A. Characteristics of Muscles for Naming. What are muscles named for?
1.  Number of heads or number of muscles w/i a complex, or number of “origins”
Examples, Biceps Brachii, 2 heads, long/short
                Triceps Brachii, 3 heads, lateral/long/middle
                Quadriceps, 4 parts, Rectus femoris, Vastus Lateralis, Vastus Medialis,
                 and Vastus Intermedius
2. Size.
Examples, Gluteus Maximus (largest), Gluteus Medius (middle size),
              and Gluteus Minimus (smallest).
3. Action.
Examples, Flexors: Flexor carpi ulnaris, Flexor Carpi radialis
                 Abductors: Abductor Pollicis Longus
                 Adductors: Adductor longus, adductor magnus, adductor brevis (note: action
                                   and size are combined)
                 Extensors: Extensor Carpi Randialis Longus
                                  Extensor Carpi Ulnaris
                                  Extensor Digitorum
                  Levator,   Levator Scapulae
                  Pronator, Pronator teres
4.  Shape.
Examples, Trapezius (trapezoid shape=4 sided plane,figure with 2 parallel sides)
                 Deltoid complex (Deltoid, means triangular)
                 Rhomboid major/minor (Rhomboideus, Diamond shape)
                 Sarratus Anterior (sarrated=saw tooth appearance)
5. Direction of fibers (which way do the fibers run?)
Examples, External oblique, internal oblique, transverse abdominus
6.  Bones muscles attach on.
Example, sternocleinomastoid

B.  Fiber Arrangement and Direction
1. Longitudinal arrangement. Muscle fibers are parallel with the long axis of the muscle.
Examples, Sartorius and Rectus abdominus
2. Fusiform: Muscle fibers are in the form of a spindle. Example. Biceps brachii
3. Radiate muscle: Muscle fibers fan out from a single attachment. Example, gluteus medius
4. Penniform arrangement. Groups of muscle fibers are attached to a tendon running the length of the msucle, resulting in a feather like appearance.
Types of penniform arrangements: (A) Unipennate, origin of muscle is from a large area of bone and fibers run obliquely to a single tendon (tibialis posterior, flexor pollicis longus),
(B) Bipennate muscle: Oblique fibers that are attached to both borders of a central tendon (rectus femoris, soleus), (c)muscle fibers appear as a combination of several bepennate muscles; there are a numbers of tensdons that the fibers converge and attach to. (Deltoid complex

C.  Magnitude of force production is directly proportional to the size of the muscle and the number of muscle fibers located within the muscle. Estimated force production of a muscle is approximatel 20-80 Newtons per centimeter squared of muscle.(average, 50 N/cm2).
Penniform muscles provide a greater number of muscle fibers w/i a cross-sectional area than do longitudinal fiber arrangement. Longitudinal, fusiform, and radiate muscles are more designed for speed. Understand that the total muscular force developed is partitioned into a rotatory force (force which causes a limb to rotate) and a stabilizing force (a force acting along the lever and directed into the joint).

D.  Types of muscular action.
Concentric, a shortening contraction
Eccentric, a lengthening of the muscle while generating tension
Isometric, developing tension without any appreciable shortening or lengthening
Isotonic, muscle tension remains constant as the muscle shortens or lengthens
Isokinetic, literally means equal or same motion. Maximal muscular effort throughout the range of motion at a constant angular speed.

E.  Lever systems.  Distinguish between a first, second, and third class lever system.
1st class, axis of rotation is located between the resistance and effort (example, head balance on vertebrae column)
2nd class, resistance is located between the axis (fulcrum) and effort (example, standing up onto the balls of your feet--fulcrum=balls of feet, effort=soleus and gastrocnemius acting @ calcaneus, resistance=body weight)
3rd class, the effort is located between the axis and the resistance, (example, biceps brachii acting at the elbow joint)

F.    Energy for muscular action.  Derived from both aerobic and anaerobic metabolism. The resynthesis of energy for muscular work (Adenosine triphosphate, ATP) comes predominantly from aerobic metabolism. Aerobic metabolism resynthesizes ATP at a slow rate, but is able to produce a great amount of ATP compared to the anaerobic system.  The aerobic system is important in aerobic like activities (walking, jogging) while the anaerobic system (fast rate of ATP resynthesis) is important in sprint like events (400 meter sprint).

G. Muscle twitch.
When a muscle is innervated (stimulated), it will develop a twitch if the stimulus is of sufficient magnitude.  The components of a twitch include (A) latent period, stimulus has arrived and calcium is released into the sarcoplasm, and myosin binds to the active site on actin; (B) Period of contraction, onset of contraction to peak tension, actin “slides” past myosin.;
(C)Period of relaxation, initiated by the reuptake of calcium by the sarcoplasmic reticulum, therefore muscle tension decreases to zero as muscle fiber returns to its pre-contracted state (“normal” length).  Interestingly, some of the recoil tendency in non-contractile tissue (i.e., sarcolemma, and other tissues associated with the muscle fiber)help the muscle fiber return to its initial length.  Keep in mind that motor units are alternately recruited.  Therefore, you have both relaxed muscle fibers and active muscle fibers within a muscle.  The number of muscle fibers activated depends on the number of motor neurons acting and the frequency of neural delivery to the fibers.