response to stimuli Flashcards
autonomic nervous system
- autonomic means self-governing. Autonomic nervous system controls the involuntary/ self-governing activities of internal muscles and glands
Has two divisions: - sympathetic nervous system. Stimulates effectors and so speeds up any activity. Controls effectors when we exercise strenuously or experience powerful emotions. Prepares for flight or fight. Sympathetic neurones secrete noradrenalin- another type of neurotransmitter that increases heart rate
- parasympathetic nervous system. Inhibits effectors and slows down any activity. Controls activities under normal resting conditions and is concerned with conserving energy and replenishing the bodys reserves. Parasympathetic neruones secrete acetylcholine- a type of neurotransmitter that decreases heart rate
how does the heart ensure complete ventricular filling
- important as the ventricle needs to be completely full to ensure maximum blood volume is pumped to the lungs/ the body
- occurs during atrial systole
- atrial systole must be complete before ventricular systole can begin
- the SA node (sino-atrial node)/ pacemaker is found in the right atrium. The sino-atrial node sends electrical impulses/ a wave of depolarisation across to the left atrium. Means left and right atrium essentially contract at the same time
- However, the electrical depolarisation moves across the heart walls at a high speed of 100m/s. This suggests the ventricles should start to contract before atrial systole is complete
- the wave of depolarisation however cannot go into the ventricles, as there is a layer underneath the atrium where electrical impulses cannot pass. This is a layer of non-conductive tissue (atrioventricular septum)
-The electrical impulses are instead passed to the atrial-ventricular node (AVN). This holds the electrical impulses, causing a delay, allowing the atrium to fully contract before ventricle systole occurs.
the heart muscle
- heart muscle is known as cardiac muscle
- myogenic, so its contraction is initiated from within the muscle itself, rather than by nervous impulses from outside (neurogenic)
- SA node within the upper lateral wall of the right atrium. It is from here that the initial stimulus for contraction originates. The SA node has a basic rhythm of stimulation that determines the beat of the heart
How does the heart achieve complete ventricular emptying
- there is a problem as the wave of depolarisation coming from the AVN is at the top of the ventricle. Blood needs to be squeezed from the bottom of the ventricle to the top/ out of the artery’s to allow for complete ventricular emptying
- bundle of His conducts impulses to the base of the heart. The bundle branches into smaller fibres of Purkyne tissue which conveys and then releases the electrical impulses, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards
- wave of electrical impulses passes over both ventricles at the same time, through the Purkyne fibres
modifying the resting heart rate
- resting heart rate of a typical human adult around 70 beats per minute. Essential that this rate can be altered to meet varying demands and needs for oxygen.
- changes to heart rate are controlled by a region of the brain called the medulla oblongata, which contains the cardiovascular centre. Has two centres concerned with heart rate:
- centre that increases the heart rate- linked to the sinoatrial node by the sympathetic nervous system
- centre that decreases the heart rate, linked to the sinoatrial node by the parasympathetic nervous system
- baro receptors (monitor blood pressure) and chemo receptors (monitor blood pH/02 conc/ CO2 conc) are both found in the carotid bodies (in the carotid artery) and in the aortic arch
control by chemoreceptors
found in walls of carotid artery/ in the carotid body or in the aortic arch. Sensitive to changes in pH of blood/ O2 conc/ CO2 conc
-if a person begins to exercise, more CO2 will be produced, reducing pH and therefore increasing H+ conc, causing more H2C03
- chemoreceptors detect this change in pH
- this creates an increase in the frequency of action potentials which travel along the sensory neurone to the cardiovascular centre in the medulla oblongata
- this then increases the frequency of action potentials sent along the sympathetic nerve which are stimulated in the cardiovascular system. The frequency of action potentials along the vagus nerve therefore decreases, as the vagus and sympathetic neve are antagonistic pairs
- this causes the SAN to cause the heart rate to increase, as electrical impulses sent along the heart have increased
- the increased blood flow that this causes leads to more carbon dioxide being removed by the lungs and so the carbon dioxide concentration of the blood returns to normal
- as a consequence the pH of the blood rises to normal and the chemoreceptors in the carotid body and aortic arch reduces the frequency of action potentials to the medulla oblongata
- the medulla oblongata then reduces the frequency of impulses to the SAN, which therefore leads to a reduction in the heart rate
control by pressure receptors
Baro-receptors are also found in the aortic arch and carotid bodies
- baro-receptors will detect an increase in blood pressure.
-This increases the frequency of action potentials sent along the sensory neurone to the cardiovascular centre in the brain, which is the medullar oblongata
- stimulates an increase in the frequency of action potentials sent along the vagus nerve via the parasympathetic nervous system. This may decrease the frequency of action potentials along the sympathetic nerve
- causes the SAN in the heart to cause the heart rate to decrease and therefore cause less electrical impulses to be sent along the heart
If baro receptors detect a decrease in blood pressure- pressure receptors transmit more nervous impulses along sensory neurones to the medulla oblongata. This increases the frequency of impulses sent down the sympathetic nerves to the SAN, which increases the rate at which the heart beats
Percinian corpsule
