 Chapter 48 Gaby Gonzalez Joyce Kim Stephanie Kim

Introduction to Information Processing  Sensory neurons transmit information from eyes and other sensors.  Neurons in the brain are interneurons  Motor neurons transmit signals to muscle  The nervous system is divided into central nervous system (CNS) and peripheral nervous system (PNS).

Neuron Structure and Function - A neuron has numerous dendrites, which receives signals from other neurons. - A neuron has an axon, which transmits signals to other cells. - The axon hillock is where the signals that travel down the axon are generated.

Neuron Structure and Function  Neurotransmitters pass info from the transmitting neuron to the receiving cell.  Interneurons have highly branched dendrites that take part in about 100,000 synapses.

Formation of the Resting Potential - Ion pumps use the energy of ATP to actively transport NA+ out of the cell and K+ into the cell. - The concentration gradients of K+ and Na+ across the plasma membrane represent a chemical form of potential energy. - The diffusion of K+ through open potassium channels is important for the resting potential. - The negative charge within the neuron is the source of the membrane potential.

Modeling of the Resting Potential -A concentration gradient of K+ needs a solution of 140 mM potassium chloride in the inner chamber and 5mM KCI in the outer. - The magnitude of the membrane voltage at equilibrium for a ion is called equilibrium potential. - The resting potential of an actual neuron is -60 to -80 mV.

 Action potentials are the signals conducted by axons 48.3

Basics of Electrical signaling  Gated Ion potentials: ion channels that open/close in response to stimuli  Alters membrane’s permeability/potential  Hyperpolarization: increase of magnitude of membrane potential  Depolarization: decrease  Graded potentials

Action Potentials: Production  VOLTAGE-gated ion channels: open/close in response to a change in membrane potential  Action potential(nerve impulse) : all or nothing response to depolarization of the membrane of the nerve cell

Action Potentials: Production  Threshold: the level of depolarization needed to activate action potential  The membrane potential is restored to its normal resting value by the inactivation of NA+ channels and by opening voltage gated K+ channels, which increases K+ leaving the cell

Generation of Action Potential

Conduction  Refractory period: follows the action potential, a period in which another another action potential can’t be activated  Action potentials are propagated along the axon  Zone of depolarization/repolarization  Currents only move ahead

Conduction Speed  Myelin Sheath: a layer of electrical insulation  Produced by 2 types of glia (oligodendrocytes and Schwann cells)  Saltadory conduction: the jumping of the nerve impulse between “nodes of Ranvier” (area on the axon not covered by the myelin sheath), speeds up the conduction of the nerve impulse.

 Neuron communicate with other cells at synapses 48.4

 The signal is conducted from the axon of a presynaptic cell to the dendrite of a postsynaptic cell by an electrical or chemical synapses.

Electrical Synapses  Electrical synapses: allow electrical current to flow directly from one neuron to another - both vertebrates and invertebrates, this synapses synchronize the activity of neurons responsible for certain rapid, unvarying behaviors.

Chemical Synapses  Involve the release of chemical neurotransmitter by the presynaptic neuron.  At each terminal, the presynaptic neuron synthesizes the neurotransmitter and packages it in multiple membrane- bounded compartments called synaptic vesicles

Chemical Synapses 1)An action potential depolarized the plasma membrane of the synaptic terminal 2)It opens voltage-gated calcium channels in the membrane, triggering an influx of Ca^2+ 3)The elevated Ca^2+ concentration in the terminal causes synaptic vesicles to fuse with the presynaptic membrane

Chemical Synapses 4) The vesicles release neurotransmitter into the synaptic cleft 5)The neurotransmitter binds to the receptor portion of ligand-gated ion channels in the postsynaptic membrane, opening the channels. In the synapse illustrated here, both Na+ and K+ can diffuse through the channels 6) The neurotransmitter is released from the receptors, and the channels close. Synaptic transmission ends when the neurotransmitter diffuses out of the synaptic cleft, is taken up by the synaptic terminal or by another cells, or is degraded by an enzyme.

Two postsynaptic potentials  Excitatory postsynaptic potential : an electrical change, or depolarization, in the membrane of a postsynaptic cell caused by the binding of an excitatory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more likely for a postsynaptic cell to generate an action potential

 Inhibitory postsynaptic potentials : an electrical change,or hyperpolarization, in the membrane of a postsynaptic neuron caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more difficult for a for a postsynaptic neuron to generate an action potential.

Neurotransmitters  Acetylcholine : most common neurotransmitter -Binds to receptors on ligand-gated channels in the muscle cell, producing an EPSP. -excitatory to vertebrate skeletal muscles -excitatory or inhibitory at other sites. ex)heart muscles-> inhibitory -certain bacteria produce a toxin that specifically inhibits presynaptic release of acetylcholine; toxin caused of food poisoning called botulism -secretion cites: CNS; PNS; vertebrate neuromuscular junction

Other Neurotransmitters NeurotransmitterFunctional classSection sites Biogenic Amines Norepinephrine Dopamine Serotonin Excitatory/inhibitory Generally excitatory Generally inhibitory CNS;PNS CNS Amino Acids GABA Glutamate Glycine Inhibitory Excitatory Inhibitory CNS; invertebrate neuromuscular junction CNS; invertebrate neuromuscular CNS Neuropeptides Substance P Met-enkephalin Excitatoty Generally inhibitory CNS;PNS CNS Gas Nitric AcidExcitatory/ inhibitoryPNS