CHAP: 8 EXCITATION & CONTRACTION OF SMOOTH MUSCLE

Question 1

smooth muscle can be generally divided into 2:

Answer 1

1. Multi-unit smooth muscle
2. unitary (single) smooth muscle

Question 2

this type of smooth muscle is composed of discrete, separate smooth muscle, it operates independently.

Answer 2

Multi-unit smooth muscle

Question 3

the outer surface of multi-unit smooth muscle are covered by a thin layer of _____ & _____ that helps insulate the separate fibers from one another

Answer 3

fine collagen & glycoprotein

Question 4

the most important characteristic of multi-unit smooth muscle fiber is?

Answer 4

each fiber can contract independently of the others & their control is exerted mainly by nerve signals.

Question 5

in contrast what is the major share control of unitary smooth muscle ?

Answer 5

it’s excreted by non-nervous stimuli

Question 6

what are the 2 example of multi-unit smooth muscle ?

Answer 6

1. iris muscle
2. pilo-erector muscle of hairs

Question 7

this type of muscle means a mass of hundreds to thousands of smooth muscle fibers that contract together as a single unit.

Answer 7

Unitary smooth muscle

Question 8

In unitary s. muscle, the cell membranes are joined by many ______ through which ion can flow freely from one muscle cell to the next so that even without action potentials ion can travel from one fiber to the next & cause muscle fiber to contract.

Answer 8

gap junctions

Question 9

Unitary smooth muscle is also known as?

Answer 9

1. syncytial smooth muscle
2. visceral smooth muscle

Question 10

it’s called this _____ because of it’s syncytial interconnections among fibers.

Answer 10

syncytial smooth muscle

Question 11

it’s called ______ because it’s found in the walls of most viscera of the body, like G.I tract, bile ducts, ureters, uterus & many blood vessels

Answer 11

visceral smooth muscle

Question 12

comparison of smooth m. & skeletal m. contraction.

Answer 12

skeletal muscle contract & relax rapidly
while smooth muscle contraction prolonged tonic contraction

Question 13

how many energy is required to sustained the same tension of contraction in smooth muscle as in skeletal muscle?

Answer 13

1/10 to 1/300 energy

Question 14

this mechanism is used to maintain prolonged tonic contraction smooth muscle for hours with little use of energy.

Answer 14

Latch mehanism

Question 15

when volume suddenly decreased, the pressure falls drastically at first but then rises in another few seconds or minutes to or near to the original level, this phenomena are called?

Answer 15

stress-relaxation & reverse stress-relaxation

Question 16

what is the importance of stress-relaxation & reverse stress-relaxation?

Answer 16

they allow hollow organ to maintain about the same amount of pressure inside it’s lumen despite long-term, large changes in volume,

Question 17

in place for troponin, smooth muscle cells contain large amount of another regulatory protein called?

Answer 17

calmodulin

Question 18

The activation & subsequent contraction occur in the ff sequence:

Answer 18

1. Calcium ions bind w/ calmodulin
2. Calmodulin-calcium complex then joins w/ & activates myosin light chain kinase, a phosphorylating enzyme
3. Regulatory chains becomes phosphorylated in response to this myosin kinase,

Question 19

One of the light chains of each myosin head is called ______ when this chain is not phosphorylated, the attachment-detachment cycling of the myosin head with the actin filaments does not occur

Answer 19

Regulatory chains

Question 20

when the calcium ion concentration falls below a critical level, the aforementioned process automatically reverse, except the phosphorylation of the myosin head, reversal of this requires another enzymes called?

Answer 20

myosin phosphatase

Question 21

what is the maximum force of contraction in smooth muscle?

Answer 21

4-6kg/cm

Question 22

what is the maximum force of contraction in skeletal muscle?

Answer 22

3/4 kg

Question 23

what are important characteristics of smooth muscle, especially the visceral unitary type of smooth muscle of hollow organs?

Answer 23

is the ability to return to nearly it’s original force of contraction seconds or minutes after it has been elongated or shortened

Question 24

this is important in cessation of contraction, or when calcium ions falls below critical level, process automatically reverse, this reversal need another enzyme called?

Answer 24

Myosin phosphate

Question 25

myosin phosphate is located in the ______ that splits the phosphate from the regulatory chains.

Answer 25

Cytosol of the smooth muscle

Question 26

this ____ secrete their transmitter substance into the matrix coating of the smooth muscle often a nanometers to a few micrometers away from the muscle cell

Answer 26

diffuse junctions

Question 27

the vesicles of autonomic nerve fiber contains

Answer 27

1. acetylcholine & norepinephrine

Question 28

is an excitatory transmitter substance for smooth muscle fibers in some organs but an inhibitory transmitter for smooth muscle in other organs.

Answer 28

Acetylcholine

Question 29

when acetylcholine excites a muscle fiber this _____ ordinarily inhibits it. Conversely, when acetylcholine inhibits a fiber, this usually excites it.

Answer 29

Norepinephrine

Question 30

in the normal resting state, the intracellular potential is usally how many volts?

Answer 30

-50 to -60 mV, which is about 30 mV less negative than in skelatl muscle

Question 31

Action potentials occur in this _______ than multi-unit types of smooth muscle .

Answer 31

Unitary smooth muscle

Question 32

the action potentials of visceral smooth muscle occur in one of 2 forms?

Answer 32

1. spike potentials 2. action potentials w/ plateaus

Question 33

the duration of the spike potentials is how many milliseconds?

Answer 33

10 to 50 millisecond

Question 34

In action potential w/ plateaus instead of rapid repolarization, it's being delayed here for how many second?

Answer 34

1 second

Question 35

what is the importance of the plateu?

Answer 35

it can account for prolonged contraction that occurs in some types of smooth muscle, ex. Ureter

Question 36

it's a local property of the smooth muscle fibers that make up the muscle mass.

Answer 36

Slow wave rhythm

Question 37

what is the importance of slow waves?

Answer 37

when they are strong enough, they can initiate action potenials

Question 38

how many negative mV for a slow wave to initiate an action potentials develops & spread over the muscle & contraction.

Answer 38

-60 to about -35 mV

Question 39

slow waves are called?

Answer 39

pacemaker waves

Question 40

when visceral smooth muscle is stretched sufficiently, spontaneous action potentials are usually generated, they result from a 2 combination

Answer 40

1. nornal slow wave potential' 2. decrease in overall negativity of the mebrane potential caused by the stretched it self