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: Intercalated = inserted between

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 The Central Nervous System initiates a sequence to begin the sequence of events leading to contraction Action potential from the motor neuron moves down to terminal end and then calcium ions (Ca++) diffuse into the terminal Ca++ trigger the synaptic vesicles to release acetylcholine (ACh) ACh diffuses across synaptic clef to a receptor site on the sarcolemma ACh cause new action potential to spread from nerve to muscle Action potential spreads over the sarcolemma until it finds an opening It enters the opening to the sarcoplasmic reticulum, where it triggers the release of Ca++ into the sarcoplasm Ca++ cause active sites on actin to be exposed Myosin crossbridges link up with the active sites on actin Actin moves inward, sarcomere shortens, muscle fibers contract and use ATP Action potential = impulse

Stopping Muscular Contraction Acetylcholinesterase (AChE - enzyme) is released as muscle contracts and neutralizes the ACh No more action potential is traveling to muscle Calcium does not tighten so the crossbridges on mysoin release Muscles relax