Skeletal Muscle Tissue Flashcards
What’s excitability
Respond to stimuli
Produce action potentials (they get muscles to contract)
(Relates to nervous system)
What’s contractility
Contracts forcefully when stimulated
What’s extensibility
What muscle has the greatest stretch?
Ability to stretch within limits
-smooth muscle greatest stretch
Properties of muscle tissue? (4)
Excitability
Contractility
Extensibility
Elasticity
What’s elasticity?
ability to return to original length & shape after contraction
(why when you pull a muscle, it takes a while to feel better bc it went past contraction)
What are the functions of skeletal muscle tissue?
moves bones (produce movement) help maintain body temp (generate heat)
What is involved in the functions of skeletal muscle?
description? how many muscles in body?
700 muscles in body elongated cells w/ many nuclei striated (banded) voluntary control regeneration is limited (which is why it's hard to build back muscle)
Each skeletal muscle is a ____ organ
Separate
What does each skeletal muscle contain?
Contains 1000s of individual cells called muscle fibers
What are muscle fibers surrounded by? Penetrated by? description? how develop?
Surrounded by connective tissue Penetrated by blood vessels and nerves -long cylindrical cells w/ striations and multiple nuclei -develop from mesoderm cells- myoblasts -individual cells
Connective tissue coverings ?
3 layers that strengthen skeletal muscle
1) epimysium
2) perimysium
3) endomysium
What’s the epimysium
Outer most layer
Encircles each whole muscle
Perimysium ?
Surrounds groups of 10 to 100 muscle fibers
Separates fibers into bundles called fascicles
Endomysium
Separates each individual muscle fiber within the fascicles
-connective tissue that surrounds each muscle cell/fiber
Levels of organization within skeletal muscle? Largest to smallest
Skeletal muscle (epimysium, yellow) Fasicle (perimysium, purple) Muscle fiber (endomysium, green) Myofibril (individual pencil) Myofilaments (action & myosin, lead & wood)
Skeletal muscle fibers develop from what?
Mesoderm cells- myoblasts
Shape and size of skeletal muscle fibers ?
Long cylindrical
Do skeletal muscles have striations? Multiple or single nuclei?
Striations (bc myosin & actin over lap)
Multiple nuclei
Sarcolema?
(Anatomy of a skeletal muscle fiber)
Aka cell/plasma membrane
T tubules
what do they surround? what do they form? what does it contain? function?
Aka transverse tubules
Form a tunnel like network into the muscle fiber
-filled with extracellular fluid
-terminal cisternae
They are deep extensions of sarcolemma that surround each myofibril
carry action potentials
Sarcoplasm
contains?
aka cytoplasm
Contains: glycogen- used for ATP synthesis
myoglobin-red-colored protein, binds oxygen in muscle cells
Sarcoplasmic Reticulum
SR aka modified endoplasmic reticulum
-forms a weblike network surrounding myofibrils
Myofibrils
contains?
contractile unit of a muscle (make up muscle)
Contains 2 types of protein filaments
-thick & thin filaments
Thick and thin filaments? made of? what forms when together?
thick- made of protein myosin
thin-made of protein actin
together form light & dark bands (striations)
how are filaments arranged? what separates each?
arranged in units called sarcomeres
-Z line separate 1 sarcomere from another
What surrounds myofibrils? What does it do?
Sarcoplasmic Reticulum surrounds myofibirls, stores & releases Ca 2+ ions
Terminal Cisternae
enlarged sections of SR found beside each T tubule
What forms a triad?
2 terminal cisternae & 1 T tubule
What does the sarcomere structure involve?
I bands, A bands, H zone, M line, and it extends from 1 z line to another
A band description
region of myofibril’s striation w/ DARK appearance
made of myosin
contains overlapping thick and thin filaments, H zone, & M line
I band description
region of myofibril’s striation w/ LIGHT appearance
made of actin
contains only thin filaments
connect to Z lines
H zone
lighter stripe in center of dark A band in the region btwn thin filaments (consists of only myosin)
decreases in size when muscle contracts
M line
line in the center of H zone consisting of protein fibers special protein that binds thick filaments in place (connects thick filaments together)
Z disc
aka Z line
zig zag line bisecting I band, sarcomere stretches from 1 to the other
function: protein disc that anchors thin filaments & connects adjacent myofibrils
Structure of a myofibril
made of? what do they consist of?
each myofibrils made of thousands of myofilaments
myofilaments consist of
-contractile proteins
-regulatory proteins
-structural proteins
(contains 2, thick and thin, protein filaments)
what are the 2 types of myofilaments?
thick & thin
thick filaments contain and are made of?
- bundles of contractile protein myosin
- Globular head- has an active site to bind w/ actin
thin filaments contain and are made of?
how does actin act?
- composed of proteins actin, troponin, and tropomyosin
- Actin forms “bead like” strings w/ active sites to bind w/ myosin heads
Tropomyosin
made of? function?
Rope-like regulatory protein
Covers actin’s active sites
troponin
made of? function?
