* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Neural Pathways and Transmission
Response priming wikipedia , lookup
Types of artificial neural networks wikipedia , lookup
Central pattern generator wikipedia , lookup
Optogenetics wikipedia , lookup
Multielectrode array wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Mirror neuron wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Signal transduction wikipedia , lookup
Synaptogenesis wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Psychophysics wikipedia , lookup
Neural engineering wikipedia , lookup
Patch clamp wikipedia , lookup
Neuroanatomy wikipedia , lookup
Metastability in the brain wikipedia , lookup
Node of Ranvier wikipedia , lookup
Pre-Bötzinger complex wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Development of the nervous system wikipedia , lookup
Neural coding wikipedia , lookup
Neurotransmitter wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Action potential wikipedia , lookup
Chemical synapse wikipedia , lookup
Membrane potential wikipedia , lookup
Electrophysiology wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Resting potential wikipedia , lookup
Single-unit recording wikipedia , lookup
End-plate potential wikipedia , lookup
Synaptic gating wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Biological neuron model wikipedia , lookup
Neural Pathways and Transmission Neural Circuits There are two basic responses to stimuli coming in from the environment – The Reflex Arc – The Neural Circuit The Reflex Arc The reflex arc is an automatic response which cuts out the pathway to the brain The body responds without thinking about it 5 basic steps to the reflex arc Reflex Arc 1. 2. 3. 4. 5. Stimulus: The receptors receive information from the environment big enough to illicit a response from the nervous system Sensory Neurons: Carry information from the receptors to the interneurons in the spinal cord Interneurons: transmit the message through the spinal cord immediately to the motor neurons Motor Neurons: carry the message away from the CNS to the peripheral nervous system to illicit a muscle response Muscle Response: When the effectors (muscles) respond to the stimuli received from the motor neurons Ex. Hand pulls away in response to a hot burner on a stove REFLEX ARC http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/stretch_reflex_v2.html The Neural Circuit The neural circuit is very similar to the reflex arc, however, the information is carried all the way to the brain to allow for decision making and analysis of the stimuli Once the information is relayed to the CNS via the interneurons, the information continues onto the brain Brain decides response and carries the message back to the spinal cord via interneurons to be carried to the motor neurons and illicit response Ex. After hand has been pulled away, respond “ouch” Electrochemical Impulses But how does information travel within the neuron to reach the CNS? Each neuron is polarized This means that charged particles, called ions, line the membrane of the neuron, causing a difference in charge across the membrane Potassium and sodium ions line the membrane in unequal distribution to cause a positive exterior and a negatively charged interior Potassium (K+) is concentrated on the interior of the cell, sodium (Na+) on the outside When the neuron is stimulated, the charges reverse, causing the message to be carried down the neuron in one direction only Neuron Ion Movement Neuron membrane has more K+ channels than Na+ channels – Channels – facilitated diffusion – More potassium out than sodium in Na/K Pump – Active transport – Moves K+ back into the neuron – Moves Na+ out of neuron Resting State of the Neuron At resting, sodium lines the exterior of the cell membrane, potassium lines the interior of the cell, although not in equal proportions This creates an overall charge that is negative within the cell at rest The internal environment is generally at –70 mV Depolarization When the stimuli elicits a response big enough to break the neuron’s threshold, the neuron will transmit the message down the axon to other neurons This is an “all or nothing” response, firing regardless of the strength in stimuli, or not firing at all If threshold is reached, the neuron will have a response During this period, the membrane becomes more permeable to sodium than potassium http://www.youtube.com/watch?v=pbg5E9 GCNVE&feature=related Depolarization Ion channels specific for sodium open within the cell membrane, allowing sodium to move into the neuron This causes a very temporary reversal in charges, in which the interior is now positively charged, and the exterior is negatively charged Internal environment is, on average, 30 mV at this state This depolarization can also be referred to as the action potential, which shows the differences in charges from resting to depolarization Once the maximum amount of sodium has diffused in, the cell begins to repolarize Repolarization During repolarization, the cell must remove the sodium from the internal environment within the cell This is accomplished using sodium/potassium pumps, a form of active transport, requiring ATP Repolarization only takes about 0.001s, in which the cell returns to it’s resting state During this process, the cell cannot be stimulated again, until the resting state has been re-established Hyperpolarization For an instant after repolarization, the cell overcompensates by transporting more sodium than necessary across the membrane, called hyperpolerization The cell becomes slightly more negative than normal Sodium will move back across the membrane until resting state is returned (-70 mV) Again, no new impulses can be fired at this point The refractory period is the time after depolarization, through repolarization, and to hyperpolarization http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/action_potential_v2.html Action Potential of a Myelinated Neuron (saltatory conduction) In myelinated axons, depolarization happens only at the nodes (A) and an action potential jumps to the next node (B). The red arrows show the direction of the nerve impulse and the black arrows show the flow of ions. http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/saltatory_conduction.html Neuron threshold and the All-orNone Response The threshold level is the minimum level of a stimulus required to produce a response – each neuron has its own threshold level - once threshold has been met the neuron will fire All-or-none response: The intensity of the nerve impulse and speed of transmission remain the same How do we determine intensity of a response???