The Muscular System

Four Functions

Four Functions

• Irritability

• Contractibility

• Elasticity

• Conductivity

Types of Muscle Tissue

Types of Muscle Tissues

Types of Muscle Tissue

• All highly vascular for transport of oxygen, CO2, waste and sugars

• Human body has three types:

Skeletal Muscle

Skeletal Muscle

• Made of elongated cells called muscle fibers

• Each fiber has many nuclei and striations– Striations:

• Skeletal muscles are voluntary muscles and work in pairs– Antagonistic:

Function of Skeletal Muscles

• Five major functions:

Smooth Muscle

Smooth Muscle

• Forms the walls of the stomach, intestines, blood vessels, and internal organs

• Individual cells are spindle shaped with one nucleus

• No striations

Cardiac Muscle

Cardiac Muscle

• Location:

• Cells are cigar shaped

• Intercalated disc:

• Shares three characteristics with other types of muscle:

Moving Muscles• Muscles are attached to the outer layer of bone

with a tough fibrous cord called a tendon– Origin:

– Insertion:

– Action:

• Most muscles work in pairs; one contracts while one relaxes for smooth movement– Flexor:

– Extensor:

Muscle Structure

Muscle Structure

• From the outside in…– Epimysium:

– Fascicle:

• Perimysium:

• Muscle fiber: muscle cell, large, long, cylindrical, multinucleated and made mostly of microfilaments

– Sarcolema

– Sarcoplasma

– Sarcosomes

– Sarcoplasmic reticulum

– Endomysium

The Sarcomere Each muscle fiber is made up of threadlike

structures called myofibrils– Myofibrils –

• Actin:

• Myosin:

• These overlap, giving the striated appearance

– Thin actin filaments are anchored to a structure called the Z line

• Region from one Z line to the next is called…

The Sarcomere

The Sarcomere• Unit of muscle contraction is called the sarcomere

– Z disc: boundary found on either end of the sarcomere

• I, A, H bands: in-between Z discs, alternating light and dark bands

• I band – first band moving in from Z disc, composed of actin, light in color

• A band – second band, composed of actin and myosin, dark in color

• H Zone – middle of sarcomere, only myosin present, relatively light in color but darker than the I band

• H Zone – middle of the sarcomere• M line – dark line in the middle of H Zone

Sliding Filament Theory

• In May 1954, Hugh Huxley and Allan Huxley published their findings of the sliding filament theory

• The theory stated that skeletal muscle contracted when two types of filaments, consisting of the proteins myosin and actin, “slid” past each other without either filament’s length actually changing

Muscular Contraction

Steps of Muscular Contraction

1. The Central Nervous System initiates a sequence to begin the sequence of events leading to contraction

2. Action potential from the motor neuron moves down to terminal end and then calcium ions (Ca++) diffuse into the terminal

3. Ca++ trigger the synaptic vesicles to release acetylcholine (ACh)4. ACh diffuses across synaptic clef to a receptor site on the

sarcolemma5. ACh cause new action potential to spread from nerve to muscle6. Action potential spreads over the sarcolemma until it finds an

opening7. It enters the opening to the sarcoplasmic reticulum, where it

triggers the release of Ca++ into the sarcoplasm8. Ca++ cause active sites on actin to be exposed9. Myosin crossbridges link up with the active sites on actin10. Actin moves inward, sarcomere shortens, muscle fibers contract

and use ATP

Stopping Muscular Contraction

1. Acetylcholinesterase (AChE - enzyme) is released as muscle contracts and neutralizes the ACh

2. No more action potential is traveling to muscle

3. Calcium does not tighten so the crossbridges on mysoin release

4. Muscles relax