Heart Contraction (6)
Increased intensity of exercise leads to an increased heart rate. Explain how.
-(Oxygen / carbon dioxide) detected by chemoreceptors -Medulla / cardiac centre involved; -More impulses to SAN / along sympathetic nerve
The pulse felt in the artery in the wrist can be recorded and used to measure heart rate. Suggest why the pulse felt can be used to measure heart rate.
-Caused by pressure / surge of blood -From (one) contraction / beat of (left) ventricle / heart
Describe how a heartbeat is initiated
-SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction; -Non-conducting tissue prevents immediate contraction of ventricles / prevents impulses reaching the ventricles; -AVN delays (impulse) whilst blood leaves atria / ventricles fill; -(AVN) sends wave of electrical activity / impulses down Bundle of His; -Causing ventricles to contract from base up;
Where are chemoreceptors located?
-aorta -cartoid artery -medulla of brain
The stroke volume of a trained athlete is greater than the stroke volume of a non-athlete of equal body size. Explain why.
-greater volume of blood retiring to right side of hear stretches ventricle >contracts more forcefully, increasing stroke volume -at rest, required volume of blood can be pumped round body with fewer beats >as stroke volume is higher
After exercise, the heart rate slows down. Explain how.
-higher oxygen and pH levels -chemosrecptors detect chemical changes and send impulses to cardiac centre in medulla >more impulses along parasympathetic nerve to SAN
The heart rate changes when a person is exercising vigorously. Explain how
-increased respiration increases carbon dioxide levels, so pH falls, oxygen levels decrease -chemorecpetors detect low pH and send impulses to medulla -more impulses along sympathetic nerve >secretes noradrenaline which binds to receptors on SAN
Explain why the collagen in the heart wall also has a role in helping to ensure that the ventricles contract at the right time
-it prevents the wave of electrical activity from travelling from the atria to the ventricles -this makes sure that the ventricles only respond to signals from the AVN, transferred via the Bundle of His
What to remember when blood pressure, blood oxygen and pH levels are HIGH (& CO2 levels low)
-parasympathetic neurones -secret acetylcholine (ACh) -decrease heart rate
What to remember when blood pressure, blood oxygen and pH levels are LOW (& CO2 levels high)
-sympathetic neurones -secrete noradrenaline -increase heart rate
Regular beating of the heart
-the cardiac muscle controls the regular beating of the heart -the cardiac muscle is 'myogenic'- it can contract and relax without receiving signals from nerves
Describe the route taken when electrical impulses are transmitted form the SAN to the muscles of the ventricles in a healthy heart
-through cardiac muscle -to atrioventricular node -along bundle of His / Purkyne fibres
Describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles in a healthy heart
-through cardiac muscle; -to atrioventricular node; -along bundle of His / Purkyne fibres
Describe the role of the SAN, AVN and bundle of His in the cardiac cycle
1) SAN initiates impulses; spread across atria, causing atrial systole; 2) non-conducting tissue prevents immediate contraction of ventricle 3) slight time delay at AVN to allow atria to empty completely; 4) AVN sends impulses pass very quickly down bundle of His; 5) allows ventricles to contract from the apex upwards
High blood pressure
1) baroreceptors detect high blood pressure 2) impulses are sent to medulla >sends impulses along parasympathetic neurones >these secrete acetylcholine (neurotransmitter) 3) acetylcholine binds to receptors on the SAN 4) the effector is the cardiac muscle and the response is the heart slowing down to reduce blood pressure back to normal >release of ACh / inhibits SAN / decreases impulses from SAN >decreases impulses to AVN / decreased stimulation of AVN / decreases impulses from AVN
Low blood pressure
1) baroreceptors detect low blood pressure 2) impulses are sent to medulla >sends impulses along sympathetic neurones >these secrete noradrenaline 3) noradrenaline binds to receptors on SAN 4) the heart rate speeds up to increase blood pressure back to normal
Low blood oxygen, high carbon dioxide or low pH levels
1) chemoreceptors detect chemical changes in blood 2) impulses are sent to medulla >sends impulses along sympathetic neurones >secrete noradrenaline >binds to receptors on SAN 3) response: heart rate increases to return oxygen, carbon dioxide and pH levels back to normal
High blood oxygen, High pH levels, Low carbon dioxide
1) chemoreceptors detect chemical changes in blood 2) impulses are sent to the medulla >sends impulses along parasympathetic neurones >they secrete acetylcholine >binds to receptors on SAN 3) response: heart rate decreases to return oxygen, carbon dioxide and pH levels back to normal
Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process.
