JOEL G. SORIA, PT, MD

Chapter 7 - The Muscular System

• Body Movement• Maintenance of Posture• Respiration• Production of Body Heat• Communication• Constriction of Organs and Blood

Vessels• Heart Beat

Functions

• CONTRACTILITY: ability of skeletal muscle to shorten with force.

• EXCITABILITY: capacity of skeletal muscle to respond to a stimulus.

• EXTENSIBILITY: skeletal muscle can be stretched to their normal resting length and beyond to a limited degree.

• ELASTICITY: ability of skeletal muscle muscles to recoil to their original resting length after they have been stretched.

Functional Characteristics

Sarcomer

e

SarcoplasmicReticulum

Transverse Tubule

Capillaries

Nuclei

Bone

Tendon

Skeletal muscle

Epimysium(fascia)

Fasciculi

Endomysium

Muscle fiber

Mito

chondria

Myofibrils

Actin

Myosin

Sarcolema

Sarcomere – Basic structural and functional unit of skeletal muscle.– Each sarcomere extends from one Z-disk to

another Z-disk

Z-Disk – a network of protein fibers forming an attachment site for actin myofilaments

Sarcomere – Basic structural and functional unit of skeletal muscle.– Each sarcomere extends from one Z-disk to

another Z-disk

Z-Disk – a network of protein fibers forming an attachment site for actin myofilaments

ActinMyosi

n

• Troponin – attached at a specific interval along the actin and provide calcium binding sites on the actin myofilament

• Tropomyosin – located along the groove between the twisted strands of actin myofilament.

Actin

Myosin

1st the Central Nervous System

gives the order for muscle contraction

The order (to contract) reaches the Muscle thru

the Neuro-Muscular Junction

• Charge Difference– Higher concentration of Potassium (K+)

inside the cell membrane.– Potassium is more permeable than other

ions• Action Potential – Rapid depolarization and

repolarization of the cell membrane

IN

- - - --

-KPotassium

OUT

+ + + + ++

NaSodium

Mem

bra

ne p

ote

nti

al

Cell Membrane

1.Action potential arriving at the presynaptic terminal causes synaptic vesicles to move and to bind with the cell membrane

2.Synaptic vesicles release acetylcholine (Ach) into the synaptic cleft by exocytosis

3.Acetylcholine diffuses across the synaptic cleft

4.Acetylcholine binds to Acetylcholine receptor sites on Na+ channels in postsynaptic (muscle) cell membrane

5.Combination of Acetylcholine with its receptor site opens Na+ channels and causes and increase in the permeability of the muscle cell membrane to Na+. The movement of Na+ into the cell can result to action potential

ACh binds to receptors in the sarcolema band

spreads in all direction

Sends electrical impulse to the t-

tubules

Releases Calcium

Repolarizatio

nD

epol

ariz

atio

n

• Force of contraction:• Summation – Increase the force of the

contraction• Recruitment – Increase the number of muscle

fibers contracting

• Tetanus – Sustained contraction

• Rigor mortis – Muscles become rigid

– Types of muscle contraction– Isometric contraction – equal distance– Isotonic contraction – equal tension

– Concentric contraction– Eccentric contraction

–Muscle tone – Refers to the constant tension produced by the muscle over long periods of time

• Agonist – muscle that accomplishes a certain movement.

• Antagonist – muscle acting to oppose the agonist.

• Synergist – members of the same group acting to produce a movement

• Prime movers• Fixators