PCBI101: MUSCULAR

• Muscle


  Soft tissue of the human body which primarily functions for movement
• Myology


  The branch of science which is the study of muscle
• Functions of Muscles

  • Maintenance of posture
  • Communication
  • Body movement
  • Heart beat
  • Respiration
  • Constriction of organs and vessels
  • Production of body heat
• Excitability


  • Ability of muscle to respond to a stimulus
• Contractility


  • Ability of muscle cells to shorten forcefully

  
• Extensibility


  • Ability of a muscle to be stretched
• Elasticity


  • Ability of muscle to recoil or bounce back to the muscle's original length after being stretched
• Types of Muscle Tissue

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle

  
• Actin


  Actin myofilament made up of actin molecule, tropomyosin and troponin complex
• Myosin


  Myosin filament consisting of a long rod-shaped tail called myosin rod and two globular intertwined myosin head
• Muscular Physiology Terms


  • Acetylcholine (ACh)
  • Actin
  • Action potential
  • Depolarize
  • Neuromuscular junction (NMJ)
  • Neurotransmitter
  • Synaptic cleft
  • T-tubule
  • Repolarization

  
• Sliding Filament Theory


  Proposed mechanism of muscle contraction where actin and myosin filaments slide over each other to shorten the length of muscle fibers, requiring ATP as an energy source

  
• Types of Muscle Fibers

  • Slow-Twitch Oxidative; Red Muscle (Type 1)
  • Fast-Twitch Oxidative-Glycolytic; Red Muscle (Type 2A)
  • Fast-Twitch Glycolytic; White Muscle (Type 2X)

  
• Slow-Twitch Oxidative; Red Muscle (Type 1)


  • Slowest speed of development of maximum tension, slow myosin ATPase activity, small diameter, longest contraction duration, moderate Ca2+-ATPase activity in SR, fatigue resistant, most used for posture, oxidative metabolism, high capillary density, numerous mitochondria, dark red color

  
• Fast-Twitch Oxidative-Glycolytic; Red Muscle (Type 2A)


  • Intermediate speed of development of maximum tension, fast myosin ATPase activity, medium diameter, short contraction duration, high Ca2+-ATPase activity in SR, fatigue resistant, used for standing and walking, glycolytic metabolism becoming more oxidative with endurance training, medium capillary density, moderate mitochondria, red color

  
• Fast-Twitch Glycolytic; White Muscle (Type 2X)


  • Fastest speed of development of maximum tension, fast myosin ATPase activity, large diameter, short contraction duration, high Ca2+-ATPase activity in SR, easily fatigued, least used for jumping and quick fine movements, glycolytic metabolism, low capillary density, few mitochondria, pale color
• Myasthenia Gravis


  Chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles

  
• Fibromyalgia


  Disorder characterized by widespread musculoskeletal pain accompanied by fatigue, widespread pain and cognitive difficulties, causes may include genetics, infections, physical or emotional trauma

  
• Muscular Dystrophy


  Group of diseases that cause progressive weakness and loss of muscle mass due to abnormal genes (mutations) that interfere with the production of proteins needed to form healthy muscle

  
• Bell's Palsy


  Condition in which the muscles on one side of a person's face become weak or paralyzed, caused by trauma to the seventh cranial nerve (facial nerve)
• Pulled Hamstring


  Tear of the hamstring muscle fibers, a group of muscles important in extending the hip joint and bending the knee joint

  
• Muscle Cramp


  Strong, painful contraction or tightening of a muscle that comes on suddenly and lasts from a few seconds to several minutes, often occurs in the legs, causes may include overuse, dehydration, muscle strain, inadequate blood supply, nerve compression, mineral depletion
• Muscle Contractions


  • Isometric (equal distance)
  • Isotonic (equal tension)
• Isometric Contractions


  • The amount of tension increases during the contraction process, but the length of the muscle does not change
  • Responsible for the constant length of the postural muscles of the body, such as the muscles of the back
• Isotonic Contractions


  • The amount of tension produced by the muscle is constant during contraction, but the length of the muscle decreases
  • Concentric Contractions: Muscle tension increases as the muscle shortens
  • Eccentric Contractions: Tension is maintained as the muscle lengthens
• Muscle Tone


  The resistance of a muscle to active or passive stretch, or the overall stiffness of the muscle
• Functions of Muscle Tone

  • Assists in maintaining good posture
  • Can store energy and release it at a later time (stamina)
  • Allows for more "fluidlike" movements of most muscles
• Hypotonia


  Low muscle tone with reduced muscle strength
• Hypotonia is not a specific health sickness, but a possible sign of various disorders that affect muscle strength or motor nerve control by the brain
• Causes of Hypotonia


  • Genetic (born with low muscle tone)
  • Central nervous system disorders
  • Progressive neuromuscular disorders
• Medical Conditions that may cause Hypotonia

  • Down syndrome
  • Muscular Dystrophy
  • Cerebral palsy
  • Prader-Willi syndrome
  • Myotonic dystrophy
  • Tay-Sachs disease
• Symptoms of Hypotonia


  • Muscle feeling extremely soft
  • Difficulty extending the limb beyond what is normal
  • Delay in achieving gross motor skills and problems with feeding
  • Shallow breathing
  • Underactive gag reflex
• Down Syndrome


  • Physical characteristics: Single Palmer Crease, Short Fifth Finger that Curves Inward, White Spots on the Colored Part of the Eye, Small Ears, Small Mouth, Flattened Nose and Face, Upward Slanting Eyes, Wide, Short Hands with Short Fingers, Separated Joints between the Bones of the Skull, Excess Skin at the Nape of Neck, Widely Separated First and Second Toes and Increased Skin Creases, Decreased Muscle Tone at Birth
• Cerebral Palsy


  • Caused by damage to the immature, developing brain, most often before birth
  • Signs in infants: Abnormal muscle tone, Crossed or stiffened legs, Delays in motor skills, Difficulty grasping, Excessive drooling, Inability to lift head, Overextended back/neck, Stiffness
  • Signs in toddlers: Abnormal posture, Lopsided crawling, Difficulty with fine motor skills, Hearing/vision loss, Hopping on knees, Inability to stand, Uncontrollable muscle movement, Scooting, Speech problems, Stiff muscles/joints/tendons
• Prader-Willi Syndrome


  • Caused by missing genetic material on chromosome 15
  • Symptoms: Excessive appetite and overeating, Restricted growth, Hypotonia, Learning difficulties, Lack of sexual development, Behavioural challenges
• Myotonic Dystrophy


  • Part of the muscular dystrophy group
  • Most common adult-onset muscular dystrophy
  • Characterized by progressive muscle wasting and weakness, Prolonged muscle contractions (myotonia), Difficulty relaxing muscles
• Tay-Sachs Disease


  • Rare genetic disorder
  • Caused by absence of enzyme that breaks down fatty substances
  • Fatty substances build up in brain and spinal cord, affecting nerve cell function
  • Most common form starts at 3-6 months, leads to seizures, vision/hearing loss, paralysis, early death
  • Less common juvenile and late-onset forms
• Types of Muscular Dystrophy

  • Duchenne (DMD)
  • Becker
  • Limb-Girdle
• Hypertonia


  • Increased muscle tone and reduced capacity to stretch, caused by injury to central nervous system or spinal cord
  • Takes the forms of spasticity (stiffness related to uncontrolled reflexes) and rigidity (stiffness not associated with reflexes)
• Hypertonia


  Stiff limbs, high muscle tone, difficulty moving, muscle spasms