Muscular-Skeletal Lecture:

I. Skeletal Tissue

II. Skeleton

III. Articulations

IV. Muscle Tissue

Skeletal Tissue

The skeleton includes various types of connective tissues, primarily cartilage and bone. During embryological

life, the skeleton is primarily cartilage but this is replaced by bone with minor amounts of cartilage persisting in

adult life.

I. Structure and Location of Cartilage

A. Basic structure

1. Primarily water

2. Non-vascular

3. No nervous tissue

4. Perichondrium—dense connective tissue surrounding cartilage

5. Cellular components

a. Chondrocytes

i. Secrete extracellular matrix

B. Types of cartilage

1. Hyaline—most abundant

a. Articular cartilage

b. Costal cartilage

c. Laryngeal cartilage

d. Tracheal and bronchial cartilage

e. Nasal cartilage

2. Elastic—more elastic fibers

a. Ears and epiglottis

3. Fibrocartialge—compressible with tensile strength

a. Alternating parallel rows of chondrocytes and collagen

b. Sites of heavy pressure and stretch

i. Vertebral discs

ii. Knee

C. Growth

1. Appositional

a. Cartilage forming cells embedded in perichondrium layer

2. Interstitial

a. Chondrocytes within lacunae in center of cartilage

*Although cartilage can be calcified, calcified cartilage is not bone. Bone is a separate type of connective tissue.

II. Bone

A. Function

1. Support

2. Protection

3. Movement

4. Mineral storage

5. Hematopoiesis

III. Classification of Bone

A. Type

1. Compact—external

2. Spongy—internal

B. Shape

1. Long bone

a. Longer than wide

b. Shaft with two ends

c. Mostly compact

d. Bones of limbs

2. Short bone

a. Cube-like

b. Mostly spongy

c. Sesamoid—bones embedded in tendon

i. Patella

3. Flat bone

a. Spongy bone embedded within parallel layers of thin compact bone

4. Irregular bone

a. Vertebrae and hip bones

b. Complicated shapes

c. Mostly spongy with a thin covering of compact bone

IV. Bone Structure

A. Structural levels

1. Gross anatomy

2. Microscopic anatomy

3. Chemical composition

B. Gross anatomy of long bones

1. Diaphysis: shaft; long axis

a. Constructed of a collar of thick compact bone

b. Central medullary cavity

i. Contains fat—yellow marrow

2. Epiphysis: bone ends

a. Exterior is compact bone

b. Interior is spongy bone

c. Articular cartilage covers joint surface

i. Absorbs stress

d. Epiphyseal line

i. Remnant of epiphyseal plate

ii. Region of hyaline cartilage that grows during development

C. Gross anatomy of short bones

D. Hematopoietic tissue: Red marrow

a. Red marrow cavities

i. Spongy bone of long bones

ii. Diploe of short bones

b. In adults, fat containing medullary cavity extends into epiphysis

i. Little red marrow

c. RBC’s produced primarily in diploe

V. Microscopic Structure of Compact Bone

A. Structural unit: Haversian System; Osteon

1. Elongated cylinders parallel to bone long axis

a. Concentric rings: lamella

2. Central (Haversian) canal: core of osteon

a. Blood vessels and NT

3. Perpendicular canals (perforating or Volkmanns)

a. Connect periosteum to central and medullary cavities

i. Blood supply and NT innervation

4. Lacunae: cavities containing osteocytes

5. Canaliculi: connect lacunae to each other and central canal

VI. Microscopic Structure Spongy Bone

A. Trabeculae: needle-like (flat) pieces

B. Trabeculae appear less organized than structures of compact bone

a. No osteon

b. Organization is based on lines of stress

c. Lamella and osteocytes are irregularly organized;

VII. Chemical Composition of Bone

A. Organic

1. Cells

a. Osteocytes

b. Osteoblasts

c. Osteoclasts

2. Osteoid: organic part of matrix; made by osteoblasts

a. Proteoglycans

b. Glycoproteins

c. Collagen fibers

B. Inorganic

1. Hydroxyapatites (mineral salts)

a. Calcium crystals in and around extracellular matrix

i. Make bones hard

Skeletal System

Skeleton is comprised of axial and appendicular structures.

