Human muscular system

HUMAN MUSCULAR SYSTEM

1. HUMAN MUSCULAR SYSTEM JAI NARAIN VYAS UNIVERSITY, JODHPUR ASSISTANT PROFESSOR:- ASHWIN SINGH CHOUHAN DEPARTMENT:- PHARMACOLOGY E-mail:- [email protected]

2. MUSCULAR SYSTEM Muscular system is the system of Human Body that provides motor power for all movements of body parts. Muscular system is composed of special tissue called muscular tissue. Muscles have the ability to contract actvely to provide the force for movements of body parts. Muscular system is an important system of human body because without it, life will completely stop. Muscles produce not only those movements that are under the control of our will and that we can see and feel, but also those movements that are responsible for activities like breathing, digestion of food, pumping of blood etc. JNVU PHARMACY, JODHPUR

3. MUSCLE TISSUES SHARE FOUR BASIC PROPERTIES  Excitability : the ability to respond to stimulation Skeletal muscles normally respond to stimulation by the nervous system. Cardiac and smooth muscles respond to the nervous system and circulating hormones.  Contractility : the ability to shorten actively and exert a pull or tension that can be harnessed by connective tissues.  Extensibility : the ability to continue to contract over a range of resting lengths.  Elasticity : the ability of a muscle to rebound toward its original length after a contraction. JNVU PHARMACY, JODHPUR

4. MUSCLES Muscles are body tissues that provide the force for all body movements. They are made of special types of cells. For details of structure and types of muscles. TYPES OF MUSCLES Muscles are basically of three types. Skeletal Muscles Smooth Muscles Cardiac Muscles JNVU PHARMACY, JODHPUR

5. Skeletal Muscles Skeletal muscles form most of the human body weight. They are under the control of human will and all body movements occurring by our will are produced by skeletal muscles. They are called skeletal muscles because they are almost always found attached to the skeleton and produce movements in different parts of the skeleton . JNVU PHARMACY, JODHPUR

6. Smooth Muscles: Smooth muscles form the soft body organs like stomach, intestine, blood vessels etc. They are not under the will of human beings and are responsible for unconscious body activities like digestion of food. They are called smooth muscles because when seen under the microscope, they do not have any striation in contrast to the other two types of muscles. JNVU PHARMACY, JODHPUR

7. Cardiac Muscles: Cardiac muscles are exclusively found in human heart and no where else. They are extremely strong and powerful muscles. They are not under the control of human will and are involuntary. The pumping of blood by human heart is because of the force provided by the contraction of cardiac muscles. JNVU PHARMACY, JODHPUR

8. FUNCTIONS OF MUSCULAR SYSTEM MOVEMENTS OF BODY PARTS:  Skeletal muscles are responsible for all voluntary movements of human body parts. They provide the force by contracting actively at the expense of energy. In other words, muscles are motors of body where chemical energy of food is converted into mechanical work . STABILITY AND POSTURE:  Skeletal muscles stabilize human skeleton and give a proper posture to human beings. Some joints of human body are weak and they require the support of muscular system to achieve stability. Skeletal muscles are very important for such joints. JNVU PHARMACY, JODHPUR

9. HEAT PRODUCTION:  A large share of body’s energy is used by muscular system. As a result of high metabolic rate, muscles produce great amount of heat in the body. Heat produced by muscles is very important in cold climates . CIRCULATION:  Cardiac muscles provide the main force for circulation of blood throughout human body. The regular pumping of heat keeps the blood in motion and nutrients are readily available to every tissue of human body . HELP IN DIGESTION:  Smooth muscles of organs like stomach and intestine help the digestive system in the process of digestion of food. JNVU PHARMACY, JODHPUR

10. SKELETAL MUSCLE JNVU PHARMACY, JODHPUR Skeletal muscle  is a voluntary muscle, which means that we can actively control its function. It’s attached to the bone and forms a distinct organ of muscle tissue, blood vessels, tendons, and nerves that covers our bones and allows movement. JNVU PHARMACY, JODHPUR

11. Skeletal muscles often exist in pairs, whereby one muscle is the primary mover and the other acts as an antagonist. For example when you bend your arm, your biceps contracts whilst your triceps is relaxed. When your arm returns to the extended position it is the triceps that contracts and the biceps relaxes. JNVU PHARMACY, JODHPUR

12. JNVU PHARMACY, JODHPUR Skeletal muscle is a fascinating tissue with a complex structure. It consists of elongated multinuclear cells called the  myocytes  (or myofibers ). The muscle cells can be anything from 1 mm to 30 cm in length. The longest muscle cell in our bodies can be found in the sartorius muscle and is 30 cm (nearly 12 inches!) long.

