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Motor Unit. single motor neuron all muscle fibers controlled by motor neuron. 9-9. Neuromuscular Junction. site where axon and muscle fiber communicate motor neuron motor end plate synaptic cleft synaptic vesicles neurotransmitters. 9-8. Ion Channels.

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motor unit
Motor Unit
  • single motor neuron
  • all muscle fibers controlled by motor neuron


neuromuscular junction
Neuromuscular Junction
  • site where axon and muscle fiber communicate
  • motor neuron
  • motor end plate
  • synaptic cleft
  • synaptic vesicles
  • neurotransmitters


ion channels
Ion Channels

Gated Channels – open and close in response to specific stimuli

Chemically (Ligand)Gated Channel – opened and closed by chemicals

2. Voltage Gated Channel – opened and closed based on membrane potential

  • Mechanically Gated Channel – open and closed by physical deformity
  • of receptor

Leakage Channels – always open

resting membrane potential
Resting Membrane Potential
  • occurs when cell is not being stimulated
  • inside is negative relative to the outside
  • polarized membrane = electrically charged due to distribution of ions
  • Na+/K+ pump = pumps Na+ out and K+ in



Depolarization – reduction in membrane potential

-- becomes less negative

-- increases probability of impulse conduction

Hyperpolarizaiton – increase in membrane potential

--becomes more negative

-- reduces probability of impulse conduction

release of neurotransmitter
Release of Neurotransmitter
  • Nerve impulse reaches end of the axon and opens Ca2+ channels; Ca2+
  • diffuses into the cell
  • Presence of Ca2+ in axon causes synaptic vesicles to bind with cell
    • membrane of the axon.
  • Neurotransmitter is released from axon into synaptic cleft
  • by exocytosis (Acetylcholine (ACh))
  • ACh binds receptors on the motor end plate of the sarcolemma; chemically
  • gated channels

5. Stimulation of sarcolemma generates an impulse/action potential

action potential
Action Potential
  • Ach opens chemically gated channels on the sarcolemma
  • Na+ goes into the cell and makes the inside of the membrane positive
  • relative to the outside
  • Change in charge inside of the cell opens voltage gated channels
  • Depolarization moves down the sarcolemma = Action Potential
  • Membrane repolarizes as ions move back to starting position
excitation contraction coupling
Excitation Contraction Coupling
  • muscle impulses travels along the sarcolemma and into T tubule causing terminal cisternae to release Ca2+
  • calcium binds to troponin to change its shape
  • position of tropomyosin is altered
  • binding sites on actin exposed
  • actin and myosin bind


cross bridge cycling
Cross-bridge Cycling
  • actin and myosin cross-bridge bind
  • myosin cross-bridge pulls actin
  • ADP and phosphate released from myosin
  • new ATP binds to myosin
  • linkage between actin and myosin cross-bridge break
  • ATP splits
  • myosin cross-bridge goes back to original position



  • Nerve stops secreting Ach
  • acetylcholinesterase – breaks down acetylcholine
  • muscle impulse stops
  • calcium moves back into sarcoplasmic reticulum
  • myosin and actin binding prevented