CHAPTER 9 - MUSCULAR SYSTEM: HISTOLOGY & PHYSIOLOGY
I. FUNCTION
A. SPECIALIZED - only 1
B. CONTRACTION - can only pull, can’t push !
C. CONTROLS MOVEMENTS - VOLUNTARY & INVOLUNTARY
1. LEVERS/BONES è BODY MOVEMENT- SKELETAL
2. BLOOD - CARDIAC
3. FOOD - SKELETAL & SMOOTH
4. SECRETIONS - urinary & reproductive secretions - SMOOTH
5. GOOSE BUMPS - SMOOTH
D. FUNCTIONAL CHARACTERISTICS – EEEC (easy!)
1. EXTENSIBLE - stretchable
2. ELASTIC - recoils to original length when stretched
3. EXCITABLE - stim. by nerves & hormones
4. CONTRACTILE - shorten forcibly
II. 3 MAJOR TYPES (Tab. 9.1, p. 276) - Read MUSCLE TISSUE (Ch. 4, p. 133-135)
- 50% of body mass
A. SKELETAL - VOLUNTARY, ATTACHED TO BONES (mostly)
1. MULTINUCLEATE, PERIPHERAL
2. LONG 1-40 mm
3. STRIATIONS - lines - regular
B. SMOOTH - INVOLUNTARY/VISCERAL
1. UNINUCLEATE, CENTRAL
2. SHORT, SPINDLE/FUSIFORM FIBERS
3. LACK STRIATIONS
4. INNERWOVEN BANDS AROUND VISCERA & VESSELS
5. AUTORHYTHMIC - contract spontaneously
C. CARDIAC - HEART ONLY/INVOLUNTARY
1. UNINUCLEATE
2. IRREGULAR/BRANCHED
3. STRIATED
4. INTERCALATED DISKS - elec. contin. w/ entire organ
5. AUTORHYTHMIC - regular, self-perpetuating A. P.
III. SKELETAL MUSCLE STRUCTURE
A. C. T. SHEATHS OF MUSCLE FIBER = CELL (Fig. 9.1, p. 277)
1. ENDOMYSIUM - surrounds/between fibers
2. PERIMYSIUM - surrounds FASCICULUS, bundle of fibers
3. EPIMYSIUM/FASCIA - surrounds many FASCICULI, muscle & groups
a. DENSE, tough, fibrous collagenous C. T.
b. FASCIA = sheet of tissue under skin, muscle groups
c. MUSCLE C.T. SHEATHS CONTINUOUS W/ TENDON & PERIOSTEUM
OF BONE (Fig. 9.3a, p. 279)
B. MUSCLE CELL/FIBER ULTRASTRUCTURE (Fig 9.3, p. 279)
1. SARCOLEMMA = MUSCLE P.M.
2. SARCOPLASM = MUSCLE CELL CYTOPLASM
3. SARCOMERE = FUNCTIONAL UNIT OF MUSCLE CONTRACTION
a. MYOFIBRILS - contain MYOFILAMENTS
b. MYOFILAMENTS - 2 TYPES: - i. ACTIN - THIN
- ii. MYOSIN - THICK
c. “HAZI” (Fig. 9.5, p. 281)