I. Skeleton

A. Components

1. Bones

a. 206

2. Cartilage

3. Joints

4. Ligaments

B. Organization

1. Axial

a. Skull

b. Vertebral column

c. Rib cage

2. Appendicular

a. Limbs

b. Girdles that attach to axial

i. Shoulder and hip bones

II. Axial Skeleton--Skull

A. Skull Bones

1. Organization

a. Cranial

b. Facial

B. Cranial bones

1. Functions

a. Site for head muscle attachment

b. Encase brain and particular sense organs

C. Facial bones

1. Functions

a. Site for facial muscle attachment

b. Cavities for particular sense organs

i. Gustation

ii. Olfaction

iii. Vision

c. Framework for the face

d. Openings for air and food passage

e. Secure teeth

D. Sutures—connections (joints) between bones of skull

1. All bones of the skull except mandible

2. Cranial bone sutures

a. Coronal

b. Sagittal

c. Squamous

d. Lamboid

3. Sutures of facial bones are named based on name of bones that are connected

E. Organization of the skull

1. Cranial vault (calvaria; skullcap)

a. Forms the superior, lateral and posterior aspects as well as the forehead

2. Cranial base (floor)

a. Forms inferior aspect

b. Fossae—steps

a. Anterior

b. Middle

c. Posterior

3. Cavities

a. Cranial

i. Brain

b. Orbits

i. Eyeballs

c. Paranasal sinuses

i. Nasal cavity

d. Middle and inner ear

4. Openings

a. Foramina and fissures

b. Canals

III. Bones of the Cranium

A Paired

1. Parietal

2. Temporal

B. Unpaired

1. Frontal

2. Occipital

3. Sphenoid

4. Ethmoid

C. Frontal bone

1. Structural contribution

a. Anterior portion of cranium

b. Roofs of the orbits

c. Anterior cranial fossa

D. Parietal bone

1. Structural contribution

a. Superior and lateral aspects of the skull

E. Occipital bone

1. Structural contribution

a. Posterior wall and base of skull

b. Walls of the posterior cranial fossa

F. Temporal bones

1. Structural contribution

a. Lateral surface

b. Inferior to parietal (inferolateral aspects of skull)

G. Sphenoid bone

1. Articulates with all other cranial bones

2. Shape

a. Central Body

b. Three pairs of processes

i. Greater wings

ii. Lesser wings

iii. Pterygoid

H. Ethmoid bone

1. Forms bony area between nasal cavities and orbits

IV. Facial Bones: 14 Bones

A. Unpaired

1. Mandible

2. Vomer

B. Paired

1. Maxillae

2. Zygomatics

3. Nasals

3. Lacrimals

4. Palatines

5. Inferior conchae

C. Mandible: Unshaped lower jaw

1. Structure

a. Ramus (branch)

b. Body

2. Landmarks

a. Mandibular notch

b. Mandibular condyle (rounded articular projection)

c. Mandibular angle

d. Coronoid process

i. Attachment for temporalis muscle

e. Alveolar margin

i. Holds teeth

D. Maxillay bones (Maxillae): Upper jaw and central portion of facial skeleton

1. Keystone—all other facial bones articulate with maxillae

2. Landmarks

a. Aveolar margins

b. Palatine processes

i. Posterior projection

ii. Anterior 2/3’s of hard palate

c. Frontal processes

i. Superior projection to frontal bone

d. Zygomatic processes

i. Articualtions with zygomatic bones

E. Zygomatic bones: Cheek bones

1. Interolateral margins of orbits

F. Nasal bones

1. Bridge of nose

G. Lacrimal bones

1. Medial walls of each orbit

H. Palatine bones

1. Posterior part of the hard palate

I. Vomer: Nasal septum

J. Inferior nasal conchae

1. Part of the lateral wall of nasal cavity

K. Hyoid bone: Acts as moveable base for tongues

1. Not part of skull

2. Does not articulate with any other bones

3. Raise and lower larynx during swallowing

V. Vertebral Column (Spine)

A. General characteristics

1. 26 irregular bones

2. Transfers weight of trunk to lower limbs

3. Protects the spinal cord

4. Attachment point for ribs

5. Attachment point for muscles of back

B. Divisions (5)

1. Cervical curvature

a. 7 vertebrae (C1-C7)

