Lecture 14: Muscles III

I. Comparison of Skeletal, Cardiac and Smooth Muscle






Attached to bones, fascia and skin

Walls of heart

Single-unit: visceral organs

Multi-unit: Internal eye muscles, large airways and arteries


Single, long, cylindrical, striated, multinucleate

Branching chains of cells, uni-nucleate, striated

Single, non-striated, uni-nucleate

Connective Tissue

Epimysium, perimysium, endomysium







T Tubules

Present at each end

Present at on end


Gap Junctions


Intercalated discs

In single-unit

Neuromuscular Junctions



In multi-unit

Regulation of


Somatic NS; voluntary

Autonomic NS, intrinsic (pacemaker), hormones, involuntary

Autonomic NS, hormones, local regulation, response to stretch

Ca2+ Source


SR, extracellular fluid

SR, extracellular fluid

Role of Ca2+

Via troponin/actin interactions

Via troponin/actin interactions

Via calmodulin/myosin interaction




In single-unit

Nervous System



Excitation or inhibition

Excitation or inhibition

Speed of Contraction

Varies: slow to fast


Very slow

Rhythmic Contraction



In single-unit

Response to Stretch

Strength of contraction increases

Strength of contraction increases

Stress-relaxation response


Aerobic or anaerobic


Primarily anaerobic


II. Abnormal Muscle Function

A. Fatigue—progressive muscle weakness and fatigue

1. Failure to respond to external stimuli (i.e., NS activation)

2. Causes:

            a. Depletion of nutrients, ATP and/or O2

            b. Buildup of lactic acid and/or CO2

B. Abnormal contractions

1. Spasm—a sudden involuntary contraction of short duration

2. Cramps—painful spasmodic contraction of muscle fibers

3. Convulsion—violent tetanic contraction of entire muscle groups

4. Fibrillation—asynchronous contraction of individual muscle fibers resulting in flutter with no effective movement

5. Tic—spasmodic twitching common in eyelid and facial muscles

C. Myalgia—pain in one or more muscles

D. Myositis—inflammation of muscle tissue

E. Poliomylitis—viral based destruction of motor neurons in the anterior horn of the spinal cord

1. Muscular dystrophy results from a loss of motor neural innervations

F. Muscular dystrophy—term that describes any hereditary myopathy that causes muscle atrophy and degeneration (Polio is a muscular dystrophy)

1. Duchenne form

            a. Sex-linked

                        i. Carried by females; expressed by males

            b. Progressive loss of motor function

            c. Onset during early childhood

                        i. 2-6 years old

2. Fascioscapulohumeral form

            a. Affects muscles of face and shoulders

                        i. Expressed later in life

G. Myasthemia gravis—muscle weakness resulting from abnormalities in the neuromuscular junction

1. Likely cause: reduced number of ACh receptors

2. Affects face and neck—swallowing, speaking, chewing, eye movements

H. Tetanus—toxin of tetanus bacillus blocks ACh receptors


III. Muscle Mechanics

A. Lever systems


1. Levers are rigid bars that moves at a fixed point

            a. Fulcrum—fixed point

            b. Effort—applied force

            c. Load—resistance

2. Levers provide mechanical advantage or disadvantage

            a. Power lever—force (small) exerted over a relatively long distance

                        i. Mechanical advantage

                        ii. Large load over a small distance

            b. Speed lever—small loads over large distances

                        i. Mechanical disadvantage

3. Types of levers

            a. First-class

                        i. Load and effort are at ends, fulcrum in between

ii. Mechanical advantage or disadvantage depending on whether load or effort is closer to fulcrum

                        iii. Lift head off chest

            b. Second-class

i. Effort applied to one end, fulcrum at the other end and load is in between

ii. Mechanical advantage

iii. Standing on toes

            c. Third-class

                        i. Effort applied at point in between fulcrum and load

                        ii. Always at a mechanical disadvantage

                        iii. Most muscles

                        iv. Force is lost, speed is gained


IV. Muscle Shape

A. Based on organization of fascicles

B. Types




1. Parallel


            a. Short

            b. Attach to a central tendon

            c. Uni, bi, and multi—to how many sides of the tendon do the fascicles attach

3. Convergent—broad origin converging to a single tendon

4. Circular—fascicles arranged in concentric rings


V. Interactions of Muscles

A. Classification

1. Prime movers (agonists)—provide the major force for a specific movement

2. Synergists—aid prime movers

            a. Promote same movement

            b. Reduce unnecessary movements

3. Antagonists—muscle that opposes prime mover

a. Generally relaxed during prime movement although often provide opposing resistance

b. Can also be prime movers to return body to its original position

4. Fixators—type a synergist

            a. Immobilize a bone or a muscle origin

            b. Example: scapula


V. Criteria for Naming Muscles

There are about 650 skeletal muscles with 75 pairs that are involved in posture and general body movement. Skeletal muscles are named according to a number of criteria, each of which focuses on a particular structural or functional characteristic.

