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Human Physiology I exam 1 > L12 Smooth Muscle > Flashcards

L12 Smooth Muscle Flashcards

1
Q

Smooth muscle is

A

Unstriated

Involuntary

Autonomic

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2
Q

Where is smooth muscle found?

A

Walls of “hollow” organs and tubes

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3
Q

Smooth muscle functions

A

Maintain organ shape

Produces motility

Maintains pressure

Regulates internal flow

Autonomic nervous system, hormones, other local paracrine agents controls smooth muscle tone, contraction, and relaxation

Doesn’t necessarily require motor innervation!

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4
Q

How are smooth muscle cells nucleated?

A

Single nucleated

No T-tubules

Body tubes can have circumferential and longitudinal layers of muscle

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5
Q

What are type things about the smooth muscle cell structure

A

Less developed SR that is in contact with membrane

Lipids rafts for extracellular communication -caveolae (concave )

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6
Q

How is smooth muscle innervated?

A

ANS

Axon of postganlionic autonomic neuron has terminals that branch

Swellings that contain neurotransmitters are called varicosities ( not motor endplate!)

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7
Q

Two types of smooth muscle

A

Multi unit (neurogenic)

Single-unit (unitary) (myogenic)

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8
Q

Multi unit/ neurogenic smooth muscle

A

No gap junctions

High density of autonomic neurons

Every cell needs input of autonomic nervous system in order to function

Allows finer motor control

Eye, skin hair follicles, large blood vessels, small airways, vas deferens

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9
Q

Unitary /myogenic smooth muscle

A

Gap junctions (which permits coordianted contraction)

Low density autonomic innervation

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10
Q

Gap junctions

A

Cells linked by connexon tunnels

Connected anatomically

Connected electrically to form a functional syncytium

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11
Q

What muscle types are gap junctions found?

A

Single unit / unitary smooth muscle

Cardiac muscle

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12
Q

Types of filaments in smooth muscle

A

Thick myosin (longer than skeletal)

Thin actin
contain tropomyosin (present, not blocking)
NO TROPONIN

Actin/myosin gathered by dense bodies making them more diamond shaped than square

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13
Q

Arrangements of thick and thin filaments in smooth muscle cell

A

Relaxed- filaments not bound

Contracted- filaments interacting , allows sliding, muscle as a whole is reduced in size

Same as skeletal muscle

Uses ATP every cycle

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14
Q

How is cross bridge cycling regulation in smooth muscle?

A

Occurs on thick myosin head by light weight proteins attached to the myosin (myosin light chains)

Part where head bends have light chain portion

This area has high capacity phosphorylation site (not in skeletal muscle)

Kinase is enzyme that phosphorylates that portion - activates heads affinity for actin and ATPase

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15
Q

Calcium in smooth muscle may come from

A

SR or outside

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16
Q

What does Ca interact with when it comes out of the SR or outside in smooth muscle contraction?

A

Calmodulin

Ca-calmodulin complex

Complex activated myosin light chain kinase (MLCK) to phosphorylate myosin light chain

Turns on ATPase and myosin affinity for actin , crossbridge cycling and contraction occur

17
Q

What happens when Ca drops in smooth muscle?

A

Not as much Ca-calmodulin complex

MLCK not activation

Myosin light chain phosphatase (MLCP) becomes activate and dephosphorylates myosin light chain

No ATPase activity , low affinity for actin , no cross bridge activity

18
Q

What’s a main difference between crossbridge cycling mechanisms in skeletal and smooth muscle ?

A

Skeletal - physical reposition of troponin and tropomyosin

Smooth- series of biochemical events. Has an additional P on neck of myosin as well as ADP and Pi on head

19
Q

How does Ca rise in smooth muscle?

A

Electro-mechanical coupling -Depolarization

Pharmaco-mechanical coupling- hormones or neurotransmitters

20
Q

Electro-mechanical coupling/depolarization of smooth muscle

A

Action potential arrives, depolarizes cell

Opens voltage-gated Ca channels (outside to inside of cell) (if sufficient, will produces contraction)

If not - Ca induced Ca release from SR , Ca can act as second messenger to open rydianine receptors to allow more calcium in

Only in single unit smooth muscle (doesn’t require autonomic nerve to command it)

21
Q

Pharmacy-mechanical coupling

A

Hormones/neurotransmitters require input from autonomic nervous system

Hormone/ neurotransmitter interact w/ receptor it may create second messenger IP3-gated Ca channels or open ligand-gated Ca channel

In both single unit and multi unit smooth muscle

22
Q

What do IP3 gated Ca channels do?

A

Release Ca from SR through SERCA

Doesn’t go to Ca induced Ca release mechanism

23
Q

What do Ligand gated Ca channels do?

A

Let Ca in

If not enough - can go to Ca induced Ca release from SR

24
Q

Ca promotes actin-myosin interaction by stimulating myosin

A

Phosphorylation

25
Q

A single excitation in smooth muscle does not cause

A

All cross bridges to switch on
(In contrast to skeletal muscle)

Ca conc increases, more cross bridges, greater tension

26
Q

What are the ATPases and exchangers in smooth muscle?

A

SERCA -primary active (in cell)

Na/K ATPase- primary active (on membrane)

Sacrolemmal Na/Ca exchanger - secondary active (on membrane)

Sacrcolemmal Ca ATPase -primary active (on membrane)

To decrease contractile force , decrease conc of intracellular Ca

27
Q

How do they correlate to smooth muscle relaxation?

A

Na/K ATPase creates ion gradient

SERCA reduces cytosolic Ca conc by returning Ca into SR

Sarcolemma Na/Ca exchanger pumps Ca outside cell through Na/K ATPases Na gradient

Sarcolemma Ca ATPase pumps Ca out actively

This allows phosphatase to be more active in the cell and promotes relaxation

28
Q

How’s smooth muscle tone regulated?

A

Intercellular amount of Ca

MLCK to MLCP ratio

29
Q

Smooth muscle drugs

A

Calcium antagonists

cAMP

cGMP (stimulus and inhibitors)

30
Q

Calcium antagonists directly

A

Vasodilators

Block voltage gated Ca channels DIRECTLY, can’t get Ca-calodulim complex, MLCK not recruited, no possibility of crossbridge formation

RELAXATION

31
Q

Calcium antagonists indirectly

A

Potassium channel openers

Vasodilators

Opening of channel hyperpolarizes membrane will reduce ability to open voltage gated Ca channels

Reduces Ca-calmodulin complex and MLCK

RELAXATION

32
Q

cAMP smooth muscle drug

A

RELAXES smooth muscle by inhibiting MLCK even with Ca present

Beta2 adrenergic receptor agonists ,

when activated adrenergic receptor procures cAMP and blocks MLCK

33
Q

cGMP smooth muscle drug

A

RELAXES smooth muscle by decrease Ca and activating MLCP (myosin dephosphorylation)

Nitric oxide Stimulates cGMP production

phosphodiesterase- inhibit cGMP degradation which increases cGMP and activates MLCP

34
Q

Nitrates and phosphodiesterase inhibitors

A

Reduces Ca flow from Ca voltage gated channels

Enhances MLCP

Human Physiology I exam 1 (12 decks)

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