TBL 5A Physiology Part 2 - Muscle Flashcards
Myocytes are a type of ______ cells. They develop to form myoblasts.
Muscle
There are small contact regions at the terminal ends of an axon at a synpase known as ______.
boutons
_______ are neuromuscular junctions between a ________ and a muscle fiber.
They are highly complex structures involving pre/post synaptic membranes, neurotransmitter (________) containing vesicles, and many receptors and enzymes.
Synpases - formed between a motor neuron and a muscle fiber.
neurotransmitter - acetylcholine
_______ is the basic unit of a striated muscular tissue.
It is a repeating unit between 2 Z lines.
Sarcomere
Sarcomeres are made up of long fibrous _____ filaments sliding past each other during muscle contraction/relaxation.
protein
actin/myosin mainly
The _________ membrane is highly invaginated, thus increasing surface area for neurotransmitter receptors to be embedded in.
post-synaptic membrane
__________ (enzyme) on the postsynaptic membrane breaks down bound acetylcholine to end transmission, to prevent the continuous stimulation of the nerve.
Acetylcholinesterase
Acetylcholine is broken down into _____ and _____.
Choline and Acetyl-CoA
After acetylcholine is broken down, choline is taken up by the ________ cell and recycled, whereas acetyl-CoA enters the ______ and is metabolised.
Choline - taken up by the pre-synaptic cell
Acetyl-CoA - enter Krebs Cycle
The acetylcholine receptor is made up of __ peptides. (__ alpha subunits, __ beta subunits)
5 peptides - 2 alpha, 3 beta
The acetylcholine receptor forms a ___ channel, where ___ can pass through when the gate opens from acetylcholine binding.
ion channel; Na+ ions can pass through down the concentration gradient into the cell
(depolarisation)
The 5 subunits in the acetylcholine receptor has a _____ site for acetylcholine to change its conformation of the pore.
binding
The ____________ in the muscle cell is the intracellular Ca2+ store.
sarcoplasmic reticulum
The two receptors involved in Ca2+ diffusion in muscle cells are __________ receptor present on the T-tubule membrane and ________ receptor present on the sarcoplasmic reticulum membrane.
dihydropyridine receptor on T-tubule membrane
ryanodine receptor on SR membrane
_______ are extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cells. Action potentials transmitted down the muscle fibres will be transmitted along this structure to reach the centre of the cell.
Transverse tubules
(T-tubules)
Mainly functions to carry the action potential into the muscle fiber
T-tubules are connected to the _________ fluid, so the ion concentration is the same as outside.
extracellular
The _______ receptor changes conformation in response to depolarisation, which affects the conformation of the _______ receptor, opening the ion gate and allowing ___ ion to flow out of the sarcoplasmic reticulum.
The dihydropyridine receptor changes conformation in response to depolarisation, which affects the conformation of the ryanodine receptor, opening the ion gate and allowing Ca2+ ion to flow out of the sarcoplasmic reticulum.
Ca2+ ion interacts with ______ (protein) on the actin filaments, causing conformational changes in the _________ (protein) that allows for cross-bridge formation and muscular contraction.
Ca2+ ion interacts with troponin (protein) on the actin filaments, causing conformational changes in the tropomyosin (protein) that allows for cross-bridge formation and muscular contraction.
What happens to the Ca2+ ions in the cytoplasm of the muscle cell when muscular contraction is over?
There are Ca2+ pumps which will pump the remaining Ca2+ ions from the cytoplasm back into the SR. (Relaxation of muscle)
Muscle fiber refers to a single __________.
Each muscle fiber is made up of many _____, which appear striated.
muscle cell; myofibrils
Each sarcomere is made up of thick filaments known as _____ and thin filaments known as ______, ______ and _______.
thick filament - myosin
thin filaments - actin (mainly), troponin and tropomyosin
The thick myosin filaments have _________ sticking out to form cross-bridges with different directionalities on different ends.
globular heads
_______ molecules wind around the groove of the actin filament; whereas troponin molecules occur at every __ actin monomers.
Tropomyosin; troponin - every 7 actin monomers
________ functions as the plasma membrane of the muscle fiber.
Sarcolemma
Skeletal muscle fibers have more than one _____.
nucleus
Skeletal muscles are joined to bones via _____.
tendons
_______ are present on the surface of muscle fibres on top of the sarcolemma. They are multipotent stem cells that can differentiate into muscle cells when the tissue is damaged.
Satellite cells
Within the sarcomere, there are three types of bands.
H-band consists of ____ filaments only.
I-band consists of ____ filaments.
A -band consists of ___________.
H-band: Only myosin (thick) filaments
I-band: Only thin (actin) filaments
A-band: Both myosin and thin filaments in the overlap region
M-line joins the ______ filaments together; whereas the ______ joins the actin filaments together.
M-line: Myosin
Z-line: Actin
The length of thick filaments (myosin) is ___um, and contains exactly ___ myosin molecules with ___ globular heads arranged in a helical fashion.
1.6um; 294 myosin molecules with 588 globular heads
Myosin filaments are assembled by first forming a _____, which is then elongated by the addition of myosin molecules to the ends until there are ___ myosin molecules in the filament.
dimer; 294
The thin filaments made up actin monomers have lengths of ____.
1.1 um
The bare zone where there are no myosin heads protruding is always ____ wide.
