muscle system

properties of muscle tissues

• Electrical excitability – produce and propagate action potentials

  • autorhythmic (heart)

  • chemical (NT)

• Contractility – generate force /tension in response to AP

• Extensibility – stretch without being damaged

• Elasticity – return to original shape after contraction or extension

5 basic functions 

• Produce movement

• Stabilize body position

• Store and remove materials from the body (sphincters)

• Generate heat

• Protect

coverings- superficial fascia

• Hypodermis

• Separates muscle form skin

• Areolar CT and adipose

• Functions

  • pathway for nerves and vessels

  • stores most of body’s triglycerides

  • insulation from heat loss

  • protection

coverings- deep fascia (Levels of organization)

• Epimysium – encircles the entire muscle

• Perimysium – surrounds fascicles (bundles)

• Endomysium - areolar CT that surrounds each myofiber in the bundl

details of deep fascia

Tendons

• dense regular CT that attaches to periosteum of bone

organelles in skeletal muscle

• Sarcolemma

• Transverse tubules

  • AP travel along t-tubules

• Sarcoplasm

  • contains myoglobin (binds oxygen within muscle cell)

• Sarcoplasmic reticulum

  • stores calcium

    • Ca2+ release from cistern triggers muscle contraction

• Triad

  • T-tubule and two cistern

basic structural unit of muscle cell sarcomere

• Myofilaments form sarcomeres which then make myofibrils

• Z disc

• Isotropic (I) band

• Anisotropic (A) band

• H zone

• M line

sarcomere contractile proteins

• Actin – contains a myosin binding site for each myosin head to attach

• Myosin – motor protein (push or pull to generate movement

sarcomere structural proteins

titin, myomesin, nebulin and dystrophin

Titin

• one molecule covers from Z disc to M line

• anchors myosin to M line and Z dics

• helps return to resting length after contraction

myomesin

 forms the M line

Nebulin

• long, non-elastic

• wraps around each actin filament

• anchors to Z disc

dystrophin

• cytoskeletal protein

• links actin filaments to sarcolemma

• re-enforce sarcolemma

• assist in transmission of tension to the tendon

sarcomere regulatory proteins

• Troponin

  • holds tropomyosin in place

• Tropomyosin

  • covers myosin binding site on the actin and prevents contraction

sliding filament mechanism

• Sarcomere length decreases; thus muscle fiber length decreases

  • Z discs are closer together

  • actin slides toward A band to produce maximum overlap (I band disappears)

• No change in actin or myosin length

motor unit

• Nerve axons branch and innervate three to several hundred skeletal muscle fibers

• Somatic motor neuron plus all the myofibers it stimulates

• Motor unit recruitment –weakest units recruited first with stronger ones late

neuromuscular junction

• NMJ components

  • neural – end brush with end bulbs of the neuron (axon terminal of motor nerve)

  • motor end plate – region of the sarcolemma directly across the synapse from the end bulbs

• Anatomy of the NMJ

  • axon terminal with End bulb

  • synaptic vesicles filled with neurotransmitter (ACh)

  • synaptic cleft (intermembranous space)

  • synaptic trough (gutter)

  • subneural cleft

muscle metabolism: ATP

• ATP present in a myofiber is enough to power contraction for a few seconds

• Muscle fibers must make more AT

muscle metabolism- oxygen debt

• Oxygen Debt = Recovery Oxygen Uptake

  • oxygen over resting consumption needed for activity

  • converts lactic acid back to glycogen stores in liver

  • re-synthesizes CrP

  • re-oxygenates myoglobin

muscle contraction types

twitch, tetanus, treppe, isotonic, isometric and muscle fatigue

twitch

• Brief contraction

• Stimulus

• Latent period (2 msec)

• Contraction period (10 - 100 msec)

• Relaxation period (10-100 msec)

• Refractory period

tetanus

• Incomplete or Unfused Tetanus : Stimulate 20-30 times per second

• Complete or Fused Tetanus: Stimulate 80-100 times per second

treppe

• Staircase phenomenon

• Increase concentrations of Ca2+ in successive contractions

• Warming up

isotonic

• Muscle tension remains almost constant

• Length changes

• Types

  • concentric isotonic contraction (lift load)

  • eccentric isotonic contraction (put down load)

Isometric

• Increased tension

• tension is less than load resistance

• No change in muscle length

• Used to stabilize joints

muscle fatigue

• Inability of a muscle to maintain force of contraction

• Central fatigue – brain says you are tired before muscle fatigue sets i

general info of muscle tone

• Even at rest, tautness or tension exists within healthy muscle

  • Involuntary contraction of motor units

    • Groups of motor units are alternating between active and inactive

    • Constantly shifting pattern

  • Established by brain and spinal cord neuron

tone types

• Flaccidity

• Hypotonia

• Hypertonia

  • Spasticity

    • Stiffness

  • Rigidity

    • Increased muscle tone without altered reflexes

muscle fibers

• contraction- relaxation speed: slow oxidative fibers

• contraction- relaxation speed: fast oxidative- glycolytic fibers

• contraction- relaxation speed: fast glycolytic fibers

myoglobin content

red muscle fibers and white muscle fibers

general information of muscle lever systems

• Lever – rigid structure that moves around affixed point

• Fulcrum – fixed point

• Effort – force that causes movement

• Load (Resistance) – force that opposes movement

• Mechanical Advantage – smaller effort can move a heavier load

• Mechanical Disadvantage – larger effort moves a lighter load

lever classes

• first class (EFL)

• second class (FLE)

• third class (FEL)