Muscle Anatomy and Physiology

Muscle Tissue

Muscle Tissue ½ of body mass same brief description as tissue chapter ½ of body mass able to convert ATP (chemical energy) to mechanical energy

1. Cardiac Muscle in heart only striated and branching involuntary

2. Smooth Muscle visceral – GI tract walls, urinary bladder, bronchi, arrector pili, iris

2. Smooth Muscle smooth spindle shape involuntary contractions are slow and sustained without fatigue

2. Smooth Muscle cells are surrounded by connective tissue - endomysium usually arranged in sheets running in different directions

3. Skeletal Muscle make up the skeletal muscles striated (banded) voluntary muscles respond rapidly but fatigue easily

Functions of Skeletal Muscle

Functional Characteristics of Skeletal Muscle contractibility - shortens with force excitability - responds extensibility - stretches elasticity - recoils

Function of Muscle Movement Posture maintenance - continuous tiny adjustments Heat generation - by product of metabolism nearly ¾ of energy released from ATP escapes as heat skeletal muscle is at least 40% of body mass

Structure of Skeletal Muscle

Structure of Skeletal Muscle entire gross structure covered by connective tissue - epimysium muscle is made of small bundles called fascicle which are bound by perimysium each fascicle is made of a bundle of muscle cells or fibers which are surrounded by endomysium (all coverings are continuous extensions)

Muscle Fiber Structure

Muscle Fiber Structure sarcolemma – muscle fiber plasma membrane sarcoplasm – muscle fiber cytoplasm, contains myoglobin – a red pigment that stores oxygen Each muscle fiber is made of bundles of rod-shaped structures of myofibrils (organelles). (100’s to 1000’s per cell)

They have repeating pattern of striations called sarcomeres.

The banding is caused by an orderly overlapping arrangement of protein filaments - myofilaments.

Myofilaments: myosin - thick, extend entire length of A band actin - thin, extend across the I band and part way into A band

Z line - attachment site for actin, ends of sarcomere I band - light bands, actin only A band - dark bands, myosin and actin overlap

H zone - only visible in relaxed, myosin only M line - sarcomere center

(contracting organelle) Myosin – thick filament Structure Connective Tissue surrounds organ Gross muscle Epimysium Fascicle (bundles of cells) surrounds tissues Perimysium Muscle fiber (muscle cell) Endomysium cells surrounds Myofibril (contracting organelle) organelles Myofilaments Actin – thin filament Myosin – thick filament molecules

(contracting organelle) Myosin – thick filament Connective Tissue Structure surrounds Gross muscle organ Epimysium Fascicle (bundles of cells) tissues surrounds Perimysium Muscle fiber (muscle cell) Endomysium surrounds cells Myofibril (contracting organelle) organelles Myofilaments Actin – thin filament Myosin – thick filament molecules

Molecular Structure of Myofilaments

Myosin rod like tail or axis ending in 2 globular heads - “crossbridges” - heads contain ATPase (enzyme) tail heads

Actin globular subunits - G actin are found in long strands, like a double strand of twisted beads

Actin tropomyosin spirals around beads, to add strength and stiffen, thin ribbon troponin molecules bond actin to tropomyosin, has binding sites that will join with myosin crossbridge Binding sites

Sarcoplasmic Reticulum

Sarcoplasmic Reticulum smooth endoplasmic reticulum of muscle cells storage area for Ca ions At H zones and A - I junctions tubes fuse and form lateral channels - terminal cisternae which feed into transverse tubules (T tubules) at each Z line. T tubules receive nerve stimuli and provide a pathway for oxygen, glucose, and Ca ions. (because continuous with membrane, nerve impulse allowed deep into muscle)

The End

Muscles are attached to bones directly or indirectly by extensions of epimysium. indirect - are more common 1. rope like tendons 2. flat aponeurosis direct - a direct connection

Patterns of Arrangement arrangement of fascicle produce muscles with different shapes and function most common arrangements are: 1. parallel - strap-like muscles, ex: biceps 2. pennate - short, obliquely attached to central tendon, feather shape, ex: rectus femoris 3. convergent - broad origin converging to a single tendon, ex: pectoralis major 4. circular - circular fibers, control openings and closings, ex: sphincters, orbicularis oris, orbicularis oculi

They have repeating pattern of striations called sarcomeres. Z line - attachment site for actin, ends of sarcomere I band - light bands, actin only A band - dark bands, myosin and actin overlap H zone - only visible in relaxed, myosin only M line - sarcomere center

The banding is caused by an orderly overlapping arrangement of protein filaments - myofilaments. myosin - thick, extend entire length of A band actin - thin, extend across the I band and part way into A band Z line - disklike protein sheet, anchors actin and connects each myofibril to the next H line - less dense (myosin only) M line - darker, fine strands connect adjacent myosins in this area

Sarcoplasmic Reticulum smooth endoplasmic reticulum of muscle cells its connecting tubules lie in spaces between myofibrils and run parallel to them storage area for Ca ions At H zones and A - I junctions tubes fuse and form lateral channels - terminal cisternae which feed into transverse tubules (T tubules) at each Z line. (from penetration of sarcolemma) T tubules receive nerve stimuli and provide a pathway for oxygen, glucose, and Ca ions. (because continuous with membrane, nerve impulse allowed deep into muscle)