Lecture 10 and 11 Muscular System PDF

Introduction To Human Anatomy 7101101 Lectures 10 and 11: Muscular system (4hrs) Description and types of muscles Three types of muscle are described based on distinct characteristics relating to: Whether it is normally willfully controlled (voluntary vs. involuntary) Whether...

Introduction To Human Anatomy 7101101 Lectures 10 and 11: Muscular system (4hrs) Description and types of muscles Three types of muscle are described based on distinct characteristics relating to: Whether it is normally willfully controlled (voluntary vs. involuntary) Whether it appears striped or unstriped when viewed under a microscope (striated vs. smooth or unstriated) Whether it is located in the body wall (soma) and limbs or makes up the hollow organs (viscera) of the body cavities or blood vessels (somatic vs. visceral) Types of muscles Skeletal striated muscle Cardiac striated muscle Smooth muscle Cardiac striated muscle Cardiac striated muscle is involuntary visceral muscle that forms most of the walls of the heart and adjacent parts of the great vessels, such as the aorta, and pumps blood. Smooth muscle Smooth muscle: (unstriated muscle) is involuntary visceral muscle that forms part of the walls of most vessels and hollow organs (viscera), moving substances through them by coordinated sequential contractions (pulsations or peristaltic contractions) Skeletal Muscles Skeletal striated muscle is voluntary somatic muscle that makes up the gross skeletal muscles that compose the muscular system, moving or stabilizing bones and other structures (e.g., the eyeballs). Constitute the great majority of the named muscles Composed of one specific type of muscle tissue “skeletal striated muscle” Muscles are organs of locomotion, but they also provide static support, give form to the body, and provide heat (by shivering). Structure of Skeletal Muscles Skeletal muscles have fleshy, reddish, contractile portions (one or more heads or bellies) Some muscles are fleshy throughout, but most also have white non-contractile portions (tendons), composed mainly of organized collagen bundles, that provide a means of attachment When referring to the length of a muscle, both the belly and the tendons are included Structure of Skeletal Muscles Myofibril: (also known as a muscle fibril) is a basic rod-like unit of a muscle cell composed of actin, myosin and other proteins that hold them together. These proteins are organized into thick (myosin) and thin Muscle fiber (cell) (actin) filaments which repeat along the length of the myofibril. Muscles contract by sliding the thick and thin filaments along each other. Structure of Skeletal Muscles Muscle fiber (cell): A cylindrical, multinucleate cell that make up skeletal muscles and is composed of numerous myofibrils that contract when stimulated each muscle fiber is enclosed by a layer of connective tissue called the endomysium Muscle fascicle: a bundle of skeletal muscle fibers. Each fascicle enclosed by a layer of connective tissue called the perimysium Muscle: a group of muscle fascicles Epimysium: the layer of connective tissue enclosing the entire muscle (also called deep fascia) Structure of Skeletal Muscles (deep fascia) Attachment of Skeletal Muscles Most skeletal muscles are attached directly or indirectly to bones, cartilages, ligaments, or fascias or to some combination of these structures Some muscles are attached to organs (the eyeball, for example), skin (such as facial muscles), and mucous membranes (intrinsic tongue muscles) Attachment of Skeletal Muscles The tendons of some muscles form flat sheets (aponeuroses) that anchor the muscle to: the skeleton (usually a ridge or a series of spinous processes) and/or to deep fascia such as the latissimus dorsi muscle of the back in (next slide), or to the aponeurosis of another muscle (such as the oblique muscles of the anterolateral abdominal wall). Attachment of Skeletal Muscles Latissimus dorsi: Latin; latissimus "broadest” + dorsum "back”: "broadest [muscle] of the back“ Origin: Spinous processes of vertebrae T7-L5, thoracolumbar fascia, iliac crest, inferior 3 or 4 