50.5 Smooth and Cardiac Muscle

Question 1

vertebrate cardiac muscle

Answer 1

only found in the heart
-striated-cells interlock at intercalated disks

Question 2

cardiac muscle vs

skeletal muscle

Answer 2

• CARDIAC: makes APs by itself (ion channels in the plasma membrane allow it to depolarise rhythmically)
  
  • Aps last 20x longer than skeletal muscle
• SKELETAL: need motor neuron input (acetylcholine) to stimulate APs

Question 3

intercalated disks

Answer 3

where cardiac muscle cells interlock
-gap junctions there provide direct electric coupling between the cells

(Maps generated by cells in one part of heart reaches the entire heart)

Question 4

vertebrate smooth muscle

Answer 4

• walls of hollow organs (blood vessels and organs the digestive tract)
• unstriated
• can contract by signals from autonomic nervous system
• or can generate APs without neurons
• contract and relax slower than striated muscle

Question 5

why is smooth muscle unstriated

Answer 5

• the myosin and actin filaments are not regularly arrayed along the length of the cell (thick bodies in cytoplasm- thin attached to dense bodies on the plasma membrane)

Question 6

smooth vs

striated

Answer 6

SMOOTH: -contract and relax slower

• not troponin complex or T tubule- underdeveloped SR
• in AP, Ca2+ enters cytosol directly from membrane
  - the Ca2+ cause contractions by binding to calmodulin (protein)
  - calmodulin activates an enzyme that phosphorylates myosin head to make cross bridges

Question 7

muscles in invertebrates

Answer 7

• identical arthropod skeletal muscle
• flight muscles in insects can contract independently rhythmically
• thick filaments in clam shells (closed) has a protein that lets it remain closed for like a month