Skeletal and smooth muscles comparative characteristics



Skeletal muscles Smooth muscles
They are the structural part of musculo-skeletal apparatus. They have no plastic tonus. They have fast short-termed depolarization and short absolute refractory period. They have no the ability for differentiation and division. They are innerved by somatic nervous system.   They are contracted under impulses transduction through the motor nerves from spinal motoneurons (automatism absence). They have the ability to fast phasic contractions. They realize arbitrary muscular movements that are accompanied by significant energy loss. They have weak sensitivity to chemical substances.  They react to medicines in some extent. They are the structural part of inner organs and vessels membranes. They have plastic tonus. They have slow depolarization and long-termed absolute refractory period.   They have the feature of differentiation, division and regeneration under injury. They are innerved by vegetative nervous system and have their own innervation apparatus (metasympathic nervous system. They are contracted both under impulses that occur in muscles themselves (automatism existance) and impulses transduction through vegetative nerves. They have the ability to long-termed tonic contractions. They realize arbitrary muscular movements that are accompanied by insignificant energy loss. They have high sensitivity to chemical, pharmacological, endogenous and exogenous biologically active substances. They react to medicines in large extent.

Further events (common for skeletal and smooth muscles) –

ATP-dependent contraction part

1. Myosin head binds ATP molecule.

2. Myosin head decomposes ATP till ADP and phosphate, ADP and phosphate are remained binded with myosin head; myosin head containing ADP and phosphate is turned and is binded to actin.

3. ADP and phosphate are disconnected from myosin head binding to actin; at the moment myosin head makes rowing movement and myosin molecule passes alongside actin molecule (with other words, myosin molecule stretches actin out to itself).

4. Myosin head binds new ATP molecule and right after this it is disconnected from actin and acquires its initial location.

5. So, muscle can neither contract nor relax without ATP. Myosin head possesses ATP-ase activity only under contraction condition.

Materials for auditory self-work.

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

Materials and methods: vertical myograph, stimulator, irritating electrods, kymograph, universal stand, preparating instruments set, pipette, gauze napkin, Ringer’s solution.

Investigation object: frog.

Task 1. Frog’s stomach smooth muscles contractions registration

To cut the ring 5 mm wide from the frog’s stomach. One end should be fixed on motionless hook, another one – on hook connected with writing lever. Hooks are electrods in parallel. As smooth muscles excitability is low one should use strong and long-termed current for the irritation. Kymograph must have very slow working (movement).

To registrate and to analize smooth muscles contractive process. To compare with the frog’s skeletal muscle contractions registration.

Task 2. To compare frog skeletal and smooth muscle to chemicals

To put 2-3 drops of acetylcholine solution (warmed a little) to the frog nervous-muscular preparation. To note reaction presence or absence while recording on kymograph stripe.

To repeat the same in the second experiment but with 2-3 drops of adrenaline. To note reaction presence or absence while recording on kymograph stripe.

To do the same with stomach smooth muscle.

To glue received curves in a copy-book, to compare kymograms taken. To compare skeletal and smooth muscles sensitivity to chemicals.

5. 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. 120-149.

6.Materials for self-control:

A. Control questions.

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

2. Where and in what organs are there skeletal and smooth muscles?

3. What are the differences between smooth and skeletal muscular contraction?

4. Give the characteristics of smooth muscles excitability, conduction and automatism.

LESSON 6
Excitation transmission investigation through nervous fibers and nervous-muscular synapses

The topic studied actuality.

Doctor often meets excitement conductance disorders in nervous-muscular synapses and nervous fibers. He must influence on them well-singlemindedly with impulses conductance enforcement or weakening. So, he should know excitement conductance mechanisms and regularities. Nervous fiber is reflectory arc afferent or efferent part. Reflex disappears at nervous impulse conductance disturbance. Different nervous fibers possess various excitability and excitement conductance different speed. It should be taken into account while medicines dosage prescription. Nervous fibers conductance laws are used in neurology and anaesthesiology.

Axons can be injured at some diseases. Both distal and proximal part can degenerate after axon cutting. It regenerates in peripheral nervous system after several weeks but its growing locuses first are non-myelinized. At different-origined neuropathies axons also loose their myeline sheath becoming demyelinated. Besides, doctor can meet axone neuropathies main symptome of which is, probably, axon transport disorder.

