LJM TBL 3 - Skeletal Muscle, Muscular Control and Movement

What are the three main energy systems in muscle contraction?

Phosphocreatine system, anaerobic glycolysis, and aerobic metabolism

Which energy system provides ATP most rapidly?

Phosphocreatine system

Which energy system is primarily used during prolonged exercise?

Aerobic metabolism

What is the role of creatine kinase in muscle metabolism?

It catalyzes the conversion of phosphocreatine to ATP

What is a key by-product of anaerobic glycolysis?

Lactate

What is the end product of aerobic metabolism of glucose?

Carbon dioxide and water

What type of muscle contraction occurs without change in muscle length?

Isometric contraction

During which type of contraction does the muscle lengthen while generating force?

Eccentric contraction

What is the primary contraction type during the upward phase of a bicep curl?

Concentric contraction

What role does the agonist muscle play in movement?

It initiates and produces the primary movement

What is the role of the antagonist muscle during movement?

It opposes the action of the agonist

Which muscle stabilizes a joint to allow movement by another muscle?

Fixator

What is the role of a synergist in movement?

It assists the agonist by adding force or reducing unnecessary motion

What genetic mutation causes Duchenne muscular dystrophy?

Mutation in the dystrophin gene

What protein is absent in Duchenne muscular dystrophy?

Dystrophin

What is the difference between Duchenne and Becker muscular dystrophy?

Becker has partially functional dystrophin; Duchenne lacks it entirely

Which disorder is caused by a deficiency of muscle glycogen phosphorylase?

McArdle disease

What is the hallmark symptom of McArdle disease?

Exercise intolerance with risk of muscle damage

Which hereditary myopathy presents with delayed muscle relaxation?

Myotonic dystrophy

What causes calcium release from the sarcoplasmic reticulum?

Activation of ryanodine receptors by DHP receptors

What binds calcium to initiate muscle contraction?

Troponin

What prevents actin-myosin interaction in resting muscle?

Tropomyosin

What is the function of the sarcoplasmic reticulum in muscle?

Stores and releases calcium ions

What structure conducts the action potential deep into the muscle fibre?

Transverse (T-) tubules

What happens during the latent phase of a muscle twitch?

Calcium is released, but no contraction has started yet

What is a fused tetanus?

Sustained contraction with no relaxation due to high-frequency stimulation

What is a motor unit?

A motor neuron and all the muscle fibres it innervates

What determines the strength of a muscle contraction?

Number of motor units recruited and frequency of stimulation

Which reflex maintains muscle length during stretch?

Stretch reflex

Which receptor detects muscle stretch?

Muscle spindle

What is the function of the Golgi tendon organ?

It inhibits contraction when muscle tension is too high

Which reflex withdraws a limb from a painful stimulus?

Flexor withdrawal reflex

What reflex supports the body when the opposite limb withdraws?

Crossed extensor reflex

Which fibre type is slow, oxidative, and fatigue-resistant?

Type I

Which muscle fibre type is fast and glycolytic?

Type IIb

Which fibre type is both oxidative and glycolytic?

Type IIa

Which fibre type predominates in postural muscles?

Type I

Which fibre type is most affected by inactivity?

Type II

What is sarcopenia?

Age-related loss of muscle mass and strength

How does endurance training affect muscle fibres?

Increases mitochondrial density and capillarity

How does resistance training affect muscle?

Induces hypertrophy and increases force production

What is the mechanical definition of torque?

Force multiplied by the moment arm

What is mechanical work in muscles?

Force times displacement

How is mechanical power calculated?

Work divided by time

Which type of contraction produces the most force?

Eccentric contraction

What happens to sarcomeres during contraction?

Z-lines move closer together, and H-zone shortens

What protein provides elasticity in the sarcomere?

Titin

What is the function of dystrophin?

Links the cytoskeleton to the extracellular matrix

What is the role of actin in muscle contraction?

Serves as the track for myosin crossbridges

What does myosin do during contraction?

