MUSCLES

CHAPTER 6A

VOCABULARY 6acetylcholine muscle fatigue sarcoplasm actin muscle fibers sarcoplasmic reticulumaction potential muscle tone skeletal muscle cardiac muscle muscle twitch smooth

muscle cross bridges myosin striated muscleendomysium neurotransmitter synaptic

cleft isometric contractions oxygen debt thick

filaments isotonic contractions sarcomeres thin

filaments motor unit

COLOR CODE – PLATE 7Smooth muscle cells – light blueNucleus – redConnective tissue – brownCells with striations – yellowIntercalated discs – purpleCapillaries – blueSarcolemma – light greenMyofibrils - gray

COLOR CODE – PLATE 24

Tendon – tanEpimysium – orangeMuscle belly – peach/fleshPerimysium/fascicle – yellowEndomysium/muscle fiber – redMyofibril – grayI Band – pinkA Band – dark brownH Band – brownSarcomere – dark greenZ line – greenActin – light greenMyosin – aquaCross bridges – light blue

COLOR CODE – PAGE 36Skeletal muscle - ---------peach/fleshMuscle cell – ---------------orangeMotor nerve - --------------dark brownAxon – -----------------------brownAxon branch – -------------aquaAxon terminal – ------------yellowNeuromuscular junction – redMotor end plate - -----------blue

I. MusclesA. All muscles →contract (essential

function)B. Makes up approx. ½ body’s massC. similarities:

1. contractions depend u/p 2 types of myofilaments2. muscle fibers

*elongated cells wh/ contract*skeletal & smooth muscle cells

3. myo-, mys-, sarco-prefixes used when muscle is being

referred toex: sarcoplasma – muscle cells’

cytoplasm

D. Muscle Functions1. maintains posture2. movement3. helps maintain constant body

T (contractions → ATP to break ↓ → generates heat)

4. stabilizes joints (tendons hold bones t/g)

E. Muscle Coverings1. layered w/ conn. tiss. coverings2. endomysiuma. delicate conn. tiss. sheath surrounding each individual muscle fiberb. allows capillaries & nerves to reach muscle fibers3. perimysium – surrounds fascicles (bundles of muscle fibers)4. epimysiuma. covers an entire muscleb. separates muscles from ea. other

II. Muscle TypesA. Smooth Muscle

1. in walls of hollow organs2. involuntary3. cells:

a. uninucleatedb. non-striatedc. spindle-shaped (tapered)\

4. very slow to contract

B. Cardiac Muscle1. in heart walls2. involuntary3. cells:a. uninucleatedb. striatedc. branching chains of cells4. cells interlock @ intercalated disks5. slow to contract6. fibers completely relax b/t rhythmic contractions → prevents fatigue

C. Skeletal Muscle1. attach to skeleton (bones) by tendons2. voluntary (only muscle type subject to conscious control)3. cells:a. multinucleatedb. striatedc. cylindrical (tubular)4. variable speed of contractions (slow-fast)5. fibers contract arhythmically

NOTE: page 179 for muscle types

III. Microscopic Anatomy (skeletal)A. Muscle fiber components

1. sarcolemma – cell membrane2. sarcoplasm – cytoplasm3. sarcoplasmic reticuluma. specialized smooth ERb. stores Ca & releases it on demand when muscle is stimulated to contract4. myofibrilsa. encased in SRb. have striationsc. contractile portion of muscle fibers

5. sarcomeresa. chains of tiny contractile units

of myofibrilsb. contractile unit b/t 2 Z-linesc. aligned end-to-end

6. myofilamentsa. smaller structures of

threadlike proteins w/I sarcomeres

b. arrangement gives banding pattern

c. 2 types

1) thick filaments*contains bundles of protein molecules → myosin*also contain enzyme to split ATP → power for muscle contraction2)thin filaments*contains contractile protein→ actin*only filament found in the light “I” bands

