characteristics of muscle tissue...microanatomy of skeletal muscle • sarcolemma = plasma membrane...
TRANSCRIPT
Characteristics of muscle tissue:
1. it is excitable
2. it is elastic
3. it is contractile Totally unique to this tissue
The Muscular System
Muscle Functions:
• Body movement
• Heart contractions
• Maintains arterial pressure
• Produces heat
• Visceral contractions
Types of muscle:
• Smooth
• Cardiac
• Skeletal
Gross Anatomy
• Tendons (aponeuroses) connect muscle to bone
• The insertion (more movable end) moves toward the origin (less movable end)
• Muscles can only contract
• Muscles pull, they don’t push!
Anatomy of Skeletal Muscle
• Epimysium is continuous w/ tendons, subdividing muscle into fascicles
• Perimysium is the connective tissue surrounding each fascicle (fasiculus)
• Myofibers = muscle fibers = muscle cells (very long and multi-nucleated)
• Endomysium surounds each muscle cell
Microanatomy of Skeletal Muscle
• Sarcolemma = plasma membrane
• Sarcoplasm = cytoplasm
• Myofibrils = long proteins organized into sarcomeres
• Sarcoplasmic reticulum = specialized ER
• Transverse (T) tubules = continuous with the sarcolemma
Microanatomy of Skeletal Muscle
Thick filaments: Myosin
Microanatomy of Skeletal Muscle
• Thin filaments:
• Actin
• Troponin (regulatory protein)
• Tropomyosin (regulatory protein)
Microanatomy of Skeletal Muscle
How Muscle Cells Shorten
• How does the gross muscle get shorter?
• Do the proteins shorten?
• Do the proteins slide past one another?
• Motor neurons release acetylcholine (ACh) into the synapse
• An electric signal travels down the muscle cell membrane through the T tubules
• Ca++ ions are released from the sarcoplasmic reticulum
How Muscle Cells Shorten
• Ca++ binds to troponin,
• Troponin pushes tropomyosin off the binding sites on actin
• Myosin heads immediately bind to actin and a power stroke occurs
How Muscle Cells Shorten
How does it end?
• Somatic motor neuron stimulation ceases
• Ca++ is pumped into the SR
• ATP disconnects myosin from actin
• Acetylcholinesterase degrades ACh, removing the it from the synapse
Contraction of a Skeletal Muscle (Gross Level)
If each cell is “all-or-none” then how is stimulus intensity graded?
Myogram
• Twitch
• Latent period
• Period of contraction
• Period of relaxation
• Summation
• Tetanus or tetanic contraction
Motor Units
• Motor unit = a single somatic motor neuron and all of the muscle fibers it innervates.
• More work ! more recruitment of motor units
Energy and Exercise
• ATP
• Energy currency of all cells
• Where does it come from?
Cellular Respiration
• Is the conversion of glucose into ATP (mostly in mitochondria)
• If oxygen is present:
• 34 ATP / glucose (CO2 is the waste product)
What if Oxygen is Limited?
• Anaerobic respiration:
• 2 ATP / glucose (lactic acid is the waste product)
• What if you push past the burn?
• Muscle fatigue, Muscle cramps
• What if ATP really runs out?
How ATP is Used in Muscle Cells
• Energizing the myosin head
• Disconnecting the myosin head from it’s binding site on actin
• Pumping Ca++ back into SR
Effects of Exercise on Muscle
• Aerobic Exercise increases muscle strength, flexibility & resistance to fatigue
• more mitochondria / cell
• more blood supply to muscles
• myoglobin increases
Effects of Exercise on Muscle
• Anaerobic Exercise will increase muscle size
• increasing amts. of connective tissue and enlargement of muscle fibers due to increasing numbers of myofibrils
Steroids
• Enhancement of muscle strength and endurance
• Side-effects: bloated face, shriveled testes, infertility, liver damage (incl. liver cancer), increase in blood cholesterol (increasing risk of heart disease), mental problems, including extreme violence, manic behavior, depression and delusions.