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Physiology notes

Skeletal muscle

1. Great mass of somatic musculature

2. Well-developed cross-striations, does not normally contract in the absence of

nervous stimulation

. !acks anatomic and functional connections bet"een individual muscle fibres

#. Generally under voluntary control

$ardiac muscle

1. %as cross striations

2. &unctionally snycytial 'a multinucleate mass of cytoplasm that is not

separated into cells

a. (hough can be modulated via the )*S 'autonomic nervous system+

. $an contract rhythmically in the absence of eternal innervations o"ing to

presence of myocardium of pacemaker cells that discharge spontaneously

Smooth muscle

1. !acks cross-striations

2. &urther subdivided to 2 broad types unitary 'visceral+ and multiunit

. nitary

a. &ound in most hollo" viscera 'organs in the cavities of the body+

b. &unctionally syncytial and contains pacemakers that discharge

irregularly

#. /ultiunit

a. &ound in the eye

b. Some other locations 0 not so spontaneously active and resembles

skeletal muscle in graded contractile ability

Skeletal muscle organiation

1. /ost skeletal muscle begin and end in tendons

2. /uscle fibers are arranged in parallel bet"een the tendinous ends 0 so that

the force of contraction of the units is addictive

. ach muscle fiber0a. Single cell, multinucleated

b. !ong, cylindrical

c. Surrounded by a membrane, sarcolemma

d. *o syncytial bridges bet"een cells

#. /uscle fibers are made of myofibrils, divisible into individual filaments

a. /yofilaments contains several proteins, make up the contractile

machinery of the skeletal muscle

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3. $ontractile mechanism

a. 4epends on the proteis0 myosin II, tropomyosin, troponin

b. Troponin:

i. /ade up of subunits 0 troponin 5, troponin (, troponin $

6. 7ther important proteins

a. 5nvolve in maintaining the proteins that participate in contraction inappropriate structural relation to one another and to the etracellular

matri

/uscle striations

1. (he light 5 band is divided by the dark 8 line

2. 4ark ) band has the lighter % band in its center

. /iddle of % band0 a transverse / line is seen

a. (his line pulls the narro" light areas on either side of it, sometimes

called pseudo-%-one

#. )rea bet"een 2 ad9acent 8 lines : sarcomere

(hick filaments

1. ("ice '2;+ the diameter of thin filaments

2. /ade up of myosin

. !ined up to form the ) bands

#. ach thick filaments is surrounded by 6 thin filaments in a regular heagonal

pattern

3. $ontains several hundred myosin molecules

(hin filaments

1. /ade up of actin, tropomyosin, and troponin

2. )rray of thin filaments etends out of the ) band into the less dense staining

5 bands

1.

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a. When muscle is relaed, the thin filaments do not overlap the thick

filaments

2. 8 lines allo" anchoring of the thin filament

/yosin

1. &orm0 myosin 55

a. 2 globular heads and a long tail

b. %eads of myosin molecules form cross-bridges "ith actin

2. $ontains light and heavy chains

a. %eads are made of light chains

b. )mino terminals heavy chains

c. %ead contain an actin-binding site and a catalytic side that hydrolyses

)(P

. )rranged symmetrically on either side of the center of sarcomere

a. (his arrangement creates the light, pseudo % one

#. / linea. Site of reversal of polarity of the myosin molecules in each of the thick

filaments

b. )t these points 'sites+, there are slender connections that hold the

thick filaments in proper array

(hin filaments 'part 2+

1. Polymers made up of 2 chains of actin0 form a long double heli

2. (ropomyosin

a. !ong filaments located in the groove bet"een 2 chains of actin

. (hin filaments have == to #== actin molecules and #= to 6= tropomyosinmolecules

#. (roponin

a. Small globular units located at intervals at along the tropomyosin

molecules

b. &unctions0

i. (roponin ( : binds troponin components to tropomyosin

ii.(roponin 5 : inhibits the interaction of myosin "ith actin

iii.(roponin $ : contains the binding sites for calcium ion '$a2>+,

that helps to initiate contraction

)dditional structure proteins

Actinin, titin, desmin

1. )ctinin : binds actin to 8 lines

2. (itin

a. !argest kno"n protein

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b. $onnects the 8 line to the / lines and provides scaffolding for the

sarcomere

c. $ontains 2 kinds of folded domains, provide muscle "ith its elasticity

i. When muscle is stretched, there is little resistance as the

domains unfold

ii.&urther stretching, rapid increase in resistance to protect thestructure of sarcomere

. 4esmin

a. )dds structure to 8 line, binding 8 lines to the plasma membrane.