The Muscular System Chapter 10 Lever Systems The operation of most skeletal muscles involves the use of levers and lever systems Lever A rigid bar that moves on a fixed point Fulcrum A fixed point of leverage Effort The forced applied to move a resistance Load The resistance to me moved Lever Systems In the human body Levers Fulcrums Effort Load
The bones of the skeleton Fulcrums The joints of the body Effort Applied by the muscles of the body Load Bone, overlying tissue, and other objects to which your body applies force Lever Systems A lever allows a given effort to move a heavier load or to move a load farther or faster that it otherwise could A small difference in the site of a muscles insertion can translate into large differences in the amount of force must generate to move a given load Mechanical Advantage A small effort applied over a relatively long distance can be used to move a large load over a small distance Such a lever operates at a mechanical advantage and is commonly called a power lever because it can lift heavy loads Mechanical Disadvantage
When the load is far from the fulcrum and the force is applied near the fulcrum, the force exerted by the muscle must be greater than the load moved These levers are useful because they allow the load to move rapidly through a large distance and are called speed levers Lever Systems Regardless of type, all levers follow the same basic principle: Effort farther than load from fulcrum = mechanical advantage Effort nearer than load to fulcrum = mechanical disadvantage Depending on the relative position of the three elements (effort, fulcrum, load) a lever is classified as either a first, second, or third class lever First Class Levers In first class levers the effort is applied at one end of the lever and the load is at the other end with the fulcrum in between them (LFE) Extension/flexion of the head, other exist but usually operate at a mechanical disadvantage Second Class Levers In second class levers the effort is applied at one end the fulcrum is at the other with the load somewhere in between(FLE) Plantar flexion of the foot Third Class Levers In third class levers, the effort is applied at a point between the load and the fulcrum(LEF) These levers operate with great speed and always at a mechanical disadvantage Most levers of the body are third class levers which permit an insertion close to the joint and allow rapid movement with little shortening of the muscle Which Lever is it? Fulcrum in the middle? 1st Class
Load in the middle?2nd Class Effort in the middle?3rd Class Lever Summary Difference in the positioning of the three elements modify muscle activity with respect to Speed on contraction Range of movement Weight of the load that can be lifted Speed levers act at a mechanical disadvantage Force is lost, but speed is gained Power levers act at a mechanical advantage Force is gained, but speed is lost Arrangement of Fascicles
Arrangement of fascicles within a muscle will vary Arrangements result in differing shapes and capabilities Common forms are Parallel Pennate Convergent Circular or sphincteral Parallel Arrangement of Fascicles
In parallel arrange- ment the long axis of the fascicles run parallel to the long axis of the muscle Form long straplike muscles that have greatest potential for shortening Act over a long excursion Not very powerful Pennate Arrangement of Fascicles
Pennate fascicles are short and they attach obliquely to a central tendon Occur as pennate, bipennate and multipennate forms Pennate muscles with the highest concentration of fibers, shorten little, but are very powerful A)Pennate / Ext. digitorum longus B)Bipennate / Rectus Femoris C)Multipennate / Deltoid Convergent Arrangement of Fascicle
A convergent muscle has a broad origin and its fascicles converge toward a single tendon Muscle has a broad triangular shape Muscle can act upon the joint from a variety of positions Pectoralis major Circular Arrangement of Fascicles
Fascicular pattern is arranged in concentric rings Muscles with this arrangement surround external body openings which they close by contracting This type of muscles are called sphincters which literally means squeezers Interactions of Skeletal Muscles
