REGULATION OF HEART BEAT

2

CHANGING HEART RATE SAN sets heart rate at

beats per minute Nerves act as Vagus nerve Sympathetic nerve

about 120

brake and acceleratorslows heart rate

speeds up heart rate

The intrinsic impulses of the SAN set the heart beat

These timings can be altered through the neural control & hormones.

Central to the regulation of heart rate is the Cardiac Control Centre in the medulla- made up of 2 components.

Autonomic Nervous System

ParasympatheticSympathetic

SLOWER FASTER

Via Vegus Nerve adrenaline/noradrenaline

Acetylcholine These both act on the SA node to change HR

ON YER BIKE! Think of a cyclist going down hill. Speed of the bike is like the speed of

your heart Brakes- vagus nerve Pedals- sympathetic nerve To reduce the speed you use the brakes To speed up you pedal faster To go fast downhill you take the brakes off completely (vegus nerve) and pedal faster (sympathetic nerve)

5

INCREASING HEART RATE

Exercise - blood CO2 levels rise

Detected by chemoreceptorsMedulla

Decreased vagus impulses to SAN - lets

heart beat faster

Increased sympathetic impulses to SAN - lets heart beat even faster

6

REDUCING HEART RATE

Stop exercise – blood pressure falls

Detected by baroreceptors

Medulla

Increased vagus impulses to SAN - lets heart beat slower

Decreased sympathetic impulses to SAN - allows

heart rate to slow

LETS SUMMARISE...

Sympathetic system Parasympathetic system

DESCRIBE HOW THE PARASYMPATHETIC AND SYMPATHETIC NERVOUS PATHWAYS

CONTROL HEART RATE DURING A GAME (5)

A.Controlled by medulla/cardiac centre B. Sympathetic pathway increases heart

rate C. By release of

adrenaline/noradrenaline D. Increase stroke volume/ejection

fraction E. Parasympathetic decreases HR F. By vagus nerve G. Production of Acetylcholine H. (Both) act on sino atrial node/SAN

EXPLAIN HOW LEVELS OF CO2 IN BLOOD CAUSE HEART RATE TO

INCREASE

Increase in C02 Causes increase in blood acidity,

decrease in pH. Detected by Chemorecepetors Sends impulse to medulla – Cardiac

control centre Decreases Vegus simulation Increase sympathetic pulses Heart rate increases!*Breathing rate= respiratory control centre

NEURAL CONTROL OF THE HEART

The CCC receives information from lots of different sources in the body.

Mechanoreceptors & Proprioceptors-Extent of movement taking place in the

muscles. In movement = in HR.

Chemoreceptors -Detect changes in pH.

Baroreceptors-stretch receptor based in arteries and vena

cava. Detect increases in blood flow and pressure

WHAT DO THEY DO? CCC responds to information from these

sensory receptors during exercise. Stimulate the SA Node via sympathetic

nerve. This causes heart rate and stroke

volume to increase. Once exercise stops- stimulation of

sympathetic nerve decreases and allows parasympathetic vagus nerve to take over and slow heart rate down.

HORMONES! Adrenaline and noradrenaline are

released during times of stress- ‘butterflies’

Prepares body for impending exercise by increasing heart rate and strength of ventricular contraction.

Mimicking the action of the sympathetic system

Anticipatory Rise

ANTICIPATORY RISE

HORMONES.. Action of another hormone

Acetylcholine released by Parasympathetic system that slow the heart rate down

HOW DOES THE CARDIAC CONTROL CENTRE REGULATE

HEART RATE? (5 MARKS)

Neural Factors; Proprioceptors & mechanoreceptors in

muscles relay info to the brain that amount of movement has increased and muscles will need more blood.

Chemoreceptors in aorta and carotid arteries detect changes in composition of the blood- C02

Baroreceptors respond to changes in blood pressure

HOW DOES THE CARDIAC CONTROL CENTRE REGULATE

HEART RATE?

Hormonal factors;Release of adrenaline and noradrenaline

increase heart rate and strength of contraction

Release of Acetylcholine following exercise to reduce the heart rate

Intrinsic factorsIncrease in temperature- blood flows

better less viscous

QUESTIONS Describe how the parasympathetic

and sympathetic nervous pathways control heart rate during a game.

Explain how levels of CO2 in blood cause heart rate to increase

How does the cardiac control centre regulate heart rate?

DEFINITIONS! Stroke Volume- blood ejected per beatNot all blood in ventricle is ejected.. Ejection Fraction- amount of blood that

leaves the ventricle Cardiac Output – amount of blood

pumped out of a ventricle per minute Heart rate x stroke volume 5 litres resting male

EXAM QUESTION Explain the terms stroke volume and

cardiac output and the relationship between them

(3 marks)

ANSWER Amount of blood ejected form the

ventricle per beat Amount of blood ejected from the

ventricle per minute Relationship- SV x HR = Cardiac output

WORK OUT THE CARDIAC OUTPUT

Subject A heart rate= 80bpm; stroke volume

=90mls

Subject B- heart rate=110bpm; stroke volume =

100mls

Subject C- heart rate160bpm; stroke

volume=120mls

STROKE VOLUME When we exercise this will change...1) More blood enters the ventricle during

diastole (venous return) as it is flowing faster round the body

2) Walls of the ventricle stretch and contract more forcibly.

Starlings law of the heart

STARLINGS LAW

The greater the venous return, the greater the strength of contraction.

???

How does stroke volume increase during exercise?

HOW DOES STROKE VOLUME INCREASE DURING EXERCISE?

Increased venous return Greater diastolic filling Cardiac muscle stretched Greater strength/ force of contraction

Increased ejection fraction

EFFECTS OF EXERCISE Increased exercising heart rate and

increased stroke volume have a huge impact on Cardiac Output

Heart rate 200bpm Stroke volumes 180mls 36 litres per minute Increase in Cardiac Output (Q) is to

supply working muscles with oxygen

???What are the effects of exercise on the heart?

EFFECTS OF EXERCISE ON THE HEART (4-5 MARKS)

heart rate increases

stroke volume increases

due to Starlings Law

cardiac output increase

because cardiac output= SV x HR