116560
Description
Mind Map by harry_bygraves, updated more than 1 year ago
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Created by harry_bygraves
over 11 years ago
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Control of the heart rate
- The heart is able to contract without any external stimulation, a condition refered to as myogenic
- The heart rate is normally determined by pacemaker cells in the SAN.
The pacemaker initiates a heart beat by passing waves of electrical
stimulation first of the atria and then, via the AVN, over the ventricles. A
heart with no nervous or hormonal stimulation contracts at a rate of
around 100 beats per minute. However, nervous stimulation coordinated
by the CV centre in the medulla oblongata overrides this inherent rhythm
- Nervous control of the heart beat is mainly
by reflex actions which in volve reflex arcs
orginiating in sensory receptors
- Baroreceptors; are loacted in the carotid sinus and the walls of the heart
- Chemoreceptors; sensitive to changes in pH and the concentration
of blood carbon dioxide and blood oxygen are located in the walls of
the heart, the carotid and aortic arteries, and the medulla oblongata
- These recoetors pass their sensory information via
sensory neurones to the CV centre from which two
nerves, the vagus nerve and the sympathetic
nerve, lead to the pacemaker in the SAN. These
nerves are part of the autonomic nervous system,
the part of the pheripheral nervous system that
regualtes body activities that are usually involuntary
and performed unconciously. A persons actual
heart rate depends in part of the relative activity of
these two nerves which act antagonistically;
- The vagus nerve; runs directly from the CV centre to
the pacemaker region in the SAN. It has an inhibitory
effect - stimulation causes the heart to slow down
- The sympathetic nerve goes to the SAN
via the spinal cord. It is on excitatory nerve
- stimulation accelerates the hearts rate
- The vagus nerve; runs directly from the CV centre to
the pacemaker region in the SAN. It has an inhibitory
effect - stimulation causes the heart to slow down
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