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Summary Reviewer for Muscular System
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Reviewer for Chapter 7 of Anatomy and Physiology
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Seeleys Anatomy and Physiology, 12th Edition (VanPutte, 2020), Chapter 1-29
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Seeleys Anatomy and Physiology, 12th Edition (VanPutte, 2020), Chapter 1-29
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- range in length 1mm to 30cmMUSCULAR SYSTEM - alternating light and dark bands give muscle fibers
a striated appearance
Types of Muscles - number of muscle fiber remains constant after birth
Skeletal - enlargement of muscles: increase in size not in
fiber number
• attached to bones
• striated Electrical Component Structures
• voluntary Sarcolemma – cell membrane of the muscle fiber
Cardiac
• located in the heart Transverse tubules (T tubules) – tube-like invaginations or
• striated inward folds which occur at regular intervals along the
• involuntary muscle fiber
Smooth Sarcoplasmic reticulum – T tubules that are associated
• located in blood vessel, hollow organs with enlarged portion of smooth E.R
• non-striated
• involuntary Terminal Cisternae – enlarged portion
Functions of Muscular System Muscle Triad – 2 terminal cisternae and their associated T
1. Movement of the body. tubule
2. Maintenance of posture.
Sarcoplasmic Reticulum - has a relatively high
3. Respiration
concentration of Ca2+; major role in muscle contraction
4. Production of body heat
5. Communication Sarcoplasm – cytoplasm of a muscle fiber
6. Constriction of organs and vessels
7. Contraction of the heart Myofibrils – bundles of protein filaments
Functional Characteristics of Muscles - Actin Myofilaments - (thin filaments; purple)
1. Contractility – ability to shorten forcefully - Myosin Myofilaments - (thick filaments; green)
2. Excitability – capacity to respond to a stimulus
3. Extensibility – ability to be stretched to its Sarcomere – arranged repeating units of actin + myosin
normal resting length and still be able to contract myofilaments; provide mechanical aspect of muscle
4. Elasticity – ability to recoil to their original contraction
resting length - basic structural and functional unit of skeletal
Whole Skeletal Muscle Anatomy muscle
Skeletal Muscle - joined end to end to create myofibrils
o Constitutes approx. 40% of body weight Z disks – network of protein fibers forming an anchor for
o Muscles are attached to the skeletal system, some actin myofilaments and separate one sarcomere from the
is attached to skin or connective tissue sheets next
o Also called Striated Muscle; transverse bands or - organization of actin and myosin myofilaments
striations gives skeletal muscle its striated appearance and
o Individual skeletal muscles, such as the biceps gives it the ability to contract
brachii, are complete organs, as a result of being - myofilaments slide past each other, causing
comprised of several tissues: muscle, nerve, and sarcomeres to shorten
connective tissue. - consists of 2 light-staining bands separated by
Connective Tissue Coverings dark-staining band
Epimysium/Muscular fascia – connective tissue sheath I bands – consists of actin myofilaments; extend from Z
that surrounds a skeletal muscle disk to the ends of myosin myofilaments
Fascicles – groups of muscle cells that make up skeletal A bands – dark staining bands, extends the length of
muscle myosin filaments
Perimysium – loose connective tissue that surrounds each Muscle contraction - actin and myosin overlap on both
fascicle ends of the A band
Endomysium – loose connective tissue covering that H zone – second light zone that consists of myosin
surrounds each skeletal muscle fiber myofilaments
Skeletal Muscle Fiber Anatomy
Muscle fibers – a large cell with several muscle cells; nuclei
located at its periphery
labd
, - The arrangement of the actin and myosin filaments - voltage difference or electrical charge difference
in sacromeres gives the myofibrils a banded – exists across each cell membrane
appearance. - charge difference is because of differences in
- The alternating I bands and A bands of the concentration of ions
sacromeres are responsible for the striations in the
skeletal muscle fibers. Ion Channels – membrane proteins that permit ions to pass
through the membrane
Myofilament Structure
Troponin molecules – binding sites for Ca2 Leak channels – always open; allow the slow leak of ions
down their concentration gradient
Tropomyosin filaments – block the myosin filament
binding sites on the actin myofilaments Gated channels – may open or close in response to various
types of stimuli.
Myosin myofilaments, or thick myofilaments - resemble
bundles of tiny golf clubs. Resting Membrane Potential - electrical charge difference
across the cell membrane of an unstimulated cell
Myosin heads – have ATP binding sites, ATPase and - due to the inside of the membrane being negatively
attachment spots for actin charged in comparison to the outside of the
membrane which is positively charged
Neuromuscular Junction Structure
Motor neurons – specialized nerve cells that stimulate The resting membrane potential exists because of:
muscles cells • The concentration of K+ being higher on the inside
of the cell membrane and the concentration of Na+
Neuromuscular junction – synapse where neuron connects being higher on the outside
with a muscle fiber • The presence of many negatively charged
Synapse – cell-to-cell junction between a nerve cell and molecules, such as proteins, inside the cell that are
another nerve cell/effector cell too large to exit the cell
• The presence of leak channels in the membrane
Motor unit – group of muscle fibers that a single motor that are more permeable to K+ than they are to
neuron stimulates Na+
• Na+ tends to diffuse into the cell and K+ tends to
Presynaptic terminal – end of a neuron cell axon fiber diffuse out.
Synaptic cleft – the space between the presynaptic terminal • In order to maintain the resting membrane
and postsynaptic membrane potential, the sodium-potassium pump recreates
the Na+ and K+ ion gradient by pumping Na+ out
Postsynaptic membrane – the muscle fiber membrane of the cell and K+ into the cell.
(sarcolemma)
Action Potentials - reverses the resting membrane potential
Synaptic vesicles – vesicle in the presynaptic terminal that so that the inside of the cell becomes positive and the
stores and releases neurotransmitter chemicals outside negative
Neurotransmitters – chemicals that stimulates/inhibits a - occurs because gated ion channels open when the
postsynaptic cell cell is stimulated
- lasts for 1 to 3 milliseconds
Acetylcholine (ACh) – neurotransmitter that stimulates - entry of Na+ causes the inside of the cell
skeletal muscles membrane to become more positive than when the
cell is at resting membrane potential
Acetylcholinesterase – an enzyme that rapidly breaks - rapid change in charge across membrane
down the synaptic cleft bet. the neuron and the muscle fiber - results in muscle contraction
Cross-bridges – myosin heads attach to the myosin Depolarization – increase in positive charge inside the cell
attachment sites on the actin myofilaments membrane
Sliding Filament Model Threshold – membrane potential value when action
Muscle contraction - sliding of actin myofilaments past potential is triggered
myosin myofilaments; shorten the sarcomere
Repolarization – changes back to the resting; Na+ channels
Muscle Relaxation – sarcomeres lengthen close change back to resting potential
Excitability of Muscle Fibers Function of the Neuromuscular Junction
- electrically excitable ✓ Each muscle fiber is innervated by a branch of a
- electrically excitable cells are polarized motor neuron at a neuromuscular junction.
- inside of cell membrane is negatively charge ✓ Contact between the axon terminal and the
compared with the outside sarcolemma results in an action potential in the
labd
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