Ch. 8 MUSCLE

Question 1

_{MUSCLE TYPES}

Answer 1

_{3 Types of mucles}

• ^{<u>Skeletal</u> - voluntary striated}
• ^{<u>Cardiac</u> - one place in body, involuntary}
• ^{<u>Smooth</u> - visceral, involuntary}

_Terminology

• ^{Myo - refers to muscle (ex: myocyte)}
• ^{Sacro - refers to muscle cells}

Question 2

_{Microscopic Anatomy of Skeletal Muscles}

Answer 2

• _{cell membrane = <strong>sarcolemma</strong>}
  
  • _{Transverse ( T ) tubules}
• _{Numerous nuclei}
• _{Cytoplasm = <strong>sarcoplasm</strong>}
  
  • _{<strong>Sarcoplasmic reticulum (SR)</strong>}
  • _Myofibrils
    
    • _{Actin (thin); I Band}
    • _{Myosin (thick); A Band}
• _{<strong>Sarcomere</strong> = contracting unit of skeletal muscle (area from one Z line to the next Z line)}

Question 3

_{Skeletal Muscle Actions}

Answer 3

• _{Work in groups to produce desired movement <strong>(<u>prime mover</u> or agonist) </strong>w/ others stabilizing joints <strong><u>(fixator)</u></strong> &providing smooth control over movements.}
• _{<strong><u>Synergist</u></strong> - contracts at same time as prime mover & assists its movement}
• _{<strong><u>Antagonist</u></strong> - directly opposes actions of prime mover; w/ partial contractios can smooth out movements or prime mover}

Question 4

_{Neuromuscular Junction}

Answer 4

• _{Skeletal muscle is under concious voluntary control & must recieve nerve impulses to contract & produce the desired action.}
• _{<strong>Neuromuscular junction = </strong>site where ends of motor nerve fibers “connect” w/ muscle fibers}
  
  • _{<strong>Synaptic space</strong>}
  • _{<strong>Synaptic vesicles </strong>w/ <strong>acetylcholine</strong>}
  • _{<strong>Acetylcholinsterase in synaptic space</strong>}

Question 5

_{Motor Unit}

Answer 5

• _{one nerve fiber & all the muscle fibers innervates}
• _{The number of muscle fibers per nerve fiber determines the size of the resulting movement}
• _{Delicate muscles have fewer muscle fibers per motor unit than large mucsles mkaing larger movements.}

Question 6

_{MUSCLE CONTRACTION}

^{Nervous Control of Muscle Contraction}

Answer 6

• _{Individual muscle fibers contract completely when stimulated by their nerve(s) = <strong>(all-or-nothing principal)</strong> but whole muscles do not so…}
• _{To produce movements that vary in range & strength, the numbers of muscle fibers stimulated for a particular movement is carefully controlled.}

Question 7

_{MUSCLE CONTRACTION}

^{Twitch Contraction}

Answer 7

_{= a single muscle fiber contraction}

• _{<u>Latent phase</u> - time between the nerve stimulus & beginning of contraction}
• _{<u>Contracting phase</u>}
• _{<u>Relaxation phase</u>}
• _{Entire contraction cycle lasts ~0.1sec}
• _{Nerve impulses are timed to that twitches of individual muscle fibers occur at slightly different times resulting in smooth, sustained muscle contractions.}

Question 8

_{MUSCLE CONTRACTION}

^{Initiation of Muscle Contraction}

Answer 8

_{Acetylcholine binds to receptors on <u>sarcolemmal surface</u> –> impulse travels through <u>transverse tubules</u> to interior cell –> to <u>sarcoplasmic reticulum</u> –> release of stored calcium ions (CA}⁺⁺_{) into the <u>sarcoplasm</u> –> diffuse myofilaments –> shorten (contraction) -powered by ATP}

Question 9

_{MUSCLE CONTRACTION}

^{Muscle Relaxation}

Answer 9

• _{Sarcoplasmic reticulum pumps calcium ions back in, pulling it out of the myofibrils –> muscle fiber returns to original length (relaxes)}
• _{Energy (ATP) neede to pump calcium back into SR}