The arrangement of body muscles permits them to work either together or in opposition to achieve a movement As muscle contract they can only pull on the skeleton; they can never push If you are pushing an object it is the contraction of some group of muscles in the body that will accomplish it Generally muscles are grouped to undo an action done by another group Quadriceps / Hamstrings Working out with Muscles
Muscle contraction causes shortening, not lengthening of a muscle Concentric / shortening against resistance Eccentric / lengthening against resistance Typically as a muscle contracts it moves its insertion toward its origin Lat. bar pull down / Latissimus dorsi However, some muscles can contract and move its origin toward its insertion Pull ups / Latissiums dorsi Functional Muscle Groups
Muscles can be classified into four functional groups Prime movers Antagonists Synergists Fixators Prime Movers A muscle that provides the major force for producing a specific movement is called a prime mover or agonist The biceps brachii is the prime mover of elbow flexion Origin of Biceps Brachii Coracoid Process Antagonist Muscles that oppose a particular movement are called antagonist When a prime mover is active, the antagonist muscles are often stretched and in the relaxed state Antagonists also regulate the action of prime mover Synergist Synergists aid agonists by promoting the same movement and by reducing extraneous movements that may be produced when the prime mover acts In two joint muscles synergists stabilize a joint as the muscle acts on the other Synergist can also restrict rotary movement at a joint so the muscles full effort be applied to the desired movement Fixator When a synergist immobilize a muscles origin they are called fixators Their action serves to stabilize the bone upon which a prime mover acts Serratus anterior holds the scapula against the thorax while a prime mover acts upon the arm Naming Skeletal Muscles
Location of the muscle Intercostal, Temporalis Shape of the muscle Deltoid; Trapezius Relative size of the muscle Maximus; medius; minimus; brevis; longus Direction of muscle fibers Rectus (straight) fibers run parallel to line of pull Transverse; fibers run perpendicular to line Oblique; fibers are oblique to the line Naming of Muscles Number of origins
Biceps; triceps; quadriceps Location of muscle origin and/or insertion Sterno (sternum); cleido (clavicle); mastoid (mastoid process of temporal bone) Action of the muscle Flexor; extensor; adductor, supinator Major Skeletal Muscles
There are over 600 muscles in the body Approximately 125 are presented in text There will be 55 assigned to you to learn As you learn these muscles try to relate to its attachments and position and what joint(s) it acts across The best way to learn muscle actions is to act them out in your body Major Muscles: Anterior Major Muscles: Posterior Muscle of Head: Facial Expression
Table 10.1 Muscles of Head: Facial Expression
Promote facial expression and non-verbal expression Highly variable in shape and strength Unusual in that they insert into skin or other muscles and not bone Innervated by Cranial nerve VII (facial) Muscles of Head: Mastication
Table 10.2 Muscles of Head: Mastication
Four pairs of muscles are involved with mastication Chewing and biting Masseter Temporalis Grinding movements Pterygoid Buccinator Trigeminal and Facial nerves Muscles of Head: Tongue Movement
Table 10.2 Muscles of Head: Tongue Movement
The extrinsic muscles of the tongue serve to anchor and move the tongue These muscles serve to protrude, depress, and retract the tongue Innervated by the hypoglossal nerve Muscle that Promote Swallowing
Table 10.8 Muscles that Promote Swallowing
Lateral view of the constrictor muscles of the pharynx These muscles are shown in their proper anatomical relationship Muscles of Anterior Neck & Throat
Table 10.3 Muscles of Anterior Neck & Throat
Most of these muscles are involved with the coordinated action of swallowing which have the following sequence Widening the pharynx and closing the larynx Closing the superior nasal cavity Propulsion of food through the pharynx into the esophagus Return of musculature to normal positioning Muscles of Neck Sternocleidomastoid is a head flexor
