Topic 6- Control of heart rate Flashcards
What is the autonomic nervous system?
-means self- governing
-the autonomic nervous system controls the involuntary (subconscious) activities of internal muscles and glands
what are the two divisions of the autonomic nervous system?
-the sympathetic serous system
-the parasympathetic nervous system
what is the sympathetic nervous system?
-stimulates effectors and so speeds up activity
-it controls effectors when we exercise or experience powerful emotions
-helps us in stressful situations by heightening our awareness and preparing us for activity
what is the parasympathetic nervous system?
-this inhibits effectors and slows down any activity
-it controls activity under normal resting conditions
-It is concerned with conserving energy and replenishing the body’s reserves
what describes the actions of the sympathetic and parasympathetic nervous system?
-normally oppose one another
-they are antagonistic
-if one system contracts a muscle, the other relaxes it
-the activities of internal glands and muscles are therefore regulated by a balance of the two systems
Cardiac muscle is myogenic, what does this mean?
It can contract and relax without receiving electrical impulses from nerves
where is the sinoatrial node (SAN) located and what does it do?
-located in the wall of the right atrium
-SAN are a distinct group of cells
-it is from here that the initial stimulus for contraction originates
-the SAN has a basic rhythm of stimulation that determines the beat of the heart
what is the SAN also referred to as?
-the pace maker
|> this is because it is from here that the initial stimulus for contraction originates
-The SAN has a basic rhythm of stimulation that determines the beat of the heart
Describe the myogenic stimulation of the heart and a transmission of a subsequent wave of electrical activity
|> the sequence of events that controls the basic heart rate
1) Wave of excitation spreads from the sinoatrial node across both atria, causing the atria to contract
2)A layer of non- conductive tissue (atrioventricular septum) prevents the wave crossing to the ventricles
3)Wave of excitation enters the atrioventricular node (AVN) which lies between the atria
4)The AVN delays the impulse
- allowing the atria to fully contract and empty before the ventricles contract
- after the delay, the AVN conveys a wave of electrical excitation between the ventricles
5)AVN sends a wave of electrical excitation down the bundle of His, conducting wave between ventricles to the apex where in branches into purkyne tissue
6)The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards
what is the typical resting heart rate in an adult?
70 bpm
what is altered to meet the demands for oxygen?
-it is essential that this rate is altered to meet varying demands for oxygen
-during exercise for example, the resting heart may need to more than double
what are changes to heart rate controlled by?
the region of the brain called the medulla oblongata
what are the two centres in the medulla oblongata that are concerned with heart rate?
-a centre that increases heart rate-> which is linked to the sinoatrial node by the sympathetic nervous system
-a centre that decreases heart rate-> which is linked to the sinoatrial node by the parasympathetic nervous system
Which of the two centres in the medulla oblongata that are concerned with heart rate are stimulated depends on?
which of these centres is stimulated depends upon the nerve impulses they receive from two types of receptor
|> which respond to stimuli of either chemical or pressure changes in the blood
where are chemoreceptors found?
in the wall of the carotid arteries
