Notes on the Web
Muscular System: Introductory Basic Material on Muscular System

Bruce G. Stewart

Related Textbook Readings

Related Human Anatomy Coloring Book Assignments

Required plates for coloring introductory topic plates on the muscular system will be assigned in class. Required colorings for the actual muscle organs are presented in separate Notes on the Web in this unit.

Lecture Outlines

Recall that we have previously studied (and tested over) muscle histology and physiology, including that of skeletal muscle. We will not duplicate those studies here. The following outline covers introductory basic information about the muscular system. Muscle organs and their functions will be covered in the next part of this unit.

I. Muscular System

A. Definitition - muscle organs composed of skeletal muscle tissue and associated connective tissues

1. excludes cardiac muscle (part of cardiovascular system) and smooth muscle (part of many other body organ systems)

2. Example: biceps brachii muscle

II. Production of Movement by Muscle Organs

A. Movements produced by transfer of forces from muscles to tendons, aponeuroses, etc. then to bones, skin etc.

B. Movements usually draw one bone toward another

1. origin - attachment to the more stationary bone

2. insertion - attachment to the bone that exhibits most movement during muscle's contraction

3. analogy with door spring attachments - origin is analogous to spring attachment to door jam, and insertion is analogous to attachment to spring door

4. belly (gaster) - fleshy portion of a muscle between ends

III. Mechanical Advantages - Levers, Leverage, Arrangements of Fasculi, and Group Actions

A. Definitions related to levers

1. lever - rigid rod that moves about some fixed point

2. fulcrum - point about which a lever moves

3. resistance - force acting on level & to be overcome

4. effort - force (load) on lever applied to overcome resistance

. B. Types of levers

1. types of levers

a. first-class lever

  • "seesaw" type with fulcrum in the middle and effort and resistance alternating on opposite ends
  • example - head on vertebral column where the fulcrum is the point of contact between the atlas (first cervical vertebra) and the occipital bone of the skull

b. second-class lever

  • wheel barrow" with the fulcrum on one end (analogous to the wheel of the wheel barrow), the resistance in the middle (the load of the wheelbarrow), and the effort on the opposite end (the lift applied to the handles of the wheelbarrow)
  • uncommon in the human body but one important example is the body raised on the toes (or ball of the foot)
    • resistence - the weight of the body above the foot
    • fulcrum - point of contact of ball of foot with ground
    • effort - the force of the calf muscles applied to the calcaneous (achilles) tendon

c.third-class lever

  • fulcrum is on one end, resistance on the other end, and effort is applied to the middle
  • the third-class lever is by far the most common lever design in the human body
  • Example - flexing forearm
    • resistence - weight of forearm
    • fulcrum - point of contact of humerus and ulna at elbow
    • effort - force generated by the biceps brachii and applied to upper ulna

C. Concept of leverage

1. different architectural designs gives specific mechanical advantages

2. specific placement of origins and insertions affects strength and ease of movement (how rapid a bone can be moved, for example)

c. natural variation in the human species relates in some cases to natural physical advantages of individuals for specific athletic sports events (some may be better at the 100 meter dash, for example, while others are "built" for the mile race).

D. Arrangement of Fasciculi

1. Definition of fasciculi - bundles of myfibers that run parallel within the bundle.

2. Arrangements of fasciculi within the muscle organs varies

a. parallel - fasciculi run parallel to long axis of the muscle and terminate at ends with flat tendons

  • Example - stylohyoid muscle that is ribbon-like and originates on the styloid process of the temporal bone of the skull and inserts on the hyoid bone in the throat. It doesn't need to to be especially powerful, but needs to lift the hyoid rapidly during speech and swallowing.

b. fusiform - a slight modification of parallel with nearly parallel fasciculi

  • Example - biceps brachii muscle of the upper arm that has fasciluli that all run in the same general longitudinal direction, but narrow on the ends to as they approach the origin and insertion

c. convergent - this design has a broad origin of fasciculi, but they converge to narrow, restricted insertion giving the muscle a sort of triangular shape

  • Example - deltoid muscle of the shoulder. This muscle broadly originates on the clavicle and scapula, but narrows continuously to the point of insertion on the deltoid tuberosity of the humerus

c. pennate - fasciculi are short relative to the whole muscle due to the fact that they run at oblique (diagonal) angles across the muscle. The fasciculi are attached on one end to the tendon of the muscle which runs almost the entire length of the muscle. This produces the following two subtypes of feather-like designs

  • unipennate - fasciculi attach on one side of the tendon (example - extensor digitorum longus muscle)
  • bipennate - fasciculi attach to both sides of the tendon in a more "typical" feather-like appearance (example - the rectus femoris muscle of the thigh)

d. circular - fasciluli for a circular pattern around on orifice

  • Example - orbicularis oris muscle around the orbit of the eye

3. Power and range of movement are related to type of fascicular arrangements

a. the more fasciculi pulling at once the greater the power; even though two muscles may have the same mass of skeletal muscle tissue, muscles with parallel fasciculi have fewer fasculi than a same-sized muscle with pennate fasciculi.

b. Examples - pennate designs are powerful, but limited in range of motion; parallel designs have allow excellent range of motion but are less powerful

D. Group Actions -

1. Most actions are affected by several muscles and most muscles have an opposing one that creates movement in an opposite direction.

a. prime mover (agonist) causes action while antagonist relaxes; these roles reverse during opposite action

  • flexors/extensors
    • Example - biceps brachii and triceps brachii during flexion and extension of lower arm
  • abductors/adductors

b. synergists - steady the movement and may contribute some lesser force to action

c. fixators - stabilize (origin in particular)

  • Example - deltoid which helps hold scapula in position when arm is moved

IV. Naming Skeletal Muscles

A. General note on muscle names - muscle names are not named to confuse students! Rather the names contain elements that have useful meanings regarding such things as the design, position, function, etc. of a muscle

B. Elements of muscle names

a. name or part of the name reflects direction of muscle fasculi

b. name or part of the name reflects location of the muscle

c. name or part of the name reflects the size or length of the muscle

c. name or part of the name reflects the number of origins of the muscle

c. name or part of the name reflects the shape of the muscle

d. name reflects the origin (usually first part of name) and the insertion

e. name reflects the type of action

V. Study of Specific Muscle Organs

The study of the specific muscle names, origins, insertions, functions, and identifications is described in the next Notes on the Web of this unit. This will include an extensive vertebrate dissection exercise using ranch raised mink and a substantial amount of work in the human anatomy coloring book.

Reminder about Textbook Study

As with other topics, your textbook has excellent presentations of the materials on the muscular system. While you should focus on the specific material in the Notes on the Web, you should always use your textbook as a resource for illustrations and for understanding content that your notes cover.

As with all materials throughout the semester, you will have opportunities to ask questions or ask that any relevant material from your assignments be discussed in class.

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