Studied by 0 peopleWhat are contractile filaments?
the basic contractile units of muscle; thick and thin filaments
What is contraction?
the shortening of muscle which results in the generation of force and/or movement
What is cross-bridge cycling (contraction relaxation cycle)?
the sequence of events that occur at the level of the thick and thin filaments resulting in the shortening of skeletal muscle and the generation of force and/or movement
what is excitation-contraction coupling?
the generation of an action potential in a skeletal muscle fibre and subsequent increase in intracellular Ca2+ that initiates contraction
What is motor unit?
a single alpha motor neuron and all the muscle fibres that it innervates
what is muscle fibre?
one individual muscle cell
What is neuromuscular junction?
the specialized synapse between an alpha motor neuron terminal and individual muscle fibre
what is the primary function of all muscles?
to generate force and/or movement in response to a physiological stimulus
What are some examples of some primary functions of muscles?
body movement
maintenance of posture
respiration
production of body heat
communication
constriction of organs and vessels
heartbeat
what does the generation of force depend on in all muscle types?
the conversion of chemical energy (ATP)
what are striation caused by?
due to arrangement of thick and thin filaments
what are some functions of skeletal muscles?
respiration
helps circulatory system
move skeleton
what is the stimulus source for skeletal muscles?
somatic motor neurons
True or False. skeletal muscles are striated and uninucleated.
False, they are striated and multinucleated
is the skeletal muscles primarily voluntary or involuntary?
voluntary
what is the stimulus for cardiac muscle?
spontaneous electrical activity
is the cardiac muscle primarily involuntary or voluntary?
involuntary
True or False. Cardiac muscle is striated and uninucleated.
True
what can the cardiac muscle be altered by?
autonomic NS, hormones
what is the stimulus for smooth muscle?
autonomic control
spontaneous
hormones
paracrines or autocrines
is the smooth muscle primarily involuntary or voluntary?
involuntary
True or False. Smooth muscles are striated and uninucleate.
False, they are non-striated and uninucleate
what does smooth muscle provide mechanical control of?
digestive tract
urinary tract
reproduction tract
blood vessels
airways
what is the main role of smooth muscles?
movement of substances into, out, or throughout the body
what is the origin of skeletal muscles?
the closest to the trunk or to more stationary bone
how are the skeletal muscle attaches to bones?
by tendons
what is the insertion of skeletal muscles?
more distal or more mobile attachment
what are the antagonistic muscle groups in skeletal muscles?
flexor-extensor pairs
what is the flexor?
brings bones together
what is the extensor?
moves bones away
what percent is skeletal muscle of the total body weight?
40%
what is the muscle fiber?
It is a muscle cell.
what is the sarcolemma?
muscle cell membrane
what is the sarcoplasm?
cytoplasm of a muscle cell
what is the sarcoplasmic reticulum?
the modified endoplasmic reticulum
what is the muscle fasicle?
bundle of muscle fibers
arrange the muscle components from largest to smallest: muscle fibre, myofibril, fasicle, muscle, sarcomere
muscle > fasicle > muscle fibre > myofibril >sarcomere
what do striations correspond to?
the ordered arrays of thick and thin filaments within myofibrils
What is the thin myofilament?
actin
What is F actin made of?
back bone of thin filaments, double stranded alpha helical polymer of G-actin molecules.
what does F-Actin contain?
binding site for thick filaments (myosin)
what is Tropomyosin?
two identical alpha helicies that coil around each other and sit in the two grooves formed by actin strands, regulates the binding of myosin to actin
what is the troponin complex?
heterotrimer situated every 7 actin molecules
what does the troponin complex consist of?
troponin T (TnT)
troponin C (TnC)
troponin I (TnI)
what is troponin T (TnT)?
binds to a single molecule of tropomyosin
what is troponin C (Tnc)?
Ca2+ binding site
what is Troponin I (TnI)?
under resting condition is bound to actin inhibiting contraction
What do thick myofilaments consist of?
myosin
what does the myosin molecule consist of?
