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.