Lecture VIII

• One of the cell membranes, the sarcolemma is primarily for excitability
• Charged ions move across the sarcolemma
• Sodium enters cells to excite it
• Potassium leave cell for reseting for next contraction
• Motor units, single somatic motor neuron
• Motor units are only seen to control skeleton muscle
• Motor units connect to multiple muscle fibers
• When one neuron sends a signal, multiple muscle fibers contract
• Neural action potential requires a lot of ATP
• The system tries to save ATP
• Fine motor units are small in size
• Fine motor units tend to be one neuron to up to a hundred muscle fibers
• Fine motor units are weak but have a lot of control
• Examples of fine motor units include subtle facial actions and expressions
• Coarse motor units are larger
• Coarse motor units tend to be one neuron to up to thousands of muscle fibers
• Coarse motor units are strong but have little control
• Coarse motor units can increase the total force of contraction
• Examples of coarse motor units include the back
• The need to activate more motor units to get more force is also known as motor unit recruitment
• Motor unit recruitment can combat fatigue
• As muscle fibers tire out, they get substituted with different motor units
• Contraction types:

  • isotonic
  • concentric
  • eccentric
  • passive stretch
  • isometric
• Isotonic holds the same tension, changes length
• Concentric, muscle shortens
• Eccentric, muscle lengthens
• Passive stretch, connective tissue is stretched
• Isometric, build tension but no length change
• Neuromuscular junctions is where the somatic motor neuron communicates with muscle fibers
• Neuromuscular junctions is the center of the muscle
• Somatic motor neuron releases acetylcholine in the neuromuscular junction
• First, the axon of the somatic motor neuron carries action potential
• After the axon of the somatic motor neuron carries action potential, the axon branches into telodendria
• Once the axon branches into telodendria, the telodendria ends at a synaptic bulb
• From the telodendria ending at the synaptic bulb, electrical signals of action potentials open up calcium channels
• Upon the electrical signals of action potentials open up calcium channels, calcium helps vesicles go to the neurolemma
• When the calcium helps vesicles go to the neurolemma, vesicles of acetylcholine are released
• Because vesicles of acetylcholine are released, acetylcholine is released into the fluid in synaptic cleft where it diffuses into concentrations
• Since acetylcholine is released into the fluid in synaptic cleft where it diffuses into concentrations, acetylcholine binds to nicotinic acetylcholine receptors
• Once acetylcholine binds to nicotinic acetylcholine receptors, receptor activation causes sodium to enter the cell and excite it