Muscular System 1
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Transcript of Muscular System 1
Muscular System 1
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• 3 types:1. Skeletal– striated & voluntary
2. Cardiac– striated & involuntary
3. Smooth – Smooth & involuntary
Types of Muscle Tissue
• most attached to bone• striations: – see light & dark bands under microscope
Skeletal Muscle Tissue
• found only in walls of heart chambers• heart has a pacemaker that initiates each contraction– called autorhymicity– controlled by hormones & neurotransmitters
Cardiac Muscle Tissue
• in walls of hollow organs• attached to hair follicles• some autorhythmic (wall of intestines)• regulated by ANS motor neuron& hormones
Smooth Muscle Tissue
• 1. producing body movements–moving whole body or parts of body
Functions of Muscular Tissue (#4)
• 2. stabilizing body position– skeletal muscles stabilize joints & halp
maintain body positions– postural muscles hold sustained contractions
(holding head up all day)
Functions
• 3. storing & moving substances w/in body– storing: accompanied by sustained
contractions of ringlike bands of smooth muscle called sphincters (hold material in organ)
– contraction/relaxation of smooth & cardiac muscle moves material thru bld vessels heart bld vessels
Functions
• 4. generating heat– process called thermogenesis–most of heat generated by muscle contraction
maintains normal body temp of 37°C– shivering: involuntary contraction of skeletal
muscle increases heat production
Functions
• 1. electrical excitability– ability to respond to certain stimuli by
producing electrical signals called action potentials
– 2 main types stimuli:1. autorhythmic electrical signals2. chemical stimuli (neurotransmitters) released
by neurons
Properties of Muscle Tissue (#4)
• 2. contractility– ability of muscle fibers to contract forcefully
when stimulated by an action potential–muscle fiber shortens & pulls on whatever it is
attached to• if force > resistance of object, movement occurs
Properties
• 3. extensibility– ability of muscle tissue to stretch w/out being
damaged– smooth muscle fibers are stretched every time
your stomach or bladder is really full
Properties
• 4. elasticity– ability of muscle tissue to return to original
length & shape after contraction or extension
Properties
• fascia: sheet or broad band of fibrous CT that supports & surrounds muscles or other organs– 2 layers: superficial & deep
CT Components
• 2. 3 layers of CT extend from deep fascia deeper into muscle tissue1. epimysium: outermost layer, encircles entire
muscle2. perimysium: surrounds groups of 10 – 100
muscle fibers = a fascicle3. endomysium: surrounds individual muscle
fibers
CT Components
• 3. tendon: extension of epimysium, perimysium, & endomysium beyond muscle that attaches the skeletal muscle to another structure (bone or another muscle)
CT Components
• hypertrophy: enlargement of existing muscle fibers– ex: muscle growth in newborn
• hyperplasia: increase in # of muscle fibers– ex: growth hormone causes increase in #s from
childhood adult• fibrosis: replacement of muscle by fibrous scar
tissue• satellite cells: stem cells in muscle tissue; limited
capacity
Muscle Histology Terms
Why Muscle Fibers are Multinucleated
• sarcolemma: plasma membrane • sarcoplasm: cytoplasm• myofibril: contractile organelles; thread-like
structures; each extends length of muscle fiber
Terms for Muscle Fiber Organelles
• T tubules: (transverse) invaginations of sarcolemma into sarcoplasma; increasing surface area– filled with interstitial fluid– ensures action potentials excites all parts of
muscle fiber
Terms for Muscle Fiber Organelles
• sarcoplasmic reticulum: (SR) endoplasmic reticulum that encircles individual myofibrils– dilated end sacs called terminal cistern – T tubule + 2 terminal cisterns = triad– in relaxed muscle fiber SR stores Ca++– release of Ca++ triggers contraction
Terms for Muscle Fiber Organelles
• 3 kinds proteins in myofibrils:1. contractile proteins– myosin make up thick filaments, golf-club shape
(myosin head)– actin thin filaments
2. regulatory proteins– tropomyosin & troponin: both in thin filaments
3. structural proteins– ~12 different ones function in alignment,
stability, elasticity, & extensibility of myofibrils
Muscle Proteins
1. ATP hydrolysis– ATP attached to myosin head
