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

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.

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

Resources available… Anatomy and Physiology Laboratory Study Pages; submenu: Muscle http://ctle.hccs.edu/biologylabs/AP1/AP1index.html

Laboratory Lecture

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

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

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 10.1.1 Muscular power and range of motion are influenced by fascicle organization and leverage 8

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 10.1.2 Muscular power and range of motion are influenced by fascicle organization and leverage 9

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 10.1.3 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

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 10.1.4 Muscular power and range of motion are influenced by fascicle organization and leverage 11

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

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)

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

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

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

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

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

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)

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

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

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)

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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.

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

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

An Overview of the Major (SUPERFICIAL) Skeletal Muscles

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

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

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

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!