Scalenes contribute to lateral flexion of the neck Splenius is a head extensor Muscles of Neck The head is moved by muscles originating from the axial skeleton which include Sternocleidomastoid / head flexors Scalenes / lateral head flexion Splenius / head extension Muscles of Vertebral Column Muscle of the Vertebral Column
Trunk extension is effected by the deep muscles of the back The erector spinae is the largest of the group and it consist of three columns Iliocostalis Longissimus Spinalis Other muscles of the vertebral column include Semispinalis / extends head Quadratus lumborum / Lateral flexion Muscle of the Thorax: Breathing External Intercostals
O - Inferior border of rib above I - Superior border of rib below A - Pulls ribs upward to aid in respiration Internal intercostals
O - Superior border of rib below I - Inferior border of rib above Draws ribs together; aids in expiration Muscles of the Thorax: Breathing Diaphragm O - Inferior border of rib cage, costal cartilages of last 6 ribs, and lumber vertabrae I - Central tendon A - Inspiration Muscles of the Abdominal Wall Muscles of Abdominal Wall
The anterior and lateral abdominal wall has no bony reinforcement It is composed of four paired muscles, their investing fasciae and their aponeuroses The muscles of the abdominal wall include Rectus abdominis External oblique Internal oblique Transverse abdominis Muscles of the Abdominal Wall Muscles of the Abdominal Wall
Illustration of how the aponeuroses of the lateral abdominal muscles contribute to the rectus abdominis sheath Enclosure of the Rectus abdominis within the aponeuroses prevents anterior protrusion or bowstringing of the muscle The Linea alba represents the central fusion of the aponeurses along the midline Rectus abdominis O - Pubic crest and symphasis
I - xiphoid process and costal cartilages of ribs 5 - 7 A - Flex and rotate lumbar region of the vertebral column External oblique O - by fleshy strips from outer surfaces of ribs 5-7
Linea alba; pubic crest and tubercle via aponeurosis A - flexing vertebral column Internal oblique O -Lumbodorsal fasica, iliac crest and inguinal ligament I - Linea alba, pubic crest and last 3 ribs A - Flex vertebral column Transverse abdominis O - inguinal ligament, lumbo- dorsal fascia, cartilages of last 6 ribs, iliac crest I - Linea alba, pubic crest A - compresses abdominal contents Muscles of the Pelvic Floor Muscles of the Pelvic Floor
Stretching between the two sides of the pelvic arch is the urogenital diaphram The Sphinter urethrae surrounds the urethra and allow voluntary urination Muscles of the Pelvic Floor
Superficial space contains muscles (Ischocavernosus, Bulbospongiosus) that help maintain erection of the penis and clitoris The external anal sphinter encircles the anus and allows for voluntary control of defectation Muscles of the Anterior Thorax Pectoralis minor O - anterior surfaces of ribs 3-5
I - coracoid process of scapula A - ribs fixed draws scapula forward and downward Serratus anterior O - ribs 1-9
I - entire anterior surface of vertebral border of scapula A - Protract the scapula; rotates scapula Muscles of the Posterior Thorax Trapezius O - Occipital bone, ligamentum nuchae, spines of C7 & all thoracic vert. I - Acromium and spine of scapula and lateral 1/3 of clavicle A - elevate and rotate scapula Levator scapulae O - transverse processes of C1 - C4
I - superior angle of scapula A - elevates and adducts scapula Rhomboid major O - spinous processes of T2 - T5
I - medial border of scapula A - retract; rotate; and stabilize scapula Rhomboid minor O - spinous processes of C7 and T1
I - medial border of scapula A - retract; rotate; and stabilize scapula Muscles Crossing the Shoulder Joint
A total of nine muscles cross the shoulder joint to insert on the humerus The three prime movers of the shoulder joint are Pectoralis major Lastissimus dorsi Deltoid The remaining six muscles are synergists and fixators Four of these six are muscles of the rotator cuff Muscles Crossing the Shoulder Joint Pectoralismajor O - clavicle, sternum, and cartilages of ribs 1 - 6
I - greater tubercle of humerus A - arm flexion, medial arm rotation, arm adduction Latissimus dorsi O - spines of T6 - T12 and L1 - L5 etc
