Bio 1104 1st EditionExam # 3 Study Guide Lectures: 17 - 21Overview of Nervous System1. The Nervous System a. The nervous system is a combination of electrical and chemical signalsi. As opposed to the endocrine function, which is only chemical signalsb. Peripheral nervous systemi. Somatic- voluntaryii. Autonomic- involuntary1. Sympathetic- flight or fight2. Parasympathetic- housekeepingc. Central nervous system- brain and spinal cordd. The sensory nervous system transmits information from the peripheral to the central nervous system 2. Central Nervous System a. Glia cells- the caretakers of neuronsi. Regulate the environment, nourish, and insulate the cell b. Neuron cells Describe how information travels within a neuron.Information is relayed as an electrical signal, which is caused by ion flow across a cell membrane. The signal enters through the dendrites, is integrated in the cell body (soma), and exits through the axon to another cell. Parts of the neuron to know:1. Dendrites- structures that receive messages from other neurons2. Synapses- junctions between neurons3. Axon hillock- area between the axon and cell body (where the action potential originates)4. Axon- propagates an electrical signal between the cell body and the synapse5. Axon terminals- endings that receive electrical signals from sending neurons and release achemical signal 1. Ionsa. Molecules- made up of atoms that may or may not have a chargeb. Ions- charged atoms or molecules c. What are some important ions in the nervous system?i. Positive atoms- K+ (potassium), Na+ (sodium), Ca2+ (calcium)ii. Negative ions- Cl- (chlorine)iii. Molecules- A- (negatively charged proteins, aka organic anions)d. Why is charge important?i. The cell membrane, aka the barrier between the inside and the outside of cell, is composed of phospholipid with hydrophilic heads and hydrophobic tails ii. Non-charged molecules can pass through the phospholipid bilayer, but ions cannot 1. So ions need channels to cross the cell membrane 2. Ion Channelsa. Ion channels are embedded in the cell membrane of the neuroni. made of proteins that form a pore/channelii. only allows certain ions to pass through 1. ex. potassium channels only allow K+ through b. What are the two different types of channels?i. Leak channels are permanently openii. Gated channels open and close1. Gated channels are further subdivided into three categories, based on how they open. What are they?a. Chemical gated- open when a specific chemical binds to the channel b. Mechanically gated- open when physically pulled or pushed open c. Voltage gated- open when membrane potential reaches a certain voltagei. For Na+ channels: open when the membrane potential raises above -55 mV1. This is why the threshold for action potentials is -55 mV, and why action potentials are all or none c. What is an electric potential?i. Also called a voltage, an electric potential is a difference of electrical charge between any two points ii. Membrane potential- when the two points that differ in charge are on opposite sides of the membrane 1. Measured by a voltmeterd. How is membrane potential measured?i. The membrane potential is measured relative to the outside of the cell. Essentially, the outside is considered to be “0”, and the inside is relative to that. If the membrane potential is negative, that means the inside of the cell is more negative than the outside; if the membrane potential is positive, then the opposite is true. 3. Resting Potentiala. Describe resting potential. i. Resting potential occurs when a neuron is not transmitting an electrical signal. At this point, there is more potassium inside the cell and more sodium outside of the cell.1. To remember this, think of a “salty banana”ii. Resting potential of human neurons is between -60 and -85 mV1. So at resting potential, the inside of the neuron is more negative than the outside b. What are the two forces that can move ions through channels and across a membrane? i. Diffusion is the movement of particles from an area of high concentration to an area of low concentration1. This is caused by the random, constant movement of particles (although the overall pattern is predictable)ii. Electrostatic pressure- movement away from particles with the same charge and towards particles with the opposite charge1. Aka “opposites attract”iii. Net flow is an important concept to consider when looking at the movement of ions. Although ions are constantly moving, net flow refers to the overall direction, caused by the fact that the forces acting on different ions are not balanced. 1. Why doesn’t equilibrium between the two sides of the membrane occur?a. Two reasons:i. The cell membrane is not equally permeable to all ions1. There are not the same amount of leak channels for every ionii. The cell membrane has pumps that actively create the “Salty banana” by pumping sodium out of the cell and potassium into the cell iv. Describe the overall distribution of leak channels in the cell membrane.1. There are not very many sodium or chlorine leak channels2. There are about 100 times more potassium leak channels than sodium leak channels 3. There are no leak channels for A-, meaning that it cannot pass through the cell membrane Electrical Signals in NeuronsDescribe a neuron at resting potential.Outside the cell: High concentrations of sodium and chlorine-low concentrations of potassiumInside the cell: High concentrations of potassium and A--low concentrations of sodium and chlorine1. Action potentialsa. What is an action potential?i. Read by a voltmeter ii. Specific movement of ions across a cell membrane, resulting in a rapid, temporary change in membrane potential1. aka, a rapid reversal of membrane potential, which is then followedby a return to resting potential2.Define polarization and depolarizationa. Polarization- occurs when the charges on the two sides of the membrane are different i. i.e., there is a membrane potentialb. Depolarization- the charges on the two sides of the membrane become more equal3. What are the three stages of an action potential? Describe them.a. Depolarization- the membrane becomes less polarized than beforei. Aka, it moves from -70 towards 0 and then becomes briefly positive (around -30 mV)ii. Usually depolarization begins because of some sort stimuli that leads to a change in ion flow across the membrane (i.e. chemicals, pressure, light, temperature)iii. If the depolarization shifts from resting potential