Nervous Control of the Nervous Control of the HeartHeart

Internal Control of Heart Internal Control of Heart RateRate

The heart or The heart or cardiaccardiac muscle beats muscle beats involuntarilyinvoluntarily..

The beat of each cell of heart muscle is The beat of each cell of heart muscle is in in synchronysynchrony or or in pacein pace with the beat of with the beat of every other heart muscle cell.every other heart muscle cell.

Nervous impulsesNervous impulses from a specialized from a specialized bundle of nervous tissue called the bundle of nervous tissue called the Sinoatrial (SA) NodeSinoatrial (SA) Node control the ratecontrol the rate of of the heart beat and also the heart beat and also synchronizesynchronize the the beating of all cardiac cells.beating of all cardiac cells.

Internal Control of Heart Internal Control of Heart RateRate

The sinoatrial or The sinoatrial or SASA node is known as the node is known as the pacemakerpacemaker..

The SA node causes a The SA node causes a wave of contraction to wave of contraction to start in both the and start in both the and

This wave of This wave of contraction causes contraction causes the the Atrioventricular Atrioventricular (AV)(AV) node to initiate node to initiate contractions of the contractions of the ventricles.ventricles.

Internal Control of Heart Internal Control of Heart RateRate

The The bundle of HISbundle of HIS carries the nervous carries the nervous stimuli to all parts of stimuli to all parts of the ventricle via the ventricle via Purkinje FibresPurkinje Fibres which which brings the impulse to brings the impulse to each cardiac cell.each cardiac cell.

The SA node paces the The SA node paces the heart at heart at 72 beats/min72 beats/min which can be which can be considered a “normal” considered a “normal” resting heart rate.resting heart rate.

External Control of Heart External Control of Heart RateRate

The The Medulla OblangataMedulla Oblangata in the brain controls in the brain controls the nerves that influence heart rate.the nerves that influence heart rate.

O2 and CO2 concentration levels in the O2 and CO2 concentration levels in the blood are measured by blood are measured by chemoreceptorschemoreceptors that that stimulate one of two nerves to the heart in stimulate one of two nerves to the heart in order to maintain order to maintain homeostasishomeostasis..

1.1. Increased or accelerated heart rate is caused by Increased or accelerated heart rate is caused by stimulation of the stimulation of the sympatheticsympathetic nerve. nerve.

2.2. Decreased or slowing of the heart rate is caused Decreased or slowing of the heart rate is caused by the stimulation of the by the stimulation of the parasympatheticparasympathetic nerve. nerve.

Pressure sensitive Pressure sensitive baroreceptorsbaroreceptors in the arteries in the arteries respond to changes in the blood pressure.respond to changes in the blood pressure.

Factors Affecting Heart Factors Affecting Heart RateRate

Increase Physical Increase Physical Activity = Increase Activity = Increase in Heart Ratein Heart Rate

Increase in Increase in Emotions = Emotions = Increase in Heart Increase in Heart RateRate

Chemicals that IncreaseChemicals that Increase Heart Rate Heart Rate

1.1. NicotineNicotine

2.2. AdrenalineAdrenaline

3.3. ThyroxinThyroxin

4.4. CaffeineCaffeine

Chemicals that Decrease Chemicals that Decrease Heart RateHeart Rate

1.1. Carbon MonoxideCarbon Monoxide

2.2. AlchoholAlchohol

TachycardiaTachycardia

When your heart beats When your heart beats moremore than than 7272 beats per minute, such as during beats per minute, such as during exercise or from the consumption of exercise or from the consumption of caffeine or nicotinecaffeine or nicotine..

BradycardiaBradycardia

When the heart beats very slowly, When the heart beats very slowly, lessless than than 7272 beats per minute, such beats per minute, such as athletes who have an elevated as athletes who have an elevated cardiac output even during rest.cardiac output even during rest.

Heartbeat SoundsHeartbeat Sounds

LubLub • The sound which is a result The sound which is a result

of the closing of both atrio-of the closing of both atrio-ventricular valves ventricular valves (tricuspid/bicuspid)(tricuspid/bicuspid)

• Occurs during Systole, or Occurs during Systole, or ventricular contraction (i.e. ventricular contraction (i.e. atricular relaxation)atricular relaxation)

• Is louder and longer of the Is louder and longer of the 2 sounds2 sounds

If you listen to your heartbeat through a If you listen to your heartbeat through a stethoscope you hear 2 characteristic sounds stethoscope you hear 2 characteristic sounds that repeat over and over as the heart continues that repeat over and over as the heart continues to beat: Lub-dub, lub-dub…to beat: Lub-dub, lub-dub…

Heartbeat SoundsHeartbeat Sounds

DubDub • The sound which is The sound which is

the result of the the result of the closing of both semi-closing of both semi-lunar valves lunar valves (pulmonary/aortic)(pulmonary/aortic)

• Occurs during Occurs during Diastole, or Diastole, or Ventricular relaxation Ventricular relaxation (or atrial contraction)(or atrial contraction)

• Is the softer and Is the softer and shorter of the 2 shorter of the 2 sounds.sounds.