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Muscles lecture test
79
Anatomy
Undergraduate 1
07/04/2010

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Term
Convergent
Definition
This term describes a muscle which has a broad origin that runs to a single tendon
Term
Circular -
Definition
- fascicles form circle of muscle fibers around external body opening.
Example: Orbicularis oris and oculi
Term
Pennate
Definition
Describes a muscle with short fibers attached to central tendon. It would resemble a feather).
Example: Extensor digitorum longus - unipennate ; Rectus femoris - bipennate
Term
Parallel
Definition
Long axis of fascicles run with long axis of muscle
Example: Sartorius – straplike; Biceps - fusiform
Term
fibers
Definition
Skeletal muscle consists of long, striated (striped) cells
Term
The cells have a striated appearance due to
Definition
A-bandsI-bands which are alternating light and dark bands which are aligned along the length of the myofibrils.
Term
consists of long multinucleate cells with nuclei pushed to one side by myofibrils packed into the cytoplasm
Definition
Skeletal muscle
Term
Striations
Definition
are produced by alternating light and dark bands composed of thick and thin filaments.
Term
Myofibrils are composed of myofilaments which are made up of two proteins
Definition
actin and myosin. Actin and myosin slide across each other during muscle contraction resulting in shortening of cell
Term
sarcomere
Definition
is defined as the portion of a myofibril between two Z-lines. It extends from one I band to the middle of the next and is the actual contractile unit of the muscle fiber
Term
Epimysium
Definition
surrounds intact muscle
Term
Perimysium
Definition
surrounds fascicles
Term
Endomysium
Definition
surrounds individual muscle fibers
Term
skeletal muscles are composed of many muscle fibers bundled together by connective tissue. Layers of connective tissue help to arrange the muscle fibers into patterns:
Definition
Epimysium -surrounds intact muscle
Perimysium - surrounds fascicles
Endomysium - surrounds individual muscle fibers
Term
neuromuscular junction
Definition
is the junction between a nerve fiber and a muscle cell. The nerve fiber carries the message to contract to the muscle fiber.
Term
motor unit
Definition
consists of motor neuron and all of the muscle fibers it stimulates
Term
Prime movers or Agonists
Definition
are mostly responsible for producing a movement while antagonists oppose or reverse a movement.
Term
Synergists
Definition
aid and smooth out action of prime movers.
Term
Fixators
Definition
prevent movement at the origin of a prime mover allowing all of the tension to be exerted at the insertion.
Term
Humans have three types of muscle tissue
Definition
skeletal, smooth and cardiac
Term
skeletal
Definition
consists of long, multinucleate cells with cross striations. voluntary muscle
Term
cardiac
Definition
which is found in the heart, has branched fibers with intercalated disks which mark the boundaries between cells. This muscle is involuntary
Term
smooth muscle
Definition
consists of spindle shaped cells which surround tubes such as in the digestive system. These cells have one nucleus and are involuntary
Term
Movement
Definition
Muscle contraction provides movement as in walking or eye movement
Term
Posture maintenance
Definition
Contraction of muscle allows us to remain upright!
Term
Joint stabilization
Definition
Tendons of muscles often extend across joints and keep them stable.
Term
Heat Generation
Definition
Muscle contraction produces heat used to maintain body temperature
Term
Excitability
Definition
refers to the ability to respond to stimuli which in muscle is usually a neurotransmitter released by a nerve cell. This chemical gives the muscle cell the “message to contract
Term
Contractility
Definition
refers to the ability of a muscle cell or fiber to shorten producing movement. This property sets muscle apart from other tissues.
Term
Extensibility
Definition
refers to the ability of muscle fibers to be stretched or extended.
Term
Elasticity
Definition
refers to the ability of muscle fibers to contract or extend and return to their original length.
Term
Striations
Definition
are produced by alternating light and dark bands composed of the thick and thin filaments that make up the myofibrils. The striated appearance is due to A-bands and I-bands.
