Neuromuscular Physiology and Exercise Bioenergetics Flashcards

Comprehensive vocabulary study cards covering key terms, structures, and metabolic pathways from Units 1 and 2 on Neuromuscular Physiology and Exercise Bioenergetics.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord that processes sensory information, plans and controls movement, and sends commands to effectors.

Peripheral Nervous System (PNS)

The neural structures outside the brain and spinal cord, divided into sensory (afferent) and motor (efferent) pathways.

Afferent Pathways

Sensory neural pathways that carry information from the periphery toward the central nervous system, such as touch, pain, temperature, and proprioception.

Efferent Pathways

Motor neural pathways that carry commands from the central nervous system to an effector, encompassing the autonomic and somatic nervous systems.

Autonomic Nervous System

A branch of the efferent peripheral nervous system that regulates involuntary physiological functions, consisting of sympathetic and parasympathetic divisions.

Somatic Nervous System

A branch of the efferent peripheral nervous system that controls skeletal muscle for voluntary movement and involuntary control of muscles such as the diaphragm.

Neuromuscular Junction (NMJ)

The chemical synapse formed between a somatic motor neuron axon terminal and a skeletal muscle fiber motor end plate.

Axon Hillock

The initial segment region of a neuron where an action potential is initiated once membrane threshold is reached.

Saltatory Conduction

The rapid mode of action potential propagation along a myelinated axon, where the electrical signal regenerates at the nodes of Ranvier.

Multiple Sclerosis

A neurological condition that damages myelin in neurons, impairing signal conduction and producing symptoms such as ataxia, loss of coordination, and muscle weakness.

Amyotrophic Lateral Sclerosis (ALS)

A neurodegenerative disease characterized by progressive degeneration of upper and lower motor neurons, causing loss of voluntary muscle control, speech, swallowing, and breathing.

Small vs Large Motor Units

Small motor units innervate fewer fibers with smaller motor neurons for fine, precise movements, whereas large motor units innervate more fibers with larger motor neurons for gross, high-force movements.

Size Principle

The physiological principle stating that smaller, lower-threshold motor units are recruited prior to larger, higher-threshold motor units as muscle force demand increases.

Rate Coding

The mechanism of increasing muscle force output by increasing the firing frequency of active motor neurons.

Epimysium

The connective tissue layer that surrounds the entire skeletal muscle and helps define its volume.

Perimysium

The connective tissue layer that surrounds groups of muscle fibers, organizing them into fascicles.

Endomysium

The connective tissue layer surrounding individual muscle fibers, containing blood vessels, capillaries, nerves, and satellite cells.

SERCA

Sarcoplasmic reticulum $\text{Ca}^{2+}$-ATPase, an ATP-dependent pump responsible for sequestering cytosolic calcium back into the sarcoplasmic reticulum to allow muscle relaxation.

Transverse Tubules (T-tubules)

Membranous invaginations of the sarcolemma that conduct action potentials into the interior of the muscle fiber to trigger calcium release from the sarcoplasmic reticulum.

Ryanodine Receptors (RYR)

Calcium-release channels located in the sarcoplasmic reticulum membrane that open in response to DHP receptor activation during excitation-contraction coupling.

Sarcomere

The fundamental contractile unit of a muscle fiber, delimited between Z lines and composed of thick and thin myofilaments.

Tropomyosin

A regulatory protein residing in the groove of actin filaments that physically covers myosin-binding sites when the muscle is at rest.

Troponin

A regulatory protein complex attached to actin and tropomyosin that has a strong affinity for calcium ions and shifts tropomyosin away from active sites upon binding calcium.

Titin

A structural protein in the sarcomere that anchors and centers the thick filament between Z lines while contributing to passive elastic tension.

Type 1 Muscle Fiber

A slow-twitch, slow oxidative muscle fiber featuring high oxidative capacity, high fatigue resistance, slow contraction speed, and smaller motor-neuron size.

Type 2A Muscle Fiber

A fast oxidative-glycolytic muscle fiber characterized by fast contraction speed, high glycolytic capacity, moderately high oxidative capacity, and moderate fatigue resistance.

