Muscle Tissue PDF

Muscle tissue  Muscle tissue Muscle Tissue is composed of cells that are specialized to contract to produce voluntary or involuntary movement of body parts. One of the basic tissues of the body. Muscle Cells (Muscle Fibers / Myocytes) are long and narrow. - ‘Sarc...

Muscle tissue  Muscle tissue Muscle Tissue is composed of cells that are specialized to contract to produce voluntary or involuntary movement of body parts. One of the basic tissues of the body. Muscle Cells (Muscle Fibers / Myocytes) are long and narrow. - ‘Sarco’: Greek for Muscle - ‘Myo’: Latin for Muscle Both used as prefixes when speaking of muscle.  Properties of Muscle Tissue – Excitability: respond to nerve cells by generating electrical signals – Contractility: can shorten and generate force – Extensibility: can be stretched – Elasticity: returning back to its original shape Vincent Rodrigues  Functions Responsible for movements Maintain posture Stabilize joints Thermogenesis Transforms chemical energy into mechanical energy, therefore, producing force Increase muscle mass, increases immune system Vincent Rodrigues  Types of Muscle tissue  Skeletal muscle  Smooth muscle  Cardiac muscle  Skeletal Muscle Skeletal muscles connect to your bones (skeleton) by tendons and allow you to perform a wide range of movements and functions. Most common and abundant of the three (3) types of muscles. Striated and under voluntary control E.g. Muscles of the limbs and body wall  Characteristics of Skeletal Muscle MICROSCOPIC Made up of long cylindrical muscle fibers (muscle cells or myocytes) Exhibit cross striations Multi nucleated. Nuclei have peripheral distribution Unbranched LOCATION Attached by tendons to bones (found attached to skeleton) NERVOUS CONTROL Voluntary (supplied by somatic nerves, governed by Somatic Nervous System) SPEED OF CONTRACTION Fast – Responds quickly to stimuli SIZE Very Large – 10-100 µm diameter, up to 35cm length CONNECTIVE TISSUE COMPONENTS Endomysium Perimysium Epimysium Presence of contractile proteins organized into sarcomeres No junctions between muscle fibers (Muscle Cells / Myocytes) No Auto rhythmicity Contractions regulated by Neurotransmitter, Acetylcholine Regulator Proteins for Contraction are Troponin and Tropomyosin  Parts of a muscle Tendon Muscle contains 2 parts Belly (fleshy part) Belly Tendons (fibrous part) Belly - highly vascular and contractile part Tendon - attached to the bones or cartilages, made of collagen fibers, less vascular and non elastic Aponeurosis- thin sheath of fibrous connective tissue (primarily bundles of collagen) that helps connect muscles to bones, support the muscles and give the body strength and stability. Fibrous part present in the flat muscles e.g. abdominal aponeurosis (rectus sheath) Tendon  Attachment of muscles All muscles have at least 2 attachments - origin and insertion Origin: – Attachment of a muscle that remains relatively fixed during muscular contraction – Generally the proximal part Insertion: – Attachment of a muscle that moves during muscular contraction – Generally the distal part  Strap - Muscle organization sartorius (arrangement of muscle fibers) 1) Parallel muscles: Muscle fibers run parallel to Fusiform length of muscle Most of the skeletal muscle are of this type Parallel muscles are different types – fusiform, strap, quadrilateral eg. biceps brachii, sartorius, pronator quadratus Quadrilateral 2) Convergent muscles: Muscle fibres spread out like fan on one end and converge to single point on other end eg. Pectoralis major Convergent 3) Pennate Muscles (feather like): Muscle fibers are arranged at an angle to tendon Unipennate: Muscle fibers angled on one side of tendon (eg. palmar interossei) Bipennate: Tendon in the middle with angled muscle fibers on each side (eg dorsal interossei) Multipennate: Branched tendon with muscle fibers organised around each branch (eg. Deltoid) 4) Circular muscle: Concentric arrangement of muscle fibres Guard the openings and decrease the diameter of openings eg. Orbicularis oculi, orbicularis oris Vincent Rodrigues  Nomenclature of muscles According to their shape: e.g., trapezius, deltoid, pronator teres (round) According to size: eg adductor magnus, gluteus maximus, adductor longus According to number of heads of origin: e.g., Biceps brachii, Triceps brachii, Quadriceps femoris According to their location: e.g., Biceps brachii, Supraspinatus, Intercostales, pectoralis major, gluteus medius  According to their relative position: eg obturator internus and externus, flexor digitorum superficialis, flexor digitorum profundus (deep), tibialis anterior, tibialis posterior, vastus medialis and vastus lateralis According to their attachment: e.g., stylohyoid, cricothyroid, sternocliedomastoid According to their function: e.g., adductor pollicis, flexor carpi ulnaris, abductor pollicis longus, pronator teres According to direction of fibres: e.g., rectus abdominis, external oblique, transversus External oblique abdominis  Actions of skeletal muscles Agonist (Prime mover) – Muscle most responsible for the movement. – Directly brings about the desired movement Antagonist – Muscle which opposes the action of agonists  Actions of skeletal muscles Synergist o Muscle(s) that stabilises a joint around which movement is occurring, which in turn helps the agonist function effectively o Synergist muscles also help to create the movement E.g. In the biceps curl the synergist muscles are the brachioradialis and brachialis which assist the biceps to create the movement and stabilise the elbow joint  Actions of skeletal muscles Fixator – Stabilize the proximal joints to allow the movements at the distal joints – A muscle that acts as a stabilizer of one part of the body during movement of another part E.g. Rotator Cuff (Subscapularis, Infraspinatus, Teres Minor, Supraspinatus) is the fixator during biceps curl  Skeletal Muscle – structure Muscle is surrounded by a connective tissue called the epimysium Muscle is made up of smaller bundles known