Muscle Tissue PDF

Muscular System Hamza Abu Hilail M.Sc. Physiology  Introduction The purpose of the chapter is to: Learn about the structure and function of the 3 types of muscular tissue Examine the events at the neuromuscular junction Describe energy use in muscle cells Understand how mus...

Muscular System Hamza Abu Hilail M.Sc. Physiology  Introduction The purpose of the chapter is to: Learn about the structure and function of the 3 types of muscular tissue Examine the events at the neuromuscular junction Describe energy use in muscle cells Understand how muscle tension is controlled  Type and function of muscles Types of Muscles: 1.Skeletal Muscles 2.Cardiac Muscle 3.Smooth muscles Functions of Muscles: 1.Producing body movement 2.Stabilizing body position 3.Storing and moving substances within the body 4.Generating heat  Properties of Muscles 1. Electrical Excitability: ability to respond to certain stimuli by producing electrical signal 2. Contractility: ability of muscular tissue to contract forcefully when stimulated by an action potential 3. Extensibility: ability of muscle tissue to stretch without being damaged 4. Elasticity: ability of muscular tissue to return to its original length & shape after contraction or extension  SKELETAL MUSCLE TISSUE (Connective tissue) Three layers of connective tissue protect and strengthen skeletal muscle: 1.Epimysium: the outermost layer of dense, irregular connective tissue, encircling the entire muscle 2.Perimysium: is also a layer of dense, irregular connective tissue, but it surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles 3.Endomysium: penetrates the interior of each fascicle and separates individual muscle fibers from one another. The endomysium is mostly reticular fibers.  Nerve & blood supply Generally, an artery and one or two veins accompany each nerve that penetrates a skeletal muscle. The neurons that stimulate skeletal muscle to contract are somatic motor neurons. Each somatic motor neuron has axon that extends from the brain or spinal cord to a group of skeletal muscle fibers each muscle fiber is in close contact with one or more capillaries.  Microscopic Anatomy of skeletal muscles The multiple nuclei of a skeletal muscle fiber are located just beneath the sarcolemma Sarcolemma: the plasma membrane of a muscle cell Transverse (T) tubules : are tunnel in from the surface toward the center of each muscle fiber. Muscle action potentials travel along the sarcolemma and through the T tubules  Microscopic Anatomy of skeletal muscles Sarcoplasm: the cytoplasm of a muscle fiber. Sarcoplasm includes a substantial amount of glycogen Glycogen can be used for synthesis of ATP. Sarcoplasm contains a red-colored protein called myoglobin Myoglobin binds oxygen molecules that diffuse into muscle fibers from interstitial fluid.  Myofibril & Sarcoplasmic Reticulum Myofibrils: The contractile organelles of skeletal muscle Their prominent striations make the entire skeletal muscle fiber appear striped (striated) Sarcoplasmic reticulum (SR) Is represented the endoplasmic reticulum in the muscles Release of Ca2 from the terminal cisterns of the sarcoplasmic reticulum triggers muscle contraction. In a relaxed muscle fiber, the sarcoplasmic reticulum stores calcium ions (Ca2).  Filaments & the sarcomere Myofibril composed of Thin & Thick filament Filaments are arranged into Sarcomeres The extent of overlap of the thick and thin filaments depends on whether the muscle is contracted, relaxed, or stretched. The pattern of thick and thin filaments overlap, consisting of a variety of zones and bands creates the striations.  Filaments & the sarcomere A band: The darker part of the sarcomere, which extends the entire length of the thick filaments. The I band: is a lighter part, that containing only actin filaments Z disc: passes through the center of each I band.  Separates one sarcomere from the other 1. H zone: in the center of each A band contains thick but not thin filaments.  contain overlapping actin and myosin filaments Supporting proteins that hold the thick filaments together at the center of the H zone form the M line  Muscle Proteins Contractile 1.Actin 2.Myosin Structural 1.Titin Regulatory 1.Troponin 2.Tropomyosin  The Neuromuscular Junction (NMJ) Somatic motor neurons  release acetylcholine NMJ  synaptic cleft  Motor end plate  contain 30-40 million ACH receptors Activation of ACH receptors  channel open  sodium flow across membrane  Production of muscle action potential Termination of Ach activity: acetylcholinesterase breaks down Ach into acetyl and choline  Excitation-Contraction Coupling Excitation  contraction AP propagate along sarcolemma and into T tubules  calcium release channels in SR open  calcium flow into cytosol around thick & thin filament  calcium bind with troponin  troponin change its shape move tropomyosin away from the myosin binding sites  sites become free  myosin heads bind to the sites  contraction cycle begins Relaxation Calcium active transport pump  use ATP to move calcium from cytosol to SR  Relaxation  Muscle Metabolism ATP is needed Creatine Phosphate Muscle relaxed  produce more for: ATP Excess ATP  synthesize 1.Contraction cycle creatine phosphate (found only in muscle cells). 