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HA. Ch. 9

Muscular System I: Skeletal Muscle Tissue and Muscle Organization

3 types of muscle tissue skeletal, cardiac, smooth
skeletal muscle attaches to skeleton
skeletal muscles have...very...and... single...long...cylindrical striated cells
skeletal muscle multinucleate (peripherally located)
skeletal muscle can be controlled voluntarily
cardiac muscle occurs in the heart wall
cardiac muscle has branching chains of striated cells
cardiac muscle has one nucleus per cell; some can be binucleate
intercalated discs of cardiac muscle contain several types of cell junctions
cardiac cells are electrically coupled by gap junctions
cardiac muscles are controlled involuntarily
smooth muscle occurs chiefly in walls of hollow organs
smooth muscle has what type of cells single, fusiform nonstriated cells
smooth muscle cells are uninucleate
smooth muscle is controlled involutnarily
3 types of tissues share 4 specialized properties
4 specialized properties excitability, contractility, elasticity, extensibility
excitability is the ability of a muslce cell to respond to nerve signals or other stimuli, causing electrical impulses to travel along the muscle plasma membrane
contractility is the ability to generate a strong pulling force while muscle cells shorten or contract
elasticity is the ability of a muscle after being stretched, to recoil passively to its original or resting length
extensibility is the ability to continue to contract over a range of resting lengths
skeletal muscle tissue produces movement
skeletal muscle tissue maintains posture and body position
skeletal muscle tissue supports soft tissue
skeletal muscle tissue regulates entrance and exit of materials
skeletal muscle tissue generates heat through muscle contractions to maintain body temperature
skeletal muscle tissue stabilizes joints
skeletal muscles is surrounded by...and is comprised of epimysium...bundles of muscle fascicles
muscle fascicle is a group or bundle of muscle fibers surrounded by a perimysium
muscle fiber (myofiber or muscle cells) a highly elongated cell comprised of myofibrils surrounded by endomysium
sarcolemma (skeletal) plasma membrane of muscle fiber which is comprised of abundant myofibrils
sarcoplasm cytoplasm of muscle fiber which contains numerous myofibirls
myofibril is a cylindrical structure which is as long as the entire cell and consists of sarcomeres; surrounded by sarcoplasmic reticulum
myofibrils can...and are shorten...responsible for contraction of the skeletal muscles fiber
myofibril contraction leads to shortening the entire cell bec. a myofibiril is attached to the sarcolemma at each end of the cell
sarcoplasmic reticulum (SR) internal membrane complex that is similar to the SER of other cells
the SR is closely associated with the transverse tubules (T)
SR plays important role in controlling the contraction of individual myofibrils via the release of calcium ions
transverse (T) tubules deep invaginations of the sarcolemma which allow electrical impulses to quickly travel to the interior of the cell
terminal cisternae expanded chambers on either side of a transverse tubule where the tubule of the SR has enlarged and fused
triad combination of a pair of terminal cisternae plus a transverse tubule
sarcomere myofibrils consist of sarcomeres, which are repeating units of myofilaments; smallest functional units of muscle fibers
myofilaments sarcoplasm of muscle contains protein filaments, which generate contractile force
myofilaments determine the striation pattern in skeletal muscle fibers
myofilaments fill most of the sarcoplasm of each musle fiber (cytoplasm)
myofilaments are organized in the repeating units called sarcomeres
2 primary types of myofilaments in muscle cells actin and myosin
actin protein filaments found in thin filaments
myosin protein filaments found in thick filaments
the striated apperance of skeletal muscle tissue arises from the organization of the thick and thin filaments within the myofibrils of the sarcomere
myofibrils are arranged parallel to the long axis of teh cell, with their sarcomeres arranged side to side
myofibrils of the sacromere give the apperance of distinct dark and light bands (striations correspond to these bands of the individual sarcomeres)
m line group of proteins which link the thick filaments that lie in the center of the sarcomere
z lines or z discs are open meschworks of interconnecting proteins called actinins, which occur where thin filaments from adjacent sarcomeres join
thin filaments are attached to the z lilne and extend toward the m line
zone of overlap area where the thin filaments pass between the thick filaments
in a 3-D cross-sectional view each thin filament is surrounded by 3 thick filaments arranged in a triangle, while 6 thin filaments surround each thick filament
a band area containing thick filaments, including the m line, the h band, and the zone of overlap; appears as a "dark band"