A. Location—bone or area of body with which the muscle is associated

B. Action

1. Flexor, extensor, abductus, etc.

C. Shape


1. Deltoid, trapezius, etc.

D. Relative size

1. Maximus, minimus, longus, etc

E. Point of attachment—origin and insertion points are included in name

1. Origin is always first

            a. Sternocleidomastoid

F. Number of origins (divisions)

1. Biceps, triceps, quadraceps

G. Direction of muscle fibers

1. Oblique, tranversus, rectus (parallel to axis)


VI. Muscles of the Axial Skeleton


A. Muscles of the head—eyes, facial expression and mastication

1. Facial expression






            a. Epicranius

                        i. Occipitalis

                                    Origin: Occipital bone

                                    Insertion: Galea aponeurotica

                                    Action: Pulls scalp posteriorly

                        ii. Frontalis

                                    Origin: Galea aponeurotica

                                    Insertion: Skin of eyebrows

                                    Action: Raise eyebrows; wrinkle forehead

            b. Corrugator supercillii

                                    Origin: Frontal bone

                                    Insertion: Skin of eyebrow

                                    Action: Draws eyebrows together; wrinkles forehead

            c. Orbicularis oculi

                                    Origin: Frontal and maxillary bones

                                    Insertion: Tissue of eyelid

                                    Action: Draws eyebrows downward (blink, squint)

            d. Orbicularis oris

                                    Origin: Maxilla and mandible (indirect)

                                    Insertion: Muscles and skin at edge of mouth

                                    Action: Closes lips; purses and protrudes lips (kiss)

e. Bucinator

                                    Origin: Maxilla and mandible

                                    Insertion: Orbicularis oris

                                    Action: Draws corner of mouth laterally

            f. Zygomaticus

                                    Origin: Zygomatic bone

                                    Insertion: Muscles and skin at edge of mouth

                                    Action: Raises corners of mouth upwards

            g. Platysma

                                    Origin: Fascia of chest

                                    Insertion: Lower margin of mandible

                                    Action: Depress mandible

            h. Risorius

                                    Origin: Fascia of masseter

                                    Insertion: Angle of mouth

                                    Action: Draws lips laterally

            i. Levator labii superioris

                                    Origin: Zygomatic and maxilla

                                    Insertion: Skin and muscle of upper lip

                                    Action: Opens lips; flares nostril

            j. Depressor labii inferioris

                                    Origin: Mandible

                                    Insertion: Skin and muscle of lower lip

                                    Action: Draws lower lip downward


2. Mastication


            a. Masseter

                                    Origin: Zygomatic arch

                                    Insertion: Angle of mandible

                                    Action: Prime mover—jaw movement


            b. Temporalis

                                    Origin: Temporal fossa

                                    Insertion: Coronoid process of mandible

                                    Action: Closes jaw; retracts mandible (jaw closed at rest)


