Lecture 16: Smooth muscle Flashcards
Kinds of Muscle
- skeletal muscle
- cardiac muscle
- smooth muscle
Smooth muscle cell components 6
- cell nucleus
- oval with ends long and thin shape
- cytoskeleton: thi, thin, dense
4 * Smooth muscle has no visible sarcomeres
- Contraction is still via actin and myosin
6 * Control of contraction is from Ca2+ binding to calmodulin and
phosphorylation of myosin by MLCK.
Smooth (visceral) Muscle: 2
- Not striated
- Controlled by Autonomic nerves, hormones, local mediators
Smooth (visceral) Muscle found in: 5
1 − Blood vessels.
2 − Respiratory system
3 − Alimentary tract
4 − Bladder
5 − Uterus
Smooth (visceral) Muscle Characteristics = 5
1 ➢ Contractions are SLOW
2 ➢ Very RESISTANT TO FATIGUE
3 ➢ Contraction used lLITTLE ENERGY
4 ➢ TONE can be maintained indefinably
5 ➢ Some smooth muscle are PHASIC i.e. they show
rhythmic contractions.
Multi Unit Smooth Muscle Characteristics = 5
1 ➢Discreet motor units (like skeletal muscle)
2 ➢Units must be activated separately
3 ➢Always produced smooth TONIC contractions
when activated.
4 ➢Not rhythmic
5 ➢Found in eye, Large blood vessels, Airways
Single Unit Smooth Muscle = 5
1 ➢Cells function as a single unit (like Heart)
2 ➢GAP. JUNCTIONS between cells
3 ➢TONIC in Bladder, small blood vessels.
4 ➢PHASIC (rhythmic) in Gut, Uterus
5 ➢Often show SLOW WAVES or BASAL ELECTRICAL RHYTHM
Interstitial Cells of Cajal (ICC) = 2
1 ➢ Gastric and intestinal smooth muscle is
electromechanically coupled
2 ➢ Interstitial cells of Cajal are the pacemaker cells which
trigger depolarisation
GAP JUNCTIONS = 3
1 ➢ Pacemaker potential travels cell to cell from ICC to SM
2 ➢ Connections by gap junctions
3 ➢ Pores between cells formed by connexon allow passage of ions
Smooth Muscle Action Potential
calmodulin
REST
inside low Ca+2
Kv not in receptor NOT OPEN
Kir receptor OPEN for K+ out
Ltype receptor NOT OPEN , Ca+2 cannot enter
DEPOLARISATION
inside high Ca+2
Kv not in receptor NOT OPEN
Kir receptor CLOSED for K+ from coming
Ltype receptor OPEN , Ca+2 enters
REPOLARISATION
inside high Ca+2
Kv OPEN receptor FOR K+ OUT
Kir receptor CLOSED for K+ from coming
Ltype receptor CLOSED , Ca+2 NOT enters
Phasic Smooth Muscle = 6
1 ➢IINTERSTITIAL CELLS OF CAJAL generate
pacemaker potentials “SLOW WAVES”
2 ➢Slow waves last second and ~10-15mV
3 ➢Pass to muscle through gap juntions
4 ➢Action potential due to opening of voltage
gated calcium channels (L-type channel)
5 ➢Repolarization from opening Kv channels
6 ➢Resting potential from open Kir channels
Excitation Contraction Coupling slide 21
Actin
- contraction
pmyosin
—> MLCP —> myosin
<—MLCK
Calmodulin Ca2+
Excitation Contraction Coupling slide 22
Actin
- contraction
Pmyosin
—-> MLCP = myosin
myosin <—MLCK (CalM -Ca2+)
Smooth Muscle Contraction = 7
1 ➢Contraction produced by ACTIN and MYOSIN
2 ➢Rise in intracellular Ca2+ is the trigger for
contraction
3 ➢Calcium binds CALMODULIN
4 ➢Ca2+-Calmodulin activates MYOSIN LIGHT CHAIN KINASE (MLCK).
5 ➢ Myosin is phosphorylated and binds actin
6 ➢Contraction occurs
7 ➢Dephosphorylation by MYOSIM LIGHT CHAIN PHOSPHATASE (MLCP)
Smooth Muscle Contraction
- where and what do they use and influx? = 4
1 ➢Some smooth muscles use intracellular
calcium stores (e.g. airways, blood vessels)
2 ➢Some smooth muscles rely on extracellular
calcium (e.g. gut)
3 ➢Calcium influx can be triggered by action
potentials (e.g. gut)
4 ➢Calcium influx can be triggered by receptor
binding (e.g. blood vessels and adrenaline)
Neural control:
Tissue: Blood Vessel
Acetylcholine and Noradrenaline what it does?
Acetylcholine -Relax, vis nitric oxide
Noradrenaline - Constrict, a-adrenergic
Neural control:
Tissue: AIRWAYS
Acetylcholine and Noradrenaline what it does?
Acetylcholine = Constrict, M-cholinergic
Noradrenaline = Relax, b-adrenergic
Neural control:
Tissue: GUT
Acetylcholine and Noradrenaline what it does?
Acetylcholine = Constrict, M-cholinergic
Noradrenaline = Relax, b-adrenergic
Neural control:
Tissue: GUT SPHINCTERS
Acetylcholine and Noradrenaline what it does?
Acetylcholine =Relax, vis nitric oxide
Noradrenaline = Constrict, a-adrenergic
understanding Neural Control = 5
1 ➢ Acetylcholine (ACh) acting on muscarinic (M)
receptors always constricts smooth muscle
2 ➢ ACh induced relaxation from a second transmitter,
nitric oxide.
3 ➢ * a-adrenergic* receptors typically constrict
4 ➢ b-adrenergic receptors mostly relax
5 ➢ Need to know about G-protein coupled receptors
(GPCR)
summary
1 * Three kinds of muscle
2 * Smooth muscle has no visible sarcomeres
- Contraction is still via actin and myosin
4 * Control of contraction is from Ca2+ binding to calmodulin and
phosphorylation of myosin by MLCK.
5 * Tonic muscle produces constant contraction (blood vessels),
phasic muscle shows rhythmic contraction (gut)
6 * Slow waves in gut generated by ICC depolarize smooth muscle
causing contraction
7 * Gut muscle contraction triggered by opening L-type calcium
channels, direct calcium entry
8 * ACh mostly causes contraction but can relax via a second
transmitter. NA relaxes via b-receptors and stimulates via areceptors