h band is the area containing thick filaments only
i band the area containing thin filaments only, appears as a "light band"
during contraction, the z lines/discs move closer together, and the I bands and H bands shorten
memory aid A bands are dArk, I bands are lIght (anisotropic characteristics and isotropic characteristics respectively)
thin filaments F actin, nebulin, G actin, tropomyosin, troponin
F actin strand of 300-400 globular G actin molecules
nebulin slender strand of proteins that holds the F actin strand together
G actin molecules contains an active site that can bind to a thick filament, in the same manner that a substrate molecule binds to an enzyme's active site
tropomyosin: protein molecules that form a long chain, which covers the active sites, preventing actin-myosin interaction
troponin protein molecules that hold the tropomyosin strand in place
troponin changes position to move the tropomyosin molecule, exposing the active site prior to a muscle contraction
troponin acts as the regulator molecule of a muscle contraction
thick filaments myosin, proteins of M line, cross bridges, titin
approximately how many myosin molecules comprise the thick filament? 500
each myosin molecule consists of a double myosin strand with an attached, elongate tail and a free globular head
proteions of the m line interconnect adjacent thick filaments, midway along their length
myosin heads are also known as cross-bridges bec they connect thick filaments and thin filaments during a muscle contraction
myosin heads project outward toward the surrounding thin filaments, as the entire myosin molecules are oriented away from the M line
titin protein molecule that makes up the core of each thick filament
a strand of titin extends the length of the filament and attaches the M line to the Z line
an exposed portion within the I band is highly elastic and will recoil after stretching
titin is completely relaxed in the normal resting sarcomere
titin becomes tense only when some external force stretches the sarcomere
when sarcomere of titin is stretched the titin strands help maintain the normal alignment of the thick and thin filaments
when the stretching force is removed, titin fibers help return the sarcomere to its normal resting length
shapes of skeletal muscle spindle-shaped cylinders, triangles, sheets
each skeletal muscle is an...and contains organ...tissue elements, blood vessels and nerves, as well as being comprised mostly of muscle fiberss
organization levels in a skeletal muscle whole muscle - fascicle - fiber - myofibril - sarcomere - myofilament (actin and myosin)
connective tissue elements epimysium, perimysium, endomysium
epimysium DICT sheath wrapped around a whole muscle
perimysium fibrous CT sheath around a fascicle
endomysium thin reticular fiber CT sheath around each muscle fiber
every skeletal muscle fiber is innervated and stimulated by a nerve cell to contract
every skeletal muscle fiber has a rich blood supply and has fine nerve fibers and capillaries in the endomysium
origin of skeletal muscle immovable attachment from which a muscle extends
insertion of skeletal muscle more movable attachment
skeletal muscles attach to bones through tendons, aponeuroses or direct attachments
skeletal muscle contraction exerts a pull, or tension, and shortens the muscle fiber in length
the skeletal muscles attach to the skeleton in a way that keeps them at a near-optimal length for generating maximum contractile forces
muscle contraction is accurate for muscles involved in activities such as walking where the muscles contract and relax repeatedly
muscle fibers(skeletal) are stretched to near optinmal length before stimulation of contraction occurs
the presence of calcium ions is the trigger for a contraction in skeletal muscle
the presence of ATP is required for the contraction to occur
sliding filament theory or mechanism explains the physical changes that occur between the thin and thick filaments during muscle contraction
the h band and i band get...with the sliding filament theory smaller
the zone of overlap gets...with sliding filament theory larger
the z lines move...with sliding filament theory closer
the width of the a band ...during sliding filament theory remains constant throughout the contraction
mechanism steps of the sliding filament theory 1) myosin heads of thick filaments bind to active sites on thin filaments, causing sliding to occur
step 2) cross-bridge binding; myosin head pivots toward the m line, pulling the thin filament toward the center of the sarcomere
step 3) cross bridge then detaches and returns to irs original position and is ready for the next cycle of "bind, pivot, detach, return" regarding its original position
step 4) z lines move toward the m line when the thick filaments pull on the thin filaments, causing the sarcomere to shorten
when a nerve cell stimulates a muscle fiber, it sets up an impulse in the sarcolemma that signals the sarcoplasmic reticulum to release calcium ions
