Physiology: Chp 12 C PDF

Physiology: Chp 12 C Autonomic & Somatic Motor Control Juan J. Bustamante, Ph.D. Assistant Professor Pharmaceutical Science Phone (361) 221-0643 Email: [email protected] Office: Room 223 © 2016 Pearson Educ...

Physiology: Chp 12 C Autonomic & Somatic Motor Control Juan J. Bustamante, Ph.D. Assistant Professor Pharmaceutical Science Phone (361) 221-0643 Email: [email protected] Office: Room 223 © 2016 Pearson Education, Inc. Asynchronous recruitment of motor units helps avoid fatigue Motor unit: group of muscle One muscle may have fibers that function together many motor units of SPINAL CORD different fiber types. and the somatic motor neuron that controls them Recruitment of additional motor units by the nervous system increases contraction force Neuron 1 Neuron 2 Neuron 3 Asynchronous recruitment of Motor motor units helps avoid fatigue nerve Different motor units take KEY turns maintaining tension Motor unit 1 Muscle Motor unit 2 fibers Motor unit 3 Figure 12.17 Motor units © 2016 Pearson Education, Inc.  Mechanics of Body Movement Isotonic Contraction. In an isotonic contraction, the muscle contracts, shortens, and creates enough force to move the load. 35 30 Muscle Tension developed (kg) relaxes. Muscle 25 contracts. Force required to move load 20 15 Muscle 10 relaxes. 5 20 kg 20 kg Time Load moves. Muscle stimulated © 2016 Pearson Education, Inc. Figure 12.18a Isotonic and isometric contractions  Mechanics of Body Movement Isometric Contraction. In an isometric contraction, the muscle contracts but does not shorten. The force created cannot move the load. 35 Force required to move load Tension developed (kg) 30 Muscle 25 relaxes. Muscle contracts. 20 15 Muscle 10 relaxes. 5 Load does 30 kg 30 kg not move. Time Muscle stimulated Isometric contractions create force without moving a load Series elastic elements Sarcomeres shorten while elastic elements stretch, resulting in little change in overall length © 2016 Pearson Education, Inc. Figure 12.18b Isotonic and isometric contractions  Muscle Disorders Muscle cramp: sustained painful contraction Overuse Disuse leads to atrophy Acquired disorders © 2016 Pearson Education, Inc.  Muscle Disorders Inherited disorders – Duchenne muscular dystrophy Loss of a structural protein, dystrophin, which links actin to proteins in the cell membranes. – Progressive muscle weakness – Patients usually die before age 30 from failure of the respiratory muscles. https://www.mda.org/disease/duchenne-muscular-dystrophy/causes-inheritance © 2016 Pearson Education, Inc. Figure 12.1 The three types of muscles Skeletal muscle fibers are large, multinucleate cells that appear Nucleus striped or striated under the microscope. Muscle fiber (cell) Striations Nucleus Cardiac muscle fibers are also striated but they are smaller, Muscle fiber branched, and uninucleate. Cells are joined in series by junctions called intercalated disks. Intercalated disk Striations Smooth muscle fibers are small and lack striations. Nucleus Muscle fiber © 2016 Pearson Education, Inc.  Smooth Muscle Classification By location – Vascular, gastrointestinal, urinary, respiratory, reproductive, ocular By contraction pattern – Phasic smooth muscles – Tonic smooth muscles By communication with neighboring cells – Single-unit smooth muscle, or visceral smooth muscle – Multi-unit smooth muscle © 2016 Pearson Education, Inc. Figure 12.22 Smooth muscle contractions © 2016 Pearson Education, Inc.  Smooth Muscle Not arranged in sarcomeres Contraction initiated by electrical or chemical signals or both Controlled by the autonomic nervous system Lacks specialized receptor regions Ca2+ is from the extracellular fluid and sarcoplasmic reticulum ATP is required © 2016 Pearson Education, Inc. Figure 12.23a Smooth muscle coordination Single-unit smooth muscle cells are connected by gap junctions, and the cells contract as a single unit. Autonomic neuron varicosity Small intestine Gap junctions Neuro- transmitter Smooth muscle Receptor cell © 2016 Pearson Education, Inc. Figure 12.23b Smooth muscle coordination Multi-unit smooth muscle cells are not electrically linked, and each cell must be stimulated independently. Eye Varicosity Neuron © 2016 Pearson Education, Inc.  