I - Inter- tubicular groove of humerus A - arm extension, adduction and med. rotation Deltoid O - Lateral 1/3 of clavicle, acromium, and spine of scapula
I - Deltoid tuberosity of humerus A - arm abduction; flex/ ext. arm; med./ lat. rotate arm Subscapularis O - subscapular fossa of scapula
I - lesser tubercle of humerus A - medial rotator of arm Supraspinatus O - supra spinatus fossa of scapula
I - superior part of greater tubercle of humerus A - holds head of humerus in glenoid fossa to stabilize shoulder joint Infraspinatus O - infra spinatus fossa of scapula
I - greater tubercle of humerus A - laterally rotates scapula Teres minor O - lateral border of dorsal scapular surface
I - greater tubercle of humerus A - laterally rotates scapula Teres major O - posterior surface of scapula at inferior angle
I - lesser tubercle of humerus A - extends, medially rotates and adducts humerus Coraco- brachialis O - coracoid process of scapula
I - medial surface of shaft of humerus A - flexion and adduction of humerus Muscles Crossing the Elbow Joint
Since the elbow is a hinge joint the movement promoted by these muscles are limited almost to flexion and extension of the forearm There are three muscles anteriorly Biceps brachii Brachialis Brachioradialis There is one muscle posteriorly Triceps brachii Muscles Crossing the Elbow Joint Triceps brachii O - long head/ infraglenoid tubercle; lat. and medial heads / posterior humerus; I - Olecranon process of ulna A - forearm extensor; long head assist in adduction Biceps brachii O - short head/ coracoid process of scapula; long head / supra glendoid tubercle I - radial tuberosity A - flexes arm and forearm; supinates Brachialis O - anterior, distal humerus I - coracoid process of ulna
A - forearm flexor Brachio radialis O - lateral supracondylar ridge
I - styloid process of radius A - forearm flexion; a semi pronated position gives it its best mechanical advantage Muscles ofForearm Muscles of the forearm are divided equally into flexors and extensors Flexors on the medial epicondyle Extensors on the lateral epicondyle Pronator teres O - medial epicondyle of humerus
I - lateral radius at midshaft A - pronates forearm; weak elbow flexor Flexor carpi radialis O - medial epicondyle of humerus
I - base of second and third metacarpals A - powerful wrist flexor; Palmaris longus O - medial epicondyle of humerus
I - palmer aponeurosis A - weak wrist flexor; tenses palmer aponeurosis Flexor carpi ulnaris O - medial epicondyle of humerus
I - pisiform bone and base of 5th metacarpal A - flexor of wrist Muscles Crossing the Hip and Knee
Muscles crossing the hip and knee can be grouped into Hip flexors (4) Gluteal muscles (3) Medial compartment (5 adductors) Anterior compartment (4 knee extensors) Posterior compartment (3 knee flexors) Lateral rotators (5) Muscles Crossing the Hip and Knee Iliacus O - iliac fossa I - lesser trochanter of femur A - hip flexion Psoas major O - transverse processes and bodies of T12 and all lumbar vertebrae I - lesser trochanter of femur A - hip flexion and lateral hip flexion Psoas minor O - Transverse processes and bodies of T12 and L1
I - Rim of acetabulum A - flexes lumbar vertebrae Sartorius O - anterior superior iliac spine
I - medial aspect of proximal tibia A - Flexes and laterally rotates thigh; flexes knee Adductors Adductors Adductor magnus Adductor longus Adductor brevis
Pectineus Gracilis Adductor magnus O - ischial and pubic rami and ischial tuberosity
I - linea aspera and adductor tubercle A - adducts and laterally rotates thigh Adductor longus O - pubis near pubic symphysis I - linea aspera
A - adducts, flexes and laterally rotates thigh Adductor brevis O - body and inferior ramus of pubis I - linea aspera
A - adducts and laterally rotates thigh Pectineus O - pectineal line of pubis I - lesser trochanter of femur
A - adducts, flexes,and laterally rotates thigh Gracilis O - inferior ramus and body of pubis
I - medial surface of tibia just inferior its media condyle A - adducts thigh, flexes and medially rotates thigh Quadriceps femoris Muscles include Rectus femoris Vastus lateralis
Vastus medialis Vastus intermedius Rectus femoris O - anterior inferior iliac spine
