Chapter 9 The Muscular System

Skeletal Muscle Structure Tendon – Fascia – outermost covering; covers entire muscle & continuous w/tendon; separates muscle from adjacent muscles Aponeuroses-

Skeletal Muscle Structure Coverings: Epimysium – covers entire muscle (under fascia) Perimysium – Endomysium – covers each fiber (cell) Sarcolemma –

Skeletal Muscle Structure – Cont. Sarcoplasmic reticulum (SR) channels for transport Myofibrils – threads that compose muscle fibers; contain protein filaments: 1. actin – 2. myosin –

Skeletal Muscle Structure

Muscle Fiber (muscle cell) Cisternae of SR – enlarged portions Transverse tubules (T-tubules) – important in muscle contraction Sarcoplasm –

Breakdown of Skeletal Muscle

Parts of a Sarcomere (functional unit of a muscle)

Parts of a Sarcomere Z lines – end points M line – I band – on either side of Z line; actin filaments only H zone – on either side of M line; myosin filaments only A band –

Parts of a Sarcomere

4 Proteins in Muscle Cells:

Troponin & Tropomyosin 4 proteins are found in muscle cells: actin, myosin, troponin & tropomyosin troponin – appear as globules; provide a binding site for Ca+² tropomyosin –

Sliding Filament Theory (How Muscles Contract) Muscle fiber stimulated by release of ACh from synaptic vesicles of neuron Transverse tubules (T-tubules) carry impulse deep into muscle fibers Ca²+ bind to troponin, tropomyosin moves, exposing binding sites on actin filaments

Cross Bridge Animation

Sliding Filament Theory (How Muscles Contract ) Linkages form b/t actin & myosin Actin filaments move inward, shortening the sarcomere The enzyme cholinesterase (or AChesterase) decomposes ACh

Sliding Filament Theory Relaxed muscle – binding sites on actin are covered by tropomyosin

Sliding Filament Theory Ca²+ binds to troponin Tropomyosin slides out of the way Myosin binds to actin & pulls inward Sarcomeres shorten & muscle contracts

Sliding Filament Animation

Sliding Filament Theory

Neuromuscular Junction – junction b/t motor neuron & muscle Motor end plate – end of muscle fiber; many nuclei & mitochon- dria located here

Neuromuscular Junction Neurotransmitters (ntm) chemicals that help carry impulses Motor unit – Synaptic vesicles – store neurotransmitter; most common – acetylcholine (ACh)

Electron Micrograph Neuromuscular Junction

Neuromuscular Junction Animation

Energy for Muscle Contraction ATP (adenosine triphosphate) When ATP is converted to ADP (adenosine diphosphate) by losing the last phosphate, energy is released.

Energy for Muscle Contraction Cells depend on cellular respiration of glucose to synthesize ATP An additional source is creatine phosphate

Energy for Muscle Contraction Creatine phosphate stores excess energy Anaerobic respiration (in the absence of O2) provides few ATP’s, while aerobic resp. (in the presence of O2) provides many ATP’s

Creatine Phosphate High amts. of ATP - ATP is used to Low amts. of ATP – CP is used synthesize CP, which stores energy to resynthesize ATP. for later use.

Importance of Myoglobin l.a. carried by blood to liver; liver can convert l.a. to glucose, but requires ATP (ATP being used for muscle contraction) myoglobin –

Aerobic vs. Anaerobic Respiration

Aerobic vs. Anaerobic Respiration Carried by blood to liver; liver can convert l.a. to glucose, but requires ATP (ATP being used for muscle contraction) Imp. b/c blood supply during muscle contr. may decrease As l.a. accumulates, O2 debt occurs

Oxygen Debt Strenuous exercise leads to O2 deficiency & lactic acid buildup ATP provides energy for muscle contraction Amt. of O2 needed to convert accumulated l.a. to glucose & restore ATP levels = L.A. accumulation leads to muscle fatigue b/c pH of muscle cell is lowered & muscle cannot contract

Muscle Cramp Muscle cramp – Rigor mortis – takes up to 72 hrs. to occur; sarcolemma becomes more permeable to Ca+² & ATP levels insufficient

Myogram Pattern or graph of a muscle contraction A single contraction is called a 3 parts: Latent (lag) phase – brief pd. of delay b/t when the stimulus is applied & actual contraction occurs Contraction Relaxation –

Patterns of Contraction a) Muscle Twitch – b) Staircase Effect many stimuli closely spaced w/complete relaxation in b/t; each contraction generate incr. force

Patterns of Contraction c) Summation – when the 2nd stimulus occurs during the relaxation pd. of 1st contr.; the 2nd contr. generates more force d) Tetany –

Muscle Facts If a muscle is stimulated twice in quick succession, it may not respond the 2nd time – called refractory period Threshold – All-or-none – increasing the strength of the stimulation does NOT incr. the degree of contraction (a muscle contracts completely or not at all)

More Facts Incr. stimulation from motor neurons causes a greater # of motor units to contract & vice versa Called recruitment of motor units Incr. the rate of stimulation also incr. the degree of contraction Muscle tone –

Hypertrophy vs Atrophy Hypertrophy- with intense exercise where muscle exerts more than 75% of its max tension there is an increase in actin and myosin fibers and increase muscle fiber diameter. Inc diameter= Atrophy-

Origin & Insertion Origin – end of muscle that attaches to stationary bone Insertion – During contr., insertion is pulled toward origin

Muscle Functions in Groups Prime mover – responsible for most of the movement (ex.- biceps) Synergist – aids the prime mover Antagonist –

Structural Differences of 3 Types of Muscle Skeletal Muscle Smooth Muscle Cardiac Muscle Cells elongated w/multiple nuclei/cell Cells spindle-shaped w/1 nucleus/cell No T-tubules T-tubules lg.; releases lg. amts. of Ca++; can contract longer (Ca channel blockers) Striated/voluntary Striated/invol.

Functional Differences of 3 Types of Muscle Skeletal Muscle Smooth Muscle Cardiac Muscle Needs nerve impulse for contraction Displays rhythmicity & cells stimulates each other (as in peristalsis) Ca+² binds to calmodulin Ca+² binds to troponin Not affected by hormones Hormones may affect rate of contr. Slower to contract but can maintain contraction longer

Functional Differences - Continued Skeletal Muscle Smooth Muscle Cardiac Muscle Not affected by stretching Stretching of fibers may stimulate contr. (ex.-stomach) Remains in a refractory pd. until contraction ends (tetany won’t occur)

Fast vs Slow Twitch Fibers Fast vs Slow Twitch Video

Fast Twitch vs. Slow Twitch Muscle Contracts quickly, tires easily (sprinter) Contracts slowly, tires slowly (long distance) More mitochondria Less myoglobin Red muscle Composes smaller muscles (eyes, hands, etc.)