Smooth Muscle Must operate over a range of lengths Layers may run in several directions Contracts and relaxes much more slowly Uses less energy Sustains contractions for extended periods without fatiguing Small, spindle-shaped cells with one nucleus © 2016 Pearson Education, Inc. Figure 12.25 Smooth muscle organization Intermediate filaments and protein dense bodies form a cytoskeleton. Actin attaches to the dense bodies. Each myosin molecule is surrounded by actin filaments. Connective Actin Myosin tissue Cell 2 Cell 1 Dense body Intermediate filament Smooth muscle myosin has hinged heads all along its length. Myosin filament Actin filament Figure courtesy of Marion J. Siegman, Jefferson Medical College. © 2016 Pearson Education, Inc. Figure 12.24 Duration of muscle twitch in the three types of muscle © 2016 Pearson Education, Inc. Figure 12.26 Smooth Muscle Contraction and Relaxation Smooth Muscle Contraction and Relaxation Smooth muscle contraction and relaxation are similar to those of skeletal muscle, but differ in several important ways: (1) Ca2+ comes from the ECF as well as the sarcoplasmic reticulum, (2) an action potential is not required for Ca2+ release, (3) there is no troponin, so Ca2+ initiates contraction through a cascade that includes phosphorylation of myosin light chains, and (4) an additional step in smooth muscle relaxation is dephosphorylation of myosin light chains by myosin phosphatase. Smooth Muscle Contraction Relaxation in Smooth Muscle Increased cytosolic calcium is the signal for contraction. Removal of Ca2+ from the cytosol is the first step in relaxation. Ca2+ Ca2+ ECF Ca2+ Na+ ECF ATP Sarcoplasmic Sarcoplasmic reticulum Na+ reticulum Intracellular Ca2+ concentrations increase when Ca2+ Free Ca2+ in cytosol decreases enters cell and is when Ca2+ is pumped out of Ca2+ Ca2+ released from Ca2+ ATP Ca2+ the cell or back into the sarcoplasmic reticulum. sarcoplasmic reticulum. CaM Ca2+ binds to CaM calmodulin (CaM). Ca2+ unbinds from calmodulin Ca2+ CaM (CaM). MLCK activity Ca2+-calmodulin decreases. activates myosin light Ca2+ CaM Inactive chain kinase (MLCK). MLCK Active Myosin phosphatase (MLCP) ATP MLCK MLCK phosphoryl- removes phosphate from ates light chains in myosin light chains, which myosin heads and decreases myosin ATPase increases myosin ATP activity. ATPase activity. Inactive Myosin Inactive myosin myosin phosphatase ADP + P P Myosin ATPase activity decreases. ADP + P P Active myosin ATPase Actin Less myosin ATPase activity results in decreased muscle tension. Active myosin crossbridges slide along actin Decreased Increased and create muscle P P muscle muscle tension. tension tension © 2016 Pearson Education, Inc.  Smooth Muscle Regulation Many smooth muscles are controlled by both sympathetic and parasympathetic neurons Hormones and paracrines also control smooth muscle contraction – Histamine constricts smooth muscle of airways – Nitric oxide relaxes smooth muscles of blood vessels – Response depends on the second messenger pathway © 2016 Pearson Education, Inc. Figure 12.1 The three types of muscles Skeletal muscle fibers are large, multinucleate cells that appear Nucleus striped or striated under the microscope. Muscle fiber (cell) Striations Nucleus Cardiac muscle fibers are also striated but they are smaller, Muscle fiber branched, and uninucleate. Cells are joined in series by junctions called intercalated disks. Intercalated disk Striations Smooth muscle fibers are small and lack striations. Nucleus Muscle fiber © 2016 Pearson Education, Inc.  Cardiac Muscle has both smooth and skeletal features Like skeletal muscle – Striated – Sarcomere structure Unlike skeletal – Muscle fibers are shorter – May be branched – Have single nucleus © 2016 Pearson Education, Inc.  Cardiac Muscle has both smooth and skeletal features Like smooth muscles – Electrically linked to one another – Some exhibit pacemaker potentials – Under sympathetic and parasympathetic control as well as hormone control Unlike smooth muscle – Gap junctions in intercalated disks © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc.  When a skeletal muscle lengthens, its sarcomeres a. shorten. b. stay the same length. c. lengthen. © 2016 Pearson Education, Inc.  Why does rigor mortis occur after death? Select all that apply a. Body temperature drops. b. The connective tissue surrounding muscle fascicles starts to harden. c. Myosin is tightly bound to actin. © 2016 Pearson Education, Inc.  If you want to study smooth muscle, it doesn’t matter what organ it comes from because all smooth muscle is alike. a. True b. False © 2016 Pearson Education, Inc.  Which of the following phases of a muscle twitch requires ATP? Select all that apply a. latent period b. contraction period c. relaxation period © 2016 Pearson Education, Inc.  Drug “X” inhibits acetylcholinesterase action within the neuromuscular junction. What would drug “X” do to the membrane potential of the muscle fiber? a. It would remain depolarized. b. It would repolarize more quickly than normal. c. It would hyperpolarize. d. Drug “X” would have no effect on the membrane potential. © 2016 Pearson Education, Inc.