Lecture 05 Intro to Myology

Types of Muscle

• Skeletal – • Cardiac – • Smooth – • What characterizes each? Where is each found?

• Muscles pull on skeletal parts to ___________

• Muscles maintain _______________

• Muscle _____________ body cavities

• Muscles ___________ openings and thus _____________ entrance/exit of material from the body.

• Muscles produce body _________ and thus aid in maintenance of ____________.

Associations with Connective Tissue Coverings:• Superficial fascia • Deep fascia • Connective tissue associated with muscle- what do each of these

layers cover?

– epimysium– perimysium– endomysium

– All contribute to formation of a tendon

Nerve and Blood Vessel Supply• Artery - Each muscle is supplied by an

artery• Veins – 1-2 drain each muscle• Found in Epimyceum• Capillaries – ramify through

endomyceum, 1 or 2 per muscle cell – wrap around muscle fiber

• Skeletal Muscles are Controlled via Motor Neuron

• Motor unit = one somatic motor neuron & all the skeletal muscle cells (fibers) it stimulates –One nerve cell supplies on average

150 muscle cells that all contract in unison.

• Total strength of a contraction – # motor units activated –Size of motor units

The Motor Unit

• Tendon– Tie muscle to bone– Dense fibrous connective tissue– Little vascular supply– Slow to heal– May be enclosed within synovial sheath

(wrist, ankles)• Aponeurosis –

– Broad sheet of connective tissue– Epicranial aponeurosis

Connective Tissue Components

aponeurosis

tendon

Micro-Anatomy of Muscle Fibers: Sarco Muscle

• Sarcolemma-excitable membrane (T tubules)

• Sarcoplasm- glycogen, myoglobin, myofibrils

• Sarcoplasmic reticulum– Stores calcium– Triad- regulates calcium movement

• Sarcomere = contractile unit of myofibril

Myofibrils• Specialized cytoskeletal

elements contraction of muscle fiber• 100’s – 1000’s / muscle fiber • Organized into Sarcomeres

• ca. 10,000/myofibril• Basic contractile unit

• Composed of:– Contractile proteins

• Actin: thin filaments• myosin: thick filaments

– Regulatory proteins• Tropomyosin, troponin

– Structural proteins• Titin, myomesin, dystrophin

Neural Control – via motor neuron Arrives at Neuromuscular Junction:– motor end plate: sarcolemma at NMJ,

location of neurotransmitter receptors– Synaptic region – microscopic gap

between neuron and muscle fiber• Neurotransmitter (chemical) diffuses across

gap to initiate contraction

• One NMJ/muscle fiber

Neuromuscular Junction (NMJ) or Synapse

• NMJ = myoneural junction– end of axon nears the surface of a muscle fiber at its motor

end plate region (remain separated by synaptic cleft or gap)

Structures of NMJ Region

• Synaptic end bulbs are swellings of axon terminals

• End bulbs contain synaptic vesicles filled with acetylcholine (ACh)= neurotransmitter

Muscle Contraction – Sliding Filament Theory

• Interaction between thick and thin filaments:– Nerve impulse at neuromuscular junction

causes release of Na ions following binding of acetylcholine on motor endplate

– Na ions cause release of Ca ions within muscle cells

– Ca ions make binding of thick and thin filaments possible

– ‘Heads’ on myosin (thick) filament bind at binding sites on Actin (thin) filament

– Binding causes myosin head to move, pulling actin filaments together

Muscle Cell Response• THRESHOLD STIMULUS Muscle twitch

(contraction) relaxation – ALL OR NONE Response of a motor unit

• RECRUITMENT = strength of contraction from stimulation of additional fibers (activation of motor units)

• MUSCLE TONE = result of percentage of individual fibers contract and subsequently relax – thus lending support

• Muscle tone controlled by interaction of muscle spindle and muscle fibers in a motor unit

• TETANUS =smooth contraction from repeated stimulus - summation

Muscular DisordersCrampsspasmsTwitches

Involuntary –low ATP level – failure of myosin fibers to relax

Tendonitis

Inflammation of connective tissues - injury

Tetanus, curare

Toxin blocks release of neuro transmitter

Myasthenia gravis

Auto-immune destruction of acetycholine receptor

MS genetic disorders weakening + degeneration of muscles

Energy Required for Muscle Contraction• ‘cocking of myosin head• Pumping of Ca ions into sarcoplasmic

reticulum• Pumping of Na out of muscle fiber to

neuromuscular cleft• Energy as ATP• Production of energy requires

– Oxygen– Nutrient source (glucose from carbs)

Different Kinds of Muscle• Fast fibers: (white fibers)

– High concentration of myofibrils– Little reserve energy/replenishment capacity– Rapid contraction

• Slow Fibers: (red fibers)– Smaller diameter– Replenish energy (ATP) as used– Store oxygen in myoglobin within cell– Dark color

• Intermediate Fibers – convert to fast fibers – intermediate properties

Variations in Skeletal Muscle Fibers

• Myoglobin, mitochondria and capillaries– red muscle fibers

• more myoglobin, an oxygen-storing reddish pigment • more capillaries and mitochondria

– white muscle fibers• less myoglobin and less capillaries give fibers their pale

color

• Contraction and relaxation speeds vary– how fast myosin ATPase hydrolyzes ATP

• Resistance to fatigue– different metabolic reactions used to generate ATP

Classification of Muscle Fibers

• Slow oxidative (slow-twitch)– red in color (lots of mitochondria, myoglobin & blood vessels)– prolonged, sustained contractions for maintaining posture

• Fast oxidative-glycolytic (fast-twitch A)– red in color (lots of mitochondria, myoglobin & blood vessels)– split ATP at very fast rate; used for walking and sprinting

• Fast glycolytic (fast-twitch B)– white in color (few mitochondria & BV, low myoglobin)– anaerobic movements for short duration; used for weight-lifting

Fiber Types within a Whole Muscle• Most muscles contain a mixture of all three

fiber types• Proportions vary with the usual action of the

muscle– neck, back and leg muscles have a higher

proportion of postural, slow oxidative fibers– shoulder and arm muscles have a higher

proportion of fast glycolytic fibers• All fibers of any one motor unit are same.• Different fibers are recruited as needed.

The End.