Study guide chap 10

Q: What are the 5 major functions of muscle tissue?

A:

1. Movement

2. Posture

3. Stabilizing joints

4. Generating heat

5. Regulating flow in hollow organs

Q: Which function of muscle helps maintain body temperature?

A: Heat generation from contractions (especially skeletal muscle)

Q: What muscle type regulates flow in hollow organs, like blood vessels or intestines?

A: Smooth muscle

Q: Which type(s) of muscle are voluntary and striated?

A: Skeletal muscle is both voluntary and striated.
(Cardiac = striated but involuntary. Smooth = involuntary and not striated.)

Q: Where are cardiac and smooth muscle found?

• Cardiac: Heart walls only

• Smooth: Walls of hollow organs (e.g. stomach, blood vessels, bladder)

Q: Which muscle types can contract without nervous system input?

A: Cardiac and smooth — they’re involuntary and can contract automatically

Q: What are the 4 main properties of muscle cells?

1. Excitability – responds to signals

2. Contractility – shortens to produce force

3. Extensibility – stretches without damage

4. Elasticity – returns to original shape

Q: What property allows muscles to return to their resting length after stretching?

A: Elasticity

Q: What makes a muscle cell respond to a neural signal?

A: Excitability — the ability to detect and react to stimuli

Q: What is the sarcolemma and what does it do?

A: The sarcolemma is the cell membrane of a muscle fiber; it transmits action potentials and surrounds the fiber.

Q: What is a sarcomere, and what are its parts?

• Sarcomere = basic unit of contraction

• Contains:
  • Z lines (ends)
  • A band (dark, thick + thin overlap)
  • I band (light, only thin)
  • H zone (only thick)
  • Actin (thin) & Myosin (thick)

Q: What do myosin heads do during contraction?

A: They bind to actin, pull it toward the center, and use ATP (adenosine triphosphate) to power the movement.

Q: What is the sliding filament mechanism?

A: It's how actin and myosin slide past each other, shortening the sarcomere and causing the muscle to contract.

Q: What role do myosin heads play in contraction?

A: They bind to actin, pull it inward (power stroke), release, and reset using ATP.

Q: How does sarcomere shortening lead to muscle contraction?

A: As sarcomeres shorten, the entire myofibril shortens, which causes the whole muscle fiber to contract.

Q: What’s the first step in triggering an action potential in a muscle cell?

A: A motor neuron releases ACh (acetylcholine) into the synaptic cleft at the neuromuscular junction.

Q: What happens after ACh binds to receptors on the sarcolemma?

A: Na⁺ channels open, causing influx of sodium → leads to depolarization (end plate potential).

Q: What causes the action potential to fire and spread?

A: If threshold is reached, voltage-gated Na⁺ channels open, and the action potential travels across the sarcolemma and into T-tubules.

Q: What is a ligand-gated channel?

A: Opens when a chemical (like ACh) binds to it.
🧠 Example: ACh binding to open Na⁺ channels at the NMJ.

Q: What is a voltage-gated channel?

the channel opens when the charge (voltage) changes.

🧠 Example: Na⁺ channels opening when depolarization reaches threshold.

Q: What is a motor unit?

A: A motor neuron and all the muscle fibers it controls.

Q: What are the 3 main parts of the neuromuscular junction (NMJ)?

• Axon terminal (releases ACh)

• Synaptic cleft (space between neuron & muscle)

• Sarcolemma of the muscle cell (has ACh receptors)

Q: What is the neurotransmitter at the NMJ and what does it do?

A: Acetylcholine (ACh) – it binds to receptors on the sarcolemma to start muscle contraction.

Q: What’s the first step in starting a skeletal muscle contraction?

A: A motor neuron releases ACh, which binds to receptors on the sarcolemma and triggers an action potential.

What is action potential?

A rapid sequence of changes in the voltage across a membrane.

Q: What happens after the action potential reaches the T-tubules?

A: It causes the sarcoplasmic reticulum to release Ca²⁺ (calcium) into the muscle cell.

Q: What happens when calcium is released into the cell?

A: Calcium binds to troponin, shifting tropomyosin and exposing actin sites so myosin can bind and contraction can begin.

Q: What is muscle tension at the fiber level?

A: It’s the force a single muscle fiber produces when stimulated — depends on sarcomere length, cross-bridges, and stimulation frequency.

Q: What is muscle tension at the organ level?

A: The combined force of many motor units contracting in a whole muscle — affected by recruitment and motor unit size.

Q: What increases tension at the organ level?

A: Recruitment (activating more motor units) and stronger neural signals increase total muscle force.

Q: What is ATP used for in muscle contraction?

• Energizes myosin heads

• Breaks cross-bridges

• Pumps Ca²⁺ back into the Sarcoplasmic reticulum

Q: What causes muscular fatigue?

• Low ATP, ion imbalance, or build-up of byproducts like lactic acid that reduce contraction ability

Q: What happens during the recovery period?

• ATP is replenished, lactic acid is cleared, and ion levels reset so muscle can contract normally again

Q: Is smooth muscle voluntary or involuntary? How does it contract differently than skeletal?

A: Smooth muscle is involuntary and slower, but it can sustain contractions longer without fatigue.

Q: What triggers smooth muscle contraction?

A: Calcium still triggers it, but it binds to calmodulin, not troponin like in skeletal muscle.

Q: Where do contractions happen in smooth vs. skeletal muscle?

A:

• Skeletal: sarcomeres arranged in striations

• Smooth: no striations — filaments are scattered, causing a twisting motion when it contracts

Q: Where are smooth and cardiac muscle found?

• Smooth: Walls of hollow organs (e.g. intestines, blood vessels)

• Cardiac: Heart only ❤

Q: What’s the structure of smooth vs. cardiac muscle?

• Smooth: Spindle-shaped, one nucleus, no striations

• Cardiac: Branched, striated, one nucleus, intercalated discs

Q: What are their main functions?

• Smooth: Moves materials (digestion, blood flow)

• Cardiac: Pumps blood throughout the body