Sinoatrial node also activates a potassium channel, which allows K to flow out of the cell, making the membrane potential more negative and slowing the pacemaker potential, therefore decreasing the rate of action potential production and therefore decreasing heart rate. A decrease in heart rate is known as negative chronotropy. The first cell to produce the action potential in the SA node isn’t always the same, this is known as pacemaker shift. In certain species of animals, for example, in dogs, a superior shift (i.e. the cell that produces the fastest action potential in the SA node is higher than previously) usually
Lymph node range in size from a few millimeters to about 1–2 cm long. Each lymph node is surrounded by a fibrous capsule, which extends inside the lymph node to form trabeculae. The substance of the lymph node is divided into the outer cortex and the inner medulla. The cortex is continuous around the medulla except where the medulla comes into direct contact with the hilum. Thin reticular fibers of reticular connective tissue, and elastin form a supporting meshwork called a "reticulin" inside the node. B cells are mainly found in the outer (superficial) cortex where they are clustered together as follicular