Muscular System Anatomy of Muscle Fibrils Physiology of Muscle Contraction • http://www.biologycorner.com/anatomy/chap8.html websites Did you know that ? - More than 50% of body weight is muscle ! - Muscle is made up of proteins and water • Muscles are responsible for all movement of the body • There are three basic types of muscle • Skeletal (Striated or Voluntary) • Cardiac (Heart) • Smooth (Involuntary) The Muscular System 3 Types of Muscles Info About Muscles • Only body tissue able to contract • Create movement by flexing and extending joints • Body energy converters (many muscle cells contain many mitochondria) • Produce external movement • Maintain posture – hold body still or in a particular position • Stabilize joints • Movement of substances inside the body – cardiac and smooth (visceral) muscles transport blood and food • Generate heat by contractions – High metabolic rate of contracting produces lots of waste heat; small contractions to maintain body temperature Functions of Muscles Skeletal Cardiac Smooth Three types of muscle All muscles share some terminology • Prefixes myo and mys refer to muscle • Prefix sarco refers to flesh Muscle Terms Classification of Muscle Skeletal Cardiac Smooth Limbs Heart Viscera Movement Heartbeat Move food & and other substances through the body Striated and Striated Not striated Branched Multi- nucleated Uni-nucleated Uni-nucleated Fibers in sheets Fibers in bundles Lots of mitochondria Voluntary Involuntary Involuntary Contracts in short, strong bursts All fibers contract at the same time Contracts slowly, but steadily Skeletal Muscle • Also called Striated Muscle • Always connect to skeleton in at least one place • Most attached to two bones by a tendon • Act independently of neighboring muscle fibers • Striated - have stripes, banding • Multi-nucleated - cells have more than one nucleus • Voluntary - subject to conscious control, CNS • Long cylindrical fibers are arranged in bundles Skeletal or Striated Muscle • Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. • Tendons – strong collagen fibers • One bone is pulled toward the other bone, which remains stationary. Muscles move Bones • Muscle connected to stationary bone by tendons at the Origin. The basis for the action. • Muscle connected to moving bone by tendons at the Insertion. The effects of the action. • Muscles are always attached to at least 2 points • Movement is attained due to a muscle moving an attached bone How are Muscles Attached to Bone? Insertion Origin Muscle Attachments • Location • Origin and Insertion • Number of Origins • Shape, Size and Direction • Function Naming Muscles The layers of connective tissue are the cement that holds the muscle cells and bundles together • Epimysium – surrounds the whole muscle • Perimysium – surrounds the Fascicle (individual bundles of muscle cells) • Endomysium – surrounds the Muscle Fiber (Muscle Cell) Three types of Connective Tissue Bone to Muscle Fiber / cell Progression of Anatomy • Each Muscle Cell or Fiber is long and cylindrical • 50-60 mm in diameter, and up to 10 cm long (length is greater than width) • The contractile elements of skeletal muscle cells are Myofibrils • Sarcolemma – special cell membrane that conducts electrochemical signals Structure of skeletal muscle Vesicles and Tubules that surround the Muscle Fiber (cell) • T-System or Tubules – connect to sarcolemma and transmits the nerve impulse to the middle of the cell and all the thousands of myofibrils that make up the muscle cell • Sarcoplasmic Reticulum - forms a curtain around each myofibril and a storehouse of the calcium ions (Ca + 2) that are part of the contraction mechanism Sarcotubular System Sarcomere Myofibrils – muscle fiber structure; contractile elements A Bands - Dark and thick – Myosin H Band (zone) – darker area in the middle of the A Band I Bands – Light and thin – Actin Z Line (band, disc) – narrow, dark band in the central region of the I Band Sarcomere – area between two Z Lines – functional unit of muscle fiber Dark and Light Bands 1. Neuroelectrical Factors – Nerve impulse causes Potassium ions (K +) and Sodium ions (Na¯ ) to switch places across the cell membrane and create an Action Potential that travels along the TSystem. 2. Chemical Interactions – Actin unites with Myosin to form Actomyosin. 