Chapter 2 - Slides Posted.pdf

Chapter 2 Communication Within the Nervous System Dr. Kimberley Campbell Neurons  Neurons: cells that convey sensory information into the brain, carry out operations, and transmit commands to the body  Structure:  Cell body  Nucleus  Dendrites  Axon  Axon terminals General Str...

Chapter 2 Communication Within the Nervous System Dr. Kimberley Campbell Neurons  Neurons: cells that convey sensory information into the brain, carry out operations, and transmit commands to the body  Structure:  Cell body  Nucleus  Dendrites  Axon  Axon terminals General Structure Types of Neurons  Motor neuron: carries commands to the muscles and organs  Sensory neurons: Carry information from the body and outside world into brain and spinal cord  Interneurons: neurons which connect one neuron to another in the same part of brain or spinal cord Cell Membrane Energy and the Cell Membrane  Polarization: a state in which there is a difference in electrical charge between the inside and outside of the neuron  Voltage: measure of the difference in electrical charge between two points  Resting potential: difference in charge between inside & outside of membrane of a neuron at rest Energy and the Cell Membrane  Ions: atoms that have lost or gained electrons  Positive: Na+, K+  Negative: Cl-, A- What Moves the Ions?  Force of diffusion: tendency of ions to move through membrane to less concentrated side K+ K+ K+ K+ K+ What Moves the Ions?  Electrostatic pressure: force where ions are repelled from similarly charged, attracted to oppositely charged Negatir to attracted as positive Cl- K+ Anions more ↳ do not -> too are large Cl- K+ stack inside Cl- K+ K+ Cl- What Moves the Ions?  Sodium potassium pump: large protein molecules that move sodium ions through cell membrane to outside, potassium ions back inside Ion Channels  Ion channels: gated pores in the membrane formed by proteins; limit the flow of ions into and out of the cell  Can be chemically gated or electrically gated  Chemically: neurotransmitters or hormones  Electrically: change in electrical potential of the membrane excitetory Inhibitory -> - -> increase ↳) - likelyhood becomes more of polarization positive 70m --90 vs decreases - 70m likelyhood of -)-40mv polarization -- Depolarization  Local potential: partial depolarization   Polarity in an area shifts toward zero when disturbed Local potential is a graded potential  Varies in magnitude with the strength of the stimulus that produced it ~ wave of local potentials down the axun . Depolarization  If local potential exceeds the threshold for activating electrically gated channels, then an action potential occurs Depolarization  Action potential: abrupt depolarization of membrane that allows neuron to communicate Depolarization  Action potential: abrupt depolarization of membrane that allows neuron to communicate  Action potential is ungraded   All-or-none law: occurs at full strength or it does not occur at all Action potential is nondecremental  Travels down the axon without any decrease in size  Propagated at each successive point along the way Refractory Periods  Absolute refractory period: sodium ion channels are unresponsive to further stimulation   A new action potential cannot occur Relative refractory period: sodium ion channels could support another action potential, but potassium channels are still open  A new action potential can occur, if the stimulation is sufficiently strong enough to overcome the charge Rate Law  Rate law: axon encodes stimulus intensity not in the size of its action potential but in its firing rate ↳ if ↳ want we we send ↳ lots of do a stronger signal ... more AP's options to this my Increase Rate v7 Increase Signal us Increase reach probability AP' next cells will Part 2 Glial Cells  Nonneural cells that provide a number of supporting functions to neurons Myelination and Conduction Speed ~  as acts if axons than a re they are bigger misom/s faster in speed . Myelin: fatty tissue that wraps around axon to insulate it  Keeps cell separate from extracellular fluid and other neurons  Nodes of Ranvier: Gaps in the myelin sheath  Saltatory conduction: A form of transmission in which action potentials appear to jump from node to node ↳ depends survival a message can on how travel rapidly through our neurons ↳ ↑ speed ↳ my make giant axons Bigger/fatter squid ↳ motor neurons 0 . 5 mm in diamate Myelination and Conduction Speed  What are the benefits of the myelin sheath?  Reduces capacitance  Electrical effect of the membrane, slows movement of ions down the axon  Signal regeneration at nodes of Ranvier  Use less energy Myelin-Producing Glial Cells  Oligodendrocytes: Glial cells which produce myelin in the brain and spinal cord   Almost 75% of glial cells in the brain are oligodendrocytes Schwann cells: Glial cells which produce myelin in the rest of the nervous system Myelin-Producing Glial Cells Other Glial Functions  Radial glia: during fetal development they form “scaffolds” that guide new neurons to their destinations  Microglia: provide energy to neurons and respond to injury and disease by removing cellular debris blood brain "talk" system -> immune Alls kill in nurons -  , can also blood to get Astrocytes: trigger the formation of seven times as many connections in neurons 4) look ↳ like stars more ↳ Related branches to intelligence 27 More Complexity 3 . & correlates - - play a role in neurotransmitters to intelligence-slarger/mue complex vessels nutrients to How Neurons Communicate  Synapse: the connection between two neurons  Synaptic cleft: the small gap which separates neurons so they are not in direct physical contact at the synapse  Presynaptic: transmitting neuron  Postsynaptic: receiving neuron How Neurons Communicate How Neurons Communicate  Chemical Transmission at the Synapse  First shown by Otto Loewi in the early 1900s  Neurons release at least two different chemicals that have opposite effects Chemical Transmission at the Synapse  Vesicles: membrane-enclose bubbles at axon terminals which store neurotransmitters  Ionotropic receptors: receptors which form the ion channel and open quickly to produce the immediate reactions  Metabotropic receptors: receptors which open channels indirectly through a second messenger Excitation and Inhibition  Partial depolarization: depolarization which is excitatory and facilitates the occurrence of an action potential  Hyperpolarization: increased polarization which is inhibitory and makes an action potential less likely to occur Excitation and Inhibition  Excitatory postsynaptic potential (EPSP): when receptors open sodium channels to produce a partial depolarization of the dendrites and cell body  Inhibitory postsynaptic potential (IPSP): when receptors open potassium channels, chloride channels, or both to produce a hyperpolarization of the dendrites and cell body Postsynaptic Integration  Spatial summation: combines potentials occurring simultaneously at different locations on the dendrites and cell body  Temporal summation: combines potentials arriving a short time apart, from either the same or separate inputs Postsynaptic Integration Removing Neurotransmitters  Reuptake: transmitters taken back into the terminals by transporter proteins, where they are repackaged into vesicles for reuse Regulating Synaptic Activity  Presynaptic excitation: increases the presynaptic neuron’s release of neurotransmitter onto the postsynaptic neuron  Presynaptic inhibition: decreases the presynaptic neuron’s release of neurotransmitter onto the postsynaptic neuron Regulating Synaptic Activity  Autoreceptors: receptors on presynaptic terminals which sense amount of transmitter in cleft Neurotransmitters  Dale’s principle: erroneous belief that a neuron was capable of releasing only a single transmitter  Neurotransmitter release:  Corelease  Cotransmission  Release of different transmitters from various terminals Neurotransmitters Neural Codes and Neural Networks  Neural codes  Varied intervals between spikes in nerve signals  Neural networks: groups of neurons that function together  Human Connectome Project: large-scale, multi-university effort to map brain’s circuits In Perspective  It’s impossible to understand the brain (or behavior it produces) without understanding capabilities and limitations of the neuron.  Modern tools and cooperative efforts are the key to moving forward in biological-psychology research.