sets heart rate at about 120 beats per

sets heart rate at about 120 beats per minute � Nerves act as brake and accelerator � Vagus nerve slows heart rate � Sympathetic nerve � SAN 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 Sympathetic FASTER Via Vegus Nerve adrenaline/noradrenaline Acetylcholine � These both act on the SA node to change HR

� 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)

Exercise - blood CO 2 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

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

Sympathetic system Parasympathetic system

� 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

� Increase in C 02 � Causes increase in blood acidity, decrease in p. H. � Detected by Chemorecepetors � Sends impulse to medulla – Cardiac control centre � Decreases Vegus simulation � Increase sympathetic pulses � Heart rate increases! *Breathing rate= respiratory control centre

� 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 p. H. � Baroreceptors -stretch receptor based in arteries and vena cava. Detect increases in blood flow and pressure

� 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.

� 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

� Action of another hormone Acetylcholine released by Parasympathetic system that slow the heart rate down

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. C 02 Baroreceptors respond to changes in blood pressure

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

� Describe how the parasympathetic and sympathetic nervous pathways control heart rate during a game. � Explain how levels of CO 2 in blood cause heart rate to increase � How does the cardiac control centre regulate heart rate?

� 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

� Explain the terms stroke volume and cardiac output and the relationship between them (3 marks)

� Amount of blood ejected form the ventricle per beat � Amount of blood ejected from the ventricle per minute � Relationship- SV x HR = Cardiac output

� Subject A heart rate= 80 bpm; stroke volume =90 mls � Subject Bheart rate=110 bpm; stroke volume = 100 mls � Subject Cheart rate 160 bpm; stroke volume=120 mls

� When 1) 2) we exercise this will change. . . More blood enters the ventricle during diastole (venous return) as it is flowing faster round the body Walls of the ventricle stretch and contract more forcibly. Starlings law of the heart

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

How does stroke volume increase during exercise?

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

� Increased exercising heart rate and increased stroke volume have a huge impact on Cardiac Output � Heart rate 200 bpm � Stroke volumes 180 mls � 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?

� heart rate increases � stroke volume increases � due to Starlings Law � cardiac output increase � because cardiac output= SV x HR