Muscle Tissue

Geoffrey T. Geoffrey T. MeyerMeyer

Muscle - Prefixes

Myo (Greek) = muscleeg. Myology = the study of muscle Myositis = inflammation of muscle

Sarco (Greek) = “flesh”eg. Sarcoplasm = the cytoplasm of muscle

Sarcomere = basic contractile unit of muscle

Contractile mechanisms

This is fundamental to many cell types -not just “muscle”

eg. Macrophages

Contractile mechanisms

Macrophages = phagocytes which move freely to engulf (phagocytose) cell debris & micro-organisms

Macro = bigPhage = swallowCyte = cell

Muscle

Packaging of contractile proteins is related to the functions required

Thus there are different such arrangements

These are classified into different “types” of

MUSCLE

Specialised contractile proteins

Muscle is a concentration of such proteinsMyosinActin

TroponinTropomysin

& many structuralproteins

Packaging of muscle proteins

Depends on the force required

eg. Slow steady contraction of tubes in the body - to maintain “tonus” or steady contractions

Use individual cells with orientated packages of contractile proteins

Slow contracting packages of muscle proteins

Common in tubes of the bodyArteries & veins

IntestineLungs

Urinary systemReproductive tubes

Slow contracting packages of muscle proteins

PROPERTIESCells contract slowly

Often rhythmically – eg. peristalsis in gut tubeHave tonic and slowly changing tensions

Under nervous control of the Autonomic Nervous System (involuntary)

Called then INVOLUNTARY muscle

Slow contracting packages of muscle proteins

Contractile proteins arranged in a dispersed pattern - not in regular parallel arrays as

in muscle which moves the skeletonie. Skeletal muscle is “striped” in

appearanceINVOLUNTARY muscle is not striped

& is thus then calledSmooth muscle

Skeletal muscle

Muscles which move the skeleton need

1. Much more power2. Tougher connective tissue support3. Much faster contraction

Skeletal muscle - massMuch more power = mass – many Kg

Geoff Geoff in his in his early early athletic athletic careercareer

Skeletal muscle – anatomical forms

Skeletal muscle – Connective tissue

--Epimysium

Perimysium

Endomysium

Tougher connective tissueTougher connective tissue support - fascial layers & support - fascial layers & tendonstendons

Skeletal muscle – Connective tissue

AponeurosisA fibrous orMembranoussheet-like tendon

FasciaFibrous sheetbinding skin tounderlying musclesor supporting/separating muscles

TendonBand of connectivetissue that attaches muscle to bone

Skeletal muscle - contraction

Crossstriations

Much faster contraction, highly ordered contractile Much faster contraction, highly ordered contractile filaments and a very rapid nerve supplyfilaments and a very rapid nerve supply

Skeletal muscle

Design characteristics

Large cells = syncytium of fused myoblasts to form long multinuclear muscle fibres

Highly organised contractile protein myofilaments

Why multi-nucleation?

From a physical perspective?Contractile force can be efficiently generated by the shortening of a long tube

From a regulatory view?It takes fewer neurons to synchronise contraction of a few large cells versus many individual smaller cells

But there are problems with having such a large cellWhen cells become very large, signals from the cell membrane would not be able to efficiently reach a single nucleus.Also a single nucleus cannot efficiently regulate a very large cell

So large cells become multinucleated with each nucleus controlling a given volume of cytoplasm = DNA unit.

Skeletal muscle

Design characteristics

Large cells = syncytium of fused myoblasts to form long multinuclear muscle fibres

Highly organised contractile protein myofilaments

Skeletal muscle – cell = fibre

Packaging Myofilaments(contractile proteins) into small bundlesmyofibrils MyofilamentsMyofilaments

MyofibrilsMyofibrils

Sarcomere

ZZ ZZ

Sliding myofilaments

Much fasterMuch faster contractioncontraction

Skeletal muscle - LS

Skeletal muscle - tubules

Transport problem because of huge cells1. To transport wave of depolarisation into

contractile filaments – T Tubes, which are extensions of the sarcolemma

2. Internal tubules to hold calcium -Sarcoplasmic reticulum

Skeletal muscle – tubulesComplex system of tubes within fibres (cells) for internal transport

Transport Problem 1. External2. Internal

Skeletal muscle - TS

Large fibres & peripheral nuclei

Skeletal muscle – large cells

Comparison of Smooth & Skeletal muscle

Skeletal muscle – Nerve supply

Skeletal muscle – Nerve supply

Skeletal muscle – Nerve supply

MuscleSpindle

Skeletal muscle – Capillaries

Skeletal muscle – Blood supply

Large muscle fibres & metabolically active & need a large amount of blood = oxygen

But some muscles can work without oxygen for short times

Skeletal muscle – Blood supply

These areFast twitch muscles as in sprinters

Most muscles use oxygen & can work for a long time – with an adequate blood supply

These are Slow Twitch muscles

Skeletal muscle - Types

Cardiac Muscle

HeartLeft Ventriclemuscle

Cardiac muscle

A variant of skeletal muscle -Striated or stripedVery fast contraction – but critical relaxationInternal tubular system

Differences:Individual cells joined very tightly atIntercalated discsBranched individual fibresCentral nuclei – like smooth muscle

Cardiac Muscle - size

Smooth – Cardiac Skeletal

5 µmPeripheral nuclei

50 µmCentral nuclei

15-25 µm

Cardiac Muscle - TS

Cardiac Muscle - LS

Cardiac muscle

A variant of skeletal muscle -Striated or stripedVery fast contraction – but critical relaxationInternal tubular system

Differences:Individual cells joined very tightly atIntercalated discsBranched individual fibresCentral nuclei – like smooth muscle

Cardiac Muscle - LS

Intercalateddisc