the release of calcium ions then initiates the sliding of the myofilaments (translates to muscle contraction)
motor neurons innervate individual skeletal muscle fibers at neuromuscular synapses or junctions (motor end plates)
neuromuscular synapse is a specific synapse between a motor neuron and a muscle cell
synaptic terminal is the expanded tip of the motor neuron's axon, at the neuromuscular synapse
synaptic vesicles are small secretory vesicles in the cytoplasm of the synaptic terminal
synaptic vesicles contain acetylcholine
neurotransmitter is a chemical released by a neuron to communicate with another cell
acetylcholine is a (ACh) neurotransmitter that signals the muscle cell to contract; released at the axon terminal
synaptic cleft is a narrow space that seperates the synaptic terminal from the motor end plate of the skeletal muscle fiber
acetylcolinesterase or cholinesterase is an enzyme which breaks down ACh molecules and is released into the synaptic cleft
an electrical impulse arrives at the synaptic terminal
ACh is released and binds to receptor sites on motor end plate
a change in local transmembrane potential occurs and results in generation of an electrical impulse, or action potential
electrical impulse travels all over the surface of the sarcolemma and into each T tubule
action potential's continue to be generated until AChE removes the bound ACh
immediately after ACh signals a single contraction it is broken down by AChE
each muscle fiber must be served by a neuromuscular junction
motor unit consits of one motor neuron and all the skeletal muscle fibers it innervates(controls)
motor units contain different numbers of muscle fibers distributed widely within a muscle
the size of a motor unit indicates the level of control of the movement
a motor neuron that controls 2 or 3 muscle fibers (eye) has more precise control of muscle movement than a motor neuron that innervates up to 2000 muscle fibers (leg)
muscle twitches contain different numbers of muscle fibers distributed widely within a muscle
all-or-none principle states that a characteristic in which each muscle fiber either contracts completely or not at all
all or none principle says that all muscle fibers in a motor unit contract simultaneously
all or none principle says that the amount of force, exerted by the muscle as a whole, depends on how many motor units are activated
recruitment is the smooth, but steady incrase in muscular tension that is produced by increasing the number of motor units that are activated
muscle tone is teh resting tension in a skeletal muscle
in a resting muscle, some motor units are always active w/o producing enough tension to cause movement, but the activity tenses the muscle
intermediate fibers contract quickly
fast glycolytic fibers or white fibers are .... fibers bec.... white...contain little myoglobin
few...are in white fibers...but there are mitochondria or capillaries...abundant glycosomes that contain glycogen as a fuel source
white fibers contract...fatigue rapidly...quickly
levers are rigid bars or structures that move on a fixed point
fixed point is called fulcrum
when effort is applied to the lever a load is moved
a motor neuron that controls two or three muscle fibers (eye) has more...control of muscle movement than a motor neuron that.. precise...innervates up to 2000 muscle fibers (leg)
muscle twitch a single, momentary contraction, which is a response to a single stimuli
muscle twitches contain different numbers of muscle fibers distributed widely within a muscle
all or none principle says that a characteristic in each muscle fiber either contracts completely or not at all
all or none princple says that all muscle fibers in a motor unit contract simultaneously
all or none principle says that the amount of force exerted by the muscle as a whole depends on how many motor units are activated
recruitment is the smooth, but steady, increase in muscular tension that is produced by increasing the number of motor untis that is activated
muscle tone the resting tension in a skeletal muscle
muscle tone in a resting muscle, some motor units are always active without producing enough tension to cause movement, but the activity tenses the muscles
muscle tone stabilizes the position of bones and joints
muscle spindles are specialized muscle cells that are monitored by sensory nerves, which control the muscle tone in the surrounding muscle tissue
muscle hypertrophy is the enlargment of skeletal muscles that undergo excessive repeated stimulation that produces near maximal tension
muscle atrophy is reduction in skeletal muscle size, tone, and power, as a result of inadequate stimulation to maintain resting muscle tone in the affected area
types of skeletal muscle fibers slow oxidative (red I), intermediate (fast oxidative, IIa),fast glycolytic fibers (white, type IIx)
red fibers are relatively thin fibers which are red becasue of their abundant myoglobin
red fibers obtain energy from aerobic metabolic reactions
