Exploring Muscular System

o o HUMAN ANATOMY AND PHYSIOLOGY CHAPTER 7 - MUSCULAR SYSTEM FUNCTIONS OF MUSCULAR SYSTEM • • • • • • • • o Movement Maintain posture Respiration Production of body heat Communication Heart beat Contraction of organs and vessels Types of Muscles o Skeletal o Cardiac o Smooth o Sarcoplasm - cytoplasm of muscle fiber (cell) Sarcolemma ▪ cell membrane ▪ contains T-tubules T-tubules (transverse) ▪ wrap around sarcomeres at A band ▪ associated with sarcoplasmic reticulum Sarcoplasmic reticulum ▪ type of SER ▪ surrounds myosin ▪ stores and releases Ca2+ SKELETAL MUSCLES • • • • • • • • • Abilities o Contractility - ability to shorten o Excitability - respond to stimulus o Extensibility - can stretch o Elasticity - recoil Characteristics o Makes up 40% of body weight o Named because attached to bones (skeleton) o Many nuclei per cell (near periphery) o Striated o Longest of muscle types • Skeletal Muscle StructuresActin and Myosin Myofilaments o Actin ▪ thin myofilament ▪ resemble 2 strands of pearls o Myosin ▪ thick myofilament ▪ resemble golf clubs o Troponin ▪ attachment site on actin for Ca2+ o Tropomyosin ▪ filament on grooves of actin ▪ attachment site on actin for myosin • Skeletal Muscle StructuresSarcomeres o Sarcomere - contractile unit; contains actin & myosin Skeletal Muscle StructuresConnective Tissue Coverings Epimysium - connective tissue that surrounds entire skeletal muscle (outside) Muscle fasciculus - bundle of muscle fibers Perimysium - connective tissue around each muscle fasciculus Muscle fiber skeletal muscle cells; many nuclei Endomysium connective tissue that surrounds each muscle fiber Skeletal Muscle StructuresMuscle Fiber Structure o Myofibril - thread-like proteins that make up muscle fibers o Myofilament - proteins that make up myofibrils; Ex. actin and myosin o o o o o Z disk - protein fibers forming attachment site for actin H zone - center of sarcomere; contains only myosin I band - contains only actin A band - where actin and myosin overlap M line - where myosin are anchored RESTING MEMBRANE POTENTIAL • • • • • • • • OUTSIDE CELL INSIDE CELL Na+ • K+ + charge • – charge Na+ channels closed • Some K+ channels open Why is the inside of cell negative if K + is positive? o K+ is able to diffuse out of cell freely but other larger negative molecules cannot. Action Potential o “electricity” o stimulus that causes rapid depolarization and repolarization o causes muscle to contract Depolarization o change in charges o inside becomes more + and outside more – o Na+ channels open Repolarization o Na+ channels close o change back to resting potential Sodium-Potassium Pump o pumps Na+ out of cell and transports K+ into cell o restores balance NERVE SUPPLY • • • • • • • • Motor neuron - nerve cells that carry action potentials to muscle fibers Neuromuscular junction (synapse) - where nerve cell and muscle fiber meet Presynaptic terminal - end of nerve cell (axon) Postsynaptic membrane - muscle fiber membrane Synpatic cleft - space between presynpatic terminal and postsynaptic membrane Synaptic vesicle - in presynaptic terminal; store and release neurotransmitters Neurotransmitter - chemicals that stimulate or inhibit a muscle fiber; Ex. Acetylcholine Motor unit -group of muscle fibers that motor neuron stimulates MUSCLE CONTRACTION 1. An action potential travels down motor neuron to presynaptic terminal causing Ca2+ channels to open. 2. Ca2+ causes synaptic vesicles to release acetylcholine into synaptic cleft. 3. Acetylcholine binds to receptor sites on Na+ channels, Na+ channels open, and Na+ rushes into postsynaptic terminal (depolarization). 4. Na+ causes sarcolemma and t-tubules to increase the permeability of sarcoplasmic reticulum which releases stored calcium. 5. Ca2+ binds to troponin which is attached to actin. 6. Ca2+ binding to troponin causes tropomyosin to move exposing attachment sites for myosin. 7. Myosin heads bind to actin. 8. ATP is released from myosin heads and heads bend toward center of sarcomere. 9. Bending forces actin to slide over myosin. 