BCMB 230 1st Edition Lecture 8 Outline of Last Lecture I Messengers II Pathways through Second Messengers III G Protein Coupled Receptors Outline of Current Lecture I Overview of the Nervous System II Motor Division III Sensory specialized Muscle Cells IV Cells in the Nervous System V The PNS vs the CNS VI Membrane Potential Current Lecture The Nervous System and Cell Membrane Potential I Overview of the Nervous System The nervous system can be divided into two main parts anatomically CNS central nervous system made up of the brain and spinal cord PNS peripheral nervous system made up of nerves that connect the brain or spinal cord with the body s muscles glands and sense organs primarily everything outside of the brain and spinal cord Communicating with each other From PNS to CNS called afferent or sensory pathway From CNS to PNS called efferent or motor pathway II Motor Division somatic motor controls skeletal muscle can easily be taken under conscious control is only excitatory all or none which means it can tell something to act all the way or to stop completely ex breathing visceral motor autonomic controls smooth cardiac muscles and glands under unconscious control not something we can easily control ourselves but can learn how to has a These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute graded response which means it can tell a muscle to contract a little bit moderately or a whole lot can have different levels of excitatory or inhibitory visceral autonomic has two divisions can both be excitatory and inhibitory with complementary actions sympathetic fight or flight ex speed up heart rate inhibit stomach activity parasympathetic rest digest ex slow down heart rate excite stomach activity III Sensory specialized Muscle Cells that send information about muscle can be divided into four categories special sensory require a fairly complex sense organ of some sort deals with vision hearing taste smell olfaction and equilibrium somatosensory sensory from the body gets information from the skin touch pressure vibration temperature propriosensory coming from sensory cells in skeletal muscle joints tendons gives information about body position ex hold finger behind your back you know which finger you re holding up required for somatic motor control visceral sensory from the viscera gut stretch receptors in stomach that tell us when stomach is full stretch receptors in bladder when bladder is full carotid body aortic body tells you what goes on inside your body with sensory cells that tell you about blood pressure blood pH and blood oxygen levels IV Cells in the Nervous System Two major groups of cells Neurons basic unit of the nerve system that help us to move information from one part of the body to another Two ways of doing that By the length of the neuron info is moved by an electrical charge called a membrane potential From one cell to another use a chemical messenger a neurotransmitter which can initiate a membrane potential on the next cell Features of neurons 1 cell body contains the nucleus and ribosomes and thus has the genetic info and machinery necessary for protein synthesis 2 dendrites a series of highly branched outgrowths of the cell body that helps the cell body receive most of the inputs from other neurons 3 axon also called a nerve fiber a long extension from the cell body that carries output to its target cells Message goes from dendrite across the cell body to an axon axon then splits into axon terminals which have a swelling called a synaptic bulb at the end where the neurotransmitter is contained also has an axon collateral which is a branch off the axon so one neuron can control two different parts Neuroglial don t carry information have a support function of some sort help neurons do what they do Cells in the PNS use Schwann cells that wrap around the axon multiple times forming a segment at regular intervals Schwann cell made of myelin covering of myelin over the axon called at myelin sheath which helps send signals much faster each Schwann cell is only associated with a single axon nodes of Ranvier are the spaces between adjacent sections of myelin where the axon s plasma membrane is exposed to extracellular fluid the signal jumps from these nodes if you cut a cell in the PNS Schwann cell will regenerate Cells in the CNS use an oligaodendrocyte which is a myelin forming cell in the brain and spinal cord also produces a myelin sheath also made of myelin each cell reacts with multiple axons cut a cell cell will not regenerate another type of cell in CNS is an astroycyte which acts to physically connect neurons to their blood supply manipulate neuron and the capillary control permeability of the capillary have a protective function causes formation of tight junctions between cells of the blood vessel wall which blocks paracellular transport V The PNS vs the CNS Cell body PNS cell body structures are called ganglia ganglion singular CNS cell bodies in different areas in brain they are called a nucleus in spinal cord they are called horns Axons PNS cells bundled together to form nerves CNS there are no nerves in your brain instead it is called a tract the difference is in connective tissue associated with it VI Membrane Potential Membrane potential electrical charges important for nervous system to work Three kinds all happening on the dendrite most of the time resting potential a potential difference across the cell plasma membranes with the inside of the cell negatively charged with respect to the outside exists because of a tiny excess of negative ions inside the cell and an excess of positive ions outside the magnitude of the resting membrane potential depends mainly on two factors 1 differences in specific ion concentrations in the intracellular and extracellular fluids 2 differences in membrane permeabilities to the different ions which reflect the number of open channels for the different ions in the plasma membrane Resting membrane potential happens over the whole cell means that it is in a ready state neuron is ready to receive and transmit information it takes a lot of energy to maintain this state First thing needed is Na K and ATPase 3 Na out for every 2 K in moving more positive out than in generates a small charge it is electronegative and creates a small charge difference also creates an ion gradient which is also a charge gradient a lot more K