Muscular System
description
Transcript of Muscular System
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Muscular System
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Muscle Tissues
Skeletal Muscle Smooth Muscle Cardiac Muscle
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Skeletal Muscle
Usually attached to bones Under conscious control Striated
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Smooth Muscle
Walls of most viscera, blood vessels, and skin
Not under conscious control Not striated
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Cardiac Muscle
Wall of heart Not under conscious control Striated
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Structure of a Skeletal Muscle
Organ of the muscular system Skeletal muscle tissue Nervous tissue Blood Connective tissues Fascia Tendon aponeuroses
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Structure of a Skeletal Muscle
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Structure of a Skeletal Muscle Epimysium Perimysium Fascicle Endomysium
Muscle Fascicles Muscle fibers Myofibrils Thick and thin filaments
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Skeletal Muscle Fiber Sarcolemma Sacroplasm Sarcoplasmic reticulum Transverse tubule Traid
Cisterna of sarcoplasmic reticulum
Transverse tubule Myofibril Actin filaments Myosin filaments sarcomere
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Sarcomere
I band A band H zone Z line M line
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Myofilaments
Thick filaments Composed of
myosin Cross-bridges
Thin filaments Composed of actin Associated with
troponin and tropomyosin
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Neuromuscular Junction
Site where axon and muscle fiber communicate
Motor neuron Motor end plate Synaptic cleft Synaptic vesicles Neurotransmitters
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Motor Unit
Single motor neuron
All muscle fibers controlled by motor neuron
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Stimulus for Contraction Acetylcholine (ACh) Nerve impulse causes
release of ACh from synaptic vesicles
Binds to ACh receptors on motor end plate
Generates a muscle impulse
Muscle impulse eventually reaches sarcoplasmic reticulum
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Excitation Contraction Coupling
Muscle impulses cause sarcoplasmic retuculum to release calcium ions into cytosol
Calcium binds to troponin to change its shape
Position of tropomyosin is altered Binding sites on actin exposed Actin and myosin bind
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Sliding Filament Theory
When sarcromeres shorten, thick and thin filaments slide past one another
H zones and I bands get narrower
Z lines move closer together
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Cross-Bridge Cycling Actin and myosin cross-bridge bind Myosin cross-bridge pulls actin ADP and phosphate released from myosin New ATP binds to myosin Linkage between actin and myosin cross-
bridge break ATP splits Myosin cross-bridge goes back to original
position
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Relaxation
Acetylcholinesterase- breaks down Ach Muscle impulse stops Calcium moves back into sarcoplasmic
reticulum Myosin and actin binding prevented
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Energy Sources for Contraction 1)Creatine
phosphate Creatine
phosphate stores energy that quickly converts ADP to ATP
2) Cellular respiration
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Oxygen Supply & Cellular Respiration
Anaerobic Phase Glycolysis Produces little ATP
Aerobic Phase Citric acid cycle Electron transport
chain Produces most ATP Myoglobin stores
extra oxygen
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Oxygen Debt Oxygen debt- amount of oxygen needed by
liver to convert lactic acid to glucose
Oxygen not available Glycolysis continues Pyruvic acid converted
to lactic acid Liver converts lactic
acid to glucose
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Muscle Fatigue
Inability to contract Commonly caused from
Decreased blood flow Ion imbalances Accumulation of lactic acid
Cramp- sustained, involuntary contraction
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Heat Production
By product of cellular respiration Muscle cells are major source of body
heat Blood transport heat throughout body
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Muscular Responses Threshold Stimulus- minimal strength required to
cause contraction Recording a muscle
contraction Twitch Latent period Period of contraction Period of relaxation Refractory period All-or-none response
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Summation
(a) Process by which individual twitches combine
(b) Produces sustained contractions
(c) Can lead to tetanic contractions
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Recruitment of Motor Units
Recruitment- increase in the number of motor units activated
Whole muscle composed of many motor units
As intensity of stimulation increases, recruitment of motor units continues until all motor units are activated
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Sustained Contractions
Smaller motor units recruited first Larger motor units recruited later Produces smooth movements Muscle tone- continuous state of
partial contraction
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Types of Contractions
Isotonic- muscle contracts and changes length
Concentric- shortening contraction Eccentric- lengthening contraction Isometric- muscle contracts but does
not change length
