Muscle Mechanics and Smooth Muscle

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Muscle Mechanics and Smooth Muscle
2011-01-03 14:04:18

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  1. Describe difference between type 1 and type 2 muscle fibers
    • Type 1:
    • - Slow oxidative
    • - Use cellular respiration
    • - High endurance
    • Type 2:
    • - IIa: fast oxidative
    • - IIb: fast glycolytic
    • - Use anaerobic metabolism
    • - Low endurance
  2. Discuss difference between type I and type IIb fibers
    • Type 1:
    • Structure:
    • - Slow contraction time + high resistance to fatigue
    • - Small motor neuron and fiber diameter
    • - High mitochondrial and capillary density
    • - High myoglobin content
    • Energy:
    • - Low creatine phosphate
    • - Low glycogen
    • - Large triglycerides stores
    • - Use oxidative metabolism (Krebs + ETC)
    • Function:
    • - Low force, long duration activities i.e. walking
    • Type IIb:
    • Structure:
    • - Quick contraction + low resistance to fatigue
    • - Large motor neuron and fiber diameter
    • - Low mitcohondrial and capillary density
    • Energy:
    • - High creatine phosphate and glycogen levels
    • - Low triglycerides
    • - Many glycolytic enzymes but few oxidative enzyme
    • Function:
    • - Short duration, high intensity activity i.e. hurdling
  3. Discuss structure of cardiac muscle
    • Outside cell:
    • - striated
    • - intercalated discs; contain gap junction, desmosomes, fascia adherens
    • - branches
    • Inside cell:
    • - Sarcomeres (requiring AP, Ca, activation of Troponin-Tropomyosin complex)
    • - Contract via CICR mechanism
    • - T-tubules more developed, less SR
  4. Describe Calcium induced calcium release mechanism
    • Function: contraction of cardiac muscle
    • Mechanism:
    • - depolarization of membrane
    • - direct activation DHPR; opening of ion channels
    • - Ca+ enters cell; activates RyR; opening of Ca+ channels in SR
    • - Contraction occurs
    • - Re-uptake of Ca+ by SERCA 2 and Ca/Na exchanger
  5. Discuss the properties of a motor unit
    • Made up of a-motor neuron and all mucle fibers it innervated
    • Starts from cell body in ventral horn (or cranial nerve nucleus) end at NMJ’s
    • Muscle fibers innervated by a single motor unit are SAME (fast or slow twitch)
    • Some units are big (to postural muscles) some are small (to hand muscles)
  6. Define motor control
    The systematic transmission of impulses from the motor cortex to motor units, resulting in coordinated muscular contractions
  7. Discuss the all-or-nothing response of a motor unit. Why is this important?
    • If one motor neuron fires, ALL the muscle fibers within it fire as well
    • In large fibers, there is large contraction, stabalize posture
    • In small fibers, there is less contraction, more controlled movement
  8. Define force gradation
    Gradual recruitment of more motor units to increase force
  9. Define Motor Unit Potential (MUP)
    Sum of action potentials or all the muscle fibres in one motor unit
  10. Discuss muscle “twitch”
    • Cells that contract and produce force are called twitch fibres
    • The contraction produced is called “twitch”
    • Number of fibres recruited per impulse is “recruitment gradation”
    • Slow twitch fibres are easily recruited
    • Fast twitch fibres are mor difficult
  11. What is an electromyography
    • Test that measures the health of muscles and nerves which control those muscles
    • 2 types:
    • - Needle EMG and Surface EMG
    • - displayed on oscilloscope or heard through speaker
  12. Describe a needle EMG
    • Test muscles at rest (increased electrical acivity in disease)
    • Test voluntary contractions
  13. Define distal latency
    • Time between nerve stimulation and response being recorded
    • Measures the conductivity (not velocity) of segment of a nerve
  14. How do you measure conduction velocity?
    • Stimulate nerve at two points along its course
    • V= d/ tp – td
    • *d distance between two points
    • *tp proximal latency
    • *td distal latency
  15. Discuss EMG results in a patient with myasthenia gravis
    • Repetitive stimulation produce progressively weaker responses
    • This is called Decrement of the Compound Muscle Action Potential (CMAP)
  16. Describe excitation-contraction coupling
    • AP reaches nerve terminal; Depolarization at NMJ
    • Voltage-gated Calcium channels open; calcium pours in
    • Stimulates fusion of s. vesicles with pre s. membrane
    • Release of Ach by exocytosis
    • Activates NAchR fast ion channels in post s. membrane; (Ach broken down by Ach-esterase)
    • Influx of Na down electrochemical gradient
    • Local depolarization of sarcolemma (end plate potential)
    • Initiates AP which spreads along muscle fibre membrane
    • AP carried through muscle fibre along transverse tubules
    • Activates Dihydropyradine receptors
    • DHPR a-subunit interact with extracellular domain of RyR in SR; opens Ca+ channel
    • Calcium ions rush into sarcoplasm surrounding myofibrils
    • Muscle contraction occurs
    • Re-uptake of Ca ions by SERCA primarily and Calsequestrin
  17. State the function and location of SERCA. Heck, just tell me what it stands for and you pass!
    • Name: Sarcoplasmic/endoplasmic reticulum Calcium ATPase
    • Function:
    • - actively absorb Ca+ back into SR
    • - pumps 2 Ca+ for every ATP used
    • Location: SR
  18. Discuss structure and fnction Ryanodine receptors
    • Structure:
    • - tetramer
    • - 3 isomers: RyR1 (SKM); RyR2 (Cardiac); RyR3 (Brain)
    • - Largest ion channel known
    • - located in terminal cisternae of SR
    • Function: release Ca+ from SR into sarcoplasm surrounding myofibrils
  19. Discuss mechanism of action of smooth muscle contraction
    • Increased calcium conductance (nervous, hormonal, stretch)
    • Calcium binds with calmodulin
    • Ca-Cal complex activates MLC Kinase
    • Phosphorylates MLC (regulatory chain)
    • Interaction between myosin and actin
    • Contraction occurs
    • Inhibited by Myosin phosphatase (which is itself regulated by Rho-kinase)
  20. Describe gross architecture of smooth muscle cell
    • Spindle shaped cells
    • Non-striated (actin + myosin form loose bundles)
    • Single nucleus
    • Attached to dense bodies
  21. State the function of dense bodies
    • Form attachment between smooth muscle cells
    • Spread force ofcontraction from one cell to another
  22. Discuss two types of smooth muscle fibers
    • Multi unit:
    • Discrete and seperated
    • Contract independently
    • Stimulated by nerve impulse ONLY
    • Seperated by membrane
    • Found in ciliary muscles of eye; piloerector muscles
    • Unitary:
    • Forms sheets
    • Contract as a unit
    • Nervous and non-nervous impulses
    • Joined together by gap junctions
    • Found in walls of viscera + blood vessels
  23. Define the following:
    • Summation: stimulation of muscle fiber before full relaxation
    • Tetany: high frequency stimulation – no relaxation. Can be incomplete or complete.
    • Treppe: low frequency stimulation
    • Isometric contraction: tension changes – length constant
    • Isotonic contraction:
    • - muscle tension constant – length changes.
    • - can be eccentric: muscle lengthens
    • - concentric: muscle shortens
  24. Compare contraction of smooth vs skeletal muscles
    • Smooth muscle contractions is more prolonged
    • Requires less energy
    • Produces more force
    • Because of slow cycle of actin myosin binding