            c. Pterygoids

                        i. Medial

                                    Origin: Sphenoid; p. plate, med. surface

                                    Insertion: Mandible

                                    Action: Elevates jaw


                        ii. Lateral

                                    Origin: Sphenoid; greater wing

                                    Insertion: Condyle of mandible

                                    Action: Protrudes mandible


d. Bucinator

                                    Origin: Maxilla and mandible

                                    Insertion: Orbicularis oris

                                    Action: Draws corner of mouth laterally


3. Muscles that move the tongue


            a. Extrinsic

                        i. Genioglossus

                                    Origin: Mandible, internal surface

                                    Insertion: Bottom of tongue, body of hyoid

                                    Action: Protrudes tongue


                        ii. Hyoglossus

                                    Origin: Hyoid

                                    Insertion: Bottom and lateral aspects of tongue

                                    Action: Depress tongue


                        iii. Styloglossus

                                    Origin: Styloid process of temporal bone

                                    Insertion: Bottom and lateral aspects of tongue

                                    Action: Retracts tongue


B. Muscles of the neck

1. Muscles that move the hyoid bone


            a. Insert on and either elevate or depress hyoid bone and larynx

            b. Form floor of oral cavity

            c. Suprahyoid—elevate

                        i. Digastric

                                    Origin: Lower margin of mandible

                                    Insertion: Hyoid

                                    Action: Elevates hyoid


                        ii. Stylohyoid

                                    Origin: Styloid process of temporal bone

                                    Insertion: Hyoid

                                    Action: Elevates hyoid


                        iii. Mylohyoid

                                    Origin: Medial aspect of mandible

                                    Insertion: Hyoid

                                    Action: Elevates hyoid


                        iv. Geniohyoid

                                    Origin: Inner surface of mandible

                                    Insertion: Hyoid

                                    Action: Superior and anterior movement of hyoid



            d. Infrahyoid—depress hyoid

                        i. Omohyoid

                                    Origin: Scapula

                                    Insertion: Hyoid

                                    Action: Depress hyoid


                        ii. Sternohyoid

                                    Origin: Manubrium

                                    Insertion: Hyoid

                                    Action: Depress larynx


                        iii. Thyrohyoid

                                    Origin: Thyroid cartilage

                                    Insertion: Hyoid

                                    Action: Depress hyoid


                        iv. Sternothyroid

                                    Origin: Manubrium and clavicle

                                    Insertion: Thyroid cartilage

                                    Action: Pulls thyroid cartilage inferiorly


2. Muscles of the neck and vertebral column


            a. Anterolateral

                        i. Sternocleidomastoid

                                    Origin: Manubrium and clavicle

                                    Insertion: Temporal bone

                                    Action: Prime mover—head flexion


                        ii. Scalenes

                                    Origin: Cervical vertebrae (transverse process)

                                    Insertion: First two ribs

                                    Action: Elevates ribs; flex and rotate neck


            b. Intrinsic muscles of the back (superficial)

                        i. Splenius (capitis and cervicis)

                                    Origin: Spinous process of C7-T6

                                    Insertion: Temporal and occipital bones (capitis); C2-C4, transverse process (cervicis)

                                    Action: Extend head (group); rotate and bend head (individual)


            c. Deep muscles of back: Erector spinae


            Multiple origins and insertions

                         i. Iliocostalis

                                    Origin: iliac crests (lumborum); inferior 6 ribs (thoracis); ribs 3-6 (cervicis)

                                    Insertion: Angles of ribs (L & T); C6-C4 (C)

                                    Action: Extend vertebral column; bend vertebral column when acting on one side


                        ii. Longissimus

                                    Origin: Transverse processes of lumbar through cervical vertebrae

                                    Insertion: Vertebrae and ribs superior to origin; Temporal bone (C)

                                    Action: L & T: Extend vertebral column; bend vertebral column when acting on one side; C: extend head, turn face towards same side


                        iii. Spinalis

                                    Origin: Spines of upper lumbar and lower thoracic vertebrae

                                    Insertion: Spines of upper thoracic and lower cervical vertebrae

                                    Action: Extend vertebral column


                        iv. Quadratus lumborum

                                    Origin: iliac creat

                                    Insertion: Upper lumbar vertebrae and 12th rib

                                    Action: Independent action: flex v. column laterally; Jointly: extend lumbar spine


3. Muscles of the thorax

            a. Intermediate back muscles—elevate and depress ribs


            a. Thoracic cage

                        i. External intercostals—vertebral column to costachondral junction

                                    Origin: Inf. Border of rib above

                                    Insertion: Sup. Border of rib below

                                    Action: Elevate rib cage (inspiration)


                        ii. Internal intercostals—sternum to angle of ribs

                                    Origin: Sup. Border of rib below

                                    Insertion: Inf. Border of rib above

                                    Action: Depress rib cage (expiration)


                        iii. Thoracic diaphragm—floor of thoracic cavity

                                    Origin: Inf. Border of rib cage and sternum

                                    Insertion: Central tendon

                                    Action: Prime mover of inspiration: Flattens and enlarges dimensions of thorax


4. Muscle of anterior and lateral abdominal wall

            a. Four paired flat muscles



                        i. Rectus abdominis—pubic crest to xyphoid process

                                    Origin: Pubic crest and symphysis

                                    Insertion: Xiphoid process and costal cartilages

                                    Action: Flex lumbar region of vertebral column


                        ii. External oblique—outer surfaces of lower 8 ribs to linea alba

                                    Origin: Outer surfaces of lower 8 ribs

                                    Insertion: Linea alba

                                    Action: Jointly: flex vertebral column; Individually: rotation and lateral flexion


iii. Internal oblique—iliac creasr to cartilage of lower 3 ribs, linea alba and pubic bone

                                    Origin: Fascia connecting to lumbar spine; iliac crest

                                    Insertion: Linea alba, pubic crest, last 3 ribs

                                    Action: Jointly: flex vertebral column; Individually: rotation and lateral flexion


iv. Tansverse abdominis—horizontal from 6 lower ribs, lumbar vertebrae, iliac crest to linea alba and pubic bone

                                    Origin: Inguinal ligament; fascia connecting to lumbar spine; iliac crest, last 6 ribs

                                    Insertion: Linea alba; pubic crest

                                    Action: Compress abdominal cavity


5. Muscles of pelvic floor


a. Pelvic diaphragm—muscles closing pelvic outlet

                        i. Levator ani

                        ii. Coccygeus

b. Urogenital diaphragm

                        i. Deep transverse perineus

            c. Superficial space

                        i. Ischiocavernosus

                        ii. Bulbospongiosus

                        iii. Superficial transverse perineus