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Muscular System
lecture 10/25/11
68
Anatomy
Undergraduate 1
10/25/2011

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Term
Smooth muscle tissue:
Definition
In the walls of hollow organs, e.g., stomach, urinary bladder, and airways
Uninucleate
Not striated
Involuntary
Term
cardiac muscle
Definition
striated, intercalated discs, involuntary, mononuclear
Term
skeletal muscle
Definition
voluntary, striated, multi-nucleate, powerful
Term
Extensibility:
Definition
ability to be stretched
Term
Elasticity:
Definition
ability to recoil to resting length
Term
Major Muscular System Functions:
Definition
Movement of bones or fluids (e.g., blood)
Maintaining posture and body position
Stabilizing joints
Heat generation (especially skeletal muscle)
Term
Each muscle is served by:
Definition
one artery, many arterioles, many capillaries; one nerve, many axons, many axonal terminals
one or more veins
Term
Epimysium is:
Definition
a layer of connective tissue, which ensheaths the entire muscle.
Term
Endomysium
Definition
meaning within the muscle, is a layer of connective tissue that ensheaths a muscle fiber and is composed mostly from reticular fibers. It also contains capillaries, nerves, and lymphatics. It overlies the muscle fiber's cell membrane: the Sarcolemma.
Term
Perimysium:
Definition
fibrous connective tissue surrounding fascicles(groups of muscle fibers) (strong!)
Term
Glycosomes for:
Definition
glycogen storage, myoglobin for O2 storage
Term
T-Tubule
Definition
a deep invagination of the sarcolemma, which is the plasma membrane, only found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.
Term
Myofibrils are:
Definition
A myofibril is a basic unit of a muscle. Muscles are composed of tubular cells called myocytes or myofibers. Myofibers are composed of tubular myofibrils. composed of long proteins such as actin, myosin, and titin, and other proteins that hold them together.
Term
Sarcomere
Definition
One part of a myofibril - Smallest contractile unit (functional unit) of a muscle
The region of a myofibril between two successive Z discs
Composed of thick and thin myofilaments made of contractile proteins
Term
one sarcomere goes from:
Definition
z-disc to z-disc
Term
Thick filament
Definition
myosin
Term
Myosin tails contain:
Definition
2 interwoven, heavy polypeptide chains
Term
Myosin heads contain:
Definition
2 smaller, light polypeptide chains that act as cross bridges during contraction
Binding sites for actin of thin filaments
Binding sites for ATP
ATPase enzymes
Term
Thin Filament -
Definition
Actin
Term
Sarcoplasmic Reticulum (SR)
Definition
Network of smooth endoplasmic reticulum surrounding each myofibril
Pairs of terminal cisternae form perpendicular cross channels
Functions in the regulation of intracellular Ca2+ levels
Term
Invagination means:
Definition
to fold inward or to sheath.
Term
T tubules conduct:
Definition
impulses deep into muscle fiber (voltage sensors)
Term
Requirements for Skeletal Muscle Contraction:
Definition
Neural Activation:
neural stimulation at a neuromuscular junction
Muscle Cell Excitation- Contraction Coupling
Generation and propagation of an action potential along the sarcolemma
Final trigger: due to a brief rise in intracellular Ca2+ levels
Term
What is the Neuromuscular Junction?
Definition
Situated midway along the length of a muscle fiber
Axon terminal and muscle fiber are separated by a space called the synaptic cleft
Synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh)
Sarcolemma contain ACh receptors
Term
3 step: electro - chemical process
Definition
Depolarization – initiating a charge
Propagation of action potential
Repolarization – resetting the resting membrane potential
Term
Events at the Neuromuscular Junction:
Definition
Nerve impulse (action potential) arrives at axon terminal
Causing Ca ions to flow into the axonal terminal
Presence of Ca causes vesicles containing ACh to migrate to the membrane
ACh is released by exocytosis into the synaptic cleft
ACh binds to receptors on the sarcolemma
Ach binding opens Na channels – Na flows into the muscle cell
This leads to the generation of an action potential on the sarcolemma = transfer of electrical energy to chemical energy and back to electrical energy - called depolarization
Term
Repolarization-
Definition
Na+ channels close and voltage-gated K+ channels open
K+ is pumped out rapidly - restores the resting membrane potential
Fiber cannot be stimulated and is in a refractory period until repolarization is complete and …
Ionic conditions of the resting state are restored
Term
Role of Calcium (Ca2+) in Contraction/
At low intracellular Ca2+ concentration:
Definition
Tropomyosin blocks the active sites on actin
Myosin heads cannot attach to actin
Muscle fiber is relaxed
Term
Role of Calcium (Ca2+) in Contraction/
At higher intracellular Ca2+ concentrations:
Definition
Ca2+ binds to troponin
Troponin changes shape and moves tropomyosin away from active sites
