REGULATION OF HEART BEAT CHANGING HEART RATE SAN sets heart rate atabout 120 beats per minute Nerves act as brake and accelerator
Vagus nerve slows heart rate Sympathetic nerve speeds up heart rate 2
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 Parasympathetic SLOWER Via Vegus Nerve
Acetylcholine Sympathetic FASTER adrenaline/noradrenaline 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) INCREASING HEART RATE Exercise - blood CO2 levels rise Medulla
Detected by chemoreceptors Decreased vagus impulses to SAN - lets heart beat faster Increased sympathetic impulses to SAN - lets heart beat even faster 5
REDUCING HEART RATE Medulla Stop exercise blood pressure falls Detected by baroreceptors Increased vagus impulses to SAN - lets heart beat slower Decreased sympathetic impulses to SAN - allows heart rate to slow
6 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 stressbutterflies
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 factors Increase 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 beat Not 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 Bheart rate=110bpm; stroke volume =
100mls Subject Cheart 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
