Post on 30-May-2018
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The MUSCLE
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Functions of muscle tissue
s Muscle tissue performs three functions: movement and stabilisation storage and movement of substances within the
body
generation of heat
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Properties of muscle tissue
s Electrical excitability responds to certain stimuli by transmission of action
potentialss Contractility shortens, generating tension
s Extensibility can be stretched without damage
s Elasticity returns to original shape after contraction or extension
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Nerve and blood supply
s Nerves and blood vesselstravel through connectivetissues to the muscle fibres. Motor neurons
s convey impulses for muscular contraction
Neuromuscular junction
Blood vesselss provide nutrients and oxygen
for contraction Each muscle fibre in contact
with one or more capillaries
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Histology of skeletal muscle
s Skeletal muscle fibres(cells) Sarcolemma Transverse tubules Sarcoplasmic
reticulum Sarcoplasm
s
myoglobin Multiple nuclei Myofibrils Other organelles
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Neuromuscular junction
s Neuromuscular junction
junction of motor neuron
axon terminal and muscle
fibre sarcolemma
s Acetylcholine released at
junction Depolarises sarcolemma
leading to generation of
muscle action potential
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Contraction of skeletal muscle
s
Skeletal musclecontracts accordingto the slidingfilament theory
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Muscle metabolism
s Only enough ATP present to
fuel contraction for a few
seconds ATP must be used as replaced
3 mechanisms for ATP production
s Aerobic respiration
s Anaerobic respiration (glycolysis)
s Creatine phosphate
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Motor unit
s Motor unit motor neuron and the
muscle fibres it stimulates.s Number of fibres in a motor
unit variables All fibres within motor unit
same types Muscle fibres typically
dispersed throughout muscle
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Motor unit
s All-or-none principle all fibres in motor unit contract maximally or not at all
s Hennemans size principle Motor units recruited according to size of motor neuron
s Size of motor axon related to number of muscle fibres it innervates and size of cell body within spinal cord
Smaller motor units recruited first (i.e. generally slow twitch)
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Tension development
s Force of contraction graded by
Increasing tension development of individual motor units
s wave summation
Recruiting more motor unitss multiple motor unit summation
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Tension development
s Length-tension effect length of muscle affects
tension developeds related to degree of overlap of
actin and myosin
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Skeletal muscle fibre typess
Fibres classified on basis of structure andfunction
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Skeletal muscle hypertrophy
s Can achievesignificanthypertrophy of skeletal
muscle
From: Who Weekly, May 16,2005
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Skeletal muscle hypertrophy
s Can achievesignificanthypertrophy of skeletal
muscle
From: Who Weekly, May 16,2005
From: Who Weekly, May 16,2005
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Cardiac muscles Cardiac muscle tissue
found only in the walls of the heart
s Fibres contain single central
nucleus.
branch freely - connected viagap junctions.
have very high aerobiccapacity
s Contract according tosliding filament theory
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The function of the cardiacmuscle:
contraction of the atria
and ventricle of theheart, causes beating of
heart.
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Smooth muscle
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Types of smooth muscle tissues Single-unit
Autorhythmic
Coupled by gap junctions
contract synchronously
Located in walls of smallarteries, hollow organs etc
s Multi-unit independent innervated fibres
Located in walls of largearteries, airways of lungs,arrector pili, ciliary body thatadjusts lens in eye etc
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Smooth Muscle Histology
s Single, oval, centrally locatednucleus
s No T-tubuless Poorly developed sarcoplasmic
reticulums Actin and myosin not in orderly
sarcomeres no troponin-tropomyosin.
s Contain intermediate filaments
and dense bodies During contraction tension
transmitted to intermediatefilaments which pull on dense
bodies
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Characteristics of smooth muscle
s Contraction and relaxation of smooth
muscle fibres slower and longer lastingcompared with skeletal muscle
s Smooth muscle can shorten and stretch
to a greater extent than other muscletypes
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Contraction of smooth muscle
s Increase in cytosolic Ca 2+ initiates contraction Calcium comes from interstitial fluid and SR
s
Takes more time than in skeletal muscle Contributes to slower onset of contraction
s Calcium - binds to calmodulin Calmodulin activates myosin light chain kinase
s Myosin light chain kinase transfers phosphate group from ATPto myosin to activate myosin head
Myosin light chain kinase works slowly - contributes to slow rate of contraction
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Superficial
FacialMuscles(allinnervatedby VII)
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Some muscles of mastication(Innervated by V3)
Deeper FacialMuscles (All
innervated by VII)
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