b. Concave posteriorly

2. Thoracic vertebrae

a. 12 vertebrae (T1-T12)

b. Convex posteriorly

3. Lumbar curvature

a. 5 vertebrae (L1-L5)

b. Concave posteriorly

4. Sacrum: 5 fused vertebrae

a. Convex posteriorly

5. Coccyx: 4 fused vertebrae

C. Ligaments

1. Anterior and posterior ligaments

D. Intervertebral discs (shock absorbers)

1. Functions as a cushion-like pad between vertebrae

2. Two parts

a. Nucleus pulposus—semi-fluid

i. Gives elasticity and compressibility

b. Annulus fibrous

i. Forms outer collar to limit expansion

ii. Connects successive vertebrae

iii. Rupture: herniated disc (slipped disc)

E. General structure of vertebrae

1. Body (centrum)

2. Vertebral arch

a. Pedicle

b. Transverse process

c. Superior articular process

d. Laminae

e. Transverse process

f. Vertebral foramen

i. Successive foramen form vertebral canal

g. Intervertebral foramina

i. Spinal nerves pass through laterally

VI. Thoracic Cage

A. Elements

1. Dorsal (posterior): Vertebrae

2. Lateral: Ribs

3. Anterior: Sternum and costal cartilages

B. Function

1. Protective cage for vital organs

2. Attachment for muscle

3. Supports shoulders girdle and upper limbs

4. Participates in breathing

C. Sternum (fusion of three bones)

1. Manubrium, body and xiphoid process

2. Landmarks

a. Jugular notch

i. Common carotid artery issues from aorta

ii. Level of second and third vertebrae

b. Sternal angle

i. Level of second rib

ii. Disc between fourth and fifth thoracic vertebrae

c. Xiphisternal joint

i. Ninth thoracic vertebra

D. Ribs

1. Nomenclature based on Attachments

a. Posterior: thoracic vertebrae

b. Anterior

i. Vertebrosternal—True (7 pairs): sternum via intercostals cartilages

ii. Vertebrochondral—False (3 pairs): indirect attachment to sternum via costal cartilage

iii. Vertebral—Floating (2 pairs): no anterior attachment

2. Size:

a. Increase from 1-7

b. Decrease from 8-12

3. Structure

a. Head of rib: articulates with same-numbered thoracic vertebra

b. Neck

c. Tubercle: articulates with transverse process of same-numbered thoracic vertebra

d. Shaft: bulk of rib

VII. Appendicular Skeleton

A. General characteristics

1. Limbs and girdles

2. Pectoral girdle: attaches upper limbs to body trunk

3. Pelvic girdle: attached lower limbs to body trunk

4. Limb fundamental plan

a. Three segments connected by moveable joints

B. Pectoral girdle (not really a girdle—not connected posteriorly)

1. Bones (2)

a. Clavicle

i. Anterior

b. Scapula

i. Posterior

2. Characteristics

a. Only clavicle attaches to thoracic

b. Scapula is free to move across thorax

i. Arm very mobile

c. Socket of shoulder joint (glenoid cavity of scapula)

i. Shallow and poorly reinforced

ii. Does not restrict movement of humerous

3. Clavicle—double curve

a. Sternal end

i. Articulates sternum (manubrium)

b. Acromial end

i. Articulates scapula

c. Function

i. Restricts medial movement of arms

ii. Attachment for thoracic and shoulder muscles

d. Fracture

i. Curvature promotes anterior displacement

4. Scapula

a. Structure (triangle; three sides and angles)

b. Important landmarks

i. Acromion—anterior projection of spine; articulation with clavicle

ii. Coracoid process—anterior projection of superior scapular border; anchors bicep muscle

iii. Glenoid cavity—articulates with humerous

VIII. Upper Limb (30 bones)

A. Arm: shoulder to elbow

1. Humerus

2. Clinical consideration

a. Surgical neck (most likely site of fracture)