ribs and inferior angle of scapula Insertion: Floor of intertubercular groove of the humerus Note how the aponeuroses of the 3 lateral abdominal muscles envelop the rectus abdominis and form the linea alba Skeletal Muscles names Most muscles are named on the basis of their function or the bones to which they are attached. The abductor digiti minimi muscle, for example, abducts the little finger. Other muscles are named on the basis of their position (medial, lateral, anterior, posterior) or length (brevis, short; longus, long). Skeletal Muscles names Most muscles are named on the basis of their function or the bones to which they are attached. The sternocleidomastoid muscle (G. kleidos, bolt or bar, clavicle) attaches inferiorly to the sternum and clavicle and superiorly to the mastoid process of the temporal bone of the cranium. Term Meaning Term Meaning Maximus or ‫اﻟﻛﺑرى‬ latissimus ‫اﻟﻌرﯾﺿﺔ‬ magnus The largest muscle in a related the largest muscle "in group of muscles width" in a group Gluteus ‫اﻷﻟوﯾﺔ‬ trapezius ‫ﺷﺑﮫ اﻟﻣﻧﺣرﻓﺔ‬ Gluteal: Latin for the buttock Minimus ‫اﻟﺻﻐرى‬ serratus saw-like ‫اﻟﻣﻧﺷﺎرﯾﺔ‬ the smallest muscle of a group of muscles Longus ‫اﻟطوﯾﻠﺔ‬ Rectus ‫اﻟﻣﺳﺗﻘﯾﻣﺔ‬ longest of a group Brevis ‫اﻟﻘﺻﯾرة‬ Zygomaticus ‫اﻟوﺟﻧﯾﺔ‬ the shortest of a group Sartorius ‫اﻟﺧﯾﺎطﯾﺔ‬ Transverse ‫اﻟﻣﺳﺗﻌرﺿﺔ‬ Pollicis of the thumb Risorius ‫اﻟﺿﺣﻛﯾﺔ‬ ‫ ﻧﺳﺑﺔ ﻻﺑﮭﺎم اﻟﯾد‬،‫اﻻﺑﮭﺎﻣﯾﺔ‬ Hallucis of the big toe ‫ﻧﺳﺑﺔ ﻻﺑﮭﺎم اﻟﻘدم‬ Masseter ‫اﻟﻣﺎﺿﻐﺔ‬ Flexor ‫اﻟﺛﺎﻧﯾﺔ‬ Pronator ‫اﻟﻣﻛﺑﺔ‬ Extensors ‫اﻟﻣﺎدة‬ supinator ‫اﻟﺑﺎطﺣﺔ‬ Term Meaning Term Meaning Levator ‫اﻟراﻓﻌﺔ‬ Teres “rounded (cylindrical)” ‫ﻣدورة‬ Depressor ‫اﻟﺧﺎﻓﺿﺔ‬ Gastrocnemius «‫ﻋﺿﻠﺔ ﻣﻌدة اﻟﺳﺎق » ﺑطﺔ اﻟﺳﺎق‬ Gaster “stomach” + knḗmē "leg"; meaning "stomach of leg" (referring to the bulging shape of the calf). Rotator ‫ُﻣ َد ّ ِو َرة‬ Semitendinosus ‫ﻧﺻف وﺗرﯾﺔ‬ ‫ﺗﻣﺗﺎز ﺑطول وﺗرھﺎ ﻟذا ﺳﻣﯾت‬ ‫ﺑﺎﻟﻧﺻف اﻟوﺗرﯾﺔ‬ Sphincter ‫ﺻﺎرة؛ ﻋﺎﺻرة؛‬ Externus ‫ﱠ‬ ‫اﻟظﺎ ِھ َرة‬ ‫ﻣﺻرة‬ Abductor ‫ﻣﺑﻌدة‬ Internus ‫اﻟﺑﺎطﻧﺔ‬ ِ ،‫اﻟﻐﺎﺋِ َرة‬ Adductor ‫ﻣﻘرﺑﺔ‬ Vastus ‫اﻟﻣﺗﺳﻌﺔ‬ Pectoralis ُ‫ﺻ ْد ِرﯾﱠﺔ‬ ‫اﻟ ﱠ‬ Digitorum ‫اﻻﺻﺑﻌﯾﺔ‬ Major ‫اﻟﻛﺑرى‬ Orbicularis oculi ِ َ‫ﺿﻠَﺔُ اﻟﻌ‬ ‫ﯾن اﻟداﺋرﯾﺔ‬ َ ‫ﻋ‬ َ Minor ‫اﻟﺻﻐرى‬ Orbicularis oris ‫ﻋﺿﻠﺔ اﻟﻔم اﻟداﺋرﯾﺔ‬  Skeletal Muscles shapes Muscles may be described or classified according to their shape, for which a muscle may also be named: Flat muscles: Have parallel fibers often with an aponeurosis Ex: the external oblique (broad flat muscle). The sartorius is a narrow flat muscle with parallel fibers. Pennate muscles: Feather-like in the arrangement of their fascicles. May be unipennate, bipennate, or multi-pennate. Ex: the extensor digitorum longus (unipennate), the rectus femoris (bipennate), and deltoid (multi-pennate) Fusiform muscles: Spindle shaped with a round, thick belly (or bellies) and tapered ends: for example, biceps brachii. Skeletal Muscles names Convergent muscles arise from a broad area and converge to form a single tendon—for example, the pectoralis major. Quadrate muscles: Have four equal sides (L. quadratus, square). Ex: the rectus abdominis, between its tendinous intersections Circular or sphincteral muscles: Surround a body opening or orifice, constricting it when contracted Ex: orbicularis oculi (closes the eyelids). Multi-headed or multi-bellied muscles: Have more than one head of attachment or more than one contractile belly Ex: Biceps muscles have two heads of attachment (e.g., the biceps brachii) triceps muscles have three heads (e.g., triceps brachii) Ex: the digastric muscle have two bellies Contraction of Muscles Skeletal muscles function by contracting; they pull and never push. However, certain phenomena—such as the musculovenous pump take advantage of the expansion of muscle bellies during contraction. ‫بتكون العضلة ماسكة بشيئني من‬، ‫ رح تقصر‬contraction ‫ملا العضلة تنقبض ويصيرلها‬ ‫ رح يضل ثابت‬attachment‫ بالتالي نتيجة النقباض العضلة احدى ال‬attachment‫اطرافها‬ When a muscle contracts and insertion ‫ باتجاه الجزء الثابت وهو‬pulled ‫واالخر رح ينسحب‬،origin‫وهو ال‬ shortens, one of its attachments usually remains fixed while the other (more mobile) attachment is pulled toward it, often