3. Energy Sources – ATP 3 Factors cause a Muscle Contraction Where Does the Energy Come From? • This all happens in the Mitochondria • Energy is stored in the muscles in the form of ATP • ATP comes from the breakdown of glucose during Cellular Respiration • Acetylcholine – released from synaptic vesicles, stimulates a muscle impulse • Cholinesterase – enzyme that stops action of acetylcholine Neurotransmitters • More Potassium ions inside the cell than outside. More Sodium ions outside the cell than inside. Inside the cell is negatively charged and outside is positively charged – Resting Potential • At the neuromuscular junction (end of the axon), a nerve impulse causes release of acetylcholine from the synaptic vesicles into the synaptic cleft. • Acetylcholine diffuses across the neuromuscular junction and binds to receptors on the sarcolemma (muscle cell membrane). Steps in a Contraction 1 Action Potential • Impulse spreads across sarcolemma and increases the permeability to K+ ions (depolarization) - the potassium ions rush outside the cell and the sodium ions rush inside the cell. This creates an electrical potential - and the Action Potential is generated. • Action Potential travels by way of the T-Tubules to all the cells and causes the Sarcoplasmic Reticulum to release Calcium ions that diffuse into the sarcoplasm. Steps in a Contraction 2 • The Calcium ion concentration at the myofilaments increases and negates the troponin and tropomyosin which keeps the filaments apart. This causes the formation of cross bridges between the actin and myosin filaments and they slide between each other and make Actomyosin. The Z Lines move together. • Contraction – the formation of the Actomyosin shortens the myofibril which shortens the muscle fibers which shortens the muscles Steps in a Contraction 3 Actin and Myocin • Sodium –Potassium Pump operation restores the Na and K distribution to the resting potential. Calcium ions are actively reabsorbed (Calcium Pump using ATP) into the Sarcoplasmic Reticulum and the concentration in the myofilaments decreases. • Contraction stops. The Z Lines move apart. The muscle cell relaxes and lengthens. Enzyme Cholinesterase stops action of the Acetylcholine. Steps in a Contraction 4 • Muscle Fatigue - a muscle is tired and unable to contract because of lack of oxygen, energy (ATP) and too many waste products. • Oxygen Debt - the amount of oxygen that the body needs to restore muscle cells to resting state. You feel out of breath! Too Little Oxygen & ATP Too Much CO₂ • Motor Unit – one motor neuron and the muscle fibers (cells) that it sends impulses to; they all contract together • Average 150 muscle cells • 200 muscle cells for gross movement (hand) • 10 muscle cells for fine movement (eye) • Muscle Cells have four properties: • • • • Excitability – stimulated by a nerve cell (neuron) Conductivity – response can travel throughout cells Contractility – the response to the stimulus Elasticity – return to original shape after contraction Contraction Physiology Contraction Cycle - Latent Period to Contraction Period (Shortening of fibers) to Relaxation Period Strength of contraction depends on: • • • • • • Number of Motor Units sending signals Strength of stimulus Duration of stimulus Speed of application Weight of the load (table vs. coffee cup) Temperature of the body (98.6⁰) Contractions A stimulus that elicits a response will produce a maximum contraction. The contraction occurs or it does not. All or None Law Single nerve impulse of a motor neuron will cause a motor unit to contract briefly before relaxing • A single brief small contraction • Not a normal muscle function Muscle Twitch Motor neuron provides many nerve impulses in rapid succession, the muscle has a complete and lasting contraction. • One contraction immediately followed by another • Effects are compounded • Remains in tetanus until the nerve signal slows or the muscle too fatigued to continue • Muscle never completely returns to a relaxed state Muscle Tetanus A natural condition of in which a muscle stays partially contracted at all times. • Some muscle cells will always be contracting while other muscle cells are at rest. • Maintain body posture without tiring • Slight and steady pull on attached bones • Pressure on abdominal contents • Blood pressure in arteries and veins • Assists in digestion in stomach and intestines • Prevents damage to muscle and joints from sudden movements