Types of smooth muscle. Membrane potentials and action potentials in smooth muscle. Source of calcium ions that cause contraction: role of the cell membrane and the sarcoplasmic reticulum.

Question 1

list the types of smooth muscles

Answer 1

visceral/ single unit
multi unit
unitary

Question 2

visceral smooth muscle - location

Answer 2

CURRD

circulatory system
- blood vessels

urinary system
- urinary bladder

reproductive system
- uterus

respiratory system
- lung

digestive system
- stomach
- intestines

Question 3

visceral smooth muscle - characteristics

Answer 3

• interconnected cells via gap junctions = direct communication
• spindle shaped cells with single nucleus
• spontaneous + rhythmic contractions
• innervated by ANS as no neuromuscular junction

Question 4

visceral smooth muscle - functions

Answer 4

circulatory system = vessels control blood pressue/ blood volume

urinary system = micurition

respiratory system = lungs for bronchodilation/ bronchoconstriction

reproductive system = uterine contractions

digestive system = peristalsis movements

Question 5

multi-unit smooth muscles - location

Answer 5

iris of eye
cilary body of eye
erector pilli muscles

Question 6

multi unit smooth muscles - characterisitcs

Answer 6

• individual muscle fibres that is innervated by its own nerve ending
• rapid response in response to hormones/stimuli to make quick adjustments
• no gap junctions

Question 7

multi-unit smooth muscles - functions

Answer 7

iris of eye = controls how much light enters in

cilary body of eye = focus on objects at different distances

erector pilli = contract pili muscles to increase hair follicles for heat trapping

Question 8

unitary smooth muscle - location

Answer 8

GI tract
bladder
uterus

Question 9

unitary smooth muscles - characteristics

Answer 9

• individual muscle fibres innervated by their own nerve ending
• gap junctions may be present
• rhythmic + coordinated contractions
• plasticity = adapts to changes in volume

Question 10

unitary smooth muscles - function

Answer 10

GI tract
bladder
uterus

Question 11

membrane potential 1

Answer 11

RESTING MEMBRANE POTENTIAL

when there are no ions going in/out of cell

RMP is -50mv

due to unequal distribution of ions inside/ outside membrane

due to selective permeability to these ions

Question 12

membrane potential 2

Answer 12

DEPOLARISATION

• caused by arrival of stimulus (hormone/ neurotransmitter)

voltage gated sodium channels open
na+ influx
making inside positive

Question 13

membrane potential 3

Answer 13

REPOLARISATION

voltage gated potassium ion channels open
k+ efflux
making inside negative

Question 14

membrane potential 4

Answer 14

HYPERPOLARISATION

overshooting of k+ efflux making inside cell even more negative

Question 15

action potential - 1

Answer 15

spike potential

• fast AP
• rapid depolarisation + repolarisation

Question 16

action potential - 2

Answer 16

plateau potential

• prolonged depolarisation = more calcium influx

Question 17

sources of calcium ions that cause contraction - type 1

Answer 17

EXTRACELLULAR

voltage gated calcium channels L type open
- ca2+ influx from ECF into cell

Question 18

sources of calcium ions that cause contraction - type 2a

Answer 18

IP3 receptors of SR

g-coupled receptor channels bind to ligand, g-coupled protein activated which stimulates associated g-coupled protein channel to produce phospholipase C which breaks down PIP2 into IP3 + DAG

IP3 ligand binds to IP3 receptors in SR stimulating Ca2+ release into cytoplasm

Question 19

sources of calcium ions that cause contraction - type 2b

Answer 19

DHPR receptors on T tubules + RyR receptors on SR = pump ca2+ into cytoplasm

Question 20

role of sarcolemma

Answer 20

• entry of calcium ions
• barrier function
• maintains RMP

Question 21

role of sarcoplasmic reticulum

Answer 21

calcium storage
= calsequestrin to keep calcium levels high in SR

calcium release