I - patella and tibial tuberosity A - extends knee and flexes thigh at hip Vastus lateralis O - greater trochanter, intertrochanteric
I - patella and tibial tuberosity A - extends knee Vastus medialis O - linea aspera, intertrochanteric line
I - patella and tibial tuberosity A - extends knee Vastus intermedius O - anterior and lateral surfaces of proximal femur shaft I - patella and tibial tuberosity A - extend knee Tensor fascia latae O - anterior aspect of iliac crest
I - iliotibial tract A - flexes and abducts thigh Gluteus maximus O - dorsal ilium, sacrum and coccyx
I - gluteal tuberosity of femur A - thigh extension Gluteus medius O - between anterior and posterior gluteal lines on lateral surface of ilium I - greater trochanter of femur A - abducts and medially rotates thigh Gluteus minimus O - between anterior and inferior gluteal lines on external surface of femur I - greater trochanter of femur A - abducts and medially rotates thigh Biceps femoris O - (long) ischial tuberosity, (short) linea aspera
I - head of fibula and lateral condyle of tibia A - extends thigh and flexes knee, laterally rotates leg Semi tendinosus O - ischial tuberosity
I - medial aspect of upper tibial shaft A - extends thigh at hip; flexes knee, medially rotates leg Semi membranosus O - ischial tuberosity I - medial condyle of tibia
A - extends thigh and flexes knee, medially rotates leg Muscles -Anterior Compartment
Muscles of the anterior compartment are primarily toes extensors and dorsiflexors Tibialis anterior Extensor digitorum longus Extensor hallucis longus Peroneus tertius Important in walking during the recovery phase of gait Tibialis anterior O - lateral condyle and upper 2/3 of tibia
I - inferior medial surface of medial cuneiform and 1st metatarsal bone A - dorsiflexion, inverts foot Extensor digitorum longus
O - lateral condyle of tibia, proximal 3/4 of fibula I - 2nd & 3rd phalanges of toes 2-5 via extensor expansion A - Dorsiflexion, toe extension Peroneus tertius O - distal surface of fibula and interosseous membrane I - dorsum of fifth metatarsal A - dorsiflexes and everts foot Extensor hallucis O - anteriomedial fibula shaft and interosseous membrane I - distal phalanx of great toe A - extends great toe, dorsiflexes foot Muscles - Lateral Compartment
Muscles of the lateral compartment are primarily plantar flex and evert the foot Peroneus longus Peroneus brevis Peroneus longus O - head and upper portion of fibula
I - under the foot to first metatarsal and medial cuneiform A - plantar flexes and everts foot Peroneus brevis O - distal shaft of fibula
I - proximal end of the 5th metatarsal A - Plantar flexes and everts foot Muscles of Posterior Compartment
Muscles of the posterior compartment are primarily plantar flexors and flex the toes Gastrocnemius Soleus Tibialis posterior Flexor digitorum longus Flexor hallucis longus Gastrocnemius O - from medial and lateral condyles of femur
I - calcaneus via calcaneal tendon A - plantar flexes foot, flexes knee Soleus O - superior tibia, fibula and interosseus membrane
I - calcaneus via calcaneal tendon A - plantar flexes ankle Plantaris O - posterior femur above lateral condyle I - calcaneus
A - plantar flexion, knee flexion Popliteus O - lateral condyle of femur I - proximal tibia
A - flexes and rotates knee medially to unlock knee from full extension Flexor digitorum longus
O - posterior tibia I - distal phalanges of toes 2-5 A - plantar flexes and flexes toes Flexor hallicus longus
O - medial part of shaft of fibula, interosseous membrane I - distal phalanx of great toe A - plantar flexes and inverts foot, flexes great toe Tibialis posterior O - superior tibia and fibula and interosseous membrane I - tarsals and metatarsals 2-4 A - inversion, plantar flexion Intrinsic Muscles of the Foot
The intrinsic muscles of the foot help to flex, extend, abduct, and adduct the toes Collectively the muscles support the arches of the foot assisted by some tendons of leg muscles The muscles occur in four layers from superficial to deep Intrinsic Muscles of the Foot
Muscles of the second layer flex, adduct, and abduct the toes Muscles include Flexor digitorum brevis Abductor hallucis Abductor digiti minimi Intrinsic Muscles of the Foot Intrinsic Muscles of the Foot Intrinsic Muscles of the Foot