13. JNVU PHARMACY, JODHPUR The individual muscle cells appear striated under the microscope (see image below). This is due to the highly organsied structure of the muscle fibers where  actin and myosin myofilaments  are stacked and overlapped in regular repeating arrays to form sarcomeres . Actin and myosin filaments slide against each other and are responsible for the muscle contraction.

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15. JNVU PHARMACY, JODHPUR The energy for muscle function comes from intracellular organelles called the  mitochondria . Mitochondria are the powerhouses of every cell in our bodies and responsible for delivering energy that the cells need to function. Muscles are ennervated by  motor neurons . A motor neuron and the muscle fibers ennervated by it form a  motor unit . Size of motor units varies in the body, depending on the function of the muscle. Fine movements (eyes) have fewer muscle fibers per neuron to allow for fine movement. Muscles that require a lot of strength have many muscle fibers per unit. The body can control strength by deciding how many motor units it activates for a given function.

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17. JNVU PHARMACY, JODHPUR There are two types of skeletal muscles in our bodies, which vary in function. Slow twitch muscle fibres are better for endurance activities and can work for a long time without getting tired. Fast twitch muscles are good for rapid movements as they contract quickly, but get tired fast, and consume lots of energy.

18. STRUCTURE OF SKELETAL MUSCLE Muscle attachments Tendons These are dense connective tissue that attaches the muscle to bone. When a muscle contracts, it shortens and puts tension on the tendon and the bone. The muscle tension causes movement of the bone at a synovial joint Origin: The less moveable attachment of the muscle is called the origin. At the girdles and appendages the most proximal muscle attachment is the origin. JNVU PHARMACY, JODHPUR

19. JNVU PHARMACY, JODHPUR Insertion Movement of the bone at the synovial joint causes one of the attached bones to move more than the other. The more moveable bony attachment of the muscle is called the insertion. In muscles associated with girdles and appendages the more distal attachment is the insertion. Belly The fleshy thick part of the muscle. It is alsocalled the gaster . Aponeuroses It is a flattened sheet like tendon Retinaculum It is a strong band of connective tissue that covers entire groups of tendons and keeps the tendons from bowing during muscle contraction. They are attached to articulating bones and are found at the wrist and the ankle.

20. JNVU PHARMACY, JODHPUR Associated Connective Tissue : Endomysium : The outer covering of individual muscle fibers . It binds individual fibers together and supports capillaries and nerve endings serving the muscle. Perimysium : Another sheath covering that binds groups of muscle fibers together into bundles called fasciculi . The perimysium supports the nerves and blood vessels that serve the surrounding fasciculi . Epimysium : The entire muscle is covered by a sheath called the Epimysium , which in turn is part of a tendon.

21. JNVU PHARMACY, JODHPUR Fascia It is a fibrous connective tissue that covers the muscle and attaches to the skin. Superficial fascia: It is secures skin to the underlying structures . In areas such as the abdomen, buttocks the fascia is thick and is laced with adipose tissue. In areas such as the back of the hand, around the face and the elbows, ankles and wrists, the superficial fascia is very thin. Deep fascia: It is an extension of the superficial fascia to deeper surfaces. It lacks adipose tissue and blends with the epimysium . It is composed of dense connective tissue. Deep fascia surrounds adjacent muscle, compartmentalizing and binding them into functional groups.

22. JNVU PHARMACY, JODHPUR Subserous fascia: It is extends between deep fascia and serous membranes. It is composed of loose connective tissue.

23. MUSCLE GROUPS BASED ON THEIR ACTIONS: Synergistic: Muscle groups that contract together to accomplish a particular movement. Most large movements of the body require several synergistic muscles to accomplish the task. Prime movers: Muscles that are primarily responsible for a movement are called prime movers. Fixators : Muscles that aid and allow prime movers to act efficiently by stabilizing the joint to prevent unwanted movements. Synergists that stabilize a joint are known as fixators . JNVU PHARMACY, JODHPUR

24. Antagonistic: Muscles that have opposing actions and are located on opposite sides of a joint. An example would be the biceps brachii together with the brachialis which flex the elbow. The antagonist is the triceps muscle which extends the elbow when contracted. Antagonists are needed because the fibers in a contracted muscle are shortened and need to be elongated (stretched) before they can cause movement via contraction again. JNVU PHARMACY, JODHPUR

25. MUSCLE TYPES BY FIBER ARRANGEMENT JNVU PHARMACY, JODHPUR Parallel (Longitudinal): It is strap-like long excursion, contracts over a long distance. Good endurance (stamina), not especially strong. Examples: Sartorius. rectus abdominus Convergent (Radiate): Fan shaped, force of contraction focused on a single point of attachment. It is Stronger than parallel. Examples: Pectoralis muscles. Sphincteral (Circular): Fibers concentrically arranged around an orfice . Act as a sphincter (constrictor) when contracted. Examples: Orbicularis oris , orbicularis oculi

