Nervous systems are composed of neurons and glial cells Support neurons provide nutrition A bundle of axons coming from many different neurons Lecture 9 Neurons Glial cells Axon Nerve Neural network Afferent and sensory Heat light tough Efferent Carry information away from the nervous system To muscles glands Interneurons Intergrate and store information Help with communication between efferent and afferent Sit between afferent and efferent Carry the information to the nervous system from any sensory neuron Nervous systems vary in size and complexity Nerve net Simplest type of nervous system Cnidarians Surrounds oral cavity and on tenticles Helps to sense danger and food Ganglia Squid bilaterally symmetrical animals Organize ganglia into pairs Larger ganglia can be brain Central nervous system Brain and spinal chord Information processing storage retrieval Peripheral nervous system Everything else Neurons are the functional unit of the nervous system Neurotransmitter Presynaptic Pre before Synapse space Postsynaptic Post after Synapse space Dendrites Cell body Axon terminal Axon hillock Typically receive information then pass it into the cell body Transfers information to the axon Can end in many branches can affect many things Where all the information from the dendrites gets concentrated If there is enough information and action potential will occur Specialized neurons Many dendritic branches Extremely long axons Tiny neuron in eye Glia are supportive parts of the nervous system Oligodendrocytes CNS Produces myelin Schwann cells PNS Produces myelin Myelin Astrocytes Fatty substance Insulator for an electrical current Found around neurons Found in brain Blood brain barrier Prevents chemicals from entering the brain Electrical signals are transmitted by neurons due to membrane potential Difference of 60 mV between the outside and the inside of the cell Inside of the cell is more negative than the outside of the cell One side of the membrane has a difference from the other Resting potential Voltage difference Membrane potential ATPase Requires ATP Membrane potential is generated and maintained by the Na K pump Sodium potassium pump Active transport Leaky K channels Channel proteins that are always open K wants to leave the cell because it is higher inside Pump One molecule of ATP pulls out 3 Na 2 K pulled in Antiporter One thing going out one thing going in Ion channels contribute to the membrane potential Electrochemical gradient Neurons have different ion channels K is always open Voltage gated K channels Voltage gated Na channels Activation gate Inactivation gate Voltage gated Chemical gated Depolarization Open and close when the chemical is present Na following into the cell depolarizes it Na open Leads to action potential Hyperpolarization More K flowing out of the cell hyperpolarizes it Leads to the inside to become more negative K Gated ion channels respond to chemical voltage and mechanical changes Action potentials result when there are sudden changes in voltage gated channels Resting potential 60 70 mV Receives message from pre synaptic cell Opens sodium channels Charge begins to change inside axon If it hits treshold it will go through action potential If it doesn t hit threshold it will NOT go through an action potential Voltage difference Undershoot Occurs when trying to reestablish resting potential K flows out too quickly More negative vs more positive Depolarization starts when Na channels open 1 Resting potential 2 Depolarization 3 Action potential threshold 3 5 Repolarization 4 Hyperpolarization undershoot 1 Most channels closed Leaky K 2 Na gates open When you start depolarization sodium channels begin to open 3 Na gates open 3 5 Na inactivation gates close K gates open 4 K gates slow to close 5 Na K pump restores Action potentials move down the axon All or none response Must hit threshold for action potential to occur Self regenerating Axon hillock Refractory period Dendrites receive message comes into cell body messages become concentrated Decides if there are enough messages to send Must reestablish resting potential before you can have another response Action potentials jump along vertebrate axons Insulators buffer change Schwann cells Produce myelin cases Myelination Insulation for electrical charge Nodes of ranvier Spaces between myelin sheaths Salutatory conduction Jumping from node to node Depolarize just a node not the entire neuron Guillain barre syndrome Myelin sheath attacked Attacks PNS Autoimmune disease own body attacking Causes peralysis Multiple sclerosis Myelin sheath attacked Attacks CNS Can be caused by autoimmune or environment Low vitamin D or smoking Some toxins bind to ion channels in the axon and muscle Toxin binds to sodium channel In cell Unable to repolarize the cell cannot have another action potential In graph Resting potential can never be reestablished Synaptic transmission occurs using neurotransmitters Voltage gated calcium channels vesicles Triggered when more positive Calcium binds to vesicles causing vesicles to bind to the axon membrane Released into synaptic cleft Binds to receptors found in the muscle cell membrane When bounds opens up channels that let sodium flow in Depolarizes the muscle cell or postsynaptic cell Dedrobatidae Batrachotoxin family poison dart frogs Batracho frog Secreted from skin glands Lipid steroid molecule What happens Synaptic cleft Space Chemically gated channels Acetylcholine Ach Neuromuscular junction Neuron to muscle Causes muscle to contract Axon hillock Ach Picked back up by axon terminal and put back into vesicles until next message comes along Recycled Postsynaptic cell sums up excitatory and inhibitory input Excitatory Inhibitory Causes action potential to occur Causes cell to become more negative Stops firing of message Spatial summation Temporal summation Several messages arrive at the axon hillock simultaneously One message arrives constantly over and over again The effect of a neurotransmitter depends on the neurotransmitter and its receptor Inhibitory vs excitatory Cell becomes more negative Inhibitory GABA causes post synaptic cell to open up channels for Cl ions Excitatory Ach causes sodium to rush in leads to depolarization Depol leads to an action potential Ionotropic nicotine vs metabotropic muscarinic Ionotropic excitatory Metabotropic inhibitory Many drugs can alter activity at the synapse Oxycodone oxycontin Prevents release of Ach Not having a response set to muscles