Muscle Tone • Isotonic Contraction – tone or tension remains the same; the muscles become shorter and thicker; lifting a weight • Isometric Contraction – muscles remain at a constant length while the tension against the muscle increases; push against a wall or lift a large rock Two types of Contractions • Isotonic - muscles shorten and movement occurs ( most normal exercise) • Isometric - tension in muscles increases, no movement occurs (pushing one hand against the other); help develop tone or firmness in muscles Exercise and Muscles • Hypertrophy – increase in size due to repeated forceful contractions (exercise); 75% maximum effort • Atrophy – disuse or very low intensity use causes muscle to shrink – fibers shorten and replaced with fat and connective tissue (CT). More or Less • No striations • Spindle shaped • Single nucleus • Involuntary - no conscious control, ANS • Found mainly in the walls of hollow organs Smooth Muscle • Lines walls of viscera • Hollow Structures • Intestines • Blood Vessels • Urinary Bladder Location of Smooth Muscle Hollow Organs • 2-Layer Arrangement • longitudinal and circular layers • Alternate contraction of circular & longitudinal muscle in the intestine leads to peristalsis Intestines • Elongated Spindle shaped uni-nucleated cells • Striations not observed • Actin and myosin filaments are present (protein fibers) but not as regularly arranged Structure of smooth muscle • Slower and more rhythmic contractions • Greater extensibility of the muscle • Slow wave of contraction over the entire muscle mass Physiology of Smooth Muscle • • • • • Striations – very strong cells Branching or y-shaped cells Involuntary – ANS – autorhythmic Uni-nucleated Found only in the heart – responsible for pumping blood • Cells connected by Intercalculated Discs that spread signals quickly from cell to cell to beat as a unit Cardiac Muscle • • • • Main muscle of heart Pumping mass of heart Critical in humans Heart muscle cells behave as one unit • Heart always contracts to full extent Cardiac muscle Structure of cardiac muscle • Cardiac muscle cells (fibers) are short, branched and interconnected • Cells are striated & usually have 1 nucleus • Adjacent cardiac cells are joined via electrical synapses (gap junctions) • These gap junctions appear as dark lines and are called Intercalated Discs • Rapid rhythm of contractions • Impulse – contract – relax - another impulse – contract… • About 75 contractions per minute • Fibrillation – rapid uncontrolled contractions of individual cells; blood is not pumped properly Contractions of Cardiac Muscle Muscle Control Type of muscle Skeletal Skeletal Cardiac Smooth Nervous control Controlled by CNS Regulated by ANS Controlled by ANS Type of control Example Voluntary Lifting a glass Involuntary Heart beating Involuntary Peristalsis END OF ANATOMY AND PHYSIOLOGY Types of Musculo-Skeletal Movement Flexion Extension Hyperextension Abduction, Adduction & Circumduction Rotation • • • • • Inversion- turn sole of foot medially Eversion- turn sole of foot laterally Pronation- palm facing down Supination- palm facing up Opposition- thumb touches tips of fingers on the same hand More Types of Movement…… The Skeletal Muscles There are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this section we will only study a sample of the major muscles. Sternocleidomastoideus Flexes and Rotates Head Masseter Elevate Mandible Temporalis Elevate & Retract Mandible Trapezius Extend Head, Adduct, Elevate or Depress Scapula Latissimus Dorsi Extend, Adduct & Rotate Arm Medially Deltoid Abduct, Flex & Extend Arm Pectoralis Major Flexes, adducts & rotates arm medially Biceps Brachii Flexes Elbow Joint Triceps Brachii Extend Elbow Joint Rectus Abdominus Flexes Abdomen External Oblique Compress Abdomen External Intercostals Elevate ribs Internal Intercostals Depress ribs • • • • • • Flexor carpi—Flexes wrist Extensor carpi—Extends wrist Flexor digitorum—Flexes fingers Extensor digitorum—Extends fingers Pronator—Pronates Supinator—Supinates Forearm Muscles Diaphragm Inspiration Gluteus Maximus Extends & Rotates Thigh Laterally Rectus Femoris Flexes Thigh, Extends Lower Leg Gracilis Adducts and Flexes Thigh Sartorius Flexes Thigh, & Rotates Thigh Laterally Biceps Femoris Extends Thigh & Flexes Lower Leg Gastrocnemius Plantar Flexes Foot & Flex Lower Leg Tibialis Anterior Dorsiflexes and Inverts Foot