IV. THIN MYOFILAMENT - ACTIN (Fig. 9.4, p. 280)
- complex, 3 subunits
A. F-ACTIN - helix
1. G-ACTIN - globular, “pearls on a string”
2. F-ACTIN – 2 strands of G-actin twisted together
B. TROPOMYOSIN - filamentous protein
1. In spiral groove of F-actin
C. TROPONIN - globular protein, 3 subunits
affinity for: 1. F-actin
2. Ca2+
3. Tropomyosin
D. F-ACTIN has ACTIVE/BINDING SITES
1. NORMALLY COVERED BY TROPOMYOSIN; 7 sites/TROPOMYOSIN
2. TROPONIN LOCATED @ end of TROPOMYOSIN
V. THICK MYOFILAMENT - MYOSIN (Fig. 9.4, p.280)
A. 2 MYOSIN PROTEINS - “GOLF CLUBS”
1. “HEAD” – “LIGHT”, GLOBULAR
2. “TAIL/ROD” – “HEAVY”, FILAMENTOUS
3. 300 PROTEINS/THICK MYOFILAMENT
A. 150 HEADS/END
VI. SARCOPLASM MODIFICATIONS (Fig. 9.13, p. 289)
A. SARCOLEMMA INVAGINATES è T-TUBULES
1. 5-6 MILLION/40 mm FIBER
2. OPENS MUSCLE INTERIOR & SARCOMERES TO EXTRACEL FLUIDS
B. SARCOPLASMIC RETICULUM - stores Ca2+
1. TERMINAL CISTERNAE - enlarged cisternae of S. R.
2. TRIAD = T-TUBULE + 2 ADJACENT S. R. CISTERNAE
VII. PHYSIOLOGY OF CONTRACTION (SKIP p. 282-286 till Ch. 11)
A. NEUROMUSCULAR JUNCTION (Fig. 9.11, p. 287; Fig. 9.12, p. 288)
1. A. P. FROM BRAIN è MOTOR NEURON è MUSCLE FIBER
2. PRESYNAPTIC MEMBRANE = neuron
a. é permeability to Ca2+
b. Ca2+ into neuron è EXOCYTOSIS of ACETYLCHOLINE
3. SYNAPTIC CLEFT
a. ACETYLCHOLINE è POSTSYNAPTIC MEMBRANE on muscle
b. RECEPTORS on POSTSYNAPTIC MEMBRANE
c. é permeability to Na+ ions
d. A. P. passed to muscle cell
e. ACETYLCHOLINE removed & degraded by Acetylcholinesterase
4. POSTSYNAPTIC MEMBRANE - MOTOR ENDPLATE = muscle cell
a. A. P. passed over sarcolemma
b. A. P. passes into T-tubules è TRIADS (Fig. 9.14, p., 290)
c. Rapid flooding of Ca2+ from S. R. cisternae INTO SARCOPLASM
B. EXCITATION CONTRACTION COUPLING
- SLIDING FILAMENT THEORY (Fig. 9.6, p. 283)
- STEPS (Fig. 9.15, p. 291) & HANDOUT
1. Ca2+ binds to TROPONIN
2. TROPONIN “TIGHTENS” TROPOMYOSIN into F-ACTIN groove è
exposes ACTIVE SITES on F-ACTIN
3. CROSS-BRIDGES FORM between ACTIN & MYOSIN
a. ATP already attached to MYOSIN head, “cocks Head”
b. MUST have ATP before cross bridge forms
4. ACTIN-MYOSIN CROSSBRIDGE = ATPase
a. ATP è ADP + Pi
b. POWER STROKE = CONTRACTION, shorten SARCOMERE (p. 283)
5. ANOTHER ATP required to:
a. RELEASE CROSSBRIDGE - RELAXATION
b. “RE-COCK” MYOSIN HEAD to prepare for another stroke
C. NOTES:
1. T-tubules right over region where ACTIN & MYOSIN overlap (p. 290)
2. Contractions can continue as long as:
a. A. P.
b. ATP
c. Ca2+
3. LOTS OF HEAT generated w/ heavy use
a. SHIVERING = invol. contractions to é body temp.
D. RELAXATION
1. REMOVE STIMULI - no A. P.
2. Ca2+ pumped back into S. R. from SARCOPLASM
a. No Ca2+ for TROPONIN
b. 100-300X more Ca2+ in S. R. than SARCOPLASM
3. MUSCLE relaxes PASSIVELY - ELASTIC RECOIL
VIII. PHYSIOLOGY OF SKELETAL MUSCLE
A. MUSCLE TWITCH - CONTRACTION (Fig. 9.16, p. 293 & Tab.9.2, p. 293)
1. LAG: from STIMULUS è BEGINNING OF CONTRACTION
2. CONTRACT
3. RELAX
4. ALL OR NONE FOR EACH FIBER
B. TYPES OF MUSCLE CONTRACTION (Tab. 9.3, p. 298)
1. MOTOR UNITS = NEURON + MUSCLE FIBERS THEY INNERVATE (p. 294)
a. SMALL, DELICATE MUSCLES - eye muscles
<10 fibers/neuron
b. INTERMEDIATE MUSCLES - fingers
30-50 fibers/neuron
c. LARGE, NON-DELICATE MUSCLES - back
up to 1,000 fibers/neuron
d. é MOTOR UNITS è é TENSION = MULTIPLE MOTOR UNIT SUMMAT.
