Muscular System Note Slides Naming of · PDF fileMuscular System Note Slides 9/23/2013 Naming...
Transcript of Muscular System Note Slides Naming of · PDF fileMuscular System Note Slides 9/23/2013 Naming...
9/23/2013
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Muscular System Note Slides
9/23/2013
Naming of Names
• The roots…
• Myo- and Mys- = muscle
– Epimysium: connective tissue that wraps the muscle
• Sarco = flesh
– Sarcolemma: muscle plasma membrane
• Skeletal and Smooth Muscle cells are called fibers
Characteristics of Muscle Tissue • Excitability: responsiveness/irritablility; the ability
to receive and respond to stimuli
– Stimuli from the internal and external environments
• Contractility: ability to shorten forcibly when adequately stimulated
• Extensibility: ability to be stretched or extended
• Elasticity: ability of a muscle cell to recoil and resume its resting length after being stretched
• Conductivity: ability to propagate electrical signals over membrane
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Side Note • Muscles contract, they do NOT flex
– Flexion is a description of the movement of a joint
– Contraction is the shortening of a muscle
• Extensibility does NOT equal Extension
– Extensibility is one of the special characteristics of muscle; stretch
– Extension is a description of a joint movement
Functions of Muscle • Produce Movement: just about all movements
in the human body and its parts result from muscle contraction
– All three types: skeletal, cardiac and smooth
• Maintain Posture and Body Position: skeletal muscle continuously adjusts posture and positioning in relation to gravity
• Stabilize Joints: skeletal muscles stabilize and strengthen the joints of the skeleton
Functions Continued • Generate Heat: muscles generate heat as they
contract – Maintains normal body temperature
– Skeletal muscle accounts for ̴40% of body mass (most responsible for heat production)
• Miscellaneous – Skeletal muscle: protects organs by encasing them
– Smooth muscle: maintain blood pressure, passage of internal substances, dilate and constrict pupils of the eye, form arrector pili muscles attached to hair follicles
– Cardiac Muscle: propels blood through the body
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Smooth Muscle Tissue • Location: walls of hollow visceral organs
– i.e., stomach, urinary bladder, respiratory passages, walls of arteries
• Cell Description: elongated fibers without striations
• Contraction: slow, sustained, involuntary – Lacks neuromuscular junctions
– Under autonomic control – sypathetic, parasympathetic
– Peristalsis: wave of contraction followed by relaxation
Cardiac Muscle Tissue
• Location: the heart
• Cell Description: short, striated, quadrangle shaped
• Contraction: in syncytium (all-at-once)
– NOT voluntary
– Autorhythmic: heart has its own pacemaker
– Under Autonomic control – sympathetics and parasympathetics will speed up and slow down rate
Skeletal Muscle Tissue • Skeletal Muscle = Voluntary Muscles • Cell Description: long, cylindrical,
multinuecleated • Contraction: rapid, but tires easily
– Some predetermined by brain stem and can be over-ridden
• Skeletal Muscle Tissue has obvious stripes called striations
• Each muscle is served by one nerve, an artery and one or two veins
• Each motor neuron supplies multiple muscle cells – Neuromuscular junction: each muscle fiber is supplied
with a nerve ending that controls contraction
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Skeletal Muscle Tissue 2 • Requires huge amounts of Oxygen and
nutrients via blood supply, and give off large amounts of metabolic wastes
• Individual Muscle Fibers are held together by several connective tissue sheaths
– Support to each cell and reinforce the whole muscle (prevent muscles from bursting during strong contraction
– Continuous with one another and tendons
– Contribute to elasticity, entry and exit for blood vessels and nerve fibers
Connective Tissue Sheaths • Epimysium
– “Outside the muscle”: dense irregular connective tissue that surrounds the whole muscle
– Sometimes blends with deep fascia between muscles or superficial fascia deep to skin
• Perimysium – “Around the muscle”: fibrous connective tissue surrounds
fascicles – Groups of muscle fibers are grouped into fascicles that
resemble bundles of sticks
• Endomysium – “Within the muscle”: areolar connective tissue surrounds
individual muscle fiber – Not to be confused with the sarcolemma (coming up)
Attachments
• Most skeletal muscles span joints and are attached to bone in at least two place
– Dierect: Epimysium of muscle is fused the periosteum of bone
– Indirect: Connective tissue wrappings extend beyond the muscle as
• Tendon
• Aponeurosis
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Microscopic Anatomy 1 • Sarcolemma: plasma membrane surface of a
muscle fiber
• Sarcoplasm: cytoplasm of a muscle cell – Large amounts of glycosomes (stored glycogen)
and myoglobin (oxygen binding protein)
• Myofibrils: rodlike bundles of contractile filaments found in muscle fibers ̴80% cell volume – Contractile organelle
– Striations: repeating series of dark (A) and light (I) bands along the length of the myofibril
Microscopic Anatomy 2 • Sarcomere: smallest contractile unit
– Region between two Z discs; functional unit of skeletal muscle
• Myofilaments: molecular level of the sarcomere – Made of contractile proteins
– Thick filaments: protein myosin ( ̴ 300 molecules) • Ea. Molecule has a rod-like tail and two globular heads
called cross bridges ( ATP and Actin binding sites)
• Held in place by M Line proteins
– Thin filaments: contractile protein actin (contains binding sites for myosin • Regulatory proteins tropomyosin (covers binding site) and
troponin (moves tropomyosin)
The Bands, Zones, Discs and Lines… • A Bands: Actin and Myosin overlap
• I Bands: no Myosin (lighter)