2.Calcium active pump Creatine kinase  catalyze the reaction Creatine is synthesized in the liver, 3.Metabolism kidneys, pancreas  transported to muscle fibers. 4.Relaxation Creatine phosphate ATP  enough energy for 15 seconds (100 meter dash)  Aerobic Cellular Respiration Production of ATP in mitochondria Begins after half a minute of activity Each glucose molecule  36 ATP molecules Fatty acid molecules  100 ATP molecules Prolonged activity In activities lasting more than 10 minutes  AR provide more than 90 % of needed ATP  Anaerobic Cellular Respiration ATP producing without need for oxygen. Glucose from blood or from glycogen  10 reactions  glycolysis  2 pyruvic acid mitochondria Pyruvic acid  lactic acid  blood ACR  enough energy for 30-40 seconds For each glucose molecule  2 ATP molecules  Motor Unit A motor unit consists of: 1.Motor Neuron: A single motor neuron located in the spinal cord or brainstem. 2.Muscle Fibers: All the muscle fibers that the motor neuron innervates Key Features of Motor Units: Size: Motor units vary in size depending on the muscle. Small motor units control fewer muscle fibers, which allows for finer control (e.g., in muscles controlling the eyes or fingers). Larger motor units control more fibers, leading to more forceful contractions but less precise control (e.g., in leg muscles). Motor Unit  Types of Motor Units Slow (Type I): These motor units are associated with slow-twitch fibers, which are resistant to fatigue and are important for endurance activities like walking or maintaining posture. Fast (Type II): These motor units are associated with fast-twitch fibers, which fatigue quickly but are capable of generating rapid and powerful contractions, important for activities like sprinting or lifting heavy objects. Types of muscle fiber  Tetanus Summation → Muscle fiber does not have time to relax completely between two stimuli Relaxation between contractions diminishes until the muscle fiber achieves the state of maximal contraction known as tetanus. There are two types of tetanus: 1.incomplete, or unfused, tetanus 2. Complete, or fused, tetanus Summation of contractions  Muscle tension Muscle tension refers to the force generated by a muscle during contraction. It occurs when a muscle attempts to shorten against a resistance  Types of Muscle Contractions Leading to Tension 1. Isotonic Contractions: The muscle changes length → reproducing movement. a. Concentric Contraction: The muscle shortens as it generates tension (e.g., weight lifting). b. Eccentric Contraction: The muscle lengthens while maintaining tension (e.g., weight lowering). 2. Isometric Contractions: The muscle generates tension without changing length, meaning no movement occurs (e.g., holding a weight steady in one position).  Factors Affecting Muscle Tension: 1. The number of motor units activated: More motor units produce greater tension. 2. Frequency of Stimulation: increase muscle tension through summation, leading to tetanus 3. Length-Tension Relationship: influenced by the initial length of the muscle fibers. Muscles generate the most force when they're at an optimal length (not too stretched or too contracted). 1. Fatigue: As muscles work, they can become fatigued, leading to a decrease in tension over time. The most force when they're at an optimal length (not too stretched or too contracted). Anatomy of the muscles  Terms Related to movements Flexion Abduction Extension Adduction Hyperextension Circumduction Rotation  Terms Related to movements Flexion: bending movement, usually along the sagittal plane, that decreases the angle of the joint and brings the articulating bones closer together Extension: is the reverse of flexion and occurs at the same joints Hyperextension: Continuing such movements beyond the anatomical position is called Terms Related to movements 55 Terms Related to movements 56  Terms Related to movements Abduction (“moving away”): is movement of a limb away from the midline or median plane of the body, along the frontal plane Adduction (“moving toward”): is the opposite of abduction, so it is the movement of a limb toward the body midline or, in the case of the digits, toward the midline of the hand or foot Circumduction: is moving a limb so that it describes a cone in space. The distal end of the limb moves in a circle, while the point of the cone (the shoulder or hip joint) is more or less stationary. Rotation: is the turning of a bone around its own long axis Terms Related to movements 58  Naming of Skeletal Muscles Individual muscles are named according to their: Number of heads: Shape: 1.Biceps: Two heads 1.Deltoid: Triangular 2.Quadriceps: Four 2.Rectus: Straight heads Size: Position: 1.Major: Large 1.Pectoralis: Of the chest 2.Latissimus: 2.Brachii: Of the arm Broadest  Naming of Skeletal Muscles Individual muscles are named according to their: Depth 1.Superficialis: Superficial Actions 2.Externus: External 1. Extensor: Extend 2.Flexor: Flex Attachments 3.Constrictor: Constrict 1.Sternocleidomastoid: From sternum and clavicle to mastoid process.