Muscles Part 3

Question 1

control of cardiac muscle

Answer 1

involuntary- contraction without nerve stimulation

Question 2

5 characteristics of cardiac muscle

Answer 2

1. cylindrical, branching cells
2. single central nucleus (2 nucleoli)
3. lots of myoglobin
4. almost 50% of volume is mitochondria
5. cells joined together by intercalated disks

Question 3

intercalated disks

Answer 3

form “stair step” junctions between adjacent cardiac muscle cells

Question 4

desmosomes

Answer 4

anchoring junctions to resist the pulling of cells as they contract (transverse portion)

Question 5

gap junctions

Answer 5

membrane protein channels that electrically couple all cardiac myocytes together into a functional synctium (lateral protion)

Question 6

what is the importance of gap junctions

Answer 6

cytoplasm continuous with next cell;

all get the signal to contract at the same time

Question 7

what is the importance of desmosomes

Answer 7

keeping cells together;

velcro holding on for strength

Question 8

smooth muscle cell characteristics

Answer 8

small, spindle-like, can stretch

Question 9

cytoskeleton of SM is composed of

Answer 9

extensive network of intermediate filaments

Question 10

dense bodies

Answer 10

in SM, connect intermediate filaments with sarcoplasm

Question 11

dense plaques

Answer 11

in SM, anchor intermediate filaments to inner sarcolemma

Question 12

what are contractile proteins in SM

Answer 12

the thick and thin filaments

Question 13

where are contractile proteins located in SM

Answer 13

between dense bodies

Question 14

caveolae

Answer 14

sub-membrane vesicles that store Ca^2+ in SM

Question 15

4 unique features of SM

Answer 15

1. lack sarcomeres –> no striations
2. thin filaments have actin and tropomyosin (no troponin)
3. no SR –> caveolae instead
4. contraction requires a series of additional proteins

Question 16

what 3 additional proteins are required for SM contraction

Answer 16

calmodulin, myosin light-chain kinase, myosin light-chain phosphatase

Question 17

calmodulin

Answer 17

protein that binds Ca^2+

Question 18

myosin light-chain kinase

Answer 18

adds a phosphate to the myosin tail for activation

Question 19

myosin light-chain phosphatase

Answer 19

removes P from the myosin tail for inactivation

Question 20

basic steps of SM contraction

Answer 20

1. stimulus triggers opening of Ca^2+ channels out of caveolae
2. Ca^2+ binds to calmodulin to form Ca^2+-calmodulin complex
3. Ca^2+-calmodulin complex activates myosin light-chain kinase
4. activated MLCK adds a P to a myosin tail, activating it
5. activated myosin unfolds and goes through cross bridge cycling. The force generated pulls the anchoring filaments and the smooth muscle cell compresses 3D

Question 21

basic steps of SM relaxation

Answer 21

1. cessation of stimulation
2. removal of Ca^2+ from sarcoplasm
3. deactivation of myosin by myosin light-chain phosphatase

Question 22

3 characteristics of SM contraction

Answer 22

1. long latent period
2. long duration
3. fatigue-resistant

Question 23

multiunit smooth muscle

Answer 23

cells are arranged into motor units with each one recieving signal to contract individually;
degree of contraction depends on number of motor units activated

Question 24

single-unit smooth muscle

Answer 24

SM cells arranged in sheets and stimulated to contract in unison by neurons that pass close to smooth muscle cells (most common)