M2MS

• Skeletal Muscle

  • Usually attached to bones

  • Under conscious control

  • Somatic nervous control

  • Striated
• Cardiac Muscle

  • Wall of heart

  • Not under conscious control

  • Autonomic nervous control

  • Striated
• Smooth Muscle

  • Walls of most viscera, blood vessels

  and skin

  • Not under conscious control

  • Autonomic

  • Not striated, involuntary
• Smooth Muscle

  • Shorter

  • Single, centrally located nucleus

  • Elongated with tapering ends

  • Myofilaments randomly organized

  • Lack striations

  • Lack transverse tubules

  • Sarcoplasmic reticula (SR) not well developed
• Involuntary muscle

  • eyes
  • stomach
  • intestines
  • uterus
  • bladder
• Cardiac Muscle

  • Located only in the heart

  • Muscle fibers joined together by intercalated discs

  • Fibers branch

  • Network of fibers contracts as a unit

  • Self-exciting and rhythmic

  • Longer refractory period than skeletal muscle
• Skeletal Muscle Actions

  • Skeletal muscles generate a great variety of body

  movements.

  • The action of each muscle mostly depends upon the kind of joint it is associated with and the way the muscle is attached on either side of that joint.
• Structure of Skeletal Muscle

  • Organ of the muscular system

  • Skeletal muscle tissue
  • Nervous tissue
  • Blood
  • Connective tissues

  • Fascia

  • Tendons

  • Aponeuroses
• Muscle coverings:

  • Epimysium

  • Perimysium

  • Endomysium
• Skeletal Muscle Fibers

  • Sarcolemma

  • Sarcoplasm

  • Sarcoplasmic reticulum (SR)

  • Transverse (‘T’) tubule

  • Triad

  • Cisternae of SR

  • T tubule

  • Myofibril

  • Actin myofilaments

  • Myosin myofilaments

  • Sarcomere
• Neuromuscular Junction

  • Also known as NMJ or

  myoneural junction

  • Site where an axon and

  muscle fiber meet

  • Parts to know:

  • Motor neuron

  • Motor end plate

  • Synapse

  • Synaptic cleft

  • Synaptic vesicles

  • Neurotransmitters
• Motor Unit

  • Single motor neuron

  • All muscle fibers controlled

  by motor neuron

  • As few as four fibers

  • As many as 1000’s of muscle fibers
• Stimulus for Contraction

  • Acetylcholine (ACh)

  • Nerve impulse causes release of ACh from synaptic vesicles

  • ACh binds to ACh receptors on motor end plate

  • Generates a muscle impulse

  • Muscle impulse eventually reaches the SR and the cisternae
• Excitation-Contraction Coupling

  • Muscle impulses cause SR to release calcium ions into cytosol

  • Calcium binds to troponin to change its shape

  • The position of tropomyosin is altered

  • Binding sites on actin are now exposed

  • Actin and myosin molecules bind via myosin cross-bridges
• Cross Bridge Cycling

  • Myosin cross-bridge attaches to actin binding site

  • Myosin cross-bridge pulls thin filament

  • ADP and phosphate released from myosin

  • New ATP binds to myosin

  • Linkage between actin and myosin cross-bridge break

  • ATP splits

  • Myosin cross-bridge goes back to original position
• The Sliding Filament Model of Muscle Contraction

  • When sarcromeres shorten, thick and thin filaments slide past one another

  • H zones and I bands narrow

  • Z lines move closer together
• Relaxation

  • Acetylcholinesterase – rapidly decomposes Ach remaining in the synapse

  • Muscle impulse stops

  • Stimulus to sarcolemma and muscle fiber membrane ceases

  • Calcium moves back into sarcoplasmic reticulum (SR)

  • Myosin and actin binding prevented

  • Muscle fiber relaxes