B. Forearm (antebrachium)

1. General considerations

a. Two parallel long bones: ulna and radius

b. Articulations

i. Proximal: humerus

ii. Distal: bones of wrist

iii. Radioulnar joints: radius and ulna both proximally and distally

2. Ulna: forms elbow joint with humerus; wide at proximal end, narrow at distal

3. Radius: narrow proximally, wide distally

C. Hand

1. Carpus: proximal structure of hand

a. Group of 8 bones (carpals) tied together with ligaments

b. Two irregular rows of four bones each

2. Metacarpus (5 wrist-like spokes)

a. No names; numbers (1-5) instead; 1 on thumb side

3. Phalanges (fingers or digits): 14 bones

a. Numbered 1-5 beginning with pollex (thumb)

b. Distal, middle and proximal phalanges for each digit

c. No middle phalanx for pollex

IX. Pelvic Girdle

A. Paired coxal (hip) bones

1. Coxal bones unite anteriorly

2. Coxal bones unite with sacrum posteriorly

3. Regions of coxal bone (fused during childhood)

a. Ilium: majority of the coxal bone

b. Ischium: posteriorinferior part of hip bone

c. Pubis

4. Pubic symphysis—fibrocartilage joining two pubic bones

X. Lower Limb

A. Thigh

1. Femur: largest, strongest bone in the body

a. Proximal articulation with hip

b. Distal articulation with tibia

c. Courses medially

i. Center of gravity

2. Patella

a. Sesamoid bone enclosed in tendon

B. Leg: two parallel bones connected by interosseous membrane; articulate with each other proximally and

distally (tibiofibular joints do not allow movement)

1. Tibia

a. Receives weight of the body from femur and transmits it to foot

b. Second strongest bone in body

2. Fibula

a. Head—superior end

b. Lateral malleolus

i. Articulates with talus

ii. Lateral ankle bulge

C. Foot: segmented; lever-like; support

1. Tarsus—7 tarsal bones (corresponds to carpus of the hand)

2. Metatarsus—5 small long bones (metatarsal bones)

a. Metatarsal 1-5

3. Phalanges—14 bones; smaller and less moveable than those of hand

Articulations

I. Classification of Joints

A. Structural classification

1. Based on material binding bones together and presence or absence of a cavity

2. Types

a. Fibrous

b. Cartilaginous

c. Synovial

B. Functional classification

1. Based on amount of movement permitted

2. Types

a. Synarthroses

i. Immoveable

b. Amphiarthroses

ii. Slightly moveable

c. Diarthroses

iii. Freely moveable

II. Synovial Joint Movement

A. Background

1. Skeletal muscles have a minimum of two attachment points

a. Origin—immoveable bone

b. Insertion—moveable bone

2. Contraction across joint moves insertion towards origin

3. Types of movement

a. Gliding (simple)

i. Surfaces slip or glide over another similar surface

b. Angular—increase or decrease angle between bones

i. Flexion—decrease angle on sagittal plane

ii. Extension—increase angle on sagittal plane

iii. Abduction—away from midline

iv. Adduction—toward midline

v. Circumduction—movement describing a conical space

vi. Rotation—turn bone along its own long axis

vii. Supination and pronation—movement of radius and ulna; s. parallel; r. radius over ulna

viii. Inversion and eversion—sole of foot medial or lateral

ix. Protraction and retraction—non-angular anterior and posterior movement in transverse plane

