BCMB 230 1st EditionExam # 2 Study Guide Lectures: 8 - 14Lecture 8 (September 19)The nervous system can be anatomically divided into two main parts: the central nervous system and the peripheral nervous system. The central nervous system (CNS) is made up of the brain and spinal cord. The peripheral nervous system (PNS) is made up of the nerves that connect the brain or spinal cord with the body’s muscles, glands, and sense organs—basically everything outside of the brain and spinal cord. In order to communicate with each other, they use the afferent or sensory pathway or the efferent or motor pathway. The afferent or sensory pathway is the pathway that the PNS uses to communicate with the CNS. The efferent or motorpathway is the pathway that the CNS uses to communicate with the PNS.The efferent division of the PNS can be divided into a somatic nervous system and autonomic nervous system. The somatic motor only controls one out of the three types of muscle, and that is skeletal muscle. It can easily be taken under “conscious” control and is described as excitatory or being all-or-none which means it can only tell something to act all the way or to stop completely. An example of something controlled by somatic motor is breathing. The visceral motor (also called autonomic) controls the other two types of muscle which is the smooth and cardiac muscles as well as the glands. The visceral/autonomic motor is under “unconscious” control so it is not something we can easily control ourselves. However, it is something that we can learn how to control. As opposed to being all-or-none, the visceral motor gives a graded response which means it can tell a muscle to contract a little bit, moderately, or a whole lot at a time. This means there can be different levels of excitatory or inhibitory responses. Visceral/autonomic can be further divided into two divisions. These are called the sympathetic and parasympathetic nervous system. The sympathetic nervous system is called the fight or flight response and can control heart rate or inhibit stomach activity. The parasympathetic nervous systems is called the rest-digest response and can slow down the heart rate or excite stomach activity. The two divisions are complementary and can be excitatory or inhibitory.There are sensory-specialized muscle cells that can send information about muscle. These cells can be divided into four categories: special sensory, somatosensory, propriosensory, and visceral sensory. Special sensory cells require a fairly complex sense organ of some sort and deals with vision, hearing, taste, smell (olfaction), and equilibrium. Somatosensory is sensory from the body and gets information from the skin such as touch, pressure, vibration, or temperature. Propriosensory comes from sensory cells in the skeletal muscle, joints, and tendons and gives information about body position; this is require for somatic motor control. Visceral sensory comes from the viscera, also known as the gut using stretch receptors in the stomach to tell us when the stomach is full or using stretch receptors in the bladder to tell whenthe bladder is full; carotid body or aortic body also tells you what goes on inside your body with sensory cells that tell you about blood pressure, blood pH, and blood oxygen levels.There are two major groups of cells in the nervous system. There are neurons which are the basic unit of the nerve system that help us to move information from one part of the body to another. They can do this by two ways. This can happen by the length of the neuron where info is moved by an electrical charge called a membrane potential. It can also happen from one cell to another by using a chemical messenger, a neurotransmitter, which can initiate a membrane potential on the next cell. Important features of neurons to know: (1) cell body which contains the nucleus and ribosomes and thus has the genetic information and machinery necessary for protein synthesis; (2) dendrites which are a series of highly branched outgrowths of the cell body that helps the cell body receive most of the inputs from other neurons; and (3) the axon (also called a nerve fiber) which is a long extension from the cell body that carries output to its target cells. The process of moving information is: the message is received by the dendrite which travels across the cell body to the axon; the axon then splits into axon terminals which have a swelling called a synaptic bulb at the end where the neurotransmitter is contained. The axon can also have an axon collateral which is a branch off the axon so one neuron can control two different parts.There are also neuroglial cells that don’t carry information but have a support function of some sort and help neurons with their function. Neuroglial cells in the PNS are called Schwann cells. These cells wrap around the axon multiple times to form segments of myelin sheaths at regular intervals. These myelin sheaths help send signals much faster. Each Schwann cell is only associated with a single axon. The spaces between each adjacent sections of myelin where the axon’s plasma membrane is exposed to the extracellular fluid are called the nodes of Ranvier. The signal jumps from these notes. If a cell in the PNS is cut, the Schwann cell will regenerate. In the CNS, neuroglial cells are called oligadendroctyes which is a myelin forming cell in the brain and spinal cord. They also produce a myelin sheath, however, each cell can reactwith multiple axons. Also if one of these cells are cut, they will not regenerate. Another type of neuroglial cell in the CNS is the astroyctye which acts to physically connect neurons to their blood supply. They can manipulate the neuron and the capillary (control permeability which hasa protective function) and can also cause a formation of tight junctions between cells of the blood vessel wall which blocks paracellular transport.As a quick summary of comparisons between the PNS and CNS: the cell body structures in the PNS are called ganglia (or ganglion for singular) and in the CNS are called different things depending on where they are—in the brain they are called a nucleus, in the spinal cord they arecalled horns; the axons in the PNS are cells bundled together form nerves while in the CNS there are no nerves, instead it is called a tract—the difference is the connective tissue associated with it.A membrane potential is an electrical charge that is important for the nervous