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The tenth cranial nerve (X) is the vagus nerve. It is the longest cranial nerve. (Its name means "wanderer"). It supplies most of the organs in the thoracic and abdominal cavities. This nerve also contains motor fibers to the larynx (voice box) and pharynx, and to glands that produce digestive juices and other secretions. The vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech. Parasympathetic innervation of the heart is partially controlled by the vagus nerve and is shared by the thoracic ganglia. To be specific, vagal and spinal ganglionic nerves mediate the lowering of the heart rate. 

Heart beat is initiated by the nodal cells of the SA node. It starts the heart beat. The electrical impulse is then carried by the nerves to the AV node and the Purkinje fibres. Thus the nerves help to spread the impulse throughout the heart. Hence the rate and rhythm of heart beat is controlled by the impulses travelling through the nerves.

The cardiac activity is controlled by the sympathetic nervous system through the epinephrine. It fastens the heartbeat and the cardiac output so that more concentration of oxygen can be supplied to the body parts.

The calcium ions are responsible for muscle contraction by generating the action potential in the muscle cells. More influx of calcium ions may contract the heart muscle to a prolonged state of contraction, which will lead to abnormal increase in the heart rate. 

An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain by using sensors (electrodes). EEG is most often used to diagnose epilepsy, which causes abnormalities in EEG readings. It is also used to diagnose sleep disorders, coma, encephalopathies, and brain death. EEG used to be a first line method of diagnosis for tumors, stroke and other focal brain disorders.

Magnetoencephalography (MEG) is a non-invasive neurophysiological technique that measures the magnetic fields generated by neuronal activity of the brain. The spatial distributions of the magnetic fields are analyzed to localize the sources of the activity within the brain, and the locations of the sources are superimposed on anatomical images, such as MRI, to provide information about both the structure and function of the brain. 

Electroencephalography (EEG) is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain. German physiologist and psychiatrist Hans Berger recorded the first human EEG in 1924. 

Sympathetic nerves release norepinephrine and stimulate the adrenal medulla to release epinephrine, both of which accelerate the heart rate. Acetylcholine is a parasympathetic neurotransmitter that slows the heart rate.

The mammalian heart is myogenic, meaning the heartbeat originates from specialized muscle cells (the SA node) rather than from external nerve impulses.