EMG and Smooth Muscles PDF

Department of Human Physiology Faculty of Medical Sciences University of Warmia and Masuria in Olsztyn  ELECTROMYOGRAPHY -EMG IS A TECHNIQUE FOR EVALUATING AND RECORDING THE ELECTRICAL ACTIVITY PRODUCED BY SKELETAL MUSCLES. The potential differences between the...

Department of Human Physiology Faculty of Medical Sciences University of Warmia and Masuria in Olsztyn  ELECTROMYOGRAPHY -EMG IS A TECHNIQUE FOR EVALUATING AND RECORDING THE ELECTRICAL ACTIVITY PRODUCED BY SKELETAL MUSCLES. The potential differences between the interior of the muscle cell and the extracellular environment formed during the muscle cell stimulation cause the electric field formation around this muscle cell The potential differences in the electric field can be recorded using special electrodes positioned in the field and connected with the corresponding registrant equipment  ELECTROMYOGRAPHY -EMG EMG IS PERFORMED USING AN INSTRUMENT CALLED AN ELECTROMYOGRAPH, TO PRODUCE A RECORD CALLED AN ELECTROMYOGRAM. the degree of stimulation of the muscle activity can be examined by recording the muscle electrical activity through electrodes placed inside the muscle or on its surface.  ELECTROMYOGRAPHY -EMG INTRAMUSCULAR EMG a needle electrode or a needle containing two fine-wire electrodes is inserted through the skin into the muscle tissue this electrodes record the action potentials of individual fibers, the part, or the whole of the motor unit (it depends on the size of the receiving surface area of the muscle) the needle electrodes are used primarily in the diagnosis of neuromuscular diseases and disorders of motor control  ELECTROMYOGRAPHY -EMG SURFACE EMG recording electrodes are applied to the skin surface and pick up the activity of the muscles beneath them. the surface electrodes may be used to monitor the general picture of muscle activation (global electromyogram) the surface electrodes are also used in the biochemical studies of skeletal muscle  ELECTROMYOGRAPHY -EMG SURFACE EMG THERE ARE TWO WAYS TO PLACE THE SURFACE ELECTRODES ON THE SKIN – UNIPOLAR or BIPOLAR UNIPOLAR RECORDING ❖ the active (recording) electrode is placed over the examined muscle but in some distance a zero electrode (ground) is located. ❖ unipolar recording allows to register the potential differences between the zero electrode (ground) and the active electrode  ELECTROMYOGRAPHY -EMG SURFACE EMG THERE ARE TWO WAYS TO PLACE THE SURFACE ELECTRODES ON THE SKIN – UNIPOLAR or BIPOLAR BIPOLAR RECORDING ❖ two active electrodes pick up the impulses from the studied muscle and record the potential differences between the points with which they come into contact.  ELECTROMYOGRAPHY -EMG WHAT CAN BE LEARNED FROM AN EMG? Time course of muscle contraction Contraction force Coordination of several muscles in a movement sequence These parameters are DERIVED from the amplitude, frequency, and change of these over time of the EMG signal PHYSIOLOGY OF SMOOTH MUSCLES Leonardo da Vinci  SMOOTH MUSCLE ✓ Found in walls of most hollow organs and tubes (except heart) ✓ Usually in two layers (longitudinal and circular) Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section) Small intestine Mucosa Circular layer of smooth muscle (shows longitudinal views of smooth muscle fibers)  SMOOTH MUSCLE LONGITUDINAL LAYER – OUTER LAYER Fibers run parallel to long axis of organ during contraction → the organ dilates and shortens © 2013 Pearson Education, Inc.  