Membrane Potential and Muscle Activation

Membrane Potential

The membrane potential is the electrical difference across the cell membrane, crucial for muscle and nerve cell function.

• Depolarization: Stimulus causes depolarization, making the inside of the cell less negative.

• Threshold: When reached, Na+ enters the cell, initiating an action potential.

• Repolarization: K+ leaves via channels, restoring the resting state.

• Na/K Pump: Restores ions to resting state using ATP.

Hyperpolarization

Hyperpolarization occurs when the membrane potential becomes more negative, making it harder for the cell to reach threshold and fire an action potential.

• Threshold decreases: Easier to reach (depolarization).

• Threshold increases: Harder to reach (hyperpolarization).

Muscle Contraction and Synaptic Transmission

Synapse and Signal Transmission

Muscle contraction is initiated by electrical signals transmitted across synapses.

• Na+ Depolarization: Converts electrical signal into chemical signal, then back to electrical after crossing synaptic cleft.

• T-tubules: Transmit signals deep into muscle fibers.

• Ca2+ Release: Triggers muscle contraction by binding to troponin, moving tropomyosin, and exposing actin sites.

• ATP: Required for myosin head movement and muscle contraction.

• Relaxation: Ca2+ pumped out, stopping contraction.

Action Potential and Muscle Fiber Types

Action potentials trigger muscle contraction and vary between muscle fiber types.

• Type I Fibers: Endurance, slow-twitch, use oxygen, contract slowly, resist fatigue.

• Type II Fibers: Fast-twitch, use glycogen, contract quickly, fatigue faster.

EMG (Electromyography)

EMG measures electrical activity in muscles, indicating muscle activation and fatigue.

• Electrical activity: Indicates muscle contraction.

Proprioception and Joint Receptors

Joint Receptors

Joint receptors provide feedback about joint position and movement.

• Pacinian Capsule: Detects joint rotation.

• Golgi-type Capsule: Senses tension and relaxation from stretch.

Proprioceptors

Proprioceptors detect changes in muscle length and tension.

• Muscle Spindles: Detect rate of stretch, cause contraction from a stretch.

• Golgi Tendon Organs (GTOs): Respond to tension, relax muscle when overstimulated.

Excitatory and Inhibitory Potentials

EPSP vs IPSP

Excitatory and inhibitory postsynaptic potentials regulate neuron firing.

• EPSP (Excitatory): Increases likelihood of neuron firing.

• IPSP (Inhibitory): Decreases likelihood of neuron firing.

• Interaction: EPSPs and IPSPs sum to determine if threshold is reached.

Muscle Adaptation and Hypertrophy

Strength and Endurance Adaptations

Muscle adapts to training through hypertrophy and increased strength.

• Strength Hypertrophy: Neural adaptations occur first, followed by increased motor unit recruitment and synchronization.

• Endurance Training: Increases ribosome number, elevates protein synthesis, stimulates glucose uptake, and mitochondrial biogenesis.

Muscle Damage and Repair

Muscle damage promotes recovery and repair, increasing IGF secretion and inflammatory response.

• Inflammatory response: Promotes recovery and repair.

• IGF secretion: Stimulates muscle growth.

Hormonal Regulation

Hormones play a key role in muscle hypertrophy.

• Testosterone: Anabolic hormone, increases protein synthesis.

• Estrogen: Anabolic hormone, supports muscle growth.

• Growth Hormone: Stimulates release of IGFs, increases protein synthesis.

Cardiovascular Physiology

Heart Waveforms

Electrocardiogram (ECG) waveforms represent electrical activity of the heart.

• P wave: Atrial depolarization.

• QRS complex: Ventricular depolarization.

• T wave: Ventricular repolarization.

Cardiac Cycle

The cardiac cycle consists of systole and diastole, describing heart contraction and relaxation.

• Systole: Pumping blood out, ~1/3 of cardiac cycle.

• Diastole: Heart relaxes and fills with blood, ~2/3 of cardiac cycle.

• Isovolumic Contraction: No volume change, pressure increases.

Preload and Afterload

Preload and afterload are key determinants of cardiac output.

• Preload: Initial stretching of cardiac myocytes prior to contraction.

• Afterload: Pressure in aorta holding the aortic valve closed.

Frank-Starling Mechanism

The Frank-Starling law states that increased filling of the heart increases contractility and output.

• Increased filling: Stretches fibers, increases tension, increases contractility.

Cardiovascular Control

Cardiovascular control centers regulate blood pressure and heart rate.

• Pressor area: Increases blood pressure.

• Depressor area: Decreases blood pressure.

• Baroreceptor Reflex: Recognizes changes in blood pressure, sends signals to sympathetic and parasympathetic centers.

Heart Rate Variability (HRV)

HRV measures variability between heartbeats, indicating autonomic nervous system activity.

• Reduced HRV: Indicates low parasympathetic activity.

• RMS: Vagus nerve modulates HR on a beat-to-beat basis.

Poiseuille's Equation

Poiseuille's equation describes the flow of fluid through a vessel:

• F: Flow

• P1, P2: Pressure 1 and 2

• r: Radius

• L: Length

• N: Viscosity of fluid

Stroke Volume (SV) and Ejection Fraction

Stroke volume is the amount of blood ejected from the left ventricle per beat.

• SV: Volume of left ventricle

• EDV: End diastolic volume

• ESV: End systolic volume

• Ejection Fraction:

Summary Table: Muscle Fiber Types

Additional info:

• Some context and definitions have been expanded for clarity and completeness.

• Scientific terms have been italicized where relevant.

• Tables and equations have been formatted for academic study purposes.