resulting in movement. Attachments of muscles are commonly described as the origin and insertion Contraction of Muscles Origin: usually the proximal end of the muscle, which remains fixed during muscular contraction Insertion: is usually the distal end of the muscle, which is movable. However, this is not always the case. Insertion Origin Origins Insertion Contraction of Muscles Some muscles can act in both directions under different circumstances. Ex: when doing pushups, the distal end of the upper limb (the hand) is fixed (on the floor) and the proximal end of the limb and the trunk are being moved. Your book usually uses the terms proximal and distal or medial and lateral when describing most muscle attachments. Reflexive Contraction Although skeletal muscles are also referred to as voluntary muscles, certain aspects of their activity are automatic (reflexive) and therefore not voluntarily controlled. Ex: The respiratory movements of the diaphragm, controlled most of the time by reflexes stimulated by the levels of oxygen and carbon dioxide in the blood (although we can willfully control it within limits) The Myotatic (stretch) reflex, which results in movement after a muscle stretch produced by tapping a tendon with a reflex hammer Tonic Contraction Even when “relaxed” the muscles of a conscious individual are almost always slightly contracted. This slight contraction, called muscle tone (tonus), Does not produce movement or active resistance (as phasic contraction does) but gives the muscle a certain firmness, assisting the stability of joints and the maintenance of posture, while keeping the muscle ready to respond to appropriate stimuli. Muscle tone is usually absent only when unconscious (as during deep sleep or under general anesthesia) or after a nerve lesion resulting in paralysis Lectures 10 and 11: Muscular system (4hrs) Phasic (active) contraction There are two main types of phasic (active) muscle contractions: 1. Isometric contractions, in which muscle length remains the same & no movement occurs, but the force (muscle tension) is increased above tonic levels to resist gravity or other antagonistic force important in maintaining upright posture and when muscles act as fixators or shunt muscles as described below. Phasic (active) contraction 2. Isotonic contractions, in which the muscle changes length in relationship to the production of movement There are two types of isotonic contractions: A. Concentric contraction: in which movement occurs as a result of the muscle shortening Ex: when lifting a cup, pushing a door, or striking a blow. Phasic (active) contraction B. Eccentric contraction: in which a contracting muscle lengthens—that is, it undergoes a controlled and gradual relaxation while continually exerting a (diminishing) force, Often, when the main muscle of a particular movement (the prime mover) is undergoing a concentric contraction, its antagonist is undergoing a coordinated eccentric contraction. Eccentric contractions are as important as concentric contractions for coordinated, functional movements such as walking & running Motor unit The structural unit of a muscle is a skeletal striated muscle fiber, The functional unit of a muscle is a motor unit which consists of a motor neuron and the muscle fibers it controls When a motor neuron in the spinal cord is stimulated, it initiates an impulse that causes all the muscle fibers supplied by that motor unit to contract simultaneously A motor unit Motor unit The number of fibers in a motor unit varies according to the size and function of the muscle (from one to several hundred) Motor unit Large motor units, in which one neuron supplies several hundred muscle fibers, are in the large trunk and thigh muscles. In the smaller eye and hand muscles, where precision movements are required, the motor units include only a few muscle fibers. Movement (phasic contraction) results from the activation of an increasing number of motor units, above the level required to maintain muscle tone.  