10. Acetylcholinesterase (enzyme breaks down acetylcholine) is released, Na+ channels close, and muscle contraction stops. • ATP and Muscle Contractions o Energy for muscle contractions supplied by ATP o Energy is released as ATP → ADP + P o ATP is stored in myosin heads o ATP help form cross-bridge formation between myosin and actin o New ATP must bind to myosin before cross-bridge is released o Rigor mortis - person dies and no ATP is available to release cross-bridges o ATP is made in mitochondria from aerobic or anaerobic respiration. o During a muscle contraction, H zone and I band shorten but A band stays the same. o Striations of skeletal and cardiac muscle are due to sarcomeres (actin and myosin). MUSCLE TWITCH, SUMMATION, TETANUS, AND RECRUITMENT • • • • • • • • Threshold - weakest stimulus need to produce response All or None Law - muscle contracts or doesn’t (no in between) Twitch - rapid contraction and relaxation of a muscle Tetanus - muscle remains contracted Isometric - amount of tension increases (weight) Isotonic - amount of repetitions increases Tone - constant tension over a long period of time Slow and Fast Twitch Fibers o Slow Twitch Fibers ▪ Contract slowly ▪ Fatigue slowly ▪ Long distance runners ▪ Use aerobic respiration ▪ Energy from fat ▪ Dark meat ▪ Red or dark because of myoglobin ▪ Myoglobin: helps O2 bind in muscle o Fast Twitch Fibers ▪ Contract quickly ▪ Fatigue quickly ▪ Sprinters ▪ Use anaerobic respiration ▪ Energy from glycogen o o o ▪ White meat Humans have both types of fibers Distribution of fibers is genetically determined Neither type can be converted but capacity can be increased through intense exercise o • SKELETAL MUSCLE ANATOMY • • • • • • • • • • • • Origin - nonmovable end Insertion - movable end Belly - middle Synergists - muscles that work together Antagonist - muscles that oppose each other Nomenclature - Muscles are named according to o Location - Ex. tibialis anterior o Origin/insertion - Ex. Sternocleidomastoid o Size - Ex. gluteus maximus o Shape - Ex. deltoid (triangular) o Function - Ex. Masseter Muscles of Head and Neck o Occipitofrontalis - raises eyebrows (forehead) o Orbicularis oculi - allows blinking (eyes) o Orbicularis oris - kissing muscle (mouth) o Zygomaticus - smiling muscle (cheek) o Masseter - chewing (mastication) muscle Muscles of Facial Expression Thoracic Muscles o External intercostals - elevate ribs for inspiration o Internal intercostals - depress ribs during forced expiration o Diaphragm - moves during quiet breathing Abdominal Wall Muscles o Rectus abdominis - center of abdomen; compresses abdomen o External abdominal oblique - sides of abdomen; compresses abdomen o Internal abdominal oblique - compresses abdomen o Transverse abdominis - compresses abdomen Upper Limb Muscles o Trapezius - shoulders and upper back; extends neck and head o Pectoralis major - chest; elevates ribs o Serratus anterior - between ribs; elevates ribs o Deltoid - shoulder; abductor or upper limbs o Triceps brachii - 3 heads; extends elbow o Biceps brachii - “flexing muscle”; flexes elbow & shoulder o Brachialis - flexes elbow o Latissimus dorsi - lower back; extends shoulder Muscles of Hips and Thighs o Iliopsoas - flexes hip • Gluteus maximus - buttocks; extends hip and abducts thigh o Gluteus medius - hip; abducts and rotates thigh Muscles of Upper Leg o Quadriceps femoris - 4 thigh muscles o Rectus femoris - front of thigh; extends knee and flexes hip o Vastus lateralis - extends knee o Vastus medialis - extends knee o Vastus intermedius - extends knee o Gracilis - adducts thigh and flexes knee o Biceps femoris, semimembranosus, emitendinosus - hamstring; back of thigh; flexes knee, rotates leg, extends hip Muscles of Lower Leg o Tibialis anterior - front of lower leg; inverts foot o Gastrocnemius - calf; flexes foot and leg o Soleus - attaches to ankle; flexes foot CARDIAC AND SMOOTH MUSCLES • Cardiac Muscle ▪ Heart ▪ 1 centrally located nucleus/cell ▪ Striated ▪ Rich in mitochondria ▪ Intercalated disks - special cell junctions that allow cells to act as a unit • Smooth Muscle ▪ Found on organs ▪ 1 centrally located nucleus/cell ▪ Not striated ▪ Less actin and myosin ▪ Under involuntary control