Muscular System Ch. 9 & 10

Muscle tissue *1 of the 4 major categories of tissues: 1.Epithelial Tissue 2.Connective Tissue a.CTP b.Cartilage c.Bone d.Blood 3.Muscle Tissue (1/4 body mass) 4.Nervous Tissue

Characteristics of Muscle Tissue 1.Excitability (responsiveness)– can receive & respond to stimuli 2.Contractility – can shorten when stimulated 3.Extensibility – can stretch beyond resting 4.Elasticity – can return to original shape

Functions of Muscle Tissue 1.Movement- 1.active generation of force 2.Smooth, cardiac too 2.Maintain posture 3.Heat production-shivering 4.Stabilize joints

Types of Muscle Tissue A.Skeletal – striated & voluntary B.Cardiac – striated & involuntary C.Smooth – unstriated & involuntary

1.Nerves & blood vessels – Every skeletal muscle fiber innervated by 1 nerve ending – Highly vascularized for nutrients, oxygen, energy, waste removal (1 artery, >1 veins) – Connective tissue sheaths hold fibers together Gross Anatomy of Skeletal Muscle

2. Connective tissue wrappings a.Epimysium - surrounds whole muscle Dense irregular connective tissue b.Perimysium - surrounds each fascicle (bundles of muscle fibers) Dense regular connective tissue c.Endomysium - surrounds each muscle fiber Areolar loose connective tissue

Functions of Connective Tissue Wrappings 1.Support muscle fibers 2.Hold muscle together 3.Keeps muscles from overstretching 4.Contribute to elasticity of muscle 5.Carries blood vessels & nerves to individual muscle fibers

Gross Anatomy of Skeletal Muscle 3. Attachments (tendons/aponeuroses) a)Origin - point of attachment to immoveable (or less moveable) bone b)Insertion - point of attachment to moveable bone Origins/insertions may be: 1)Direct attachments - epimysium fused to periosteum or perichondrium 2)Indirect attachments - via tendons or aponeuroses

Microscopic Anatomy of Skeletal Muscle *Muscle cells = muscle fibers 1.Muscle fiber a.Large cells: 10 to 100 µm in diameter and up to 30 cm long! b.Multi-nucleate c.Sarcolemma = plasma membrane d.Sarcoplasm = cytoplasm Contains organelles found in other cells Has glycosomes - granules of stored glycogen Has myoglobin - red pigment that carries oxygen e.Sarcoplasmic reticulum = smooth ER around the myofibrils that store, regulate, and release calcium

Microscopic Anatomy of Skeletal Muscle 2. Myofibrils (organelle)-contain filaments 3. Myofilaments (protein filaments) a.Thick = Myosin b.Thin = Actin

Myofibril Anatomy 1.Z line (disc) – anchor for thin filaments 2.M line – anchor for thick filaments 3.A band – dark area; extends length of the thick filaments 4.I band – light area; thin myofilaments only Z disc is center of I band 5.H zone – thick myofilaments only M line is center of H zone 6.Sarcomere = functional unit of skeletal muscle; Z disc to Z disc; aligned end to end within myofibril

Striations -I BAND AND A BANDS OF EACH MYOFIBRIL IN EACH MUSCLE FIBER NEARLY PERFECTLY ALIGNED -CONTRACTION-, SARCOMERE SHORTENS (Z DISCS COME CLOSER TOGETHER) AND H ZONE DISAPPEARS ENTIRELY

Molecular Composition of Myofilaments 1. Myosin – Makes up thick myofilaments (~300 myosin molecules per thick myofilament) – Rodlike tail & 2 globular heads – Heads contain binding sites for actin & ATP

Molecular Composition of Myofilaments 2. Actin – Makes up thin myofilaments – Made of G-actin (polypeptide subunits) Contain binding sites for myosin heads G-actin strung together; 2 twisting strands make up thin myofilaments

