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	Action
HEAD REGION
Occipitalis	Occipital/galea aponeurosis	draws scalp backwards
Frontalis	Frontal/galea aponeurosis	draws scalp forwards, wrinles forehead
Orbicularis oris	skin at corners of mouth	closes lips
Zygomaticus	zygomatic process/mouth corner	smiling
Depressor anguli oris	mandible/mouth corner	frowning
Buccinator	maxilla/orbicularis oris	sucking
Risorius	parotid fascia/corner of mouth	“rage” expression
Orbicularis oculi	orbit/orbit	closes eyes
Masseter	zygomatic arch/mandible	chewing
Temporalis	parietal/coranoid process of  mandible	chewing

 

TRUNK
Rectus abdominus	pubis/rib cartilages	tightens mid-line in defecation
External oblique	ribs/linea alba	compresses abdomen
Internal oblique	iliac crest/rib cartilages	compresses abdomen
Transverse abdominus	iliac crest/linea alba	compresses abdomen

 
 
 

Thoracic - deep
Diaphragm	ribs + 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 minor	ribs #3-5 /coracoid of scapula	moves scapula anteriorly, elevates rib cage

 

Label as above. See p. 347.

 

Serratus anterior

ribs/scapula

abducts scapula, elevates ribs.  What is winged scapula?

Back
Trapezius	occipital + vertebrae/clavicle + scapula	upper div. elevates clavicle; for climbing, elevates scapula
Levator scapulae	cervical vertebrae/scapula	elevates scapula
Rhomboideus	thoracic vertebrae/scapula	adducts and fixates scapula
Latissimus 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.)
 
 

SHOULDER/ARM - See p. 351.

(Back-see above)

Teres major	scapula/intertubular groove of humerus	adducts arm
Teres minor	inf. border scapula/great.tub.of humerus	rotates arm laterally
Deltoid	clavicle + scapular spine/deltoid        tuberosity of humerus	flexes and abducts arm

 
 

ARM - See p. 352-354.
 

Biceps brachii	coracoid + scapula/radius	flexes forearm, flexes arm
Brachialis	ant. humerus/ulna	flexes forearm
Brachioradialis	distal humerus/radius	flexes forearm
Triceps brachii	post.scapula, glenoid fossa and humerus/olecranon process	extends  forearm
Pronator teres	med. epicondyle of humerus/radius	pronates arm
Supinator	lat. epicondyle of humerus/radius	supinates arm and hand

 
 

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.

QUADS
 

Rectus femoris	iliac spine/patella	flexes thigh and extends leg
Vastus lateralis, medialis, intermedius	greater trocanter and linea aspera/tibial tuberosity via the patellar tendon	extends leg

 

HAMSTRINGS
 
 

Biceps femoris	ischial tuberosity + linea aspera/fibula and lat. condyle of tibia	extends thigh and flexes leg
Semitendinosus	ischial tuberosity/tibia	flexes leg
Semimembranosus	ischial tuberosity/med.condyle of tibia	as above

 
 

OTHERS
 
 

Gracilis	pubis/tibia	adducts thigh
Sartorius	iliac spine/tibia	rotates leg laterally
Tibialis anterior	tibia/ superior first metatarsal	dorsiflexes foot
Extensor digitorum longus	tibia + fibula/phalanges	extends toes
Peroneus longus	fibula + 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.
 
 

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