Chapter 10 Muscular tissue

Chapter 10 Muscular tissue

1. Types of muscular tissue

   • 3 Types
     • Skeletal- attach to bone, striated, and voluntary
     • Cardiac- heart muscle, striated, involuntary, and has intercalated discs
     • Smooth- Found in blood vessel linings, non striated, and involuntary
   • Differ from each other by
     • Microscopic anatomy
     • location
     • type of control
   • 40%-50% of body weigh is muscle

2. Functions of muscular tissue

   • Producing body movements
   • Stabilizing body positions- Posture
   • Moving substances within the Body
     • Heart muscle pumping blood
     • Moving substances through the digestive tract
   • Generating Heat
     • Contracting muscle produces heat

3. Properties of Muscular Tissue

   • for every nerve that penetrates a skeletal muscle there are generally :
     • ONE ARTERY AND ONE OR TWO VEINS
   • Excitability- ability to respond to stimuli
   • Contractility- ability to contract forcefully when stimulated
   • Extensibility- Ability to return to original length

4. Connective tissue components

   • Epimysium- aka -DEEP FASCIA
     • The outermost layer
     • surrounds the entire muscle
   • Perimysium
     • Surrounds groups of fibers separating them into bundles called fascicles
   • Endomysium
     • surrounds individual fibers
   • Perimysium, Epimysium, Endomysium = one broad sheet of connective tissue

5. Axon terminal clusters at the ends of neuromuscular junctions are referred to as: SYNAPTIC END BULBS

   • Nerve and Blood Supply
     • Neurons that stimulate skeletal muscle to contract are somatic motor neurons
     • Each muscle fiber is in close contact with one or more capillaries

6. Microscopic Anatomy

   • Scarcolemma- The plasma membrane of a muscle cell
     • Mitochondria in the muscle fiber are arranged closely to the sarcolemma
   • Transverse (T tubules) -Tunnel in from the plasma membrane
   • Sarcoplasm- the cytoplasm of a muscle fiber
     • includes glycogen for synthesis, of ATP and a red-colored protein called myoglobin which binds oxygen molecules
     • Myoglobin releases oxygen when it is needed for ATP production

7. Muscle Proteins

   • Myofibrils are built from 3 kinds of proteins
     • 1) Contractile proteins (ACTIN & MYOSIN)
       • -Generate force during contraction
     • 2) Regulatory proteins (Tropomyosin & Troponin found in actin molecule
       • switch the contraction process on and off
   • 3) Structural Proteins
     • Align the thick and thin filaments properly
     • Link the myofibrils

8. Contractile Proteins

   • Myosin- Thick filaments
     • convert ATP to energy of motion
       • Molecular structure has "head like projections"
         • Functions as a motor protein in all three types of muscle tissue
   • Actin
     • Thin filaments
       • Actin molecules provide a site where a myosin head can attach
     • Tropomyosin and Troponin are regulatory proteins and are also part of the thin filament
     • In a relaxed muscle tropomyosin covers the myosin binding sites, MYOSIN CANT BIND TO ACTIN
     • Release of calcium Ions changes shape if troponin tropomyosin complex allows myosin to engage actin

9. The sliding Filament Mechanism (How muscles contract)

   • Myosin grabs and pulls Actin, which bring s the Z-disc closer together and ultimately leads to shortening of the muscle
   • Myosin functions as a motor protein in 3 types of muscular tissue
   • In the sliding filament mechanism the thin filament is being pulled towards the M-line
   • MOTOR UNIT- is the somatic motor neurons plus all skeletal muscle fibers it stimulates

10. The neuromuscular junction

    • Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers
      • Action potential arise at the interface of the motor neuron and the muscle fiber
    • Synapse- where communication occurs between a somatic motor neuron and a muscle fiber

11. Muscle Action Potential

    • Nerve Impulses elicit a muscle action potential in the following way
      • 1. Release of Acetylcholine (ACH)
        • Nerve impulse arriving at the synaptic end bulbs causes many synaptic vesicles to release ACh into the synaptic cleft
      • 2. Activation of ACh receptors
        • Binding of ACh to the receptor on the motor end plate opens an Ion channel
    • 3. Production of muscle action potential
      • (The muscle action potential then propagates to the SR (Sarcoplasmic Recticulum) to release its stored Ca++ ( Calcium Ions)
    • 4.) Termination of ACh activity
      • Ach effects last only briefly because it is rapidly broken down by acetylcholinesterase AChE

12. Muscle Fatigue

    • Inability of muscle to maintain force of contraction after prolonged activity
      • Causes:
        • 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

13. Muscle tension

    • the tension or force of muscle cell contraction varies
      • MAXIMUM tension (force) is dependent on
        • The rate at which nerve impulses arrive
          • The amount of stretch before contraction
            • The nutrient and oxygen availability
              • The size of motor unit

14. Control of muscle tension

    • Motor Units
      • A motor neuron makes contact with about 150 muscle fibers
        • A Motor unit recruitment - Increasing the # of active motor units
      • The total strength of a contraction depends on the size of motor units and the number that are activated
    • Twitch Contraction- The brief contraction of the muscle fibers in a motor unit in response to an action potential
      • Twitches last from 20 - 200 msec L
        • Latent period (2 sec)
          • A brief delay between the stimulus and muscular contraction
      • Tetnus- A substantial contraction- Tight stretch
    • --Relaxation Period-- (10-100 msec)
      • Ca++ is transported to the SR
        • Myosin binding sites are covered by tropomyosin
          • Myosin heads detach from actin
    • --Refractory Period-
      • When a muscle fiber contracts, it temporarily cannot respond to another action potential
        • -Skeletal muscle has a refractory period of 5 milliseconds
          • -Cardiac muscle has a refractory period of 300 milliseconds
    • Contractions
      • Isotonic Contraction- SAME tension, Changing LENGTH
      • Isometric- Same LENGTH, CHANGING tension

15. Red Muscle fibers

    • TYPES OF SKELETAL MUSCLE FIBERS based on Myoglobin
      • White muscle fibers
        • Have a low content of myoglobin
        • Appear lighter (white meat In chicken)
    • Have a high myoglobin content
    • Appear darker and thighs
    • Contain more mitochondria
    • Supplied by more blood capillaries

16. Types of skeletal Muscle fibers

    • Muscle fibers contract a different speeds, and vary how quickly they fatigue
    • Muscle fibers are classified into three main types
      • 1) Slow oxidative fibers -Least powerful
        • 2) Fast oxidative -glycolytic fibers- Intermediate
          • 3) Fast glycolytic fibers- MOST powerful

17. Cardiac Muscle Tissue

    • Principal tissue in heart wall
      • -intercalated discs connect the ends of cardiac muscle fibers to one another
        • Allow muscle action potentials to spread from one cardiac muscle fiber to another

18. Smooth Muscle tissue

    • Found in the
      • walls of arteries and veins
        • walls of hollow organs
          • walls of airways to the lungs
            • Muscles that attach to hair follicles
              • Muscles that adjust pupil diameter
                • Muscles that adjust focus of the lens in the eye

19. Aging & muscular tissue

    • Aging brings
      • a progressive loss of skeletal muscle mass
      • a decrease in maximal strength
      • a slowing of muscle reflexes
      • loss of flexibility
    • with aging the relative number of slow oxidative fibers appears to increase
    • Aerobic activities and strength training can slow the decline in muscular performance