lecture 7 muscle

8/9/2019 Lecture 7 Muscle

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MUSCLE

1. Classification of Muscles

A. Classification of muscle by location and function

skeletal muscles visceral muscles

cardiac muscleB. Classification of muscle by structure

striated muscle

skeletal muscles cardiac muscle

smooth muscles

visceral muscles


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C. Classification of muscle by mode of action and control

voluntary muscles skeletal muscles

involuntary muscles

smooth muscles

cardiac muscle

2. Skeletal Muscle

A. Structure of skeletal muscles

origin (proximal end)

muscle belly

insertion (distal end)


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Tendons

antagonistic pairs

Flexors

Extensors

Epimysium

Perimysium

Endomysium

fasciculi


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B. Cellular and molecular structure of skeletal muscle

muscle fibers myofibrils; myofilaments (actin and myosin

filaments)

- sarcomere

A-band

I-band

M-line

Z-line (Z-disc)

H-zone


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myofilaments

- thin filaments (actins)

- tropomyosin (troponin-I, -T and -C)

- thick filaments (myosins)

cross-bridges

- Accessory protiens: Titin and Nebulin

sarcolemma

- traverse tubules (t-tubules)

sarcoplasmic reticulum

- terminal cisternae


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C. Contractile process

requirements for this process:

the actin and myosin must interact

- Role of tropomyosin and troponin

the myosin cross-bridges must flex

the system must be able to convert chemical

energy to mechanical energy

Sliding filament theory of contraction

D. Contraction of muscle

isometric contraction

isotonic contraction


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A. In the relaxed state,

troponin partially blocks the

myosin-binding sites onactin.

B. Contraction begins when

Ca2+ binds to troponin, which

uncovers the myosin-bindingsite on actin.


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muscle twitch

Twitch summation length-tension relationship

E. Nervous control of skeletal muscle

neuromuscular (myoneural) junction or motor end-plate

Ach secretion by the nerve terminals opening of chemical-gated ion channels by Ach

end-plate potential destruction of released Ach by

acetylcholinesterase

Coupling of action potential and Ca++ release

Dihydropyridine (DHP) receptors


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Length-tension relationships


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A.Acetylcholine creates

an action potential that

moves across the fibermembrane and down the

t-tubules.

B. Ca2+ from

sarcoplasmic reticulumcombines with troponin

uncovering binding sites

on actin, initiating

contraction.


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drugs that affect transmission at the neuromuscularjunction

drugs of acetylchloline-like action:

-Methacholine

-Carbachol

-nicotine drugs that block transmission at the

neuromuscular junction

- botulinum toxin (presynaptic blockade)

- curare (postsynaptic blockade) drugs that inactivate acetylcholinesterase

- Neostigmine

- Physostigmine

- diisopropyl flurophosphate (nerve gas)


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Skeletal muscle contraction and supply of ATP

Phosphocreatine

Glycolysis: anaerobic pathway

Oxidative phosphorylation: aerobic metabolism

Oxygen debt: requirement of O2 for conversionof lactic acid to pyruvate

Types of skeletal muscle fibers (Table 12-3)

- White fibers (fast muscle fiber, glycolytic)- Red fibers (oxidative)

Fast twitch type

Slow twitch type


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3. Smooth Muscle

Structure No troponin

Dense bodies as anchorprotein

Actin/myosin ratio: 10-12:1

Myosin light chains


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Types of smooth muscle

Single-unit smooth muscle

Multi-unit smooth muscle


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Smooth muscle contraction and relaxation


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Regulation of contraction in smooth muscle


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Muscle contraction duration


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lecture 7 muscle

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