anaphy

• Types of Muscular Tissue

  • Skeletal
  • Cardiac
  • Smooth
• Skeletal Muscle Tissue

  • Most skeletal muscles move bones
  • Attached to bones by tendons
  • Composed of thousands of muscle fibers bundled together
• Skeletal muscle tissue

  • Striated: Alternating light and dark bands (striations)
  • Organized arrangement of fibers leads to stripe pattern
• Skeletal muscle tissue

  • Works mainly in a voluntary manner
  • Its activity can be consciously controlled
  • Predominantly involved in our movements
• Most skeletal muscles are also controlled subconsciously to some extent
• Cardiac Muscle Tissue

  • Found only in the walls of the heart
  • Striated like skeletal muscle
  • Action is involuntary
• Cardiac muscle contraction

  Initiated by a node of tissue called the "pacemaker"
• Smooth Muscle Tissue

  • Located in the walls of hollow internal structures
  • Lacks the striations of skeletal and cardiac muscle tissue
  • Usually involuntary
• Smooth muscle cells have filaments that can connect into a nest-like network to allow uniform contraction
• Functions of Muscular Tissue


  • Producing body movements
  • Stabilizing body positions
  • Moving substances within the body
  • Generating heat
• Properties of Muscular Tissue


  • Excitability - Ability to respond to stimuli
  • Contractility - Ability to contract forcefully when stimulated
  • Extensibility - Ability to stretch without being damaged
  • Elasticity - Ability to return to an original length
• Connective Tissue Components of Skeletal Muscle


  • Fascia/Fascicle
  • Epimysium
  • Perimysium
  • Endomysium
  • Tendon
  • Aponeurosis
• Nerve and Blood Supply of Skeletal Muscle

  • Somatic motor neurons originate in the CNS and project axons to skeletal muscle
  • Each muscle fiber is in close contact with one or more capillaries
• Microscopic Anatomy of Skeletal Muscle

  • Number of muscle fibers set before birth, most last a lifetime
  • Muscle growth occurs by hypertrophy (enlargement of existing fibers)
  • Testosterone and growth hormone stimulate hypertrophy
  • Satellite cells can regenerate damaged muscle fibers
• Microscopic Structures of Skeletal Muscle

  • Sarcolemma
  • Transverse (T) tubules
  • Sarcoplasm
  • Myofibrils
  • Sarcoplasmic reticulum
  • Filaments
  • Sarcomeres
  • Z discs
  • A band
  • I band
  • H zone
  • M line
• Muscle Proteins


  • Contractile proteins
  • Regulatory proteins
  • Structural proteins
• Contractile Proteins


  • Myosin - Thick filaments, motor protein that converts ATP to motion
  • Actin - Thin filaments, provide sites for myosin binding
• Structural Proteins


  • Titin - Stabilize myosin position, contribute to elasticity
  • Nebulin - Help align thin filaments
  • Dystrophin - Link thin filaments to sarcolemma
• Contraction and Relaxation of Skeletal Muscle

  1. Sliding filament mechanism

  2. Contraction cycle (ATP hydrolysis, cross-bridge formation, power stroke, detachment)

  3. Excitation-contraction coupling (Ca2+ release and reuptake)

  4. Length-tension relationship
• Neuromuscular Junction


  • Motor neurons extend from CNS to muscle fibers
  • Neuromuscular junction is where action potentials arise
  • Synaptic cleft separates motor neuron and muscle fiber
  • Neurotransmitter (acetylcholine) released from synaptic vesicles
  • Motor end plate on muscle fiber contains acetylcholine receptors
• Filaments


  Diminished tension (forcefulness)
• When a muscle fiber is shortened


  1. Filaments are compressed

  2. Fewer myosin heads make contact with thin filaments

  3. Tension is diminished
• Motor neurons


  • Have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers
• Neuromuscular junction (NMJ)


  Where action potentials arise at the interface of the motor neuron and muscle fiber
• Synapse


  Where communication occurs between a somatic motor neuron and a muscle fiber
• Synaptic cleft


  Gap that separates the two cells
• Neurotransmitter (acetylcholine)


  Chemical released by the initial cell communicating with the second cell
• Synaptic vesicles


  Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach)
• Motor end plate


  • The region of the muscle cell membrane opposite the synaptic end bulbs
  • Contain acetylcholine receptors
• Nerve impulses elicit a muscle action potential

  1. Release of acetylcholine

  2. Activation of ACh receptors

  3. Production of muscle action potential

  4. Termination of ACh activity
• Botulinum toxin


  • Blocks release of ACh from synaptic vesicles
  • May be found in improperly canned foods - a tiny amount can cause death by paralyzing respiratory muscles
  • Used as a medicine (Botox®) for strabismus, blepharospasm, spasms of the vocal cords, cosmetic treatment to relax muscles that cause facial wrinkles, and to alleviate chronic back pain due to muscle spasms in the lumbar region
• Curare


  • A plant poison used by South American Indians on arrows and blowgun darts
  • Causes muscle paralysis by blocking ACh receptors inhibiting Na+ ion channels
  • Derivatives of curare are used during surgery to relax skeletal muscles
• Anticholinesterase


  • Slow actions of acetylcholinesterase and removal of ACh
  • Can strengthen weak muscle contractions
  • Examples: Neostigmine - treatment for myasthenia gravis, antidote for curare poisoning, terminate the effects of curare after surgery
• A huge amount of ATP is needed to power the contraction cycle and pump Ca++ into the SR
• The ATP inside muscle fibers will power contraction for only a few seconds
• Muscle fibers have three ways to produce ATP


  1. From creatine phosphate

  2. By anaerobic cellular respiration

  3. By aerobic cellular respiration
• Creatine Phosphate


  • Excess ATP is used to synthesize this energy-rich molecule
  • Creatine phosphate transfers its high energy phosphate group to ADP regenerating new ATP
  • Creatine phosphate and ATP provide enough energy for contraction for about 15 seconds
• Anaerobic Respiration


  • Series of ATP producing reactions that do not require oxygen
  • Glucose is used to generate ATP when the supply of creatine phosphate is depleted
  • Glycolysis breaks down glucose into molecules of pyruvic acid and produces two molecules of ATP
  • If oxygen levels are low, anaerobic reactions convert pyruvic acid to lactic acid which is carried away by the blood
  • Anaerobic respiration can provide enough energy for about 30 to 40 seconds of muscle activity
• Aerobic Respiration


  • Activity that lasts longer than half a minute depends on this
  • Pyruvic acid entering the mitochondria is completely oxidized generating ATP, carbon dioxide, water, and heat
  • Each molecule of glucose yields about 36 molecules of ATP
  • Muscle tissue has two sources of oxygen: from hemoglobin in the blood and oxygen released by myoglobin in the muscle cell
  • Aerobic respiration supplies ATP for prolonged activity and provides more than 90% of the needed ATP in activities lasting more than 10 minutes
• Muscle Fatigue


  • Inability of muscle to maintain force of contraction after prolonged activity
  • Factors that contribute: inadequate release of calcium ions from the SR, depletion of creatine phosphate, insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, failure of the motor neuron to release enough acetylcholine