Exam 3

• Graded potentials


  Variable-strength signals that can be conveyed over small distances
• Action potentials


  Massive depolarizations (when it reaches the threshold) that can be transferred over long distances
• Types of channels


  • Ligand-gated
  • Mechanically-gated
  • Leakage
  • Voltage-gated
• Ligand-gated channels


  Only open when a ligand binds to it, usually a neurotransmitter
• Mechanically-gated channels


  Channels open due to some physical change of the plasma membrane (somatosensation-touching skin and cells get squished)
• Leakage channels

  Randomly gated and switch between open and close, contribute to resting potential
• Voltage-gated channels


  Respond to changes in electrical/chemical changes, very specific about what goes in (sodium) and out (potassium)
• Sodium channel gates have unique characteristics
• Sodium-potassium pump

  1. [Na+] higher outside, [K+] higher inside, both moving against concentration gradient

  2. Three sodium & one ATP bind to pump

  3. ATP is split and sodium moves outside

  4. Sodium is released and enzyme changes shape

  5. Potassium binds and is transported inside
• Saltatory conduction


  Along a length of a myelinated axon segment (faster impulses), opening multiple channels at a time and "leaping"
• Continuous conduction


  Along an unmyelinated axon (slowly)
• Be able to label a picture of a membrane potential and know the important values
• Key neurotransmitters


  • Acetylcholine (Cholinergic system)
  • Norepinephrine (Adrenergic system)
• Cholinergic system


  Synapse of the autonomic nervous system where acetylcholine (ACh) is released
• Parasympathetic branch of ANS


  ACh binds to muscarinic (cholinergic) receptors & causes muscle contraction

  
• Adrenergic system


  Synapse of the autonomic nervous system where norepinephrine is released
• Neurotransmitters and their receptors


  • Acetylcholine binds to muscarinic receptors
  • Epinephrine and norepinephrine bind to adrenergic receptors
• Major proteins involved in muscle contraction


  • Actin
  • Myosin
  • Tropomyosin
  • Troponin

  
• Sarcomere


  Extends from one Z-line to the next Z-line, I-bands are the region of thin filaments not moving along thick filaments, A-bands are the length of a single thick filament, H-zone is the area of the A-band without any thin actin filament, M-line is in the middle of the H-zone and formed from the cytoskeleton
• Calcium ions


  Crucial for unshielding binding sites, when they bind to troponin, the troponin-tropomyosin complex moves, exposing myosin binding sites
• Sliding filament model of muscle contraction

  1. Myosin heads attach to actin at binding sites while ADP and Pi are attached

  2. Pi is released and myosin attaches more strongly to actin and pulls ~10nm (power stroke)

  3. New ATP binds and myosin heads detach from actin

  4. ATP is hydrolyzed by myosin ATPase, which positions the myosin head for more movement (re-cock)

  
• Muscle metabolism pathways


  • Creatine Phosphate
  • Glycolysis
  • Aerobic Respiration
• Creatine Phosphate


  Sources of ATP and Muscle Metabolism that is quick but only lasts ~15 seconds, formed by creatine & ATP, broken down by Creatine Kinase into ATP (for muscle contraction) and Creatine
• Glycolysis


  Muscle Metabolism that is not very efficient & only sustained for ~1 minute, glucose is converted to 2 ATP & 2 Pyruvate, aerobic respiration uses oxygen to keep going, lactic acid builds up in the blood if no oxygen is used
• Aerobic Respiration


  Accounts for 95% of ATP used by muscles, muscles store oxygen in myoglobin to power aerobic respiration through mitochondria
• Oxygen debt


  Amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction, associated with build-up of lactic acid and creatine
• Isometric muscle contraction


  Tension changes, while length remains constant
• Isotonic muscle contraction


  Tension remains constant, while length is changed, can be eccentric (muscle lengthens) or concentric (muscle shortens)
• Types of muscle contractions


  • Twitch
  • Summation
  • Tetanus
• Optimal muscle tension


  Maximum tension & overlap of binding sites occurs at 80-120% of sarcomere resting length, less tension is produced at <80% or >120%

  
• Hypertonia


  Too many contractions at rest, associated with excessive reflex response, rigidity, and spasticity, patients experience reduced mobility
• Hypotonia


  Absence of contractions at rest, associated with damage to CNS, over 600 conditions can cause it
• Muscle fiber types


  • Type I (Slow twitch, aerobic respiration)
  • Type IIA (Fast twitch, aerobic respiration and glycolysis)
  • Type IIB (Fast twitch, anaerobic glycolysis)
• Building muscle fibers


  Fast twitch muscle is useful for anaerobic, explosive exercise like weightlifting, increased myofibrils & muscle fiber thickness
• Hypertrophy


  Addition of structural proteins to muscle fibers, increasing diameter of cell
• Atrophy


  Loss of structural proteins and corresponding decrease in muscle mass
• Muscle cells


  • Myoblasts
  • Satellite cells
  • Pericytes