as fascicles Bundles are surrounded by a connective tissue sheath called the perimysium Fascicle is made up of several cylindrical muscle cells or muscle fibres Muscle cell is surrounded by a connective tissue sheath known as the endomysium  Each muscle fiber (muscle cell) contains all of the organelles that we find in other cell types Muscle fiber contains multiple peripherally placed flat nuclei Under the microscope, stripes called striations are visible in muscle fibers Plasma membrane of the muscle cell is known as sarcolemma T-tubules: Invaginations of sarcolemma at A Band and I Band junction (permit rapid transmission of the action potential into the cell)  Cytoplasm of the muscle cell - sarcoplasm Sarcoplasmic reticulum is the smooth endoplasmic reticulum of the muscle cell containing calcium Terminal cisternae are enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules- store calcium Triad: 2 terminal cisterna and 1 T-tubule Myoglobin: red pigment that stores oxygen within muscle Glycosomes: granules of stored glycogen within the muscle  Muscle fiber contains several myofibrils Myofibril is a cylindrical bundle of contractile proteins Each myofibril contains several sarcomeres Sarcomere is the functional or contractile units of muscle One sarcomere is separated from the other by the Z line Sarcomeres of myofibrils contain myofillaments  Myofilaments are generally divided into thick and thin myofilaments Thin myofilaments are composed mainly of a protein known as actin Thick myofilaments are composed mainly of the protein myosin Orderly overlapping of the thick and thin myofilaments give skeletal muscle their striated appearance (light and dark bands) I Band (isotropic; light band), A Band (anisotropic; not isotropic; dark band) I Band cantinas only thin (actin) myofilaments and A Band contains thick and thin (actin and myosin) H zone - middle of A, only myosin  Skeletal muscle (cross section) Perimysium Muscle fibre Nucleus  Smooth Muscle Involuntary, non-striated muscle with fusiform shaped cells containing single centrally located nuclei. LOCATIONS S – Skin (arrector pilli muscles) T – Tracts in the reproductive, respiratory and urinary system O – Organs that are hollow (e.g. intestines, bladder, uterus and stomach) V – Vessels (Blood vesels) E – Eyes (iris contraction/dilation, as well as lens movement)  Characteristics of Smooth Muscle Muscle fiber is an elongated, spindle (fusiform) shaped cell Contains centrally placed spindle shaped nucleus Myofibrils, sarcomeres and T tubules are absent Do not exhibit cross or transverse striations under microscope, being plane and smooth in form Supplied by autonomic nerves, not under voluntary control Small in size (3-8µm dimater) Contains only Endomysium connective tissue component. Contain gap junctions in visceral smooth muscle and no junctions in multiunit smooth muscle Auto rhythmicity of visceral smooth muscle Slow speed of contraction  Smooth muscle structure Network of filaments are responsible for contraction Three(3) types of filaments Thick filaments (myosin) Thin filaments (actin) Intermediate filaments (desmin and vimentin) Dense bodies attach to the sarcolemma and they work like the Z disc in a sarcomere. Thin filaments and Intermediate filaments attach to dense bodies. The cells contract via the sliding filament mechanism (similar to skeletal and cardiac muscle) Vincent Rodrigues Single unit Smooth Muscle: Innervated by one or very few nerve fibers per bundle. One nerve fiber can contract an entire sheet of smooth muscle in unison due to presence of gap junctions allowing electrical signals to spread rapidly to all adjoining smooth muscle cells. Sometimes caused visceral smooth muscle. E.g. Hollow organs like intestines. Multi-unit Smooth Muscle: Contains fewer gap junctions so electrical impulses cannot spread across cells as efficiently. Each cell therefore requires its own electrical impulse. You’d find multiple nerve fibers present to deliver this impulse. E.g.: Found in skin, eyes and blood vessels. Smooth muscle – slide 26 Vincent Rodrigues Smooth muscle – slide 26  Cardiac Muscle It is present exclusively in the heart and is also called myocardium of heart Is striated but involuntary muscle demonstrating auto rhythmicity Cardiac muscle resemble skeletal muscle partially Consists of short, branched cylindrical muscle fibers Each cardiac muscle fiber contains many muscle cells (cardiomyocytes) which are united by intercalated discs  Intercalated disc holds the ends of the muscle cells together and allows transmission of ions, they contain gap junctions, fasciae adherens and desmosomes (maculae adherens). Muscle fibers branch and anastomose with the neighboring fibers Each muscle cell contains centrally placed, single oval or round nucleus Contain many large mitochondria Transverse striations are present but not as prominent as in skeletal muscle. Contractile proteins organized into sarcomeres. Connective tissues: endomysium and perimysium Moderate speed of contraction Large diameter of ~10-20µm Regulator proteins for contraction: troponin and tropomysin. Cardiac muscle – slide 27 Vincent Rodrigues Cardiac muscle  Myasthenia gravis Neuromuscular disorder that causes weakness in the skeletal muscles Happens when communication between nerve cells and muscles becomes impaired. This impairment prevents crucial muscle contractions from occurring, causing muscle weakness Most common primary disorder of neuromuscular transmission Autoimmune disorder caused by antibodies that attack components of the postsynaptic membrane, impair neuromuscular transmission and lead to weakness and fatigue of skeletal muscle  Duchenne muscular dystrophy Genetic disorder characterized by the progressive weakness and loss (atrophy) of both skeletal and heart muscle Caused by a change in the dystrophin gene (muscles are not able to function or repair themselves properly) Loss of muscle results in a loss of strength and function Occurs primarily in males, in rare cases may affect females