Autonomic Nervous System and Reflexes

• The autonomic nerve system controls the four 'F's': fight, flight, feeding, and fucking
• Autonomic reflexes regulate involuntary physiological functions like heart rate, digestion, and blood pressure
• These reflexes occur at different levels of the nervous system:

Reflex Control Operation

• Sensory receptors detect changes in internal conditions
• Signals travel via afferent neurons to integration centers.
• Integration centers include the ganglion, spinal cord, brainstem, and higher centers.
• Responses are relayed via sympathetic or parasympathetic pathways to effector organs.
• Brain regions, including the brain stem, integrate sensory inputs from diverse sources to produce a coordinated output
• The brain regions influence the sympathetic and parasympathetic systems in tandem

Parasympathetic and Sympathetic Systems

• The parasympathetic system dominates during rest
• The sympathetic system dominates during fight or flight
• The parasympathetic system carries visceral senses like distension or blood chemistry
• The sympathetic system carries a pain sense
• The parasympathetic and sympathetic systems tend to work in opposition, like a brake and an accelerator
• The enteric system is autonomous for 100,000,000 neurons controlling gut motility and secretion
• Sensory inputs mainly come from autonomic and visceral afferents located in innervated tissue, traveling in the same nerve as efferents
• Higher centers integrate inputs from broader regions
• Somatic inputs are integrated to provide fast or predictive responses

Anatomical Organization of Sympathetic and Parasympathetic Systems

Efferent Autonomic Nervous System:

• Composed of: Central nervous system, peripheral ganglion, and target cell
• Consists of : Preganglionic neuron and postganglionic neuron
• The sympathetic system includes the sympathetic chain
• The parasympathetic system works on a collateral ganglion model

Sympathetic Chain Organization

• Autonomic neurons form synapses on target organs, exerting strong effects by acting on multiple release sites
• The synaptic cleft is wider at somatic synapses
• The autonomic synapse works like the neuromuscular junction

Neurotransmitters and Receptors:

• The parasympathetic system uses acetylcholine as its neurotransmitter, and relies on nicotinic and muscarinic receptors
• The sympathetic system uses acetylcholine, norepinephrine, and epinephrine; it relies on nicotinic and adrenergic receptors

Autonomic Nervous System Effects on Organs

• Heart: Parasympathetic decreases heart rate and conduction velocity; sympathetic increases heart rate and conduction velocity
• Lungs: Parasympathetic causes bronchial muscle contraction and stimulates bronchial gland secretion; sympathetic causes relaxation and inhibits secretion
• Digestive Tract: Parasympathetic increases motility and secretions and relaxes sphincters; sympathetic decreases motility, inhibits secretions, and contracts sphincters
• Urinary Bladder: Parasympathetic causes bladder wall contraction and sphincter relaxation; sympathetic causes bladder wall relaxation and sphincter contraction
• Male Reproductive Tract: Parasympathetic causes vasodilation for erection; sympathetic causes ejaculation
• Female Reproductive Tract: Parasympathetic effects are unknown; sympathetic causes relaxation in nonpregnant uterus and contraction in pregnant uterus
• Skin: Parasympathetic stimulates sweat gland secretion; sympathetic stimulates secretion and piloerector muscle contraction (hairs stand up)
• Eye: Parasympathetic constricts the circular muscle (pupillary constriction) and contracts ciliary muscles for near vision; sympathetic contracts the radial muscle (pupillary dilation) and relaxes ciliary muscles for far vision

Blood Pressure Regulation

• Increased sympathetic activity restores blood pressure by increasing peripheral vasoconstriction
• Reduced parasympathetic activity increases heart rate.

Cardiovascular System (CVS)

• The CVS functions to supply O2 and other nutrients and remove CO2 and other waste products
• The heart performs sensory and endocrine functions that regulate blood pressure and volume, and blood vessels regulate blood pressure and distribution
• Blood carries hormones and other substances to the tissue
• The CVS comprises:
  • Heart (muscular pump)
  • Blood vessels (pipes)
  • Blood (the liquid)

Heart Structure:

• Hollow muscular organ enclosed within the pericardium
• Located in the middle of the chest with a broad base at the top and a pointed tip (apex) at the bottom
• Weighs between 250 and 350 grams
• Has two separate pumps: -Right side for pulmonary circulation -Left side for systemic circulation

