Bio221Lec10_Skeletal Muscle I

7/28/2019 Bio221Lec10_Skeletal Muscle I

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Essentials of Anatomy and Physiology

dr. Arie Nugroho

Gunabangsa 2012

Slide 2.1Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Chapter 7: Muscular System


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The Muscular System


Muscles are responsible for bodymovement

Three types are found in the body

Skeletal muscle**

Cardiac muscle

Smooth muscle


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Types of Muscle

Three types of muscle

Skeletal Cardiac Smooth


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Functions of Skeletal Muscles


Make up flesh of the body Maintain Posture

Voluntary movement

Aid in breathing, eating, speech

Provide facial expression

Generate reflexes Produce body heat


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Characteristics of Skeletal Muscles


Muscle cells are elongated(muscle cel l = muscle fiber)

Muscles are specialized to contract

Terminology:

Prefix myo, mys refer to muscle

Prefix sarco refers to flesh


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Characteristics of Skeletal Muscles


Most are attached by tendons to bones

Cells are multinucleate

Striated have visible banding

Voluntary subject to conscious control

Muscles and their fibers are wrapped byconnective tissue


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Connective Tissue Wrappings ofSkeletal Muscle

Slide 6.4aCopyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Endomysiumaround single

muscle fiber

Perimysiumaround afascicle(bundle) offibers Figure 6.1


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Connective Tissue Wrappings ofSkeletal Muscle

Slide 6.4bCopyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Epimysium covers theentire skeletalmuscle

Fascia on theoutside of theepimysium

Figure 6.1


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Skeletal Muscle Attachments Slide 6.5

Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Epimysium blendsinto a connectivetissue attachment

Tendon cord-likestructure

Aponeurosissheet-like structure

Fig. 7.2abc


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Skeletal Muscle Attachments


Sites of muscle attachment

Bones

Cartilages

C. T. coverings

i.e., aponeuroses


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Microscopic Anatomy of SkeletalMuscle


Cells are multinucleate

Nuclei are deep to the sarcolemma

Figure 6.3a


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Microscopic Anatomy


Sarcolemmaspecialized plasmamembrane

Sarcoplasmic reticulumspecializedsmooth E.R.

Stores Ca++

Required for

contraction

Figure 6.3a


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Microscopic Anatomy


Myofibril: organelleunique to muscleBundles ofmyofilaments

Myofibrils alignment produces distinct bands

I band =light band

A band =

dark band


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Microscopic Anatomy


Banding Pattern depends onarrangement of proteins in myofibrils

Actin: thin

A and I bands

Myosin: thick

A bands

Figure 6.3b

A-bandI-band


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Microscopic Anatomy


Sarcomere

Contractile subunit of a muscle fiber

From Z to Z One A band +

Two half Ibands

Figure 6.3b


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Microscopic Anatomy


Organization of the sarcomere

Thick filaments = myosin filaments

Composed of the protein myosinHas ATP-ase enzymes

Figure 6.3c


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Microscopic Anatomy


Organization of the sarcomere, cont

Thin filaments = actin filaments

Composed of the protein actin

Figure 6.3c


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Microscopic Anatomy


Myosin filaments have heads (extensions,or cross bridges)

Myosin andactin overlap

Figure 6.3d


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Microscopic Anatomy


At rest, there is a bare [H] zone thatlacks actin filaments

Figure 6.3d


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Properties of Skeletal Muscle


Irritability ability to receive and

respond to a stimulus

Contractility ability to shorten when anadequate stimulus is received


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Nerve Stimulus to Muscles


Skeletalmuscles requireinnervation

Motor unitOne motor

neuron +

Muscle cellsinnervated bythat neuron

Figure 6.4a


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Neuromuscularjunction:

communicationsite between amotor neuronand a muscle

fiber

Figure 6.5b

Fig. 7.5a

Motor Neuron

Neuromuscular Junction


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Synaptic cleft :gap betweennerve andmuscle

Nerve andmuscle do notmake direct

contact

Figure 6.5b


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Transmission of Nerve Impulse toMuscle


Neurotransmitter chemical releasedby motor nerve

initiates contraction Causes sarcolemma to depolarize

For skeletal muscle: acetylcholine (Ach)


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Transmission of Nerve Impulse toMuscle

Slide 6.16a


Action ofNeurotransmitter

Crosses synapticcleft

Attaches toreceptors on thesarcolemma

Fig. 7.6


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Muscle Contraction


An electrochemical event

Ach is the chemical

Before contraction can occur,

sarcolemma must bepolarizedA polarized membrane is more + outside

and more - inside

Movement of ions creates actionpotential

The ability to do work


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Muscle Contraction


Ach attaches to receptor sites

Sarcolemma becomes permeable tosodium (Na+)

Sodium rushes into the cell

Initiates sliding filament process


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Muscle Contraction


Membrane of sarcoplasmic reticulumalso depolarizes

Ca++ ions are released

Bind to sites on actin

Open attachment sites for myosin


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The Sliding Filament Theory ofMuscle Contraction


Depolarizationallows myosin

heads to attachto binding siteson actin

calledcrossbridges

ATP required

Figure 6.7

Fig. 7.7a


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Actin is pulled pastmyosin by movementof heads

ATP required

Myosin heads detach

ATP required

Then bind to the nextsite on actin

ATP required

Fig. 7.7b


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This continuedaction causes asliding of the actinalong the myosin

I band narrows

H zone narrows

A band stays the same


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Slide 6.17bCopyright 2003 Pearson Education Inc publishing as Benjamin Cummings

Actin slides pastmyosin

Results in shorteningof the sarcomere

Muscle fiber hasthousands of

sarcomeresAll shorten at one time

Muscle contracts

Figure 6.7

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Bio221Lec10_Skeletal Muscle I