• H Zone: Myosin only; thin (actin) and thick (myosin) filaments do not overlap
• M Line: appear darker due to the presence of desmin (aka myomesmin); helps anchor thick filaments – M Line of the H Zone of the A Band
• Z Disc: coin shaped sheet of proteins (titins = connectins) that anchor thin filaments and connects myofibrils to one another
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Microscopic Anatomy 3 • Sarcoplasmic Reticulum: elaborate smooth ER
– endoplasmic reticulum:“network within the cytoplasm”)
– Runs longitudinally and surrounds each myofibril communicating at the H Zone • Extensive system of interconnected tubes and parallel
membranes enclosing fluid filled cavities (cisternae)
• Terminal cisternae: “end sacs” at the A Band – I Band junction – Calcium Ion storage
• T Tubules: elongated tubes that penetrate into the cell at A Band – I Band Junction – Invaginations of the sarcolemma that conduct
impulses deep into the cell
Sliding Filament Model of Contraction • Think of it as Myosin ratcheting itself along Actin
which shortens the Sarcomere
– Calcium is released→ Calcium binds to troponin→ Troponin moves tropomyosin→ Myosin binds to Actin → Actin is pulled toward center of Sarcomere→ Sarcomere shortens→ muscle fiber shortens→ muscle shortens
• Thick and thin filaments do NOT change length
• Requires ATP
Muscle Metabolism and ATP • ATP: Adenosine Triphosphate
– Adenine + ribose + 3 phosphates
– Stores and releases chemical energy
– Hydrolysis reactions: uses water to break bonds • ADP +P
• Muscle only stores 4-6 seconds of ATP – After hydrolized into ADP + P, quickly regenerated to ATP
• Muscle fatigue: state of physiologic inability to contract even though muscle is still receiving stimuli
• Contractures: state of continuous contraction due to lack of ATP, cross bridges are unable to detach
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Sliding Filament Model of Contraction • 6 Steps
– 1)Calcium released from terminal cisternae • Action potential in the Sarcolemma causes Calcium release
• Change in the conformation of the Troponin-Tropomyosin complex, tropomyosin slides over
– 2) Myosin binds to Actin • When binding site is exposed, energized Myosin head can
bind and form a cross bridge
– 3) Power stroke of the myosin head causes sliding of thin filaments • The chemical energy of ATP is changed to mechanical energy
of contraction
• Myosin head flexes pulling Actin toward the center of the Sarcomere
Sliding Filament Model of Contraction • 6 Steps
– 4) ATP binds to Myosin head resulting in disconnect from Actin
• ATP molecule must bind to its site on the myosin head for Actin to be released – If ATP in muscle is depleted, muscle will stay in a state of “rigor”
– 5) Hydrolysis of ATP leads to re-energizing and repositioning of myosin heads
• Energy is transferred to the myosin head returning is to its high energy conformation
– 6) Transport of Calcium back into terminal cisternae
• Active transport – requires ATP
Innervation of a Muscle: Vocabulary • Motor Neuron: nerve cell that activates a muscle
fiber – Motor neurons reside in the brain, but their long axons
travel to the muscle fiber
• Neuromuscular junction: region where motor neuron comes into close contact with fiber – Synaptic Cleft: functional space between muscle fiber and
the motor neuron
– Acetycholine (Ach): neurotransmitter released within synaptic cleft, stimulates electrical impulse creating action potential
– Acetylcholinesterase (AChE): binds with and breaks down Ach; terminates action potential
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For Contraction to Occur • For a Skeletal Muscle to contract
– it must be activated (stimulated by a nerve ending) causing a change in the membrane potential
– It must generate and propagate an electrical current (action potential) along its Sarcolemma • A resting Sarcolemma is polarized – it has a potential
difference or voltage across the membrane with the inside being relatively negative
– A short-lived rise in intracellular Calcium ion levels occurs to trigger contraction • This is caused by the action potential traveling down
the T Tubules
Excitation-Contraction Coupling
• Sequence of Events by which transmission of an action potential leads to the sliding of filaments
• Depolarization: loss or reduction of negative membrane potential
• Repolarization: movement of the membrane potential to the initial negative resting (polarized state)
• Refractory Period: period during the repolarization phase when the cell cannot be stimulated again until repolarization is complete
At the Neuromuscular Junction • Action Potential arrives at axon terminal • Voltage-gated calcium ion channels open
– calcium enters axon terminal
• Calcium Ion release causes release of Ach • Ach diffuses across cleft and binds to receptors • Ach binding opens ion channels that allows Sodium
into and Potassium out of the muscle fiber – More Sodium goes in than Potassium out, this causes
depolarization – Action potential is propogated as the local depolariztion
spreads to adjacent areas
• Ach effects are terminated by enzymatic breakdown by AChE
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Muscular System Images
Skeletal Muscle System
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3 Types of Muscle
Smooth Muscle
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Cardiac Muscle
Skeletal Muscle
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Nerve and Blood Supply
Connective Tissue Sheaths
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From Gross to Microscopic Anatomy
Thin and Thick Filaments
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The Bands, Zones, Discs and Lines…
Sarcoplasmic Reticulum and T Tubule
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Sliding Filament Model of Contraction
Sliding Filament Model of Contraction
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At the Neuromuscular Junction