Demyelinated axons especially often interact with abnormal interactions. Impulses passing through nervous fibers groups induce the excitement of other parallel axons. So, law of impulse isolated coming (see below) becomes injured. It is known as ephaptic transmission. When such abnormal action potentials are generated in sensory nervous fibers abnormal sensations appear in patient. They can be agonizing especially if they are connected with nociceptive (pain) fibers. Neuralgy (pain by nervous fibers course), causalgy (pain without definite origine), neuromic pain and other hardly-treated and non-pleasant syndromes can appear. Interaxonal problems can be the result both of insufficient isolation (with myeline sheathes) and increased axons excitability.

Multiple sclerosis is a neurological disease usually diagnosed in people between the ages of 20 and 40. It is a chronic, degenerating, remitting, and relapsing disease that progressively destroys the myelin sheaths of neurons in multiple areas of the CNS. Initially, lesions form on the myelin sheaths and soon develop into hardened scleroses, or scars (from the Greek word sclerosis, meaninf “hardened”). Destruction of the myelin sheaths prohibits the normal conduction of impulses, resulting in a progressive loss of functions. Because myelin degeneration is widespread and affects different areas of the nervous system in different people, multiple sclerosis has a wider variety of symptoms than any other neurological disease. Although the causes of it are not fully known, there is evidence that the disease involves a genetic susceptibility combined with an immune attack on the oligodendrogliocytes and myelin, perhaps triggered by viruses. Inflammation and demyelination then occur, leading to the symptoms of multiple sclerosis.

Alongside with exciting or inhibitory functional signals transmittance, synapses provide trophic (dealing with growth and differentiation) interconnections of contacting cells realized by means of trophic proteinic factors (probably accumulating in “dark” vesicles). Such influencings are especially expressed in neuro-muscular (myoneural) synapses directed to myocytes metabolic support.

Denervation leads to skeletal muscular fibers features changing: to fast muscles retardation as well as slow ones acceleration id est to differentiation loosing.

Muscular denervation effects are imitated with actions of toxins which disturb synaptic transmission namely botulinic and diphtherial one.

They know high synapses sensitivity to different influencing which makes these neuronal parts the mostly vulnerable. Moreover, switching definite synapses quantity off brain function and injury of any synapses system are able to form clinical symptomal complexes by themselves, influence on brain diseases dynamics as a whole. Electronic microscopy can show several clinical syndromes which are developed only or first of all due to synapses injuries.

Synapses ultrastructure pathological changings are not specific to aethiological moments caused their injury.

Synapses injuries reasons:

1. ionizing irradiation;

2. electrical trauma;

3. pharmacological actions;

4. intoxications;

5. hypoxy.

It makes tryings to classify synapses pathological changings by traditional ethiological principle rather difficult. Absence of rather detailed information about local physiological and biochemical changings in synapses does not allow apply also pathogenetical principle at this classification processing. Moreover, identical by pathogenesis influencings (hypoxy, axon cutting) cause sometimes non-equal changings of axons presynaptic parts even in one system of fibers.

4 main types of synapses injury:

1. dark degeneration (cytoplasm staining with black osmium increasing);

2. filamentary degeneration (like ring);

3. light degeneration (cytoplasm staining with black osmium decreasing);

4. focal degeneration (synapse decomposition).

Dark degeneration is the most widely-spread; focal one – the least one.

Dark degeneration is observed at axon cutting. Synapses changings by light type occur not only as a result of axons injury but they are characteristic symptom of brain injury at hypoxy. Synapse focal or partial destruction is characterized by non-equal changings of presynapse different parts.

Synapses changings at hypoxy:

1.presynaptic process strong swelling;

2.synaptic vesicles amount significant decreasing up to their complete disappearance;

3.synaptic vesicles agglutination (gluing) in groups located near presynaptic membrane in axon center;

4.mitochondria decomposition;

5.appearance other structures absent under normal conditions in presynaptic processes such as lysosomes, large vacuoles, concentric membranes accumulations;

6.synapses partial focal destruction which is of a special significance for tiny pathological mechanisms understanding.

Local anesthesia physiological basement in dentistry.

Significance of excitement conductance laws (through nervous fibers) in dentistry.

Nervous fibre physiological integrity law is used in dental practice for local anesthesia performance: nervous impulse conductance through nervous fibre is possible only at its physiological integrity; narcotic substance, cooling action, ligature or weak electrical current influence lead to nervous fibre structures functioning stoppage and prevent excitement distribution.

Conductive anaesthesia - analgetic (novocaine) introduction - and excitement in pharmacological blockade zone is not distributed.

Electroanalgesia – anode (positive electrode) putting from current origin blockates receptory cells membranes depolarization; that is why noceoceptive impulses do not occur.

Electrical magnetical waves application – analgesia is the result of neurons membranes depolarization prevention.


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