2. TETANUS - continuous stim è stay contracted MULTIPLE WAVE
3. ISOTONIC - Muscle SHORTENS, most movements
a. CONCENTRIC - as muscle shortens tension é mostly
b. ECCENTRIC - tension same, length é ; put heavy weight down
4. ISOMETRIC - Muscle length stays same, constant tension, postural muscles
5. MUSCLE TONE - maintenance of constant tension for long time, ISOM.
6. TREPPE - é tension w/ repeated stimuli in rested muscle, "warm up" (p. 294)
7. LENGTH vs TENSION - less than maximal force if muscle length
too short or too long - optimum (Fig. 9.21, p. 297)
C. FATIGUE - ê ability to do work
1. PSYCHOLOGIC - you think you can’t, but still can, most common
2. MUSCULAR - êATP in muscle fiber, 2nd most common
3. SYNAPTIC - Acetylcholine use exceeds synthesis
4. PHYSIOLOGIC CONTRACTURE - extreme fatigue, no ATP,
muscles can’t contract or relax
5. RIGOR MORTIS - 2-4 hours after death
a. No pump, no Ca2+ gradient
b. Ca2+ leaks into sarcoplasm è binds to TROPONIN è
CROSS-BRIDGES form & don’t relax è No ATP è STIFF
D. ATP - ENERGY FOR CONTRACTION (*KNOW Tab. 9.4, p. 301)
1. CREATINE PHOSPHATE + ADPè 1 ATP + CREATINE; 10 seconds
2. ANAEROBIC - O2 NOT AVAILABLE
a. GLUCOSE è GLYCOLYSIS è 2 ATP + LACTIC ACID
b. ATP AVAILABLE FROM GLUCOSE FASTER THAN AEROBIC
c. SHORT TERM (2-3 minutes), not much ATP (2 vs. 36/28 aerobic)
d. MAXIMAL, INTENSE, SHORT BURST EXERCISE è SPRINT
e. “O2 DEBT” - DUE TO ANAEROBIC EXERCISE
i. LACTIC ACID è KREBS CYCLE TO COMBUST COMPLETELY
ii. BREATHE HEAVILY AFTER ANAEROBIC TO “PAY BACK”
f. CAN’T USE FATTY ACIDS
3. AEROBIC - O2 AVAILABLE
a. GLUCOSE + O2 è 36/38 ATP + CO2 + H2O
b. SUSTAINED MODERATE EXERCISE è DISTANCE RUN
c. MORE EFFICIENT THAN ANAEROBIC
d. CAN USE FATTY ACIDS
E. TYPES OF MUSCLE FIBERS (Tab. 9.5, p. 303 *KNOW)
SLOW TWITCH, HI-OXIDATIVE, TYPE I FAST TWITCH, LO-OXIDATIVE, TYPE II
1. SMALLER DIAMETER 1. LARGER DIAMETER
2. MORE MYOGLOBIN, binds O2 2. LESS MYOGLOBIN
3. LOTS OF MITOCHONDRIA 3. FEWER MITOCHONDRIA
4. MOSTLY AEROBIC 4. MOSTLY ANAEROBIC
5. FATIGUE RESISTANT 5. FATIGUE QUICKLY
6. SLOWER USE OF ATP 6. FASTER USE OF ATP
7. LESS GLYCOGEN 7. MORE GLYCOGEN
8. DARK MEAT è DUCK BREAST 8. LIGHT MEAT èTURKEY BREAST
9. MORE BLOOD/VESSELS 9. FEWER BLOOD/VESSELS
IN HUMANS: 1. MIX OF SLOW & FAST TWITCH
2. GENETICS DETERMINES %, then via development
3. SLOW-LONG DISTANCE RUNNERS
4. FAST-SPRINTERS
F. EXERCISE
1. é SIZE OF FIBERS, NOT #
2. ANAEROBIC è é FAST TWITCH MUSCLE
3. AEROBIC è é SLOW TWITCH MUSCLE
4. ATROPHY è NO EXERCISE/STRESS
IX. SMOOTH MUSCLE (p. 305)
A. DIFFERENCES W/SKELETAL
1. NO SARCOMERES è NON-STRIATED
2. NO T-TUBULES., CAVEOLAE (little caves) instead
3. CALMODULIN instead of TROPONIN
4. SPARSE S. R. - Ca2+ not stored, comes from extracel. fluid
5. SLOWER CONTRACTION - often in waves
6. AUTONOMIC N. S./INVOLUNTARY CONTROL
7. é HORMONAL CONTROL THAN SKELETAL
8. NO O2 DEBT
9. RMP -50/60 mV
B. TYPES - 2
1. VISCERAL - most common 2. MULTIUNIT - less common
a. Contract slowly a. Contract rapidly
b. Gap junctions - contract as a unit b. Each cell independent
c. Autorhythmic- dig. sys., bladder c. Vessels, arr. pili, iris