Events of the cross bridge cycle occur (myosin heads rise & bind with actin, ATP activates the cocking action which moves the actin filament in a power stroke)
When nervous stimulation ceases, Ca2+ is pumped back into the SR and contraction ends
Term
Cross Bridge Cycle:
Definition
Continues as long as the Ca2+ signal and adequate ATP are present
Working (power) stroke - myosin head sticks and pulls the thin filament toward M line
Term
fast twitch
Definition
thinner, smaller muscles
Term
slow twitch
Definition
larger muscles
Term
Isometric contraction:
Definition
no shortening - muscle tension increases but does not exceed the load
Term
Isotonic contraction:
Definition
muscle shortens because muscle tension exceeds the load
Term
muscle mass is increased by:
Definition
gaining myosin heads
Term
Motor unit =
Definition
a motor neuron and all (few to several hundred) muscle fibers it supplies
Term
Muscle fibers from a motor unit are spread throughout the muscle so that -
Definition
1 single motor unit causes a weak contraction of entire muscle
Term
Motor units in a muscle usually contract:
Definition
asynchronously - helps prevent fatigue
Term
A Muscle Twitch -
Definition
Response of a muscle to a single, brief threshold stimulus
Term
3 phases of a muscle twitch:
Definition
Latent period: events of excitation-contraction coupling
Period of contraction: cross bridge formation; tension increases
Period of relaxation: Ca2+ reentry into the SR; tension declines to zero
Term
Variations in the degree of muscle contraction are called -
Definition
Graded Muscle Response
Term
Graded Muscle Responses are graded by: (2)
Definition
Changing the frequency of stimulation
Changing the strength of the stimulus
Term
Threshold stimulus:
Definition
stimulus strength at which the first observable muscle contraction occurs
Term
Contraction force is precisely controlled by:
Definition
recruitment (multiple motor unit summation), which brings more and more muscle fibers into action
Term
Muscle Tone -
Definition
Constant, slightly contracted state of all muscles
Term
Isotonic contractions are either:
Definition
concentric or eccentric
Term
Isotonic contractions/concentric
Definition
the muscle shortens and does work
Term
Isotonic contractions/eccentric
Definition
the muscle contracts as it lengthens
Term
the only source used directly for contractile activities is:
Definition
ATP
Term
ATP is regenerated by:
Definition
Direct phosphorylation
ADP + creatine phosphate (CP)
Term
Anaerobic Glycolysis – without oxygen
Definition
70% of maximum contractile activity:
Bulging muscles compress blood vessels
Oxygen delivery is impaired
Pyruvic acid is converted into lactic acid
2 ATP yield
60 seconds duration
Term
Lactic acid build up =
Definition
sore muscles
Term
Lactic acid
Definition
Slowly diffuses into the bloodstream
Used as fuel by the liver, kidneys, and heart
Converted back into pyruvic acid by the liver
Term
Aerobic Pathway – with oxygen
Definition
Produces 95% of ATP during rest and light to moderate exercise
Fuels: stored glycogen, then bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids
Term
in citric acid cycle, one glucose molecule gets you:
Definition
32 ATP molecules
Term
myofilaments in smooth muscles are arranged:
Definition
SPIRALLY
Term
Prime movers:
Definition
Provide the major force for producing a specific movement
Term
Antagonists
Definition
Oppose or reverse a particular movement
Term
Synergists:
Definition
Add force to a movement
Reduce undesirable or unnecessary movement
Term
Fixators:
Definition
Synergists that immobilize a bone or muscle’s origin
Term
Naming Skeletal Muscles
Definition
Location—bone or body region associated with the muscle
Shape—e.g., deltoid muscle (deltoid = triangle)
Relative size—e.g., maximus (largest), minimus (smallest), longus (long)
Direction of fibers or fascicles—e.g., rectus (fibers run straight), transversus, and oblique (fibers run at angles to an imaginary defined axis)
Number of origins—e.g., biceps (2 origins) and triceps (3 origins)
Location of attachments—named according to point of origin or insertion
Action—e.g., flexor or extensor, muscles that flex or extend, respectively
Term
muscle pairs
Definition
work against each other
Term
muscle groups
Definition
work together
Term
Arrangement of Fascicles/Circular -
Definition
Fascicles arranged in concentric rings
Term
Arrangement of Fascicles/Convergent -
Definition
Fascicles converge toward a single tendon insertion (e.g., pectoralis major)
Term
Arrangement of Fascicles/Parallel -
Definition
Fascicles parallel to the long axis of a straplike muscle (e.g., sartorius)
Term
Arrangement of Fascicles/Fusiform -
Definition
Spindle-shaped muscles with parallel fibers (e.g., biceps brachii)
Term
Arrangement of Fascicles/Pennate -
Definition
Short fascicles attach obliquely to a central tendon running the length of the muscle (e.g., rectus femoris)
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