2. attachment of myosin head to actin to form cross bridges
3. power stroke– cross bridges rotate center slides thin
filament past thick filament4. detachment of myosin from actin– ATP binds to myosin head & cross bridges
released
Contraction Cycle Steps
• somatic motor neurons innervate muscle fibers to contract
Neuromuscular Junction (NMJ)
• synapse: functional junction between 2 neurons or between a neuron & an effector (muscle or gland); may be electrical or chemical
• 1st side of synapse: end of axon of motor neuron called synaptic end bulb
• then synaptic cleft (the space)• lastly, motor end plate: part of sarcolemma
that has receptors for neurotransmitter acetylcholine (ACh)
NMJ
• 1. release of ACh• 2. activation of ACh receptors• 3. production of muscle action potential• 4. termination of ACh activity
Steps in Nerve Action Potential Muscle Action Potential
• ACh stored in vesicles in synaptic end bulb• action potential travels down axon reaches
synaptic end bulb induces exocytosis of neurotransmitter from synaptic vesicles
• ACh diffuses across synaptic cleft toward motor end plate
Release of ACh
• 2 molecules of ACh bind to ACh receptors embedded in sarcolemma opens ion channel allows Na+ diffuse across membrane
Activation of ACh receptors
• inflow Na+ makes inside of muscle fiber more + charged
• this change in membrane potential triggers a muscle action potential propagates along sarcolemma T tubules
• this causes SR to release Ca++ sarcoplasm contraction
Production of Muscle Action Potential
• @ midpoint of muscle fiber:–muscle action potential propagate both ends
of fiber– allows simultaneous activation & so
contraction of all parts of muscle fiber
NMJ
• South American plant derivative• causes paralysis by binding to & blocking ACh
receptors on motor end plates• curare-like drugs used in general anesthesia to
relax skeletal muscles
Curare
• disease caused by Clostridium botulinum toxin that blocks exocytosis of synaptic vesicles so no ACh released so no muscle contraction– toxin one of most lethal chemicals known– causes death by paralyzing skeletal muscles:
breathing stops when diaphragm & intercostal muscles stop contracting
Botulism
• “equal tension”• force of contraction developed by muscle
remains almost constant while muscle changes its length
• used for body movements & for moving objects
• 2 types:1. concentric isotonic contraction2. eccentric isotonic contraction
Isotonic Contractions
• when tension generated is enough to overcome resistance of object being moved …muscle shortens & pulls on another structure (tendon) ….producing movement that reduces angle at a joint
Concentric Isotonic Contraction
• tension exerted by the muscle resists movement of the load (whatever was lifted up) slowing the lengthening process
Eccentric Isotonic Contraction
• tension generated by the muscle is < tension needed to overcome resistance of the object
• muscle does not change its length
Isometric Contraction
• same arrangement actin/myosin: striations• muscle fibers branched• *intercalated discs: unique to cardiac muscle• autorhymicity alone: 75 bpm• remains contracted 10-15 x’s longer than
skeletal muscle after 1 action potential– due to prolonged delivery of Ca++ (SR +
interstitial fluid– larger & more #s of mitochondria
Cardiac Muscle Tissue
• +thick & thin filaments but no T tubules & less SR so no striations
Smooth Muscle Tissue
Development of Muscle
• from mesoderm• starts ~4 wks• cardiac muscle forms
tubes bends & folds to form heart
• spasm: sudden involuntary contraction of a single muscle is a large group of muscles
Medical Terminology
• tic: an involuntary twitching by muscles that are normally under voluntary control
Medical Terminology
• tremor: rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement
Medical Terminology
• fasiculation: involuntary, brief twitch that is visible under the skin; occurring irregularly & not ass’c with movement– seen in MS or ALS
Medical Terminology
• fibrillation: spontaneous contraction of single muscle fiber that is not visible under skin but can be recorded by EMG (electromyograph) – signals destruction of motor neurons
Medical Terminology
• muscle strain: tearing of muscle due to forceful impact + bleeding +pain–most often affect quadraceps femoris– tx‘d RICE (rest, ice, compression ie a wrap,
elevation)
Medical Terminology