Lecture for Week Four-1

8/4/2019 Lecture for Week Four-1

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Exercise 14: Anatomy and Organization ofSkeletal Muscle

A. Muscle fibers:

a. Myofibrils - small fibers that alternate

light(I) band and dark (A) bands and makeup the fibers as a whole; light & dark bandsline up along myofibrils to give striatedappearance

b. Myofiliment - small thread like structuresthat make up the myofibrils; made up of

contractile proteins actin and myosinB. Muscle cells:

a. Actin/Myosin - contractile proteins that slidepast one another during muscle activity to

cause shortening or lengthening of themuscle cells

b. Sarcomeres - the actual contractile units;reach from the middle of one I band (the Z

disc) to the middle of the nexti. Z-disc - where sarcomeres meet

ii. M line - middle of sarcomere, no actin

iii. I band - light, thin filaments (actin)

iv. A band - dark, thick filaments (myosin)C. Network of internal membranes: allow the

electrical message from the outside of themuscle to communicate with the inside of the

muscle and all along the myofibril, causing themuscle to contract.

a. Sarcoplasmic Reticulum (SR) - smoothendoplasmic reticulum, does not open tothe outside and runs parallel alongmyofibrils; contains INTRAcellular fluid;

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stores and releases Ca2+ ions that triggermuscle contraction

b. Transverse Tubule (T-tubule) part of the

cell membrane that extends deep inside thefiber at junction of I and A bands, opens to

the outside and runs perpendicular to themyofibrils; contains EXTRAcellular fluid

c. Terminal Cisternae - sac-like vesicles oneach side of the transverse tubule, cross

channels of SRD. Organization of Skeletal Cells into Muscle

a. Endomysium - encloses each muscle fiberb. Perimysium - surrounds several muscle

fibers and encloses them into a bundlecalled a Fascicle or Fasciculus-

c. Epimysium - dense connective tissue thatsurrounds the fascicles that comprise the

entire muscle; blends into the deep fasciad. Deep Fascia - course dense connective tissue

that binds muscles into functional groups &into tendons/aponeuroses

e. Tendons/Aponeuroses- attach muscles toeach other or indirectly to bones

E. Neuromuscular junction junction betweennerve fiber (axon) & muscle cell:

a. Motor unit - a neuron and all the musclecells it stimulates

b. Synaptic cleft - a small fluid filled gap b/t theneuron and the muscle cell membranes

c. Axon terminal- part of the neuron that is inclose contact with the muscle cell

d. Neurotransmitter - substance released fromthe axon terminal onto the muscle cell;

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acetylcholine is neurotransmitter involved inthe neuromuscular junction

Exercise 15: Gross Anatomy of Skeletal MusclesA. Vocabulary

a. Origin - the stationary, immovable or lessmovable point

b. Insertion - the moveable attachment; theinsertion is pulled closer to the origin during

movement.

c. Flexion - movement that decreases the angle

of the joint; typical of hinge joints (knee orelbow) or at ball and socket joints (hip)

d. Extension - movement that increases theangle of the joint; opposite of flexion; ex:

straightening knee or elbow

e. Abduction - movement of limbs away from

the midline or the fanning movement oftoes or fingers when they are spread apart

f. Adduction - movement of the limb towardthe midline; opposite of abduction

g. Supination - to turn or rotate (the hand orforearm) so that the palm faces up or

forward or to turn or rotate (the foot) byadduction and inversion so that the outeredge of the sole bears the body's weight.

Exercise 16B: Skeletal Muscle PhysiologyA. Events that lead to muscle contraction

i. Action potential triggers acetylcholine to bereleased from the axon terminal

ii. Acetylcholine causes the resting membranepotential to change, and this then initiates

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an action potential that spreads inside themuscle fiber via the transverse tubule

iii. The sarcoplasmic reticulum releases Ca2+

ions, Ca2+ release frees binding sites on actiniv. Sliding Power-stroke :

1. ATP is hydrolyzed on myosinhead to allow myosin headbinding to actin

2.Actin and myosin slide past one

another toward the M line andcontraction occurs

B. Vocabulary1. Three Phases of Muscle Contraction

i. Latent Phase- short period b/tstimulation & start of contraction

- no force on muscle yet- chemical changes occurring in cell

ii. Contraction Phase - sliding power-stroke, causing muscle to shorten

iii. Relaxation Phase normal resting stateafter contraction ends

2. Threshold Stimulus- specific point inmembrane voltage that once reached during

depolarization will trigger an action potential(all or none)

3. Subthreshold Stimulus- a stimulus too weakto evoke an action potential

4. Maximal Stimulus- maximum force of thecontraction

Ways to Increase the force of muscle contraction:

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1. Multiple Motor Unit Summation (Recruitment) -process by which the strength of thecontraction reflects the number of stimulated

muscle cells i.e., increased force ofcontraction = more activated motor units, less

force = fewer motor units

2. Treppe - warming up of the muscle; when amuscle cell is stimulated in rapid succession at

the same intensity after the muscle is allowedto fully relax between stimuli, then the

strength of the contraction increases eventhough there is no increase in stimulus; lookslike a staircase when plotted on graph

3. Wave or Temporal Summation - if a musclecell is stimulated in rapid succession at the

same intensity before complete relaxation isallowed to occurthen the strength of thecontraction will increase

- extreme wave summation is called

tetanus; plotted on a graph as solidline b/c peaks fuse.

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- Tonus- muscular tone

- Tetanus- fusion of twitches due to musclestimulation at a high frequency causing asteady, sustained contraction.

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Lecture for Week Four-1