Smooth and Cardiac Muscle

Question 1

What type of muscle has intercalated discs?

Answer 1

cardiac muscle

Question 2

what type of muscle has no striations?

Answer 2

smooth muscle

Question 3

cardiac muscle appearance

Answer 3

-elongated branching cells, joined by intercalated discs
-single central nucleus typical, some cell binucleate
-striated fibers

Question 4

cardiac muscle contractility

Answer 4

-involuntary muscle, spontaneously contractile, autonomic modulation
-sliding filament mechanism of contraction

Question 5

cardiac muscle organization

Answer 5

-prominent endo-, peri, and epimysium
-arrangement of contractile proteins into sarcomeres

Question 6

smooth muscle organization

Answer 6

-endo-, peri-, and epimysium
-bound together into highly irregular, branching fascicles, specialized for prolonged contraction with low force
-no sarcomeres

Question 7

smooth muscle appearance

Answer 7

-small cells, fusiform shape
-single central nucleus
-surrounding network of collagen
-no striations
-nucleus spiral shaped when contracted

Question 8

smooth muscle contractility

Answer 8

-involuntary
-inherent contractility- rhythmic, wave-like contractions independent of neurological stimulation; can respond to local changes & hormones
-cells shorten and broaden on contraction

Question 9

smooth muscle Z-disc equivalent

Answer 9

dense bodies- provide attachment site for actin

Question 10

dense bodies

Answer 10

-in smooth muscle
-lacks troponin to control myosin binding
-uses calmodulin instead

Question 11

calmodulin

Answer 11

binds Ca & activates myosin cross-bridging in smooth muscle

Question 12

caveolae

Answer 12

structure of smooth muscle cell membrane that allows for calcium diffusion

Question 13

smooth muscle contraction mechanism

Answer 13

-thin filaments of actin associated with tropomyosin
-myosin (thick filaments) only bind to actin if one chain is phosphorylated
-on membrane excitation, free Ca ions released into cytoplasm & bind to calmodulin
-calmodulin activates an enzyme that phosphorylates myosin allowing it to bind to actin
-energy efficient (uses little ATP)

Question 14

smooth muscle innervation

Answer 14

-influenced by autonomics (along with hormones and local metabolites)
-most smooth muscle has dual sympathetic & parasympathetic innervation

Question 15

in the gut, sympathetic stimulation of smooth muscle is:

Answer 15

inhibitory

Question 16

in the gut, parasympathetic stimulation of smooth muscle is:

Answer 16

stimulatory

Question 17

smooth muscle single unit

Answer 17

-tonic smooth Mm
-fibers contract as a unit

Question 18

smooth muscle multi-unit

Answer 18

-phasic smooth Mm
-individual muscle fibers contract independently

Question 19

diad

Answer 19

-present in cardiac muscle
-composed of one T-tubule & one cisterna of ER
-located @ Z-disc

Question 20

intercalated discs

Answer 20

-fuses two cardiac Mm cells together
-unique to cardiac muscle
-allows synchronous contractions
-want heart to function as single cell

Question 21

intercalated discs made of:

Answer 21

desmosomes, fascia adherens & gap junctions

Question 22

cardiac muscle contraction mechanism

Answer 22

similar to skeletal muscle
-depolarization of sarcoplasm travels through T-tubules down to sarcoplasmic reticulum (takes longer in cardiac Mm)
-calcium channels (located in walls of T-tubules & sarcoplasmic reticulum) open & release Ca ions into sarcoplasm
-Ca allows myosin & actin to form cross-bridges & slide past each other
-excitation & contraction passed on to neighboring cells via intercalated discs

Question 23

can cardiac muscle proliferate?

Answer 23

yes

Question 24

components of conducting system of the heart

Answer 24

-SA node
-AV node
-Bundle of His
-Purkinje fibers

Question 25

cardiac conduction system

Answer 25

-all structures consist of highly modified myocytes that coordinate conduction
-joined by extensive gap junctions
-larger than surrounding myocytes –> conduct impulses faster

Question 26

cardiac conduction system staining

Answer 26

paler staining than surrounding myocytes due to higher glycogen content