Muscle & Neural Physiology & Bioenergetics: Key Concepts and Systems

What are myofibrils composed of?

Myofibrils are composed of repeating contractile units called sarcomeres.

During prolonged, moderate-intensity exercise, the body increasingly relies on:

A) Fat

The primary function of an enzyme is to:

C) Lower the activation energy and facilitate breakdown (catabolism)

How many ATP are produced directly (substrate-level) in glycolysis from one glucose?

B) 2 ATP (net)

The immediate source of energy to re-synthesize ATP during the first few seconds of intense exercise is:

C) Phosphocreatine (PCr)

What does the AV node delay allow?

The AV node delay allows the atria to contract before the ventricles.

What effect does parasympathetic stimulation have on heart rate?

Parasympathetic stimulation causes a decreased heart rate.

What effect does sympathetic stimulation have on heart rate?

Sympathetic stimulation causes increased heart rate and increased contractility.

What does Q̇ represent in the Fick equation?

In the Fick equation, Q̇ represents the function of the cardiovascular system.

What does the (a - v̄ )O₂ difference represent in the Fick equation?

It represents how much oxygen the muscles extract from the blood.

What is the primary chemical stimulus that drives ventilation during exercise?

Increased carbon dioxide (hypercapnia) and decreased pH.

According to the Fick equation, what is the primary factor responsible for the increase in VO₂max with training?

Increased (a - v̄ )O₂ difference.

What is NOT a reason for increased blood flow to active muscle with training?

Decreased total blood volume.

What is the 'interference effect' in concurrent training?

Endurance training blunting strength gains when performed concurrently.

Which type of training is NOT negatively affected by concurrent training?

Neither strength nor endurance gains are negatively affected.

What does the central nervous system (CNS) consist of?

The CNS consists of the brain and spinal cord.

What does the peripheral nervous system (PNS) include?

The PNS includes all nerves outside the brain and spinal cord.

Which division of the PNS carries sensory information toward the CNS?

The afferent (sensory) division carries sensory information toward the CNS.

Which division of the PNS carries motor commands away from the CNS to skeletal muscle?

The somatic motor division carries motor commands away from the CNS to skeletal muscle.

What is the correct order of events in excitation-contraction coupling?

The correct order is: Action potential → ACh release → Ca²⁺ release → cross-bridge formation.

What triggers the release of acetylcholine (ACh) from the motor neuron?

An action potential arriving at the axon terminal triggers the release of ACh.

Where does acetylcholine bind to initiate depolarization of the muscle fiber?

ACh binds to motor end-plate receptors on the plasmalemma to initiate depolarization.

After ACh binding, where does the action potential travel next?

The action potential travels down the T-tubules after ACh binding.

What event directly triggers the release of calcium from the sarcoplasmic reticulum?

An action potential traveling down the T-tubules directly triggers the release of calcium from the sarcoplasmic reticulum.

Calcium released from the sarcoplasmic reticulum binds to which protein?

Calcium binds to troponin.

When calcium binds to troponin, what happens next?

Tropomyosin moves off the myosin-binding site on actin.

What is formed when myosin binds to actin during contraction?

A cross-bridge is formed when myosin binds to actin during contraction.

According to the sliding filament theory, during contraction:

Filaments slide past each other as myosin pulls actin toward the center.

What condition must occur for muscle contraction to end?

Action potentials must stop arriving at the neuromuscular junction for muscle contraction to end.

When action potentials stop, what happens to calcium?

Calcium is actively pumped back into the sarcoplasmic reticulum.

The reuptake of calcium into the SR requires:

The reuptake of calcium into the SR requires ATP (active transport).

What happens to troponin and tropomyosin when calcium is removed from the sarcoplasm?

Troponin and tropomyosin return to resting conformation, covering the myosin-binding site.

Which of the following would stop cross-bridges from forming?

Tropomyosin covering the myosin-binding site on actin would stop cross-bridges from forming.

What is the gap between two neurons where communication occurs called?

The gap is called the synapse.

The neuron that releases neurotransmitters is called the:

The neuron that releases neurotransmitters is called the presynaptic neuron.

What is the primary neurotransmitter for motor neurons that innervate skeletal muscle?

The primary neurotransmitter is acetylcholine (ACh).

What is the primary neurotransmitter for most sympathetic neurons?

The primary neurotransmitter for most sympathetic neurons is norepinephrine.

What does an excitatory postsynaptic potential (EPSP) cause?

An EPSP causes depolarization of the postsynaptic membrane.

What does an inhibitory postsynaptic potential (IPSP) cause?

An IPSP causes hyperpolarization of the postsynaptic membrane.

What does a motor unit consist of?

A motor unit consists of one alpha motor neuron and all the muscle fibers it innervates.

Which motor unit would produce the finest control (least force)?

A motor unit with a small neuron innervating <300 fibers would produce the finest control.

According to the Size Principle, which motor units are recruited FIRST?

Type I motor units (smallest) are recruited first.

According to the Size Principle, which motor units are recruited LAST during maximal force production?

Type IIx (largest) motor units are recruited last.

What is a myelin sheath primarily composed of?

A myelin sheath is primarily composed of lipid-rich insulating layers from Schwann cells.

What is the primary function of myelin sheaths?

The primary function of myelin sheaths is to increase the speed of nerve impulse conduction.

What is the process by which an action potential 'jumps' from one Node of Ranvier to the next called?

The process is called saltatory conduction.

Which type of nerve fiber has the FASTEST conduction velocity?

Large myelinated alpha motor nerves have the fastest conduction velocity.

What is the resting membrane potential (RMP) of a neuron approximately?

The resting membrane potential (RMP) of a neuron is approximately -70 mV.

At rest, the inside of a neuron is __________ relative to the outside.