Globular regulatory protein
Holds tropomyosin in place & assists turning contractions on & off
-molecule that has binding site for Ca ion
Where motor neurons activates muscle fibers to contract
Called a neuromuscular junction NMJ
definition of a neuromuscular junction
area where action potentials occur
define synapse
region btwn neuron & target cell where action potential (stimulus) is transmitted
define synaptic cell
aka cleft
space that separates a neuron & target cell
define neurotransmitters
chemicals that carry the stimulus
*** Steps in action potential (excitation & excitation-contraction coupling)
1) Action potential arrives at axon terminal
2) Calcium ions enter the axon terminal
3) Synaptic vesicles fuse to membrane of axon terminal & release ACh
4) ACh binds to receptor sites of the motor end plate
5) Motor end plate becomes depolarized w/ exchange of sodium ions across membrane (& potassium moves out of the muscle cell)
6) Action potential is initiated on the sarcolemma & propagates down into the T tubules
7) Ca ions are released from terminal cisternae
8) Muscle cell contracts
what causes a skeletal muscle to contract?
motor neuron or action potential (bc of the impulses)
What is the place called where a motor neuron stimulates a muscle cell?
neuromuscular junction
Synaptic vesicles in the axon terminal of a motor neuron contain what neurotransmitter?
Acetylcholine (ACh)
an action potential in the axon terminal of a motor neuron opens w/ what type of ion?
Calcium
space btwn the axon terminal and motor end plate
synaptic cleft
swollen distal end of the motor neuron
axon terminal
muscle cell membrane
sarcolemma
structures within the axon terminal that contain neurotransmitter acetylcholine
synaptic vesicles
contractile unit of the muscle cell that extends from z line to the next
sarcomere
structures within skeletal muscle cells that serve as reservoirs of calcium ions
terminal cisternae
folded region of the sarcolemma at the neuromuscular junction
motor end plate
*** What do Ca 2+ ions cause inside the axon terminal?
cause synaptic vesicles to release ACh into the synaptic cleft
*** What happens to ACh after it is released into the synaptic cleft?
binds to receptor sites in the motor end plate (of a muscle cell, which causes ion channels to open)
*** What happens to the ACh after it diffuses away from its receptor on the motor end plate?
causes depolarization or is broken down & return to axon terminal
*** How is the neurotransmitter removed from the synaptic cleft?
1) diffuses away from receptor site & back up into axon terminal
2) broken down by the enzyme acetylcholinesterase
What attaches muscle to bone?
tendons
whole muscle is composed of muscle cells (fibers) grouped in bundles called _______
fascicles
connective tissue that surrounds the whole muscle is the
epimysium
connective tissue that surrounds each fascicle is the
perimysium
connective tissue that surrounds each muscle cell is the
endomysium
sites for ATP synthesis
mitochondria
interconnected tubules of the ER that surround each myofibril
SR
part of sarcolemma that carries action potentials
t tubule
what is actin and myosin made out of ?
protein
flexing the head of the thick filament provides what?
a power stroke
what are the two parts of a myosin molecule?
head (2) and tail (1)
cross bridge (myosin head) contains binding sites for what two molecules?
actin and ATP
what 3 molecules make up a thin filament?
actin
tropomyosin
troponin
what molecule in a thin filament has a binding site for myosin?
actin
what molecule in a thin filament covers the binding site when not activated
tropomyosin
what molecule in a thin filament has a binding site for calcium ions?
troponin
function of tropomyosin?
covers binding sites on actin
function of troponin?
attach to tropomyosin which causes tropomyosin to move off the binding sites on actin
what causes tropomyosin to move away from myosin binding sites?
calcium ions binding to troponin
what causes tropomyosin to cover back over actin binding sites?
when calcium releases
2 roles of ATP in muscle contraction
1) attach to the myosin for power stroke
2) release energy and release myosin from actin
what molecule is connected to the z line?
actin
*** what shortens in muscle contraction
SARCOMERE & H ZONE
thin and thick filaments do not shorten
sliding filament mechanism is also known as what?
crossbridge cycle
*** describe the sliding filament/cross-bridge cycle
(starts as a relaxed muscle)
1) Release of CA 2+ from SR exposes binding sites on thin filament. Ca 2+ binds to troponin & tropomyosin is pulled aside
2) Cross-bridge binds actin to myosin
3) Cross-bridge pulls actin filament (POWER STROKE) and ADP & P release from myosin
4) New ATP binds to myosin, causing linkage to release (myosin releases from actin)
*** What ion is most important in muscle contraction? Why?
Calcium
A skeletal muscle cell can only contract from the impulses from an action potential. Without calcium, the action potential in the axon terminal of a motor neuron would not be able to open, so no contraction would be possible bc ACh would not be released. (synaptic vesicles would not be able to release ACh into the synaptic cleft via exocytosis)
*** Why are there striations in a skeletal muscle cell?
because the A band is made of overlapping actin & myosin. this formation of the thick and thin filaments forming light and dark bands in a myofibril causes striations.
*** What does ACh do?
it is what triggers a muscle action potential
Sarcomere
functional unit of contracttion in striated muscle that extends from z line to z line. considered that bc all components for contraction are contained within each sarcomere. contains I band, A band, H zone, M line, and Z line
how is muscle tension caused?
contraction causes tension
conductivity?
property of muscle tissue
- conducts impulse/carries stimulus through the muscle fiber (ability for nerve impulse)
actin
protein that compoases the major portion of thin filaments
1 of the proteins that make up a myofibrils, has a binding site for myosin
myosin
protein that composes major portion of thick filaments
1 of the proteins that make up a myofibril
difference btwn SR and terminal cisternae?
SR is between the terminal cisternae and terminal cisternae is next to the T tubules
structural and functional relationship btwn neurons and skeletal muscle fibers?
structural: synaptic cleft forms btwn the two
functional: neurons activate skeletal muscle to contract
