Sinoatrial node Ca into the cell), and the activation of potassium channels, which allows the flow of K out of the cell, making the membrane potential more negative. Heart rate depends on the rate at which the sinoatrial node produces action potentials. At rest, heart rate is between 60 and 100 beats per minute. This is a result of the activity of two sets of nerves, one acting to slow down action potential production (these are parasympathetic nerves) and the other acting to speed up action potential production (sympathetic nerves). The sympathetic nerves begin in the thoracic region of the spinal cord
Lymph node biopsy enlargement (swollen glands or lymphadenitis). It may also determine whether tumors in the lymph node are cancerous or noncancerous. Enlarged lymph nodes may be caused by a number of conditions, ranging from very mild infections to serious malignancies. Benign conditions can often be distinguished from cancerous and infectious processes by microscopic examination. The pathologist may also perform additional tests on the lymph node tissue to assist in making a diagnosis. Some of the conditions where abnormal values are obtained are: Lymph node biopsies may be performed to evaluate the spread of cancer. See Lymphadenectomy#With_sentinel_node_biopsy. However, Sentinel lymph node biopsy for