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HUMAN MUSCLES
Chapter 10, Marieb Human A and P text, 8th Ed.
MUSCULAR FUNCTION
Muscles pull on bones and act as lever systems. Muscles have an tendinous origin which is immovable, and a tendinous insertion which is movable.
Classes of Levers (review) - see p. 325.
First Class Lever - resembles a see-saw with a fulcrum in the middle of the force and effort. It is diagrammed as E-F-R. An example is the splenius capitis which inserts on the occipital bone of the skull, extending it (the force) and pulling the chin (the resistance). Examine the illustration on p. 325, which joint is the fulcrum?
Second Class Lever - resembles a wheel barrow - the gastrocnemius muscle pulls the heel (calcaneus) upward [like you are lifting the handles of the wheel barrow], this causes the metatarsal/phalange [the wheel] joint to press against the floor. When you stand up on your toes, the resistance is the weight of the body pressing down on the ankles. The second class lever is diagrammed F-R-E.
Third Class Lever - the fulcrum and resistance are at opposite ends, the effort in between. The historical Jesus picked up and shouldered his cross this way. Examples are the adductors of the thigh, tweezers, and lifting a shovel of dirt. The fulcrum is the hip joint, the effort is the adductors' contractions and the resistance is the weight of the leg. The third class lever is diagrammed F-E-R.
ACTIONS
For instance, your biceps will flex your forearm by pulling on its insertion on the radius. The biceps of the anterior muscle compartment is the primary mover or agonist. Opposing the action of the biceps is the triceps of the posterior muscle compartment of the arm - the triceps is the antagonist of the movement. If you extend your forearm, the actions and functions of the two muscles are reversed.
In order to flex or extend a forearm carrying a heavy load, the shoulder (scapula) must be held in place. The rhomboideus muscles would serve as fixators.
Many movements also require that muscles serve as synergists which assist the movement.
SELECTED MUSCLES AND FUNCTIONS
Most of the muscles and their movements will be covered in lab.
Muscle Principal Origin/Insertion ActionHEAD REGIONOccipitalis Occipital/galea aponeurosis draws scalp backwards
Frontalis Frontal/galea aponeurosisdraws scalp forwards, wrinles forehead
Orbicularis oris skin at corners of mouth closes lipsZygomaticus zygomatic process/mouth corner smilingDepressor anguli oris
mandible/mouth corner frowning
Buccinator maxilla/orbicularis oris sucking Risorius parotid fascia/corner of mouth “rage” expressionOrbicularis oculi orbit/orbit closes eyesMasseter zygomatic arch/mandible chewing
Temporalisparietal/coranoid process of mandible
chewing
Label as above. See p. 330.
Digastricmandible + mastoid/hyoid
opens mouth
Mylohyoid inner mandible/hyoidaids swallowing, flattens floor of mouth and elevates the tongue
Label as above. See p. 341
.
Sternocleidomastoidsternum + clavicle/mastoid
turns head R or L, shrug shoulders
Splenius capitis vertebrae/occipital extends head
Label as above. See p. 333.
TRUNKRectus abdominus pubis/rib cartilages tightens mid-line in defecationExternal oblique ribs/linea alba compresses abdomenInternal oblique iliac crest/rib cartilages compresses abdomenTransverse abdominus iliac crest/linea alba compresses abdomen
Thoracic - deep
Diaphragmribs + lumbar vert./central tendon
inhalation, increases volume of the thoracic cavity
External intercostals
adjacent ribs elevates rib cage in inhalation
Internal intercostals
adjacent ribs depresses rib cage
Pectoralis minorribs #3-5 /coracoid of scapula
moves scapula anteriorly, elevates rib cage
Label as above. See p. 347.
Thoracic - superficial
Pectoralis majorsternum and clavicle/greater tubercle of humerus
adducts arm
Label as above. See p. 343.
Serratus anterior ribs/scapula abducts scapula, elevates ribs. What is winged scapula?
Label as above. See pg. 352.