Functions of muscles Prime mover (agonist): The main muscle responsible for producing a specific movement of the body. It contracts concentrically to produce the desired movement, doing most of the work (expending most of the energy) required. In most movements, there is a single prime mover, but some movements involve two prime movers working in equal measure  Functions of muscles An antagonist: A muscle that opposes the action of another muscle. A primary antagonist directly opposes the prime mover. As the active movers concentrically contract to produce a movement, antagonists eccentrically contract, relaxing progressively in coordination to produce a smooth movement Functions of muscles A fixator The fixator in a movement is the muscle(s) that stabilizes (through isometric contraction) the origin of the agonist and the joint that the origin spans (moves over) in order to help the agonist function most effectively. In the bicep curl this would be the rotator cuff muscles, the ‘guardians of the shoulder joint’. The majority of fixator muscles are found working around the hip and shoulder joints.  Functions of muscles A synergist: Complements the action of a prime mover It may directly assist a prime mover, providing a weaker or less mechanically advantaged component of the same movement or it may assist indirectly, by serving as a fixator of an intervening joint when a prime mover passes over more than one joint. It is not unusual to have several synergists assisting a prime mover in a particular movement Clinical note: Absence of Muscle Tone Although a gentle force, muscle tone can have important effects; the tonus of muscles in the lips helps keep the teeth aligned, for instance. When this gentle but constant pressure is absent (due to paralysis or a short lip that leaves the teeth exposed), teeth migrate, becoming everted (“buck teeth”). The absence of muscle tone in an unconscious patient (e.g., under a general anesthetic) may allow joints to be dislocated as he or she is being lifted or positioned. Clinical note: Absence of Muscle Tone When a muscle is denervated (loses its nerve supply), it becomes paralyzed (flaccid, lacking both its tonus and its ability to contract phasically on demand or reflexively). In the absence of a muscle’s normal tonus, that of opposing (antagonist) muscle(s) may cause a limb to assume an abnormal resting position. In addition, the denervated muscle will become fibrotic and lose its elasticity, also contributing to the abnormal position at rest. Growth and Regeneration of Skeletal Muscle Skeletal striated muscle fibers cannot divide, but they can be replaced individually by new muscle fibers derived from satellite cells of skeletal muscle. Satellite cells represent a potential source of myoblasts, precursors of muscle cells, which are capable of fusing with each other to form new skeletal muscle fibers if required. The number of new fibers that can be produced is insufficient to compensate for major muscle degeneration or trauma. Instead of becoming regenerated effectively, the new skeletal muscle is composed of a disorganized mixture of muscle fibers and fibrous scar tissue. Growth and Regeneration of Skeletal Muscle Skeletal muscles are able to grow larger in response to frequent strenuous exercise, such as body building. This growth results from hypertrophy of existing fibers, not from the addition of new muscle fibers. Hypertrophy lengthens and increases the myofibrils within the muscle fibers, thereby increasing the amount of work the muscle can perform. ‫ ينتج هذا النمو عن تضخم‬.‫ مثل بناء اجلسم‬,‫العضالت الهيكلية قادرة على النمو بشكل أكبر استجابة ملمارسة التمارين الرياضية الشاقة املتكررة‬ ‫ وبالتالي يزيد من كمية‬,‫ يطيل التضخم ويزيد من األلياف العضلية داخل األلياف العضلية‬.‫ وليس عن إضافة ألياف عضلية جديدة‬,‫األلياف املوجودة‬ ‫العمل الذي ميكن أن تؤديه ال عضالت‬ Cardiac striated muscle Form the muscular wall of the heart, the myocardium. Some cardiac muscle is also present in the walls of the aorta, pulmonary vein, and superior vena cava Cardiac striated muscle contractions are not under voluntary control Heart rate is regulated intrinsically by a pacemaker, an impulse-conducting system composed of specialized cardiac muscle fibers; they, in turn, are influenced by the autonomic nervous system (ANS) Cardiac striated muscle has a distinctly striped appearance under microscopy. Both types of striated muscle—skeletal and cardiac—are further characterized by the immediacy, rapidity, and strength of their contractions.  