Muscular System Im going to pump you up

Muscular System I’m going to pump…. you up!

Origins • Latin musculus "a muscle, " literally "little mouse, " • The shape and movement of some muscles (notably biceps) were thought to resemble mice. Myo- is the Greek prefix. • sarco- "flesh, fleshy, of the flesh, "

Sarcasm • Greek sarkasmos "a sneer, jest, taunt, mockery, " literally "to strip off the flesh, “ Can you give me examples of sarcasm?

Muscular System Functions • • • Body movement (Locomotion) Maintenance of posture Production of body heat (Thermogenesis) Stabilizing Joints Respiration – Diaphragm and intercostal contractions • Communication (Verbal and Facial) • Constriction of organs and vessels – Peristalsis of intestinal tract/blood vessels; pupils • Heart beat

Properties of Muscle • Excitability: capacity of muscle to respond to a stimulus • Contractility: ability of a muscle to shorten and generate pulling force • Extensibility: muscle can be stretched back to its original length • Elasticity: ability of muscle to recoil to original resting length after stretched

Types of Muscle • Skeletal – Attached to bones (40% of body weight) – Voluntary • Smooth – In the walls of hollow organs, blood vessels, eye, glands, uterus, skin – Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow, – Involuntary • Cardiac – Heart: major source of movement of blood – Involuntary

Connective Tissue Sheaths – Epimysium. Dense regular connective tissue surrounding entire muscle – Perimysium. Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle – Endomysium. Loose connective tissue that surrounds individual muscle fibers

Structure of a Skeletal Muscle Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

Nerve and Blood Vessel Supply • Motor neurons – stimulate muscle fibers to contract – Neuron axons branch so that each muscle fiber (muscle cell) is innervated – Form a neuromuscular junction (myoneural junction) • Capillary beds surround muscle fibers – Muscles require large amounts of energy – Extensive vascular network delivers necessary oxygen and nutrients and carries away waste.

Muscle Tissue Types

Skeletal Muscle • • • Long cylindrical cells Many nuclei per cell Striated Voluntary Rapid contractions

Basic Features of a Skeletal Muscle • Muscle attachments – Most skeletal muscles run from one bone to another – One bone will move – other bone remains fixed • Origin – less movable attachment • Insertion – more movable attachment

Muscle Attachments

Antagonistic Muscles

Skeletal Muscle Structure • Composed of muscle cells (fibers), connective tissue, blood vessels, nerves • Fibers are long, cylindrical, and multinucleated • Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm- 4 cm in length • Develop from myoblasts; numbers remain constant • Striated appearance • Nuclei are peripherally located

Microanatomy of Skeletal Muscle

Muscle Fiber Anatomy • Myofibrils -cylindrical structures within muscle fiber – Are bundles of protein filaments (myofilaments) • Two types of myofilaments 1. Actin filaments (thin filaments) 2. Myosin filaments (thick filaments) – When myofibril shortens, muscle shortens (contracts)

Parts of a Muscle

Sarcomeres: Z Disk to Z Disk

Structure of Actin and Myosin

• • • Thin Filament: composed of 3 major proteins 1. F (fibrous) actin 2. Tropomyosin 3. Troponin Two strands of fibrous (F) actin form a double helix Composed of G actin monomers each of which has a myosin-binding site (see yellow dot) Tropomyosin: an elongated protein winds along the groove of the F actin double helix. Troponin - protein which is released when there is muscle damage. In a myocardial infarction (heart attack) they look for troponin in the blood to help diagnose a heart attack. Actin (Thin) Myofilaments

Z line

Sarcomere Relaxed

Sarcomere Completely Contracted

Sliding Filament Model of Contraction • Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree • In the relaxed state, thin and thick filaments overlap only slightly • Upon stimulation, myosin heads bind to actin and sliding begins

Neuromuscular Junction

Neuromuscular Junction • Region where the motor neuron stimulates the muscle fiber • The neuromuscular junction is formed by : 1. End of motor neuron axon (axon terminal) • Terminals have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh) 2. The motor end plate of a muscle • A specific part of the sarcolemma that contains ACh receptors • Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft

Motor Unit All the muscle cells controlled by one nerve cell