1. “Skeletal Muscle Gross Anatomy”
Laboratory Exercise:
“Skeletal Muscle Gross Anatomy”

2. Skeletal Muscle – Gross Anatomy
In this exercise, you will identify the major muscles of the skeletal muscle system, their landmark structures and describe their function (body movement).
These terms should be familiar to you: location, size, shape, direction of fibers, number of origins, muscle action, origin and insertion.
This laboratory exercise correlates with Chapter 11 of your textbook.

3. What procedures are we doing?
Examine a human model (arm, leg, eye, head or torso) and identify muscles.

4. Resources available…
Anatomy and Physiology Laboratory Study Pages; submenu: Muscle

5. Laboratory Lecture

6. An Introduction to the Muscular System
Muscle organization affects the power, range and speed of muscle movement
Skeletal muscle cells (myofibers) are organized into bundles, called fascicles

7. Fascicle Arrangement
Skeletal muscles are classified by several criteria:
By the relationships of fascicles to tendons
The patterns of fascicle organization
Parallel
Convergent
Pennate
Circular

8. the cross section of the muscle
In a parallel muscle, the fascicles are parallel to the long axis of the muscle
Tension depends on the total number of myofibrils and is directly related to
the cross section of the muscle
An example is the Biceps brachii muscle
Figure Muscular power and range of motion are influenced by fascicle organization and leverage 8

9. on common attachment point (tendon, aponeurosis or raphe)
In a convergent muscle, the fascicles extend over a large area and converge
on common attachment point (tendon, aponeurosis or raphe)
Muscle fibers pull in different directions, depending on their stimulation
An example is the Pectoralis major muscle
Figure Muscular power and range of motion are influenced by fascicle organization and leverage 9

10. In pennate muscles, the fascicles form a common angle with the tendon
Pennate muscle does not move as far as parallel muscle, but develops
more tension
Examples are shown below…
Extensor digitorum muscle
Rectus femoris muscle
Deltoid muscle
(3c)
(3a)
Tendons
Figure Muscular power and range of motion are influenced by fascicle organization and leverage
Extended
tendon 3
(3b)
Unipennate: fibers are
on the same side of the
tendon,.
Bipennate: fibers on
both sides of the
tendon
Multipennate: the tendon
branches within the muscle 10

11. Circular muscles are also referred to as sphincter muscles
The fascicles are concentrically arranged around an opening
An example is the Orbicularis oris muscle of the mouth
Figure Muscular power and range of motion are influenced by fascicle organization and leverage 11

12. Levers Skeletal muscles attach to the skeleton to produce motion
The type of muscle attachment affects the power, range, distance and speed of muscle movement

13. Mechanically, each bone is a lever - a rigid, moving structure
Mechanically, each bone is a lever - a rigid, moving structure. Each joint is a fulcrum (F) - a fixed point
Muscles provide an applied force (AF) that is required to overcome a load (L)
(applied force)

14. Three Classes of Levers
There are three classes of levers
They depend on the relationship between the applied force, the fulcrum, and the resistance
First-class lever
Second-class lever
Third-class lever

15. i.e. sternocleidomastoid muscle
First-class Lever
A “seesaw” or “teeter-totter” is an example of a first-class lever
The fulcrum is centered between the applied force and the load
Thus, the force and the load are balanced
i.e. sternocleidomastoid muscle

16. i.e. gastrocnemius muscle
Second-class Lever
A “wheelbarrow” is an example of a second-class lever
The load lies between the applied force and the fulcrum
The advantage is that a small force moves a large weight (disadvantage is that speed and distance traveled decrease) b
Second-class lever.
The load (L) lies between the applied force (AF) and the fulcrum (F).
Load AF
Example: Wheelbarrow AF AF
Fulcrum L L F
Applied force L F F
i.e. gastrocnemius muscle

17. i.e. biceps brachii muscle
Third-class Lever
A third-class lever is the most common type in the body
The force is applied between the load and the fulcrum
The advantage is that speed and distance traveled are maximized (disadvantage is that a greater force moves smaller load) C
Third-class lever.
Applied force
The applied force (AF) is between the load (L) and the fulcrum (F).
Load AF L L AF F AF
Biceps brachii muscle
Fulcrum L F
Example: Catapult F
i.e. biceps brachii muscle

18. Muscle Attachments to Other Tissues
Origins and Insertions
Muscles have one fixed point of attachment, called an origin, and one moving point of attachment, called an insertion
Most muscles originate or insert on the skeleton
The origin is usually proximal to the insertion, which is distal

20. Actions
Actions are the body movements produced by a muscle contraction (i.e. flexion, extension, etc…)
Actions are described in two terms:
Of the bone or region affected (i.e. the Biceps brachii muscle performs flexion of the forearm)
Of the joint involved (i.e. flexion at the elbow)

21. When complex movements occur, muscles work in groups to maximize efficiency
Smaller muscles reach a maximum tension first, followed by larger, primary muscles, which bear the brunt of the load
Based on their functions, muscles are described as:
An agonist, which produces a prime movement
An antagonist, which contradicts the movement caused by the agonist
A synergist (stabilizer), which assists the larger agonist to start motion
A fixator, which stabilizes the origin of the agonist