Cardiac striated muscle ‫ إال أن املصطلحات اخملططة شائعة االستخدام لتعيي العضالت‬,‫على الرغم من أن السمة تنطبق على كل من العضالت اخملططة الهيكلية والقلبية‬. ‫اخملططة الهيكلية االرادية‬ Note: Even though the trait applies to both skeletal and cardiac striated muscle, in common use the terms striated and striped are used to designate voluntary skeletal striated muscle To support its continuous level of high activity, the blood supply to cardiac striated muscle is twice as rich as that to skeletal striated muscle Hypertrophy of the Myocardium In compensatory hypertrophy, the myocardium responds to increased demands by increasing the size of its fibers. ‫عندما تتلف ألياف العضالت اخملططة القلبية بسبب فقدان إمدادات الدم أثناء النوبة‬ Myocardial infarction ‫ يصبح النسيج نخر )ميوت( ويشكل النسيج الندبي الليفي الذي يتطور احتشاء‬,‫القلبية‬.(‫ وهي منطقة نخر عضلة القلب )املوت املرضي ألنسجة القلبية‬,(MI) ‫عضلة القلب‬ When cardiac striated muscle fibers are damaged by loss of their blood supply during a heart attack, the tissue becomes necrotic (dies) and the fibrous scar tissue that develops forms a myocardial infarct (MI), an area of myocardial necrosis (pathological death of cardiac tissue). Cardiac muscle cells that degenerate are not replaced, because cardiac muscle cells do not divide. Furthermore, there is no equivalent to the satellite cells of skeletal muscle that can produce new cardiac muscle fibers. ‫ ال يوجد ما‬,‫ عالوة على ذلك‬.‫ ألن خاليا عضلة القلب ال تنقسم‬,‫ال يتم استبدال خاليا عضلة القلب التي تتدهور‬.‫ للعضالت الهيكلية التي ميكن أن تنتج ألياف عضلية قلبية جديدة‬satellite ‫يعادل اخلاليا ال‬  Smooth muscle named for the absence of striations in the appearance of the muscle fibers under microscopy, forms Involuntary; directly innervated by the ANS. Its contraction can also be initiated by hormonal stimulation or by local stimuli, such as stretching. Forms: a large part of the middle layer (tunica media) of the walls of blood vessels larger than capillaries the muscular parts of the walls of the alimentary tract and ducts, uterine wall and tubes, and ureters The arrector muscles of hairs The constrictor pupillae muscle (Iris sphincter muscle) which controls pupil size. The ciliary muscle which controls the lens thickness (changes the shape of the lens within the eye)  Smooth muscle responds more slowly than striated muscle and with a delayed and more leisurely (‫ ﺑروﯾﺔ‬،‫ )ﻋﻠﻰ ﻣﮭل‬contraction can undergo partial contraction for long periods has a much greater ability than striated muscle to elongate without suffering paralyzing injury. Both of these factors are important in regulating the size of sphincters and the caliber of the lumens (interior spaces) of tubular structures. In the walls of the alimentary tract, uterine tubes, and ureters, smooth muscle cells are responsible for peristalsis, rhythmic contractions that propel the contents along these tubular structures. ‫خاليا العضالت امللساء مسؤولة عن التمعج االنقباضات التي تدفع احملتويات على طول هذه‬, ‫ واحلالب‬,‫ وأنابيب الرحم‬,‫ف جدران اجلهاز الهضمي‬ ‫الهياكل األنبوبية‬ Hypertrophy and Hyperplasia of Smooth Muscle Smooth muscle cells undergo compensatory hypertrophy in response to increased demands. Smooth muscle cells in the uterine wall during pregnancy increase not only in size but also in number (hyperplasia) because these cells retain the capacity for cell division. In addition, new smooth muscle cells can develop from incompletely differentiated cells (pericytes) that are located along small blood vessels ‫تزداد خاليا العضالت امللساء ف جدار الرحم أثناء احلمل ليس فقط من حيث احلجم ولكن أيضا ف العدد )فرط التنسج( ألن هذه اخلاليا حتتفظ‬.‫بالقدرة على انقسام اخلاليا‬ ‫( تقع على طول األوعية الدموية‬pericytes) ‫ ميكن أن تتطور خاليا العضالت امللساء اجلديدة من خاليا متباينة غير كاملة‬,‫باإلضافة إلى ذلك‬ ‫الصغيرة‬ Lectures 10 and 11: Muscular system (4hrs)