Skeletal Muscle Structure

Muscle (from Latin musculus "little mouse") is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. It is classified as skeletal, cardiac, or smooth muscle, and its function is to produce force and cause motion, either locomotion or movement within internal organs. Much of muscle contraction occurs without conscious thought and is necessary for survival, like the contraction of the heart, or peristalsis (which pushes food through the digestive system). Voluntary muscle contraction is used to move the body, and can be finely controlled, like movements of the eye, or gross movements like the quadriceps muscle of the thigh. There are two broad types of voluntary muscle fibers, slow twitch and fast twitch. Slow twitch fibers contract for long periods of time but with little force while fast twitch fibers contract quickly and powerfully but fatigue very rapidly.

Skeletal muscle structure. Skeletal muscle fibers are multinucleated, with the cell's nuclei located just beneath the plasma membrane. The cell is comprised of a series of striped or striated, thread-like myofibrils. Within each myofibril there are protein filaments that are anchored by dark Z lines. The fiber is one long continuous thread-like structure. The smallest cross section of skeletal muscle is called a sarcomere which is the functional unit within the cell. It extends from one Z line to the next attached Z line. The individual sarcomere has alternating thick myosin and thin actin protein filaments. Myosin forms the center or middle of each sarcomere. The exact center of the sarcomere is designated the M line. Thinner actin filaments form a zig zag pattern along the anchor points or Z line. Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped heads that project toward the actin filaments. Larger structures along the myosin filament called myosin heads are used to provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style, they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. This is called a rachet type drive system. This process consumes large amounts of adenosine triphosphate (ATP). Energy for this comes from ATP, the energy source of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must continuously recycle the discharged adenosine diphosphate molecule (ADP) into ATP rapidly. Muscle tissue also contains a stored supply of a fast acting recharge chemical, creatine phosphate which can assist initially producing the rapid regeneration of ADP into ATP. Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.Control of muscle contraction. Neuromuscular junctions are the focal point where a motor neuron attaches to a muscle. Acetylcholine, (a neurotransmitter used in skeletal muscle contraction) is released from the axon terminal of the nerve cell when an action potential reaches the miscoscopic junction, called a synapse. A group of chemical messengers cross the synapse and stimulate the formation of electrical changes, which are produced in the muscle cell when the acetylcholine binds to receptors on its surface. Calcium is released from its storage area in the cell's sarcoplasmic reticulum. An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, tetanus. Also, a loss of function at the junction can produce paralysis. Skeletal muscles are organized into hundreds of motor units, each of which involves a motor neuron, attached by a series of thin finger-like structures called axon terminals. These attach to and control discrete bundles of muscle fibers. A coordinated and fine tuned response to a specific circumstance will involve controlling the precise number of motor units used. While individual muscle units contract as a unit, the entire muscle can contract on a predetermined basis due to the structure of the motor unit. Motor unit coordination, balance, and control frequently come under the direction of the cerebellum of the brain. This allows for complex muscular coordination with little conscious effort, such as when one drives a car without thinking about the process.

Тема № 5

Название темы: «The Cardiovascular System».

2. Формы работы: подготовка к практическим занятиям, подготовка материалов по НИРС.

3. Перечень вопросов для самоподготовки по теме практического занятия.

Знать лексический минимум по теме, основную медицинскую на иностранном языке, грамматический материал: времена группы Perfect уметь использовать знания лексико-грамматического материала, владеть иностранным языком в объеме, необходимом для возможности коммуникации и получения информации из зарубежных источников.

 

Задания.

1. Отработка лексико-грамматического материала. Различные формы глагола сказуемого. (№1 - №3 стр. 64)

 

2. Изучающее чтение и перевод текста “The Cardiovascular System ”

 

3. Ответьте на вопросы.

1. What is the cardiovascular system?

2. How many chambers does the human heart have?

3. What does the right heart do?

4. What size does the heart have?

5. How much does the human heart weight?

6. What do we mean by the arteries?

7. What is the aorta?

8. What are systole and diastole?

9. How do we call narrow veins?

10. What is the function of the largest artery in the human body?

 

4. Выявление ключевых мыслей для составления резюме текста.

 

5. Подбор антонимов, синонимов, английских эквивалентов к латинским словам (упражнения №12- 14 (1, стр. 68).

 

6. Описать работу сердечно-сосудистой системы пользуясь рис.3 и планом:

- The structure of the heart

- The functioning of the heart as the pump.

- The process of nourishment of the body.

 

7. Отработка лексико-грамматического материала. Степени сравнения прилагательных. №17 (стр. 68). №2 (стр. 70)

 

8. Чтение и нахождение изученных грамматических явлений в тексте “The Cardiovascular System” (стр. 70).

 

9. Дайте более полную информацию к данным суждениям используя информацию из текста.

1) The blood capillaries are absent in some parts of the body.

2) The veins are more immune to disease than the arteries.

3) Phlebitis is due to some infection.

3. Изучающее чтение и перевод текста “The Cardiovascular System ”

 

10. Ответьте на вопросы.

1. What is the centre of the cardiovascular system?

2. Where is the human heart situated?

3. Are the walls of the capillaries thick?

4. What is the pulmonary vein?

5. What does the blood consist of?

6. What do the walls of blood vessels contain?

7. What is the most important difference between vessels and the capillaries?

8. What is the main function of the vena cava?

 

11. Аннотация текста “The Human Heart” 

 

12. Составление ассоциограммы к слову «Heart»

 

13. Поисковое чтение и ответы на вопросы по тексту “Angina Pectoris”

1. What is angina pectoris?

2. What are the types of angina?

3. What are the causes of angina pectoris?

4. Where does the patient feel the pain?

5. How long does the pain usually last?

6. Where does the pain radiate to?

7. What factors may cause an attack?

8. What are the main drugs for treating angina pectoris?

 

14. Повторение грамматического материала времена группы Perfect (Active Voice), степени сравнения.

Степени сравнения.

Три степени сравнения: положительная, сравнительная и превосходная.

Односложные прилагательные и некоторые двусложные прилагательные образуют сравнительную степень путем прибавления к положительной степени суффикса -е r [q], а превосходную степень — путем прибавления суффикса -е st [qst].

При образовании степеней сравнения при помощи суффиксов -е r , - est соблюдаются следующие орфографические правила:      

Если прилагательное в положительной степени оканчивается на немую букву -е, при прибавлении суффиксов - er и - est эта буква отпадает:

pale бледный, paler бледнее, palest самый бледный.

Если прилагательное в положительной степени оканчивается на согласную букву с предшествующей гласной, имеющей краткое чтение, то в сравнительной и превос-ходной степени эта конечная согласная удваивается:

big большой, bigger больше, biggest самый большой

Многосложные прилагательные и большинство двусложных прилагательных образуют сравнительную степень при помощи слова more [mo :] - более, а превосходную степень - при помощи слова most [moust] - самый, наиболее. Само прилагательное при этом остается без изменения:

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