At rest, the inside of a neuron is negatively charged relative to the outside.

The resting membrane potential is primarily maintained by:

The resting membrane potential is primarily maintained by the sodium-potassium pump (3 Na⁺ out, 2 K⁺ in).

What does the sodium-potassium pump transport?

The sodium-potassium pump transports 3 Na⁺ out and 2 K⁺ in.

At rest, the cell membrane is most permeable to which ion?

At rest, the cell membrane is most permeable to potassium (K⁺).

What occurs during depolarization?

Depolarization occurs when the inside of a neuron becomes less negative (e.g., -60 mV).

What is hyperpolarization?

Hyperpolarization occurs when the inside of a neuron becomes more negative, such as -80 mV.

How do graded potentials differ from action potentials?

Graded potentials are localized and vary in strength, while action potentials are all-or-none events that travel long distances down the axon.

How do action potentials differ from graded potentials?

Action potentials are all-or-none and travel the full length of the axon, while graded potentials decrease in strength over distance.

What does the all-or-none principle state?

The all-or-none principle states that once threshold is reached, an action potential fires at maximum strength.

What happens if a stimulus depolarizes the neuron to threshold?

A full-strength action potential occurs.

What happens if a stimulus does NOT reach threshold?

No action potential occurs.

What is the neuromuscular junction?

The neuromuscular junction is the site where an alpha motor neuron communicates with a muscle fiber.

Where is acetylcholine released at the neuromuscular junction?

Acetylcholine is released from the presynaptic axon terminal.

Where does acetylcholine bind?

Acetylcholine binds to receptors on the motor end-plate (plasmalemma of the muscle fiber).

Why does muscle contraction require ATP?

Muscle contraction requires ATP for myosin head power stroke, detachment of myosin from actin, and calcium reuptake into the sarcoplasmic reticulum.

What provides the energy for the myosin head to pull actin during the power stroke?

The hydrolysis of ATP (ATP → ADP + Pᵢ) provides the energy.

What allows myosin to detach from actin after the power stroke?

A new ATP molecule binding to myosin allows detachment.

How is calcium pumped back into the sarcoplasmic reticulum?

Calcium is pumped back into the SR using energy from ATP hydrolysis.

What are muscle spindles sensitive to?

Muscle spindles are sensitive to muscle length and the rate of change of length.

Where are Golgi tendon organs located?

Golgi tendon organs are located in the tendon, proximal to the muscle-tendon attachment.

What are Golgi tendon organs sensitive to?

Golgi tendon organs are sensitive to changes in muscle tension (force).

What happens when a muscle spindle is stretched?

It triggers reflexive contraction of the stretched muscle to resist further stretching.

What happens when a Golgi tendon organ detects excessive tension?

It inhibits the contracting (agonist) muscle and excites the antagonist.

What is the force-velocity relationship for concentric contractions?

Maximal force decreases as contraction velocity increases.

What is the force-velocity relationship for eccentric contractions?

Maximal force increases at higher speeds.

Which type of contraction produces the greatest force at the same absolute velocity?

Eccentric contractions produce the greatest force.

What connective tissue layer surrounds the entire muscle?

The epimysium surrounds the entire muscle.

What connective tissue layer surrounds individual fascicles?

The perimysium surrounds individual fascicles.

What connective tissue layer surrounds individual muscle fibers?

The endomysium surrounds individual muscle fibers.

What is the primary function of the sarcoplasmic reticulum?

The sarcoplasmic reticulum primarily functions to store and release calcium ions (Ca²⁺).

What are T-tubules extensions of?

T-tubules are extensions of the plasmalemma (sarcolemma).

What is the primary function of T-tubules?

The primary function of T-tubules is to carry the action potential deep into the muscle fiber.

What role does actin play in muscle contraction?

Actin is part of the thin filament and interacts with myosin during contraction.

What role does myosin play in muscle contraction?

Myosin is part of the thick filament and has globular heads that bind to actin and pull during contraction.

What is the function of titan in muscle fibers?

Titan acts as a spring, stabilizes the sarcomere, and prevents overstretching.

What protein covers the myosin-binding site on actin at rest?

Tropomyosin covers the myosin-binding site on actin at rest.

Which protein binds calcium during excitation-contraction coupling?

Troponin binds calcium during excitation-contraction coupling.

What happens to tropomyosin when calcium binds to troponin?

Tropomyosin moves off the myosin-binding site on actin.

What is the position of tropomyosin in a relaxed muscle?

In a relaxed muscle, tropomyosin is positioned to block the myosin-binding site on actin.

What is beta-oxidation?

Beta-oxidation refers to the breakdown of free fatty acids into acetyl-CoA.

Where does beta-oxidation occur?

Beta-oxidation occurs in the mitochondria.

Does beta-oxidation require oxygen?

Yes, beta-oxidation requires oxygen (aerobic).

Which energy system can sustain maximal intensity exercise for the LONGEST duration?

C) Oxidative system (aerobic)

The ATP-PCr system can sustain maximal exercise for approximately:

A) 3-15 seconds

The glycolytic (anaerobic) system can sustain high-intensity exercise for approximately:

B) 15 seconds to 2 minutes

The oxidative (aerobic) system can sustain exercise for:

C) Hours

Which energy system produces the MOST ATP per molecule of substrate?

C) Oxidative system (aerobic)

Which energy system produces ATP at the FASTEST rate?

A) ATP-PCr system

At rest, the typical fuel mixture is approximately:

C) 50% carbohydrate, 50% fat

During low-intensity exercise, the body primarily uses:

A) More fat, some carbohydrate

During high-intensity exercise, the preferred fuel source is:

B) Carbohydrate (glycogen/glucose)

The major fuel source for the brain is:

B) Glucose