Muscular System

Functions:

1. Movement

2. Stabilization

3. Storing and moving substances internally

4. Thermogenesis

Properties:

Excitability

Contractility

Extensibility

Elasticity

Skeletal Muscle

•Striated

•Multiple Nuclei

•Long fibers

•Tendons and bones

•Voluntary movement

Cardiac Muscle

•Striated

•Intercalated discs

•Branched fibers

•Heart

•Involuntary movement

Smooth Muscle

•Not striated

•Spindle shaped fibers

•Walls of hollow organs

•Involuntary movement

Muscle Names

Direction of fascicles (ex. Rectus, transverse, oblique)

Size (ex. Maximus, longus, latissimus)

Shape (ex. Deltoid, trapezius, orbicularis)

Action (ex. Flexor, abductor, pronator)

Number of origins (ex. Biceps, triceps)

Location (ex. Temporalis, frontalis)

Origin and insertion (ex. Sternocleidomastoid)

Deep FasciaEpimysium – superficial

Perimysium – surrounds fascicles

Endomysium – surrounds fibers

Join to form tendons and aponeuroses

Motor unitsMotor neuron and all the fibers contacted

“All or nothing”

Neuromuscular junction - synapse between neuron and motor end plate

Acetylcholine (ACh)

Excitation-contraction couplingAction potential moves down T-

tubules to SR

SR releases calcium through release channels

Ca2+ binds to troponin - moves complex and opens binding sites

Contraction begins

Ca2+pumps and calsequestrin

Sliding Filament MechanismCa2+ binds to troponin

Myosin binding sites open

ATP hydrolysis energizes myosin

Crossbridges form

Power stroke (ADP released)

Detachment (New ATP binds)

Muscular controlPrecision vs. power - how many fibers are in the

motor unit?

Twitch contraction

Refractory period

Muscular controlWave summation due to increased frequency

of stimulation Tautness of elastic components + partial filament

contraction Tetanus (unfused and fused)

Muscular control

Motor unit recruitment - more active units

Tone - small numbers of motor units always active (weak, involuntary contractions)

Muscle Action

•Origin/Insertion

•Muscles work in groups:•Agonist•Antagonist•Synergist

Isotonic vs. Isometric

Isotonic -muscle changes length (generates movement)

Isometric - muscle holds position