muscle

• Acetylcholinesterase

  An enzyme that degrades acetylcholine
• Voltage-gated sodium channels

  Responsible for the depolarizing phase of the skeletal muscle action potential
• Voltage-gated potassium channels

  Responsible for the repolarizing phase of the skeletal muscle action potential
• Isometric contraction

  A muscle generates tension but does not change length.
• Isotonic contraction

  A muscle maintains constant tension as it changes length.
• Creatine kinase derived ATP fuels only the first few seconds of contraction
• Anaerobic glycolysis derived ATP kicks in during high intensity exercise but can only power short periods of muscle activity
• Glycogen is typically the first substrate used, then glucose and fatty acids are utilized
• Order of recruitment of motor units during skeletal muscle contractions

  1. Slow oxidative fibers recruited first

  2. Fast oxidative fibers recruited second

  3. Fast glycolytic fibers recruited last
• Fast oxidative fibers have medium diameter, intermediate ATP hydrolysis, use oxidative phosphorylation and glycolysis, generate moderate tension, and fatigue second
• Possible mechanisms of muscle fatigue

  • Build up of ADP
  • High extracellular K+ concentration
  • Disruption of calcium regulation
• Highest level of motor control

  Motor cortex neurons responsible for coordination, planning, and intention of movement
• Primary motor cortex

  Region in cerebral cortex that plays major role in initiation of complex movements
• Basal nuclei

  Group of gray matter in cerebrum that play major role in suppressing unwanted movements
• Cerebellum's role in motor control

  Monitors movement, sends corrective feedback, compares command signals with sensory information, and monitors intention of movement
• Locations of smooth muscle

  • Blood vessels
  • Gut
  • Urinary bladder
  • Uterus
• Sources of calcium for smooth muscle contraction

  • Voltage-gated calcium channels
  • Ligand-gated calcium channels
  • Mechanically gated channels
  • G-protein coupled receptors
• Smooth muscle contraction

  1. Calcium enters cell

  2. Calcium binds calmodulin and activates it

  3. Calmodulin activates myosin light chain kinase

  4. Myosin light chain kinase phosphorylates myosin light chain

  5. Myosin binds actin and power stroke occurs
• Smooth muscle is innervated by the autonomic nervous system
• Single-unit smooth muscle

  Smooth muscle cells connected by gap junctions so excitation spreads between cells
• Multi-unit smooth muscle

  Smooth muscle cells are independent and not connected by gap junctions
• Smooth muscle pacemaker depolarization

  Voltage-gated calcium channels open
• Smooth muscle pacemaker repolarization

  Voltage-gated calcium channels close, voltage-gated potassium channels open
• Conditions where smooth muscle can contract

  • Action potential
  • Depolarization to threshold
  • No change in membrane potential
• Slow wave

  Autorhythmic behavior in gastrointestinal smooth muscle generated by fluctuations in sodium movement