Smooth muscle physiology

Question 1

is skeletal muscle striated or unstriated, voluntary or involuntary, and somatic or autonomic?

Answer 1

Striated
Voluntary
Somatic (a- and y- motor neurones)

Question 2

is cardiac muscle striated or unstriated, voluntary or involuntary, and somatic or autonomic

Answer 2

Striated
Involuntary
Autonomic

Question 3

is smooth muscle striated or unstriated, voluntary or involuntary, and somatic or autonomic?

Answer 3

Unstriated
Involuntary
Autonomic

Question 4

describe skeletal muscle

Answer 4

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

Question 5

describe cardiac muscle

Answer 5

Individual muscle fibers are large, cylindrical and possess multiple nuclei

Question 6

describe smooth muscle

Answer 6

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

Question 7

smooth muscle function of vasculature

Answer 7

controls diameter regulates flow and pressure

Question 8

smooth muscle function of airways

Answer 8

controls diameter regulates flow and resistance

Question 9

smooth muscle function of the urinary system

Answer 9

propulsion or urine into ureters, bladder tone, tone of intestinal sphincter of the bladder

Question 10

smooth muscle function of gastrointestinal

Answer 10

controls tone, motility, opening/closing of sphincters

Question 11

smooth muscle function of the male reproductive tract

Answer 11

secretion, propulsion of semen

Question 12

smooth muscle function of the female reproductive tract

Answer 12

propulsion (fallopian tubes), parturition (uterus)

Question 13

smooth muscle function of the skin

Answer 13

pili erection

Question 14

what are the two types of smooth muscle

Answer 14

single-unit and multi-unit

Question 15

what does the electrical isolation of cells allow

Answer 15

finer motor control

Question 16

what do gap junctions permit

Answer 16

coordinated contraction

Question 17

how does smooth muscle contract

Answer 17

like in skeletal muscle, smooth muscle relies on the sliding filament mechanism generated during actin-myosin cross-bridge formation

Question 18

Cross-bridge formation and sliding filament in smooth muscle

Answer 18

1. Driven by a rise in [Ca2+]i which binds to calmodulin
2. Ca2+-calmodulin complex activates myosin light chain kinase (MLCK)
3. Myosin light chain (MLC) is phosphorylated on the myosin head
4. Phosphorylation of myosin head ‘cocks’ it and increases it’s ATPase activity readying it to interact with actin to form a cross-bridge

Question 19

what are the factors affecting striated muscle cross-bridge formation

Answer 19

increased intracellular [Ca2+]
Stretch (frank-starling relationship)

Question 20

what are the factors affecting smooth muscle cross-bridge formation

Answer 20

Increased intracellular [Ca2+]
Phosphorylation of myosin light chain kinase
Inhibition of myosin light chain phosphatase

Question 21

what is calmodulin

Answer 21

a multifunctional Ca2+ binding protein present in the cytoplasm of all eukaryotic cells

Question 22

relaxation of smooth muscle

Answer 22

relaxation involves a drop in [Ca2+]i and dephosphorylation

Question 23

innervation of smooth muscle

Answer 23

innervated by the autonomic nervous system
→ Arterial smooth muscle – sympathetic innervation with noradrenaline
→ Other smooth muscle - sympathetic and parasympathetic innervation with acetylcholine

Vast networks of neural supply over the surface of the smooth muscle cells

Question 24

by convention contraction of smooth muscle can be described as what

Answer 24

Pharmacomechanical coupling
Electromechanical coupling

Question 25

what is Pharmacomechanical coupling

Answer 25

→ refers to 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
very important second messengers are:
→ inositol trisphosphate (IP3) causing contraction
→ cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), both causing relaxation

Question 26

what is electromechanical coupling

Answer 26

→ refers primarily to the opening of plasma membrane voltage-activated L-type Ca2+ channels in response to depolarisation with, or without, action potential generation

in reality the two overlap to some extent