1) chemoreceptors detect rise in CO2 2) send impulses to medulla 3) more impulses to SAN >by sympathetic nerve
A women take moderate exercise. Explain what causes her heart rate to increase while she exercises.
1) rate of respiration increases (in muscle cells); 2) carbon dioxide concentration increases 3) chemoreceptors in aortic >impulses to medulla 4) along sympathetic pathway to sinoatrial node (SAN)
Myogenic stimulation of the heart
1) sinoatrial node (SAN) in wall of right atrium sets the rhythm of the heart beat by sending out regular waves of electrical activity to the atrial walls 2) this causes the right and left atria to contract at the same time (atrial systole) >a band of non-conducting collagen tissue prevents waves of electrical activity from being passed from the atria to the ventricles 3) instead, the waves of electrical activity are passed from the SAN to the AVN (atrioventricular node) 4) AVN passes waves of electrical activity on to bundle of His >there is a delay to ensure the atria fully empty before ventricles contract 5) bundle of His (muscle fibres) conduct electrical activity between the ventricles to the apex (bottom) of the heart 6) the bundle of His splits into finer fibres called Purkyne tissue >it carries the waves of electrical activity into the muscular walls of the right and left ventricles >causing them to contract simultaneously from the bottom up
When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN.
1. Electrical activity only through Bundle of His 2. Wave of electrical activity passes over / through both ventricles at the same time
The heart controls and coordinates the regular contraction of the atria and ventricles. Describe how.
1. SAN → AVN → bundle of His / Purkyne fibres; 2. Impulses / electrical activity (over atria); 3. Atria contract; 4. Non-conducting tissue (between atria and ventricles); 5. Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract; 6. Ventricles contract from apex upwards;
Some drugs inhibit the transmission of nerve impose;les to the heart. Explain how these drugs high blood pressure.
1. inhibit impulses in sympathetic nerves / from cardio-acceleratory centre 2. SAN not stimulated / noradrenaline not released so heart rate lowers / does not increase
When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay.
Allow atria to empty / contract / ventricles to fill >Before ventricles contract
Transducer
Converts light energy to electrical energy
Explain how nervous control in a human can cause increased cardiac output during exercise
Coordination via medulla (of brain) / cardiac centre; (Increased) impulses along sympathetic ( / cardiac accelerator) nerve To S.A. node / pacemaker; More impulses sent from / increased rate of discharge of S.A. node / pacemaker;
Rate at which SAN fires
I.e heart rate >is unconsciously controlled by a part of the brain called the medulla oblongata >animals need to alter their heart rate to respond to internal stimuli (e.g. to prevent fainting due to low blood pressure)
Differences between rod and cone cells
Rod cells -more numerous than cone cells -do not give colour vision -usually located in periphery of retina -inner end has a small knob Cone cells -far fewer than rod cells -give blue, green and red colour vision -usually located in centre of retina -inner end is branched
Visual acuity
The ability to distinguish fine details such as closely spaced dots as separate
Stimuli of the heart
are detected by pressure receptors and chemical receptors
Electrical impulse (from baroreceptors and chemoreceptors)
are sent to the medulla >along sensory neurones
Stimuli detected by receptors (different stimuli)
cause heart rate to speed up or slow down
Where are pressure receptors (baroreceptors) located?
in the aorta and carted arteries (major arteries in neck) >stimulated by high and low blood pressure
Chemical receptors (chemoreceptors)
in the aorta, carotid arteries and in the medulla >they monitor oxygen level in the blood >also carbon dioxide nd pH (indicators of oxygen level)
Control of heart rate
involves the brain and autonomic nervous system 1) SAN generates electrical impulses >which causes cardiac muscles to contract
Describe the function of the AVN (conducts)
it conducts waves of electrical activity, after a short delay >from the SAN to the Bundle of His
Explain the importance of the layer of insulating tissue between the atria and the ventricles (AKA collagen in heart wall)
it prevents the waves of electrical activity from going from the atria to the ventricles >thus the ventricles only respond to signals form the AVN
Describe how an impulse reaches the base of the ventricles of the heart from the sinoatrial node
it spreads through the atria / right atrium / through cardiac muscle; to the atrioventricular node; then through conduction fibres / bundle of His / Purkyne fibres);
In one cardiac cycle, the volume of blood flowing out of the heart along the pulmonary artery is the same as the volume of blood resting along the pulmonary vein. Explain why the volumes are the same although the speed of flow in the artery is greater than in the vein.
larger / wider lumen so greater volume carried
Medulla
processes the information and send impulses to the SAN >along sympathetic and parasympathetic neurones (part of the nervous system)
Define myogenic
the heart does not need stimulation by nerves to contract
How do you convert dm3 to cm3?
x 1000