2 intertwined heavy chains, each heavy chain contains 2 light chains
what do myosin heads contain?
a region for binding actin as well as a site for binding and hydrolyzing STP (ATPase)
what is the regulatory light chain?
chain regulates ATPase activity of myosin
what is the essential light chain?
chain stabilizes myosin head
what is titin?
a very large protein extending from M line to Z line, appears to be involved in stabilization and the elastic recoil behavior of muscle
what is nebulin?
a large protein that interacts with the thin filaments, believed to regulate the length of thin filaments and contribute to the structural integrity of myofibrils
What is the Z-disk of the sarcomere?
zigzag protein structure that is the attachment site for the thin filaments
What are I bands of the sarcomere?
lightest band of sarcomere, region occupied only by thin filaments
What is the A Band of a sarcomere?
darkest band of sarcomere, encompasses entire length of the thick filament, including very dark area where thin and thick filaments overlap
What is the H zone of a sarcomere?
central region of A band, consists only of thick filaments
What are M-lines in sarcomeres?
proteins form the attachment site for he thick filaments, equivalent to z disk for thin filaments
what is the mitochondrion needed for in muscle fibre?
to produce ATP depending on type of muscles
what is the function of sarcoplasmic reticulum?
store and release calcium
what is glucose stored as within the sarcoplasm?
glycogen
what is the function of transverse tubules?
to deliver action potential to the interior of the muscle fiber
what is the function of terminal cisternae?
swollen regions of sarcoplasmic reticulum, stores and release Ca2+
what is muscle tension?
the force generated by a contracting skeletal muscle is referred to as muscle tension
what regions of the sarcomere shorten during contraction?
H zone and I band shorten, while A band remains constant
what is neuromuscular junction?
point of synaptic contact between somatic motor neuron and individual muscle fibre
What is excitation-contraction coupling?
an action potential initiated in the skeletal muscle fibre results in an increase in intracellular (sarcoplasmic) calcium
what regions are involved in voluntary movement?
basal ganglia
premotor cortex (motor association)
thalamus
midbrain
cerebellum
where do upper motor neurons travel?
from primary motor cortex to spinal cord (output signal)
what is the corticospinal tract?
descending tract (ventral and interior lateral white matter)
what is upper motor neuron?
brain to spinal cord, carried in descending tract, crosses over at medulla to synapse with alpha motor neuron
what is alpha (lower) motor neuron?
spinal cord to muscle
what is a motor unit?
a single motor neuron and all the muscle fibres it innervates
what are the characteristics of alpha motor neurons?
large diameter, myelinated axon, 15-120 m/sec
True or False. One muscle fiber will only ever have synaptic input by one neuron.
True
what is amyotrophic lateral sclerosis (ALS)?
neurodegenerative motor neuron disease that degenerates upper and/or lower motor neurons leading to muscle atrophy and weakness from disuse
what happens in ALS?
upper and/or lower motor neurons degenerate leading to muscle atrophy and weakness from disuse
what are three components of neuromuscular junction?
presynaptic motor neuron filled with synaptic vesicles
the synaptic cleft
the postsynaptic membrane of the skeletal muscle fibre
what is the motor end plate?
region of sarcolemma at the neuromuscular junction
what do junctional folds do?
on sarcolemma increases surface area
what do motor neuron vesicles contain?
acetylcholine
What does muscle sarcolemma contain?
nicotinic acetylcholine receptors
what is the extracellular matrix?
meshwork of proteins and proteoglycans
what does the sarcolemma of muscle fibre contain?
nicotinic acetylocholine receptors
what are monovalent cation channel?
member of cys-loop receptor family of ligand gated ion channels (permeable to Na+ and K+
what is required to open the ACh receptor?
requires two acetylcholine molecules
what is myasthenia gravis?
means severe weakness of muscle
disorder of neuromuscular transmission
what is autoimmune?
body produces antibodies that bind to ACh receptors
what are DHP receptor?
L-type Ca2+ channel (voltage sensitive)
what is RyR?
ryanodine receptor (Ca2+ release channel on SR)
what is ATP binding?
ATP binds to the head of myosin heavy chain reducing affinity of myosin for actin
What is ATP hydrolysis?
ATP is broken down to ADP and inorganic phosphate (Pi) resulting in the myosin head pivoting around hinge into cocked state. the cocked head is now aligned with and binds to a new actin molecule on thin filament
What is the powerstroke?
dissociation of Pi from myosin head strengthens bond between actin and myosin and triggers power stroke, a conformational change in which the myosin head returns to its un-cocked state and while doing so pulls the actin filaments generating force and motion
what is the ADP release?
dissociation of ADP from myosin causes myosin to remain bound to actin until ATP initiates the cycle again
what does the termination of contraction require?
removal of Ca2+
how can Ca2+ be removed to the extracellular space?
by the Na-Ca exchange or by the Ca2+ pump which uses ATP
what is rigor mortis?
development of rigid muscles several hours after death
what happens when ATP is stopped by rigor mortis?
Ca2+ cannot be removed (SERCA pump is ATP powered)
ATP needed to release myosin head from actin, remains in latched cross bridge formation until muscles begin to deteriorate
what is the timing of E-C coupling?
slight delay between motor neuron AP and muscle fibre AP (synaptic release)
delay between muscle fibre AP and contraction (latent period) time when Ca2+ is being released and binding troponin
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