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Fast & Slow Twitch Muscle Fibers Slow-Twitch fibers
(type I) Always
oxidative Resistant to
fatigue Red fibers Most
myoglobin Good blood
supply
Fast-Twitch glycolytic fibers (type IIa) White fibers (less myoglobin) Poorer blood supply Susceptible to fatigue
Fast-Twitch fatigue-resistant fibers (type IIb) Intermediate fibers Oxidative Intermediate amount of
myoglobin Pink to red in color
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Smooth Muscle Fibers
Compared to skeletal muscle fibers Shorter Single nucleus Elongated with tapering ends Myofilaments randomly organized No striations Lack transverse tubules Sarcoplasmic reticula not well developed
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Types of Smooth Muscle Visceral Smooth Muscle
Single-unit smooth muscle Sheets of muscle fibers Fibers held together by gap junctions Exhibit rhythmicity Exhibit peristalsis Walls of most hollow organs
Multiunit Smooth Muscle Fibers function separately Irises of eye Walls of blood vessels
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Smooth Muscle Contraction Resembles skeletal muscle contraction
Interaction between actin and myosin Both use calcium and APT Both depend on impulses
Different from skeletal muscle contraction Smooth muscle lacks troponin Smooth muscle depents on calmodulin Two neurotransmitters affect smooth muscle
Acetlycholine and norepinephrine Hormones affect smooth muscle Stretching can trigger smooth muscle contraction Smooth muscle slower to contract and relax Smooth muscle more resistant to fatigue
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Cardiac Muscle
Only in the heart Muscle fibers joined together by
intercalated discs Fibers branch Network of fibers contracts as a unit Self-exciting and rhythmic Longer refractory period than skeletal
muscle
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Skeletal Muscle Actions Origin- immovable end Insertion- movable end Prime mover (agonist)
– primarily responsible for movement (deltoid)
Synergists – assist prime mover
Antagonist – resist prime mover’s action and cause movement in the opposite direction
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Major Skeletal Muscles
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Major Skeletal Muscles
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Muscles of Facial Expression
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Muscles of Mastication
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Muscles of Facial Expression & Mastication
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Muscles that Move: Head & Vertebral Column
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Muscles that Move: Pectoral Girdle
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Muscles that Move the Arm
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Deep Muscles of the Back & Neck
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Muscles of the Shoulder & Back
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Muscles of: Anterior Chest & Abdominal Wall
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Muscles that Move the Forearm
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Muscles that Move the Head
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Muscles of the Shoulder & Arm
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Cross Section of the Arm
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Muscles of the Shoulder & Arm
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Muscles of the Arm & Forearm
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Muscles of the Arm & Forearm
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Cross Section of the Forearm
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Muscles of the Abdominal Wall
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Muscles of the Abdominal Wall
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Muscles of the Pelvic Outlet
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Muscles of Pelvic Outlets & Urogenital Diaphragm
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Muscles that Move the Thigh
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Muscles that Move the Leg
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Muscles that Move the Foot
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Muscles of the Thigh & Leg
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Muscles of the Thigh & Leg
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Muscles of the Thigh & Leg
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Cross Section of the Thigh
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Muscles of the Leg
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Muscles of the Leg
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Muscles of the Leg
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Cross Section of the Leg
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Life-Span Changes
Myoglobin, ATP, and creatine phosphate decline
By age 80,half of muscle mass has atrophied
Adipose cells and connective tissues replace muscle tissue
Exercise helps to maintain muscle mass and function
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Clinical Application Myasthenia Gravis
Autoimmune disorder Receptors for acetylcholine on muscle cells
are attacked Weak and easily fatigued muscles result Difficulty swallowing and chewing Ventilator needed if respiratory muscles are
affected Treatments include:
Drugs that boost acetylcholine Removing thymus gland Immunosuppressant drugs antibodies