Lecture 10 - Physiology Of Smooth Muscle

Question 1

Where is smooth muscle mostly found

Answer 1

In the wall of hollow organs and tubes

Question 2

What is the function of the smooth muscle within the walls and tubes of hollow organs

Answer 2

They are involved in mediating propulsive movements and exerting pressure within the blood vessels

Question 3

What does smooth muscle control within the vessels

Answer 3

The diameter, blood flow and pressure

Question 4

What does smooth muscle control within the lung airways

Answer 4

The diameter, airflow and air resistance

Question 5

What does the smooth muscle control within the urinary system

Answer 5

The propulsion of urine through the ureters, bladder tone and the tone of the internal sphincter

Question 6

What does the smooth muscle control within the gastrointestinal tract

Answer 6

the tone, motility and the opening/closing of the sphincers

Question 7

What does smooth muscle do in the male reproductive system

Answer 7

It aids the secretion and propulsion of semen

Question 8

What does smooth muscle do in the female reproductive tract

Answer 8

It aids propulsion within the fallopian tubes and aids child birth through the pressure exerted by the uyterus

Question 9

What does smooth muscle do in the eye

Answer 9

It controls the pupil diameter and the lens shape

Question 10

What muscles control pupil diameter of the eye

Answer 10

The iris muscles

Question 11

What muscles control the lens shape of the eye

Answer 11

The ciliary muscles

Question 12

What does smooth muscle do within the skin

Answer 12

It is involved in hair erectrion

Question 13

What muscles cause hair erection

Answer 13

The pili muscles

Question 14

What are the three types of filaments within smooth muscle

Answer 14

Thick myosin filaments, thin actin filaments and intermediate sized filaments

Question 15

Within smooth muscle what do the actin filaments contain

Answer 15

Tropomyosin

Question 16

What are the intermediate filaments involved in

Answer 16

Only involved in cytoskeletal elements but not contraction

Question 17

What does smooth muscle respond to

Answer 17

An increase in cytosolic levels of Ca2+

Question 18

How is smooth muscle arranged

Answer 18

In sheets

Question 19

What does contraction occur by

Answer 19

The sliding filament mechanism

Question 20

What is the cross bridge cycle regulated by

Answer 20

By intracellular Ca2+

Question 21

Within smooth muscle what does Ca2+ bind to

Answer 21

Calmodulin

Question 22

What are the differences between skeletal muscle and smooth muscle

Answer 22

Smooth muscle fibres do not form myofibrils and it also has no sarcomere pattern and no Z-line

Question 23

What do the actin filaments in smooth muscle join to

Answer 23

The dense bodies

Question 24

Where are dense bodies attached to

Answer 24

The inner surface of the plasma membrane

Question 25

What proteins are the dense bodies made up of

Answer 25

Titin (the same protein that forms the Z line)

Question 26

What are the dense bodies held in place by

Answer 26

The intermediate filaments

Question 27

How many thin filaments surround each thick filament

Answer 27

10-15

Question 28

What is smooth muscle innervated by

Answer 28

The autonomic nervous system

Question 29

Are the thin filaments in smooth muscle all pulled in the same direction

Answer 29

No they are pulled in all different directions

Question 30

Where does most of the calcium required to trigger contraction in smooth muscle come from

Answer 30

The extracellular fluid

Question 31

The greater the volume of free calcium, the greater

Answer 31

The force of contraction

Question 32

How can the volume of calcium be increased

Answer 32

By binding of extracellular chemical messengers to G-protein coupled receptors

Question 33

What is an example of an extracellular chemical messenger

Answer 33

Noradrenaline

Question 34

What happens when noradrenaline binds

Answer 34

It activates phospholipase C

Question 35

What is attached to the myosin chain near the neck arean

Answer 35

The myosin light chain

Question 36

What is the function of the myosin light chain

Answer 36

The myosin light chain prevents the myosin molecule from interacting with the actin molecule while it is unphosphorylated

Question 37

What allows the interaction of actin and mysoin in smooth muscle

Answer 37

Th phosphorylation of the myosin light chain

Question 38

What phosphorylates the myosin light chain

Answer 38

The myosin light chain kinase

Question 39

What does contraction result from

Answer 39

The phosphorylation of the myosin light chain the the presence of elevated intracellular Ca2+ and ATP

Question 40

What does relaxation occur from

Answer 40

The dephosphorylation of the myosin light chain

Question 41

What dephosphorylates the myosin light chain

Answer 41

Myosin phophatase

Question 42

What type of activity does myosin phosphatase have

Answer 42

Constitutive activity

Question 43

What does it mean if a receptor has constitutive activity

Answer 43

The receptor is capable of producing a biological response in the absence of bound ligands

Question 44

What allows the Ca2+ leve;s to return to a basal concentration

Answer 44

Primary and secondary active transport

Question 45

What are the different classifications of smooth muscle

Answer 45

Phasic or tonic Multiunit or single unit Neurogenic or myogenic

Question 46

What are the characteristic of phasic smooth muscle

Answer 46

It contracts in bursts, the action potentials trigger a rise in intracellular Ca2+, the contraction is phasic and vigorous

Question 47

What body part are phasic contractions associated with

Answer 47

The walls of hollow organs

Question 48

What does phasic smooth muscle contain

Answer 48

Specialised, non-contractile cells that display spontaneous changes in membrane potential, independent of neural input

Question 49

Tonic smooth muscle is usually

Answer 49

Partially contracted at all times

Question 50

What is open at relatively low resting potential of tonic smooht muscle cells

Answer 50

The voltage-activated Ca2+ channels

Question 51

Ca2+ influx in tonic smooth muscle mediates a state of

Answer 51

Partial contraction or tone

Question 52

In tonic smooth muscle what does contraction vary because of

Answer 52

Factors that alter cytostolic Ca2+

Question 53

What body part is tonic smooth muscle usually associated with

Answer 53

The walls of arterioles

Question 54

Single unit muscle cells characteristics

Answer 54

The muscle fibres are electrically coupled by gap junctions, it is self-excitable but autonomic innervation modifies its activity and it can be phasic or tonic

Question 55

What is the single function unit of single unit muscle cells known as

Answer 55

A functional syncytium

Question 56

What are the two categories of myogenic activity of single unit muscle cells

Answer 56

Pacemaker potentials and slow-wave potentials

Question 57

Pacemaker potentials

Answer 57

The membrane potential gradually depolarises spontaneously to a value sufficient to reach the threshold for the generation of an action potential

Question 58

How does excitation propagate throughout the smooth muscle sheet

Answer 58

Through gap junctions to cause a self-induced contraction

Question 59

Slow-wave potentials

Answer 59

The membrane potential oscillates spontaneously between hyperpolarised and depolarised potentials but reaches the threshold for the generation of an action potential only in the presence of an external stimulus

Question 60

How does gradation of tension occur in skeletal muscle

Answer 60

Motor unit recruitment and twitch summation

Question 61

How does the gradation of tension occur in single unit smooth muscle cells

Answer 61

Through variations in the intraceullular levels of Ca2+ which regulates the number of cross bridges that are formed

Question 62

Characteristics of multiunit smooth muscle cells

Answer 62

The muscle fibres are electrically isolated for each other, excitation/contraction of the fibres occurs independently of each other, contraction is usually driven by innervation autonomic nervous system and the muscles are usually phasic