Skeletal Muscle L12 Flashcards
what are the connective tissue components of skeletal muscles:
surrounded by: __________ _________
____________ subdivides the muscle into fascicles
each fascicle is subdivided into muscle fibres(myofibers) surrounded by _______
- fibrous epimysium
- perimysium
-endomysium
when muscles contract, do tendons absorb some of the tension?
YES!
what parts of the muscle and tendons must be pulled tight when muscles contract?
the non contractile parts:
Ligaments, joint capsules, and fascia are noncontractile components of muscle composed of collagen and elastin fibres.
muscle fibres have plasma membranes called:
sarcolemma
muscles fibres are _____________ and form a ________
multinucleated
syncytium: a single cell or cytoplasmic mass containing several nuclei, formed by fusion of cells or by division of nuclei.
muscle fibres are striated:
1. I band
2. A band
3. Z lines
- I bands: light bands
- A bands: dArk bands
- Z-lines(discs): dark lines in the middle of the I bands
each muscle fibre has densely packed units called _______ that run along length
they are composed of ______ and _________ myofilaments
stacked so ________ and _________ bands align
myofibrils
thick and thin
dark and light
striations are produced by:
thick and thin filaments
In striations, I bands contain ONLY ______________ filaments, primarily of the protein ______
thin
actin
in striations, A bands contain ALL ___________ filament with SOME _________ filament overlap.
the thick filament is the protein ________
thick
myosin
in striations, H bands are the _________ of the A band with No ________ filament overlap
center
thin
in striations, Z discs(lines) are found in the ___________ of each _______ band
center
I band
the functional unit of muscle
sarcomere
the sarcomere is 1 ____________ to the next
z-disc
the sarcomere is 1 ____________ to the next
z-disc
titin:
runs from __________ to ______________
allows___________
largest protein in body
protein that runs from Z disc to M line and allows elastic recoil
what protein in sarcomere allows elastic recoil?
titin
what is found in the center of each A band and helps hold down thick filaments
M lines
Sliding filament theory:
when a muscle contracts, sarcomeres _________
SHORTEN
in sliding filament theory when a muscle contracts:
what happens to A bands?
DO NOT shorten, but move closer together
in sliding filament theory when a muscle contracts:
I bands:
SHORTEN, but thin filaments DO NOT ( thin filaments slide toward H bond)
in sliding filament theory when a muscle contracts:
H band:
shortens or disappears
thin filaments slide toward H bond
what are the 3 subunits of troponin? (ICT)
I: inihibory part blocks myosin head binding to actin
C: binds to calcium linking it to the nerve (calcium released from sarcoplasmic reticulum)
T: binds to tropomyosin
thick filaments(myosin)
Each protein has two globular heads with
actin-binding sites and ATP-binding sites
thin filaments(actin)
Have proteins called tropomyosin and
troponin that prevent myosin binding at rest
action of sliding in sliding filament theory
Sliding is produced by several cross bridges that form between myosin and actin.
a) The myosin head serves as a myosin ATPase enzyme, splitting ATP into ADP + Pi.
b) This allows the head to bind to actin when the muscle is stimulated.
Release of Pi upon binding cocks the myosin head, producing a__________ _________ that pulls the thin filament toward the center
power stroke
After the power stroke, _______ is released and a new ATP binds.
ADP
-This makes myosin release actin.
-ATP is split.
The myosin head straightens out and rebinds to actin farther back.
Continues until the sarcomere has shortened
what does Regulation of Contraction
F-actin(fibrous actin) is made of 300-400 G-actin subunits,
arranged in a double row and twisted to form
a helix
F-actin(fibrous actin) is made of 300-400 G-actin subunits,
arranged in a double row and twisted to form
a helix
cross bridges
Troponin complex
- Troponin I inhibits binding of
- Troponin T binds to
- Troponin C binds to
- Troponin I inhibits binding of myosin.
- Troponin T binds to tropomyosin.
- Troponin C binds to calcium.
When muscle cells are stimulated, Ca2+ is released where??
some attaches to Troponin C, causing a _________
Myosin is allowed access to form cross bridges with______
inside the muscle fiber.
conformational change in troponin and tropomyosin.
ACTIN
sarcoplasmic reticulum is a modified Er that stores Ca when
most SR is stored in: _______
-muscle is at rest
-terminal cisternae
When a muscle fiber is stimulated, Ca2+ diffuses out of
calcium release channels
(ryanodine receptors).
