Chapter 9

• Three types of muscle tissue:

  • skeletal muscle
  • cardiac muscle
  • smooth muscle
• Four shared properties between the three muscle types:

  • excitability
  • contractility
  • extensibility
  • elasticity
• Excitability is the ability to respond to stimulation
• Contractility is the ability to shorten or exert pull and tension harnessed by connective tissue
• Extensibility is the ability to contract over a range of resting lengths
• Elasticity is the ability of muscle to return to original length after contraction
• The muscular system has over 700 skeletal muscles, including ones under voluntary control
• In excitability, the electricity charged ions move across the cell membrane also known as the sarcolemma
• Ions used in excitability will be sodium, potassium, and calcium
• In contractility, the contractile proteins are actin and myosin
• Sarcolemma: excitability
• Moved charged ions across the cell membrane
• Sodium enters the cell to excite it
• Potassium leaves the cell for reseting for next contraction
• Single somatic motor neuron
• Motor units only seen to control skeleton muscle
• Motor units connects to multiple muscle fibers
• When one neuron sends a signal, multiple muscle fibers contract
• Neural action potential requires a lot of ATP
• Tries to save ATP
• Fine motor units are small
• For fine motor units, one neuron can connect to 5-100 muscle fibers
• Fine motor units are weak but have a lot of control
• An example of fine motor units are subtle facial actions and expressions
• Need to activate more motor units to get more force is also known as motor unit recruitment
• As muscle fibers tire out, they get substituted with different motor units
• For coarse motor unit, one neuron can connect to 100s-1000s muscle fibers
• Coarse motor units are powerful but have little control
• An example of coarse motor units are the back (latissimus dorsi)
• Isotonic meaning holds the same tensions, changes length
• Concentric, muscle shortens
• Eccentric, muscle lengthens
• Passive stretch, connective tissue is stretched
• Isometric, build tension but not length change
• Neuromuscular junctions are where somatic motor neurons communicate with muscle fibers
• Neuromuscular junctions are at the center of the muscle
• Somatic motor neuron releases acetylcholine
• First step of the neuromuscular junction:

  • axon of somatic motor neuron carries action potential
• First step of the neuromuscular junction:

  • axon of somatic motor neuron carries action potential
• Second step of the neuromuscular junction:

  • axon branches into telodendria