x. Elevation and depression—lift body part superiorly

xi. Opposition—thumb

III. Types of Synovial Joints

A. Categories

1. Plane—articulating surfaces are flat

a. Slipping and gliding

i. Intracarpal joints

2. Hinge—projection of one bone fits into the trough of another bone

a. Uniplanar movement

b. Flexion and extension only

3. Pivot—conical end of one bone fits into sleeve of another

a. Uniaxial rotation

4. Condyloid (knucklelike)—oval surfaces fit into complimentary concavity

a. Permits angular movement

5. Saddle

a. Greater movement than condyloid

b. Both concave and convex surface

6. Ball and Socket—spherical head articulates with cuplike socket

a. Multiaxial

b. Most freely moving

Muscle and Muscle Tissue

I. Background

A. Muscle types

1. Skeletal

a. Striated

b. Voluntary

2. Cardiac

a. Striated

b. Involuntary

3. Smooth

a. Non-striated

b. Involuntary

B. Common features

1. Elongated cells—muscle fibers

2. Myofilaments

a. Actin

b. Myosin

3. Terminology

a. Myo and sacro

C. General functions

1. Movement

2. Maintain posture

3. Stabilize joints

4. Temperature homeostasis

II. Gross Anatomy of Skeletal Muscle

A. Muscles are organs comprised of:

1. Muscle fibers

2. Connective tissue

3. Blood vessels

4. Nervous tissue

B. Organization

1. Individual fibers are surrounded by endomysium

a. Areolar connective tissue

2. Multiple fibers are bundled as fascicles

3. Fascicles are bound by collagen sheath

a. Perimysium

4. Epimysium then surrounds all fascicles of an entire muscle

5. Deep fascia binds muscles into functional groups

III. Microscopic Anatomy

A. Terms

1. Sarcolemma—plasma membrane surface

2. Sarcoplasm—cytoplasm of muscle cells

3. Myofibrils—contractile elements of skeletal muscle

B. Striations

1. A bands—dark bands

2. I bands—light bands

3. H band (within A band)

a. Visible only in relaxed muscle

4. M line

a. Bisects H band

5. Z disc (membrane)

a. Midline in I band

C. Sarcomere—region of myofibril between two successive Z discs

1. Functional unit of skeletal muscle

D. Microfilaments (myofilaments) with in bands

1. Thick filaments

a. Run entire length of A band

b. Myosin

2. Thin filaments

a. Extend across I band and part of the way into A band

b. Actin

3. Z disc—protein sheet connecting myofibrils together

E. Ultrastructure and molecular composition

1. Thick filaments

a. Myosin

b. Rodlike tail terminates in two globular heads

c. During contraction heads (cross bridges) interact with thin myofilaments

2. Thin myofilaments

a. Actin

3. Regulatory proteins

a. Tropomyosin

i. Sprials around action

ii. Block myosin head binding sites during relaxed state

b. Troponin—polypeptide complex

Contraction of Skeletal Muscle

I. Sliding Theory of Contraction

Sliding Theory of Contraction: during contraction, thin filaments slide past thick ones so that actin and myosin