Path of Blood Flow

• Left ventricle pumps oxygenated blood into the aorta
• Blood becomes deoxygenated in systemic capillaries and returns to the right atrium via the superior and inferior venae cavae.
• Right atrium sends blood through the tricuspid valve into the right ventricle
• Right ventricle pumps deoxygenated blood through the pulmonary valve into the pulmonary arteries
• Blood gets oxygenated in the lungs and returns to the left atrium via the pulmonary veins
• Left atrium sends oxygenated blood through the bicuspid valve into the left ventricle
• Aortic pressure averages 120/80 mmHg (approximately 90mmHg)
  • 120 is systolic pressure
  • 80 is diastolic pressure

Blood Vessels

• Arteries carry oxygenated blood, veins carry deoxygenated blood, except in the pulmonary vessels
• Pulmonary artery pressure is about 15 mmHg
• Valves open and close passively due to pressure differences

Heart Valves

• Atrioventricular valves (tricuspid and bicuspid/mitral) are located between the atria and ventricles, flaps of endocardium anchored to papillary muscles by chordae tendineae
• Semilunar valves (pulmonary and aortic) prevent blood from returning to the ventricles, located in the pulmonary trunk and aorta, and have three cusps

Cardiac Muscle Physiology

• The heart wall has three layers: epicardium, myocardium, and endocardium
• Three types of cardiac muscle: atrial, ventricular, and specialized excitatory and conductive fibers
• Cardiac muscle fibers are excitable and electrically coupled
• Cardiac muscle is striated and arranged in a latticework
• Muscle fibers are made of individual cardiac myocytes
• Intercalated discs are present at the end of cells, containing desmosomes and gap junctions
• Sympathetic nerves excite the heart, increasing heart rate, contraction force, and pumped volume
• Parasympathetic (vagus) nerve lowers heart rate by 40%, contraction force by 20-30%, and pumped volume by 50%

Cardiac Output

• Cardiac output is the quantity of blood pumped into the aorta each minute and is determined by heart rate and stroke volume
  • Stroke volume (volume of blood pumped from each ventricle with each beat) is about 70 mL/beat
  • Cardiac Output = Heart Rate x Stroke Volume

Stroke Volume Determinants

• Preload: Stretching of myocardium prior to contraction
• Afterload: Force opposing myocardial contraction
• Contractility

Distribution of Systemic Blood Flow

Indicator Dilution Technique

• Dye is injected into a vein or right atrium, travels through the heart and into the arterial system
• Monitors dye concentration in peripherial artery over time, forming a dilution curve
• Higher blood flow leads to greater dilution
• CO(ml/min) = (mg of dye injected x 60)/((average dye concentration (mg/ml) x duration (s))

Fick Principle

• Measures cardiac output based on oxygen consumption and the difference in oxygen concentration between arterial and venous blood Steps
• Measure O2 absorbed per minute (200 mL O2/min)
• Determine O2 concentration in venous blood entering the right heart (160 mL/L) and arterial blood leaving the left heart (200 mL/L)
• Calculate the arteriovenous O2 difference: 200 – 160 = 40 mL O per L of blood
• Use the Fick equation: CO = O absorbed per minute (mL/min) / arteriovenous O difference (mL/L) Since total blood volume (TBV) is 5 L, this means the entire blood volume circulates through the body once per minute

Fluid Volume Measurement

• Measured using the indicator dilution technique
• Known amount of an indicator is injected, allowed to mix, and then sampled to determine the concentration V = I/C
  • Where I is the injected indicator amount and C is the final concentration

Indicator Requirments

• Mix quickly and evenly
• Stay within the compartment being measured
• Non toxic
• Not metabolized or excreted

Indicators for Fluid Volume Measurement:

• Plasma volume: 131I-labelled albumin, Evans blue dye
• Extracellular volume: Inulin
• Interstitial fluid volume: Extracellular volume – plasma volume
• Total body water: Tritium (3H2O), Deuterium (2H2O)
• Intracellular volume: Total body water – extracellular volume
• Red cell volume: Radioactive chromium (51Cr)

Blood Circulation

• Heart pumps blood into the arteries
• Arteries carry oxygenated blood away from the heart
• Arterioles regulate blood flow
• Capillaries allow exchange of gases, nutrients, and waste with tissues
• Venules collect deoxygenated blood from capillaries
• Veins return blood to the heart

Blood Vessel Structure and Function

• Blood flow velocity is inversely related to the total cross-sectional area.
• Arteries and veins: Small total cross-sectional area, blood flows faster.
• Capillaries: largest total cross-sectional area (~600 m²), blood flows slowest, allowing for gas, nutrient, and waste exchange.