Question 10

_{MUSCLE CONTRACTION}

^{<span>Mechanics of Contraction</span>}

Answer 10

• _{When relaxed, the actin & myosin filaments in a muscle fiber overlap a little}
• _{When stimulated to contract by a nerve impulse, cross bridges on myosin filaments move back & forth pulling the actin filaments on both sides toward the center myosin filament}
• _{Sliding of filaments over each other causes shortening of the sacromeres}
• _{Combined shortening of the end sacromeres in a muscle fiber –> <u>contraction</u>}

Question 11

_{MUSCLE CONTRACTIONS}

^{<span>Chemistry of Contraction</span>}

Answer 11

• _{ATP produced by mitochondria powers the sliding actin & myosin filaments}
• _{ADP is formed & must be converted back to ATP –> phosphate group added to ADP by splitting of <strong>creatine phosphate (CP)</strong>}
• _{Sourse used to produce ATP & CP = catabolism of nutrients –> <strong>glucose & </strong>}O_{<span>2</span>}
• _{Glucose stored as glycogen; oxygen in myoglobin}
• ^{With adequate oxygen –> process = <strong>aerobic metabolism</strong> & maximum energy is extracted from each glucose molecule}
• ^{When need for oxygen exceeds supply, muscle shift to <strong>anaerobic metabolism</strong> to produce energy –> <strong>lactic acid</strong> builds up as byproduct of incomplete glucose breakdown}

Question 12

_{Microscopic Anatomy of Cardiac Muscle}

Answer 12

• _{Striated, involuntary muscle}
• _{Only one central nucleus per cell}
• _{Long, branched fibers from networks of cells}
• _{Firm end-to-end attachments between cells = <strong><u>intercalated disks</u></strong>}
  
  • _{Transmit impulses from cell to cell to allow large groups of cardiomyocytes to contract in a coordinated manner}

Question 13

_{Cardiac Muscle Contraction}

Answer 13

• _{Contracts without external stimulation}
• _{Groups of cardiac muscle cells adopt contraction rate of the most rapid cell in the group}
• _{Cells contract in a rapid, wavelike fashion}
• _{Allows blood to be effectively “squeezed” out of the chambers}
• _{Internal impulse conduction system (“Mini internal nervous system”)}

Question 14

_{Cardiac Muscle Contraction}

^{<u>Innervation of the Heart</u>}

Answer 14

• _{Not needed to <u>initiate</u> contractions, but modifies heart’s contractile activity}
• _{Autonomic (involuntary) portion of NS}
  
  • _{sympathetic - faster}
  • _{parasympathetic - slow}

Question 15

_{Smooth Muscle}

Answer 15

• _{Nonstriated, involuntary muscle}
• _{Found in two main forms}
  
  • _{<strong>Visceral</strong> - large sheets of cells in walls of hollow organs}
  • _{<strong>Multiunit</strong> - small discrete group of cells; iris & ciliary body, blood vessels, bronchioles}

Question 16

_{Microscopic Anatomy of Smooth Muscle}

Answer 16

• _{Small, spindle shaped (tapered ends)}
• _{Single, central nucleus}
• _{Smooth homogeneous appearance; <u>dense bodies</u> - attached to actin and myosin filaments at both ends.}
• _{When the contractile units contract they cause the cell to “ball up” (not arranged into parallel sarcomeres so individual cells can shorten to greater degree than striated muscle cells)}

Question 17

Visceral Smooth Muscle

Answer 17

• _{In walls of many soft internal organs}
• _{Contracts w/o external stimulation}
• _{No fine movements possible; contracts in large rhythmic waves}
• _{It reacts to stretching by contracting more strongly (exept in uterus)}

Question 18

_{Visceral Smooth Muscle}

^{<span><u>Nerve Supply</u></span>}

Answer 18

• _{Not neccessary to initiate contractions but serves to modify them}
• _{Autonomic NS}
  
  • _{Sympathetic - slower}
  • _{Parasympathetic - faster}

Question 19

_{Multiunit Smooth Muscle}

Answer 19

• _{Made up of individual smooth muscle cells or small groups of cells}
• _{Used for small delicate movements}
• _{Require specific impulses from the autonomic nerves to contract}
• _{Actions are specific and carefully controlled}