Back
Trapeziusoccipital + vertebrae/clavicle + scapula
upper div. elevates clavicle; for climbing, elevates scapula
Levator scapulae cervical vertebrae/scapula elevates scapulaRhomboideus thoracic vertebrae/scapula adducts and fixates scapulaLatissimus dorsi vertebrae/humerus draws arm back Quadratus lumborum
iliac crest/12th rib and lumbar vertebrae
draws torso R and L inferiorly
(Use the cat terms for the three sections of the trapezius. See the Mareib lab manual.)
Label as above. See p. 354-357
SHOULDER/ARM - See p. 351.
(Back-see above)
Teres major scapula/intertubular groove of humerus adducts armTeres minor inf. border scapula/great.tub.of humerus rotates arm laterally
Deltoid clavicle + scapular spine/deltoid tuberosity of humerus
flexes and abducts arm
Use the cat terms (achromiodeltod, clavodeltoid and spinodeltoid) for the three
sections of the deltoid.
Subscapularis anterior scapula/humerus rotates arm medially
Name this muscle.
Supraspinatusposterior, upper scapula/tubercle of humerus
abducts arm
Infraspinatus inf. angle of scapula/tubercle of humerus rotates arm laterally
ARM - See p. 352-354.
Biceps brachii coracoid + scapula/radiusflexes forearm, flexes arm
Brachialis ant. humerus/ulna flexes forearm Brachioradialis distal humerus/radius flexes forearm
Triceps brachiipost.scapula, glenoid fossa and humerus/olecranon process
extends forearm
Pronator teres med. epicondyle of humerus/radius pronates arm
Supinator lat. epicondyle of humerus/radiussupinates arm and hand
Label as above. See p. 352.
Label as above. See p. 352.
HIP and THIGH - See p. 364.
Iliacus ant.iliac fossa/lesser trochanter via psoas tendon
flexes and rotates thigh laterally
Psoas major lumbar vert./lesser trochanter as above Pectineus pubis/femur flexes, adducts thigh
-
Label as above. See p. 362-369.
Gluteus maximuspost. sacroiliac area/post. femur under greater trochanter
rotates thigh laterally
Gluteus medius Iiium/greater trochanterrotates thigh medially
Tensor fasciae latae Iiiac crest/ant.tibia flexes, abducts thigh
Adductor longus/magnus
pubis/linea aspera of femur adducts thigh
Label as above. See p. 364.
QUADS
Rectus femoris iliac spine/patellaflexes thigh and extends leg
Vastus lateralis, medialis, intermedius
greater trocanter and linea aspera/tibial tuberosity via the patellar tendon
extends leg
Label as above. See p. 364.
HAMSTRINGS
Biceps femorisischial tuberosity + linea aspera/fibula and lat. condyle of tibia
extends thigh and flexes leg
Semitendinosus ischial tuberosity/tibia flexes legSemimembranosus ischial tuberosity/med.condyle of tibia as above
Label as above. See pg. 367.
OTHERS
Gracilis pubis/tibia adducts thigh Sartorius iliac spine/tibia rotates leg laterally Tibialis anterior tibia/ superior first metatarsal dorsiflexes footExtensor digitorum longus
tibia + fibula/phalanges extends toes
Peroneus longusfibula + tibia/inferior first metatarsal
everts foot, plantar flexes foot
Shinsplints is a term for inflammations of the tibial periosteum of tendinitis associated with the tibialis posterior or anterior. It usually results from running on hard surfaces.
Label as above. See p. 371.
Gastrocnemius post.knee/calcaneus plantar flexion, "standing on
toes,” flexes legFlexor digitorum longus
post.tibia/distal phalanges
flexes toes, inverts foot
Questions
1. What is RICE therapy for muscle injuries?
2. Which muscles are the typical ones for arm, hip and thigh injections?
3. Compare the lever classes and explain one example of each.
4. Review the principal actions of the muscles above by making your own table.
mailto:john.aliff@gpc.edu
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