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69 terms

Muscular System Human Anatomy

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Muscles
specialized masses of tissues that are able to contract, relax, and change their length
principal functions of muscle
movement, heat production, and posture/body support
excitability
ability to respond to neural stimulation
contractility
ability to shorten
extensibility
ability to contract over a range of resting lengths
elasticity
ability of a muscle to return to its original length after contraction
conductivity
how well stimulus is distributed throughout cell
cardiac muscle
found only in heart; involuntary; acts constantly to pump blood through blood vessels
Cardiac muscle appearance
striated; short and branching myocytes; connected by intercalated disks.
Smooth muscle
involuntary muscle found in visceral organs and vasculature
Smooth muscle appearance
fusiform in shape; no striations, but does contain actin and myosin fibers;dense bodies that attach thin filaments to the cytoskeleton
single-unit smooth muscle
most common smooth muscle; found in viscera
multi-unit smooth muscle
direct innervation to each unit, forms motor unit; found in large arteries and iris
muscle spindles
sensory cells that control muscle tone through reflexive action; found withing the belly of the muscle running parallel along it and sense change in muscle length
golgi tendon organs
sensory cell that is found withing muscle tendons that sense muscle tension
muscle tension
force that a muscle exerts
joint receptors
sensory cells that sense a change in direction and acceleration in joint movement
Endomysium
innermost layer of CT that surrounds each muscle fiber/cell, connects them to other cells and contributes to then tendon of muscle
Perimysium
middle layer of CT that surrounds bundles of muscle fibers; vasculature and nervous supply traverse here; also contributes to the tendon
Epimysium
Outer layer of CT that covers the outside of the entire muscle; considered part of the deep fascia; separates muscle from surrounding tissue or bone; also contributes to the tendon of muscle
fascicles
Bundle of muscle fibers
aponeuroses
is a fibrous connective tissue in sheets, that attaches muscle to bone or to other muscle
tendons
a cordlike or bandlike mass of white fibrous connective tissue that connects a muscle to a bone
Sarcolemma
plasma membrane of muscle cells;surrounds the cytoplasm of muscle cells
Sarcoplasm
the cytoplasm of a striated muscle fiber; surrounds individual myofibrils of muscle fibers
Transverse Tubules
network of tubules that extend inward at right angles to the sarcolemma; allow for nerve impulses to be transmitted rapidly to individual myofibrils
Sarcoplasmic Reticulum
longitudinal network of tubules that serves as a storage site for calcium
Mitochondrial Reticulum
network of structures for the energy producing biochemical "krebs cycle" which produces ATP through oxidative phosphorylation
Myofibrils
contractile units of the muscle fiber; cylindrical and as long as the muscle fiber; made of up long stands of repeating subunits called sarcomeres
Sarcomeres
smallest functional unit of the myofibril; composed of bundles of myofilaments; from one Z dsic to the next
myofilaments
responsible for muscle contraction; 2 types are myosin and actin
myosin
thickest of the 2 myofilaments; bind parallel to one another with globular heads protruding around the circumference; centered in the sarcomere; but are connected to the Z-lines by elastic filaments
Actin
thinner myofilament; troponin molecule sits on top and blocks the binding site
concentric contraction
contraction that shortens the space between Z-lines(raising the barbell in a biceps curl)
eccentric contraction
either returns sarcomere to original (or resting) length or longer (lowering the barbell in a biceps curl)
Isometric contraction
no change in length, but a constant coupling/decoupling of cross-bridges(without shortening), such as carrying an object out in front of you
isotonic contraction
contraction with a change in length but the force generated remaining at a constant(all lifting exercise)
glycogen
energy-storage polysaccharide abundant in muscle
myoglobin
oxygen-storing red pigment of muscle
Terminal cisternae
dilated ends of sarcoplasmic reticulum adjacent to a T-tubule
Thick filament
myofilament about 11nm in diameter composed of bundled myosin molecules
Elastic Filament
myofilament about 1nm in diameter composed of a giant protein, titin, that flanks a thick filament and anchors it to a Z-disc; centers and stabilizes the thick filament and prevents overstretching
Thin filament
myofilament about 5-6nm in diameter composed of actin, troponin, and tropomyosin
Regulatory proteins
troponin and myosin; proteins that do not directly engage in the sliding filament process of muscle contraction, but regulate myosin-actin binding
Tropomyosin
covers myosin binding sites on the actin molecules
troponin
A protein attached to tropomyosin that binds with calcium to shift the tropomyosin
titin
springy protein that forms the elastic filaments and anchors the thick filaments to the Z discs
dystrophin
protein is important in maintaining the integrity of muscle fiber. absence cuases muscular dystrophy
striations
alternate dark and light bands found on skeletal and cardiac muscle
A band
(anisotropic) thick and thin myofilaments that overlap
H band
Center band that contains only myosin
M line
center of the thick filament
I band
(isotropic) thin myofilaments only
Z disc
sheet of proteins that anchor thin filaments and connect myofibrils
neuromuscular junction
the junction between a nerve fiber and the muscle it supplies
synaptic knob
end of the axon, hold neurotransmitters
synaptic cleft
the fluid filled space at a synapse between neurons or neuron and effector
synaptic vesicles
sacs located in the cytoplasm at the tip of the presynaptic axon.
acetylcholine
neurotransmitter released by vesciles from the axon that bind to receptors on the sarcolemma which set up an action potential and causes the muscle to contract
acetylcholinesterase
enzyme that catalyzes breakdown of acetylcholine, preventing sustained muscle contraction from a single nerve impulse
motor unit
a neuron and the muscle fibers it controls
intercalated discs
Rings that provide a strong connection between cardiac muscle cells, to prevent tears and leaks in the heart.
dense bodies
the structure that allows smooth muscle to generate intracellular contractile tension; analogous to z-line
smooth muscle tone
smooth-muscle tension due to low-level cross-bridge activity in absence of external stimuli
peristalsis
the process of wave-like muscle contractions of the alimentary tract that moves food along
cross-bridge cycle
Binding of myosin to actin, powerstroke, rigor, unbinding, cocking of the myosin heads
peak tension
all motor units contracting at maximum rate/frequency of stimulation
sustained contractions
motor units are alternated (so muscle won't fatigue as fast) to maintain force production at given level
Resting Tension
always present (muscle tone); there is random stimulation of motor units creating isometric contraction for position, stability, balance, joint stability etc