B. bands1. precise arrangement of myofilaments →banding pattern/striations 2. A Bands – dark bands, contain both actin/thin & myosin/thick filaments3. I Bands – light bands, contain ONLY actin/thin filaments4. H Zone – contains no actin/thin filaments when @ rest5. Bare Zone – disappears during a contraction

Note: page 183

Note: In order from smallest to largest

Myofilament →myofibril(s) → muscle fiber(s) →

fascicle → muscle

IV. Skeletal Muscle Activity

A. contractions1. sarcoplasmic reticulum (SR)a. spec. smooth ERb. stores Ca & releases on demand when muscle fiber is stimulated to contract2. muscle fibers are stimulated to contract by motor neurons (nerves); muscle fibers are innervated3. axon of a motor neuron has several branches & can stimulate from a few to several muscle fibers in a particular muscle (pg. 184)4. motor unit 1 motor neuron + all mus. fibers it stimulates (pg. 184)

5. neuromuscular junction (pg. 185)a. entire region where a neuron and muscle fiber meetb. synaptic cleftgap b/t nerve endings and muscle cells’ membranes

6. neurotransmittersa. chemical released when

nerve impulse reaches the axon terminals (end of nerve fiber branches)

b. acetylcholine is neurotransmitter that diffuses a/c synaptic cleft

B. sliding filament theory (pg. 187)1. myosin/thick filaments attach to binding sites on the thin/actin filaments (cross bridges)2. during contraction the actin/thin filaments slide past the myosin/thick filaments (thin filaments are pulled t/w center of sarcomere)3. causes sarcomere to shorten4. Ca required for cross-bridges to occur5. Ca triggers the binding of filaments wh/ initiates the sliding; serves as signal for mus. contraction to b/g6. when action potential ends, Ca is reabsorbed i/t SR7. E is supplied by ATP

C. E sourcesThree ways ATP is acquired (ATP

is ONLY E source that can be used directly to power muscle activity)

1. Creatine phosphate (CP) interacting w/ADP

a. CP is a ↑ E cmpd. made when a muscle is resting

b. when CP transfers a ↑E phosphate group to ADP →regenerates ATP in fraction of a sec.

2. aerobic respirationa. supplies some 95% of ATP for mus. activityb. uses O2 c. glucose is broken ↓to CO2 and H2O & some of E released is captured in bonds of ATPd. provides a rich supply of ATP3. anaerobic respirationa. does not use O2b. produces only 5% as much ATP as aerobic resp., but is about 2.5x fasterc. produces lactic acid →promotes mus. fatigue & soreness

D. how forcefully a muscle contracts depends u/p how many of its cells are stimulatedE. Oxygen debt1. occurs when there is insufficient O2 to generate ATP aerobically & anaerobic respiration begins2. insufficient ATP supply due to > consumption3. when muscles lack O2 lactic acid b/g to accumulate as well as ATP supply starts to run low4. causes muscles to contract less effectively, finally stopping contractions alt/g (fatigue)

5. believed to result in muscle fatigue

F. muscle fatigue1. may occur when muscles have

been worked strenuously for a long period of time

2. muscle is unable to contract even though it is being stimulated

G. types of contractions Muscles do not a/w shorten when they contract1. isometrica. means “same msmt.”b. muscles do not shortenc. mmt. does not occurd. muscle tension keeps increasing, but muscle is working a/g an object that is immovablee. ex: pushing a/g a door jamb2. isotonica. means “same tone”b. muscle shortens; mmt. does occur

H. muscle twitches1. single, brief, jerky contractions2. usu. contractions are smooth and sustained (tetanic contraction)I. muscle tone1. state of continuous partial contractions2. results in muscles remaining firm, healthy, and constantly ready for action3. even relaxed muscles have some fibers that are contracting (not visible)4. ex: curved fingers when arm is hanging relaxed

J. Exercise1. increases muscle size,

strength, &/ endurance2. diff. exercises give diff.

results3. inactivity →muscle

weakness & wasting → atrophy

About.com – ALS video clip Medclip.com – neuromuscular

junction