SMOOTH MUSCLE CIRCULAR LAYER – INNER LAYER Fibers run around the circumference of organ; contraction → constricts lumen and elongates organ © 2013 Pearson Education, Inc. CHARACTERISTIC OF SMOOTH MUSCLE Contraction and relaxation slower Uses less energy to generate a given amount of force Maintains force for long periods Has Low oxygen consumption rates  SMOOTH MUSCLE STRUCTURE small, slender and spindle-shaped fibers: thiner and shorter compared with skeletal muscle fibers have only a single centrally located nucleus have no T tubules, myofibrils, or sarcomeres (no striations) have no tendons  CHARACTERISTIC OF SMOOTH MUSCLE Contains actin and myosin - Higher actin to myosin ratio and longer actin and myosin filaments Myosin fibers have more heads per thick filament (heads over entire length, arranged diagonally) Myosin has light chains (play regulatory role) Myosin ATPase activity is much slower Smooth muscle myosin has hinged heads all along its length. Myosin filament Actin filament CHARACTERISTIC OF SMOOTH MUSCLE actin is assosiated with tropomyosin no troponin complex (contains calmodulin, calponin , caldesmon)  CHARACTERISTIC OF SMOOTH MUSCLE thin filaments are attached to dense bodies in the cytoplasm and to the attachment plaques in the membrane Correspond to Z discs of skeletal muscle dense bodies bind the muscle cell to connective tissue fibers outside the cell and to adjacent cell and can transmit contractions from cell to cell 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 Cell 2 tissue Cell 1 Dense body Intermediate filament  SMOOTH MUSCLE STRUCTURE ❖ Has little sarcoplasmic reticulum with IP3-receptor channels ❖ Pouchlike infoldings (caveolae) of sarcolemma sequester Ca2+ SMOOTH MUSCLE – ACTIVATING FACTORS SMOOTH MUSCLE SHRINKING DUE TO: 1. SPONTANEOUS STIMULATION – self-excitatory cells 2. LOCAL FACTORS – mechanical or chemical agents acting directly on the cells eg. Stretching muscles, changing of pH, increase in the quantity of carbon dioxide 3. CHEMICALS (hormones) produced in the distal tissues 4. CHEMICALS (neurotransmitters) secreted from axons of neurons belonging to the autonomic nervous system  CONTRACTION OF SMOOTH MUSCLE ❖ Slow, synchronized contractions - Very energy efficient (slow ATPase activity) ❖ Sliding filament mechanism ❖ Ca2+ is obtained from the SR and extracellular space CONTRACTION OF SMOOTH MUSCLE Extracellular fluid (ECF) Ca2+ Plasma membrane Cytoplasm 1 Calcium ions (Ca2+) enter the cytosol from the ECF via voltage- dependent or voltage- Ca2+ independent Ca2+ channels, or from the scant SR. Sarcoplasmic reticulum Figure 9.29, step 1 CONTRACTION OF SMOOTH MUSCLE 2 Ca2+ binds to and activates calmodulin. Ca2+ Inactive calmodulin Activated calmodulin Figure 9.29, step 2 CONTRACTION OF SMOOTH MUSCLE 3 Activated calmodulin activates the myosin light chain kinase Enzymes (MLCK). Inactive kinase Activated kinase Figure 9.29, step 3 CONTRACTION OF SMOOTH MUSCLE 4 The activated kinase enzymes ATP catalyze transfer of phosphate to myosin, activating the myosin ADP ATPases. Pi Pi Inactive Activated (phosphorylated) myosin molecule myosin molecule CONTRACTION OF SMOOTH MUSCLE 5 Activated myosin forms cross bridges with actin of the thin filaments and shortening begins. Thin filament Thick filament Figure 9.29, step 5  RELAXATION OF SMOOTH MUSCLE RELAXATION REQUIRES: Active transport of Ca2+ into SR and ECF Ca2+ detachment from calmodulin Dephosphorylation of myosin to reduce myosin ATPase activity RELAXATION OF SMOOTH MUSCLE Relaxation in Smooth Muscle ECF Ca2+ Ca2+ Na+ 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+ Figure 12-29, step 1 RELAXATION OF SMOOTH MUSCLE Relaxation in Smooth Muscle ECF Ca2+ Ca2+ Na+ 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). Ca2+ CaM Figure 12-29, steps 1–2 RELAXATION OF SMOOTH MUSCLE Relaxation in Smooth Muscle ECF Ca2+ Ca2+ Na+ 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). Ca2+ CaM 3 Myosin 3 Myosin phosphatase removes ATP phosphate from myosin, which phosphatase decreases myosin ATPase activity. Inactive ADP + P P myosin Myosin ATPase activity decreases. Figure 12-29, steps 1–3 RELAXATION OF 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). Ca2+ CaM 3 Myosin 3 Myosin phosphatase removes ATP phosphate from myosin, which phosphatase decreases myosin ATPase activity. Inactive ADP + P P myosin Myosin ATPase activity decreases. 4 4 Less myosin ATPase results in decreased muscle tension. Decreased muscle tension Figure 12-29, steps 1–4 NEURAL REGULATION OF SMOOTH MUSCLE CONTRACTION INNERVATED BY AUTONOMIC NERVOUS SYSTEM Sympathetic and/or parasympathetic part of ANS May be excitatory or inhibitory Target cell response depends on receptor type  INNERVATION OF SMOOTH MUSCLE varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters Autonomic nerve fibers innervate smooth muscle at diffuse junctions © 2013 Pearson Education, Inc.  TYPES OF SMOOTH MUSCLES 1. SINGLE-UNIT (VISCERAL) SMOOTH MUSCLE 2. MULTI-UNIT SMOOTH MUSCLE SINGLE-UNIT (VISCERAL) SMOOTH MUSCLE Most common type Muscle fibers contract synchronously as a unit (fibers connected by gap junctions) Autonomic neuron Small varicosity intestine Gap junctions Neuro- transmitter Smooth muscle Receptor cell SINGLE-UNIT (VISCERAL) SMOOTH MUSCLE GUP JUNCTION ❑ is a specialized intercellular connection between the smooth muscle cells ❑ directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells © 2013 Pearson Education, Inc. SINGLE-UNIT (VISCERAL) SMOOTH MUSCLE Often exhibit spontaneous action potentials (pacemaker cells with spontaneous depolarization) Innervation to few cells Autonomic neuron Small varicosity intestine Gap junctions Neuro- transmitter Smooth muscle Receptor cell SINGLE-UNIT (VISCERAL) SMOOTH MUSCLE stimulation and the process of muscle contraction lasts a long time and slowly disappears LOCATION: Intestinal tract, respiratory tract, reproductive system Blood vessels Autonomic neuron Respiratory tract varicosity Small intestine Gap junctions Neuro- transmitter Smooth muscle Receptor cell  MULTI-UNIT SMOOTH MUSCLE ❑ Few if any gap junctions (each fiber acts individually as a single unit) ❑ not have their own automaticity (pacemaker cells) Eye Varicosity Neuron  MULTI-UNIT SMOOTH MUSCLE ❑ Graded contractions occur only in response to neural stimuli ❑ Arranged in motor units (each muscle fiber receives its own innervation), have very dense innervation Eye Varicosity Neuron  MULTI-UNIT SMOOTH MUSCLE ❑ stimulation of muscle contraction is short and disappears quickly ❑ LOCATION: in large airways and arteries, eye (ciliary muscle and iris) Eye Varicosity Neuron  INNERVATION OF SMOOTH MUSCLE AUTONOMIC NERVOUS SYSTEM SYMPATHETIC PARASYMPATHETIC (NORADRENALINE) (ACETYLCHOLINE) NONADRENERGIC NONADRENERGIC MUSCARINIC RECEPTORS RECEPTORS RECEPTORS (M1,M2,M3) α1, α2 β2, β3 GASTRIC MUSCLE M1 – INCREASING OF TENTION GASTRIC MUSCLE a1 - REDUCING OF TENSION M1- CONTRACTION, STIMULATION β2 - RELAXATION, INHIBITION OF PERISTALSIS OF PERISTALSIS AORTIC MUSCLE a1, a2 - CONTRACTION, VASOCONSTRICTION AORTIC MUSCLE β2 - RELAXATION, VASODILATATION M1- RELAXATION, VASODILATATION