This interactive tutorial focuses on the baroreceptor reflex, which maintains blood supply to the brain, particularly during postural changes. It covers concepts of feedback control and the regulation of blood pressure. The tutorial complements lectures and practical classes for medical, health sciences, physiology and physiotherapy students. It aims to improve understanding of:

• the mechanisms used by the body to monitor blood pressure and relay this information to the brain,
• how the brain processes this information, and
• how an appropriate response is produced in the heart and blood vessels.

The tutorial begins with a short case study of prolonged bed rest, which forms the basis for more discussion later in the tutorial.

In the first section, you familiarise yourself with the cardiovascular control centre in the brain, zooming in on a functional view of the vasomotor areas of the medulla - the cardiovascular pressor centre, cardiovascular depressor centre, and input region. More anatomical detail and a structural view of the caudal ventrolateral medulla (CVLM), nucleus of tractus solitarius (NTS), rostral ventrolateral medulla (RVLM) and nucleus ambiguus (NAm) are also provided. Feedback mechanisms in the regulation of blood pressure by the autonomic nervous system are revised, and then you look at signal inputs and ouputs. Click on the "stimulate me" buttons for animations of afferent neurones, efferent neurones and neuronal circuits, and compare bursts of action potentials using the "listen to me" buttons.

Your next task is to build a simple neuronal circuit. From a palette you create receptors and neurones (afferent neurones, sympathetic efferent neurones, parasympathetic efferent neurones, excitatory interneurones, inhibitory interneurones), and position them on a simplified template to build a functioning negative-feedback neuronal circuit. Click "raise BP" at any stage to begin the animation and see the action potentials moving around the system you have designed. Context-sensitive hints and feedback guide you in your choices. Watching the animated outcome is quite entertaining, and setting up an unworkable arrangement and watching it unfold to its logical conclusion helps to build stronger understanding and problem-solving skills.

Your main practical task is to build a model of the arterial baroreceptor reflex control of blood pressure. You select receptors and neurones as before and place them on a functional template that includes: the cardiovascular pressor centre, cardiovascular depressor centre and input region of the medulla; peripheral blood vessels; carotid sinus; carotid artery; aortic arch; vena cava; heart; parasympathetic ganglion; cervical sympathetic ganglion; thoracic sympathetic ganglion; and the cervical/thoracic, lumbar and sacral sections of the spinal cord. When you complete the model you can observe its operation and use it to answer questions from the Tasks sheet supplied. You can also get the human to stand up and see how the system maintains blood supply to the brain when posture changes, which brings us back to the initial case study.

Authors: Debbi A. Weaver, Lea Delbridge, Peter J. Harris, Tom Petrovic, Robert E. Kemm

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