Understanding the Nervous System: Organization, Cells, and Electrical Signals, Study notes of Biology

Download Understanding the Nervous System: Organization, Cells, and Electrical Signals and more Study notes Biology in PDF only on Docsity! 1 Lecture 10 Overview of the Nervous System Outline Organization of Nervous System Constituent Cells of Nervous System Electrical Signals in Neurons Source of Resting Membrane Potential Gated Ion Channels Qualitative Description of Action Potential Graded Potential Action Potential Refractory Period Outline Organization of Nervous System Constituent Cells of Nervous System Electrical Signals in Neurons Source of Resting Membrane Potential Gated Ion Channels Qualitative Description of Action Potential Graded Potential Action Potential Refractory Period Organization of the Nervous System Central nervous system Brain and spinal cord Peripheral nervous system Afferent neurons Sensory neurons Efferent neurons Send response to effector cells Somatic motor division Control skeletal muscle Autonomic division Controls smooth and cardiac muscle and exocrine/endocrine Two components: Sympathetic Parasympathetic Commonly exert antagonistic control over a single target Fig 8.1 – Organization of the nervous system Silverthorn 2nd Ed Outline Organization of Nervous System Constituent Cells of Nervous System Electrical Signals in Neurons Source of Resting Membrane Potential Gated Ion Channels Qualitative Description of Action Potential Graded Potential Action Potential Refractory Period 2 Cells of the Nervous System Neurons Basic signaling units of nervous system Consist of: Cell body Axons – carry outgoing information Dendrites – receive incoming signals Glial Cells Support cells Outnumber neurons by 10-50X Provide physical support for neural tissues Direct growth of neural tissue during repair and development Insulate axons creating myelin Fig 8.2 – Model neurons Silverthorn 2nd Ed Fig 8.6 – Formation of myelin Silverthorn 2nd Ed Outline Organization of Nervous System Constituent Cells of Nervous System Electrical Signals in Neurons Source of Resting Membrane Potential Gated Ion Channels Qualitative Description of Action Potential Graded Potential Action Potential Refractory Period Resting Membrane Potential Nernst Equation GHK Equation [ ] [ ] ⎟⎟⎠ ⎞ ⎜⎜ ⎝ ⎛ = in out ion ion ion Z E log61 [ ] [ ] ⎟⎟⎠ ⎞ ⎜⎜ ⎝ ⎛ + + = −++ −++ outClinNainK inCloutNaoutK m ClPNaPKP ClPNaPKP F RTV ][][ ][][ln Electrical Signals in Neurons If membrane permeability to ion changes: Membrane potential changes To substantially change Vm: Only small # of ions need to cross membrane Changes in Vm do not alter ion concentrations inside and outside cell 5 Fig 8.10 a – Model of the voltage-gated Na+ channel Silverthorn 2nd Ed Fig 8.10 b – Model of the voltage-gated Na+ channel Silverthorn 2nd Ed Fig 8.10 c – Model of the voltage-gated Na+ channel Silverthorn 2nd Ed Fig 8.10 d – Model of the voltage-gated Na+ channel Silverthorn 2nd Ed Fig 8.10 e – Model of the voltage-gated Na+ channel Silverthorn 2nd Ed Fig 8.11 – Ion movements during the action potential Silverthorn 2nd Ed 6 Refractory Period Double gating of Na+ channel leads to refractory period Absolute refractory period Once an AP has begun, for about 1 ms, a 2nd AP can’t be generated Relative refractory period After Na+ channel gates have been reset, but before Vm has returned to normal, a STRONG graded potential can start a 2nd AP Graded potential opens Na+ channels, but Na+ entry is offset by continuing K+ loss through K+ channels that are still open Fig 8.12 Refractory periods Silverthorn 2nd Ed Features of APs Stimulus intensity is coded by AP frequency Conduction of APs: Travel from trigger zone to axon terminal Refractory period APs travel in only one direction Speed of conduction: Depends on neuron diameter ↑ diameter ↑ speed Resistance of membrane to current leak Myelination increases speed of conduction Fig 8.14 – Action potentials along an axon Silverthorn 2nd Ed Fig 8.15 – Conduction of action potentials Silverthorn 2nd Ed Myelination Nodes of Ranvier Membrane resistance lowest at these points AP Propagation Starts at trigger zone AP flows to 1st Node of Ranvier Node has high density of voltage gated Na+ channels Na+ re-entry boosts strength of AP Saltatory Conduction “Leapfrogging” of APs 7 Fig 8.17 – Saltatory conduction Silverthorn 2nd Ed Summary Organization of Nervous System Constituent Cells of Nervous System Electrical Signals in Neurons Source of Resting Membrane Potential Gated Ion Channels Qualitative Description of Action Potential Graded Potential Action Potential Refractory Period Poem of the Day I Chop Some Parsley While Listening to Art Blakey’s Version of “Three Blind Mice” Billy Collins http://www.cduniverse.com/search/xx/music/ pid/1230695/a/Three+Blind+Mice,+Vol+1.ht m Due Dates Tuesday, October 5th HW5