Muscles and Skin

Question 1

what are the 3 main functions of muscles ?

Answer 1

• locomotion
• maintaining + changing posture
• movement of internal organs

Question 2

what are the 3 types of muscles ?

Answer 2

• skeletal muscle
• smooth muscle
• cardiac muscle

Question 3

what is structural syncytium + example ?

Answer 3

• multi-nucleated cell that can result from multiple cell fusions of uni-nuclear cells
• skeletal muscle

Question 4

what is functional syncytium + examples ?

Answer 4

• electrically coupled through gap junctions
• cardiac muscle
• smooth muscle

Question 5

structure of skeletal muscle ?

Answer 5

• multinucleate
• striations
• voluntary - somatic nervous system

Question 6

Structure of Cardiac Muscle Cells ?

Answer 6

• single centrally located nucleus
• branched
• lots of mitochondria
• has intercalated discs - allows contact with adjacent cells
• has desosomes (mechanical strength )
• gap junctions ( allow electrical and chemical communication between cells)
• Involuntary

Question 7

Structure of Smooth Muscle Cells ?

Answer 7

• no striations
• uni-nuclear
• Spindle-shaped
• Cells are often interconnected by gap junctions
• involuntary - autonomic nervous system

Question 8

structure of sarcomere (6) ?

Answer 8

• sarcomere is distance between two Z lines
• Z line
• M line
• I band
• A band
• H zone
• titin filaments

Question 9

what is the I band ?

Answer 9

• light band, contains only actin filaments
• Z-line at its center

Question 10

what is the A band ?

Answer 10

• dark band
• myosin (thick)

Question 11

what is M line ?

Answer 11

• middle of scarcomere
• myosin filaments attched

Question 12

what is Z line ?

Answer 12

• marks the boundary of each sarcomere
• anchoring the actin filaments.

Question 13

what is the H zone ?

Answer 13

• center part of the A-Band where only myosin is present

Question 14

what are titin filaments ?

Answer 14

• elastic proteins
• keep actin + mysoin aligned

Question 15

what type of proteins are actin + myosin ?

Answer 15

• myosin= fibrillar
• actin = globular

Question 16

phases of skeletal/cardiac muscle contraction ?

Answer 16

• resting stage - ATP hydrolyzed
• Ca2+ binds to troponin
• causes a conformational change in tropomyosin
• tropomyosin leaves
• exposes myosin binding site on actin filaments
• myosin heas binds to actin forms cross-bridge
• power stroke occurs = releasing ADP+Pi and mysoin pulls actin
• causes contraction
• new ATP binds to myosin causes detachment from actin + breaks cross-bridge
• hydrolysis of ATP recocks mysoin head to original position

Question 17

contraction/ depolarisation stages ?

Answer 17

• Na+ channels open
• Na+ enters cell
• depolarisation travels down t-tubule
• causes L-Type Ca²⁺ channels to open
• influx of Ca²⁺ activates ryanodine receptors (RyR) on the SR, releasing more Ca²⁺.
  -contraction activation: Ca²⁺ binds to troponin,

Question 18

relaxation/ repolarization ?

Answer 18

• Ca2+ reuptake into sarcoplasmic reticulum using Ca²⁺-ATPase pump (SERCA pump).
• withdrawal of Ca2+ to extracellular media
• exchange of Ca²⁺ out for 3 Na⁺ in with Na⁺/Ca²⁺ exchanger (NCX)
• and then Na/K+ pump exchanges 2K+ in for 3Na+ out
• activates K+ channels

Question 19

vascular smooth muscles ?

Answer 19

• walls of blood vessels
• arteries, veins + lymph vessels

Question 20

visceral smooth muscles ?

Answer 20

• airways, GI tract, urinary system

Question 21

Vascular Smooth Muscle Contraction ?

Answer 21

• excitation-depolarization due Voltage-gated L-type Ca²⁺ channels open.
• Ca²⁺-induced Ca²⁺ release from ER/SR via ryanodine receptors (RYR).
• Ca²⁺ binds to calmodulin (CaM).
• Ca²⁺-CaM complex activates Myosin Light Chain Kinase (MLCK).
• MLCK phosphorylates myosin head stimulating contraction.

Question 22

which muscle does not have a sarcomere ?

Answer 22

• smooth muscle
• still has actin myosin filaments
• contracts via Ca2+ calmodulin + myosin light chain kinase