filaments overlap to a greater degree

A. Overview

1. Prior to contraction

a. Cross bridges are disengaged

b. All bands distinct

2. Nerve impulse initiates contraction

3. Cross bridges engage

4. ATP splits

a. Energy used for swinging of cross bridges

5. Actin filaments pulled together

a. H zone and Z disc smaller or lost

6. I band reduced

7. Cross bridges disengage

8. Crossbridges and actin filaments return to original position

II. Specifics of Contraction

A. During relaxed state

1. Ca2+ concentration in sarcoplasm is low

a. Ca2+ is stored in sacroplasmic tubules

2. Troponin-tropomyosin complex attached to actin filament

a. Tropomyosin positioned to block myosin binding sites on actin filament

3. ATP and inactive ATPase bound to myosin head

a. Low energy configuration

i. Binding to actin is not possible

B. Events during contraction

1. Nerve impulse (afferent signal) from motor neuron generates action potential in nerve cell

a. AP propagated along sarcolemma and down T tubules

2. Myosin ATPase activated

a. ATP splits

i. High energy myosin-ADP complex

3. AP causes release of Ca2+ from sarcoplasmic reticulum

4. Ca2+ binds to troponin

a. Molecular shape of troponin changes

i. Tropomyosin is removed from binding site of mysosin on the actin filament

b. Myosin attaches to actin

5. Contraction: Potential energy stored in high-energy configuration is used to pivot myosin head

a. Myosin head bends as it pulls on actin

b. ADP and inorganic phosphate are released from myosin

6. New ATP attached to myosin head

a. Cross bridge simultaneously detaches

b. Following death, no ATP and muscle fibers cannot relax

i. Rigor mortis

7. If no new impulse, Ca2+ is pumped back into sarcoplasmic reticulum (SR)

a. Relaxation occurs

8. If Ca2+ present from additional impulse, cycle repeats

a. Myosin head “steps” to next binding site on actin

III. Regulation of Contraction

A. Neuromuscular junction—functional connection between somatic nervous system and muscles

1. Motor neuron axons bifurcate to form multiple endings

a. Separate endings synapse with individual nerve fibers

i. Each nerve fiber synapses with only a single motor neuron

ii. Motor neurons can synapse with multiple nerve fibers

2. Synapse—site of communication between neuron and muscle (neuron to neuron in nervous system)

a. Contact is not direct

i. Physical separation—synaptic cleft

b. Requires signal to be transduced into a chemical signal

i. Neurotransmitter

ii. ACh is NT at neuromuscular junction

3. Motor end plate—physical modification of sarcolemma where neuron synapses with fiber

a. ACh receptors located on motor end plate

B. Transduction events:

1. Nerve impulse from somatic NS

2. ACh released from pre-synaptic motor neuron

3. ACh binds to receptors

a. Na+ channels open

b. Inward depolarizing current initiates an action potential (see subsequent lectures on neurophysiology)

c. ACh is enzymatically destroyed

i. Acetylcholinesterase

4. Action potential is propagated along sarcolemma and down T tubules

5. Ca2+ is released from SR (see above for resulting effects)

6. Ca2+ is removed by continuously active Ca2+ pumps

a. At low enough concentrations, contraction ceases

7. At the level of individual muscle fibers (cells), contraction is all or nothing

a. In response to threshold stimuli, action potentials are generated in a non-graded fashion

8. Refractory period—cells must re-polarize before another AP can occur

IV. Muscle Metabolism

A. ATP is the sole source of energy for contraction

B. Little ATP is stored but it is regenerated (recycled) rapidly

1. Direct phosphorylation of ADP by creatine phosphate

2. Anaerobic glycolysis

a. In the absence of oxygen, glycolytic products (pyruvic acid) are metabolized to lactic acid producing

additional small quantities of ATP

3. Aerobic respiration

a. 95% of ATP during light exercise

b. In presence of oxygen, products of glycolysis are broken down entirely with the generation of

significant amounts of ATP

4. Glycogen is the source of glucose for both aerobic and anaerobic metabolism

V. Comparison of Skeletal, Cardiac and Smooth Muscle

Characteristic Skeletal Cardiac Smooth

Location Attached to bones,

fascia and skin

Walls of heart Single-unit: visceral

organs

Multi-unit: Internal

eye muscles, large

airways and arteries

Appearance Single, long,

cylindrical, striated,

multinucleate

Branching chains of

cells, uni-nucleate,

striated

Single, non-striated,

uni-nucleate

Connective Tissue Epimysium,

perimysium,

endomysium

Endomysium Endomysium

Sarcomere Present Present None

T Tubules Present at each end Present at on end None

Gap Junctions None Intercalated discs In single-unit

Neuromuscular

Junctions

Present None In multi-unit

Regulation of

Contraction

Somatic NS;

voluntary

Autonomic NS,

intrinsic

(pacemaker),

hormones,

involuntary

Autonomic NS,

hormones, local

regulation, response

to stretch

Ca2+ Source SR SR, extracellular

fluid

SR, extracellular

fluid

Role of Ca2+ Via troponin/actin

interactions

Via troponin/actin

interactions

Via

calmodulin/myosin

interaction

Pacemakers None Present In single-unit

Nervous System

Affects

Excitation Excitation or

inhibition

Excitation or

inhibition

Speed of

Contraction

Varies: slow to fast Slow Very slow

Rhythmic

Contraction

None Yes In single-unit

Response to Stretch Strength of

contraction

increases

Strength of

contraction

increases

Stress-relaxation

response

Respiration Aerobic or

anaerobic

Aerobic Primarily anaerobic

VI. 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

V. Muscle Shape

A. Based on organization of fascicles

B. Types

1. Parallel

2.Pennate

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

VI. 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)