The transverse tubules (T-tubules) of mammalian cardiac and skeletal muscles are
invaginations of the sarcolemma
. They play a crucial role in excitation-contraction coupling as well as in intracellular signaling and in regulation of glucose transport.
What is the T-tubule used for in muscle?
T-tubules are invaginations of the plasma membrane, which are present exclusively in striated muscle. Their role is to
maintain the SR calcium store under the tight control of membrane depolarization via the voltage sensor channel
DHPR [2].
What are T-tubules quizlet?
– T tubules are
transverse tubules formed by inward extensions of the sarcolemma
. -Function is to allow electrical impulses traveling along the sarcomere to move deeper into the cell.
Where are the T-tubules?
The T-tubules are located
in the space between the two SR cisternae
(Figure 53.2B) and the assembly of two SR and one T-tubule is called a triad. The SR, like the ER, is a totally internal membrane system that creates a segregated space: its lumen is not connected to either the cytoplasm or the extracellular space.
What happens at the T-tubules?
As T-tubules bring the sarcolemma very close to the sarcoplasmic reticulum at all regions throughout the cell,
calcium can then be released
from the sarcoplasmic reticulum across the whole cell at the same time. This synchronisation of calcium release allows muscle cells to contract more forcefully.
Does the heart have smooth muscle?
Cardiac muscle cells are located in the walls of the heart, appear striated, and are under involuntary control. Smooth muscle fibers are located in walls of hollow visceral organs,
except the heart
, appear spindle-shaped, and are also under involuntary control.
What is the main function of the sarcoplasmic reticulum?
The sarcoplasmic reticulum (SR) constitutes the main intracellular calcium store in striated muscle and plays an important role in the
regulation of excitation-contraction-coupling (ECC) and of intracellular calcium concentrations during contraction and relaxation
.
Is ATP necessary for muscle relaxation?
ATP is needed for normal muscle contraction
, and as ATP reserves are reduced, muscle function may decline. This may be more of a factor in brief, intense muscle output rather than sustained, lower intensity efforts. Lactic acid buildup may lower intracellular pH, affecting enzyme and protein activity.
What is the all or nothing response?
The all-or-none law is a principle that states
that the strength of a response of a nerve cell or muscle fiber is not dependent upon the strength of the stimulus
. … Essentially, there will either be a full response or there will be no response at all for an individual neuron or muscle fiber.
Do Myofibrils have T-tubules?
T tubules
extend from the free surface throughout
the cells in a generally transverse direction, coursing around the myofibrils at the levels of the Z bands.
Are there T-tubules in smooth muscle?
Although smooth muscle contraction relies on the presence of Ca
++
ions, smooth muscle fibers have a much smaller diameter than skeletal muscle cells.
T-tubules are not required to reach the interior of the cell
and therefore not necessary to transmit an action potential deep into the fiber.
Do T-tubules have voltage-gated channels?
Action potentials are conducted into the interior of muscle fibers via the T-tubules and there they activate voltage-gated channels known as
dihydropyridine receptors (DHPR)
. Unlike in cardiac muscle, very little calcium enters the muscle fiber from the extracellular space (via the DHPR).
What causes depolarization down the T tubule?
1) Motor neuron releases acetylcholine into the neuromuscular junction and causes the depolarization of the sarcolemma. 2) Depolarization spreads down the sarcolemma to the T-tubules, triggering the release
of Ca2+ ions
.
Which muscle cells have the greatest ability to regenerate?
Smooth cells
have the greatest capacity to regenerate of all the muscle cell types. The smooth muscle cells themselves retain the ability to divide, and can increase in number this way.
What are the steps of muscle contraction?
- exposure of active sites – Ca2+ binds to troponin receptors.
- Formation of cross-bridges – myosin interacts with actin.
- pivoting of myosin heads.
- detachment of cross-bridges.
- reactivation of myosin.
What is the main function of cardiac muscle?
12.1. 1.1 Cardiac muscle. Cardiac muscle tissue forms the muscle surrounding the heart. With the function of the muscle being
to cause the mechanical motion of pumping blood throughout the rest of the body
, unlike skeletal muscles, the movement is involuntary as to sustain life.
