bsn 1-1a-2 muscle anatomy an physiology

8/14/2019 BSN 1-1a-2 Muscle anatomy an physiology

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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




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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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bsn 1-1a-2 muscle anatomy an physiology

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