Lecture 13: AP Conduction, Cell-Cell Communication, and Skeletal Muscle, Study notes of Biology

Download Lecture 13: AP Conduction, Cell-Cell Communication, and Skeletal Muscle and more Study notes Biology in PDF only on Docsity! 1 Lecture 13 AP Conduction Cell-Cell Communication Skeletal Muscle Review of Lecture 11 Ion Channel Structure Atomic basis of ion channel selectivity 2003 Nobel Prize in Chemistry The Atomic Basis of Selective Ion Conduction in Potassium Channels http://nobelprize.org/chemi stry/laureates/2003/mackin non-lecture.html Ion Solubility in Water http://www.rockefeller.edu/pubinfo/043003.php 2 Outline Propagation of Action Potentials Synapse Structure of Skeletal Muscle Living Crystal Myofibrils Muscle Contraction Overview Excitation Contraction Coupling Length Tension Relationship Summation and Recruitment Outline Propagation of Action Potentials Synapse Structure of Skeletal Muscle Living Crystal Myofibrils Muscle Contraction Overview Excitation Contraction Coupling Length Tension Relationship Summation and Recruitment Conduction of AP Along Neuron What if we remove the space clamp that we inserted last time? Now V=V(x,t) Divide membrane into patches of length dx Set up model in terms of incremental variables Fig 3.6 Cellular Biophysics: Electrical Properties Weiss Derivation of Cable Equation Circuit diagram Step One: KVL along inner/outer membrane Step Two: KCL Cable Equation: mm ie m m mm CR rr R V t V x V = + = =+ ∂ ∂ + ∂ ∂ − τ λ τλ 2 2 2 2 0 Fig 3.11 Cellular Biophysics: Electrical Properties Weiss 5 Models of Synaptic Transmission Synaptic transmission has quantal nature Ach is packaged into discrete vesicles An integer number of vesicles are released Particularly apparent at low calcium concentration Fig 7.2 Mathematical Physiology Keener Models of Synaptic Transmission n = # ACh vesicles at presynaptic terminal, each with same amount of ACh p = probability of 1 vesicle release Probability that k sites fire? Fig 7.4 Mathematical Physiology Keener Pre-Synaptic Voltage Gated Calcium Channels In synaptic transmission: AP reaches nerve terminal Opens voltage gated calcium channels Influx of calcium Neurotransmitter release Voltage gated calcium channel: Consists of n identical subunits Each can be open (Op) or shut (S) All subunits must be open to conduct calcium Fig 7.5 Mathematical Physiology Keener 6 Outline Propagation of Action Potentials Synapse Structure of Skeletal Muscle Living Crystal Myofibrils Muscle Contraction Overview Excitation Contraction Coupling Length Tension Relationship Summation and Recruitment My Favorite Muscle Website http://muscle.ucsd.edu/musintro/jump.sht ml Three Types of Muscle Skeletal Voluntary Cardiac Involuntary Smooth Involuntary Fig 12.1 muscle Silverthorn 2nd Ed Structure of Skeletal Muscle Contracts in response to signal from a somatic motor neuron Attached to bones via tendons Fig 12.2 muscle Silverthorn 2nd Ed 7 Structure of Skeletal Muscle Skeletal Muscle: Collection of muscle cells Long cylindrical cells with several hundred nuclei on surface Muscle cells bound together with connective tissue, nerves and blood vessels in between Within muscle cell: Extensive sarcoplasmic reticulum (modified ER) Longitudinal tubules which release calcium Terminal cisternae which concentrate and sequester calcium Membrane punches in at terminal cisternae T-tubules lumen continuous with extracellular fluid These allow APs at cell surface to quickly move to cell interior Fig 12.3 b,c – Skeletal muscle Silverthorn 2nd Ed Fig 12.4 – T-Tubules and the sarcoplasmic reticulum Silverthorn 2nd Ed Myofibril Muscle cell contains >1000 myofibrils Occupy most of cell volume Made up of: Contractile proteins: Actin, myosin Regulatory proteins: Tropomyosin, Troponin Accessory proteins: Titin, nebulin Proteins: Arranged in cell to create pattern of light and dark bands under light microscope Sarcomere: one repeat of the pattern Fig 12.3 d,e,f – Skeletal muscle Silverthorn 2nd Ed Fig 12.5 – The two- and three- dimensional organization of a sarcomere Silverthorn 2nd Ed 10 Length-Tension Relationship Single twitch tension Tension of a twitch: Reflection of sarcomere lengths Sarcomere length: Reflects overlap between actin and myosin filaments Tension: Proportional to # of crossbridges between thick & thin filaments Initially: Sliding filaments interact minimally As overlap increases: They overlap more Tension increases Finally: Thick filaments run into Z disks at end of sarcomere Fig 12.14 Silverthorn 2nd Ed Control of Force of Contraction Single twitch tension is determined by length of sarcomere Time scale: Typical muscle AP lasts 1-3 ms Typical muscle contraction lasts 100 ms If time between APs is reduced: Muscle fiber can’t completely relax at time of 2nd stimulus 2nd contraction is more forceful SUMMATION Fig 12.15 Silverthorn 2nd Ed Fig 12.15 Silverthorn 2nd Ed Fig 12.15 Silverthorn 2nd Ed 11 Fig 12.15 Silverthorn 2nd Ed Control of Force of Contraction Each muscle fiber: Innervated by 1 somatic motor neuron Single motor neuron: May innervate hundreds (or thousands) of muscle fibers Within each muscle: Each muscle fiber contracts in all-or-none manner Force of muscle contraction can be increased: By recruiting additional motor units RECRUITMENT Motor neurons have different thresholds to fire As stimulus increases in intensity: Additional motor neurons fire Additional motor units recruited Summary Propagation of Action Potentials Synapse Structure of Skeletal Muscle Living Crystal Myofibrils Muscle Contraction Overview Excitation Contraction Coupling Length Tension Relationship Summation and Recruitment Poem of the Day Due Dates Tuesday, October 19th HW7 Tuesday, October 26th Exam II