Muscles - Class Flashcards
Study for Final
True or false:
Each Motor Neuron can be connected to multiple muscle fibers, but each muscle fiber can only be connected to one neuron.
TRUE!
Would it be slow or fast twitch muscles that hold your body posture?
Slow. Slow twitch muscles move slowly, but they can keep working for long periods of time.
What’s the difference between DIRECT and INDIRECT insect flight muscles?
Direct: The wing is connected to the muscle directly.
Indirect: The wing is attached to the body, and the muscles just flex the body, which causes motion in the wings.
Explain Active vs Passive Muscle Tension
Active muscle tension is created as a motor response, so it comes from nervous system signals. Passive muscle tension is STRETCHING out your muscles. So muscles can only have ACTIVE muscle tension when they’re contracting.
What is the neurotransmitter at the NMJ (Neuromuscular Junction)?
–>Why are its effects always excitatory?
The neurotransmitter at the NMJ is Acetylcholine.
–>Its affects are always excitatory because excitatory contractions are the ones that cause
Why do cardiac muscles have a long repolarization phase, and how does it differ from skeletal muscles?
1: Plateau Phase: After the initial rapid depolarization, cardiac muscle cells experience a plateau phase, where the membrane potential stays relatively depolarized for an extended period before finally repolarizing. This is primarily due to the opening of voltage-gated calcium channels, which allow calcium ions (Ca2+) to enter the cell from the extracellular space and maintain the depolarized state.
2: Calcium Influx: The influx of Ca2+ not only sustains the depolarized state but also triggers the release of more calcium from the sarcoplasmic reticulum inside the cell, which is crucial for muscle contraction. This extended influx of calcium is what lengthens the repolarization phase.
3: Prevention of Tetanus: The extended refractory period that results from the long repolarization phase prevents the cardiac muscle from undergoing tetanus (a sustained muscle contraction), which is vital for heart function. The heart needs to relax between beats to fill with blood and ensure effective pumping action.
**Differences from Skeletal Muscles:
-Action Potential Duration: Skeletal muscle cells have a much shorter action potential and refractory period compared to cardiac muscle cells. This allows skeletal muscles to relax quickly after contraction and enables them to sustain rapid, repeated contractions when necessary.
-Role of Calcium: While calcium ions play a critical role in contraction for both muscle types, the prolonged entry of calcium during the plateau phase is unique to cardiac muscle cells. In skeletal muscles, the action potential triggers a rapid release of calcium from the sarcoplasmic reticulum without the prolonged influx from the extracellular space.
-Functional Requirement: The long repolarization phase in cardiac muscles ensures a rhythmic, coordinated contraction of the heart, providing time for the chambers to refill with blood. In contrast, skeletal muscles need to respond quickly to stimuli for various voluntary movements, which requires a different pattern of electrical activity and muscle contraction.
In summary, the long repolarization phase in cardiac muscles, characterized by the plateau phase, is crucial for heart function, allowing time for cardiac chambers to fill and ensuring that the heart beats in a coordinated manner. This mechanism is distinct from skeletal muscles, where rapid repolarization allows for quick and repeated contractions.
How does summation of action Potentials work in skeletal muscle vs Cardiac mucles?
In skeletal muscles, there IS summation of action potentials but because of this, skeletal muscles are susceptible to TETANUS. Tetanus is a sustained muscle contraction that’s caused by the fusion of multiple action potentials.
and in the HEART, we cannot have tetanus, and so when action potentials are generated at too high of a frequency, what happens is, Cardiac Arrhythmia! This is when all the chambers of the heart no longer contracting in sequence with each other.
What are T-Tubules?
first, the Sarcolemma is the muscle cell membrane.
T-tubules are cavities formed in the sarcolemma, that extend into the muscle cell as tubes, and they wrap around the sections of Myofibrils.
See what they look like with this file:
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It’s a ^^ diagram of a Myofiber, which is the muscle cell.
What do T-Tubules do?
T-tubules facilitate the
What’s the science-y name for a skeletal muscle cell?
a Myofiber!
(and inside, we have the Myofibrils)
what is Sarcoplasmic reticulum, and how does it relate to endoplasmic reticulum?
Sarcoplasmic reticulum is a sub-type of endoplasmic reticulum, and it’s found in MUSCLE CELLS.
The job of the sarcoplasmic reticulum is to store and release calcium ions, which are crucial for muscle contraction.
(When a muscle cell is stimulated, calcium ions are released from the SR, initiating the contraction process.
The SR is especially prominent in skeletal and cardiac muscle cells, forming a network around the Myofibrils inside.)
Why are calcium ions vital for muscle contraction?
–>What exactly does it do?
Ca^2+ is essential for initiating muscle contraction by facilitating the interaction between actin and myosin, the fundamental process behind muscle movement. Without the precise regulation of Ca^2+ concentration inside muscle cells, controlled muscle contraction and relaxation would not be possible.
–>Specifically, in skeletal muscles, the process starts when an action potential (an electrical signal) reaches a muscle cell. This signal triggers the sarcoplasmic reticulum (a specialized form of the endoplasmic reticulum in muscle cells) to release Ca^2+ into the sarcoplasm (the cytoplasm of muscle cells).
Ca^2+ then binds to troponin, a regulatory protein that, along with tropomyosin, controls the actin-myosin interaction necessary for muscle contraction. In its resting state, tropomyosin blocks the binding sites for myosin on actin filaments, preventing contraction.
Actin Myosin Crossbridge:
When Ca^2+ binds to troponin, it causes a conformational change in the troponin-tropomyosin complex, exposing the myosin-binding sites on the actin filaments.
Myosin heads, which are part of the myosin filaments, can then attach to these exposed sites on the actin filaments, forming cross-bridges. The myosin heads then pivot, pulling the actin filaments toward the center of the sarcomere (the basic contractile unit of muscle fiber) and shortening the muscle—this is the contraction.
Termination of Contraction:
Muscle relaxation and the termination of contraction occur when Ca^2+ is actively pumped back into the sarcoplasmic reticulum, reducing its concentration in the sarcoplasm. This removal of Ca^2+ causes troponin to revert to its original shape, allowing tropomyosin to once again cover the myosin-binding sites on actin filaments.
With the actin-binding sites blocked, the actin and myosin filaments slide back to their original positions, and the muscle fiber relaxes.
Energy Supply:
ATP (adenosine triphosphate) is required for both the contraction and relaxation phases. For contraction, ATP is necessary for the myosin heads to detach from the actin filaments and return to their original position, ready to form another cross-bridge. For relaxation, ATP is used to pump Ca^2+ back into the sarcoplasmic reticulum.
What are Terminal Cisternae?
Terminal cisternae are enlarged areas of the sarcoplasmic reticulum (SR) in muscle cells that are closely associated with the transverse tubules (T-tubules). They are a component of the triad structure in skeletal muscle cells and dyads in cardiac muscle cells, which are critical for muscle excitation-contraction coupling.
I bands and A bands?
A Bands and I Bands: Within the sarcomere, myofilaments are organized into distinct bands:
A Bands: These are the darker areas that contain the entire length of the single thick filaments (myosin) and partly overlap with thin filaments (actin). The A band’s length remains constant during contraction.
I Bands: These are the lighter areas that contain thin filaments (actin) that do not overlap with thick filaments (myosin). The I band’s width decreases during muscle contraction as the actin and myosin filaments slide past each other.
Describe Excitation-Contraction coupling.
