Week 3 Material

• What are the 3 types of muscle cells?


  skeletal, cardiac, smooth
• Which muscle type has the largest diameter?


  Skeletal
• Which muscle type has the longest length?


  Smooth
• Which muscle type is multinucleated?


  Skeletal
• Which nervous system controls skeletal muscle?

  somatic nervous system (voluntary)
• Motor neurons


  Cell body in spinal cord or brain stem

  each one can innervate multiple muscle cells

  acetylcholine is neurotransmitter
• neuromuscular junction


  only 1 synapse per muscle cell (fiber)

  always excitatory

  usually, one synaptic event will provoke action potential in the muscle fiber
• End plate potential


  a single firing of the motor neuron will cause a local graded potential
• Muscle fibers


  composed of multiple myofibrils that extend the length of the muscle fiber
• Myofibrils


  bundles of contractile proteins
• When does muscles contract?

  When myofibrils shorten
• Sarcomere


  consists of a bundle of myofibrils extending from one Z line to the next and composed of overlapping actin and myosin filaments
• I band


  actin filaments only
• A band


  region of overlapping myosin and actin filaments
• H band


  zone within A-band where myosin filaments don't overlap with actin
• Z line


  line separating two neighboring sarcomeres

  made up primarily of alpha actinin
• What protein makes up the Z line


  alpha-actinin
• M line


  band of connections between myosin filaments

  primary protein is myomesin
• What protein makes up the M line


  myomesin
• Contraction in sarcomere


  sliding of actin over myosin which shortens structure
• Titin


  elastic protein which extends from the Z line to the M line and is linked to the myosin filaments to keep them centered
• Nebulin


  Is associated with the actin filaments and is essential for regulating thin filament length
• Dystrophin


  links actin to the extracellular matrix and is a large X-linked protein
• Duschenne Muscular Dystrophy


  Individuals homozygous for loss of functional alleles of dystrophin

  Cell membranes of muscle fibers become damaged and leaky, leading to death of muscle cells and weakened skeletal muscles
• Myasthenia gravis


  Cause: autoantibodies to nicotinic AChRs

  Symptoms: Skeletal muscle weakness

  Treatment: Immunosuppressant drugs
• Spinal muscular atrophy (SMA)


  Cause: mutations in SMN1 gene

  Symptoms: skeletal muscle weakness and atrophy

  Treatments: Antisense RNA, gene therapy, and enhanced expression of full length SMN2 protein
• Rigor configuration


  Starting position of muscle contraction cycle; myosin is bound tightly to actin
• Role of Ca2+ in skeletal muscle contraction

  Ca2+ binds to troponin → shifts tropomysoin → exposes myosin binding site → muscle contraction
• Where is calcium stored

  sarcoplasmic reticulum
• how is calcium released from sarcoplasmic reticulum?

  interaction of two receptors (DHP receptor and Ryanodine receptor)
• What are the mechanics of single-fiber contraction?

  isometric contraction and isotonic contraction
• isometric contraction


  Length of muscle stays the same but change in tension
• isotonic contraction


  tension stays the same but change in length
• What are the two types of isotonic contraction?


  concentric contraction and eccentric contraction
• Concentric contraction


  type of isotonic contraction where tension exceeds load and causes muscle to shorten
• Eccentric contraction


  type of isotonic contraction where load exceeds tension and causes muscle to be stretched out
• Fatigue from short term exercise


  lactic acid build up

  ATP depletion
• Fatigue from long term exercise


  ryanodyne R leakage

  Glycogen depletion

  Central command fatigue
• What are the three types of muscle fibers?

  slow oxidative fibers, fast oxidative-glycolytic fibers, and fast glycolytic fibers
• primary source of atp production in slow oxidative fibers


  oxidative phosphorylation