Lesson 23 - 24

Question 1

three properties of smooth and cardiac muscle

Answer 1

1. their cells are myocytes
2. they are involuntary
3. they receive innervation from the autonomic nervous system

Question 2

myocytes

Answer 2

smooth muscle cells, not as long and fibrous as skeletal muscles

Question 3

properties of cardiac muscle (5)

Answer 3

1. contracts with regular rhythm
2. muscle cells of a given chamber contract in unison
3. contractions must last long enough to expel blood
4. highly resistant to fatigue
5. works in sleep or wakefulness, without fail, and without conscious attention

Question 4

structure of cardiac muscle cells (3)

Answer 4

• shorter and thicker than skeletal muscle cells
• surrounded by endomysium
• no peri or epimysium

Question 5

cardiomyocytes branch and join to other cells at connections called _____ _____

Answer 5

intercalated discs

Question 6

how do intercalated discs appear?

Answer 6

thick, dak lines in stained tissue sections

Question 7

intercalated discs

Answer 7

mechanical junctions that keep cardiomyocytes from pulling apart

Question 8

_____ _____ in the intercalated discs allow each cardiomyocyte to directly stimulate its neighbors

Answer 8

gap junctions

Question 9

cardiac muscle doesn’t… (2)

Answer 9

• have satellite cells
• very limited mitosis
  muscles can easily be replaced by scar tissue

Question 10

pacemaker

Answer 10

rhythmically sets off a wave of electrical excitation

Question 11

the heart is autorhythmic, meaning…

Answer 11

it is able to contract rhythmically and independently

Question 12

places smooth muscle provide fine control (2)

Answer 12

• smooth muscles of the iris controls pupil size
• piloerector muscles raise hairs on skin

Question 13

smooth muscle myocyte structure (5)

Answer 13

1. fusiform shape
2. single nucleus near middle of cell
3. thick and thin filaments present, but not aligned
4. minimal SR and no T tubules
5. Z discs replaced by dense bodies

Question 14

dense bodies

Answer 14

protein masses that form plaques on the inner face of the plasma membrane and scattered throughout sarcoplasm
- dense bodies of neighboring cells are linked together

Question 15

types of smooth muscle: unitary (single unit) (3)

Answer 15

myocytes coupled by gap junctions, so it contracts as a single unit
- most common
- aka visceral muscle

Question 16

types of smooth muscle: multiunit

Answer 16

individual myocytes respond independently of all other

Question 17

smooth muscle can contract or relax in response to a variety of stimuli: (5)

Answer 17

• autonomic nerve fibers and neurotransmitters
• chemicals
• temperature
• stretch
• autorhythmicity

Question 18

contraction is always triggered by _____, energized by ___, and achieved by the sliding of myosin and actin

Answer 18

Ca2+, ATP

Question 19

where does smooth muscle get most of its ATP

Answer 19

the extracellular fluid through gates Ca2+ channels
- other Ca2+ comes from the limited SR

Question 20

caveolae

Answer 20

pockets on the sarcolemma

Question 21

where are calcium gated channels concentrated?

Answer 21

caveolae

Question 22

in smooth muscle, what does calcium bind to?

Answer 22

calmodulin

Question 23

what does calmodulin activate?

Answer 23

myosin light-chain kinase

Question 24

what does myosin light-chain kinase do?

Answer 24

adds a phosphate group to a regulatory protein on myosin head which then activates ATPase

Question 25

why do smooth muscles contract so much slower? (2)

Answer 25

• slow myosin ATPase, slow calcium pumps, and the presence of Ca2+ in the cytosol
• latent period in smooth muscle is 50-100 ms (2ms in skeletal)

Question 26

latch-bridge mechanism

Answer 26

myosin doesn’t immediately detach from act when Ca2+ levels fall
- resistant to fatigue, doesn’t consume any more ATP

Question 27

what does the latch-bridge mechanism maintain? (2)

Answer 27

• smooth muscle tone
• vasomotor tone in blood vessels

Question 28

peristalsis

Answer 28

waves of contraction brought about by food distending the esophagus or feces distending the colon; propels contents along the organ

Question 29

what can stretch do to smooth muscles?

Answer 29

can open mechanically gated calcium channels in the sarcolemma causing contraction

Question 30

stress-relaxation response

Answer 30

helps hollow organs gradually fill
- when stretched, tissue briefly contracts then relaxes, helping prevent emptying while something is filling

Question 31

unlike skeletal muscle, smooth muscle contracts _______ when greatly stretched

Answer 31

forcefully

Question 32

plasticity

Answer 32

the ability to adjust its tension to the degree of stretch

Question 33

why are smooth muscles able to contract forcefully even when stretched? (3)

Answer 33

• no Z discs, thick filaments cannot butt against them
• bc not arranged in orderly sarcomeres, there is no situation of too little overlap
• thick filaments have myosin heads along their entire length so cross bridge can form anywher

Question 34

muscular dystrophy (MD)

Answer 34

a group of hereditary disease in which skeletal muscles degenerate and weaken and are replaced with fat and fibrous scar tissue

Question 35

Duchenne muscular dystrophy (DMD)

Answer 35

caused by a sex-linked recessive trait on the X chromosome
- most common form

Question 36

when is DMD diagnosed

Answer 36

around the age of 5

Question 37

what causes DMD?

Answer 37

a mutation in the gene for muscular protein dystrophin, needed to link thin filaments in the sarcomere
- w/o actin isn’t linked to the sarcolemma and cell membranes are damaged during contraction

Question 38

myasthenia gravis

Answer 38

autoimmune disease in which antibodies attack neuromuscular junctions and bind ACh receptors together in clusters, then muscle fibers removed the clusters via endocytosis causing muscles to be less and less sensitive