Blood Volume Distribution

• Systemic veins and venules 60%
• Systemic arteries and arterioles: 15%
• Pulmonary blood vessels: 12%
• Heart: 8%
• Capillaries: 5%

Lymphatic System

• Accessory pathway that returns excess interstitial fluid to the bloodstream (about 3 liters/day)
• Vessels drain into the venous system
• Plays role in immune defense and fat absorption

Action Potentials Conduction System

Sinoatrial (SA) Node

• Located in the right atrium
• The pacemaker cells generate impulses at 70-80 times/min at rest
• Impulses spread through interatrial pathways and internodal pathways to the AV node

Atrioventricular (AV) Node

• Located at the base of the right atrium
• Delays conduction by 100 ms to allow the atria to finish contracting

Atrioventricular Bundle (Bundle of His)

• Conducts impulses through the septum and splits into right and left bundle branches
• Further 40 ms delay ensures ventricular filling

Purkinje Fibers

• Fastest conduction speed (4 m/sec)
• Spreads impulse for coordinated ventricular contraction
• SA node & AV node: 0.05 m/sec (slow for proper delay)
• Atrial & Ventricular muscle: 1 m/sec
• AV bundle (Bundle of His): 1 m/sec
• Purkinje fibers: 4 m/sec (fastest for rapid ventricular activation)

Autorhythmic Rates

• SA node: 70-80 beats/min (sets heart rate)
• AV node: 40-60 beats/min (backup pacemaker)
• Bundle of His/Purkinje fibers: 20-40 beats/min (last resort pacemaker)

Membrane Potentials

• For cells permeable to K+: Equilibrium potential is about -90mV
• For cells permeable to Na+: Equilibrium potential is about +70mV
• For cells permeable to Ca++: Equilibrium potential is about +100mV

Ventricular Action Potential

• Five phases driven by ion movements

Phases

• Phase 0: Rapid Depolarization
  • Fast Na+ channels open, causing a large Na+ influx.
  • K+ permeability decreases
  • Membrane potential rises rapidly to +20 mV
• Phase 1: Early Repolarization
  • Fast Na+ channels inactivate
  • Membrane potential slightly decreases
• Phase 2: Plateau Phase (unique to cardiac muscle)
  • Slow Ca2+ channels open, allowing Ca2+ influx, balancing K+ efflux
  • Prolongs depolarization
• Phase 3: Repolarization
  • K+ channels open, causing K+ efflux
  • Slow Ca2+ channels close, restoring negativity
• Phase 4: Resting Membrane Potential (-90 mV)
  • Steady K+ efflux maintains the resting state

-Refractory role

• Absolute Refractory Period (200-250 ms): No new contraction, due to inactive fast sodium channels
• Relative Refractory Period (50 ms): Heart muscle can contract with a stronger stimulus (some reset sodium channels)
• Pacemaker: Resting Membrane Potential starts at -60 mV and drifts toward -40 mV

Action potential changes

• Decrease in K+ permeability: Closing of K+ channels reduces K+ outflow
• Constant inward Na+ current: Influx of Na+ through funny channels (If)
• Increase in Ca++ permeability: Gradual opening of T-type (transient) Ca++ channels
• L-type (long-lasting) Ca++ channels open

Membrane Potential - Repolarization

• Reversal of Ca++ permeability: the L-type Ca++ channels close
• K+ channels open: Voltage-gated K+ channels causes repolarization
• The SA node controls the cardiac cycle

Pacemaker Potential vs. Ventricular Muscle Potential

Autonomic impact on heart rate

Sympathetic Nervous System (SNS)

• Increased frequency of action potentials causes:
• Increased spontaneous depolarization
• Decreased level of repolarization

Parasympathetic Nervous System (PSNS)

• Decreased frequency of action potentials causes:
• Decreased spontaneous depolarization
• Hyperpolarization of the membrane potential

Electrocardiogram (ECG)

• Non-invasive method to monitor the heart's electrical activity
• Records the electrical impulses in heart muscle and tissues
• Electrodes are placed on the wrists and the left ankle, connected to an earth electrode
• The arrangement of electrodes forms Einthoven's triangle
• The voltage difference is recorded, to create a trace

