smooth muscle experiment

7/29/2019 Smooth Muscle Experiment

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Bio-254

Experiments in Animal Physiology


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Muscle is a very specialized tissue that has both the ability tocontract and the ability to conduct electrical impulses.

Muscle tissue; voluntary

involuntary

Types of muscle tissue due to structure;

- smooth involuntary(smooth) muscle,

- striated voluntary(skeletal) muscle

- striated involuntary(cardiac) muscle.


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Specific nomenclature associated with muscle commonly

involves the prefix sarco-ormyo- .

- The cytoplasm of muscle fibers or cells is called sarcoplasm.

- The endoplasmic reticulum of fibers or cells is

called sarcoplasmic reticulum.- The plasmalemma of fibers or cells is called the sarcolemma.

- Individual muscle cells are called myocytes.


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The smooth muscle fibers (myocytes)are spindle-shaped.

The myocytes have one centrally locatednucleus.

Do no have striations . Lack clearly defined bands of actin and

myosin.

Its contraction is not under consciousnervous control, referred toas involuntary muscle.

The involuntary activity is controlled byautonomic nerves and circulatinghormones.


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Slow contractions

Little fatigue Low O2 use

Figure 12-24: Duration of muscle contraction in three types of muscle


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abundant throughout the internal organs of the bodyespecially in regions such as;

- in the walls of the digestive tract.

- in the walls of the respiratory tracts.

- in the walls of blood vessels.

- in the dermis of the skin.

- in the eye (iris diaphragm).

- in the wall of the uterus.


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- control the diameter of arterioles and help regulate bloodpressure.

- form muscle sphincters at branches of the vascular tree and

determine the distribution of blood to different capillary beds.- regulate the size and internal pressure of hollow organs.

- protect the internal organs.

- propelling the content of the internal organs.

- help to mix the chyme with the intestinal juice in the stomach,and in the intestine.


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Two types of smooth muscles are distinguished:

unitary s.m. and multiunit s.m.


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Unitary S.M.; display electrical pacemaker activity, and responseto stretch with increased tension. The extrinsic innervation ispoor, but the cells are electrically coupled by numerous gap

junctions, so that activity, once initiated, spreads rapidly

throughout the whole muscle layer, thus the multicellular muscleact as a single unit.

eg. in the walls alimentary tract


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Contractile activity of intestinal smooth muscles is responsible

for the tonic basal tension of the intestinal walls, for slowperistaltic contractions propelling the content, and for morefrequent contractions of smaller amplitude referred to asrhythmic segmentation, involved with mixing the chyme andintestinal juices.

Conditions inhibiting Na/K pump, i.e. hypoxia, low temperature,and treatment with cardiac glycosides depress slow-wave activityof smooth muscles.

Conversely, slow waves are enhanced by conditions thatstimulate sodium pumping, such as elevated temperature.


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Slow wave depolarizations appear to be generated also through

neural inf luences, including cholinergic intramural or enteric(within the intestine wall) nerve plexuses;

Application ofacetylcholine (ACh), or Ach agonist e.g., eserine

(inhibitor of ACh degrading enzyme: acetylcholine esterase)increases intestine motility,

Administration of ACh antagonist e.g., atropine (muscarinic

receptor blocker) slows it down.


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Multiunit S.M.; have motor units that resemble those of skeletalmuscle, and contractile tension is graded by variation in thenumber of active units. Intermediate between single unit smoothand skeletal muscles. Fibers are structurally independent, and

there is little or no spread of activity from cell to cell.

eg. in the walls of the blood vessels,

internal eye muscles


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Step 1.Wave of depolarizationalong membrane from theneuromuscular junction oradjacent cells.

Step 2. Calcium is releasedfrom caveolae andendoplasmic reticulum

Step 3. Calcium binds to

calmodulin Step 4. Calcium-calmodulin

complex activates and unfoldsmyosin light chain kinase


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Step 5. ATP is used tophosphorylate myosin lightchain kinase (this is unique tosmooth muscle).

Step 6. Phosphorylated lightchain kinase is activated so itcan bind actin.

Step 7.Works like an ATPase

to bind actin and move alongthe F actin chain.

! Smooth muscle myosin has a lower ATPase activity ;corresponding to slower rate of contractions of smooth muscles !


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In short, this works like thesliding filament to contractthe muscle cells.

Intermediate filaments(desmin and vimentin) help

with the contraction bypulling the cell ends in

(shortening the cell).


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What are the differences and similarities between theskeletal muscle and the cardiac muscle with the

smooth muscle, in terms of structure and mechanismof contraction???


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Biopac Student Lab System

Smooth muscle from the rats intestine

Tyrods solution

Isolated organ bath

Adrenaline

Eserine (Physostigmine)

Acetylcholine

Atropine

Oxygen source


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A. Preparation

- Pith the rat.

- Dissect a portion of small intestine from rat.

- Put Tyrods sln into the organ bath.

- Keep the system at 370C.

- Place the isolated portion of

intestine into the organ bath.

- Adjust the screw clamp onthe aeration tubing


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B. Recording normal activity

C. Effect of Tension

D. Effect of Removal of Air Supply

E. Effect of Temperature

F. Effect of Drugs - adrenalin sln.

- acetylcholine sln.

- eserine sln.

- atropine sln.


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Two types of nerves help to control the action of the digestivesystem.

Intrinsic (inside) nerves, embedded in the walls of theesophagus, stomach, small intestine, and colon. The intrinsic

nerves are triggered to act when the walls of the hollow organsare stretched by food. They release many different substancesthat speed up or delay the movement of food and the productionof juices by the digestive organs.

Extrinsic (outside) nerves come to the digestive organs from the

unconscious part of the brain or from the spinal cord. Theyrelease a chemical calledacetylcholineand anothercalledadrenaline.
http://www.fact-index.com/a/ac/acetylcholine.htmlhttp://www.fact-index.com/e/ep/epinephrine.htmlhttp://www.fact-index.com/e/ep/epinephrine.htmlhttp://www.fact-index.com/a/ac/acetylcholine.html


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Acetylcholine activates muscles by binds to acetylcholine

receptors on skeletal muscle fibers, it opens ligand-gated sodium

channels in the cell membrane. Sodium ions then enter the

muscle cell, initiating a sequence of steps that finally produce

muscle contraction.

Adrenaline functions result from its binding to a variety of

adrenergic receptors It participates in the fight-or-flight

response , and cause smooth muscle cells to relax.


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Physostigmine (eserine) acts by interfering with the metabolism

ofacetylcholine. It is an inhibitor of Acetylcholinesterase, the

enzyme responsible for the breakdown of acetylcholine in the

synpatic cleft of the neuromuscular junction. (Ach agonists)

Atropine lowers the parasympathetic activity of all muscles

and glands regulated by the parasympathetic nervous system,

because atropine is a competitive antagonist of the muscarinic

acetylcholine receptors. They block the acetylcholine receptors.

(ACh antagonists)
http://en.wikipedia.org/wiki/Acetylcholinehttp://en.wikipedia.org/wiki/Acetylcholine

smooth muscle experiment

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