Muscular System

• Function

  • Movement → By pulling on bone

  • Maintaining Posture→ Holding body upright

  • Stabilizing Joints → Strong muscles hold joints in place

  • Generating Heat → Contraction creates friction+ heat

Components

• Muscle Fiber= Muscle cell

• Attachment to skeleton:

  • Tendon= attach muscle to bone

  • Origin= Attachment point on muscle to bone that is not moving (stable)

  • Insertion= Attachment point on muscle to moving bone

  • Insertion PULLS on bone toward origin

    
    

    
    

    Muscle Attachment ( 2 types )

    • Direct (fleshy) attachment= epimysium of muscle directly fused to periosteum (bone) or perichondrium (cartilage)

    • Indirect Attachment= Fibrous connective tissue extends beyond muscle as tendon or aponeurosis (sheet like)

    • Anchors muscle to bone (or to another muscle)

• Types of Muscle tissues:

  • Cardiac Muscle

    • Heart

    • Striated

    • Involuntary

    • Contracts at steady rate (sinus rhythm)

  • Smooth Muscle

    • Walls of hollow organs

    • Non- Striated

    • Involuntary

    • Slow sustained contractions (peristalsis)

  • Skeletal Muscle

    • Attached to bones

    • Striated

    • Voluntary

    • Adaptable, powerful, tire easily, and require rest

• Characteristics of Muscle Tissue

  • Excitability/ Irritability= Ability to recieve and respond to a stimulus

  • Contractility= Ability to shorten (contract) when stimulated

  • Extensibility= Ability to recoil and go back to resting length

• Muscle Contractions

  • Isotonic (moving)= Change in muscle length to move load

  • Isometric (Not Moving)= Tension builds in muscle, but length is unchanged

• Types of Isotonic Contractions

  • Concentric Contraction= Muscle shortens and does work

    • Ex. Biceps Brachii when lifting an object

  • Eccentric Contraction= Muscle lengthens and does work

    • Ex. Gastrocnemius when walking uphill

• Also may describe phases of complete/ repetitive movement:

  • Muscles is shortening: centric phase

  • Muscles is lengthening: eccentric phase

  ex. Regarding the biceps brachii and elbow movement

  • Elbow flexion: Concentric phase

  • Elbow extension: Eccentric phase

• *MUSCLES ALWAYS PULL ON BONES NEVER PUSH*

Functional groups of Skeletal Muscles

• General contractile movement= insertion moves towards origin

• Prime Mover & Antagonist

  • Prime mover (Agonist) (first, primary)

    • Provides major force for movement

  • ex. Biceps brachii is the prime mover of elbow flexion

• Antagonist

  • Opposes (reverses, “undoes”) a movement

  • relaxed/ stretched when Prime Mover is contracted

    • ex. Triceps brachii is the antagonist of elbow flexion

  • Antagonist proves resistance for prime mover

    • prevents overshooting, helps slow down/ stop

  • Opposite sides of the joint (usually)

  • Functional roles are relative to movement

    • ex. Triceps brachii → Elbow flexion vs. extension

• Synergists

  • “syri”= together, “erg”=work

  • Help prime movers by:

    • Adding extra force to movement

    • Reducing undesirable movements

  • ex. The brachialis is the synergist of elbow flexion and extension

• Fixator (synergist subtype)

  • Immobilizes a bone or muscle’s movements

  • 1) Help maintain only desired movements

    ex. The deltoid is a fixator for elbow flexion

  • 2) Help maintain upright posture

    ex. The latissimus dorsi acts as a fixator when maintaining upright posture

• Benefits to having 4 functional groups

  • Smooth, coordinated, and percise movements

  • Gives one muscle multiple functions= efficiency

• Skeletal Muscle Anatomy

  • Entire skeletal muscle= organ→ several types of tissue together

  • Tissue in Muscle organ=

    • Proteins

    • Nervous tissue= controls voluntary contraction

    • Blood vessels (transportation):

      • Artery: O2, glucose delivery

      • Veins- CO2, waste removal

      • Capillaries- small & flexible, grow/repair as needed

• Skeletal Muscle Structure

  • Myofilament= Long, skinny protein

    • Slide over one another to shorten muscle (= sliding filamnet theory= contractions)

    • 2 Categories= thin, thick filaments

  • Sarcomere= one contractile unite

    • made of overlapping myofilaments

  • Myofibril= organelle (within cell) made of sarcomere arranged end to end (in a chain)

  • Muscle Fiber= muscle cell

    • bundle (group) of myofibrils

• Connective tissue sheaths (fascia)

  • Flat sheet of flexible collagen

  • Wrap around/ hold together structures

• Endomysium= fascia wrapped around each muscle fiber

  • Fasicle= bundle of muscle fibers

  • Perimysium= fascia wrapped around each fasicle

  • Epimysium= fascia wrapped aound group of fasicles

• Muscle Fiber=Muscle Cell

  • Plasma membrane= Sarcolemma

  • Cytoplasm= sarcoplasm

  • nucleus= fiber is a multinucleated cell

• Transvers Tubules (IT)

  • Continuation of sarcolemma “reaching” into fibers interior

  • Sarco Plasmic recticulum

    • Smooth endoplasmic recticulum (ER)

    • Stores/ releases calcium ions

• Specialized Organelles:

  • Glycosome (stores glycogen)→ stored glucose

    • Myoglobin (stores oxygen) → tons of mitochondria

      • (Sites of cellular respiration) ATP