Materials for auditory self-work. 4.1.List of study practical tasks necessary to perform at the practical class.



4.1.List of study practical tasks necessary to perform at the practical class.

Materials and methods: vertical myograph, stimulator, irritating electrodes, kymograph, strand, preparation instruments set, gauze napkins, Ringer’s solution.

Investigatioin object: frog.

 

Task 1. Skeletal muscle contractions curves registration

a)To prepare nervous-muscular preparation, to fix it in myograph and to bring the electrodes from constant current electrofeeding source. To irritate the muscle with separate key blow and to registrate (write) separate muscular contraction curve. The velocity of kymograph drum must be maximal. Mark the separate muscular contraction phases and their duration.

b)Infused (incomplete) tetanus. Right after the separate muscular contraction curve the investigator performes 10-20 fast going one after another key closing and unclosing. As a result imperfect, incomplete summation of separate muscular contractions - infused (incomplete) tetanus – occurs.

c)Smooth (complete) tetatus. For its receiving the muscle must be irritated with high frequency – 50 oscillations per second. Electrods must be brought to the unconstant current electrical feeding and the key must be closed in course of 2-5 seconds.

To measure the altitude of single muscular contraction, infused and smooth tetanus curves received at equal stimulus force.

To glue the curves received into copy-books. To make the conclusions.

Task 2. Dynamometry

The investigated person is asked to sit on the chair and to stretch his arms forward and to pressure dynamometer maximally with a hand. Every hand muscular force should be estimated 3 times.

The results should be written in a copy-book.

4. Literature recommended:

1. Lecture course.

2. Mistchenko V.P., Tkachenko E.V. Methodical instructions for dental students (short lecture course).-Poltava, 2005.-P. 6-8.

3. Mistchenko V.P., Tkachenko E.V. Methodical instructions for medical students (short lecture course).-Poltava, 2005.-P. 7-9.

4. Mistchenko V.P., Tkachenko E.V. Methodical instructions on Normal Physiology on practical classes for dental and medical students.-Poltava, 2005.-P.12-21.

5. Ganong W.F. Review of Medical Physiology.-21st ed.-2003.-Section II.

6. Kapit W., Macey R.I., Meisami E. The Physiology Colouring Book: Harpers Collins Publishers, 1987.-P. 18-24.

7. Bullock J., Boyle III J., Wang M.B. Physiology.-1991.-. P. 18-35.

8. Guyton – Ganong – Chatterjee. Concise Physiology /Ed. By Dr Raja Shahzad Gull: M.B.B.S., F.C.P.S., King Edward Medical College.-Lahore, 1998 (1st Edition).-P.19-29.

9. Guyton A.C. Textbook of Medical Physiology.-NY, 1992.-P. 120-134.

5. Materials for self-control:

A . Control questions:

1. Call and characterize main muscles types according to structure and function peculiarities.

2. Describe the gliding (sliding) fibers theory, explaining muscular contraction.

3. Call contractive proteins (effector, regulatory) and tell about their role in course of muscular contraction.

4. Give the definition of: sarcomere; sarcoplasmic reticulum; A-disc (anisotropic); I-disc (isotropic); Z-line.

5. What muscles are arbitrary (voluntary) and what are involuntary ones? What do these terms mean?

6. Where and in what organs are there skeletal muscles?

7. Give the definition of isotonic and isometric contractions.

8. What is the trigger mechanism of skeletal muscles action potential?

9. Why tetanic contraction level is bigger than single contraction level?

10. Draw the curves of skeletal muscle excitability change in course of its exaltation.

LESSON 5
Skeletal and smooth muscles comparative characteristics.

1. The topic studied actuality.

Smooth muscles are in inner organs composition. They provide motor function (alimentary tract, urinary-sexual system, blood vessels and others) due to their contraction.

Knowledge about smooth muscles functioning mechanisms and regularities allows particularly to understand vascular tone, alimentary tract motor activity disorders mechanisms. Big sensitivity to chemicals is rather important for practical doctors. It is so because pharmacological agents changing muscular contractility is in usage at many pathological conditions.

2. Study aims:

To know: excitement changing peculiarities in smooth muscles during contraction, contraction peculiarities; smooth muscles features; automatism mechanism; contraction and relaxation distinguishing features.

To be able to: draw the scheme explaining smooth muscle excitability changings during its contraction; to make the table on skeletal and smooth muscles physiological features comparative characteristics.

3. Pre-auditory self-work materials.

3.1.Basic knowledge, skills, experiences, necessary for study the topic:

Subject To know To be able to
Medical biophysics Electrical phenomena in excitable tissues, tissues activity energetic providing Work with electrical devices
Medical biology Substances transport mechanisms through biological membranes  
Histology Smooth muscles morphological-functional characteristics Prepare smooth muscles preparation and differentiate it from skeletal muscles preparation
Therapy Smooth muscles functioning peculiarities in respiratory, alimentary and uro-sexual tracts.  

