Unit 1 Neural & Skeletal Muscle Systems

Flashcards covering energy expenditure, neural control of movement, muscle mechanics, and fiber types based on lecture notes.

Calorimetry

Measurement of heat production to estimate energy expenditure.

TDEE

Total Daily Energy Expenditure = $BMR/RMR + \text{Physical Activity} + \text{Thermic Effect of Food } (+ \text{adaptive thermogenesis})$

RMR vs BMR

RMR is measured under less strict conditions; BMR requires overnight fast, complete rest, and a thermoneutral environment. BMR is slightly lower.

Components of TDEE

BMR/RMR $\sim 60–70\%$; Physical Activity $15–30\%$ (most variable); Thermic Effect of Food $\sim 10\%$.

Most variable TDEE component

Physical activity because daily movement and exercise vary greatly.

Macronutrient energy

Carbohydrate = $4\,kcal/g$; Protein = $4\,kcal/g$; Fat = $9\,kcal/g$.

RQ

Respiratory Quotient = $\frac{CO_2}{O_2}$ produced/consumed at the cellular level.

RER

Respiratory Exchange Ratio = $\frac{VCO_2}{VO_2}$ measured at the lungs; estimates fuel use during exercise.

VO2max

Maximum rate of oxygen consumption; best measure of aerobic fitness.

Exercise intensity categories

Light, Moderate, Vigorous, Near-maximal/Maximal.

Scientific intensity measures

$\%VO_2max$, $\!\%VO_2\,reserve$, $\!\%HRmax$, $\!\%HRR$, METs, RPE.

Why HRmax is limited

Large individual variation and does not account for resting HR or fitness.

Primary motor cortex

Initiates voluntary movement.

Primary somatosensory cortex

Processes touch, pain, temperature and proprioception.

Afferent neuron

Sensory neuron carrying information to the CNS.

Efferent neuron

Motor neuron carrying commands from the CNS.

3 neuron types

Sensory, interneuron, and motor.

Functions of nervous system

Sensory input, integration, and motor output.

CNS

Brain and spinal cord; integration and control.

PNS

Cranial/spinal nerves; communication between CNS and body.

Autonomic divisions

Sympathetic (fight/flight) and Parasympathetic (rest/digest).

Resting membrane potential

$\sim -70\,mV$ maintained mainly by $Na^+/K^+$ pump and $K^+$ leak channels.

Action potential steps

Resting $\rightarrow$ Threshold $\rightarrow$ Depolarization ($Na^+$ in) $\rightarrow$ Repolarization ($K^+$ out) $\rightarrow$ Hyperpolarization $\rightarrow$ Return to resting.

All-or-none principle

Once threshold is reached, the action potential occurs completely.

EPSP vs IPSP

EPSP increases chance of AP; IPSP decreases chance.

Proprioception

Awareness of body position and movement.

Muscle spindle

Detects muscle stretch; causes stretch reflex to resist overstretching.

Golgi tendon organ

Detects tendon tension; inhibits contraction to prevent injury.

Motor unit

One motor neuron and all muscle fibers it innervates.

Neuromuscular junction

Synapse between motor neuron and muscle fiber; uses acetylcholine.

Sarcomere

Functional contractile unit between Z-discs.

4 major sarcomere proteins

Actin, Myosin, Troponin, and Tropomyosin.

Sliding filament theory

Actin slides past myosin; filament lengths do not change.

Excitation-contraction coupling

Motor neuron AP $\rightarrow$ ACh release $\rightarrow$ Muscle AP $\rightarrow$ T-tubules $\rightarrow$ SR releases $Ca^{2+} \rightarrow Ca^{2+}$ binds troponin $\rightarrow$ Cross-bridge cycling.

Cross-bridge cycle

Attach $\rightarrow$ Power stroke $\rightarrow$ Detach (ATP binds) $\rightarrow$ Reactivate (ATP hydrolysis).

Muscle relaxation

$Ca^{2+}$ pumped into SR by SERCA $\rightarrow Ca^{2+}$ leaves troponin $\rightarrow$ Tropomyosin blocks actin.

Concentric

Muscle shortens while producing force.

Eccentric

Muscle lengthens while producing force.

Isometric

Force without change in muscle length.

Isotonic

Constant load; includes concentric and eccentric.

Isokinetic

Constant movement speed.

Type I

Slow oxidative; fatigue resistant; aerobic.

Type IIa

Fast oxidative-glycolytic; intermediate.

Type IIx

Fast glycolytic; highest power; fatigues quickly.

Energy systems

ATP-PC ($0–10\,s$), Anaerobic glycolysis ($\sim 10\,s–2\,min$), Aerobic ($>2\,min$).

Muscle arrangements

Fusiform = faster, larger ROM; Pennate = greater force.

Size principle

Motor units recruited from small to large.

Temporal summation

Higher firing frequency increases force.

Spatial summation

More motor units recruited increases force.

Wave summation

Repeated twitches build on each other.

Length-tension relationship

Maximum force at optimal sarcomere length.

Force-velocity

Concentric: force decreases as velocity increases; Eccentric: force increases with lengthening velocity.

Power-velocity

Power highest at moderate force and moderate velocity.

Fatigue

Reduced ability to produce force.

DOMS

Delayed onset muscle soreness, peaks $24–72$ hours after exercise.

Most likely to cause DOMS

Eccentric contractions.

Creatine kinase (CK)

Blood marker of muscle damage.