E109 Lecture 8: Muscle III PDF

E109 Lecture 8: Muscle III Learning Objectives: motor units Understand nervous system control of muscle contraction (Extrinsic control) Observe that motor unit recruitment happens in one direction Learn that the different muscle fiber types have different metabolic...

E109 Lecture 8: Muscle III Learning Objectives: motor units Understand nervous system control of muscle contraction (Extrinsic control) Observe that motor unit recruitment happens in one direction Learn that the different muscle fiber types have different metabolic needs, which impacts function Motor Unit Recruitment SPINAL CORD Neuron 1 Neuron 2 Neuron 3 Motor nerve KEY Muscle fibers Motor unit 1 A motor unit consists of Motor unit 2 one motor neuron and all the fibers it Motor unit 3 innervates 100 50 Small MU Intermediate MU Large MU 0 0 25 50 75 100 % of Motor Units Recruited Order of motor unit recruitment Fiber Types Small Motor Unit Intermediate Motor Unit Large Motor Unit Fiber Types Slow twitch Intermediate twitch Fast twitch Fiber Types Twitch tension Slow Intermediate Fast Time (ms) Velocity Vmax Cellular Metabolism all fpd to generate 518 dative require oxygen mid oxidative ca myosin atpase contraction SR ca't pump relaxation not Thsattative Fiber Types Slow Oxidative Fast Oxidative Fast Glycolytic smalloxidative good for oxygen to diffuse in Fiber Type Comparison Fiber Type Characteristics Slow Oxidative Fast Oxidative Fast Glycolytic Twitch Speed Slow Intermediate Fast Myosin ATPase Slow Intermediate Fast Fiber Diameter Small Medium Large Ca2+ Pumps in SR Fewer Many Many Endurance Fatigue Resistant Fatigue Resistant Easily Fatigued Metabolism Oxidative Oxidative Glycolytic Capillary Density High Medium Low Mitochondria High Medium Low O2 storage Myoglobin Some myoglobin None Learning Goals: smooth muscle Learn the contraction dynamics of smooth muscles Observe that they are very different from skeletal muscles: they just need to change shape Understand that the calcium signal in smooth muscles isn’t all from the SR, but can come from external sources Learn that the membrane potential of smooth muscles is unstable, making them responsive to different signals Smooth Muscle Skeletal Cardiac Smooth Attached to Skeleton Heart Internal organs Striated Striated Smooth Sarcomere Sarcomere Oblique Bundles Multinucleated Uninucleated Uninucleated Fastest Intermediate Slowest Somatic motor Autonomic Autonomic Anatomy of Smooth Muscle Slow as compared to style shrinks deforms cell during contraction T.si Anatomy of smooth muscle Circular layer Longitudinal layer Oblique layer Stomach peristaltic contraction Contractile speed not as much force longer Varicosities in Smooth Muscle Vesicle containing autonomic neuronsgoing Mitochondrion Neurotransmitter to smokthemushes consities postganglionic autonomic neuron Ñitin gemstinated Varicosities Varicosity Figure 11-8 Varicosities Smooth muscle cells Types of Smooth Muscle: Single-unit Wholetissue works as In t i Autonomic neuron varicosity manycells tonnette Small as 1 unit thru intestine gapjunction Gap junctions graded Neuro- Potennailscan transmitter carry Smooth muscle cell Receptor around tubes found Types of Smooth Muscle: Multi-unit more control able to tweak focus Eye Varicosity Neuron found in more specific areas Calcium Signal in Smooth Muscle Ligand Stretch or Signal depolarization opens channels when Membrane large areas of contration receptors Membrane are needed channels Increased Increased IP3 Ca2+ entry IP3: Inositol Triphosphate IP3-R Sarcoplasmic reticulum Muscle Ca2+ release Contraction Membrane Potentials Vary in Smooth Muscle (a) Slow wave potentials Membrane potential Action potentials Threshold Slow wave potential Time Figure 12-31a Membrane Potentials Vary in Smooth Muscle (b) Pacemaker potentials Membrane potential Threshold Pacemaker potential Time Figure 12-31b Relaxation in Smooth Muscle Ca2+ Ca2+ Na+ ECF ATP Sarcoplasmic reticulum 1 1 Free Ca2+ in cytosol decreases when Na+ Ca2+ is pumped out of the cell or back into the sarcoplasmic reticulum. Ca2+ ATP Ca2+ CaM 2 2 Ca2+ unbinds from calmodulin (CaM). in skeletal Deactivating MLCK. cart bindsto are Ca2+ CaM trinism p 3 Myosin 3 Myosin phosphatase removes P phosphate from myosin, which ATP phosphatase decreases myosin ATPase activity. Inactive P P myosin Myosin ATPase activity decreases. 4 4 Less myosin ATPase results in decreased muscle tension. Decreased muscle tension