22. Agonists and antagonists work in pairs
When one contracts, the other stretches (relaxes)
Such as the relationship between flexors & extensors or abductors & adductors

23. Naming Skeletal Muscles
Except for the platysma and the diaphragm, the names of skeletal muscles are followed by the term “muscle”
Muscles are assigned names based on their:
Location in the body
Points of origin and insertion (first/last part of name)
Fascicle organization (rectus, transverse, oblique)
Relative position (superficial, profundus, etc…)
Structural characteristics (number, shape, size)
Action (movements or actions)

24. 24

25. Abduction and Adduction
Elbow joint
EXTENSION
FLEXION
ANTERIOR
POSTERIOR
Flexor
Extensors
Flexion and Extension
The biceps brachii muscle crosses on the anterior side of the elbow joint. So
it is a flexor of the elbow joint.
The triceps brachii
muscle crosses on
the posterior side of the elbow joint.
So it is an extensor of the elbow joint.
At joints that permit flexion and extension, muscles whose lines of action cross the anterior side of a joint are flexors of that joint, and muscles whose lines of action cross the posterior side of a joint
are extensors of that joint.
The action produced by a muscle at any one joint is largely dependent upon the structure of the joint and the location of the insertion of the muscle relative
to the axis of movement at the joint. The direction, or geometric paths, of the action produced by a muscle—called lines of action—is often represented by an arrow (or more than one arrow in fan-shaped muscles).
ABDUCTION
Hip joint
LATERAL
Abductor
Abduction and Adduction
The gluteus medius and gluteus minimus muscles cross the lateral side of the hip joint. So they are abductors of the hip joint.
At joints that permit adduction and abduction, muscles whose lines of action cross the medial side of the joint are adductors of that joint, and muscles whose lines of action cross the lateral side of the joint are abductors of that joint.
MEDIAL
ADDUCTION
Adductor
The adductor magnus muscle crosses on the medial side of the hip joint. So it is an adductor of the hip joint.

26. Medial and Lateral Rotation
At joints that permit rotation, movement or turning of the body part occurs around its axis. The shoulder joint is a ball-and-socket joint that permits rotation. The subscapularis muscle has lines of action that cross the anterior aspect of the shoulder joint. When the subscapularis contracts it produces medial rotation at the joint. The teres minor muscle has lines of action that cross the posterior aspect of the shoulder joint. When the teres minor contracts, it produces lateral rotation at the shoulder.
Shoulder joint
POSTERIOR
ANTERIOR
Lateral rotator
Medial rotator
The teres minor muscle crosses the posterior side of the shoulder joint. When it contracts, it rotates the shoulder laterally.
The subscapularis muscle crosses on the anterior side of the shoulder joint. When it contracts, it rotates the shoulder medially.
Scapula
Humerus

27. Divisions of the Muscular System
Axial muscles
Position the head and the spinal column, and move the rib cage
60% of skeletal muscles
Appendicular muscles
Support the pectoral and pelvic girdles, and support the limbs
40% of skeletal muscles

28. An Overview of the Major (SUPERFICIAL) Skeletal Muscles

29. Appendicular Muscles ATLAS: Plates 1a; 39a–d An anterior view.
Gluteus medius
Tensor fasciae latae
Iliopsoas
Pectineus
Adductor longus
Iliotibial tract
Gracilis
Sartorius
Patella
Rectus femoris
Vastus lateralis
Vastus medialis
Tibia
Gastrocnemius
Fibularis longus
Tibialis anterior
Soleus
Extensor digitorum longus
Superior extensor
retinaculum
Inferior extensor
retinaculum
Lateral malleolus of fibula
Medial malleolus of tibia
An anterior view.
ATLAS: Plates 1a; 39a–d 29

30. Axial Muscles Appendicular Muscles ATLAS: Plates 1b; 40a,b
Occipital belly of
occipitofrontalis
Sternocleidomastoid
Trapezius
Deltoid
Infraspinatus
Teres minor
Teres major
External oblique
Rhomboid major
Triceps brachii (long head)
Triceps brachii (lateral head)
Latissimus dorsi
Brachioradialis
Extensor carpi radialis longus
Anconeus
Flexor carpi ulnaris
Extensor digitorum
Extensor carpi ulnaris
A posterior view
ATLAS: Plates 1b; 40a,b 30

31. Appendicular Muscles ATLAS: Plates 1b; 40a,b A posterior view
Gluteus medius
Tensor fasciae latae
Gluteus maximus
Adductor magnus
Semitendinosus
Semimembranosus
Iliotibial tract
Gracilis
Biceps femoris
Sartorius
Plantaris
Gastrocnemius
Soleus
Calcaneal
tendon
Calcaneus
A posterior view
ATLAS: Plates 1b; 40a,b 31

32. A very, very complicated system, indeed!
Note: There are many smaller, INTERNAL muscles that execute and coordinate particular movements (i.e. movement of the eye, or of the finger, etc…)
A very, very complicated system, indeed!