26. Pennate (feather): In this type one or more tendons run through the body of the muscle. Because the muscle fibers pull at an angle the tendons don’t move as far as parallel types do. Pennate muscles contain more fibers than parallel types and are capable of generating more tension (are stronger). Unipennate : It has one extended tendon. All the muscle fibers are found on the same side of the tendon. Example: gluteus maximus Bipennate : It has 2 tendons. Multipennate : It has more than 2 tendons that branch within the muscle . Example: Deltoid JNVU PHARMACY, JODHPUR

27. BLOOD AND NERVE SUPPLY TO THE MUSCLE JNVU PHARMACY, JODHPUR

28. Muscles have a high rate of metabolical activity and require an extensive blood supply to receive nutrients and eliminate wastes. Skeletal muscle cannot contract without stimulation by a nerve impulse. The muscle requires extensive innervation to ensure the connection of each muscle fiber with a nerve cell. There are 2 neural pathways for each muscle fiber : Motor (efferent) neurons: It is a nerve cell that conducts impulses to the muscle fiber , stimulating it to contract. Sensory (afferent) neurons: Nerve cells that conducts impulses away from the muscle to the CNS, which responds to the activity of the muscle fiber . Muscle fibers will atrophy (weaken) if not periodically stimulated to contract. JNVU PHARMACY, JODHPUR

29. STRUCTURE OF A SKELETAL MUSCLE FIBER JNVU PHARMACY, JODHPUR

30. JNVU PHARMACY, JODHPUR Sarcolemma : Cell membrane of the muscle fiber . Sacoplasmic reticulum: It is a network of membranous channels that extends through the cytoplasm of the cell. Sarcoplasm : The cytoplasm of the fiber . T tubules (transverse tubules): It is a system of tubules that run perpendicular to the sarcoplasmic reticulum. Myofibrils: It is a contractile element of the skeletal muscles. They are 1-2 μm in diameter and contain three smaller structures which are known as myofilament : Thin filament Thick filament Elastic filament

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32. JNVU PHARMACY, JODHPUR During the muscles contraction and relaxation, the thin and thick filaments overlap on one another. Inside the myofibril, the filament is not extent the entire length of muscles fiber but it produce compartment known as sarcomeres which are the basic functional units of straight muscles fiber . Between two filaments narrow plate shaped regions of dense material is known as Z-disc which separate one sarcomere to next. Within the sarcomere is a dark area called A-band, it consist the thick filament overlap by thin filaments. Lighter and less dense area are called the I-band, it consist only thin filament. In the centre of each A-band consist only thick filament so it is known as H-band .

33. JNVU PHARMACY, JODHPUR Each H-band is centrally divided by M-line. The Z-disc passes from the centre of each I-band. The thick filament is made up by myosin protein and thin filament is made up by actin protein, tropomyosin and troponin . Myosin proteins look like as two golf clubs twisted together or head and tail like portion. Actin has myosin binding side where myosin head are attached during the contraction and relaxation process.

34. JNVU PHARMACY, JODHPUR Structure of & myosin (thick filament) & actin (thin filament)

35. PHYSIOLOGY OF MUSCLES CONTTRACTION AND RELAXATION JNVU PHARMACY, JODHPUR

36. JNVU PHARMACY, JODHPUR CONTRACTION OF MUSCLES It is well described by sliding filament model . During the muscles contraction, myosin head attaches with the thin filaments ( actin ) It slide the muscles inward toward the H-zone at the centre of Sarcomere As the thin filament slide inward Z discs come toward each other And the sarcomeres shorten f the filaments and shortening of the sarcomeres cause shortening of the But the length of thin and thick filament do not change The sliding owhole muscles fiber

37. JNVU PHARMACY, JODHPUR Role of the calcium in contraction: An increase concentration of Ca +2 increase the contraction. While decreasing concentration of Ca +2 decrease the sliding means contraction. Role of ATP in contraction: In the relaxed condition ATP is attached with the head of Myosin. Due to hydrolysis ATP release one phosphate molecules and convert in to ADP and gives energy to myosin .

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39. JNVU PHARMACY, JODHPUR RELAXATION OF MUSCLES Ca +2 is the main mediator for muscles contraction. So in the relaxation the concentration of Ca +2 is 10,000 low in sarcoplasm . This concentration is decrease by two ways. Ach (acetyl choline ) is the main mediator who releases the Ca +2 , so in the relaxation acetyl choline esterase enzyme degrades or breaks down the Acetyl choline and lower the concentration of Ca +2 . Sarcoplasma membrane consist the Ca +2 pump which flows the out side Ca +2 in to inside the sarcoplasm , so during the relaxation calsequestrin bind to Ca +2 pump and remove the Ca +2 from the sarcoplasm .