Forms crossbridges and pulls actin filaments

What is the function of the neuromuscular junction?

Transmits signals from nerve to muscle

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine

What enzyme breaks down acetylcholine?

Acetylcholinesterase

What causes depolarization of the muscle membrane?

Binding of acetylcholine to nicotinic receptors

What is the size principle in motor unit recruitment?

Smaller units are recruited before larger ones

Which motor units are most fatigue-resistant?

Type I units

What change occurs in motor units with ageing?

Loss of motor neurons and larger, less precise units

How does inactivity affect mitochondria in muscle?

Decreases mitochondrial density and oxidative capacity

Which metabolic pathway is used during the first 10 seconds of intense activity?

Phosphocreatine system

Which metabolic pathway dominates during 1–2 minutes of moderate activity?

Anaerobic glycolysis

Which pathway is most efficient in terms of ATP per molecule of glucose?

Aerobic metabolism

What happens to lactate produced during anaerobic glycolysis?

It is transported to the liver for gluconeogenesis (Cori cycle)

What is the Cori cycle?

The conversion of lactate to glucose in the liver

What is the function of myokinase?

Converts two ADP into one ATP and one AMP

What is oxygen debt?

Extra oxygen consumed post-exercise to restore energy systems

What is the function of ATP in muscle contraction?

Breaks actin-myosin bond and energizes the myosin head

Which phase of a twitch follows peak tension?

Relaxation phase

What is the first step in excitation-contraction coupling?

Action potential travels along the sarcolemma

What links T-tubule depolarization to calcium release?

DHP receptor and RyR1 interaction

What is the role of calcium ATPase in muscle?

Pumps calcium back into the sarcoplasmic reticulum

What is a key adaptation of endurance-trained muscle?

Increased oxidative enzyme activity

What causes the “second wind” in McArdle disease?

Increased blood-borne substrates during mild aerobic activity

What is the role of muscle spindles in reflexes?

Sense stretch and initiate stretch reflex

How does the Golgi tendon reflex protect muscles?

Reduces tension to prevent tendon damage

What is the typical response in the flexor withdrawal reflex?

Flexors activated, extensors inhibited

What is reciprocal inhibition?

Inhibition of antagonistic muscles during reflexes

What happens to Type II fibres with resistance training?

Hypertrophy and increased force capacity

What happens to satellite cells with muscle damage?

They activate, proliferate, and aid repair

What is a defining feature of myotonic dystrophy on EMG?

Myotonic discharges (waxing and waning potentials)

Which disease shows nemaline rods on biopsy?

Nemaline myopathy

What is the genetic cause of myotonic dystrophy?

CTG trinucleotide repeat expansion

What triggers calcium release during contraction?

Depolarization of the T-tubule activating RyR1

Which contraction type is used to lower a weight slowly?

Eccentric

Which muscle role is active in decelerating a limb?

Antagonist

What does the moment arm determine?

The leverage and torque produced at a joint

What is an example of an isometric exercise?

Holding a plank position

How is power affected by both force and velocity?

Increased force and velocity increase power

What happens to muscle capillaries with inactivity?

Their density decreases

Which metabolic pathway requires oxygen?

Aerobic respiration

What adaptation allows muscles to store more phosphocreatine?

Repeated high-intensity training

What is the consequence of sarcomere over-stretching?

Reduced crossbridge formation and force

What happens to H-zone during full contraction?

It disappears as actin overlaps fully with myosin

What is the force–velocity relationship in muscle?

As velocity increases, force decreases in concentric contraction

What is the physiological role of titin?

Provides passive tension and centers myosin in the sarcomere

Which type of work occurs during concentric contraction?

Positive mechanical work

Which type of contraction allows most force with lowest energy?

Eccentric

What happens during the relaxation phase of a twitch?

Calcium is pumped back into the SR

Which ion initiates crossbridge formation?

Calcium

What determines how quickly a motor unit fatigues?

Fibre type and metabolic properties

Which receptor acts as a voltage sensor in excitation-contraction coupling?

DHP receptor