Molecular Composition of Myofilaments 3.Tropomyosin – In thin myofilaments – Rod-shaped protein that runs along actin – Blocks myosin-binding sites on actin when muscle relaxed 4.Troponin – In thin myofilaments – 3 polypeptide subunit complex 1 subunit bound to actin 1 subunit bound to tropomyosin 1 subunit binds Ca 2+

Skeletal Muscle Attachments Origin - point of attachment to immoveable (or less moveable) bone – Typically proximal to insertion Insertion - point of attachment to moveable bone – Typically distal to origin Origins/insertions may be: -Direct attachments - epimysium fused to periosteum or perichondrium -Indirect attachments - tendons or aponeuroses

Functional Groups 1.Prime Movers (agonists) Muscle that provides primary force for causing a specific movement Ex. Biceps brachii - forearm flexion Ex. Triceps brachii - forearm extension 2.Antagonists Opposes, reverses, or steadies a movement from prime mover Located on opposite side of joint as prime mover Ex. Triceps brachii - forearm flexion

Functional Groups 3.Synergists Assist prime movers by adding extra force to same movement or preventing unwanted movement Ex. Wrist extensors prevent wrist bending when finger flexors contract 4.Fixators Name for Synergists that immobilize bone or muscle’s origin Ex. Muscles that maintain upright posture

Naming Skeletal Muscles 1.Location - bone/body region muscle associated with Ex. Intercostals - between ribs 2.Shape - distinctive shape of muscle Ex. Deltoid = triangle, Trapezius = trapezoid

Naming Skeletal Muscles 3.Size - relative size of muscle Ex. Maximus = large (Glutues maximus), Minimus = small (Gluteus minimus)

Naming Skeletal Muscles 4.Direction of muscle fibers – In relation to some imaginary reference line Ex. Transversus = fibers run at right angles (Transversus abdominis), Rectus = straight (Rectus femoris)

Naming Skeletal Muscles 5.Number of origins - Ex. Biceps = 2 origins (biceps brachii), triceps = 3 origins (triceps brachii)

Naming Skeletal Muscles 6. Location of attachments - origin named first Ex. Sternocleidomastoid (origin = sternum & clavicle, insertion = mastoid process of temporal bone)

Naming Skeletal Muscles 7.Action - movement muscle produces Ex. Adductor = adduction (adductor longus = thigh adduction)

Arrangement of Fascicles (bundles) 1.Circular - fascicles arranged in concentric rings Ex. Orbicularis oris

Arrangement of Fascicles 2.Convergent - fascicles converge toward a single tendon (triangular) Ex. Pectoralis major

Arrangement of Fascicles 3.Parallel - long axes of fascicles run parallel to long axis of muscle Ex. sartorius

Arrangement of Fascicles 4.Fusiform - spindle- shaped Ex. Biceps brachii

Arrangement of Fascicles 5. Pennate - fascicles attach to central tendon at an angle a.Unipennate Ex. Extensor digitorum longus b.Bipennate Ex. Rectus femoris c.Multipennate Ex. Deltoid – Strong muscles, many fibers

Lever Systems Lever - rigid bar (bones) that moves about a fixed point Fulcrum - fixed point (joints) Effort - force applied by a muscle on the insertion point Load - resistance (bone itself + associated tissues)

Mechanical Advantage “Power levers” Load is closer to fulcrum than effort applied, small effort can move large load

Mechanical Disadvantage “Speed levers” Load is farther from fulcrum than effort applied, effort must be greater than the load to move it

First-class levers Effort applied at one end of lever Load at other end of lever Fulcrum in between effort & load Operate at mechanical advantage or disadvantage

Second-class levers Effort applied at one end of lever Fulcrum at other end of lever Load in between effort & fulcrum Always at mechanical advantage

Third class lever Load at one end of lever Fulcrum at other end of lever Effort in between load & fulcrum Always at mechanical disadvantage