At the end of a contraction,
Ca2+ is actively pumped back
into the
SR
role of SR
role of SR
transverse tubules are:
NT:
open to the :
able to conduct:
closely situated next to:
-Narrow membranous tunnels formed from the sarcolemma
-acetylcholine
-extracellular environment
-action potentials
-terminal cisternae
to stimulate a muscle fiber:
_____________ is released from motor neuron
conducted along__________
calcium is released)SR) and can bind to:
acetylcholine
-the sarcolemma(Na)
-troponin C
can get graded muscle contraction but not fiber..HOW?
recruitment
more motor units
Axon terminal of motor neuron forms neuromuscular junction with _______
a single muscle fibre
Signals are passed between nerve terminal and muscle fiber by means of neurotransmitter ___________
Released ACh binds to receptor sites on motor end plate of _________________
Binding triggers ____________ of specific channels in motor end plate
Ion movements _________ motor end plate, producing end-plate potential
-Acetylcholine
-muscle cell membrane
-opening
-depolarize
in muscle relaxation:
Action potentials ________
Calcium release channels ___________
Ca2+-ATPase pumps move Ca2+ ___________________________
No more Ca2+ is available to bind to
Tropomyosin moves to block the myosin heads from
-cease
-close
-back into SR (active transport).
-troponin C
-binding to actin
ACH Agonists: drugs that can stimulate a receptor: (2)
- nicotine
- muscarine
ACH antagonists: drugs that inhibit a receptor
- curare
- atrophine
- curare
- atrophine
1 motor neuron
all the muscle fibres it innervates
1 motor neuron
all the muscle fibres it innervates
NO
1 motor neuron
all the muscle fibres it innervates
site where a motor
neuron stimulates a muscle fiber
site where a motor
neuron stimulates a muscle fiber
area of the muscle fiber
sarcolemma where a motor neuron stimulates it
using the neurotransmitter, acetylcholine
TYPE I Muscle fibres are:
slow twitch fibers
slow oxidative
contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP. They produce low power contractions over long periods and are slow to fatigue.
slower contraction speed; can sustain contraction for long periods without fatigue; rich capillary supply; more mitochondria; more respiratory enzymes; more myoglobin
a. Tend to have high oxidative capacity, so are
called (slow) oxidative fibers
b. Due to high myoglobin content (which has a
red pigment), these are also called red fibers
c. Found in postural muscles
Type IIA fibers
fast oxidative
fast twitch, have high oxidative and glycolytic capacity, and are relatively resistant to fatigue
fast-twitch but with high oxidative capacity; called fast oxidative fibers
Type IIB fibers (IIX)
fast-glycolytic (myosin heavy chain, ATPase)
fast twitch, have low oxidative and high glycolytic capacity, and fatigue rapidly
faster contraction speed, fatigue fast, fewer capillaries, mitochondria, respiratory enzymes, and less myoglobin
a. Also called white fibers
b. Have more glycogen stores and are called
fast glycolytic fibers
c. Found in stronger muscles
endurance running recruits:
type I and IIa
at rest utilizes:
at rest utilizes:
each muscle fibre is activated thru impulses delivered via
motor end plate
motor end plate
when a muscle quickly contracts and relaxes after a single electrical shock of sufficient voltage (AP).
-Increasing the voltage increases the strength of the twitch up to a maximum.
-When a second shock is applied immediately after the first, a second twitch will partially piggyback the first. This is called summation
summation:
two successive action potentials (AP), if the twitch tension resulting from the
first AP does not decline to zero before asecond twitch arrives, the twitch forces summate.
tetanus:
frequency of APs(action potentials)-a rise in the contractile force of a single
muscle (fibre) until force reaches a plateau called the tetanic tension. This is the maximum tension that can be produced by a fibre.
if a muscle fibre is stimulated so rapidly that it doesnt have an opportunity to relax at all between stimuli, a maximal sistained contraction known as tetanus occurs
a. Increasing the frequency of electrical shocks decreases the relaxation time between twitches. This is called incomplete tetanus.
b. At a certain frequency, there will be no relaxation. This is called complete tetanus, a smooth, sustained contraction.
Latent period
time between the stimulus and the contraction (excitation-contraction
coupling to the attachment of myosin cross bridges to actin)