0.15um
________ are formed when the myosin heads attach to the thin filaments.
Cross-bridges
Muscle shortening is brought about by the ____________ hypotheses, which involves the interaction of myosin cross-bridges. This causes changes in the overlapping of filaments.
sliding filament
During muscle shortening, the thick and thin filaments, as well as the A-band, (change/do not change) their lengths.
do not change
**Only the H-band and I-band decreases in length due to the increasing overlap of filaments
Protein ________ is necessary for the attachment of actin filaments at the Z-line.
a-actinin
Protein _____ links the adjacent myofibrils together at the Z-lines.
Desmin
Sarcoglycan complex links the Z-line of the myofibrils to the _________.
plasma membrane (sarcolemma)
________ links the muscle fibers to the extracellular matrix.
Dystrophin
____ is a very large protein that extends from one Z-line to the other, and gives the muscle additional strength. It ensures that thick filaments stay at the centre of the sarcomeres, and is involved in muscle regulation.
Titin
Each myosin monomer contains and a-helical coil and a _______.
Globular head
The globular head of the myosin monomer contains two binding sites - one for ____ and one for ____.
2 binding sites:
1) ATP-binding
2) actin-binding
The neck domain of the myosin monomer has essential and regulatory ______ chains attached.
light chains
During the cross-bridge cycle:
Myosin is initially attached to ____ and ___.
ADP and Pi
During the cross-bridge cycle:
What happens when Pi is released from Myosin?
Myosin will bind to actin.
During the cross-bridge cycle:
After myosin binds to actin, ___ is released from myosin. (as myosin does a reverse power stroke)
ADP
During the cross-bridge cycle:
What happens when ATP binds to myosin?
Myosin detaches from actin.
During the cross-bridge cycle:
Bound-ATP is decomposed into ADP and Pi, causing ________, where myosin will be onto the next actin molecule.
gliding motion
If ATP is not present for muscular contraction, _______ occurs.
rigor mortis
Can cross-bridges push away from the centre of the sarcomere to cause lengthening of the muscles?
No. They can only cause sarcomere shortening due to their orientation.
Activation of skeletal muscles start in the following three parts of the brain:
_____, _____, _____
- Cerebral cortex (thin layer of the brain containing sensory and motor areas, regulating voluntary movement)
- Basal ganglia (group of subcortical nuclei involved in control of voluntary motor movement)
- Cerebellum (involved in coordination and regulation of muscular activity)
Upon arrival of action potential at the axon terminal, the resulting depolarisation of the pre-synaptic membrane causes the _________________.
Causes the opening of voltage-gated Ca2+ channels, allowing the influx of Ca2+ into the presynaptic knob.
This causes the migration of presynaptic vesicles containing acetylcholine to fuse to release these molecules into the synaptic cleft to bind to the receptors on the surface of the postsynaptic cell.
As the action potential propagates into the T-tubules, the _________ receptor senses the depolarisation and cause the shape of the protein link to the ________ receptor to be changed.
dihydropyridine receptor on the T-tubule senses the depolarisation; ryanodine receptor change conformation.
The ryanodine receptor located on the SR membrane consists of a _____ ion channel. Opening of the channel will cause the ion to (enter/leave) the cytoplasm, where it can interact with the muscle fibers.
calcium; enter
Ca2+ ions released from the SR binds to _____ and activate _____, which allows the cross-bridges of the thick filaments to attach to actin.
calcium ions bind to troponin and activate tropomyosin
In the activated state, (in the presence of calcium ions) _________ moves away from the actin-binding site on myosin to allow for cross-bridges to occur.
tropomyosin
How does the muscle relax?
The action potential from the nerve ceases, and there is no more depolarisation at the ______ of the muscle cell. This results in the stopping of release of ___ ions from the SR into the cytoplasm.
No more depolarisation at the T-tubule; stopping of release of Ca2+ ions from the SR.
What happens to the existing Ca2+ in the cytoplasm during muscle relaxation?
Active transport back into SR
Muscles are able to generate force during (shortening/lengthening), but unable to generate force during (Shortening/lengthening).
generate force - shortening; cannot generate force - lengthening
Factors affecting the generation of force for normal skeletal muscle include:
1) Concentration of ____ –> affects the frequency of stimulation
2) Number of active _______
3) Overlap of filaments
4) ______ of filament sliding
1) Concentration of Ca2+ ions
2) Number of active motor units
3) Overlap of filaments
4) Velocity of filament sliding (movement)
A _______ includes the motor neurone and all the muscle fibers it forms synapses with.
motor unit
Cardiac muscle fibers are known as ________.
cardiomyocytes
In each cardiomyocyte, there is (one/many) nucleus and (small/large) number of mitochondria
one nucleus, many mitochondria
Cardiomyocytes are connected to one another via _________ which act as mechanical links between the fibres.
intercalated discs
Adjacent muscle fibres are connected via ________, where ionic currents (i.e. action potential) can flow from one fibre to the next.
gap junctions
(Irregular/regular) branching pattern occurs in cardiac muscle cells.
irregular
(Skeletal muscle cell/Cardiomyocyte/smooth muscle cell) is small and short, allowing action potentials to spread easily from cell to cell.
Cardiomyocyte
Pacemaker cells are spontaneously active, which means that they (require/do not require) stimulation by action potentials.
do not require stimulation
______ muscle cells appear smooth (not striated).
Smooth muscle cells
not arranged in regular arrays - no sarcomeres
In ______ muscle cells, there is no troponin attached to the thin actin filaments of the sarcomeres. (therefore the activation by calcium ions is slightly different)
smooth muscle cells
The ______ muscle cells are the smallest types of muscle cells.
smooth muscle cells