Term
muscle fiber is served by
Definition
1 nerve, an artery and one or more veins.
Term
Muscles attachments may be direct
Definition
in which the epimysium of the muscle is fused to the periosteum of the bone
Term
indirect in which attachment
Definition
is by means of a tendon or sheet like aponeurosis.
Term
myofibrils
Definition
The interior of the cell is filled with myofibrils which are rod like contractile elements. They make up most of the muscle volume and push the nuclei to the edges of the cell
Term
The arrangement of myofibrils within a muscle fiber
Definition
is such that a perfectly aligned repeating series of dark A bands and light I bands is evident.
Term
sarcomere
Definition
is the smallest contractile unit of a muscle and is defined as the distance between 2 Z- disks. The sarcomere is composed of thick and thin myofilaments composed of contractile protein. Each sarcomere contains 1 A-band and 2 semi I bands. Thick filaments are found at center of sarcomere and thin between thick and attached at Z-disk. I Bands contain thin filaments only. A-bands contain thick with thin in between and the H-zone contains only thick
Term
Thin filaments contain
Definition
actin, tropomyosin and troponin.
Term
Thick contain
Definition
all of the myosin
Term
Thick filaments are composed of the protein myosin.
Definition
Each myosin molecule has a rod-like tail and two globular heads. The tails consist of two interwoven, heavy polypeptide chains. The heads consist of two smaller, light polypeptide chains and link thick and thin filaments together forming cross bridges.
Term
The tails consist
Definition
of two interwoven, heavy polypeptide chains
Term
The heads consist of
Definition
Term
The heads consist of
Definition
two smaller, light polypeptide chains and link thick and thin filaments together forming cross bridges.
Term
Each myosin molecule has
Definition
a rod-like tail and two globular heads. The tails consist of two interwoven, heavy polypeptide chains.
Term
sarcoplasmic reticulum (SR
Definition
at a longitudinal section showing one sarcomere endoplasmic reticulum which basically runs longitudinally surrounding each myofibril.
Term
The paired terminal cisternae
Definition
form cross channels
Term
functions in regulation of intracellular calcium levels
Definition
The sarcoplasmic reticulum
Term
The T-tubules penetrate the cell's interior at the
Definition
A-band I-band junction and associated with the paired terminal cisternae to form triads
Term
The T-tubules
Definition
which are continuous with the sarcolemma, carry impulses to the deepest parts of the muscle fiber and signal calcium release from the adjacent terminal cisternae.
Term
sliding filament model explains the mechanism of contraction:
Definition
Thin filaments slide past the thick ones so that the actin and myosin filaments overlap. Upon stimulation, myosin heads bind to actin and sliding begins. Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and move the thin filaments to the center of the sarcomere. As this occurs throughout the sarcomeres, the muscle shortens
Term
In order to contract, a skeletal muscle must:
Definition
Be stimulated by a nerve ending
Move an action potential along its sarcolemma
Have a rise in intracellular calcium levels which is the final trigger for contraction
Term
Linking the electrical signal to the contraction is called excitation-contraction coupling
Definition
This is the sequence of events by which transmission of an action potential along the sarcolemma leads to sliding of myofilaments.
Term
structure of neuromuscular junction involves
Definition
Presynaptic axonal endings which contain synaptic vesicles containing the neurotransmitter acetylcholine.
Synaptic cleft which is the space between the axon and muscle fiber.
Postsynaptic membrane which is the sarcolemma of the muscle fiber. This is called a motor end plate and contains receptors for acetylcholine
Term
Postsynaptic membrane
Definition
which is the sarcolemma of the muscle fiber. This is called a motor end plate and contains receptors for acetylcholine.
Term
Presynaptic axonal endings
Definition
which contain synaptic vesicles containing the neurotransmitter acetylcholine
Term
Presynaptic axonal endings
Definition
which contain synaptic vesicles containing the neurotransmitter acetylcholine
Term
Synaptic cleft
Definition
which is the space between the axon and muscle fiber.
