The Muscular System

• What are the components of the muscular system?

  Muscles, tendons, and connective tissues
• What is muscle fiber excitation?

  It is the process of muscle fibers responding to stimuli
• What are agonists and antagonists in muscle actions?

  Agonists are primary movers; antagonists oppose them
• What is the role of muscle fascicles?

  They organize muscle fibers to generate force

  
• What criteria are used to name skeletal muscles?

  Location, size, shape, action, and number of origins
• What are the origins and insertions of skeletal muscles?

  Origins are fixed points; insertions move during contraction
• What is irritability in skeletal muscle?

  It is the ability to respond to stimuli
• What does contractility refer to in skeletal muscle?

  It refers to the ability to shorten when stimulated
• What is extensibility in muscle fibers?

  It is the ability to be stretched
• What does elasticity mean in muscle fibers?

  It is the ability to recoil to resting length
• What type of muscle is usually attached to bones?

  Skeletal muscle
• What is the primary characteristic of cardiac muscle?

  It is involuntary and striated
• Where is smooth muscle found?

  In the walls of viscera and blood vessels
• What are the functions of skeletal muscle?

  • Movement of body parts
  • Generation of voluntary and reflex movements
  • Maintenance of posture
  • Stabilization of joints
  • Generation of body heat
• What is the structure of skeletal muscle fibers?

  Large, elongated, multinucleate cells
• What is the epimysium?

  It is the connective tissue covering the entire muscle
• What is the perimysium?

  It surrounds a bundle of muscle fibers (fascicle)
• What is the endomysium?

  It is the connective tissue around individual muscle fibers
• What are myofibrils?

  They consist of myofilaments and run the length of the cell
• What are myofilaments?

  They are actin and myosin that facilitate contraction

  
• What is the sarcoplasmic reticulum?

  It surrounds myofibrils and stores calcium
• What is the role of the sarcomere?

  It is the functional unit of muscular contraction

  
• What do I bands contain?

  Only thin myofilaments (actin)
• What do A bands contain?

  Thick myofilaments (myosin) and some overlap
• What is the H zone?

  It is a pale region with no actin overlap
• What is the M line?

  It consists of proteins holding thick filaments in place
• What happens during muscle contraction?

  Actin filaments slide towards each other

  
• What is a motor unit?

  It is one motor neuron and its muscle fibers

  
• What is the neuromuscular junction?

  It is the site where motor neuron meets muscle fiber

  
• What neurotransmitter stimulates skeletal muscle?

  Acetylcholine (ACh)

  
• What occurs when a nerve impulse reaches the axon terminal?

  Calcium channels open, allowing Ca2+ entry

  
• What happens after ACh binds to receptors on the sarcolemma?

  Ion channels open, allowing ions to pass

  
• What do synaptic vesicles carry until needed?

  Neurotransmitter

  
• What happens when a nerve impulse reaches the axon terminals?

  Calcium channels open

  
• What enters the axon terminal when calcium channels open?

  Calcium ions (Ca2+)
• What causes synaptic vesicles to release acetylcholine?

  Entry of calcium ions (Ca2+)

  
• What happens to acetylcholine after it diffuses across the synaptic cleft?

  It binds to receptors in the sarcolemma

  
• What ions pass through the ion channel in the sarcolemma?

  Sodium (Na+) and potassium (K+)
• What is the result of more Na+ entering than K+ leaving?

  Local depolarization occurs
• What enzyme breaks down acetylcholine in the synaptic cleft?

  Acetylcholinesterase