smooth muscle physiology

Question 1

what is the histology of skeletal muscle

Answer 1

striated
voluntary
somatic innervation (⍺- and 𝛾-motor neurons)

Question 2

what is the histology of cardiac muscle

Answer 2

striated
involuntary
autonomic innervation (sympathetic and parasympathetic post-ganglionic fibres)

Question 3

what is the histology of smooth muscle

Answer 3

unstriated
involuntary
autonomic innervation (sympathetic and parasympathetic post-ganglionic fibres)

Question 4

what is skeletal muscle (basic)

Answer 4

individual muscle fibres are large, elongated, cylindrical, and possess multiple nuclei

Question 5

what is cardiac muscle (basic)

Answer 5

individual muscle fibres are large, cylindrical and possess multiple nuclei

Question 6

what is smooth muscle (basic)

Answer 6

individual muscle fibres are relatively small, spindle shaped and possess one nucleus

Question 7

what is the function of smooth muscle in the vasculature

Answer 7

controls diameter
regulates flow and pressure

Question 8

what is the function of smooth muscle in the airways

Answer 8

controls diameter
regulates flow and resistance

Question 9

what is the function of smooth muscle in the urinary system

Answer 9

propulsion of urine into ureters
bladder tone
tone of internal sphincter of bladder

Question 10

what is the function of smooth muscle in the gastrointestinal tract

Answer 10

controls tone, motility, opening and closing of sphincters

Question 11

what is the function of smooth muscle in the male reproductive tract

Answer 11

secretion
propulsion of semen

Question 12

what is the function of smooth muscle in the female reproductive tract

Answer 12

propulsion (fallopian tubes)
partuition (uterus)

Question 13

what is the function of smooth muscle in the skin

Answer 13

pili erection

Question 14

what are the types of smooth muscle

Answer 14

tonic
phasic

Question 15

what is tonic smooth muscle

Answer 15

‘multi-unit’
electrical isolation of cells allows finer motor control
function ‘individually’
e.g. Iris and Vas deferens

Question 16

what is phasic smooth muscle

Answer 16

‘unitary’
gap junctions permit coordinated contraction
functions as a syncytium
e.g. stomach, urinary, bladder and bronchioles

Question 17

what is the contractile machinery of smooth muscle

Answer 17

smooth muscle relies on sliding filament mechanism generated during actin-myosin cross-bridge formation to facilitate contraction

Question 18

smooth muscle cross-bridge formation and sliding filament

Answer 18

1. driven by a rise in intracellular calcium which binds to calmodulin
   > calcium release from the SR
   > calcium influx across the plasma membrane
2. calcium-calmodulin complex activates myosin light chain kinase
3. myosin light chain is phosphorylated on the myosin head
4. phosphorylation of myosin head ‘cocks’ it and increases its ATPase activity readying it to interact with actin to form a cross bridge

Question 19

what factors affect striated muscle cross-bridge formation

Answer 19

an increase in intracellular calcium concentration
stretch - frank-starling relationship

Question 20

what factors affect smooth muscle cross-bridge formation

Answer 20

an increase in intracellular calcium concentration
phosphorylation of myosin light chain kinase
inhibition of myosin light chain phosphatase

Question 21

what is calmodulin

Answer 21

a multifunctional calcium binding protein present in the cytoplasm of all eukaryotic cells

Question 22

what is relaxation of smooth muscle

Answer 22

involves a drop in intracellular calcium concentration and dephosphorylation

Question 23

how is intracellular calcium concentration returned to pre-excitation concentrations

Answer 23

membrane bound calcium ATPases and sodium-calcium exchangers expel calcium from the cell
calcium is sequestered into stores by sarcoplasmic, endoplasmic reticulum calcium ATPases (SERCA)

Question 24

how does dephosphorylation work in relaxation of smooth muscle cells

Answer 24

myosin light chain phosphatase (MLCP)

Question 25

how is smooth muscle innervated

Answer 25

innervated by the autonomic nervous system vast network of neural supply over the surface of smooth muscle cells

Question 26

how it arterial smooth muscle innervated

Answer 26

sympathetic innervation with noradrenaline

Question 27

how is other (non-arterial) smooth muscle innervated

Answer 27

sympathetic and parasympathetic innervation with noradrenaline and acetylcholine

Question 28

what is pharmacomechanical coupling

Answer 28

the processes by which an agent causes a change in smooth muscle tone without a change in membrane potential involves the production of intracellular second messengers that either contract or relax the muscle

Question 29

what second messenger causes contraction of smooth muscle

Answer 29

inositol triphosphate, IP3

Question 30

what second messenger causes relaxation of smooth muscle

Answer 30

cGMP and cAMP

Question 31

what is electromechanical coupling

Answer 31

the opening of plasma membrane voltage-activated L-type calcium channels in response to depolarisation with, or without action potential generation

Question 32

how is relaxation caused in smooth muscle cells

Answer 32

NCX PMCA SERCA

Question 33

how does NCX cause relaxation in smooth muscle cells

Answer 33

utilises the sodium electrochemical gradient to pump calcium out of the cell

Question 34

how does PMCA cause relaxation in smooth muscle cells

Answer 34

utilises ATP hydrolysis to actively pump calcium out of the cell

Question 35

how does SERCA cause relaxation in smooth muscle cells

Answer 35

utilises ATP hydrolysis to actively pump calcium into the sarcoplasmic reticulum