red fibers contract...extremely... slowly...resistant to fatigue as long as enough oxygen is present
red fibers deliver prolonged contractions
red fibers are best for maintaining postures
inter. fibers contract quickly
inter. fibers are...dependent and have a high... oxygen...myoglobin content and have abundant mitochondria and a rich capillary supply
inter. fibers are fatigue resistant but less so than type I
inter. fibers many of their characteristrics compared to types I and IIx intermediate
inter. fibers are best for long term production of fairly strong contractions such as required locomotion of the lower limbs
white fibers are...fibers because... pale...they contain little myoglobin
white fibers are about twice the diameter or type I fibers
white fibers contain more myofilaments
white fibers generate much more power
white fibers depend on anearobic patheways to make ATP
few...are present in white fibers but there are... mitochondria or capillaries...abundant glycosomes that contain glycogen as a fuel source
white fibers contract rapidly and fatigue quickly
white fibers are best for short burts of power, such as required in lifting heavy objects for brief periods
lever is a rigid bar/structure that moves on a fixed point
fixed point fulcrum
when effor is applied to the lever a load is moved
in the human body bones = levers, joint = fulcrum, effort is exerted by skeletal muscles pulling on their insertions
1st class levers (effort-fulcrum-load) may operate at a mechanical advantage or disadvantage
2nd class levers (fulcrum-load-effort) all work at a mechanical advantage
3rd class levers (fulcrum-effort-load) all work at a mechanical disadvantage
most muscles of the body are in 3rd class lever systems to provide speed of movement
mechanicnal advanctage allows slow and strong movements
mechanical disadvantage allows muscles to move quickly and far but takes extra effort
fascicle = bundle of muscle fibers
parallel muscle long axes of the fascicles are parallel to the long axis of the muscle, and the muscle extends from origin to insertion
most of the skeletal muscles in the body are parallel muscles
parallel muscles have a central body, or belly/gaster
example of parallel muscle biceps brachii
convergent muscle origin is broad, and the fascicles converge toward the tendon of insertion, its common attachment site
convergent muscle fibers may pull on a tendon, or tendinous sheet, or a slender band of collagen fibers known as a raphe
example of convergent muscle pecoralis major of anterior chest
circular muscle (sphincter) fascicles are arranged in concentric rings around an opening or recess
in a circular muscle, when the muscle contracts, the diameter of the opening decreases
example of circular muschle orbicularis oris
pennate muscle (penna -feather) the fascicles are short and attach at an oblique angle to a tendon that runs through the body of the muscle
unipennate fascicles insert into one side of the tendon
example of unipennate extensor digitorum longus muscle
bipennate fascicles insert into both sides of the tendon
example of bipennate rectus femoris muscle of thigh
multipennate fascicles insert into a tendon that branches within the muscle
arrangement of multipennate muscles look like many feathers situated side by side, whose quills are all inserted into one tendon
example of multipennate deltoid muscle of shoulder
skeletal muscles are arranged in opposing groups across movalbe joints, allowing one group of muscles to reverse or modify the action of the opposing group
agonist (prime mover) muscle whose contraction bears the main responsibility for a particular movement
example of agonist biceps brachii for forearm flexion of the elbow
antagonist groups of muscles whose actions oppose that of the corresponding agonist
example of antagonist triceps brachii during forearm flexion but they also act as antagonist by extending the forearm
synergists aid the agonists either by adding a little extra force to the same movement or by reducing undesirable extra movements that the agonist may produce
synergists stabilize joints as fixators
naming skeletal muscles location, shape, relative size, direction of fascicles, location of attachments, number of origins, action
brachialis muscle arm
intercostal muscles between ribs
externus or supericialis describe muscles that are visible at the body surface
internus/profundus describe muscles lying beneath the body surface
extrinsic superficial muscles that position/stabilize organs
intrinsic deep muscles that function within the organ
trapezius trapezoidal shape
deltoid triangular
rhomboideus rhomboid
orbicularis circle
magnus/major/maximus vs minor/minimus
longus (long)/longissimus vs brevis
teres long and round
rectus straight
transervsus fascicles lie at right angles
oblique fascicles lie at oblique angles
origin is always named first
biceps, triceps, quadriceps 2, 3, 4
flexor vs extensor
abductor vs adductor
exceptions platysma and diaphragm
Created by: handrzej



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