Type 2X Muscle Fiber

A fast glycolytic muscle fiber characterized by fast contraction speed, highest glycolytic capacity, low oxidative capacity, and low fatigue resistance.

Hybrid Muscle Fiber

A muscle fiber expressing multiple myosin heavy-chain (MHC) isoforms, such as MHC 1/2A or MHC 2A/2X, commonly found in untrained or aging individuals.

Muscle Hypertrophy

An increase in muscle-fiber cross-sectional area resulting from an accumulation of contractile proteins, myofibrils, and structural elements.

mTOR

A central intracellular protein kinase regulating muscle protein synthesis by integrating mechanical overload, anabolic hormones, and amino acid availability.

Satellite Cells

Muscle-resident stem cells located between the basal lamina and sarcolemma that activate, proliferate, differentiate, and fuse to repair damaged muscle fibers or donate nuclei during growth.

Myostatin

A secreted protein that functions as a negative regulator of muscle growth, inhibiting muscle hypertrophy.

Concentric Contraction

An isotonic muscle contraction in which the muscle shortens while developing force.

Eccentric Contraction

An isotonic muscle contraction in which the muscle lengthens while developing force.

Isometric Contraction

A muscle contraction in which force is generated without a change in overall muscle length.

Isokinetic Contraction

A muscle contraction performed at a constant angular velocity while muscle length changes.

Delayed-Onset Muscle Soreness (DOMS)

Muscle pain and soreness appearing 1–2 days after unfamiliar or eccentric-heavy exercise, caused by structural micro-damage and inflammation rather than lingering lactate.

Phosphagen System

An immediate anaerobic energy system relying on stored ATP and phosphocreatine (PCr) to resynthesize ATP rapidly during short-duration, maximal efforts.

Creatine Kinase Reaction

The reversible enzymatic reaction $\text{PCr} + \text{ADP} + \text{H}^+ \rightleftharpoons \text{ATP} + \text{creatine}$ that buffers ATP levels during rapid increases in energy demand.

Glucose Transporters (GLUTs)

Membrane proteins responsible for facilitating cellular glucose uptake, including GLUT1, GLUT2, GLUT3, and the contraction/insulin-responsive GLUT4.

Phosphofructokinase (PFK)

The key rate-limiting enzyme of glycolysis, stimulated by AMP and ADP and inhibited by ATP and citrate.

Glycogen Phosphorylase

The rate-limiting enzyme of glycogenolysis that breaks down glycogen into glucose-6-phosphate, activated by inorganic phosphate, AMP, calcium, and epinephrine.

Lactate Dehydrogenase (LDH)

The enzyme catalyzing the reversible reaction $\text{pyruvate} + \text{NADH} + \text{H}^+ \rightleftharpoons \text{lactate} + \text{NAD}^+$, maintaining glycolysis during high-intensity conditions.

Monocarboxylate Transporters (MCTs)

Membrane transport proteins that mediate the cell-to-cell movement of lactate and pyruvate across skeletal muscle, cardiac tissue, neurons, and liver.

Cori Cycle

A metabolic pathway in which lactate produced by skeletal muscle travels through the blood to the liver, where it is converted to glucose via gluconeogenesis.

Lactate Threshold

The lowest workload or exercise intensity during incremental exercise at which arterial blood lactate concentration begins to rise noticeably above baseline.

Pyruvate Dehydrogenase (PDH)

The mitochondrial enzyme complex that converts pyruvate to acetyl-CoA, releasing $\text{CO}_2$ and producing NADH to link glycolysis to the citric acid cycle.

Carnitine Shuttle

The transport system comprising CPT I and CPT II that translocates long-chain fatty acyl-CoA molecules across the inner mitochondrial membrane into the matrix.

Beta-Oxidation

A mitochondrial pathway that sequentially cleaves two-carbon acetyl-CoA units from fatty acyl-CoA chains, generating NADH and $\text{FADH}_2$.

Crossover Concept

The physiological framework describing the shift from fat oxidation to predominant carbohydrate oxidation as exercise intensity increases.

Critical Power

The highest power output or metabolic rate that can be maintained without a continuous, progressive fall in power output.