover)

The muscle that opposes the prime mover (agonist) is called the antagonist

The quadriceps femoris muscles composed of four distinct muscles (only three shown here as the fourth is deep) are synergistic in extending the leg at the knee joint.

Skeletal muscles are named on the basis of shape, location, attachment, orientation of fibers, relative position, or function.

Naming of skeletal muscles

Naming of skeletal muscles (continued)

In a person’s mid-30s, a slow progressive loss of skeletal muscle mass begins as a direct result of increasing inactivity.

Aging causes muscular atrophy, decreased cardiovascular performance, easy fatigue, loss of muscle elasticity, and poor muscle healing following injury

These adverse changes can be delayed by regular moderate exercise and good nutrition.

Child with Duchenne muscular dystrophy

Read about the neuromuscular diseases in the clinical view in your text (except for myasthenia gravis)

Moving Right Along!

EVERYTHING PAST THIS POINT IS EXTRA OR FOR EXAMS

Motor and sensory neurons are associated with each muscle

Figure 10.08a

Skeletal muscles are attached to bones by non-elastic tendons.

Individual muscle fibers (muscle cells) are bound together to form bundles, which are in turn bound to other bundles.

Figure 10.06tab

Figure 10.co

New York strip steaks

Ribeye steaks

Fascia can be observed in steak that human ingest for nutrition

Figure 10.13