BIOL 253L Final

• Intramuscular EMG: needle electrodes inserted through the skin into the muscle
• Surface EMG: electrodes placed on the skin's surface
• An EMG represents the combined electrical activity of thousands of individual muscle fibers; as the number of electrically active muscle fibers increases, the frequency of those muscle fibers' action potentials increase making the strength of the EMG signal increase
• Motor Unit: a neuron and the muscle fibers it controls. All muscles within a motor unit act synchronously and it increases contractile strength of a whole muscle
• Coactivation: a phenomenon in which contraction of an antagonist muscle leads to a minor activity in the antagonist muscle
• Agonist muscles are the "prime movers" as they are the primary muscle responsible for generating movement through their contraction
• Antagonist muscles control(or oppose) specific movement, and return the muscle to its initial position. Depending on the movement, agonist and antagonist muscles may change their roles
• Agonist and antagonist muscles are known as an antagonistic pair
• Muscle fatigue: a state of physiologicl inability to contract effectively; associated with a variety of psychological and physiological factors, including loss of central drive, reduction in blood flow, changes in sense of effort, and build up of lactic acid
• ATP can be remade to ADP by the addition of the phosphate group through three pathways:

  • pyruvate entering the citric cycle and broken down to CO2 and H2O (aerobic glycolysis) -> this generates large amounts of ATP through oxidative phosphorylation (the electron transport chain)
  • Anaerobic glycolysis: pyruvate can't enter the citric acid cycle and gets converted to lactic acid making small amounts of ATP
  • ATP transfers phosphate to creatine obtained through the circulation from the liver making phosphocreatine
• Physiological causes of fatigue:

  • Changes in one's motivation or sense of effort.
  • Decline in central nervous system command of motor units (central drive). 
  • Failure of neuromuscular propagation.  Neurons may temporarily run low on neurotransmitter.
  • Reduction in Ca2+ release in excitation-contraction coupling.
  • Metabolic changes in the muscle cell (such as build-up of lactic acid which can make the skeletal muscle acidic inhibiting any further anaerobic glycolysis).
  • Reduction in muscle blood flow owing to compression of blood vessels.
• peripheral neuropathy: the damage or disease of the lower motor neurons or their myelin sheaths; associated with various combinations of motor, sensory, and autonomic dysfunctions
• The cessation fo signal across the NMJ occurs because 1. NT may diffuse away from the nicotinic ACh receptors on the motor end plate, and 2. AChe breaks down ACh in the synapse, preventing its activation of the ACh receptors; breakdown products are taken back into the axon terminal through uptake
• Myasthenia Gravis: an auto-immune disease resulting in most commonly from antibodies to ACh receptors, can cause fatigue quickly and usually affects muscles in the eyes, face, and neck first
• Lambert-Eaton Myasthenic Syndrome (LEMS): autoimmune disease causing muscle weakness resulting from antibodies that affect voltage-sensitive calcium channels of motor-end plates, inhibiting ACh release
• Botulism: the botulinum toxin acts directly on the NMJ to inhibit ACh release, resulting in muscle paralysis
• Myopathies: diseases affecting the muscle itself, among these are muscular dystrophies which are characterized by progressive muscle weakness as a result of the death of muscle cells
• Duchenne's muscular dystrophy, a recessive X-linked condition that develops in young boys causing a defect in dystrophin resulting an excess of Ca2+ ions entering muscle cells leading to damage to mitochondria, ultimately leading to cell death
• Becker's muscular dystrophy: deletions in dystrophin gene permit synthesis of a shorter but semifunctional protein
• Verbal encouragement is the most effective in reducing muscle fatigue whereas brief periods of rest was the least effective; visual feedback was the intermediate of the two
• An EMG records the electrical activity of the innervated muscle fibers
• During repeated skeletal muscle contraction, calcium within a single motor unit could reduce when it gets released inhibiting excitation-contraction coupling
• Label the following

  A) Onset of Fatigue

  
• Vesseal walls consist of three layers or tunics from the lumen to the outside, tunica intima (innermost layer), tunica media (middle layer), and tunica adventitia (outer layer).
• Elastic (conducting) arteries include the aorta, pulmonary, common carotid, brachiocephalic, subclavian, and iliac arteries

  Consists of a very thick tunica media layer and small arteries present in the tunica adventitia that absorbs oxygen and nutrients from their lumen by diffusion
• muscular (distributing) arteries arise from elastic arteries and are the mot abundant type of artery in the body

  Characterized by a thick tunica media made of concentric layers of smooth muscle cells and is bordered by the internal elastic lamina and external elastic lamina -> allow the arteries to contract and relax to regulate tissue blood supply
• small arteries and arterioles: arterioles are different from arteries by a lumen with a diameter smaller than 300 micrometers

  • very thin tunica intima
  • tunica media contains < 6 concentric layers of smooth muscle cells
  • tunica adventitia consists of elastin and collagen fibers
• capillaries form extensive networks within tissues

  • tunica intima consists of a single layer of endothelial cells
  • tunica media missing
  • tunica adventitia is greatly reduced/absent
• Medium veins: those with a diameter of 1-10 micrometers

  • tunica intima and tunica media are thinner than similarly-sized arteries
  • tunica intima comprises a thin layer of endothelial cells
  • tunica media consists of 2 or more layers of circularly arranged smooth muscle
  • tunica adventitia is the predominant layer consisting of elastin fibers and collagen and longitudinally arranged smooth muscle fibers
• Large muscular veins: includes the vena cavae, splenic, portal, renal, external iliac, and mesenteric veins

  • Tunica intima comprises of thin layer of endothelial cells
  • Tunica media poorly developed consisting of smooth muscle with some elastic and collagen fibers
  • Tunica Adventitia is the broadest layer comprising bundles of collagen, elastin, and smooth muscle fibers; may also contain vasa vasorum
• Elastance: the elastic properties of the vessel wall (its ability to spring back to its original shape) ΔP/ΔV
• Compliance: the distensibility of the wall (its ability to be distended or stretched) ΔV/ΔP
• If the vessel wall is easy to stretch, its elastance is small and its compliance is large
• The slope (or compliance) of both veins and arteries is not linear because the blood vessel is not a homogenous tissue - the compliance actually decreases at higher volumes and pressures
• A vein's cross sectional shape is elliptical at low volumes and circular at high volumes making it very distensible
• The vein's ability to rapidly increase its volume capacity at lower pressures explains why veins are known as capacitance vessels
• At higher pressures, when the vein is being more fully stretched, it is approximately as compliant as an artery
• Label the following:

  A) vein

  B) artery

  
• The formation of myosin-actin cross-bridges during smooth muscle contraction causes the vessel wall to become stiffer (and less compliant)

  In veins, increasing smooth muscle contraction decreases venous volume and increases venous pressure with decreasing compliance -> also seen in decreased normal aging and in disease states causing increased pulse pressure in elders
• As pressure increases, volume decreases caused by increased smooth muscle contraction