Wave Interpretations

• P Wave: Atrial depolarization
• QRS Complex: Three waves consisting of ventricular depolarization.
• T Wave: Ventricular repolarization

Intervals in ECGs

• P-R Interval: Time from P wave to QRS complex, showing time from the SA node through AV node and AV bundle.
• A prolonged interval can indicate heart block.
• S-T Segment: Ventricles are fully depolarized.
• Depression can indicate ischemia
• Elevation can indicate infarction
• Q-T Interval: Total time of ventricular depolarization and repolarization.
• The cardiac cycle
• Arrhythmias

Cardiac Cycle

• Four phases that include alternating periods of relaxation and filling (diastole) and contraction and emptying (systole)

Phases

1 - Ventricular Filling and Atrial Contraction (Ventricular Diastole):

• The ventricles are in diastole (relaxed)
• Blood flows back into the atria via the systemic and pulmonary veins
• The AV valves (atrioventricular valves) are open
• Blood passive flows into the ventricles Atria and ventricles are relaxed
• Closed valves: Pulmonary and aortic valves
• atrial contraction occurs and blood is pushes into the ventricles

2 - Isovolumetric Ventricular Contraction (Ventricular Systole):

• Ventricles begin to contract
• Ventricular pressure rises
• Ventricular pressure exceeds atrial pressure
• The AV valves close
• Pulmonary and aortic valves: Semilunar valves are closed
• . Isovolumetric contraction

3 - Ventricular Ejection (Ventricular Systole):

• Blood is ejected into the aorta and pulmonary arteries
• Starts with semilunar valves open

4 - Isovolumetric Ventricular Relaxation (Ventricular Diastole):

• The ventricles relax
• Marks the start of ventricular diastole
• The AV and semilunar valves and pressure increase

Summary of Phases

• Phase 1: Filling and atrial contraction when the atria contracts
• Phase 2: Pressure increase when the ventricles raises pressure
• Phase 3: Ejective blood and volume decrease
• Phase 4: Tension decrease in ventricles

Cardiac pressure

• Phase 1: Blood pressure increased
• Phase 2: Blood pressure in atria increased
• Phase 3: Highest point of ejection
• Phase 4: Lowest

Aortic pressure

• Phase 1: pressure stretches the tissues
• Phase 2: pressure maintains volume
• Phase 3: Highest volume is shown

Cardiac output impact from volume

• Phase 1: Max volume to provide heart
• Phase 2: Aortic volume shows a reduction

Factors affecting cardiac output

• Heart rate
  • Increases with sympathetic stimulation, adrenaline, exercise, and stress
  • Decreases with parasympathetic stimulation, rest, and sleep
• Stroke volume, determined by:
  • Preload (volume of blood filling the ventricles before contraction)
  • Afterload (pressure the ventricles must overcome to eject blood)
  • Myocardial contractility (force of ventricular contraction)

Understanding Starlings Law

• More blood returns (higher preload), the heart pumps more forcefully
• Increased end-diastolic volume (EDV) stretches the ventricle
• Leads to a stronger contraction and increased stroke volume (SV).
• Heart rate
• exercise and cardiac output increases

Afterload - Resistance The heart must overcome to eject blood.

• Increased and decreased the blood pressure by increasing and decreasing volume
• Volume has an direct impact with afterload

Cardiac Myocardial

• INCREASE*

• Myocardial with stress

• Adrenaline

• Beta 2 angonists

• Calcium

• DECREASE*

• Para stimulation

• Beta Blockers

• Heart failure

• Hypoxia

- Parasympathetic and sympathetic stimulation effect

• Pressure is generated by the highest pumping rate

Flow is generated

• Arterial Blood Pressure; varies with heart's pumping action
• Pressure

- Vessel depends on the heart rate

• DETERMINANTS*
• Resistance
• Blood viscosity

- Heart Rate

• Smallest to Largest

Cardiac Muscles

• A increase of volume in blood vessel to increase vessels wall
• Slow in capillaries
• Higher and lower heart rate with a longer vessels

Total Peripheral Resistance

- Blood - cardiac output

• Compliance ; volume with blood

Vessel

• Vessels depends on cardiac tissue and the heart for output heart
• Thins cardiac elastic

###Laminar Cardiac Outout

• Smooth output
• Higher viscosity

Reynold Numbers

• Increase pressure increase sound
• Blood flow and velocity. Vessel with vessel