Term
a nerve impulse reaches the end of an axon
Definition
neuromuscular junction:
Term
open and allow calcium ions to enter the axon.
Definition
Voltage-regulated calcium channels
Term
Calcium ions
Definition
inside the axon terminal cause axonal vesicles to fuse with the axonal membrane
Term
Calcium ions inside the axon terminal cause axonal vesicles to fuse with the axonal membrane
Definition
This fusion releases acetylcholine (ACH) into the synaptic cleft via exocytosis
Term
ACH diffuses across the synaptic cleft to ACH receptors on the sarcolemma.
Definition
Binding of ACH to its receptors initiates an action potential in the muscle.
Term
ACH bound to ACH receptors is quickly destroyed by the enzyme
Definition
acetylcholinesterase. This destruction prevents continued muscle fiber contraction in the absence of additional stimuli
Term
Events at the Neuromuscular Junction
Definition
When a nerve impulse reaches the end of an axon at the neuromuscular junction:

Voltage-regulated calcium channels open and allow calcium ions to enter the axon.
Calcium ions inside the axon terminal cause axonal vesicles to fuse with the axonal membrane.
This fusion releases acetylcholine (ACH) into the synaptic cleft via exocytosis.
ACH diffuses across the synaptic cleft to ACH receptors on the sarcolemma.
Binding of ACH to its receptors initiates an action potential in the muscle.

ACH bound to ACH receptors is quickly destroyed by the enzyme acetylcholinesterase. This destruction prevents continued muscle fiber contraction in the absence of additional stimuli.
Term
This event is called depolarization
Definition
ACH binds its receptors at the motor end plate.
Binding opens chemically gated channels.
Because more sodium ions diffuse in than potassium ions fuse out, the interior of the sarcolemma becomes less negative
Term
In order for a muscle to contract, it must receive a “message” from a motor neuron. This starts a local electrical event called
Definition
end plate potential
Term
This starts a local electrical event called an end plate potential. Later it ignites an
Definition
action potential that spreads in all directions across the sarcolemma.
Term
Excitation-Contraction Coupling
Definition
Once generated, the action potential:
Is propagated along the sarcolemma
Travels down the T tubules
Triggers calcium ion release from the terminal cisternae
Term
Calcium ions bind to troponin causing
Definition
The blocking action of tropomyosin to stop
Actin active binding sites to be exposed
Term
Excitation-Contraction Coupling As the process continues:
Definition
Myosin cross bridges alternately attach and detach.
Thin filaments move toward the center of the sarcomere.
Calcium ions are removed into the sarcoplasmic reticulum, tropomyosin blockage is restored, and the muscle fiber relaxes.
Hydrolysis of ATP powers this cycling process.
Term
Role of Ionic Calcium in the Contraction Mechanism
Definition
At low intracellular calcium ion concentration:
Tropomyosin blocks the
binding sites on actin.
2. Myosin cross bridges cannot
attach to binding sites on actin
The relaxed state of the
muscle is enforced
Term
At higher intracellular calcium ion concentrations
Definition
Additional calcium binds to troponin (inactive troponin binds two calcium ions).
Calcium activated troponin binds an additional two Calcium ions at a separate regulatory site.
Term
Role of Ionic Calcium in the Contraction Mechanism
Definition
Calcium-activated troponin undergoes a conformational (“shape”) change.

2. This change moves tropomyosin away from actin’s binding sites.
Term
Role of Ionic Calcium in the Contraction Mechanism
Definition
Myosin head can now bind and cycle
This permits contraction (sliding of the thin filaments by the myosin to begin
Term
Cross bridge formation
Definition
myosin cross bridge attaches to the actin filament
Term
Cross bridge formation
Definition
myosin cross bridge attaches to the actin filament
Term
Cross bridge formation
Definition
myosin cross bridge attaches to the actin filament
Term
Cross bridge formation
Definition
myosin cross bridge attaches to the actin filament
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