 

3.2.Topic content.

DISTRIBUTION

Smooth muscles are non-striated (plain) and involuntary muscles. These muscles form the major contractile tissues of various organs.

Muscles, which are in association with viscera, are called smooth muscles or visceral muscles. These muscles are supplied by sympathetic and parasympathetic division of autonomic nervous system. Smooth muscles form the main contractile units of wall of the various visceral organs and are present in the following structures:

a. Wall of organs like esophagus, stomach and intestine in gastrointestinal tract

b. Ducts of digestive glands

c. Trachea, bronchial tube and alveolar ducts of respiratory tract

d. Ureter, urinary bladder and urethra in excretory system

e. Wall of blood vessels in circulatory system

f. Errector pilorum of skin

g. Mammary glands, uterus, genital ducts, prostate gland and scrotum in reproductive system

h. Iris and ciliary body of the eye.

STRUCTURE

Smooth muscle fibers are fusiformed or elongated cells of different length.

Smooth muscle fibers are generally very small, measuring 2 to 5 microns in diameter and 50 to 200 microns in length. Each muscle fiber contains myofibrils. The myofibrils are made up of muscle proteins. But, there are no dark and light alternated bands. This is the cause for nonstriated appearance of the smooth muscle.

Smooth muscle fiber contains actin, myosin and tropomyosin components. But troponin or troponin like substance is not present. For the initiation of contraction in skeletal muscle, the calcium ions released from cisternae of sarcoplasmic reticulum, combine with troponin. But in smooth muscle, in addition to the absence of troponin, the sarcoplasmic reticulum is also poorly developed. So, when smooth muscle fiber is excited, the calcium ions enter the sarcoplasm from extracellular fluid through the voltage-gated calcium channels. The calcium ions combine with another protein called calmodulin leading to initiation of contraction.

Electron microscopic studies reveal that some dense bodies are attached to the cell membrane and scattered all over the body of the fibers. Actin filaments are attached to these dense bodies. In between actin filaments, the thick myosin filaments are situated. There are cross bridges between actin and myosin filaments. The cross bridges help in the sliding mechanism of muscle contraction.

CONTRACTILE PROCESS IN SMOOTH MUSCLE

In smooth muscle, latent period is long and contraction process is slow. The relaxation is also slow. Thus, the total twitch period is about 1 to 3 seconds.

MOLECULAR BASIS OF SMOOTH MUSCLE CONTRACTION

The process of excitation and contraction is very slow in smooth muscles. This is because of poorly developed L tubules (sarcoplasmic reticulum) in smooth muscle fibers. So, the calcium ions, which are responsible for excitation contraction coupling, must be obtained from the extracellular fluid. This makes the process of excitation contraction coupling slow.

Stimulation of ATPase activity of myosin in smooth muscle is different from that in the skeletal muscle. In smooth muscle, the myosin has to be phosphorylated for the activation of myosin ATPase. The phosphorylation of myosin occurs in the following manner. Calcium entering the sarcoplasm from the extracellular fluid combines with calmodulin forming calcium-calmodulin complex. This activates an enzyme called calmodulin-dependent myosin light chain kinase. This enzyme in turn causes phosphorylation of myosin followed by activation of myosin ATPase. Now, the sliding of actin filaments starts.

Phosphorylated myosin gets attached to the actin molecule for longer period. It is called latch bridge mechanism and it is responsible for sustained contraction of the muscle with expenditure of little energy.

Relaxation of muscle may occur due to the dissociation of calcium-calmodulin complex.

HORMONES INFLUENCE ON SMOOTH MUSCLE

Some hormones of the body cause the contraction of smooth muscle and some hormones inhibit the contraction. Action of the hormone depends upon receptors present in the cell membrane. Receptors are of two types namely excitatory receptors and inhibitory receptors. Hormones binding with excitatory receptors cause contraction of muscle by producing depolarization. Hormones binding with inhibitory receptors inhibit contraction by increasing the negativity of membrane potential, which is called hyperpolarization.

NERVE SUPPLY TO SMOOTH MUSCLE

Smooth muscles are supplied by both sympathetic and parasympathetic nerves, which antagonize each other in control the activities of smooth muscles. However, nerves are not responsible for the initiation of any activity in smooth muscle. Tonus of smooth muscles is independent of nervous control.

NEURO-MUSCULAR JUNCTION OF

SMOOTH MUSCLE

There is no well defined neuro-muscular junction in smooth muscle. The nerve fibers diffuse on to muscle fibers The chemical neurotransmitters are directly released in the interstitial fluid.


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