40. JNVU PHARMACY, JODHPUR PHYSIOLOGY OF NEUROMUSCULAR JUNCTION

41. JNVU PHARMACY, JODHPUR Each branch of a motoneuron forms a single junction with a muscle fiber . The myelin sheath surrounding the motor axon ends near the surface of the muscle fiber and the axon divides into a number of short processes that lie embedded in grooves on the muscle- fiber surface. This region of the sarcolemma (muscle membrane) is known as the motor end plate. Acetylcholine is the neurotransmitter in these synapses. End-plate potentials (EPPs) can be recorded at the motor end plate when the presynaptic membrane is activated to release vesicles containing the acetylcholine.

42. JNVU PHARMACY, JODHPUR STEPS IN NEUROMUSCULAR TRANSMISSION nerve action potential. calcium entry into the presynaptic terminus. release of Ach quanta. diffusion of Ach across cleft. combination of Ach with post-synaptic receptors and Ach breakdown via esterase. opening of Na+ /K+ channels ( cation channels). postsynaptic membrane depolarization (EPP). 8) muscle action potential.

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44. JNVU PHARMACY, JODHPUR A  neuromuscular junction  (or  myoneural junction ) is a chemical synapse between a motor neuron and a muscle fiber.It allow the motor neuron to transmit a signal to the muscle fiber , causing muscle contraction. Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy. In the  neuromuscular system  nerves from the central nervous system and the peripheral nervous system are linked and work together with muscles. Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage-gated calcium channels to allow calcium ions to enter the neuron.

45. JNVU PHARMACY, JODHPUR Calcium ions bind to sensor proteins ( synaptotagmin ) on synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft. In vertebrates, motor neurons release acetylcholine ( ACh ), a small molecule neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors ( nAChRs ) on the cell membrane of the muscle fiber , also known as the  sarcolemma . nAChRs are  ionotropic  receptors, meaning they serve as  ligand -gated ion channels. The binding of ACh to the receptor can depolarize the muscle fiber , causing a cascade that eventually results in muscle contraction.

46. JNVU PHARMACY, JODHPUR Neuromuscular junction diseases can be of genetic and autoimmune origin. Genetic disorders, such as  Duchenne muscular dystrophy , can arise from mutated structural proteins that comprise the neuromuscular junction, whereas autoimmune diseases, such as myasthenia gravis, occur when antibodies are produced against nicotinic acetylcholine receptors on the sarcolemma .

47. DISORDERS OF MUSCLES JNVU PHARMACY, JODHPUR Cramp Cramp is the term associated with the painful sensation caused by either prolonged or sudden extreme contraction of a muscle. The condition may be connected with electrolyte imbalance and is often associated with fatigue, stress and poor posture. Muscular Dystrophy The term muscular dystrophy refers to a group of inherited diseases where fiber degenerate muscles and replaced by fatty tissue. Increasing weakness and loss of ability result. The severity of the condition varies from slight weakness through to damage to the intercostals muscles or myocardium, with eventual fatal consequences.

48. JNVU PHARMACY, JODHPUR Poliomyelitis Poliomyelitis is actually an infectious viral disease of the central nervous system. It is often attribute to the muscular system as it can lead muscular stiffness, weakness and eventual paralysis . Strain A strain is occur when there is excessive use or stretching of muscles. This may damage the muscles fibers or tendons by tearing them and generally leads to pain and swelling. In an extreme case, the tissue is completely torn apart with extensive heamorrhage , swelling, pain and loss of function.

49. JNVU PHARMACY, JODHPUR Tendinitis Tendinitis occurs when excessive use of a particular muscle leads to a painful inflammation of the associated tendon sheath. The condition may also be caused by bacterial infection or rheumatic disease . Tension Headache A tension headache is probably the most common form of headache. It occurs when muscular contraction in the back of neck caused by emotional stress or other factor leads to pain. Muscular spasm may then constrict blood vessels and increase the problem which can be compounded by a build up of toxic waste substance in the scalp .

50. JNVU PHARMACY, JODHPUR Migraine Migraine is a condition similar to the tension headache but with much more sever symptoms. Often a migraine is initiated by a trigger factor and may occasionally be preceded by an “aura” or warning symptoms. Blood vessels supplying the brain constrict. At a some point later, they dilate causing an intense headache and perhaps including other problems like visual disturbance, dizziness, vertigo and vomiting

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